[0001] The present invention relates to a black magnetic toner and black magnetic composite
particles for the black magnetic toner, and more particularly, to black magnetic composite
particles for high-resistant black magnetic toner, which are not only more excellent
in fluidity and blackness but also show an excellent dispersibility in a binder resin
due to a less amount of carbon black desorbed or fallen-off from the surface of each
particle; a process for producing the black magnetic composite particles; and a high-resistant
black magnetic toner using the black magnetic composite particles which is more excellent
in fluidity and blackness.
[0002] As one of conventional electrostatic latent image-developing methods, there has been
widely known and generally adopted a so-called one component system development method
of using as a developer, a magnetic toner comprising composite particles prepared
by mixing and dispersing magnetic particles such as magnetite particles in a resin,
without using a carrier.
[0003] The conventional development methods of using one-component magnetic toner have been
classified into CPC development methods of using a low-resistance magnetic toner,
and PPC development methods of using a high-resistant magnetic toner.
[0004] In the CPC methods, the low-resistance magnetic toner used therefor has an electric
conductivity, and is charged by the electrostatic induction due to electric charge
of the latent images. However, since the charge induced on the magnetic toner is lost
while the magnetic toner is transported from a developing zone to a transfer zone,
the low-resistance magnetic toner is unsuitable for the PPC development method of
using an electrostatic transfer method. In order to solve this problem, there have
been developed the insulated or high-resistant magnetic toners having a volume resistivity
as high as not less than 1 × 10
13 Ω•cm.
[0005] As to the insulated or high-resistant magnetic toner, it is known that the developing
characteristics thereof are affected by magnetic particles exposed to the surface
of the magnetic toner, or the like.
[0006] Recently, with the high image quality such as high image density or high tone gradation,
or with the high copying speed of duplicating machines, it has been strongly demanded
to further enhance characteristics of the insulted or high-resistant magnetic toners
as a developer, especially a fluidity thereof.
[0007] With respect to such demands, in Japanese Patent Application Laid-Open (KOKAI) No.
53-94932(1978), there has been described "these high-resistant magnetic toners are
deteriorated in fluidity due to the high electric resistance, so that there arises
such a problem that non-uniformity of developed images tend to be caused. Namely,
although the high-resistant magnetic toners for PPC development method can maintain
necessary charges required for image transfer, the magnetic toners are frictionally
charged even when they are present in other steps than the transfer step, where the
magnetic toners are not required to be charged, e.g., in a toner bottle or on the
surface of a magnetic roll, or also slightly charged by mechano-electrets during the
production process of these magnetic toners. Therefore, the magnetic toners tend to
be electrostatically agglomerated, resulting in deterioration of fluidity thereof",
and "It is an another object of the present invention to provide a high-resistant
magnetic toner for PPC development method which is improved in fluidity, can be prevented
from causing non-uniformity of developed images, and has an excellent image definition
and tone gradation, thereby obtaining high-quality copies by indirect copying methods".
[0008] In recent years, with the reduction in particle size of the insulated or high-resistant
magnetic toners, it has been increasingly required to enhance the fluidity thereof.
[0009] With respect to such a fact, in "Comprehensive Data Collection for Development and
Utilization of Toner Materials" published by Japan Scientific Information Co., Ltd.,
page 121, there has been described "With extensive development of printers such as
ICP, a high image quality has been required. In particular, it has been demanded to
develop high-precision or high-definition printers. In Table 1, there is shown a relationship
between definitions obtained by using the respective toners. As is apparent from Table
1, the smaller the particle size of wet toners, the higher the image definition is
obtained. Therefore, when a dry toner is used, in order to enhance the image definition,
it is also required to reduce the particle size of the toner ···· As reports of using
toners having a small particle size, it has been proposed that by using toners having
a particle size of 8.5 to 11 µm, fogs on a background can be improved and toner consumption
can be reduced, and further by using polyester-based toners having a particle size
of 6 to 10 µm, an image quality, a charging stability and lifetime of the developer
can be improved. However, when such toners having a small particle size are used,
it has been required to solve many problems. There are problems such as improvement
in productivity, sharpness of particle size distribution, improvement in fluidity,
etc.".
[0010] Further, black magnetic toners widely used at the present time, have been required
to show a high degree of blackness and a high image density for line images and solid
area images on copies.
[0011] With respect to this fact, on page 272 of the above-mentioned "Comprehensive Data
Collection for Development and Utilization of Toner Materials", there has been described
"Powder development is characterized by a high image density. However, the high image
density as well as the fog density as described hereinafter, greatly influences image
characteristics obtained".
[0012] There is a close relationship between properties of the magnetic toner and those
of the magnetic particles mixed and dispersed in the magnetic toner.
[0013] That is, the fluidity of the magnetic toner is largely varied depending upon surface
condition of the magnetic particles exposed to the surface of the magnetic toner.
Therefore, the magnetic particles themselves have been strongly required to show an
excellent fluidity.
[0014] The degree of blackness and density of the magnetic toner are also largely varied
depending upon the degree of blackness and density of the magnetic particles as a
black pigment contained in the magnetic toner.
[0015] As the black pigment, magnetite particles have been widely used from the standpoints
of magnetic properties such as saturation magnetization or coercive force, low price,
color tone or the like. In addition to the magnetite particles, carbon black fine
particles may be added. However, in the case where the carbon black fine particles
are used in a large amount, the volume resistivity thereof is lowered to less than
1.0 × 10
13 Ω•cm, so that it is not possible to use the obtained toner as an insulated or high-resistant
magnetic toner. Further, the dispersibility of the magnetite particles in the binder
resin is deteriorated.
[0016] Hitherto, in order to enhance the fluidity of the black magnetic toner, there have
been many attempts of improving the fluidity of the magnetite particles mixed and
dispersed in the magnetic toner. For example, there have been proposed (1) a method
of forming spherical-shaped magnetite particles (Japanese Patent Application Laid-Open
(KOKAI) No. 59-64852(1984)), (2) a method of exposing a silicon compound to the surface
of magnetite particles (Japanese Patent Publication (KOKOKU) No. 8-25747(1996)), or
the like.
[0017] Black magnetic composite particles for black magnetic toner, which have not only
a more excellent fluidity and blackness, but also an excellent dispersibility in a
binder resin, are presently strongly demanded. However, black magnetic composite particles
capable of satisfying all of these requirements have not been obtained yet.
[0018] Namely, the above-mentioned spherical magnetite particles show a higher fluidity
than those of cubic magnetite particles, octahedral magnetite particles or the like.
However, the fluidity of the spherical magnetite particles is still insufficient,
and further the blackness is disadvantageously low.
[0019] As to the above-mentioned magnetite particles to the surface of which the silicon
compound is exposed, the fluidity thereof is also still insufficient, and the blackness
thereof is also disadvantageously low.
[0020] As a result of the present inventor's earnest studies for solving the above problems,
it has been found that by using as magnetic particles for a black magnetic toner,
black magnetic composite particles having an average particle size of 0.06 to 1.0
µm, comprising: magnetic iron oxide particles as core particles; a coating layer comprising
an organosilicon compound which is formed on the surface of each magnetic iron oxide
particle; and a carbon black coat formed onto at least a part of the surface of the
coating layer in an amount of 26 to 55 parts by weight based on 100 parts by weight
of the magnetic iron oxide particles, the obtained black magnetic toner not only exhibits
a more excellent fluidity and a more excellent blackness, but also has a high volume
resistivity value and, therefore, can realize a high image quality and a high copying
speed. The present invention has been attained on the basis of the finding.
[0021] It is an object of the present invention to provide black magnetic composite particles
for high-resistant black magnetic toner, which are not only more excellent in fluidity
and blackness, but also can show an excellent dispersibility in a binder resin.
[0022] It is another object of the present invention to provide a black magnetic toner which
is not only more excellent in fluidity and blackness, but also can have a high volume
resistivity value.
[0023] To accomplish the aims, in a first aspect of the present invention, there is provided
a black magnetic toner comprising:
a binder resin, and
black magnetic composite particles having an average particle diameter of 0.06
to 1.0 µm, comprising:
magnetic iron oxide particles;
a coating layer formed on the surface of the magnetic iron oxide particle, comprising
at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes; and
a carbon black coat formed on at least a part of the coating layer comprising
the organosilicon compound, in an amount of 26 to 55 parts by weight based on 100
parts by weight of the magnetic iron oxide particles.
[0024] In a second aspect of the present invention, there is provided black magnetic toner
comprising:
a binder resin, and
black magnetic composite particles having an average particle diameter of 0.06
to 1.0 µm, comprising:
magnetic iron oxide particles;
a coat formed on at least a part of the surface of the magnetic iron oxide particles,
comprising at least one compound selected from the group consisting of hydroxides
of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an
amount of 0.01 to 50 % by weight, calculated as Al or SiO2, based on the total weight of the magnetic iron oxide particles;
a coating layer formed on the surface of the magnetic iron oxide particle, comprising
at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes; and
a carbon black coat formed on at least a part of the coating layer comprising
the organosilicon compound, in an amount of 26 to 55 parts by weight based on 100
parts by weight of the magnetic iron oxide particles.
[0025] In a third aspect of the present invention, there are provided black magnetic composite
particles for a black magnetic toner, comprising:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95
µm;
a coating layer formed on the surface of the magnetic iron oxide particle, comprising
at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes; and
a carbon black coat formed on at least a part of the coating layer comprising
the organosilicon compound, in an amount of 26 to 55 parts by weight based on 100
parts by weight of the magnetic iron oxide particles.
[0026] In a fourth aspect of the present invention, there are provided black magnetic composite
particles for a black magnetic toner, comprising:
magnetic iron oxide particles having an average particle diameter of 0.055 to 0.95
µm;
a coat formed on at least a part of the surface of the magnetic iron oxide particles,
comprising at least one compound selected from the group consisting of hydroxides
of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an
amount of 0.01 to 50 % by weight, calculated as Al or SiO2, based on the total weight of the magnetic iron oxide particles;
a coating layer formed on the surface of the magnetic iron oxide particle, comprising
at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes; and
a carbon black coat formed on at least a part of the coating layer comprising
the organosilicon compound, in an amount of 26 to 55 parts by weight based on 100
parts by weight of the magnetic iron oxide particles.
[0027] In a fifth aspect of the present invention, there is provided a process for producing
black magnetic composite particles defined in the third aspect, which process comprises:
mixing as core particles magnetic iron oxide particles having an average particle
size of 0.055 to 0.95 µm together with at least one compound selected from the group
consisting of:
(1) alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes,
by using an apparatus capable of applying a shear force to the particles, thereby
coating the surface of the magnetic iron oxide particle with the said compounds;
mixing the obtained magnetic iron oxide particles coated with the said compounds and
carbon black fine particles having an average particle size of 0.002 to 0.05 µm in
an amount of 1 to 25 parts by weight based on 100 parts by weight of the core particles
by using an apparatus capable of applying a shear force to the particles, thereby
forming a carbon black coat on the surface of the coating layer comprising the said
compounds;
mixing the carbon black-coated magnetic iron oxide particles with dimethylpolysiloxanes
in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the core
particles by using an apparatus capable of applying a shear force to the particles;
and
mixing the obtained magnetic iron oxide particles coated with dimethyl polysiloxanes
and carbon black fine particles having an average particle size of 0.002 to 0.05 µm
in an amount of 1 to 30 parts by weight based on 100 parts by weight of the core particles
by using an apparatus capable of applying a shear force to the particles, thereby
further forming a carbon black coat through the dimethylpolysiloxanes.
[0028] The present invention is now described in detail below.
[0029] First, the black magnetic composite particles according to the present invention
are described.
[0030] The black magnetic composite particles according to the present invention, comprise
magnetic iron oxide particles as core particles; a coating layer comprising organosilicon
compound, formed on the surface of each magnetic iron oxide particle; and a carbon
black coat formed in a large amount, and have an average major axial diameter of 0.06
to 1.0 µm.
[0031] As the magnetic iron oxide particles used as core particles in the present invention,
there may be exemplified magnetite particles (
FeOx•Fe
2O
3; 0<X≤1), maghemite particles (γ-Fe
2O
3) or a mixture of these particles. In the consideration of the blackness of the obtained
black magnetic composite particles, the magnetite particles are preferred.
[0032] As the magnetic iron oxide particles as core particles, from the viewpoint of a particle
shape thereof, there may be exemplified isotropic particles having a sphericity (ratio
of an average particle length to an average particle breadth; hereinafter referred
to merely as "sphericity") of usually not less than 1.0 and less than 2.0, such as
spherical particles, granular particles or polyhedral particles, e.g., hexahedral
particles or octahedral particles, or anisotropic particles having an aspect ratio
(ratio of an average major axial diameter to an average minor axial diameter; hereinafter
referred to merely as "aspect ratio") of not less than 2:1, such as acicular particles,
spindle-shaped particles or rice ball-shaped particles. In the consideration of the
fluidity of the obtained black magnetic composite particles, the magnetic iron oxide
particles having an isotropic shape are preferred. Among them, the spherical particles
are more preferred.
[0033] In the case of the isotropic magnetic iron oxide particles, the average particle
size (diameter) thereof is 0.055 to 0.95 µm, preferably 0.065 to 0.75 µm, more preferably
0.065 to 0.45 µm. The sphericity thereof is usually not less than 1.0:1 and less than
2.0:1, preferably 1.0:1 to 1.8:1, and in case where the shape of the magnetic iron
oxide particles is spherical, the sphericity thereof is preferably 1.0:1 to 1.4:1,
more preferably 1.0:1 to 1.3:1.
[0034] In the case of the anisotropic magnetic iron oxide particles, the average major axial
diameter thereof is 0.055 to 0.95 µm, preferably 0.065 to 0.75 µm, more preferably
0.065 to 0.45 µm, and the aspect ratio thereof is 2:1 to 20:1, preferably 2:1 to 18:1,
more preferably 2:1 to 15:1.
[0035] When the average particle size of the magnetic iron oxide particles is more than
0.95 µm, the obtained black magnetic composite particles are coarse particles and
are deteriorated in tinting strength. On the other hand, when the average particle
size is less than 0.055 µm, the intermolecular force between the particles is increased
due to the reduction in particle size (fine particle), so that agglomeration of the
particles tends to be caused. As a result, it becomes difficult to uniformly coat
the surfaces of the magnetic iron oxide particles with the organosilicon compounds,
and uniformly form the carbon black coat on the surface of the coating layer comprising
the organosilicon compounds.
[0036] Further, in the case where the upper limit of the aspect ratio of the anisotropic
magnetic iron oxide particles exceeds 20:1, the particles tend to be entangled with
each other, and it also becomes difficult to uniformly coat the surfaces of the magnetic
iron oxide particles with the organosilicon compounds, and uniformly form the carbon
black coat on the surface of the coating layer composed of the organosilicon compounds.
[0037] As to the particle size distribution of the magnetic iron oxide particles, the geometrical
standard deviation value thereof is preferably not more than 2.0, more preferably
not more than 1.8, still more preferably not more than 1.6. When the geometrical standard
deviation value thereof is more than 2.0, coarse particles are contained therein,
so that the particles are inhibited from being uniformly dispersed. As a result, it
also becomes difficult to uniformly coat the surfaces of the magnetic iron oxide particles
with the organosilicon compounds, and uniformly form the carbon black coat on the
surface of the coating layer composed of the organosilicon compounds. The lower limit
of the geometrical standard deviation value is 1.01. It is industrially difficult
to obtain particles having a geometrical standard deviation value of less than 1.01.
[0038] The BET specific surface area of the magnetic iron oxide particles thereof is not
less than 0.5 m
2/g. When the BET specific surface area is less than 0.5 m
2/g, the magnetic iron oxide particles may become coarse particles, or the sintering
between the particles may be caused, so that the obtained black magnetic composite
particles also may become coarse particles and tend to be deteriorated in tinting
strength. In the consideration of the tinting strength of the obtained black magnetic
composite particles, the BET specific surface area of the magnetic iron oxide particles
is preferably not less than 1.0 m
2/g, more preferably 1.5 m
2/g. Further, in the consideration of uniformly coating the surfaces of the magnetic
iron oxide particles with the organosilicon compounds, and uniformly forming the carbon
black coat on the coating layer composed of the organosilicon compounds, the upper
limit of the BET specific surface area of the magnetic iron oxide particles, is usually
95 m
2/g, preferably 90 m
2/g, more preferably 85 m
2/g.
[0039] As to the fluidity of the magnetic iron oxide particles, the fluidity index thereof
is about 25 to about 43. Among the magnetic iron oxide particles having various shapes,
the spherical particles are excellent in fluidity, for example, the fluidity index
thereof is about 30 to about 43.
[0040] As to the blackness of the magnetic iron oxide particles, in the case of the magnetite
particles, the lower limit thereof is usually 18.0 when represented by L* value, and
the upper limit thereof is usually 26.0, preferably 25.0 when represented by L* value.
In the case of maghemite particles, the lower limit thereof is usually more than 18.0
when represented by L* value, and the upper limit thereof is usually 34.0, preferably
32.0 when represented by L* value. When the L* value exceeds the above-mentioned upper
limit, the lightness of the particles is increased, so that it is difficult to obtain
black magnetic composite particles having a sufficient blackness.
[0041] As to the magnetic properties of the magnetic iron oxide particles, the coercive
force value thereof is usually 0.8 to 31.8 kA/m (10 to 400 Oe), preferably 1.6 to
30.2 kA/m (20 to 380 Oe); the saturation magnetization value in a magnetic field of
kA/m (10 kOe) is usually 50 to 91 Am
2/kg (50 to 91 emu/g), preferably 60 to 90 Am
2/kg (60 to 90 emu/g); and the residual magnetization value in a magnetic field of
795.8 kA/m (10 kOe) is usually 1 to 35 Am
2/kg (1 to 35 emu/g), preferably 3 to 30 Am
2/kg (3 to 30 emu/g).
[0042] As the core particles, there may be used magnetic iron oxide particles wherein at
least a part of magnetic iron oxide particles is preliminarily coated with at least
one compound selected from the group consisting of hydroxide of aluminum, oxides of
aluminum, hydroxides of silicon and oxides of silicon (hereinafter referred to as
"hydroxides and/or oxides of aluminum and/or silicon") In this case, the dispersibility
of the obtained composite particles in a vehicle may become improved as compared to
those having no undercoat composed of hydroxides and/or oxides of aluminum and/or
silicon, because the percentage of desorption of carbon black from the nonmagnetic
acicular black iron-based composite particles is lessened.
[0043] The amount of the hydroxides and/or oxides of aluminum and/or silicon coat is 0.01
to 50 % by weight calculated as Al, SiO
2 or a sum of Al and SiO
2, based on the weight of the magnetic iron oxide particles as the core particles.
[0044] When the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is
less than 0.01 % by weight, the improvement of the dispersibility of the obtained
black magnetic composite particles in a vehicle cannot be achieved because of failing
to achieve the improvement of lessening the percentage of desorption of carbon black
therefrom. On the other hand, when the amount of the hydroxides and/or oxides of aluminum
and/or silicon coat is more than 50 % by weight, the obtained black magnetic composite
particles can exhibit a good dispersibility in a vehicle by the improvement of lessening
the percentage of desorption of carbon black therefrom, but the coating effect is
saturated and, therefore, it is meaningless to add such an excess amount of the hydroxides
and/or oxides of aluminum and/or silicon coat.
[0045] The black magnetic composite particles using as core particles the magnetic iron
oxide particles having the coat composed of the hydroxides and/or oxides of aluminum
and/or silicon may be substantially identical in a particle size, a geometrical standard
deviation, a BET specific surface area, a blackness (L* value), a fluidity and a magnetic
property, to those having no hydroxides and/or oxides of aluminum and/or silicon coat.
[0046] The particle shape and particle size of the black magnetic composite particles according
to the present invention are considerably varied depending upon those of the magnetic
iron oxide particles as core particles. The black magnetic composite particles have
a similar particle shape to that of the magnetic iron oxide particle as core particle,
and a slightly larger particle size than that of the magnetic iron oxide particles
as core particles.
[0047] More specifically, when the isotropic magnetic iron oxide particles are used as core
particles, the obtained black magnetic composite particles according to the present
invention, have an average particle size of usually 0.06 to 1.0 µm, preferably 0.07
to 0.8 pm, more preferably 0.07 to 0.5 µm and a sphericity of usually not less than
1.0:1 and less than 2.0:1, preferably 1.0:1 to 1.8:1, and in case where the shape
of the magnetic iron oxide particles is spherical, the sphericity thereof is preferably
1.0:1 to 1.4:1, more preferably 1.0:1 to 1.3:1.
[0048] When the anisotropic magnetic iron oxide particles are used as core particles, the
obtained black magnetic composite particles according to the present invention, have
an average particle size of usually 0.06 to 1.0 µm, preferably 0.07 to 0.8 µm, more
preferably 0.07 to 0.5 µm and an aspect ratio of usually 2:1 to 20:1, preferably 2.5:1
to 18:1, more preferably 2:1 to 15:1.
[0049] When the average particle size of the black magnetic composite particles is more
than 1.0 µm, the obtained black magnetic composite particles may be coarse particles,
and deteriorated in tinting strength. On the other hand, when the average particle
size thereof is less than 0.06 µm, the black magnetic composite particles may tend
to be agglomerated by the increase of intermolecular force due to the reduction in
particle size, thereby deteriorating the dispersibility in a binder resin upon production
of the magnetic toner.
[0050] When the aspect ratio is more than 20:1, the black magnetic composite particles may
be entangled with each other in the binder resin, so that the dispersibility in binder
resin may tend to be deteriorated.
[0051] The geometrical standard deviation value of the black magnetic composite particles
according to the present invention is preferably not more than 2.0, more preferably
not more than 1.8, still more preferably not more than 1.6. The lower limit of the
geometrical standard deviation value thereof is preferably 1.01. When the geometrical
standard deviation value thereof is more than 2.0, the tinting strength of the black
magnetic composite particles may be likely to be deteriorated due to the existence
of coarse particles therein. It is industrially difficult to obtain such particles
having a geometrical standard deviation of less than 1.01.
[0052] The BET specific surface area of the black magnetic composite particles according
to the present invention, is usually 1.0 to 100 m
2/g, preferably 1.5 to 95 m
2/g, more preferably 2.0 to 90 m
2/g. When the BET specific surface area thereof is less than 1.0 m
2/g, the obtained black magnetic composite particles may be coarse, and the sintering
between the black magnetic composite particles may be caused, thereby deteriorating
the tinting strength. On the other hand, when the BET specific surface area is more
than 100 m
2/g, the black magnetic composite particles may tend to be agglomerated together by
the increase in intermolecular force due to the reduction in particle size, thereby
deteriorating the dispersibility in a binder resin upon production of the magnetic
toner.
[0053] As to the fluidity of the black magnetic composite particles according to the present
invention, the fluidity index thereof is preferably 48 to 90, more preferably 49 to
90, still more preferably 50 to 90. When the fluidity index thereof is less than 48,
the fluidity of the black magnetic composite particles may become insufficient, thereby
failing to improve the fluidity of the finally obtained magnetic toner. Further, in
the production process of the magnetic toner, there may tend to be caused defects
such as clogging of hopper, etc., thereby deteriorating the handling property or workability.
[0054] As to the blackness of the black magnetic composite particles according to the present
invention, in the case magnetite particles are used as core particles, the upper limit
of the blackness of the black magnetic composite particles is usually 19.5, preferably
18.8, more preferably 17.8 when represented by L* value. In the case maghemite particles
are used as core particles, the upper limit of the blackness of the black magnetic
composite particles is usually 19.5, preferably 19.0, more preferably 18.8 when represented
by L* value. When the L* value thereof is more than 19.5, the lightness of the obtained
black magnetic composite particles may become high, so that the black magnetic composite
particles having a sufficient blackness may not be obtained. The lower limit of the
blackness thereof is 15 when represented by L* value.
[0055] The dispersibility in binder resin of the black magnetic composite particles according
to the present invention, is preferably 4th or 5th rank, more preferably 5th rank
when evaluated by the method described hereinafter.
[0056] The percentage of desorption of carbon black from the black magnetic composite particles
according to the present invention, is preferably not more than 20 %, more preferably
not more than 10 %. When the desorption percentage of the carbon black is more than
20 %, the desorbed carbon black may tend to inhibit the black magnetic composite particles
from being uniformly dispersed in the binder resin upon production of the magnetic
toner.
[0057] The magnetic properties of the black magnetic composite particles according to the
present invention, can be controlled by appropriately selecting kind and particle
shape of the magnetic iron oxide particles as core particles. Similarly to magnetic
properties of magnetic particles ordinarily used for the production of magnetic toner,
the coercive force of the black magnetic composite particles according to the present
invention, is usually 0.8 to 31.8 kA/m (10 to 400 Oe), preferably 1.6 to 30.2 kA/m
(20 to 380 Oe); the saturation magnetization in a magnetic field of 795.8 kA/m (10
kOe) is usually 50 to 91 Am
2/kg (50 to 91 emu/g), preferably 60 to 90 Am
2/kg (60 to 90 emu/g); and the residual magnetization in a magnetic field of 795.8
kA/m (10 kOe) is usually 1 to 35 Am
2/kg (1 to 35 emu/g), preferably 3 to 30 Am
2/kg (3 to 30 emu/g).
[0058] The coating layer formed on the surfaces of the core particles comprises at least
one organosilicon compound selected from the group consisting of (1) organosilane
compounds obtainable from alkoxysilane compounds; and (2) polysiloxanes, or (2') modified
polysiloxanes selected from the group consisting of (A) polysiloxanes modified with
at least one compound selected from the group consisting of polyethers, polyesters
and epoxy compounds (hereinafter referred to merely as "modified polysiloxanes"),
and (B) polysiloxanes whose molecular terminal is modified with at least one group
selected from the group consisting of carboxylic acid groups, alcohol groups and a
hydroxyl group (hereinafter referred to merely as " terminal-modified polysiloxanes").
[0059] The organosilane compounds (1) may be produced by drying or heat-treating alkoxysilane
compounds represented by the formula (I):
R
1 aSiX
4-a (I)
wherein R
1 is C
6H
5-, (CH
3)
2CHCH
2- or n-C
bH
2b+1- (wherein b is an integer of 1 to 18); X is CH
3O- or C
2H
5O-; and a is an integer of 0 to 3.
[0060] The drying or heat-treatment of the alkoxysilane compounds may be conducted, for
example, at a temperature of usually 40 to 200°C, preferably 60 to 150°C for usually
10 minutes to 12 hours, preferably 30 minutes to 3 hours.
[0061] Specific examples of the alkoxysilane compounds may include methyltriethoxysilane,
dimethyldiethoxysilane, phenyltriethyoxysilane, diphenyldiethoxysilane, methyltrimethoxysilane,
dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane,
decyltrimethoxysilane or the like. Among these alkoxysilane compounds, in view of
the desorption percentage and the adhering effect of carbon black, methyltriethoxysilane,
phenyltriethyoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane and isobutyltrimethoxysilane
are preferred, and methyltriethoxysilane and methyltrimethoxysilane are more preferred.
[0062] As the polysiloxanes (2), there may be used those compounds represented by the formula
(II):
wherein R
2 is H- or CH
3-, and d is an integer of 15 to 450.
[0063] Among these polysiloxanes, in view of the desorption percentage and the adhering
effect of carbon black, polysiloxanes having methyl hydrogen siloxane units are preferred.
[0064] As the modified polysiloxanes (2'-A), there may be used:
(a1) polysiloxanes modified with polyethers represented by the formula (III):
wherein R3 is -(-CH2-)h-; R4 is -(-CH2-)i-CH3; R5 is -OH, -COOH, -CH=CH2, -C(CH3)=CH2 or -(-CH2-)j-CH3; R6 is -(-CH2-)k-CH3; g and h are an integer of 1 to 15; i, j and k are an integer of 0 to 15; e is an
integer of 1 to 50; and f is an integer of 1 to 300;
(a2) polysiloxanes modified with polyesters represented by the formula (IV):
wherein R7, R8 and R9 are -(-CH2-)q- and may be the same or different; R10 is -OH, -COOH, -CH=CH2, -C(CH3)=CH2 or -(-CH2-)r-CH3; R11 is -(-CH2-)s-CH3; n and q are an integer of 1 to 15; r and s are an integer of 0 to 15; e' is an integer
of 1 to 50; and f' is an integer of 1 to 300;
(a3) polysiloxanes modified with epoxy compounds represented by the formula (V):
wherein R12 is -(-CH2-)v-; v is an integer of 1 to 15; t is an integer of 1 to 50; and u is an integer of
1 to 300; or a mixture thereof.
[0065] Among these modified polysiloxanes (2'-A), in view of the desorption percentage and
the adhering effect of carbon black, the polysiloxanes modified with the polyethers
represented by the formula (III), are preferred.
[0066] As the terminal-modified polysiloxanes (2'-B), there may be used those represented
by the formula (VI):
wherein R
13 and R
14 are -OH, R
16OH or R
17COOH and may be the same or different; R
15 is -CH
3 or -C
6H
5; R
16 and R
17 are -(-CH
2-)
y-; y is an integer of 1 to 15; w is an integer of 1 to 200; and x is an integer of
0 to 100.
[0067] Among these terminal-modified polysiloxanes, in view of the desorption percentage
and the adhering effect of carbon black, the polysiloxanes whose terminals are modified
with carboxylic acid groups are preferred.
[0068] The amount of the coating layer composed of the organosilicon compounds is usually
0.02 to 5.0 % by weight, preferably 0.03 to 4.0 % by weight, more preferably 0.05
to 3.0 % by weight (calculated as Si) based on the weight of the magnetic iron oxide
particles coated with the organosilicon compounds.
[0069] When amount of the coating layer composed of the organosilicon compounds is less
than 0.02 % by weight, it becomes difficult to adhere the carbon black on the surfaces
of the magnetic iron oxide particles. On the other hand, in case where the coating
amount of the organosilicon compounds is more than 5.0 % by weight, since the carbon
black coat can be sufficiently formed on the surface of the coating layer composed
of the organosilicon compounds, it is meaingless to coat an excess amount of the organosilicon
compounds.
[0070] A carbon black coat is formed on at least a part of the surface of coating layer
composed of the organosilicon compounds, and is composed of at least two carbon black
layers integrally adhered with each other through an adhesive. If required, 3 or more
carbon black layers are integrally adhered with each other through an adhesive to
form the carbon black coat.
[0071] The amount of the carbon black coat is 26 to 55 parts by weight based on 100 parts
by weight of the magnetic iron oxide particles as core particles.
[0072] When the amount of the carbon black coat formed is less than 26 part by weight, it
becomes difficult to obtain black magnetic composite particles having a sufficient
fluidity and blackness. On the other hand, when the amount of the carbon black coat
formed is more than 55 parts by weight, the carbon black tend to be desorbed from
the coating layer composed of the organosilicon compound. As a result, the obtained
black magnetic composite particles tend to be deteriorated in dispersibility in a
binder resin upon the production of magnetic toner.
[0073] The thickness of carbon black coat formed is preferably not more than 0.06 µm, more
preferably not more than 0.05 µm, still more preferably not more than 0.04 µm. The
lower limit thereof is more preferably 0.0001 µm.
[0074] In the black magnetic composite particles according to the present invention, at
least a part of the surface of the magnetic iron oxide particles as core particle
may be preliminarily coated with hydroxides and/or oxides of aluminum and/or silicon.
In this case, the obtained black magnetic composite particles can show a higher dispersibility
in a binder resin as compared to in the case where the magnetic iron oxide particles
are uncoated with hydroxides and/or oxides of aluminum and/or silicon, because of
achieving the improvement of lessening the percentage of desorption of carbon black
therefrom.
[0075] By coating the magnetic iron oxide particle with the hydroxides and/or oxides of
aluminum and/or silicon, the percentage of desorption of carbon black from the obtained
black magnetic composite particles of the present invention is preferably not more
than 10 %, more preferably not more than 5 %.
[0076] Next, the black magnetic toner according to the present invention is described.
[0077] The black magnetic toner according to the present invention comprises the black magnetic
composite particles, and a binder resin. The black magnetic toner may further contain
a mold release agent, a colorant, a charge-controlling agent and other additives,
if necessary.
[0078] The black magnetic toner according to the present invention has an average particle
size of usually 3 to 15 µm, preferably 5 to 12 µm.
[0079] The amount of the binder resin used in the black magnetic toner is usually 50 to
900 parts by weight, preferably 50 to 400 parts by weight based on 100 parts by weight
of the black magnetic composite particles.
[0080] As the binder resins, there may be used vinyl-based polymers, i.e., homopolymers
or copolymers of vinyl-based monomers such as styrene, alkyl acrylates and alkyl methacrylates.
As the styrene monomers, there may be exemplified styrene and substituted styrenes.
As the alkyl acrylate monomers, there may be exemplified acrylic acid, methyl acrylate,
ethyl acrylate, butyl acrylate or the like.
[0081] It is preferred that the above copolymers contain styrene-based components in an
amount of usually 50 to 95 % by weight.
[0082] In the binder resin used in the present invention, the above-mentioned vinyl-based
polymers may be used in combination with polyester-based resins, epoxy-based resins,
polyurethane-based resins or the like, if necessary.
[0083] As to the fluidity of the black magnetic toner according to the present invention,
the fluidity index is usually 78 to 100, preferably 79 to 100, more preferably 80
to 100. When the fluidity index is less than 78, the black magnetic toner may not
show a sufficient fluidity.
[0084] The blackness of the black magnetic toner according to the present invention is usually
not more than 19.0, preferably not more than 18.8, more preferably not more than 18.5
when represented by L* value. When the blackness thereof is more than 19.0, the lightness
of the black magnetic toner may be increased, resulting in insufficient blackness.
The lower limit of the blackness of the black magnetic toner is usually about 15 when
represented by L* value.
[0085] The volume resistivity of the black magnetic toner according to the present invention,
is usually not less than 1.0 × 10
13 Ω•cm, preferably not less than 3.0 × 10
13 Ω•cm, more preferably not less than 5.0 × 10
13 Ω•cm. When the volume resistivity is less than 1.0 × 10
13 Ω•cm, the charge amount of the black magnetic toner tends to vary depending upon
environmental conditions in which the toner is used, resulting in unstable properties
of the black magnetic toner. The upper limit of the volume resistivity is 1.0 × 10
17 Ω•cm.
[0086] As to the magnetic properties of the black magnetic toner according to the present
invention, the coercive force thereof is usually 0.8 to 31.8 kA/m (10 to 400 Oe),
preferably 1.6 to 30.2 kA/m (20 to 380 Oe); the saturation magnetization value in
a magnetic field of 795.8 kA/m (10 kOe) is usually 10 to 85 Am
2/kg (10 to 85 emu/g), preferably 20 to 80 Am
2/kg (20 to 80 emu/g); the residual magnetization in a magnetic field of 795.8 kA/m
(10 kOe) is usually 1 to 20 Am
2/kg (1 to 20 emu/g), preferably Am
2/kg (2 to 15 emu/g; the saturation magnetization in a magnetic field of 79.6 kA/m
(1 kOe) is usually 7.5 to 65 Am
2/kg (7.5 to 65 emu/g), preferably 10 to 60 Am
2/kg (10 to 60 emu/g); and the residual magnetization in a magnetic field of 79.6 kA/m
(1 kOe) is usually 0.5 to 15 Am
2/kg (0.5 to 15 emu/g), preferably 1.0 to 13 Am
2/kg (1.0 to 13 emu/g).
[0087] Next a process for producing the black magnetic composite particles according to
the present invention is described.
[0088] Among the isotropic magnetite particles which are magnetic iron oxide particles,
(1) octahedral magnetite particles can be produced by passing an oxygen-containing
gas through a suspension containing ferrous hydroxide colloid having a pH value of
not less than 10, which is obtained by reacting an aqueous ferrous salt solution with
an aqueous alkali solution having a concentration of not less than one equivalent
based on Fe
2+ in the aqueous ferrous salt solution, thereby precipitating magnetite particles,
and then subjecting the obtained magnetite particles to filtering, washing with water
and drying (Japanese Patent Publication (KOKOKU) No. 44-668(1969); (2) hexahedral
magnetite particles can be produced by passing an oxygen-containing gas through a
suspension containing ferrous hydroxide colloid having a pH value of 6.0 to 7.5, which
is obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution
having a concentration of not more than one equivalent based on Fe
2+ in the aqueous ferrous salt solution to produce magnetite core particles, further
passing an oxygen-containing gas through the obtained aqueous ferrous salt reaction
solution containing the magnetite core particles and the ferrous hydroxide colloid,
at a pH value of 8.0 to 9.5, to precipitate magnetite particles, and then subjecting
the precipitated magnetite particles to filtering, washing with water and drying (Japanese
Patent Application Laid-Open (KOKAI) No. 3-201509(1991); (3) spherical magnetite particles
can be produced by passing an oxygen-containing gas through a suspension containing
ferrous hydroxide colloid having a pH value of 6.0 to 7.5, which is obtained by reacting
an aqueous ferrous salt solution with an aqueous alkali solution having a concentration
of not more than one equivalent based on Fe
2+ in the aqueous ferrous salt solution to produce magnetite core particles, adding
alkali hydroxide in an amount of not less than equivalent based on the remaining Fe
2+ to adjust the pH value of the suspension to not less than 10, heat-oxidizing the
resultant suspension to precipitate magnetite particles, and then subjecting the precipitated
magnetite particles to filtering, washing with water and drying (Japanese Patent Publication
(KOKOKU) No. 62-51208(1987).
[0089] The isotropic maghemite particles can be obtained by heating the above-mentioned
isotropic magnetite particles in air at 300 to 600°C.
[0090] The anisotropic magnetite particles can be produced by passing an oxygen-containing
gas through a suspension containing either ferrous hydroxide colloid, iron carbonate,
or an iron-containing precipitate obtained by reacting an aqueous ferrous salt solution
with alkali hydroxide and/or alkali carbonate, while appropriately controlling the
pH value and temperature of the suspension, to produce acicular, spindle-shaped or
rice ball-shaped goethite particles, subjecting the obtained goethite particles to
filtering, washing with water and drying, and then reducing the goethite particles
in a heat-reducing gas at 300 to 800°C.
[0091] The anisotropic maghemite particles can be produced by heat-oxidizing the above-mentioned
anisotropic magnetite particles in an oxygen-containing gas at 300 to 600°C.
[0092] The coating of the magnetic iron oxide particles with the alkoxysilane compounds,
the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes,
may be conducted (i) by mechanically mixing and stirring the magnetic iron oxide particles
together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes
or the terminal-modified polysiloxanes; or (ii) by mechanically mixing and stirring
both the components together while spraying the alkoxysilane compounds, the polysiloxanes,
the modified polysiloxanes or the terminal-modified polysiloxanes onto the magnetic
iron oxide particles. In these cases, substantially whole amount of the alkoxysilane
compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes added can be applied onto the surfaces of the magnetic iron oxide particles.
[0093] In order to uniformly coat the surfaces of the magnetic iron oxide particles with
the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes, it is preferred that the magnetic iron oxide particles are preliminarily
diaggregated by using a pulverizer.
[0094] As apparatuses used for (a) mixing and stirring the core particles with alkoxysilane
compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes; (b) mixing and stirring the carbon black fine particles with the particles
surface-coated with alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes
or the terminal-modified polysiloxanes; (c) mixing and stirring the adhesive with
the particles having a first carbon black coat formed onto the surface-coating composed
of alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes (hereinafter referred to as "composite particles"); and (d) mixing and
stirring the carbon black fine particles with the composite particles coated with
the adhesive, there may be preferably used apparatus capable of applying a shearing
force to a layer of the particles to be treated, more preferably those capable of
conducting shearing, spatula-stroking and compression at the same time, for example,
wheel-type kneader, ball-type kneader, blade-type kneader, roll-type kneader or the
like. Among these apparatuses, the wheel-type kneader is more effective for the practice
of the present invention.
[0095] Specific examples of the wheel-type kneaders may include an edge runner (equal to
a mix muller, a Simpson mill or a sand mill), a multi-mull, a Stotz mill, a wet pan
mill, a Conner mill, a ring muller, or the like. Among them, an edge runner, a multi-mull,
a Stotz mill, a wet pan mill and a ring muller are preferred, and an edge runner is
more preferred.
[0096] Specific examples of the ball-type kneaders may include a vibrating mill or the like.
Specific examples of the blade-type kneaders may include a Henschel mixer, a planetary
mixer, a Nawter mixer or the like. Specific examples of the roll-type kneaders may
include an extruder or the like.
[0097] In order to coat the surfaces of the core particles with the alkoxysilane compounds,
the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes
as uniformly as possible, the conditions of the above mixing or stirring treatment
may be appropriately controlled such that the linear load is usually 19.6 to 1960
N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 kg/cm), more preferably
147 to 980 N/cm (15 to 100 kg/cm); and the treating time is usually 5 to 120 minutes,
preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring
speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably
10 to 800 rpm.
[0098] The amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes
or the terminal-modified polysiloxanes added, is preferably 0.15 to 45 parts by weight
based on 100 parts by weight of the magnetic iron oxide particles. When the amount
of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the
terminal-modified polysiloxanes added is less than 0.15 part by weight, it may become
difficult to form the carbon black coat on the coating layer.
[0099] On the other hand, when the amount of the alkoxysilane compounds, the polysiloxanes,
the modified polysiloxanes or the terminal-modified polysiloxanes added is more than
45 parts by weight, a sufficient amount of the carbon black coat can be formed on
the surface of the coating, and therefore, it is meaningless to add such an excess
amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes
or the terminal-modified polysiloxanes.
[0100] Meanwhile, a part of the alkoxysilanes coated on the surfaces of the core particles
may be converted into the organosilane compounds via the coating step thereof. Even
in such a case, the subsequent adhesion step with carbon black is not adversely affected.
[0101] Next, the carbon black fine particles are added to the magnetic iron oxide particles
coated with the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes, and the resultant mixture is mixed and stirred to form a first carbon
black coat on the surfaces of the coating composed of the the polysiloxanes, the modified
polysiloxanes or the terminal-modified polysiloxanes added.
[0102] In order to form carbon black coat onto the coating layer composed of the alkoxysilane
compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes as uniformly as possible, the conditions of the above mixing or stirring
treatment can be appropriately controlled such that the linear load is usually 2 to
200 Kg/cm, preferably 10 to 150 Kg/cm more preferably 15 to 100 Kg/cm; and the treating
time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to
appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably
5 to 1,000 rpm, more preferably 10 to 800 rpm.
[0103] The amount of the carbon black fine particles added for forming the first carbon
black coat, is usually 1 to 25 parts by weight, preferably 5 to 25 parts by weight
based on 100 parts by weight of the magnetic iron oxide particles. When the amount
of carbon black fine particles added for forming the first carbon black coat is less
than 1 part by weight, the amount of the adhesive capable of adhering onto the first
carbon black coat also may become insufficient. As a result, when carbon black fine
particles for forming a second carbon black coat are subsequently added such that
the total amount of carbon black adhered is not less than 26 parts by weight based
on 100 parts by weight of the magnetic iron oxide particles as core particles, the
desorption percentage of carbon black is disadvantageously increased, resulting in
deteriorated dispersibility in a binder resin upon production of the magnetic toner.
[0104] On the contrary, when the amount of carbon black adhered is as large as more than
25 parts by weight, the carbon black tends to be desorbed or fallen-off from the surface
of each composite particle. Therefore, the carbon black also tends to be desorbed
or fallen-off from the surfaces of the obtained black magnetic composite particles,
resulting in deteriorated dispersibility in a binder resin upon production of the
magnetic toner.
[0105] As the carbon black fine particles used in the present invention, there may be exemplified
commercially available carbon blacks such as furnace black, channel black or the like.
Specific examples of the commercially available carbon blacks usable in the present
invention, may include #3050, #3150, #3250, #3750, #3950, MA100, MA7, #1000, #2400B,
#30, MA77, MA8, #650, MA11, #50, #52, #45, #2200B, MA600, etc. (tradename, produced
by MITSUBISHI CHEMICAL CORP.), SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H, SEAST 300, SEAST
FM, etc. (tradename, produced by TOKAI CARBON CO., LTD.), Raven 1250, Raven 860 ULTRA,
Raven 1000, Raven 1190 ULTRA, etc. (tradename, produced by COLOMBIAN CHEMICALS COMPANY),
Ketchen black EC, Ketchen black EC600JD, etc. (tradename, produced by KETCHEN BLACK
INTERNATIONAL CO., LTD.), BLACK PEARLS-L, BLACK PEARLS 1000, BLACK PEARLS 4630, VULCAN
XC72, REGAL 660, REGAL 400, etc. (tradename, produced by CABOTT SPECIALTY CHEMICALS
INK CO., LTD.), or the like.
[0106] In order to uniformly form the carbon black coat onto the coating composed of the
alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes, or the dimethylpolysiloxane coating layer while suppressing the reduction
of volume resistivity value of the obtained composite particles, the use of carbon
black fine particles having a DBP oil absorption of not more than 150 ml/100g is preferred.
Specific examples of the commercially available carbon blacks usable in the present
invention, may include MA100, MA7, #1000, #2400B, #30, MA77, MA8, #650, MA11, #50,
#52, #45, #2200B, MA600, etc. (tradename, produced by MITSUBISHI CHEMICAL CORP.),
SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H, SEAST 300, etc. (tradename, produced by TOKAI
CARBON CO., LTD.), Raven 1250, Raven 860 ULTRA, Raven 1000, Raven 1190 ULTRA, etc.
(tradename, produced by COLOMBIAN CHEMICALS COMPANY), BLACK PEARLS-L, BLACK PEARLS
1000, BLACK PEARLS 4630, REGAL 660, REGAL 400, etc. (tradename, produced by CABOTT
SPECIALTY CHEMICALS INK CO., LTD.).
[0107] The average particle size of the carbon black fine particles used is usually 0.002
to 0.05 µm, preferably 0.002 to 0.035 µm. When the average particle size of the carbon
black fine particles used is less than 0.002 µm, the carbon black fine particles used
are too fine to be well handled.
[0108] On the other hand, when the average particle size thereof is more than 0.05 µm, since
the particle size of the carbon black fine particles used is much larger, it is necessary
to apply a larger mechanical shear force for forming the uniform carbon black coat
on the coating layer composed of the organosilicon compounds, thereby rendering the
coating process industrially disadvantageous.
[0109] It is preferred that the carbon black fine particles are added little by little and
slowly, especially about 5 to 60 minutes.
[0110] In order to form the first carbon black coat onto the coating layer composed of the
alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified
polysiloxanes as uniformly as possible, the conditions of the above mixing or stirring
treatment can be appropriately controlled such that the linear load is usually 19.6
to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 Kg/cm), more
preferably 147 to 980 N/cm (15 to 100 Kg/cm); and the treating time is usually 5 to
120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust
the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm,
more preferably 10 to 800 rpm.
[0111] Then, a second carbon black coat is formed onto the first carbon black coat through
an adhesive such as dimethylpolysiloxanes.
[0112] The first and second carbon black coats can be bonded to each other by adhering the
carbon black themselves through the adhesive, thereby obtaining a carbon black coat
wherein the first and second carbon black coats are integrated. In order to obtain
black magnetic composite particles exhibiting excellent fluidity and blackness, in
which the two carbon black coats are firmly and uniformly bonded together, dimethylpolysiloxanes
represented by the following formula is preferably used as the adhesive.
wherein v' is a is an integer of 15 to 450.
[0113] The amount of the adhesive added is usually 0.1 to 5.0 parts by weight, preferably
0.2 to 4.0 parts by weight, more preferably 0.3 to 3.0 parts by weight based on 100
parts by weight of the core particles.
[0114] When the amount of the adhesive adhered is less than 0.1 part by weight, it may be
difficult to sufficiently bond the second carbon black coat onto the first carbon
black coat, thereby failing to obtain black magnetic composite particles exhibiting
a more excellent fluidity and a more excellent blackness.
[0115] When the amount of the adhesive adhered is more than 5.0 part by weight, the carbon
black can be adhered thereon in such an amount enough to achieve the more excellent
fluidity and blackness of the obtained black magnetic composite particles. However,
since the effect is already saturated, it is unnecessary to use such a large amount
of the adhesive.
[0116] The amount of the adhesive is usually 0.04 to 1.89 % by weight, preferably 0.08 to
1.51 % by weight, more preferably 0.11 to 1.13 % by weight (calculated as Si) based
on the weight of the magnetic iron oxide particles.
[0117] After the adhesive is added to, and then mixed and stirred with the composite particles
on which the first carbon black coat is formed, the carbon black fine particles are
added to, and then mixed and stirred with the resultant mixture to form the second
carbon black coat onto the first carbon black coat through the adhesive, thereby integrating
the carbon black coats. The thus obtained composite particles may be dried and heat-treated,
if required.
[0118] The mixing and stirring conditions for adhering the adhesive onto the composite particles
on which the first carbon black coat is formed, may be appropriately selected such
that the adhesive can be uniformly coated onto the first carbon black coat of each
composite particle. More specifically, the linear load used for the mixing and stirring
is usually 19.6 to 1,960 N/cm (2 to 200 kg/cm), preferably 98 to 1,470 N/cm (10 to
150 kg/cm), more preferably 147 to 980 N/cm (15 to 100 kg/cm); the treating time is
5 to 120 minutes, preferably 10 to 90 minutes; and the stirring speed is usually 2
to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
[0119] The amount of the carbon black fine particles added for forming the second carbon
black coat is 1 to 30 parts by weight based on 100 parts by weight of the magnetic
iron oxide particles. When the amount of the carbon black fine particles added is
less than 1 part by weight, the total amount of carbon black adhered becomes insufficient,
so that it may be difficult to obtain aimed black magnetic composite particles which
are more excellent in fluidity and blackness. On the contrary, when the amount of
the carbon black fine particles added is more than 30 part by weight, the carbon black
tends to be desorbed or fallen-off from the surfaces of the obtained black magnetic
composite particles, resulting in deteriorated dispersibility in a binder resin upon
production of the magnetic toner.
[0120] The mixing and stirring conditions for forming the second carbon black coat onto
the first carbon black coat through the adhesive, may be appropriately selected such
that the second carbon black coat can be uniformly coated onto the first carbon black
coat through the adhesive. More specifically, the linear load used for the mixing
and stirring is usually 19.6 to 1,960 N/cm (2 to 200 kg/cm), preferably 98 to 1,470
N/cm (10 to 150 kg/cm), more preferably 147 to 980 N/cm (15 to 100 kg/cm); the treating
time is 5 to 120 minutes, preferably 10 to 90 minutes; and the stirring speed is usually
2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
[0121] In the case where the alkoxysilane compounds are used as the coating compound, the
resultant black magnetic composite particles may be dried or heat-treated, for example,
at a temperature of usually 40 to 200°C, preferably 60 to 150°C for usually 10 minutes
to 12 hours, preferably 30 minutes to 3 hours.
[0122] At least a part of the surface of the magnetic iron oxide particles as core particles
may be coated with at least one compound selected from the group consisting of hydroxides
of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon, in advance
of mixing and stirring with the alkoxysilane compounds, the polysiloxanes, the modified
polysiloxanes or the terminal-modified polysiloxanes.
[0123] The coat of the hydroxides and/or oxides of aluminum and/or silicon may be conducted
by adding an aluminum compound, a silicon compound or both the compounds to a water
suspension in which the magnetic iron oxide particles are dispersed, followed by mixing
and stirring, and further adjusting the pH value of the suspension, if required, thereby
coating the surfaces of the magnetic iron oxide particles with at least one compound
selected from the group consisting of hydroxides of aluminum, oxides of aluminum,
hydroxides of silicon and oxides of silicon. The thus obtained particles coated with
the hydroxides and/or oxides of aluminum and/or silicon are then filtered out, washed
with water, dried and pulverized. Further, the particles coated with the hydroxides
and/or oxides of aluminum and/or silicon may be subjected to posttreatments such as
deaeration treatment and compaction treatment.
[0124] As the aluminum compounds, there may be exemplified aluminum salts such as aluminum
acetate, aluminum sulfate, aluminum chloride or aluminum nitrate, alkali aluminates
such as sodium aluminate or the like.
[0125] The amount of the aluminum compound added is 0.01 to 50 % by weight (calculated as
Al) based on the weight of the magnetic iron oxide particles. When the amount of the
aluminum compound added is less than 0.01 % by weight, it may be difficult to sufficiently
coat the surfaces of the magnetic iron oxide particles with hydroxides and/or oxides
of aluminum, which can achieve the improvement of lessening the percentage of desorption
of carbon black therefrom, thereby failing to achieve the improvement of the dispersibility
in the binder resin upon the production of the magnetic toner. On the other hand,
when the amount of the aluminum compound added is more than 50 % by weight, the coating
effect is saturated and, therefore, it is meaningless to add such an excess amount
of the aluminum compound.
[0126] As the silicon compounds, there may be exemplified water glass #3, sodium orthosilicate,
sodium metasilicate, colloidal silica or the like.
[0127] The amount of the silicon compound added is 0.01 to 50 % by weight (calculated as
SiO
2) based on the weight of the magnetic iron oxide particles. When the amount of the
silicon compound added is less than 0.01 % by weight, it may be difficult to sufficiently
coat the surfaces of the magnetic iron oxide particles with hydroxides and/or oxides
of silicon, which can achieve the improvement of lessening the percentage of desorption
of carbon black therefrom, thereby failing to achieve the improvement of the dispersibility
in the binder resin upon the production of the magnetic toner. On the other hand,
when the amount of the silicon compound added is more than 50 % by weight, the coating
effect is saturated and, therefore, it is meaningless to add such an excess amount
of the silicon compound.
[0128] In the case where both the aluminum and silicon compounds are used in combination
for the coating, the total amount of the aluminum and silicon compounds added is preferably
0.01 to 50 % by weight (calculated as a sum of Al and SiO
2) based on the weight of the magnetic iron oxide particles.
[0129] The black magnetic toner according to the present invention may be produced by a
known method of mixing and kneading a predetermined amount of a binder resin and a
predetermined amount of the black magnetic composite particles together, and then
pulverizing the mixed and kneaded material into particles. More specifically, the
black magnetic composite particles and the binder resin are intimately mixed together
with, if necessary, a mold release agent, a colorant, a charge-controlling agent or
other additives by using a mixer. The obtained mixture is then melted and kneaded
by a heating kneader so as to render the respective components compatible with each
other, thereby dispersing the black magnetic composite particles therein. Successively,
the molten mixture is cooled and solidified to obtain a resin-kneaded product. The
resin-kneaded product is then pulverized and classified, thereby producing a magnetic
toner having an aimed particle size.
[0130] As the mixers, there may be used a Henschel mixer, a ball mill or the like. As the
heating kneaders, there may be used a roll mill, a kneader, a twin-screw extruder
or the like. The pulverization of the resin mixture may be conducted by using pulverizers
such as a cutter mill, a jet mill or the like. The classification of the pulverized
particles may be conducted by known methods such as air classification, etc., as described
in Japanese Patent No. 2683142 or the like.
[0131] As the other method of producing the black magnetic toner, there may be exemplified
a suspension polymerization method or an emulsion polymerization method. In the suspension
polymerization method, polymerizable monomers and the black magnetic composite particles
are intimately mixed together with, if necessary, a colorant, a polymerization initiator,
a cross-linking agent, a charge-controlling agent or the other additives and then
the obtained mixture is dissolved and dispersed together so as to obtain a monomer
composition. The obtained monomer composition is added to a water phase containing
a suspension stabilizer while stirring, thereby granulating and polymerizing the composition
to form magnetic toner particles having an aimed particle size.
[0132] In the emulsion polymerization method, the monomers and the black magnetic composite
particles are dispersed in water together with, if necessary, a colorant, a polymerization
initiator or the like and then the obtained dispersion is polymerized while adding
an emulsifier thereto, thereby producing magnetic toner particles having an aimed
particle size.
[0133] A point of the present invention lies in such a fact that the black magnetic composite
particles according to the present invention which are obtained by firmly adhering
carbon black onto the surfaces of magnetic iron oxide particles in an amount of 26
to 55 parts by weight based on 100 parts by weight of the magnetic iron oxide particles,
are not only more excellent in fluidity and blackness, but also have a less amount
of carbon black desorbed or fallen-off from the surface of each particle.
[0134] The reason why the black magnetic composite particles of the present invention can
exhibit a more excellent fluidity, is considered as follows. In general, the carbon
black tends to act as aggregates because of its fineness. In contrast, in the case
of the black magnetic composite particles of the present invention, since the carbon
black is uniformly and densely adhered and bonded onto the surface of each magnetic
iron oxide particle, it is considered that many fine irregularities are formed on
the surface of each magnetic iron oxide particle.
[0135] The reason why the black magnetic composite particles of the present invention can
exhibit a more excellent blackness, is considered as follows. That is, since a uniform
carbon black coat having an appropriate thickness is formed by densely adhering and
bonding carbon black onto the surface of each magnetic iron oxide particle, the color
of the magnetic iron oxide particles is hidden behind the carbon black coat, so that
an inherent black color of the carbon black can be effectively exhibited.
[0136] The reason why the amount of the carbon black desorbed (or fallen-off) from the surfaces
of the black magnetic composite particles according to the present invention, is small,
is considered as follows. In the case of the alkoxysilane compounds (1) and the fluoroalkylsilane
compounds (3), metalloxane bonds (≡Si-O-M wherein M represents a metal atom contained
in the magnetic iron oxide particles, such as Si, Al, Fe or the like) are formed between
the surfaces of the magnetic iron oxide particles and alkoxy groups contained in the
organosilicon compounds onto which the carbon black coat is formed, thereby forming
a stronger bond between the organosilicon compounds on which the carbon black coat
is formed, and the surfaces of the magnetic iron oxide particles. Further, in the
case of using the polysiloxanes or modified polysiloxanes, the functional groups in
the polysiloxanes or modified polysiloxanes onto which the carbon black coat is formed,
are strongly bonded to the surface of the magnetic iron oxide particle.
[0137] In accordance with the present invention, due to the less amount of carbon black
desorbed or fallen-off from the surface of each black magnetic composite particle,
materials present in the system can be well dispersed together without any disturbance
by the desorbed carbon black. Further, since irregularities are formed on the surface
of each magnetic iron oxide particle by the carbon black adhered and bonded thereonto,
the particles are prevented from contacting with each other, resulting in excellent
dispersibility in a binder resin upon production of the magnetic toner.
[0138] The black magnetic toner according to the present invention obtained by using the
above black magnetic composite particles adhered with a large amount of carbon black,
can exhibit more excellent fluidity and blackness while maintaining as high a resistivity
as not less than 1 × 10
13 Ω•cm.
[0139] The reason why the black magnetic toner of the present invention exhibits a more
excellent fluidity, is considered as follows. That is, the black magnetic composite
particles obtained by uniformly adhering a large amount of carbon black onto the surface
of each magnetic iron oxide particle, are exposed to the surface of the black magnetic
toner, thereby forming many fine irregularities thereon.
[0140] The reason why the black magnetic toner of the present invention exhibits a more
excellent blackness, is considered by the present inventors as follows. That is, the
black magnetic composite particles having a more excellent blackness are blended in
the black magnetic toner.
[0141] The reason why the black magnetic toner of the present invention can maintain a high
volume resistivity value nevertheless a large amount of carbon black is adhered onto
the surfaces thereof, is considered by the present inventors as follow.
[0142] That is, in general, carbon black is present in the form of aggregated particles
constituted from parallel-stacked crystallites each having a pseudo-graphite structure.
Further, the carbon black fine particles are chemically and physically bonded with
each other to form a cluster-like (grape-like cluster) structure. It is known that
the larger the cluster-like structure, the higher the electrical conductivity of carbon
black becomes. In the case where the carbon black fine particles having such a cluster-like
structure are added to and mixed with a binder resin, those exposed to the surface
of the magnetic toner also have the cluster-like structure, thereby increasing a conductivity
of the magnetic toner. As a result, it is difficult to obtain a magnetic toner having
a high volume resistivity value. On the contrary, in the case of the black magnetic
composite particles according to the present invention, the carbon black coat is formed
onto the surface of each magnetic iron oxide particle without forming the cluster-like
structure. Therefore, since the magnetic toner using such black magnetic composite
particles are also free from carbon black having the cluster-like structure, thereby
maintaining a high volume resistivity value.
[0143] The black magnetic composite particles according to the present invention are not
only more excellent in fluidity and blackness, but also show an excellent dispersibility
in a binder resin due to a less amount of carbon black desorbed or fallen-off from
the surface of each particle. Therefore, the black magnetic composite particles of
the present invention are suitable as black magnetic particles capable of achieving
a high image quality and a high copying speed.
[0144] Also, the black magnetic composite particles of the present invention have an excellent
dispersibility, i.e., an excellent handling property and are, therefore, industrially
advantageous.
[0145] The black magnetic toner obtained by using such black magnetic composite particles
having more excellent fluidity and blackness, can also exhibit more excellent fluidity
and blackness and is, therefore, suitable as black magnetic toner for achieving a
high image quality and a high copying speed.
[0146] Further, the black magnetic toner of the present invention can maintain a high volume
resistivity value nevertheless the use of black magnetic composite particles adhered
with a large amount of carbon black. Therefore, the black magnetic toner of the present
invention is suitable as high-resistant or insulating magnetic toner.
EXAMPLES
[0147] The present invention is described in more detail by Examples and Comparative Examples,
but the Examples are only illustrative and, therefore, not intended to limit the scope
of the present invention.
[0148] Various properties were measured by the following methods.
[0149] (1)
The average particle size, the average major axial diameter and average minor axial
diameter of magnetic iron oxide particles, composite particles, black magnetic composite particles
and carbon black fine particles were respectively expressed by the average of values
(measured in a predetermined direction) of about 350 particles which were sampled
from a micrograph obtained by magnifying an original electron micrograph (× 20,000)
by four times in each of the longitudinal and transverse directions.
[0150] (2) The
aspect ratio of the particles was expressed by the ratio of an average major axial diameter to
an average minor axial diameter thereof. The
sphericity of the particles was expressed by the ratio of an average particle length to an average
particle breadth thereof.
[0151] (3) The
geometrical standard deviation of particle sizes was expressed by values obtained by the following method. That is, the particle sizes
(major axial diameters) were measured from the above magnified electron micrograph.
The actual particle sizes (major axial diameters) and the number of the particles
were calculated from the measured values. On a logarithmic normal probability paper,
the particle sizes (major axial diameters) were plotted at regular intervals on the
abscissa-axis and the accumulative number (under integration sieve) of particles belonging
to each interval of the particle sizes (major axial diameters) were plotted by percentage
on the ordinate-axis by a statistical technique.
[0152] The particle sizes (major axial diameters) corresponding to the number of particles
of 50 % and 84.13 %, respectively, were read from the graph, and the geometrical standard
deviation was calculated from the following formula:
[0153] The closer to 1 the geometrical standard deviation value, the more excellent the
particle size distribution.
[0154] (4)
The specific surface area was expressed by the value measured by a BET method.
[0155] (5) The
amounts of Al and Si which were present within black magnetic composite particles or on surfaces thereof,
and the
amount of Si contained in organosilicon compounds and
the amount of Si contained in dimethylpolysiloxanes used for adhering the carbon black, were measured by a fluorescent X-ray spectroscopy
device 3063 M (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to JIS K0119
"General rule of fluorescent X-ray analysis".
[0156] (6) The
amount of carbon black coat formed on the surface of the magnetic iron oxide particles was measured by "Horiba
Metal, Carbon and Sulfur Analyzer EMIA-2200 Model" (manufactured by Horiba Seisakusho
Co., Ltd.).
[0157] (7) The
thickness of carbon black coat formed on the surfaces of the magnetic iron oxide particles is expressed by the value
which was obtained by first measuring an average thickness of carbon black coat formed
onto the surfaces of the particles on a photograph (× 5,000,000) obtained by magnifying
(ten times) a micrograph (× 500,000) produced at an accelerating voltage of 200 kV
using a transmission-type electron microscope (JEM-2010, manufactured by Japan Electron
Co., Ltd.), and then calculating an actual thickness of carbon black coat formed from
the measured average thickness.
[0158] (8) The
fluidity of magnetic iron oxide particles, composite particles, black magnetic composite particles
and magnetic toner was expressed by a fluidity index which was a sum of indices obtained
by converting on the basis of the same reference measured values of an angle of repose,
a degree of compaction (%), an angle of spatula and a degree of agglomeration as particle
characteristics which were measured by a powder tester (tradename, produced by Hosokawa
Micron Co., Ltd.). The closer to 100 the fluidity index, the more excellent the fluidity
of the particles.
[0159] (9) The
blackness of magnetic iron oxide particles, composite particles, black magnetic composite particles
and magnetic toner was measured by the following method. That is, 0.5 g of sample
particles and 1.5 ml of castor oil were intimately kneaded together by a Hoover's
muller to form a paste. 4.5 g of clear lacquer was added to the obtained paste and
was intimately kneaded to form a paint. The obtained paint was applied on a cast-coated
paper by using a 6-mil (150 pm) applicator to produce a coating film piece (having
a film thickness of about 30 µm). The thus obtained coating film piece was measured
according to JIS Z 8729 by a multi-light source spectrographic colorimeter MSC-IS-2D
(manufactured by Suga Testing Machines Manufacturing Co., Ltd.) to determine an L*
value of colorimetric indices thereof. The blackness was expressed by the L* value
measured.
[0160] Here, the L* value represents a lightness, and the smaller the L* value, the more
excellent the blackness.
[0161] (10) The
desorption percentage of carbon black desorbed from the composite particles and the black magnetic composite
particles was measured by the following method. The closer to zero the desorption
percentage, the smaller the amount of carbon black desorbed from the surfaces of the
composite particles and the black magnetic composite particles.
[0162] That is, 3 g of the sample particles and 40 ml of ethanol were placed in a 50-ml
precipitation pipe and then were subjected to ultrasonic dispersion for 20 minutes.
Thereafter, the obtained dispersion was allowed to stand for 120 minutes, and the
carbon black desorbed was separated from the sample particles on the basis of the
difference in specific gravity between both the particles. Next, the particles from
which the desorbed carbon black was separated, were mixed again with 40 ml of ethanol,
and the obtained mixture was further subjected to ultrasonic dispersion for 20 minutes.
Thereafter, the obtained dispersion was allowed to stand for 120 minutes, thereby
separating the particles and the desorbed carbon black desorbed from each other. The
thus obtained particles were dried at 100°C for one hour, and then the carbon content
thereof was measured by the "Horiba Metal, Carbon and Sulfur Analyzer EMIA-2200 Model"
(manufactured by Horiba Seisakusho Co., Ltd.). The desorption percentage of the carbon
black was calculated according to the following formula:
wherein W
a represents an amount of carbon black initially formed on the composite particles
or the black magnetic composite particles; and W
e represents an amount of carbon black still adhered on the composite particles or
the black magnetic composite particles after desorption test.
[0163] (11) The
dispersibility in a binder resin of the black magnetic composite particles was evaluated by counting
the number of undispersed agglomerated particles on a micrograph (× 200) obtained
by photographing a sectional area of the obtained black magnetic toner particle using
an optical microscope (BH-2, manufactured by Olympus Kogaku Kogyo Co., Ltd.), and
classifying the results into the following five ranks. The 5th rank represents the
most excellent dispersing condition.
- Rank 1:
- not less than 50 undispersed agglomerated particles per 0.25 mm2 were recognized;
- Rank 2:
- 10 to 49 undispersed agglomerated particles per 0.25 mm2 were recognized;
- Rank 3:
- 5 to 9 undispersed agglomerated particles per 0.25 mm2 were recognized;
- Rank 4:
- 1 to 4 undispersed agglomerated particles per 0.25 mm2 were recognized;
- Rank 5:
- No undispersed agglomerated particles were recognized.
[0164] (12) The
average particle size of the black magnetic toner was measured by a laser diffraction-type particle size
distribution-measuring apparatus (Model HELOSLA/KA, manufactured by Sympatec Corp.).
[0165] (13) The
volume resistivity of the black magnetic toner was measured by the following method.
[0166] That is, first, 0.5 g of a sample toner to be measured was weighted, and press-molded
at 1.372 × 10
7 Pa (140 Kg/cm
2) using a KBr tablet machine (manufactured by Simazu Seisakusho Co., Ltd.), thereby
forming a cylindrical test piece.
[0167] Next, the thus obtained cylindrical test piece was exposed to an atmosphere maintained
at a temperature of 25°C and a relative humidity of 60 % for 12 hours. Thereafter,
the cylindrical test piece was set between stainless steel electrodes, and a voltage
of 15V was applied between the electrodes using a Wheatstone bridge (TYPE2768, manufactured
by Yokogawa-Hokushin Denki Co., Ltd.) to measure a resistance value (Ω).
[0168] The cylindrical test piece was measured with respect to an upper surface area A (cm
2) and a thickness t
0 (cm) thereof. The measured values were inserted into the following formula, thereby
obtaining a volume resistivity X (Ω•cm).
[0169] (14) The
magnetic properties of the magnetic iron oxide particles, the composite particles and the black magnetic
composite particles were measured using a vibration sample magnetometer "VSM-3S-15"
(manufactured by Toei Kogyo Co., Ltd.) by applying an external magnetic field of 795.8
kA/m (10 kOe) thereto. Whereas, the
magnetic properties of the black magnetic toner were measured by applying external magnetic fields of
79.6 kA/m (1 kOe) and 795.8 kA/m (10 kOe) thereto.
Example 1:
<Production of black magnetic composite particles>
[0170] 20 kg of spherical magnetite particles (sphericity : 1.2; average particle size:
0.23 µm; geometrical standard deviation value: 1.42; BET specific surface area value:
9.2 m
2/g; blackness (L* value): 20.6; fluidity index: 35; coercive force value: 4.9 kA/m
(61 Oe); saturation magnetization value in a magnetic field of 795.8 kA/m (10 kOe):
84.9 Am
2/kg (84.9 emu/g); residual magnetization value in a magnetic field of 795.8 kA/m (10
kOe): 7.8 Am
2/kg (7.8 emu/g)), were deagglomerated in 150 liters of pure water using a stirrer,
and further passed through a "TK pipeline homomixer" (tradename, manufactured by Tokushu
Kika Kogyo Co., Ltd.) three times, thereby obtaining a slurry containing the spherical
magnetite particles.
[0171] Successively, the obtained slurry containing the spherical magnetite particles was
passed through a transverse-type sand grinder (tradename "MIGHTY MILL MHG-1.5L", manufactured
by Inoue Seisakusho Co., Ltd.) five times at an axis-rotating speed of 2,000 rpm,
thereby obtaining a slurry in which the spherical magnetite particles were dispersed.
[0172] The particles in the obtained slurry which remained on a sieve of 325 meshes (mesh
size: 44 µm) was 0 %. The slurry was filtered and washed with water, thereby obtaining
a filter cake containing the spherical magnetite particles. After the obtained filter
cake containing the spherical magnetite particles was dried at 120°C, 11.0 kg of the
dried particles were then charged into an edge runner "MPUV-2 Model" (tradename, manufactured
by Matsumoto Chuzo Tekkosho Co., Ltd.), and mixed and stirred at 294 N/cm (30 Kg/cm)
and a stirring speed of 22 rpm for 30 minutes, thereby lightly deagglomerating the
particles.
[0173] 110 g of methyltriethoxysilane (tradename: "TSL8123", produced by GE Toshiba Silicone
Co., Ltd.) was mixed and diluted with 200 ml of ethanol to obtain a methyltriethoxysilane
solution. The methyltriethoxysilane solution was added to the deagglomerated spherical
magnetite particles under the operation of the edge runner. The spherical magnetite
particles were continuously mixed and stirred at a linear load of 392 N/CM (40 Kg/cm)
and a stirring speed of 22 rpm for 60 minutes to form a coating layer composed of
methyltriethoxysilane on the spherical magnetite particles.
[0174] Next, 1650 g of carbon black fine particles A (particle shape: granular shape; average
particle size: 0.022 µm; geometrical standard deviation value: 1.68; BET specific
surface area value: 134 m
2/g; DBP oil absorption: 89 ml/100 g; and blackness (L* value): 16.6) were added to
the spherical magnetite particles coated with methyltriethoxysilane for 10 minutes
while operating the edge runner. Further, the mixed particles were continuously stirred
at a linear load of 392 N/cm (40 Kg/cm) and a stirring speed of 22 rpm for 60 minutes
to form the carbon black coat on the coating layer composed of methyltriethoxysilane,
thereby obtaining composite particles.
[0175] In order to determine the coating amount of methyltriethoxysilane and the amount
of carbon black adhered, a part of the thus obtained composite particles was sampled,
and heat-treated at 105°C for 60 minutes using a drier. As a result, it was confirmed
that the coating amount of methyltriethoxysilane was 0.15 % by weight (calculated
as Si), and the amount of carbon black adhered was 13.00 % by weight (equivalent to
15 parts by weight based on 100 parts by weight of the spherical magnetite particles).
Further, as a result of the observation of electron micrograph, it was confirmed that
almost a whole amount of carbon black added was adhered onto the coating layer of
an organosilane compound produced from the methyltriethoxysilane.
[0176] Next, 220 g of dimethylpolysiloxane (tradename: "TSF451", produced by GE Toshiba
Silicone Co., Ltd.) was added to the above composite particles while operating an
edge runner, and the obtained mixture was then mixed and stirred together at a linear
load of 588 N/cm (60 Kg/cm) and a stirring speed of 22 rpm for 30 minutes, thereby
obtaining composite particles on which dimethylpolysiloxane was uniformly adhered.
[0177] Next, 1,650 g of the above carbon black fine particles A were added to the above
obtained particles for 10 minutes while operating the edge runner, and then mixed
and stirred together at a linear load of 588 N/cm (60 Kg/cm) and a stirring speed
of 22 rpm for 30 minutes, thereby bonding the second carbon black coat onto the first
carbon black coat through the dimethylpolysiloxane as an adhesive. Thereafter, the
obtained particles were heat-treated at 105°C for 60 minutes using a drier, thereby
obtaining black magnetic composite particles.
[0178] The obtained black magnetic composite particles had an average particle diameter
of 0.24 µm, and a sphericity of 1.2:1 as shown in the electron photograph. In addition,
the black magnetic composite particles showed a geometrical standard deviation of
1.42, a BET specific surface area value of 12.3 m
2/g, fluidity index of 58, a blackness (L* value) of 17.6, and a desorption percentage
of carbon black: 7.8 %. The amount of the carbon black coat formed on the coating
layer composed of the organosilane compound produced from methyl triethoxysilane is
26.01 % by weight (calculated as C) based on the weight of the black magnetic composite
particles (corresponding to 30 parts by weight based on 100 parts by weight of the
spherical magnetite particles). The thickness of the carbon black coat formed was
0.0027 pm. The amount of dimethylpolysiloxanes adhered was 0.70 % by weight (calculated
as Si).
[0179] The obtained black magnetic composite particles had an a coercive force value of
4.9 kA/m (61 Oe), a saturation magnetization value (in a magnetic field of 795.8 kA/m
(10 kOe)) of 76.9 Am
2/kg (76.9 emu/g), a residual magnetization value (in a magnetic field of 795.8 kA/m
(10 kOe)) of 7.0 Am
2/kg (7.0 emu/g),
[0180] Since no carbon black were recognized on the electron photograph, it was confirmed
that a whole amount of the carbon black used contributed to the formation of the carbon
black coat.
Example 2:
<Production of black magnetic toner containing black magnetic composite particles>
[0181] 450 g of the black magnetic composite particles obtained in Example 1, 550 g of styrene-butyl
acrylate-methyl methacrylate copolymer resin (molecular weight = 130,000, styrene/butyl
acrylate/methyl methacrylate = 82.0/16.5/1.5), 55 g of polypropylene wax (molecular
weight: 3,000) and 15 g of a charge-controlling agent were charged into a Henschel
mixer, and mixed and stirred therein at 60°C for 15 minutes. The obtained mixed particles
were melt-kneaded at 140°C using a continuous-type twin-screw kneader (T-1), and the
obtained kneaded material was cooled, coarsely pulverized and finely pulverized in
air. The obtained particles were subjected to classification, thereby producing a
black magnetic toner.
[0182] The obtained black magnetic toner had an average particle size of 9.9 µm, a dispersibility
of 5th rank, a fluidity index of 84, a blackness (L* value) of 17.8, a volume resistivity
of 8.4 × 10
13 Ω•cm, a coercive force value of 4.7 kA/m (59 Oe), a saturation magnetization value
(in a magnetic field of 795.8 kA/m (10 kOe)) of 32.2 Am
2/kg (32.2 emu/g), a residual magnetization value (in a magnetic field of 795.8 kA/m
(10 kOe)) of 4.1 Am
2/kg (4.1 emu/g), a saturation magnetization value (in a magnetic field of 79.6 kA/m
(1 kOe)) of 25.3 Am
2/kg (25.3 emu/g), and a residual magnetization value (in a magnetic field of 79.6
kA/m (1 kOe)) of 3.3 Am
2/kg (3.3 emu/g).
Magnetic iron oxide particles 1 to 4:
[0183] Various magnetic iron oxide particles were prepared by known methods. The same procedure
as defined in Example 1 was conducted by using the thus prepared particles, thereby
obtaining deagglomerated magnetic iron oxide particles as core particles.
[0184] Various properties of the thus obtained magnetic iron oxide particles are shown in
Table 1.
Magnetic iron oxide particles 5:
[0185] The same procedure as defined in Example 1 was conducted by using 20 kg of the deagglomerated
octahedral magnetite particles (core particles 1) and 150 liters of water, thereby
obtaining a slurry containing the octahedral magnetite particles. The pH value of
the obtained re-dispersed slurry containing the octahedral magnetite particles was
adjusted to 4.0 by adding acetic acid, and then the concentration of the slurry was
adjusted to 98 g/liter by adding water thereto. After 150 liters of the slurry was
heated to 60°C, 2722 ml of a 1.0 mol/liter aluminum sulfate solution (equivalent to
1.0 % by weight (calculated as Al) based on the weight of the octahedral magnetite
particles) was added to the slurry. After allowing the slurry to stand for 30 minutes,
the pH value of the slurry was adjusted to 7.5 by adding an aqueous sodium hydroxide
solution. Successively, 254 g of water glass #3 (equivalent to 0.5 % by weight (calculated
as SiO
2) based on the weight of the octahedral magnetite particles) was added to the slurry.
After the slurry was aged for 30 minutes, the pH value of the slurry was adjusted
to 7.5 by adding acetic acid. After further allowing the slurry to stand for 30 minutes,
the slurry was subjected to filtration, washing with water, drying and pulverization,
thereby obtaining the octahedral magnetite particles coated with hydroxides of aluminum
and oxides of silicon.
[0186] Main production conditions are shown in Table 2, and various properties of the octahedral
magnetite particles coated with hydroxides of aluminum and oxides of silicon are shown
in Table 3.
Magnetic iron oxide particles 6 to 8:
[0187] The same procedure as defined in the production of the magnetic iron oxide particles
5 above, was conducted except that kind of magnetic iron oxide particles, and kind
and amount of additives used in the surface treatment were varied, thereby obtaining
surface-treated magnetic iron oxide particles.
[0188] Main production conditions are shown in Table 2, and various properties of the obtained
surface-treated magnetic iron oxide particles are shown in Table 3.
Examples 3 to 14 and Comparative Examples 1 to 4:
<Production of composite particles>
[0189] The same procedure as defined in Example 1 was conducted except that kind of magnetic
iron oxide particles to be treated, addition or non-addition of an alkoxysilane compound
or polysiloxane in the coating treatment with alkoxysilane compound or polysiloxane,
kind and amount of the alkoxysilane compound or polysiloxane added, treating conditions
of edge runner in the coating treatment, kind and amount of carbon black fine particles
added in the first carbon black coat forming step, and treating conditions of edge
runner used in the process for forming the first carbon black coat, were varied, thereby
obtaining composite particles.
[0190] Various properties of the carbon black fine particles B to E are shown in Table 4.
[0191] Main production conditions are shown in Table 5, and various properties of the obtained
composite particles are shown in Table 6.
[0192] The composite particles obtained in Examples 3 to 14 were observed by an electron
microscope. As a result, almost no independent carbon black was recognized. Therefore,
it was confirmed that a substantially whole amount of the carbon black contributed
to the formation of the first carbon black coat on the coating layer composed of organosilane
compound produced from the alkoxysilane compound or polysiloxane.
[0193] Meanwhile, all the additives used in Examples 11 to 13 were polysiloxanes. Specifically,
"TSF484" (tradename, produced by GE Toshiba Silicone Co., Ltd.) was methyl hydrogen
polysiloxane; "BYK-080" (tradename, produced by BYK-Chemie Japan Co., Ltd.) was modified
polysiloxane; and "TSF-4770" (tradename, produced by GE Toshiba Silicone Co., Ltd.)
was carboxylic acid-terminal-modified polysiloxane.
Examples 15 to 26 and Comparative Examples 5 to 11:
<Production of black magnetic composite particles>
[0194] The same procedure as defined in Example 1 was conducted except that kind of composite
particles, kind and amount of adhesive added, edge runner treatment conditions used
in the adhesive-treating step, kind and amount of carbon black fine particles added
in the second carbon black coat-adhering step, and edge runner treatment conditions
used in the second carbon black coat-adhering step, were changed variously, thereby
obtaining black magnetic composite particles.
[0195] Meanwhile, as a result of observing the black magnetic composite particles obtained
in Examples 15 to 26 by an electron microscope, no liberated carbon black was recognized.
Therefore, it was confirmed that almost a whole amount of carbon black added was adhered
onto the first carbon black coat.
[0196] Main treatment conditions are shown in Table 7, and various properties of the obtained
black magnetic composite particles are shown in Table 8.
Examples 27 to 38 and Comparative Examples 12 to 23:
<Production of black magnetic toner>
[0197] The same procedure as defined in Example 2 was conducted by using the black magnetic
composite particles obtained in Examples 15 to 26, composite particles obtained in
Example 5, Core particles 1 to 4, and Comparative Examples 3 and 5 to 11, thereby
obtaining black magnetic toners.
1. A black magnetic toner comprising a binder resin and black magnetic composite particles
having an average particle diameter of 0.06 to 1.0 µm and comprising:
(a) magnetic iron oxide particles;
(b) a coating layer on the surface of said magnetic iron oxide particles, comprising
at least one organosilicon compound selected from:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes; and (c) a carbon black coat which is
provided on said coating layer in an amount of 26 to 55 parts by weight per 100 parts
by weight of said magnetic iron oxide particles.
2. A black magnetic toner according to claim 1, wherein the binder resin is present in
an amount of from 50 to 900 parts by weight per 100 parts by weight of the black magnetic
composite particles.
3. A black magnetic toner according to claim 1 or 2, which has an average particle size
of 3 to 15 µm and/or a fluidity index of 78 to 100 and/or a blackness (L* value) of
not more than 19 and/or a volume resistivity of 1.0 x 1013 to 1.0 x 1017 Ω•cm.
4. A black magnetic toner according to any one of the preceding claims, wherein said
magnetic iron oxide particles (a) are particles which have a coat on at least a part
of the surface thereof comprising at least one compound selected from hydroxides of
aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount
of 0.01 to 50 % by weight, calculated as Al or SiO2, based on the total weight of the magnetic iron oxide particles.
5. A black magnetic toner according to any one of the preceding claims, wherein said
alkoxysilane compound is represented by the general formula (I):
R1 aSiX4-a (I)
wherein R1 is C6H5-, (CH3)2CHCH2- or n-CbH2b+1- (wherein b is an integer of 1 to 18); X is CH3O- or C2H5O-; and a is an integer of 0 to 3.
6. A black magnetic toner according to claim 5, wherein said alkoxysilane compound is
methyl triethoxysilane, dimethyl diethoxysilane, phenyl triethoxysilane, diphenyl
diethoxysilane, methyl trimethoxysilane, dimethyl dimethoxysilane, phenyl trimethoxysilane,
diphenyl dimethoxysilane, isobutyl trimethoxysilane or decyl trimethoxysilane.
7. A black magnetic toner according to any one of the preceding claims, wherein said
polysiloxanes are represented by the general formula (II):
wherein R
2 is H- or CH
3-, and d is an integer of 15 to 450.
8. A black magnetic toner according to claim 7, wherein said polysiloxanes are ones having
methyl hydrogen siloxane units.
9. A black magnetic toner according to any one of the preceding claims, wherein said
modified polysiloxanes are selected from:
(A) polysiloxanes modified with at least one compound selected from polyethers, polyesters
and epoxy compounds, and
(B) polysiloxanes whose molecular terminal is modified with at least one group selected
from carboxylic acid groups, alcohol groups and a hydroxyl group.
10. A black magnetic toner according to claim 9, wherein said polysiloxanes (A) are represented
by the general formula (III), (IV) or (V):
wherein R
3 is -(-CH
2-)
h-; R
4 is -(-CH
2-)
i-CH
3; R
5 is -OH, -COOH, -CH=CH
2, -C(CH
3)=CH
2 or -(-CH
2-)
j-CH
3; R
6 is -(-CH
2-)
k-CH
3; g and h are an integer of 1 to 15; i, j and k are an integer of 0 to 15; e is an
integer of 1 to 50; and f is an integer of 1 to 300;
wherein R
7, R
8 and R
9 are -(-CH
2-)
q- and may be the same or different; R
10 is -OH, -COOH, -CH=CH
2, -C(CH
3)=CH
2 or -(-CH
2-)
r-CH
3; R
11 is -(-CH
2-)
s-CH
3; n and q are an integer of 1 to 15; r and s are an integer of 0 to 15; e' is an integer
of 1 to 50; and f' is an integer of 1 to 300; or
wherein R
12 is -(-CH
2-)
v-; v is an integer of 1 to 15; t is an integer of 1 to 50; and u is an integer of
1 to 300.
11. A black magnetic toner according to claim 9 or 10, wherein said polysiloxanes (B)
are represented by the general formula (VI):
wherein R
13 and R
14 are -OH, R
16OH or R
17COOH and may be the same or different; R
15 is -CH
3 or -C
6H
5; R
16 and R
17 are -(-CH
2-)
y-; y is an integer of 1 to 15; w is an integer of 1 to 200; and x is an integer of
0 to 100.
12. A black magnetic toner according to any one of the preceding claims, wherein the amount
of said coating organosilicon compound(s) is 0.02 to 5.0 % by weight, calculated as
Si, based on the total weight of the organosilicon compound(s) and said magnetic iron
oxide particles.
13. A black magnetic toner according to any one of the preceding claims, wherein the thickness
of said carbon black coat is not more than 0.06 µm.
14. A black magnetic toner according to any one of the preceding claims, wherein said
black magnetic composite particles have a geometrical standard deviation of particle
sizes of 1.01 to 2.0.
15. A black magnetic toner according to any one of the preceding claims, wherein said
black magnetic composite particles have a BET specific surface area value of 1 to
100 m2/g, a fluidity index of 48 to 90 and a blackness (L* value) of 15 to 19.5.
16. A black magnetic toner according to any one of the preceding claims, wherein said
black magnetic composite particles have a coercive force of 0.8 to 31.8 kA/m, a saturation
magnetization of 50 to 91 Am2/kg, and a residual magnetization of 1 to 35 Am2/kg.
17. Black magnetic composite particles for a black magnetic toner, comprising:
(a) magnetic iron oxide particles having an average major axis diameter of 0.055 to
0.95 µm;
(b) a coating layer on the surface of said magnetic iron oxide particles, comprising
at least one organosilicon compound selected from:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes; and (c) a carbon black coat which is
provided on said coating layer in an amount of 26 to 55 parts by weight based on 100
parts by weight of said magnetic iron oxide particles.
18. Black magnetic composite particles according to claim 17, wherein said magnetic iron
oxide particles (a) are particles which have a coat on at least a part of the surface
thereof comprising at least one compound selected from hydroxides of aluminum, oxides
of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50
% by weight, calculated as Al or SiO2, based on the total weight of the magnetic iron oxide particles.
19. Black magnetic composite particles according to claim 17 or 18, wherein said alkoxysilane
compound is represented by the general formula (I):
R1 aSiX4-a (I)
wherein R1 is C6H5-, (CH3)2CHCH2- or n-CbH2b+1- (wherein b is an integer of 1 to 18); X is CH3O- or C2H5O-; and a is an integer of 0 to 3.
20. Black magnetic composite particles according to claim 19, wherein said alkoxysilane
compound is methyl triethoxysilane, dimethyl diethoxysilane, phenyl triethoxysilane,
diphenyl diethoxysilane, methyl trimethoxysilane, dimethyl dimethoxysilane, phenyl
trimethoxysilane, diphenyl dimethoxysilane, isobutyl trimethoxysilane or decyl trimethoxysilane.
21. Black magnetic composite particles according to any one of claims 17 to 20, wherein
said polysiloxanes are represented by the general formula (II):
wherein R
2 is H- or CH
3-, and d is an integer of 15 to 450.
22. Black magnetic composite particles according to claim 21, wherein said polysiloxanes
are ones having methyl hydrogen siloxane units.
23. Black magnetic composite particles according to any one of claims 17 to 22, wherein
said modified polysiloxanes are selected from:
(A) polysiloxanes modified with at least one compound selected from polyethers, polyesters
and epoxy compounds, and
(B) polysiloxanes whose molecular terminal is modified with at least one group selected
from carboxylic acid groups, alcohol groups and a hydroxyl group.
24. Black magnetic composite particles according to claim 23, wherein said polysiloxanes
(A) are represented by the general formula (III), (IV) or (V):
wherein R
3 is -(-CH
2-)
h-; R
4 is -(-CH
2-)
i-CH
3; R
5 is -OH, -COOH, -CH=CH
2, -C(CH
3)=CH
2 or -(-CH
2-)
j-CH
3; R
6 is -(-CH
2)
k-CH
3; g and h are an integer of 1 to 15; i, j and k are an integer of 0 to 15; e is an
integer of 1 to 50; and f is an integer of 1 to 300;
wherein R
7, R
8 and R
9 are -(-CH
2-)
q- and may be the same or different; R
10 is -OH, -COOH, -CH=CH
2, -C(CH
3)=CH
2 or -(-CH
2-)
r-CH
3; R
11 is -(-CH
2-)
s-CH
3; n and q are an integer of 1 to 15; r and s are an integer of 0 to 15; e' is an integer
of 1 to 50; and f' is an integer of 1 to 300; or
wherein R
12 is -(-CH
2-)
v-; v is an integer of 1 to 15; t is an integer of 1 to 50; and u is an integer of
1 to 300.
25. Black magnetic composite particles according to claim 23 or 24, wherein said polysiloxanes
(B) are represented by the general formula (VI):
wherein R
13 and R
14 are -OH, R
16OH or R
17COOH and may be the same or different; R
15 is -CH
3 or -C
6H
5; R
16 and R
17 are -(-CH
2-)
y-; y is an integer of 1 to 15; w is an integer of 1 to 200; and x is an integer of
0 to 100.
26. Black magnetic composite particles according to any one of claims 17 to 25, wherein
the amount of said coating organosilicon compound(s) is 0.02 to 5.0 % by weight, calculated
as Si, based on the total weight of the organosilicon compound(s) and said magnetic
iron oxide particles.
27. Black magnetic composite particles according to any one of claims 17 to 26, wherein
the thickness of said carbon black coat is not more than 0.06 µm and/or the average
particle size is 0.06 to 1.0 µm and/or the geometrical standard deviation of particle
sizes is 1.01 to 2.0.
28. Black magnetic composite particles according to any one of claims 17 to 27, wherein
the BET specific surface area value is 1 to 100 m2/g, the fluidity index is 48 to 90 and the blackness (L* value) is 15 to 19.5.
29. Black magnetic composite particles according to any one of claims 17 to 28, wherein
the coercive force is 0.8 to 31.8 kA/m, the saturation magnetization is 50 to 91 Am2/kg, and the residual magnetization is 1 to 35 Am2/kg.
30. A process for producing black magnetic composite particles defined in claim 17, which
process comprises:
(i) mixing as core particles magnetic iron oxide particles having an average particle
size of 0.055 to 0.95 µm together with at least one compound selected from:
(1) alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes,
by using an apparatus capable of applying a shear force to the core particles, thereby
coating the surface of said magnetic iron oxide particle with the said compound(s);
(ii) mixing the coated magnetic iron oxide particles thus obtained and 1 to 25 parts
by weight per 100 parts by weight of the core particles, of carbon black particles
having an average particle size of 0.002 to 0.05 µm by using an apparatus capable
of applying a shear force to the particles, thereby forming a carbon black coat on
the surface of the coated magnetic iron oxide particles;
(iii) mixing the carbon black coated magnetic iron oxide particles with 0.1 to 5 parts
by weight, per 100 parts by weight of the core particles, of dimethylpolysiloxane(s)
by using an apparatus capable of applying a shear force to the particles; and
(iv) mixing the obtained magnetic iron oxide particles with 1 to 30 parts by weight,
per 100 parts by weight of the core particles, of carbon black particles having an
average particle size of 0.002 to 0.05 µm by using an apparatus capable of applying
a shear force to the particles.
31. A process according to claim 30, wherein said magnetic iron oxide particles as core
particles are provided having a coat of at least one compound selected from hydroxides
of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon.