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(11) | EP 1 424 606 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Electrophotographic positively charged toner and manufacturing method thereof |
| (57) [Problem] To provide an electrophotographic positively charged toner and a manufacturing
method thereof, according to which even if after kneading, pulverization and classification
the toner is made spherical by melting the surfaces of the particles in a hot air
current, the charge control agent is not coated and hence the charging ability thereof
is not reduced, and thus the toner has sufficient tribo-charging ability for good
image formation, excellent transfer efficiency, and excellent charge build-up performance
and excellent charge stability upon continuous printing. [Means of Solution] In the case of an electrophotographic positively charged toner comprising a core toner that has a binder resin, a wax, a colorant and a charge control agent as principal component materials thereof and has been spherified through heat treatment, and at least fine silica particles as an external additive, the charge control agent is made to contain a resin having a quaternary ammonium salt group as a functional group and a nigrosine dye. |
[Technical Field]
[0001] The present invention relates to an electrostatic latent image toner that can be used in an electrophotographic type image forming apparatus, and in particular to an electrophotographic positively charged toner, and a manufacturing method thereof.
[Background Art]
[0002] With toners for developing electrostatic latent images used in electrostatic copiers, printers and so on that use an electrophotographic method, in a developing step, the toner is conveyed and attached to an electrostatic latent image on the surface of a photoreceptor that has been formed through previous charging and exposure steps, whereby the image is made visible. The toner image is transferred from the surface of the photoreceptor onto a transfer medium (paper etc.) in a subsequent transfer step, and is then fused in a fusing step, before the transfer medium (paper etc.) is discharged in a state having the image printed thereon as a printed image. In general, the developing step can be broadly classified into a two-component developing method in which a toner and a carrier are used in combination, and a one-component developing method in which a toner is used alone.
[0003] The toners used in these developing methods are generally obtained by dispersing carbon black, a pigment or the like as a colorant through hot melt-kneading in a binder resin comprising a thermoplastic resin such as a natural resin, and then carrying out dry pulverization into fine particles. For example, the colorant may be dispersed by kneading in a binder resin having a styrene-acrylic copolymer as a principal component thereof using an agitator such as a Kneader, an Extruder or a Banbury mixer, and then fine pulverization into particles of size approximately 5 to 20µm may be carried out to obtain the toner. Moreover, a magnetic toner can be obtained by further including a magnetic powder such as magnetite when carrying out the kneading and dispersion.
[0004] Toners used in the above-mentioned developing methods must in all cases be given a charge of positive or negative polarity corresponding to the polarity of the positive or negative charge on the surface of the photoreceptor before the formation of the electrostatic latent image, and this charge must be maintained. For the charge bestowing ability for this purpose, it is possible to use the tribo-charging ability inherent to a material such as a binder resin or a colorant that is a constituent component of the toner, but in general the charge amount obtained through the tribo-charging ability inherent to such a material is often too low for good image formation, and hence an image developed using only this tribo-charging is prone to being indistinct, with background fog being observed and so on. Consequently, in actual practice, to give a toner the necessary tribo-charging ability for good image formation, in general a substance called a charge control agent, such as a dye, a pigment or a specially synthesized organic compound, that makes it easy to bestow chargeability is specially added. As such charge control agents, there are materials for charge bestowing ability of each of positive and negative polarity, with various materials being known for each.
[0005] Of these, as positive charge control agents, colorants such as various azine compounds, nigrosine dyes, triphenylmethane dyes and phthalocyanine pigments, and also quaternary ammonium salt compounds, and resins containing a quaternary ammonium salt group or an amine group, and so on are well known materials, and these have been widely used from hitherto. Such charge control agents are usually used singly. Of these charge control agents, the nigrosine dye type positive charge control agents have often been used alone from hitherto, but because the chemical structure is complex, and chemical stability as a substance is poor, there has been a problem that chemical decomposition or degeneration is easily brought about through heat and mechanical shock due to friction during hot melt-kneading and so on, and hence the charge stability is impaired and thus the charging ability drops, and hence the original charge bestowing ability can no longer be exhibited.
[0006] Moreover, in the case of using a quaternary ammonium salt compound or a macromolecular compound (resin) containing a positively chargeable functional group such as a quaternary ammonium salt group or an amine group as a charge control agent, although problems during hot melt-kneading as in the case of the above-mentioned dyes do not occur, the tribo-charge bestowing ability is considerably lower than with the above-mentioned dyes, and hence to obtain the charge amount required for good image formation using such a compound alone, the amount added of the charge control agent must be made high. However, with a resin type charge control agent as described above in particular, if the amount added is made too high, then there will be problems such as the offset resistance being impaired, and hence suitably adjusting the amount added is extremely difficult. Details of the charge control agents described above are given in the following patent documents (1) to (8).
[0007] Moreover, in general, with styrene-acrylic copolymer resins and polyester resins that are widely used as binder resins, the tribo-charging polarity of the resin itself in the developing step is generally negative, and hence in the case of adjusting a toner to be positively charged overall through the action of an added positive charge control agent, the positive charge bestowing ability possessed by the toner may not necessarily be sufficient and stable compared with the negative charge bestowing ability. For example, upon continuous printing, due to the charge control agent gradually separating away from the toner and so on, a deterioration in charge will be prone to occurring, and as a result problems may arise such as image defects such as printing density reduction and background fog, and a phenomenon of toner filming onto the photoreceptor caused by the deterioration in charge. In this way, conventional toners, in particular positively charged toners, having a charge control agent added thereto and obtained through dry pulverization have been insufficient in terms of maintaining a stable a positive charge bestowing ability over a prolonged time.
[0008] Furthermore, in recent years, to enable image quality to be improved with electrophotographic type copiers, printers and so on, there has been a transition to smaller particle sizes for toners used in such electrophotographic apparatuses. With the above-mentioned conventional dry pulverization method, upon a decrease in particle size, there are problems such as the fluidity dropping, the chargeability becoming ununiform, and accompanying this the image quality deteriorating and the transfer efficiency dropping. To resolve these problems, wet granulation methods using emulsion polymerization or suspension of the binder resin have been developed, and toners that have a small particle size but do not have reduced fluidity have been obtained, and have already been practically implemented.
[Patent Document 1]
[Patent Document 2]
[Patent Document 3]
[Patent Document 4]
[Patent Document 5]
[Patent Document 6]
[Patent Document 7]
[Patent Document 8]
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0017] However, with such wet granulation methods, impurities such as polymerization initiators and surfactants added during the granulation are prone to remaining in the toner particles after the granulation, which often has adverse effects on the chargeability, the insulation properties and so on. Furthermore, with the above-mentioned wet polymerization granulation method, there is a limitation on what binder resins can be used, and hence the scope for selecting the resin is narrow. Furthermore, there are also problems such as the degree of freedom to select the molecular weight distribution of the resin being limited.
[0018] On the other hand, with the conventional dry pulverization method, a method is already known in which, after kneading, pulverization and classification, the toner is introduced into a hot air current, and the surfaces of the particles are melted to carry out spherification, whereby an attempt is made to resolve problems such as the above-mentioned drop in fluidity; however, a problem with this method is that the toner charge amount drops upon carrying out the spherification by melting the surfaces of the toner particles. Specifically, through the melting of the surfaces of the toner particles, the charge control agent present and exposed at the surfaces is coagulated and coated by the molten resin, whereby the charging ability drops.
[0019] In view of the points described above, it is an object of the present invention to provide an electrophotographic positively charged toner and a manufacturing method thereof, according to which even if after kneading, pulverization and classification the toner is made spherical by melting the surfaces of the particles in a hot air current, the charge control agent is not coated and hence the charging ability thereof is not reduced, and thus the toner has sufficient tribo-charging ability for good image formation, excellent transfer efficiency, and excellent charge build-up performance and excellent charge stability upon continuous printing.
[Means for Solving the Problems]
[0020] According to the present invention, the above object is attained through an electrophotographic positively charged toner comprising a core toner that has a binder resin, a wax, a colorant and a charge control agent as principal component materials thereof and has been spherified through heat treatment, and at least fine silica particles as an external additive, wherein the charge control agent contains a resin having a quaternary ammonium salt group as a functional group and a nigrosine dye.
[0021] According to the present invention, the electrophotographic positively charged toner of claim 1 is preferably made to be such that the charge control agent contains 2 to 10 parts by weight of the resin having a quaternary ammonium salt group as a functional group, and 0.5 to 5 parts by weight of the nigrosine dye, per 100 parts by weight of the binder resin.
[0022] According to the present invention, the electrophotographic positively charged toner of claim 1 or 2 is preferably made to be such that the resin having a quaternary ammonium salt group as a functional group has as a principal component thereof a styrene-acrylic copolymer resin containing a repeat unit represented by undermentioned formula (1) and a repeat unit represented by undermentioned formula (2) (where, in the formulae, R1 and R2 represent a hydrogen atom or a methyl group, R3 represents an alkylene group, and R4, R5 and R6 each represents an alkyl group, and the styrene-acrylic copolymer resin comprises 65 to 97 wt% of the repeat unit represented by undermentioned formula (1) and 35 to 3 wt% of the repeat unit represented by undermentioned formula (2), and has a weight average molecular weight in a range of 2,000 to 10,000)
[0023] According to the present invention, the electrophotographic positively charged toner of any one of claims 1 through 3 is preferably made to be such that the binder resin has a styrene-acrylic copolymer resin as a principal component thereof.
[0024] According to the present invention, the electrophotographic positively charging toner of any one of claims 1 through 4 is preferably made to contain 3 to 6 parts by weight of carbon black exhibiting a pH of at least 8.0 as the colorant per 100 parts by weight of the binder resin.
[0025] According to the present invention, the above object is attained through a method of manufacturing the electrophotographic positively charging toner of any one of claims 1 through 5, comprising mixing/agitating the binder resin, the wax, the colorant and the charge control agent as principal component materials, then hot melt-kneading, pulverizing and classifying the kneaded material obtained to produce a core toner, spherifying the core toner through hot air blast treatment, and then mixing in at least silica fine particles as an external additive.
[Effect of the Invention]
[0026] According to the present invention, in the case of an electrophotographic positively charged toner comprising a core toner that has a binder resin, a wax, a colorant and a charge control agent as principal component materials thereof and has been spherified through heat treatment, and at least fine silica particles as an external additive, the charge control agent is made to contain a resin having a quaternary ammonium salt group as a functional group and a nigrosine dye; as a result, an electrophotographic positively charged toner and a manufacturing method thereof can be provided, according to which even if after kneading, pulverization and classification the toner is spherified by melting the surfaces of the particles in a hot air current, the charge control agent is not coated and hence the charging ability thereof is not reduced, and thus the toner has sufficient tribo-charging ability for good image formation, excellent transfer efficiency, and excellent charge build-up performance and excellent charge stability upon continuous printing.
[Best Mode for Carrying out the Invention]
[0027] Following is a detailed description of the electrophotographic positively charged toner of the present invention, with reference to the drawings. The present invention is not limited to the examples described below, provided the gist of the present invention is not exceeded.
Fig. 1 is a schematic sectional view of a treating apparatus for spherifying the electrophotographic positively charged toner according to the present invention.
Fig. 2 is an SEM photograph (800x) of the electrophotographic positively charged toner of the present invention before the spherification.
Fig. 3 is an SEM photograph (800x) of the electrophotographic positively charged toner after the spherification according to the present invention.
[0028] The electrophotographic positively charged toner of the present invention is obtained by taking a binder resin, a wax, a colorant and a charge control agent as principal component materials, mixing/agitating these materials, then hot melt-kneading, pulverizing and classifying the kneaded material obtained, spherifying the core toner thus obtained, and then mixing in an external additive of silica fine particles and so on to further improve the fluidity of the toner. Following is a description of each of the above-mentioned materials, i.e. the binder resin, the wax, the colorant and the charge control agent in this order.
(Binder resin)
[0029] As the binder resin used in the present invention, a resin having as a principal component thereof an ordinary thermoplastic resin having good fusing ability well known as a binder resin from hitherto can be used. Examples are resins having as a principal component thereof one of a polyester resin, a polystyrene resin, a styrene-acrylic copolymer resin, an epoxy resin, a vinyl chloride resin, a vinyl acetate resin or the like, or a mixture of the above, or a copolymer resin of two or more of the above. In particular, in the case that the charge control agent according to the present invention, described later, has a styrene-acrylic copolymer resin as a base thereof, a styrene-acrylic copolymer resin is preferable as the binder resin, since then compatibility is excellent, and hence there is an effect of separating away of the charge control agent upon repeated use of the toner being prevented. In the case of using a styrene-acrylic copolymer resin as the binder resin, for example, to obtain both good fusing ability and good offset resistance for the toner, it is preferable for the resin to exhibit a molecular weight distribution in a range of 2,000 to 900,000, with peaks at both a low molecular weight of several thousand and a high molecular weight of several hundred thousand.
(Wax)
[0030] The electrophotographic positively charged toner of the present invention contains a wax for the purpose of improving the offset resistance. As this wax, a publicly known wax such as polyethylene wax, polypropylene wax, beeswax or carnauba wax can be used. The amount added of the wax is preferably in a range of 1 to 7 parts by weight per 100 parts by weight of the binder resin. At less than 1 part by weight, the offset resistance will become poor, and at more than 7 parts by weight, the toner particles will become prone to coagulating together.
(Colorant)
[0031] As the colorant contained in the electrophotographic positively charged toner of the present invention, a single publicly known dye or pigment such as carbon black, lamp black or iron black, or a mixture thereof can be used. In the case of using carbon black as the colorant, the amount used is preferably in a range of 3 to 6 parts by weight per 100 parts by weight of the binder resin.
[0032] It has been ascertained that if the carbon black used in the toner according to the present invention is made to be alkaline with a pH of at least 8.0, then the polarity of tribo-charging is positive. The pH of the carbon black is measured using a sludge thereof. The pH is affected primarily by the number of oxygen-containing groups on the surface of the carbon black and the amount of ash (metal oxides and other residues). It is known that in general channel black is acidic, and furnace black is neutral to alkaline.
(Charge control agent)
[0033] A resin having a quaternary ammonium salt group as a functional group and a nigrosine dye are used together as the charge control agent contained in the electrophotographic positively charged toner of the present invention. As the resin, a positive charge control agent as described in detail in Japanese Patent Application Laid-open No. S63-60458 can be used. As described in Japanese Patent Application Laid-open No. S63-60458, the weight average molecular weight Mw of this resin (copolymer) is 2,000 to 10,000. If the weight average molecular weight Mw is less than 2,000, then the drop in the charge amount under a high-temperature high-humidity environment will be large, and offset will become prone to occurring during fusing. If the weight average molecular weight Mw is more than 10,000, then the compatibility with the binder resin will be poor, and hence uniform dispersion will become difficult to obtain. In the present invention, a weight average molecular weight Mw of 3,000 to 8,000 is particularly preferable. Moreover, the viscosity of the above resin effects the ability to be kneaded with the binder resin and the fusing ability, and hence is preferably 50 to 10,000 poise, particularly preferably 100 to 5,000 poise, at 130°C. The content of the above resin in the toner is preferably 2 to 10 parts by weight per 100 parts by weight of the binder resin. At less than 2 parts by weight, the charge amount necessary for good image formation will be difficult to obtain, and thus there will be a drawback of toner clouding becoming severe. At more than 10 parts by weight, problems such as a drop in environmental resistance, a drop in compatibility, and the occurrence of offset will become prone to arising. As the resin having a quaternary ammonium salt group as a functional group, Acrybase FCA-201-PS (trade name) made by Fujikura Kasei Co., Ltd., which is a resin having a charge controlling function, is preferable.
[0034] The nigrosine dye is a black dye, and is one well known as a charge control agent from hitherto, and comprises a mixture of a plurality of azine compounds. The content of the nigrosine dye in the toner is preferably 0.5 to 5 parts by weight per 100 parts by weight of the binder resin. At less than 0.5 parts by weight, the charge amount necessary for good image formation will be difficult to obtain, whereas at more than 5 parts by weight, separation away from the toner will become prone to occurring, and hence the charge amount will become unstable. In addition to the principal component materials described above, i.e. the binder resin, the wax, the colorant and the charge control agent, a small amount of a crystalline magnetic material may be added as required with a purpose of increasing the hardness of the toner particles.
[0035] In addition to the above, a fatty acid-modified nigrosine dye, a metal-containing nigrosine dye, a metal-containing fatty acid-modified nigrosine dye, a salicylic acid chromium complex, a quaternary ammonium compound or the like can be used as a charge control agent in the present invention.
(External additives)
[0036] As external additives in the present invention, slip additives such as fine tetrafluoroethylene particles, zinc stearate and titanium oxide, abrasives such as cerium oxide and silicon carbide, fluidity bestowing agents such as hydrophobic silica, electrical conductivity bestowing agents such as carbon black and tin oxide, and so on may be added to the core toner as required. Spherification is carried out on the toner of the present invention to improve the fluidity of the core toner as described earlier, but for good image formation, it is necessary to further improve the fluidity, and hence at least hydrophobic silica is mixed in as an external additive for improving the fluidity.
[Examples]
[Example 1]
[0037] Following is a specific description of the electrophotographic positively charged toner and manufacturing method thereof according to the present invention, along with an evaluation of examples according to the present invention and comparative examples not falling under the present invention, showing how the toner of the present invention is superior.
In the following description, 'parts' always means 'parts by weight'.
| (Binder resin) Styrene / n-butyl acrylate copolymer resin (CPR250, made by Mitsui Chemicals Inc.) | 100 |
| parts (Wax) Low-molecular-weight polypropylene (Hiwax NP-055, made by Mitsui Chemicals Inc.) | 5 parts |
| (Colorant) Carbon black (Regal 330R, Cabot Corporation) | 6 parts |
| (Charge control agent) Nigrosine dye (Bontron N-01, Orient Chemical Industries, Ltd.) | 2 parts |
| Resin having quaternary ammonium salt group as functional group (Acrybase FCA-201-PS, Fujikura Kasei Co., Ltd.) | 3 parts |
| (Hiwax, Regal, Bontron and Acrybase are all registered trademarks.) | |
[0038] A mixed material of the above composition was thoroughly mixed/agitated in a Henschel mixer, and was then subjected to hot melt-kneading in a twin-screw Extruder; the kneaded material obtained was cooled down to room temperature, and then coarse pulverization, fine pulverization and classification were carried out, thus obtaining an un-spherified black core toner having a mean volumetric particle size of 10 µm and a particle size distribution of 5 to 20 µm. An SEM photograph of the un-spherified core toner is shown in Fig. 2. It was found that the un-spherified toner shown in Fig. 2 had very poor fluidity as is. It was thought that this was due to the angular shape of the particles as shown in Fig. 2.
[0039] Following is a description of the method of spherifying the un-spherified core toner. Fig. 1 shows a schematic sectional view of the spherifying apparatus for the electrophotographic positively charged toner according to the present invention. Air 102 fed in from a blower 1 is introduced into a hot air blast generator 2, and is made into a hot air blast 103 at 400°C and a flow rate of 0.2 to 0.3 m3/min. The hot air blast 103 passes through an introducing pipe 2-1 and is fired into a first cyclone 7 from a hot air blast jetting nozzle 4. Meanwhile, the untreated core toner particles 10 are conveyed from a powder fixed amount feeder 3 by a prescribed amount of high-pressure air 101 and are fed into a toner firing device 5, whereupon the untreated core toner particles 10 are jetted into the first cyclone 7 from a firing nozzle 6 by the pressure of the high-pressure air 101. The jetted core toner particles 10 instantaneously contact the hot air blast 103 the temperature of which has been adjusted as mentioned above, and are thus subjected to uniform heat treatment and hence spherified. The core toner particles 10 that have been spherified by the heat treatment are immediately cooled by cooling air 104, pass through an introducing pipe without becoming attached to an inner wall of the first cyclone 7, which is equipped with a cooling water circulating jacket 7-1, and without agglomerating together, and are fed into a second cyclone 8 equipped with a cooling water circulating jacket 8-1, whereupon the spherified toner is further cooled, before being collected in a toner storage vessel 9. The cooling air 105 escapes out from an opening in an upper part of the second cyclone 8 into a bag filter, not shown. An SEM photograph of the spherified toner collected from the spherifying apparatus is shown in Fig. 3. It can be seen from FIG. 3 that the particles of the spherified toner that has been subjected to the heat treatment have a spherical shape with no angular parts, and it was found that the fluidity of the toner was improved. However, even though the fluidity was improved, the fluidity was still not at the level required for good image formation.
[0040] According to the spherification of the toner according to the present invention, because a resin having a quaternary ammonium salt group as a functional group and a nigrosine dye are used together as the charge control agent, the problem that has occurred with conventional spherified toners in which the charge control agent is taken into the binder resin, the surface of which has melted through the heat treatment during the spherification, and hence the charge control agent is coated and thus the charge bestowing ability reduction no longer occurs. That is, with the toner of the present invention, one component of the charge control agent is a resin, and this charge control agent resin is attached to and covers the surface of the binder resin that forms the core of the toner before the spherification, and hence even upon the heat treatment during the spherification, the charge control agent resin melts first and coagulates to the binder resin, and thus during this process the charge control agent resin is still at the outermost surface of the toner, and is not coated by the binder resin, and hence the charge bestowing ability works effectively. In fact, long-term stabilization of the charge bestowing ability is obtained through the charge control agent resin being firmly fixed to the binder resin.
[0041] However, the charge bestowing ability possessed by the charge control agent resin is considerably lower than that of a nigrosine dye or the like, and hence considering that new problems will thus arise if a large amount of this resin is added alone, it was realized that using a nigrosine dye, which has a high charge bestowing ability, together with the charge control agent resin would result in good effects, whereby the present invention was accomplished.
[0042] 0.5 parts of hydrophobic silica (NA50Y made by Nippon Aerosil Co., Ltd.) as an external additive for further increasing the fluidity of the toner was mixed with 100 parts of the spherified toner obtained through the spherification described above in a 20-liter Henschel mixer for 3 minutes at 1800 revs/min, thus carrying out external additive treatment. The toner according to the present invention thus obtained had a static bulk density of 0.45, and extremely high fluidity was obtained (see Table 1).
[0043] Next, 5 parts of the toner of the present invention, and 100 parts of a silicone-resin-coated ferrite carrier having a mean particle size of approximately 60µm were mixed together with agitation, thus preparing a two-component developer. The charge amount for this two-component developer was measured using a CF-100 blow-off charge amount measuring device made by Toshiba Chemicals. The result is that the charge amount was 55µC/g. Moreover, the build-up time taken to reach this charge amount was 3 seconds (see Table 1). Next, using this developer, continuous printing of 50,000 sheets was carried out under a high-temperature high-humidity environment of 35°C and 85%RH using a printer equipped with a positively charging organic photoreceptor, and an evaluation was made. Note that the replenishing toner used in this evaluation test was the same toner of the present invention as that used in the above-mentioned developer.
(Examples 2 to 4)
[0044] Examples 2, 3 and 4 were made to be the same as Example 1, except that the contents of the nigrosine dye and the resin having a quaternary ammonium salt group as a functional group in the charge control agent were changed to more desirable combinations of contents within the ranges stipulated in claim 2, specifically 0.6 parts and 2 parts, 3 parts and 5 parts, and 5 parts and 10 parts, per 100 parts of the binder resin.
(Example 5)
[0045] Example 5 was made to be the same as Example 1, except that the content of the resin having a quaternary ammonium salt group as a functional group in the charge control agent was made to be outside the range stipulated in claim 2.
(Example 6)
[0046] Example 6 was made to be the same as Example 1, except that the content of the nigrosine dye in the charge control agent was made to be outside the range stipulated in claim 2.
(Comparative Example 1)
[0047] Comparative Example 1 was made to be the same as Example 1, except that the spherification was not carried out.
(Comparative Example 2)
[0048] Comparative Example 2 was made to be the same as Example 3, except that the spherification was not carried out.
(Comparative Example 3)
[0049] Comparative Example 3 was made to be the same as Example 1, except that the resin having a quaternary ammonium salt group as a functional group was not used in the charge control agent.
(Comparative Example 4)
[0050] Comparative Example 4 was made to be the same as Example 1, except that the nigrosine dye was not used in the charge control agent.
[Table 1]
| Nigrosine dye (parts) | Charge control agent resin (parts) | Spherification | Static bulk density | Charge amount (µC/g) | Charge build-up time (s) | |||
| Initial | After 50K sheets | Initial | After 50K sheets | |||||
| Example 1 | 2 | 3 | Yes | 0.45 | 55 | 53 | 3 | 3 |
| Example 2 | 0.6 | 2 | Yes | 0.44 | 51 | 50 | 4 | 5 |
| Example 3 | 3 | 5 | Yes | 0.45 | 53 | 51 | 3 | 4 |
| Example 4 | 5 | 10 | Yes | 0.42 | 4 8 | 47 | 4 | 3 |
| Example 5 | 2 | 12 | Yes | 0.42 | 50 | 48 | 5 | 4 |
| Example 6 | 0.3 | 5 | Yes | 0.44 | 45 | 43 | 6 | 5 |
| Comparative Example 1 | 2 | 3 | No | 0.32 | 41 | 35 | 25 | 36 |
| Comparative Example 2 | 3 | 5 | No | 0.30 | 43 | 31 | 29 | 39 |
| Comparative Example 3 | 2 | 0 | Yes | 0.41 | 35 | 23 | 18 | 26 |
| Comparative Example 4 | 0 | 3 | Yes | 0.44 | 32 | 21 | 19 | 30 |
[Table 2]
| Nigrosine dye (parts) | Charge control control agent resin (parts) | Solid image density | Background fog density | Transfer efficiency | Evaluation | |||
| Initial | After 50K sheets | Initial | After 50K sheets | |||||
| Example 1 | 2 | 3 | 1.38 | 1.39 | 0.06 | 0.07 | 98 | good |
| Example 2 | 0.6 | 2 | 1.42 | 1.40 | " | " | 95 | good |
| Example 3 | 3 | 5 | 1.40 | 1.39 | " | " | 97 | good |
| Example 4 | 5 | 10 | 1.39 | 1.40 | " | " | 96 | good |
| Exanple 5 | 2 | 12 | 1.15 | 1.38 | 0.08 | 0.10 | 93 | fair |
| Example 6 | 0.3 | 5 | 0.93 | 1.30 | 0.10 | 0.11 | 95 | fair |
| Comparative Example 1 | 2 | 3 | 1.25 | 1.10 | 0.18 | 0.25 | 75 | poor |
| Comparative Example 2 | 3 | 5 | 1.28 | 1.09 | 0.15 | 0.27 | 71 | poor |
| Comparative Example 3 | 2 | 0 | 1.10 | 0.98 | 0.11 | 0.23 | 81 | poor |
| Comparative Example 4 | 0 | 3 | 1.10 | 0.95 | 0.10 | 0.24 | 83 | poor |
[0051] The printing evaluation results are shown in Tables 1 and 2. From these tables, it can be seen that, even in the case of evaluation under the severe environmental conditions described above, looking at the row for Example 1, there was little change in the toner properties, i.e. the charge amount and the build-up time thereof, or in the image quality, i.e. the image density of solid parts and the background fog density of non-image parts, between initially and after printing 50,000 sheets, and moreover the transfer efficiency was always maintained at at least 95%, i.e. stable printing quality could be obtained. For Examples 2 to 4 in which the combination of the contents of the charge control agents components was changed as described above, the static bulk density, which indicates the fluidity, was approximately as good as for Example 1. Moreover, regarding the other evaluation results, again there was little change in the toner properties, i.e. the charge amount and the build-up time thereof, or in the image quality, i.e. the image density of solid parts and the background fog density of non-image parts, between initially and after printing 50,000 sheets, and moreover the transfer efficiency was always maintained at at least 95%, i.e. stable printing quality could be obtained. For Examples 5 and 6, the evaluation results were not as good as for Examples 1 to 4, but it can be seen that there was still an improvement compared with Comparative Examples 1 to 4.
[0052] On the other hand, regarding the evaluation results for Comparative Examples 1 to 4, from Tables 1 and 2, it can be seen that initially the charge amount was low, the charge build-up time was rather long, the solid image density was low, and the background fog density was high; moreover, there were large changes in the toner properties, i.e. the charge amount and the build-up time thereof, and in the image quality, i.e. the image density of solid parts and the background fog density of non-image parts, between initially and after printing 50,000 sheets, and furthermore the transfer efficiency was low, i.e. stable printing quality was not obtained.
[0053] In the following examples, a description will be given regarding the inventions of claims 5, 8, 10 and 11, according to which it is preferable to make the electrophotographic positively charging toner of the present invention contain 3 to 6 parts by weight of carbon black exhibiting a pH of at least 8.0 as the colorant per 100 parts by weight of the binder resin. In the following description, 'parts' always means 'parts by weight'.
(Example 7)
[0054]
| (Binder resin) Styrene / n-butyl acrylate copolymer resin (Dianal FB-1157, made by Mitsubishi Rayon Co., Ltd.) | 100 parts |
| (Wax) Low-molecular-weight polypropylene (Hiwax NP-055, made by Mitsui Chemicals Inc.) | 5 parts |
| (Colorant) Carbon black (Regal 330R, made by Cabot Corporation; pH 8.5) | 4 parts |
| (Charge control agent) Nigrosine dye (Bontron N-01, made by Orient Chemical Industries, Ltd.) | 1 part |
| Resin having quaternary ammonium salt group as functional group (Acrybase FCA-201-PS, made by Fujikura Kasei Co., Ltd.) | 4 parts |
[0055] A mixed material of the above composition was thoroughly mixed/agitated in a Henschel mixer, and was then subjected to hot melt-kneading in a twin-screw Extruder; the kneaded material obtained was cooled down to room temperature, and then coarse pulverization, fine pulverization and classification were carried out, thus obtaining a black core toner having a mean volumetric particle size of 10 µm and a particle size distribution of 5 to 20 µm. 0.5 parts of hydrophobic silica (NA50Y made by Nippon Aerosil Co., Ltd.) as an external additive for bestowing fluidity was mixed with 100 parts of the core toner obtained as described above in a 20-liter Henschel mixer for 3 minutes at 2000 revs/min, thus carrying out external additive treatment, whereby a toner of the present invention was obtained. Next, 5 parts of this toner of the present invention, and 100 parts of a silicone-resin-coated ferrite carrier having a mean particle size of approximately 60µm were mixed together with agitation, thus preparing a two-component developer.
[0056] The charge amount for this developer was measured using a CF-100 blow-off charge amount measuring device made by Toshiba Chemicals. The result was that the charge amount was 45.5µC/g (Table 3). Moreover, the build-up time taken to reach this charge amount was 4 seconds (Table 3). Next, using the toner of the present invention obtained through the external additive treatment described above, continuous printing of 10,000 sheets was carried out under a high-temperature high-humidity environment of 35°C and 85%RH using a non-magnetic one-component developing type printer equipped with a positively charging organic photoreceptor, and evaluation was carried out. Note that the replenishing toner used in this evaluation test was the same toner of the present invention.
(Examples 8 to 10)
[0057] Examples 8, 9 and 10 were made to be the same as Example 7, except that the content of the colorant carbon black was changed to 3 parts, 5 parts or 6 parts per 100 parts of the binder resin, which is within the range specified in claim 5 but is different to the content in Example 7.
(Examples 11 to 13)
[0058] Examples 11, 12 and 13 were made to be the same as Example 7, except that the colorant carbon black was made to be Raven 420 made by Columbia Chemical Company (pH 9), Raven 1020 made by Columbia Chemical Company (pH 8.3) or Black Pearls 880 made by Cabot Corporation (pH 8), all of which exhibit a pH of at least 8.0.
(Comparative Examples 5 to 7)
[0059] Comparative Examples 5, 6 and 7 were made to be the same as Example 7, except that the colorant carbon black was made to be Raven 8000 made by Columbia Chemical Company (pH 2.4), Black Pearls L made by Cabot Corporation (pH 2.5) or Regal 400 made by Cabot Corporation (pH 4), which all exhibit a pH outside the range of the present invention.
(Comparative Examples 8 to 10)
[0060] Comparative Examples 8, 9 and 10 were made to be the same as Example 7, except that the content of the colorant carbon black was made to be 2 parts, 7 parts or 9 parts per 100 parts of the binder resin, which is outside the range specified in claim 5.
[0061] The printing evaluation is shown in Table 3. From Table 3, it can be seen that, even in the case of evaluation under the severe environmental conditions described above, looking at the row for Example 7, there was little change in the toner properties, i.e. the charge amount and the build-up time thereof, or in the image quality, i.e. the image density of solid parts and the background fog density of non-image parts, between initially and after printing 10,000 sheets, i.e. stable printing quality was obtained. For Examples 8 to 10 in which the content of the carbon black was changed as described above and Examples 11 to 13 in which the carbon black was changed to ones of different pH as described above, the results were approximately as good as for Example 7. Moreover, regarding the other evaluation results, again it can be seen that there was little change in the toner properties, i.e. the charge amount and the build-up time thereof, or in the image quality, i.e. the image density of solid parts and the background fog density of non-image parts, between initially and after printing 10,000 sheets, i.e. stable printing quality was obtained.
[0062] On the other hand, regarding the evaluation results for Comparative Examples 5 to 10, from Table 3, it can be seen that initially the charge amount was low, the charge build-up time was rather long, the solid image density was low, and the background fog density was rather high; moreover, there were large changes in the toner properties, i.e. the charge amount and the build-up time thereof, and in the image quality, i.e. the image density of solid parts and the background fog density of non-image parts, between initially and after printing 10,000 sheets, and consequently stable printing quality was not obtained. From the above comparison between Examples 7 to 13 and Comparative Examples 5 to 10, it can be seen that it is preferable to make the pH of the colorant in the electrophoto graphic positively charging toner of the present invention be at least 8.0, and make the content of the colorant be 3 to 6 parts by weight per 100 parts by weight of the binder resin
[Brief Description of the Drawings]
[0063]
[Fig. 1]
A schematic sectional view of a spherifying apparatus for an electrophotographic positively
charged toner according to the present invention.
[Fig. 2]
An SEM photograph of an electrophotographic positively charged toner before spherification.
[Fig. 3]
An SEM photograph of the electrophotographic positively charged toner after spherification
according to the present invention.
[Explanation of Reference Numerals]
1. An electrophotographic positively charged toner comprising a core toner that has a
binder resin, a wax, a colorant and a charge control agent as principal component
materials thereof and has been spherified through heat treatment, and at least fine
silica particles as an external additive, the electrophotographic positively charged
toner characterized in that said charge control agent contains a resin having a quaternary ammonium salt group
as a functional group and a nigrosine dye.
2. The electrophotographic positively charged toner according to claim 1, characterized in that said charge control agent contains 2 to 10 parts by weight of said resin having a
quaternary ammonium salt group as a functional group, and 0.5 to 5 parts by weight
of said nigrosine dye, per 100 parts by weight of said binder resin.
3. The electrophotographic positively charged toner according to claim 1 or 2, characterized in that said resin having a quaternary ammonium salt group as a functional group has as a
principal component thereof a styrene-acrylic copolymer resin containing a repeat
unit represented by undermentioned formula (1) and a repeat unit represented by undermentioned
formula (2) (where, in the formulae, R1 and R2 represent a hydrogen atom or a methyl group, R3 represents an alkylene group, and R4, R5 and R6 each represents an alkyl group, and the styrene-acrylic copolymer resin comprises
65 to 97 wt% of the repeat unit represented by undermentioned formula (1) and 35 to
3 wt% of the repeat unit represented by undermentioned formula (2), and has a weight
average molecular weight in a range of 2,000 to 10,000)
4. The electrophotographic positively charged toner according to any one of claims 1
through 3, characterized in that said binder resin has a styrene-acrylic copolymer resin as a principal component
thereof.
5. The electrophotographic positively charging toner according to any one of claims 1
through 4, characterized by containing 3 to 6 parts by weight of carbon black exhibiting a pH of at least 8.0
as said colorant per 100 parts by weight of said binder resin.
6. A method of manufacturing the electrophotographic positively charging toner according
to any one of claims 1 through 5, characterized by mixing/agitating said binder resin, said wax, said colorant and said charge control
agent as principal component materials, then hot melt-kneading, pulverizing and classifying
the kneaded material obtained to produce a core toner, spherifying the core toner
through hot air blast treatment, and then mixing in at least silica fine particles
as an external additive.