BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates to an electrophotographic process for recording and preserving
an electrostatic latent image developed by wet development.
Description of the Related Art
[0002] In the field of image formation, a system in which a uniformly charged photoconductor
is selectively irradiated with light as a function of image signals and an electrostatic
latent image thus formed is developed is generally termed an electrophotographic process.
This process may be roughly classified into either a dry developing method or a wet
developing method.
[0003] The dry developing method has an advantage in that it is superior in the ease of
handling and the stability of the toners used for development, since it is based on
the principle that colorant particles are simply spread and affixed to an electrostatic
latent image. However, dry developing is second to the wet development method in meeting
the recent demand for high quality images, as exemplified by a video printer for taking
an electronic still photograph.
[0004] On the other hand, the wet developing method makes use of a liquid developer which
is produced by dispersing the dyestuff or pigment as the colorant in an insulating
medium. According to the wet developing method, a resolution and gradation comparable
to those of a silver halide photograph may be obtained, while the image exhibits superior
weatherability when a pigment is used as the colorant.
[0005] The developer used in the conventional wet developing method contains an insulating
medium which is liquid at room temperature, such as "Isopar G", a saturated hydrocarbon
produced by Esso Inc., so that it is naturally liquid at room temperature (see Fig.
20).
[0006] However, the developing method employing a developer 5′ which is liquid at room temperature
is inconvenient to use since the developer can be handled only with difficulty and
frequent maintenance is required for maintaining stable image formation.
[0007] In the preservation and supply of the wet developer, disadvantages are presented
in connection with changes in the concentration thereof caused by cohesion or precipitation
of the colorant particles and disposal of waste liquids.
[0008] The Japanese Kokai (Published Application) No. 63-25670 discloses a method of developing
an electrostatic latent image formed on the surface of a sensitized material wherein
a toner is solidified and applied under pressure to the peripheral surface of a developing
roll and the thus coated toner is dissolved by a developer and caused to flow into
a space between the sensitized material and the developing roll.
[0009] In this reference, a developer such as "Isopar" is required for dissolving the solid
toner, while a stable image cannot be obtained unless the supply of the developer
is adjusted constantly.
[0010] For recording and preserving the electrostatic latent image in the visible form,
it is preferably transferred to a suitable substrate. However, the conventional wet
developing method is not necessarily suited to the purpose of forming a high quality
image since the adsorption between the colorant particles and the sensitized material
is so strong that the transfer efficiency is thereby lowered.
[0011] US-A-3 776 723 discloses an electrophotographic process according to the preamble
of claim 1 wherein the developer may comprise a dispersion of toner particles in an
electrically insulating carrier which is normally solid at room temperature, said
developer being liquefied prior to entering the exposure zone. In this process, a
photoconductor comprising a photoconductive insulating layer overlaying a conductive
substrate is contacted with a developer-laden web. An electrostatic charge of the
same or of an opposite polarity as that of the toner in the liquid developer is applied
by a corona discharge electrode on the liquid developer-laden web previously deposited
on the photoconductor. This charged member is then exposed to a pattern of light and
shadow through the conductive transparent backing substrate. After completing these
steps, a copy may be made by bringing an image receiving web in pressure contact with
the liquid developer-laden web.
[0012] US-A-3 254 997 relates to an electrophotographic process comprising the use of a
developer consisting of a meltable plastic or resin and a pigment dispersed therein.
Said process includes the steps of forming an electrostatic image on a substrate,
melting said developer and contacting the molten developer with the substrate.
Summary of the Invention
[0013] It is therefore an object of the present invention to overcome the above described
deficiencies of the prior art and to provide an electrophotographic process for developing
an electrostatic latent image which is superior in ease of handling and is capable
of producing stable images at all times.
[0014] In view thereof, a method of the present invention comprises the use of a developer
in which the colorant is dispersed and which is an electrically insulating organic
material that is solid at room temperature and is liquefied by heating. The electrostatic
latent image is wet developed by the thus liquefied developer.
[0015] The present invention provides an electrophotographic process for image formation
wherein an electrostatic latent image is formed on the surface of a film laminated
on a sensitized material using the light of a wavelength capable of being transmitted
through the film, the image thus formed is developed and the film is then peeled off
from the sensitized material for forming a high quality image quickly at low cost
and at high transfer efficiency.
[0016] Accordingly, the subject-matter of the present invention is an electrophotographic
process as defined in claim 1.
Brief Description of the Drawings
[0017] Fig. 1 is a diagrammatic view for illustrating the principle of the developing method
used in the present invention.
[0018] Fig. 2 is an enlarged cross-sectional view showing essential parts of an embodiment
of a developing material comprised of a base material having its overall surface coated
with a developer.
[0019] Fig. 3 is an enlarged cross-sectional view showing essential parts of an embodiment
of a developing material comprised of a porous base material impregnated with a developer
and solidified.
[0020] Fig. 4 is an enlarged cross-sectional view showing essential parts of an embodiment
of a porous base material impregnated with a developer, solidified and backed with
a sheet-like base material.
[0021] Fig. 5 is an enlarged cross-sectional view showing essential parts of an embodiment
of a developing material comprised of a base material having an electrically conductive
layer and coated on its overall surface with a developer.
[0022] Fig. 6 is an enlarged cross-sectional view showing essential parts of an embodiment
of a porous base material impregnated with a developer, solidified and coated on its
reverse side with an electrically conductive layer.
[0023] Fig. 7 is an enlarged cross-sectional view showing essential parts of an embodiment
of a porous base material impregnated with a developer, solidified and backed with
an electrically conductive base material.
[0024] Fig. 8 is an enlarged cross-sectional view showing essential parts of an embodiment
of a porous base material impregnated with a developer, solidified and backed with
a base material having an electrically conductive layer.
[0025] Fig. 9 is an enlarged cross-sectional view showing essential parts of an embodiment
of a developing material having plural developer regions formed thereon.
[0026] Fig. 10 is an enlarged cross-sectional view showing an embodiment of a porous base
material backed with a sheet-like substrate and having plural developer regions formed
thereon.
[0027] Fig. 11 is an enlarged cross-sectional view showing essential parts in which a porous
base material having plural developer regions formed therein is used directly as the
developing material.
[0028] Fig. 12 is an enlarged cross-sectional view showing an embodiment of a developing
material having plural developer regions with a color mixing inhibit layer.
[0029] Fig. 13 is a diagrammatic view for illustrating the principle of the developing method
for an electrostatic latent image forming the pre-stage of image formation.
[0030] Figs. 14(A) and 14(B) show diagrammatically the formation and elimination of electrical
charges on a sensitized material on which is laminated an electrically conductive
film having a dark decay time shorter than that of a sensitized material, wherein
Fig. 14(A) corresponds to the charging step of Fig. 14(B) corresponds to the light
exposure step. Figs. 15(A) and 15(B) show diagrammatically the formation and elimination
of the electrical charges on a sensitized material on which is laminated an electrically
insulating film having a dark decay time longer than that of the sensitized material,
wherein Fig. 15(A) corresponds to the charging step of Fig. 15(B) corresponds to the
light exposure step.
[0031] Fig. 16 is an enlarged view showing diagrammatically the state of affixture of methylene
iodide on the film surface.
[0032] Fig. 17 is an enlarged cross-sectional view showing a developing apparatus employed
in the examples of the present invention.
[0033] Fig. 18 shows diagrammatically the method for developing an electrostatic latent
image by a developing material comprised of a base material and a developer held thereon.
[0034] Fig. 19 shows diagrammatically the method for developing an electrostatic latent
image with a developing material in which a developer is held on an electrically conductive
substrate.
[0035] Fig. 20 shows a prior art system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] The principle of the developing method as used in the present invention will be explained
by referring to Fig. 1, in which the respective process steps are preferably successively
applied to one long sensitized base material 1 for convenience.
[0037] In an electrical charging step, the sensitized base material 1 is electrically charged
to a minus polarity by suitable charging means, such as a corona discharge member
2. At an ensuing exposure step, selective light exposure is performed in association
with the image information, using suitable exposure means, such as semiconductor infrared
laser light source 3, for eliminating negative charges of the area exposed to light.
[0038] Irrespective of the method for forming an electrostatic latent image or the kind
of the sensitized base material 1, any well-known organic or inorganic photoconductive
materials may be used for forming the base material 1. Examples of the well-known
organic photoconductive materials now in use include electrophotographic sensitized
base materials consisting of poly-N-vinyl-carbazole and 2,4,7-trinitrofluorene-9-on,
poly-N-vinylcarbazole sensitized with pyrylium salt type colorant, poly-N-vinylcarbazole
sensitized with cyanine type colorant, an electro-photographic sensitized base material
consisting mainly of organic pigments of eutectic complexes consisting of colorants
and resins. Examples of inorganic photoconductive materials include zinc oxide, zinc
sulfide, cadmium sulfide, selenium, selenium-tellurium alloy, selenium-arsenic alloy,
selenium-tellurium-arsenic alloy and amorphous silicon type materials.
[0039] At a subsequent developing step, the sensitized base material 1, on which the electrostatic
latent image has been formed as described hereinabove, is passed over a developing
tank 4. A developer 7 for the electrostatic latent image, which consists of an electrically
insulating organic material 5 which is solid at room temperature and contains dispersed
colorant particles 6 charged to a positive polarity, is contained in the tank 4, and
is heated and melted by heating means & so that it is in the liquid state.
[0040] The developer 7 supplied to the developing tank 4 consists of colorant particles
6 dispersed in an electrically insulating organic material 5 which is solid at least
at room temperature and which is changed between the solid and liquid states upon
heating and cooling.
[0041] The electrically insulating organic material 5 has a melting point of not lower than
30°C and preferably not lower than 40°C in view of the ordinary operating environment
and for ease of handling. Although there is no specific upper limit to the melting
point, practically it is about 100°C and preferably not higher than 80°C when considering
that additional energy is consumed for heating an insulating material 5 with too high
a melting point. Also, the upper limit of the melting point should not exceed the
heat resisting temperature of the material customarily employed as the base material
when the organic material is held on a base material for use.
[0042] Among the materials meeting these requirements are paraffins, waxes and mixtures
thereof. The paraffins include various normal paraffins with 19 to 60 carbon atoms,
such as nonadecane to hexacontane. The waxes include plant waxes such as Carnauba
wax or cotton wax, animal waxes such as bees wax, ozokerite, and petroleum waxes such
as paraffin waxes, crystallite waxes or petrolatum. These materials are dielectrics
having dielectric constants ε in the order of 1.9 to 2.3.
[0043] In addition, crystalline high molecular materials having long alkyl groups at the
side chains, such as homopolymers or copolymers of polyethylene, polyacrylamide, poly-n-stearyl
acrylate or poly-n-stearyl methacrylate, such as copoly-n-stearyl acrylate ethyl methacrylate,
may be employed. However, the aforementioned paraffins and waxes are preferred in
view of their viscosity at the time of heating.
[0044] The colorant particles 6 dispersed into the electrically insulating organic material
5 may be organic or inorganic pigments or dyestuffs that are well-known in the art,
or mixtures thereof.
[0045] The inorganic pigments include for example chromium type, iron type or cobalt type
pigments, ultramarine or Prussian blue. The organic pigments or dyestuffs include
Hansa Yellow (C. I. 11680), Benzidine Yellow G (C. I. 21090), Benzidine Orange (C.
I. 21110), Fast Red (C. I. 37085), Brilliant Carmin 3B (C. I. 16015 - Lake), Phthalocyanin
Blue (C. I. 74160), Victoria Blue (C. I. 42595 - Lake), Spirit Black (C. I. 50415),
Oil Blue (C. I. 74350), Alkali Blue (C. I. 42770A), Fast Scarlet (C. I. 12315), Lodamin
6B (C. I. 45160), Lodamin Lake (C. I. 45160 - Lake), Fast Sky Blue (C. I. 74200 -
Lake), Nigrocyn (C. I. 50415) or carbon black. These may be used alone or in combination.
Those exhibiting desired coloration may be used selectively.
[0046] The developer may also contain resins, in addition to the electrically insulating
organic materials 5 and colorant particles 6, for improving dispersibility or fixation
of the colorants. These resins may be suitably selected from known materials and my
include for example rubbers such as butadiene rubber, styrene-butadiene rubber, cyclized
rubber or natural rubber, synthetic resins such as styrene, vinyl toluene, polyester,
polycarbonate or polyvinyl acetate, rosin type resin, hydrogenated rosin type resin,
alkyd resins containing modified alkyds, such as linseed oil, modified alkyd resins
and natural resins such as polyterpenes. In addition, phenol resins, modified phenol
resins such as phenol formalin resins, phthalic acid pentaerythritol, Kumaronindene
resins, ester gum resins or vegetable oil polyamide resins may also be useful. Halogenated
hydrocarbon polymers, such as polyvinyl chloride or chlorinated polypropylene, synthetic
rubbers such as vinyl toluenebutadiene or butadiene-isoprene, polymers of acrylic
monomers having long-chain alkyl groups, such as 2-ethylhexyl methacrylate, lauryl
methacrylate, stearyl methacrylate, lauryl acrylate or octyl acrylate or copolymers
thereof with other polymerizable monomers, such as styrene-lauryl methacrylate copolymer
or acrylic acidlauryl methacrylate copolymer, polyolefins such as polyethylene or
polyterpenes, may also be employed.
[0047] The above developer is usually admixed with electrical charge donors. This applies
for the developer employed herein. The electrical charge donors employed for this
purpose include, for example, metal salts of fatty acids, such as naphthenic acid,
octenic acid, oleic acid, stearic acid, isostearic acid or lauric acid, metal salts
of sulfosuccinates, oil-soluble metal salts of sulfonic acid, metal salts of phosphates,
metal salts of abietic acid, metal salts of aromatic carboxylic acid or metal salts
of aromatic sulfonic acid.
[0048] For improving the charges of the colorant particles 6, fine particles of metal oxides,
such as SiO₂, Al₂O₃, TiO₂, ZnO, Ga₂O₃, In₂O₃, GeO₂, SnO₂, PbO₂ or MgO, or mixtures
thereof, may be employed as charge increasing additives.
[0049] Referring to the relative contents of the above ingredients, the colorant particles
7 are employed preferably at a rate of 0.01 to 100 g, and more preferably at a rate
of 0.1 to 10 g, to 1 liter of the electrically insulating organic material 5 in the
melted state, while the charge donors are employed usually at a rate of 0.001 to 10
g, and preferably at a rate of 0.01 to 1 g, to 1 liter of the organic material 5.
The charge increasing additive is added in an amount of not more than the same amount,
as that of the colorant particles 6.
[0050] The above developer is heated by the heating means 8 into the melted state. The heating
temperature may be suitably set in dependence upon, for example, the melting point,
and may usually be 30 to 130°C and preferably be 40 to 110°C.
[0051] When the liquefied developer 7 is contacted with the sensitized base material 1,
the colorant particles 6 migrate towards and are deposited at the negative electrical
charges.
[0052] Finally, the colorant particles 6 affixed to the unnecessary portion in the course
of the fixation process are eliminated and, after the process of elimination of the
electrical charges, the image is formed on the sensitized base material.
[0053] Meanwhile, when the sensitized base material 1 and the developer 7 are solidified
immediately after contact, the image tends to be degraded in quality. It is therefore
preferred to provide heating means for heating either the sensitized base material
1 itself or a stage to which the sensitized base material 1 is secured.
[0054] The heating temperature for the sensitized base material 1 may be suitably set in
dependence upon the kinds and characteristics of the sensitized material used. It
is preferably not lower than the liquidus temperature of the developer 7 and is usually
set in the range from room temperature to 130°C, and preferably in the range of 30
to 110°C.
[0055] The development may be monochromatic or may form a full color image using developers
of various colors, such as yellow, magenta and cyan. In this case, the above described
developing process may be performed repeatedly for each of the color developers, and
the developing sequence is selected as a function of, for example, the kind of the
light source used for sensitization. For example, when an IR laser or a UV laser is
employed, the sequence is yellow-magenta-cyan or cyan-magenta-yellow, respectively.
If necessary, inking may be performed with black color and, in such case, the black
color may be developed at a suitable point in the course of the development of the
various colors.
[0056] Although the developer 7 may be accommodated in the tank 4, as described above, it
may also be carried on a suitable base in the form of a sheet- or tape- like developing
material. In this case, the ease of handling of the developer is improved significantly.
[0057] Fig. 2 shows the simplest form of the development material wherein the developer
7 is coated on the overall surface of a sheet-like base material 21.
[0058] The base material 21 may be made of a high molecular film, such as polyethylene terephthalate,
polypropylene, polycarbonate or polyamide, papers such as natural or synthetic paper,
cloths or non-woven cloths formed of natural fibers, such as plant fibers exemplified
by cotton or hemp or animal fibers exemplified by silk or wool, clothes or non-woven
clothes formed of synthetic fibers including organic fibers such as polyamide, polyester,
polyacetal or polyurethane and inorganic fibers such as glass, ceramics or carbon,
meshes of metals or organic high molecular materials or a high molecular foam such
as polyurethane foam.
[0059] Fig. 3 shows an example of a porous base material 22, wherein the developer 7 is
impregnated and solidified in the porous base material 22.
[0060] The porous base material 22 in which the developer 7 is impregnated and solidified
may be backed and reinforced by a sheet-like base material 21, as shown in Fig. 4.
[0061] A bias voltage may be easily applied at the time of development by affording electrical
conductivity to the base material when formed into a tape or a sheet.
[0062] The base material afforded with electrical conductivity includes both a base material
exhibiting electrical conductivity and a non-conductive base material on which an
electrically conductive layer is formed.
[0063] In Fig. 2, the sheet-like base material 21 used is a sheet-like electrically conductive
base material 21′ and the developer 7 is coated on the overall surface of the base
material 21′.
[0064] The electrically conductive base material 21 may, for example be Al, Cu, stainless
steel, electrically conductive ceramics, carbon, SiC, indium tin oxide (ITO), SnO₂
or electrically conductive high molecular materials.
[0065] When the base material itself is not afforded with electrical conductivity, an electrically
conductive layer 24 may be formed on the surface of the base material 21 and the developer
7 may then be formed on the conductive layer 24, as shown in Fig. 5.
[0066] The conductive layer 24 is formed by evaporation, sputtering or plating of metals
or by coating of a material in which electrically conductive particles are dispersed,
such as a silver paste.
[0067] Fig. 6 shows an example of a porous base plate 22, in which the developer 7 is impregnated
and solidified. In this example, an electrically conductive layer 24 is formed on
the reverse side of the porous base plate 22 to provide for electrical conductivity.
[0068] The porous base plate 22, in which the developer 7 is impregnated and solidified
in the above described manner, may be backed with a sheet-like electrically conductive
base material 21′, as shown in Fig. 7, to provide for reinforcement and electrical
conductivity.
[0069] Also, as shown in Fig. 8, a porous base plate 22 in which the developer 7 is impregnated
and solidified in the above described manner may be laminated with the base plate
21 provided with the electrically conductive layer 24.
[0070] Also developers of plural colors may be incorporated into the base materials 21 or
21′ of the porous base material 22 when the base materials are formed into sheets
or tapes and zones of the different colors may be formed by coating on one and the
same base material.
[0071] In Fig. 9, for example, a yellow-color developer layer Y, a magenta color developper
layer M and cyan color developer layer C are formed on the base material 21 to provide
for full-color image formation. When forming the full-color image, a zone for a black
developer layer B may be annexed beside the yellow, magenta and cyan colors, if so
desired.
[0072] Similarly, as shown in Fig. 10, a yellow color developer Y, a magenta color developer
M and a cyan color developer C may be impregnated and solidified in separate regions
on the porous base material 22 laminated on the base material 21. Regions 22a of the
porous material 22 between the developer regions Y, M and C are free of developer.
Of course, as shown in Fig. 11, the porous base material 22 in which the yellow color
developer Y, magenta color developer M and the cyan color developer C are impregnated
and solidified may be directly used as the developer for developing the electrostatic
latent image.
[0073] Meanwhile, when plural developer regions are formed on one and the same base material,
color mixing may be caused during, above all, heating and melting.
[0074] Thus, as shown in Fig. 12, a color mixing inhibit layer 23 is provided in between
the regions consisting of the developers Y, M and C.
[0075] This color mixing inhibit layer 23 may be of any type so long as it functions as
a spacer. Above all, a liquid absorbing material, such as that similar to the aforementioned
porous base material 22, or a liquid repellent material may be employed.
[0076] When the developers Y, M and C of the respective colors are impregnated and solidified
into porous base material 22, as shown in Figs. 10 or 11, these regions of the developers
of the various colors may be formed at a predetermined interval from one another so
that the portions of the porous base material 22a delimited between these regions
act as the color mixing inhibit layers.
[0077] For recording and preserving the developed electrostatic latent image in a state
in which it can be seen readily, it is transferred to a suitable substrate. As transfer
method, a method (a) consisting of providing heating means at a stage supporting a
photosensitive member 1 and the developer 7 is contacted with the substrate as the
developer is heated and melted, or a method (b) consisting of pressuring the substrate
by means such as a roll as the developer is cooled and solidified are contemplated.
In the above method (a), the heating temperature of the photosensitive member 1 may
be suitably set as a function of the kinds and characteristics of the photosensitive
member 1, and is preferably in the range from 30° to 110°C.
[0078] In the above method (a), when the developer 7 is contacted with the substrate as
the developer 7 is heated to the melted state, and the substrate opposite to the member
1 is charged to a polarity opposite to that of the colorant particles, the transfer
efficiency of the image to the substrate is improved. For applying these electrical
charges of the opposite polarity, suitable means of electrification, such as a corona
discharge body, may be employed.
[0079] The material used as the substrate may be selected suitably, depending on usage,
as long as it can be impregnated to a more or less great degree with the electrically
insulating organic material. Examples of this material include various papers materials,
such as natural or synthetic paper, clothes or non-woven clothes formed of plant fibers
such as cotton or hemp or animal fibers such as silk or wool, clothes or non-woven
clothes formed of organic synthetic fibers such as polyamide, polyester, polyacetal
or polyurethane or inorganic fibers such as ceramics or carbon, meshes such as metals
or organic high molecular materials, or high molecular foams, such as polyurethane
foams. For preserving the substrate in the form of a document, a paper sheet of a
white ground is preferably employed as the substrate in view of higher visibility.
The present invention is, however, not limited to this exemplary embodiment.
[0080] In accordance with the present invention, as an image forming method for high speed
formation of a high quality image at low costs and high transfer efficiency, a method
is provided consisting of laminating a film 20 which is able to transmit light from
a light source 3 onto a sensitized material 1, exposing the film to light hv for forming
an electrostatic latent image on the film, developing the latent image and peeling
the film 20 from the sensitized material 1 (Fig. 13).
[0081] As methods for forming the image at this time, a method (a) consisting of laminating
an electro-conductive film which is shorter in dark decay time than the photosensitized
material, or a method (b) consisting of laminating an insulating film longer in dark
decay time than the sensitized material are suitable. The dark decay time herein means
the time interval during which the electrical charges on a material are reduced to
one half when the material, which has been previously electrified to certain constant
charges, is allowed to stand in the dark.
[0082] Possible mechanisms of charge formation and extinction in method (a) are described
below referring to Figs. 14(A) and 14(B).
[0083] As shown in Fig. 14(A), the surface of an electrically conductive film 20a is electrified
by corona discharge or by laser irradiation to a uniform negative charge. At this
time, the positive electrical charges are induced on the sensitized material 1 opposite
to the electrically conductive film 20a.
[0084] When a selective laser irradiation is then performed, as shown in Fig. 14(B), the
laser light hv passes through the electrically conductive film 20a to reach the sensitized
material 1. At this time, the negative charges on the surface of the electrically
conductive film 20a are conducted in the direction of the film thickness towards the
boundary between the film 20a and the sensitized material 1, while, on the side of
the sensitized material, the positive charges or holes migrate towards the boundary
only at the laser irradiated zone. The result is that, in the region in which the
positive charges have migrated, the charges are neutralized and the potential is reduced
to zero on the boundary, whereas, in the region in which the positive charges have
not migrated, there exists a constant potential. Thus, the colorant particles 6, charged
to the positive potential, are selectively affixed to the region not irradiated by
the laser light hv, (as shown on the left side of Fig. 14(B)), whereas the colorant
particles do not become affixed to the region where the potential has been reduced
to zero by irradiation hv (as shown on the right side of Fig. 14(B)).
[0085] This becomes possible since the dark decay time of the electrically conductive film
20a is selected to be shorter than that of the sensitized material 1. If the dark
decay time of the sensitized material 1 is shorter than that of the film 20a, then
there is the risk that the positive charges will be dissipated before laser light
irradiation and the potential distribution cannot be formed. In short, what is critical
in the present invention is that the potential distribution as shown in Fig. 14(B)
is formed and maintained substantially unaltered until immediately before development
of the electrostatic latent image.
[0086] As may be realized from the foregoing description with reference to Fig. 13, a time
t equal t₁ + t₂ + t₃ + t₄ is required to elapse until the electrostatic latent image
is formed, wherein t₁ is the time involved in corona charging, t₂ is the time which
passes from the corona charging step until the exposure step, t₃ is the time involved
in exposure to light, and t₄ is the time which passes from the exposure step until
the developing step. Hence, from a more practical standpoint, it suffices if the dark
decay time of the electro-conductive film 20a is shorter than the above time t.
[0087] According to the present invention, as described hereinabove, the electrostatic latent
image is developed on the surface of the electrically conductive film 20a and then
the film 20a is peeled off from the sensitized material 1. If the film 20a is rigid
enough to be used by itself for preservation and perusal, it may be used directly,
as for example in the case wherein the film 20a is used directly as the sheet for
an overhead projector (OHP). Alternately, the film 20a may be bonded to the substrate
with the image forming surface of the film 20a in contact with the substrate, in which
case the film 20a acts as the protective film so that a so-called laminate coating
may be achieved simultaneously with the image transfer.
[0088] The material that may be used as the substrate may be selected suitably according
to usage as long as it can be impregnated with the aforementioned insulating dispersion
medium. Examples of this material include various paper materials, such as natural
or synthetic paper, clothes or non-woven clothes formed of plant fibers such as cotton
or hemp or animal fibers such as silk or wool, clothes or non-woven animal fibers
such as silk or wool, clothes or non-woven clothes formed of organic synthetic fibers
such as polyamide, polyester, polyacetal or polyurethane or inorganic fibers such
as ceramics or carbon, meshes such as metals or organic high molecular materials,
or high molecular foams, such as polyurethane foams. For preserving the substrate
in the form of a document, a paper sheet of a white ground is preferably employed
as the substrate in view of higher visibility. It is however not limiting of the present
invention. By bonding the film 20a in this manner to a suitable substrate, a transfer
efficiency of 100% is achieved, so that the sensitized materials 1 can be re-used.
[0089] The aforementioned organic or inorganic electrically conductive materials may be
used as the sensitized material 1, as long as the material 1 is selected so that it
has a dark decay time longer than that of the electrically conductive film laminated
thereon. The dark decay time for the exemplary sensitized materials is about 300 seconds
for polyvinyl-N-carbazole, 100 seconds for phthalocyanin, 20 to 30 seconds for amorphous
selenium, and 30 to 40 minutes for the resin dispersion system of zinc oxide.
[0090] Among the properties required of the electrically conductive film is its ability
to transmit the light from the exposure light source. Therefore, it is not always
necessary that the film is colorless when specific effects or decorative usage are
desired. On the other hand, it is necessary for the above electrically conductive
film to have a shorter dark decay time than that of the sensitized material. This
dark decay time depends, for example, on the film thickness. For example, a polyethylene
film that is 9 µm thick having a dark decay time at 25°C of about 6.5 seconds is most
preferred. In addition, polypropylene, poly-2-cyanomethyl acrylate, polybenzyl acrylate,
poly-4-butylstyrene or a polyvinylidene chloride-polyvinyl chloride copolymer may
be employed.
[0091] A shorter dark decay time means a correspondingly higher electrical conductivity.
The aforementioned materials for the electrically conductive film are generally organic
high molecular materials, such as plastics, having glass transition points Tg proper
thereto. The organic high molecular materials are known to be changed drastically
in their physical properties, inclusive of the electrical conductivity, on both sides
of the glass transition point Tg. Polyethylene, for example, has a glass transition
point Tg of -100°C which is much lower than room temperature, so that it exhibits
sufficient electrical conductivity at room temperature (25°C). The dark decay time
as measured with a film that is 9 µm thick is about 6.5 seconds, which is shorter
than the dark decay time of the ordinary sensitized materials. Thus, polyethylene
is suitable as the material of the electrically conductive material according to the
present invention. However, some of the organic high molecular materials have a glass
transition point Tg close to room temperature. These materials do not exhibit sufficient
electrical conductivity at or near room temperature. According to the present invention,
these materials having a higher glass transition point are heated to lower their dark
decay time, so that these materials may also be used as the electrically conductive
film. As will be apparent from the above explanation, the heating temperature at this
time is selected to at least be not lower than the glass transition point Tg and preferably
20 to 30°C higher than the glass transition point Tg. At any rate, the dark decay
time of the electrically conductive film is set so as to be at a desired value within
the range shorter than that of the sensitized material. Examples of organic high molecular
materials, and their glass transition points, that may be employed in the present
invention include polypropylene (-8°C), poly-2-cyanomethyl acrylate (4°C), polybenzyl
acrylate (6°C), poly-4-butylstyrene (6°C), a polyvinylidene chloride-polyvinyl chloride
copolymer (10°C), poly-4-butoxycarbonyl phenyl acrylate (13°C), polyfluoro methyl
acrylate (15°C), polyhexadecyl methacrylate (15°C), polycyclohexyl acrylate (17°C),
polymethyl acrylate (17°C), polyneopentyl acrylate (22°C), polycyano methyl acrylate
(23°C), polypropyl-2-propylene (27°C), polyisobutyl ethylene (29°C) and poly-3-ethylstyrene
(30°C). The temperatures within the parenthesis denote the glass transition points
Tg for each material.
[0092] The preestimated mechanism for generation and elimination of the electrical charges
in the method (b) is hereinafter explained with reference to Figs. 15(A) and 15(B).
[0093] As shown in Fig. 15(A) the surface of the insulating film 20b is charged to a uniform
negative polarity by corona discharge. At this time, positive charges are induced
on the sensitized material opposite to the insulating film 20b.
[0094] Then, as shown in Fig. 15(B), selective laser irradiation is performed, whereby the
laser light hv passes through the insulating film 20b to reach the sensitized material
1. Due to its properties, the insulating film 20b is unable to shift the negative
charges existing in the vicinity of its surface along the film thickness, so that
the positive charges migrate to close to the boundary between the film 20b and the
sensitized material 1 in the regions irradiated with the laser light. The result is
that a region of different potentials, that is, the distance of the negative and positive
charges, is locally produced within the laminated material. In short, the colorant
particles 6 charged to the positive polarity are selectively affixed to the non-irradiated
region, but are not affixed to the region when the distance between the two charge
types is reduced by irradiation and which may be deemed to be roughly neutral electrically.
[0095] This is made possible in that the dark decay time of the insulating film 20b is selected
to be longer than that of the sensitized material 1. Should the dark decay time of
the insulating film 20b be shorter, the negative charges are dissipated before irradiation
of the laser light so that the desired potential distribution cannot possibly be achieved.
[0096] In the above summary of the mechanism for the formation and disappearance of the
electrical charges, some residual potential unavoidably exists at the exposed region
produced by laser light irradiation. This residual potential presents practically
no disadvantage since it can be cancelled by the application of a bias voltage to,
for example, the developer side.
[0097] In this manner, according to the present invention, the electrostatic latent image
is developed on the surface of the insulating film 20b and the film is subsequently
peeled off from the sensitized material 1. The insulating film 20b may be used directly,
as in the above described electrically conductive film, or it may be bonded to another
suitable substrate. The method (b) and the materials shown therein may be used for
bonding.
[0098] The aforementioned organic or inorganic electrically conductive materials may be
used as the sensitized material 1, as long as the material 1 is selected so that is
has a dark decay time longer than that of the electrically insulating film laminated
thereon.
[0099] Among the properties required of the electrically insulating film is its ability
to transmit the light from the exposure light source. Therefore, it is not always
necessary that the film is colorless when specific effects or decorative usage are
desired. On the other hand, it is necessary for the above electrically conductive
film to have a longer dark decay time than that of the sensitized material. For example,
polyethylene terephthalate having a dark decay time of about 400 seconds is preferred.
Other materials such as polystyrene, polyphenylene sulfide, polyimide of polyamide,
may also be employed.
[0100] Since the image is formed directly on the laminated film on the sensitized material,
an image of a higher quality may be obtained when the film exhibits higher wettability
with respect to the developer, whether the film is the electrically conductive film
or the electrically insulating film. For meeting the above requirements, it is required
that the contact angle with respect to methylene iodide be of not more than 60°. In
Fig. 16, the contact angle with respect to methylene iodide defines an angle ϑ to
the surface of the film 20 as measured between a tangential line drawn at a contact
edge of the methylene iodide 30 and the plane of the film 20. When this contact angle
ϑ is of not less than 60°, a high quality image cannot be obtained because of poor
wettability with respect to the developer. Among the materials satisfying these conditions
are polyethylene, polyvinylidene chloride-polyvinyl chloride copolymer, polyvinyl
chloride (PVC), polyimide, polyamide and polypropylene. The film employed herein needs
to have a contact angle with methylene iodide of not more than 60° at the operating
temperature.
Example 1
[0101] A developing apparatus used in the present example will now be explained.
[0102] The developing apparatus is formed by an electrostatic latent image forming section
and a developing section, both accommodated in a single vessel 9, as shown in Fig.
17. The electrifying, exposure and the developing steps are carried out integratedly
in that a stage 10 holding the sensitized material 1 is shifted along a guide rod
11.
[0103] The stage 10 holding the sensitized base material 1 is provided with heating means
12 adapted for heating the sensitize base material 1 to a predetermined temperature.
[0104] The latent image forming section is subdivided into an electrifying section and a
light exposure section. In the electrifying section, the overall surface of the sensitized
base material 1 is electrified to, for example, a negative charge by an electrifying
unit 2.
[0105] The light exposure section is made up of an optical system including a laser diode
3a, a lens 3b and a reflective mirror 3c. The section plays the role of selectively
exposing the overall electrified surface of the sensitized material 1 as a function
of signals to eliminate the charges of the portions thus exposed to light.
[0106] The developing section includes three developing tanks 4a, 4b, 4c containing three
kinds of developer for full color developer, these tanks 4a to 4c being provided in
this order in the direction of extension of the guide rod 11 within an air tank 13
provided with a blower fan 14.
[0107] The developing tanks 4a, 4b and 4c are composed of first tanks 4a₁, 4b₁ and 4c₁ fitted
with stirrers 4a₃, 4b₃ and 4c₃ and second tanks 4a₂, 4b₂ and 4c₂ provided around the
outsides of the first tanks. Heating means 8a, 8b and 8c are provided on the bottom
of the tanks.
[0108] The developers 7a, 7b and 7c, accommodated in these developing tanks 4a, 4b and 4c,
are heated by the above heating means 8a, 8b and 8c to the melted state, and are adapted
to be ejected slightly upward during development via slits 4a₅, 4b₅ and 4c₅ formed
in lids 4a₅, 4b₅ and 4c₅ of the first tanks 4a₁, 4b₁ and 4c₁ into contact with the
sensitized base material 1.
[0109] Each tank 4a, 4b, 4c is separated from the other tanks by air ejected via air nozzles
13a provided extending from the air tank 13 to prevent color mixing.
[0110] The rear portion of the developing section is provided with a unit 15 for removing
unnecessary electrical charges.
[0111] In the above described developing apparatus, the overall surface of the sensitized
base material 1 is electrified to negative charges by the electrifying unit 2.
[0112] The base material 1 is then selectively exposed to light by the light exposure section
such that the charges in the exposed portion are released to form a predetermined
electrostatic latent image.
[0113] The sensitized base material 1 is then moved along the guide bar 11 to a position
facing the developer tank 4a, as it is heated, and the latent image is developed by
the developer contained in the tank 4a.
[0114] The base material 1 is then moved to the unit 15 where the unnecessary charges are
removed.
[0115] The sensitized base material 1 is then again moved to the latent image forming section
to undergo the sequential steps of electrification - light exposure - development
by the developing tank 4b - charge removal - electrification - light exposure - development
in the developing tank 4c and - charge removal to form a full color image.
[0116] Using the above described developing apparatus, a full-color image has been formed
with the following developers A, B and C contained in the tanks 4a, 4b and 4c.
Developer A
[0117] The present developer A is the cyan-color electrostatic latent image developer.
[0118] 0.625 g of Lionol Blue KX-F1 produced by Toyo Ink Co. Ltd., as colorant, and 0.5
g of IP 2825, isoparaffin solvent produced by Idemitsu Sekiyu Co. Ltd., were comminuted
by the Fouver-Maler method to produce a paste. This paste was dispersed in 50 ml of
a separate isoparaffin solvent "Isopar H" produced by Esso Inc. and admixed with 0.05
g of "Aluminum Oxide C" produced by Nippon Aerosil Co. Ltd., as the charge reinforcing
agent and the resulting mixture was dispersed for 12 hours in a paint shaker together
with alumina beads. The resulting dispersion was admixed with 9.5 g of a 50%-solution
of "FR101", acrylic resin produced by the Mitsubishi Rayon Co. Ltd. in toluene, 0.025
g of zirconium naphthenate as the charge donor and 0.025 g of calcium naphthenate
to produce a concentrated developing liquid.
[0119] Then, 120 ml of paraffin melting at 42 to 44°C was previously melted at 70°C and
5 ml of the concentrated developing liquid was dispersed in the solution to produce
a blue color latent image developer.
Developer B
[0120] The present developer B is a yellow-colored electrostatic latent image developer.
[0121] 0.5 g of Similar Fast Yellow 8GF produced by Dai Nippon Ink Co. Ltd., as colorant,
and 0.5 g IP2825, isoparaffin solvent produced by Idemitsu Sekiyu Co. Ltd., were comminuted
by the Fouver-Maler method to produce a paste. This paste was dispersed in 50 ml of
a separate isoparaffin solvent "Isopar H" produced by Esso Inc. and admixed with 0.01
g of "Aerosil 200" Ultra fine particles of dry silica produced by Nippon Aerosil Co.
Ltd., as the charge reinforcing agent and the resulting mixture was dispersed for
18 hours in a paint shaker together with glass beads. The method for preparing the
concentrated developing liquid and the electrostatic latent image developer is similar
to the method described in connection with the developer A.
Developer C
[0122] The present developer C is the magenta-color electrostatic latent image developer.
[0123] 0.8 g of Simular Rodamin Y toner F, produced by the Dai Nippon Ink Co. Ltd. as the
colorant and 0.5 g of linseed oil were comminuted by the Fouver-Maler method to produce
a paste. This paste was dispersed in 50 ml of "Isopar H", an isoparaffin solvent produced
by Esso Inc. and the dispersing operation was performed for 18 hours in a paint shaker
together with glass beads. The method for preparing the concentrated developing liquid
and the latent image developer is the same as that described in connection with the
developer A.
[0124] On the other hand, a sheet of transparent electrically conductive film (of 0.2µm
thickness) and a modified vinyl acetate resin (film thickness, 2µm) were laminated
on polyethylene terephthalate film (125µm thick) and a photosensitive layer (film
thickness, 8µm) containing 2 mg of cyanine dye ("NK 2892" produced by Nippon Kanko
Shikiso Co. Ltd.) as sensitizer was formed on the laminate to produce the sensitized
base material 1. Since the image quality may be degraded when the developers solidify
immediately after contact with the sensitized base material 1, the stage 10 for securing
the base material 1 was heated to 55°C by the heating means 12.
[0125] As a result, a satisfactory full-color image comparable in resolution and definition
with a silver halide photograph is consistently obtained.
Example 2
[0126] A developing method for an electrostatic latent image will be hereinafter explained
by reference to the example shown in Fig. 18 and using the developer of Figure 2.
[0127] The sensitized base material 1 is comprised of a sheet-like base layer 1a and a photosensitive
layer 1b formed on the base layer 1a. A latent image of the negative charges was formed
on the layer 1b by the electrification and light exposure steps as a function of the
image information.
[0128] For developing the base material 1 carrying the latent image of the negative charges
by the developer of the present example, the base material is placed so that the developer
7 in the form of a layer on a backing 21 contacts with the layer 1b and is then fed
under pressure applied by a roller 16 provided with heating means H. Of course, a
pressure plate or other means is provided opposite the roller 16 so that pressure
is exerted as the base 1 and developer 7 pass therebetween.
[0129] When the developer 7 and the photosensitive layer 1b are contacted with each other
and heated by the roller 16, the developer 7 is liquefied and the colorants contained
in the developer 7 migrate to and are deposited at the regions where the negative
charges exist. The colorants affixed to unnecessary (uncharged) regions are then removed.
The charge removing and fixing steps are then carried out to form the image on the
sensitized base material 1. Since the image quality may be degraded when the developer
solidifies immediately after contact with the sensitized base material 1, the sensitized
base material 1 or the stage 10 for securing the base material 1 is preferably heated
by heating means 12.
[0130] The present inventors tentatively produced the sheet-like developing material and
developed an electrostatic latent image. It has been found that a satisfactory full-color
image comparable in resolution and definition with the silver halide photograph could
be obtained consistently.
Example 3
[0131] A third developing method for an electrostatic latent image will be hereinafter explained
with reference to Figure 19 using the developer example shown in Fig. 5.
[0132] The sensitive base material 1 is comprised of a sheet-like base layer la and a photosensitive
layer 1b formed on the base layer 1a. A latent image of the negative charges was formed
on the layer 1b by the electrification and light exposure steps as a function of the
image information.
[0133] For developing the base material 1 carrying the latent image of the negative charges
by the developer of the present example, the base material is placed so that the developer
7 contacts with the layer 1b and pressure is applied by a roller 16 provided with
heating means H as the base material 1 is fed past the roller 16.
[0134] When the developer 7 and the photosensitive layer lb are contacted with each other
and heated by the roller 16, the developer 7 is liquefied and the colorant contained
in the developer 7 migrates to and is deposited at the regions where the negative
charges exist. The colorant affixed to the unnecessary region is then removed. The
charge removing and fixing steps are then carried out to form the image on the sensitized
base material 1. Since the image quality may be degraded if the developer solidified
immediately after contact with the sensitized base material 1, the sensitized base
material 1 or the stage 10 for securing the base material 1 is preferably heated by
heating means 12.
[0135] Since the electrically conductive layer 24 is formed on the base material 21 a d.c.
source 17 may be connected to the layer 24 to apply a bias voltage for development.
[0136] By application of this bias voltage, it becomes possible to control the relative
potential of the latent image as well as to control the degree of fixing of the colorant
6 to the electrostatic latent image.
[0137] Both the bias voltage and an a.c. voltage may be applied to the layer 24 as shown
in Fig. 19 to use the latter as the heating member to omit the heating means H for
the roller 16. Since the electrically conductive layer 24 is formed of a thermally
conductive material, such as metal, the heating temperature for the developer 7 may
be advantageously equalized.
[0138] The present inventors tentatively produced the sheet-like developing material and
developed an electrostatic latent image. It has been found that a satisfactory full-color
image comparable in resolution and definition with a silver halde photograph can be
obtained consistently.
Example 4
[0139] In the present example, an electrostatic image is formed, using a sensitized material
comprised of a laminated polyethylene film as the electrically conductive film, the
latent image is developed by a cyan-color developer, and the polyethylene film was
peeled from the sensitized material and bonded to ordinary paper.
[0140] A sheet of a transparent electrically conductive film (0.2 µm thick) and a modified
vinyl acetate resin (film thickness, 2 µm) were laminated on polyethylene terephthalate
film (125 µm thick) and a photosensitive layer (film thickness, 8 µm) containing 2
mg of cyanine coloring matter ("NK 2892" produced by Nippon Kanko Shikiso Co. Ltd.)
as a sensitizer was formed on the laminate to produce the sensitized base material.
The dark decay time of the sensitized material is 300 seconds. A polyethylene film
9 µm thick was laminated as an electrically conductive film on this sensitized material.
[0141] The developer used in this example is the aforementioned electrostatic latent image
developer previously proposed by the present Applicant. This developer was prepared
in the following manner.
[0142] First, 0.625 g of Lionol Blue KX-F1 produced by Toyo Ink Co. Ltd., as a colorant,
and 0.5 g of IP 2825, isoparaffin solvent produced by Idemitus Sekiyu Co. Ltd., were
comminuted by the Fouver-Maler method to produce a past. This paste was dispersed
in 50 ml of a separate isoparaffin solvent "Isopar H" produced by Esso Inc. and the
resulting mixture was dispersed for 12 hours in a paint shaker together with alumina
beads. The resulting dispersion was admixed with 0.5 g of a 50%-solution of "FR101",
acrylic resin produced by the Mitsubishi Rayon Co. Ltd. in toluene, 0.025 g of zirconium
naphthenate and 0.025 g of calcium naphthenate as the charge donor to produce a concentrated
developing liquid. Then, 120 ml of paraffin melting at 42 to 44°C was previously melted
at 70°C and 5 ml of the concentrated developing liquid was dispersed in the solution
to produce a cyan color latent image developer.
[0143] In forming an image, a sensitized material comprised of a laminated polyethylene
film 20 as shown in Fig. 13 is subjected to corona discharge 2 at -6 kV so as to be
charged to -700 V in its entirety. The sensitized material is then subjected to selective
light exposure by a semiconductor laser 3 of a wavelength of 780 nm to form an electrostatic
latent image. Then, as the developer 7 is heated by suitable heating means, not shown,
provided on the developer tank 4, for example, for maintaining the developer 7 in
the melted state, the electrostatic latent image was developed for forming an image
on the polyethylene film.
[0144] With the time t₁ involved in corona charging of 3 seconds, the time t₂ from corona
charging until exposure being 2 seconds, the time t₃ for exposure of 3 seconds and
the time t₄ from exposure until development being 2 seconds, the total time amounts
to 10 seconds. The 9µm thick polyethylene film used as the electrically conductive
film in the present example has the dark decay time at 25°C of about 6.5 seconds,
thus satisfying the requirement that the dark decay time be shorter than the total
time t.
[0145] After the fixation and charge removal steps, the polyethylene film is peeled from
the sensitized material 1 and bonded to an ordinary paper sheet to transfer the image
thereto.
[0146] The image, thus, transferred to the ordinary paper sheet showed high resolution of
500 lines/mm or 1000 dots/mm and excellent gradation. Since the electrically conductive
film in its entirety is bonded to the substrate, the transfer efficiency is 100%,
while the sensitized material can be used repeatedly.
[0147] Although the case of forming a cyan-color monochromatic image has been explained
in the present example, it is to be noted that the present invention can be applied
to formation of a full-color image as well. For forming the full-color image, the
steps of electrification, light exposure and charge removal are repeated for each
of the three primary colors for the same sensitized material and the transfer operation
is then performed collectively. The sensitized material may used repeatedly after
the transfer operation.
Example 5
[0148] In the present example, a sensitized material comprised of a film of a polyvinylidene
chloride-vinyl chloride copolymer, referred to hereinafter as Saran film, as the electrically
conductive film is used. The Saran film is heated to about 50°C to form an electrostatic
latent image, and this latent image was developed by using a cyan color developer
and the Saran film was then peeled off from the sensitized material and bonded on
the ordinary paper sheet.
[0149] The developer and the sensitized material used herein are the same as those used
in Example 4.
[0150] For forming the image, a 10µm thick Saran film was laminated on the sensitized material
and heating was then performed by heating means provided on a stage, not shown, adapted
for supporting the sensitized material, so that the temperature of the Saran film
was about 50°C. This Saran film has a glass transition point Tg of 10°C and a longer
dark decay time at room temperature (25°C) of not shorter than 300 seconds, so that
it can be applied only with difficulty to the present invention. This dark decay time
could be reduced to 6.6 second by heating to about 50°C as described above. This is
shorter than the dark decay time of the sensitized material employed in the present
example, which is 300 seconds, or the time t from corona charging until development,
which is 10 seconds.
[0151] The corona discharge is then performed at -6 kV to electrify the overall surface
of the Saran film to about -700 V. Then, selective light exposure is performed with
a semiconductor laser with the wavelength of 780 nm to form an electrostatic latent
image. Then, as the developer 7 is heated by suitable heating means, not shown, provided
on the developer tank 4, for example, for maintaining the developer in the melted
state, the electrostatic latent image is developed for forming an image on the Saran
film.
[0152] After the fixation and charge removal steps, the Saran film is peeled from the sensitized
material and bonded to an ordinary paper sheet to transfer the image thereto.
[0153] The image thus transferred to the ordinary paper sheet showed high resolution of
500 lines/mm or 1000 dots/mm and excellent gradation. Since the electrically conductive
film in its entirety is bonded to the substrate, the transfer efficiency is 100%,
while the sensitized material can be used repeatedly.
[0154] For comparison, a similar image was tentatively formed at room temperature, but a
satisfactory image quality could not be obtained.
[0155] Although the case of forming a cyan-color monochromatic image has been explained
in the present example, it is to be noted that the present invention can be applied
to formation of a full-color image as well. For forming the full-color image, the
steps of electrification, light exposure and charge removal are repeated for each
of the three primary colors for the same sensitized material and the transfer operation
may then be performed collectively. The sensitize material may be used repeatedly
after the transfer operation.
Example 6
[0156] In the present example, an electrostatic latent image is formed by using a sensitized
material comprised of a laminated PET film as an insulating film, this latent image
is developed with a cyan-color developer and the PET film is peeled off from the sensitized
material and bonded to an ordinary paper sheet.
[0157] The developer and the sensitized material employed herein are the same as those used
in Example 4.
[0158] In forming an image, a sensitized material comprised of a 9 µm thick laminated polyethylene
film (dark decay time, 300 seconds) is subjected to corona discharge at -6 kV so as
to be charged to -700 V in its entirety. The sensitized material is then subjected
to selective light exposure by a semiconductor laser of a wavelength of 780 nm to
form an electrostatic latent image. Then, as the developer is heated by suitable heating
means, not shown, provided on the developer tank, for maintaining the developer in
the melted state, and as the bias voltage of -400 V is applied to the developer to
prevent wasteful deposition of colorant particles due to the residual potential at
the light exposure section, the electrostatic latent image is developed to form an
image on the PET film.
[0159] After the fixation and charge removal steps, the polyethylene film is peeled from
the sensitized material and bonded to an ordinary paper sheet to transfer the image
thereto.
[0160] The image thus transferred to the ordinary paper sheet showed high resolution of
500 lines/mm or 1000 dots/mm and excellent gradation. Since the electrically conductive
film in its entirety is bonded to the substrate, the transfer efficiency is 100%,
while the sensitized material can be used repeatedly.
[0161] Although the case of forming a cyan-color monochromatic image has been explained
in the present example, it is to be noted that the present invention can be applied
to formation of a full-color image as well. For forming the full-color image, the
steps of electrification, light exposure and charge removal are repeated for each
of the three primary colors for the same sensitized material and the transfer operation
may then be performed collectively. The sensitized material may be used repeatedly
after the transfer operation.
Example 7
[0162] In the present example, an electrostatic latent image is formed by using a sensitized
material comprised of a laminated polyethylene film, this latent image is developed
with a cyan-color developer and the polyethylene film is peeled off from the sensitized
material bonded to an ordinary paper sheet.
[0163] The developer and the sensitized material employed herein are the same as those used
in example 4.
[0164] In forming the image, a sensitized material comprised of a laminated 9µm thick polyethylene
film having a contact angle of 45° with respect to methylene iodide is subjected to
corona discharge and thereby charged in its entirety to negative polarity. Then, selective
light exposure is performed by a semiconductor laser to form an electrostatic latent
image on the polyethylene film. Then, as the developer is heated by heating means,
not shown, provided for a developing tank for maintaining the developer in the melted
state, and as the bias voltage of -400 V is applied to the developer to prevent wasteful
deposition of colorant particles due to the residual potential at the light exposure
section, the electrostatic latent image is developed to form an image on the polyethylene
film. The developing time is about three seconds. After the subsequent fixation and
charge removal steps, the polyethylene film is peeled off from the sensitized material
and bonded to the ordinary paper sheet to transfer the image thereto.
[0165] The image thus transferred to the ordinary paper exhibited high resolution and gradation.
[0166] Then, by way of a comparative example, a film having a contact angle of not less
than 60° with respect to methylene iodide was used as the film laminated on the sensitized
material, and the image was formed on the film under the same conditions as in Example
7 and transferred to an ordinary paper sheet. As the film having the contact angle
of not less than 60° with respect to methylene iodide, polyvinylidene fluoride (contact
angle, 63°) and polytrifluoroethylene (contact angle, 71°) were used.
[0167] The image obtained with the use of these films having the contact angle with respect
to methylene iodide not less than 60° was inferior in resolution or gradation to that
obtained with the use of a film having the contact angle with respect to methylene
iodide of not more than 60°.
[0168] Since these images are bonded along with the films onto the ordinary paper sheet,
the transfer efficiency is 100% and the sensitized material can be used repeatedly.
[0169] Although the case of forming the cyan color monochromatic image has been explained
in the present example, it is to be noted that the present invention may be applied
to formation of full-color images.