JPH0352622B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields The present invention relates to a charging process for charging a photoconductive support, a dispersion process for dispersing light-transmitting particles containing a sublimable fuel onto the support, and a process for selecting the support through the particles. a development step in which particles are removed from the support according to the residual charge on the support to obtain a particle image remaining on the support; and a development step in which the particles forming this particle image are heated. The present invention relates to an image forming method including a coloring step of transferring a sublimable dye contained in the particles from the particles. More specifically, a charging step for uniformly charging a photoconductive support, a scattering step for uniformly and evenly dispersing light-transmitting particles onto the support, an image exposure step for exposing a document to light through the particles, and a step for exposing a document to light through the particles; A developing process in which particles whose electrostatic attraction has been weakened or removed are removed from the support to obtain a particle image of the particles remaining on the support, and the particles forming the particle image are heated to remove the sublimation contained in the particles. The present invention relates to an image forming method including a coloring step of sublimating and transferring a dye to an image receptor, and a cleaning step of removing particles. Conventional Structure and Problems There has been a conventional method of using particles with a wide particle size distribution in order to expand tone reproduction in this type of image forming method. In other words, the difference in particle size causes a difference in the optical path of light passing through the particles, resulting in a difference in the transmittance of the particles. This difference in transmittance of the particles creates a difference in the intensity of light transmitted through the particles, which in turn creates a difference in the surface potential of the photoconductive support. Due to this difference in surface potential, gradation reproduction can be expanded. An example of this developing method will be described in detail below with reference to FIG. First, as shown in FIG. 1a, a plurality of particles including particles 5L with a large particle size and particles 5S with a small particle size are placed on a photoconductive support 3 on which a photoconductive substance 2 is attached on a support 1. When the particles are scattered and the A area is irradiated with strong light, the B area is irradiated with medium intensity light, and the C area is irradiated with weak light, all of the light from particles 5S to 5L passes through the A area, and the charge directly below the particle disappears. . In region B, particles 5S
However, other particles have a long optical path and low particle transmittance.
The charge immediately below the particle remains, creating a difference in charge on the photoconductive material 2. In region C, the charge immediately below the particle 5S also remains. Therefore, by dropping the particles 5S, 5L in the A area and 5S in the B area by the vibrating force of the vibrator 4, super-reproduction in the A to C areas is achieved (hereinafter, such a developing method will be referred to as vibration development). law). However, as shown in FIG. 1b, the particles 5S with small particle diameters in the A region and B region are light, so the inertial force due to vibration is small. Therefore, the particles 5S having a small particle size are difficult to shake off, and there is a problem that the image becomes foggy. Therefore, when the vibration force is increased in order to reduce fogging, the inertial force received by the particles 5L that do not transmit the light in the C region becomes larger than the electrostatic adhesion force between the photoconductive support 3 and the particles 5L. For this reason, the particles 5 that should originally remain on the photoconductive support 3
There was a problem that L was shaken off, development became uneven, and print density decreased. FIG. 2 shows another example of the developing method, in which a dielectric material 9, which has been uniformly charged in advance, is brought into close contact with the image forming particles on the photoconductive support 3 after image exposure, and the electrostatic charge builds up between the dielectric material 9 and the particles. A method (hereinafter referred to as electrostatic development method) of removing particles 5 through which light has passed by using adhesive force will be described. At this point, the particles with a large particle size come into close contact with the dielectric material 9, and a gap is created between the dielectric material 9 and the particles 6 with a small particle size. For this reason, the electrostatic attraction between the particles 6 and the dielectric 9 becomes small, making it difficult to remove the particles 6 and causing a problem of increased fogging. OBJECTS OF THE INVENTION It is an object of the present invention to provide an image forming method that overcomes these conventional drawbacks, expands the tone reproduction range, and reproduces images with less fog. Structure of the Invention In order to achieve the above object, the present invention is characterized in that a plurality of types of particles having different transmittances are mixed. Specifically, it is characterized by a mixture of a plurality of particles having different concentrations of a coloring agent that imparts selective spectral transmittance to the particles, or an additive that exhibits white or black color. That is, since the image forming particles used in the image forming method of the present invention are a mixture of particles having the same particle size but different transmittance,
This difference in transmittance of the particles provides an image signal to the photoconductive support corresponding to the difference in density of the original. FIG. 6 is a schematic diagram showing the particle diameters of some of the light-transmitting particles used in the image forming method of the present invention. That is, they contain the same sublimable dye,
Particle groups 11 with the same particle size and different transmittances are
Each has a particle size distribution. Among the light-transmitting particles shown in FIG. 6, the particle with the highest transmittance is particle 5S, and the particle with the lowest transmittance is particle 10L. The particles used in the conventional image forming method ranged from particles 5L to 5S, for example. On the other hand, a total of 12 light-transmitting particles shown in FIG. 6 are used in the image forming method of the present invention. Figure 7 shows the current density and print reproduction of the image forming method when using four types of particles, particles 5S, particles 5L, particles 10S, and particles 10L, among the particles shown in Figure 6 to simplify the explanation. The relationship with concentration,
FIG. 2 is a schematic diagram showing a conventional image forming method using a difference in particle size of light-transmitting particles and an image forming method of the present invention using a particle group consisting of a plurality of particles having different transmittances. There are five types of brightness steps in original documents, and when these are reproduced using the conventional image forming method, only three steps are reproduced, as shown in FIG. 7, corresponding to the transmittance. In comparison, according to the image forming method of the present invention,
Five steps can be reproduced corresponding to the transmittance, and the original density can be reproduced more faithfully. In Figure 7, we tried to expand the tone reproduction range by including only one type of things with different transmittances, but even by including multiple types of things with different transmittances, the tone reproduction range is significantly expanded. Expanding. Therefore, by using the light-transmitting particles of the present invention having different particle sizes in the particle group 11 having the same particle size and different transmittance, the tone reproduction range can be further expanded significantly. Next, the material of the particles used in the present invention will be explained. The particles are generally composed of resin. Examples of the resin used include thermoplastic resins such as polyvinyl alcohol and acrylic resins, thermosetting resins such as melamine resins and phenolic resins, styrene-butadiene copolymers, and transparent resins such as gelatin. By adding a coloring agent such as a dye or a pigment to the above-mentioned resin, a color separation function is imparted to the particles. Examples of typical colorants include CI acid red 6, 14, 18, 42 for red light transmission.
Acid dyes such as or CI pigment reds
There are organic pigments such as 17, 48, and 81. In addition, for green light transmission, CI Acid Green 9, 27, 40,
Acidic dyes such as 43, metal-containing dyes such as Eisenspiron Green C-GH (manufactured by Hodogaya Chemical Industry Co., Ltd.), or CI Pigment Green 2 and 7.
There are organic pigments such as In addition, for blue light transmission, oil dyes such as CI Solvent Blue 48, 49, direct dyes such as CI Direct Blue 86, CI Acid Blue 23, 40, 62, 83, 120, etc.
There are acid dyes such as CI Pigment Blue 15 and organic pigments such as CI Pigment Blue 15. Moreover, it goes without saying that other desired spectral characteristics can be obtained by mixing a single colorant or a plurality of colorants as necessary. Furthermore, by adding a sublimable dye, a coloring function can be imparted. Examples of typical colored sublimable dyes include CI Basic Blue 5, CI Solvent Blue 2, and C.
I. Disperse Blue 1 etc. In addition, as magenta color, CI Basic Violet 14,
Examples include CI Disperse Violet 1. Also, for yellow color, CI basic yellow 2,
There are CI Day Space Yellow 2, etc. Sublimable color formers are dyes that are colorless or light colored under normal conditions, but sublimate when heated, and develop color by reacting with color developers such as clay, tartar powder, and 4,4,'-diphenylpropane. Any one is fine. Further, the sublimable color former does not normally affect the color separation function of the particles. Therefore, it is also possible to add, together with the colorant, a sublimable color former that develops a complementary color to the colorant that imparts a color separation function to the particles.
However, in the case of using a sublimable color former, it is of course necessary to use an image receptor having the above-mentioned color developer, such as clay paper. Typical examples of sublimable color formers include 3,7-bis-diethylamino-10-trichloroacetyl-phenoxazine, 4-(1,3,
3,5-tetramethyl-indolino)methyl-7
-(N-methylN-phenyl)amino-1',3',
3′,5′-tetramethyl-spiro[2H-1-benzopyran-2,2′-[2′H]-indole], N-(1
，
2-dimethyl-3-yl)methylidene-2,4-
Examples include dimethoxyaniline. When the image-forming particles used in the image-forming method of the present invention have selective spectral transparency, they need to be electrostatically deposited in a layer on a photoconductive support. For this purpose, it is desirable that at least the particle surface has electrical conductivity. Therefore, when using a non-conductive electrostatic resin, conductive treatment is applied to the surface.
Furthermore, it is required to be transparent to light even after conductive treatment and not to affect color separation. As this conductive material, copper iodide, polymer electrolyte, etc. are applied. Further, the specific resistance of the particle surface is preferably 10 ⁹ Ω·cm or less. In addition, when using a mixture of multiple types of particles with different selective light transmittances, the difference in specific resistance value of each is reduced by 1.
It is preferable to align them within digits. Examples of the white or black additive that changes the transmittance of the image forming particles used in the image forming method of the present invention include inorganic white pigments such as titanium oxide, silicon oxide, and barium sulfate, and black pigments such as carbon black. etc. As a method for changing the transmittance of particles, it is sufficient to add the above-mentioned additive exhibiting white or black color just enough to obtain the desired transmittance. Alternatively, it can also be achieved by changing the half-width of the transmission spectrum of the particles by changing the amount of the coloring agent that imparts the color separation function to the particles. Description of Examples Example 1 First, a solution having the following formulation was prepared. (1) Solution A SBR resin binder (Nippon Zeon Co., Ltd. Tanbond,
(The same applies hereinafter) ...100 parts by weight of silica (Nissan Chemical Co., Ltd.'s Statusx ST-20,
Same hereafter) ...100 parts by weight Sublimable color former 3,7-bisdiethylamino-10 trichloroacetylphenoxazine ...2 parts by weight N-(1,2-dimethyl-3-yl)methylidene-2,4-dimethly xyaniline
...2 parts by weight Colored sublimable dye CI Basic Violet 14 ...2 parts by weight (2) Solution B SBR resin binder ...100 parts by weight Silica (Snowtex ST-20)
...100 parts by weight Sublimation color former 3,7-bis-diethylamino-10-trichloroacetyl phenoxazine ...2 parts by weight N-(1,2-dimethyl-3-yl)methylidene-2,4-dimethoxyaniline ... 2 parts by weight Colored sublimable dye CI Basic Violet 14 2 parts by weight Titanium oxide (particle size 0.02 to 0.1 μm) 6 parts by weight The above two solutions were mixed and dispersed separately in a ball mill for 3 hours. Next, each was granulated separately by a spray drying method to obtain spherical particles with a particle size of 3 to 60 μm. To 100 parts by weight of the particles thus obtained, 200 parts by weight of a copper iodide solution having the following formulation was separately fluidized.
When the particles were then classified into particle sizes of 20 to 30 μm, the specific resistance was approximately 10 ⁴ Ω·cm. Copper iodide solution recipe Copper iodide...2 parts by weight Polyvinyl acetate...0.2 parts by weight Acetonitrile...100 parts by weight The transmission spectra of the two types of particles thus obtained were measured using a microspectrophotometer, and the results are shown in Figure 3. It was a spectrum like this. In addition, each particle size of 20μm
(A) is the particle obtained from solution A, and (B) is the particle obtained from solution B. Particles obtained from this solution A (hereinafter referred to as particles A)
and particles obtained from solution B (hereinafter referred to as particles B)
were mixed at the mixing ratio shown in Table 1. When mixed particles Nos. 1 to 3 in Table 1 were used to form images in the process described below, images as shown in Table 1 were obtained. As a comparative example, particle A
The case where only Here, the image forming process is as follows. A photoreceptor is obtained by vapor depositing selenium to a thickness of approximately 60 μm on an aluminum plate, and this photoreceptor is uniformly charged in a dark place using a corona charger applying +6 KV, and the mixed particles are uniformly dispersed. Thereafter, when the photoreceptor is slightly vibrated, the excessively attached particles are shaken off, and more particles are electrostatically attached onto the photoreceptor. Thereafter, the black and white original is exposed imagewise through the particles using a 500W tungsten lamp as a light source. When the photosensitive plate is vibrated after image exposure, particles whose electrostatic adhesion to the photoreceptor has been weakened or removed fall, and a particle image is obtained on the photoreceptor. Next, the entire surface is irradiated with white light to remove the charge remaining on the photoreceptor, then the clay layer side of the clay paper is brought into close contact with the particles on the photoreceptor, and a voltage of -200 to -500V is applied from the back side of the clay paper. to electrostatically transfer the particles onto clay paper. This clay paper is 180~250
℃, and then the particles are cleaned to obtain a positive image on clay paper that is faithful to the original.

[Table] As shown above, by mixing particles A and B, the tone reproduction range was 1.1 in the past, but with No. 3 it was 1.5.
expanded to. That is, as shown in FIG. 3, by mixing particles B with low transmittance,
Due to the particles B remaining in the highlighted portions of the original, the tone reproduction range was expanded. Furthermore, since the black density and white background density hardly changed, fog and uniformity of development were not impaired. Example 2 First, two doses each of red, green, and blue-violet solutions were prepared according to the following formulation.
Each type was prepared. (1) Red solution-1 Melamine resin binder (Sumitex Resin M-3 from Sumitomo Chemical Co., Ltd., the same applies hereinafter)
...100 parts by weight of curing accelerator (Sumitex Accelerator EPX, manufactured by Sumitomo Chemical Co., Ltd.; the same applies hereafter); ...8 parts by weight of coloring dye (CI Acid Red 94) (Eisen Rose Bengal, manufactured by Hodogaya Chemical Co., Ltd.; same as below)
...5 parts by weight Colored dye (CI Acid Yellow 19) (Suminol Leveling Yellow NR from Sumitomo Chemical Co., Ltd., same hereinafter) ...8.7 parts by weight Water ...100 parts by weight (2) Green solution-1 Melamine resin binder Adhesive: 100 parts by weight Curing accelerator: 8 parts by weight Colored dye (CI Acid Blue 1) (Sumitomo Mikuni Chemical Co., Ltd.'s Patent Pure Blue VX, same hereinafter) 2.5 parts by weight Colored dye Suminol Leveling Yellow NR...13.3 parts by weight Water...100 parts by weight (3) Blue-violet solution-1 Melamine resin binder...100 parts by weight Curing accelerator...8 parts by weight Colored dye (CI Acid Violet 49) (Mitsui Higashi) Acid Violet 6B by Tenshu Kagaku Co., Ltd. (the same applies hereinafter)...16.1 parts by weight Colored dye Patent Paint Blue-VX
...11.7 parts by weight (4) Red solution-2 Melamine resin binder ...100 parts by weight Curing accelerator ...8 parts by weight Colored dye Eisen Rose Bengal B
...7.2 parts by weight Colored dye Suminol Leveling Yellow NR ...12.6 parts by weight Water ...100 parts by weight (5) Green solution-2 Melamine resin binder ...100 parts by weight Curing accelerator ...8 parts by weight Colored dye Patent Pure Blue - VX
...3.6 parts by weight Colored dye Suminol Leveling Yellow NR ...19.1 parts by weight Water ...100 parts by weight (6) Blue-violet solution-2 Melamine resin binder ...100 parts by weight Curing accelerator ...8 parts by weight Colored dye acid violet 6B
...23.2 parts by weight Colored dye Patent Pill Blue-VX
...16.8 parts by weight Water ...100 parts by weight Each of these solutions was granulated separately by a spray drying method to obtain spherical particles with a particle size of 3 to 60 μm. Next, each was treated with a sublimable color former using the method described below. (1) Red Particles-1 and 2 10 parts by weight of a cyan-colored sublimable color former 3,7-bis-diethylamino-10-trichloroacetyl-phenoxazine, 1 part by weight of ethyl cellulose as a binder, and 89 parts by weight of dichloroethane as a solvent. 50 parts by weight of a solution consisting of 100 parts by weight of red particles is fluidly applied. (2) Green particles-1 and 2 Sublimable color former that develops magenta color 4-(5-chloro1,3,3-trimethyl-indolino)methyl-7-(N-methyl-N-phenyl)amino-5' -15 parts by weight of a solution consisting of 10 parts by weight of -chloro-1',3',3'-trimethyl-spiro [2H-1-benzopyran (2H)-indole], 1 part by weight of ethyl cellulose and 89 parts by weight of dichloroethane were added to 100 parts by weight of green particles. Apply fluidly to the weight part. (3) Blue-violet particles-1 and 2 sublimable color former N that develops yellow color
-(1,2-dimethyl-3-yl)methylidene-2,4-dimethoxyaniline 10 parts by weight, ethyl cellulose 1 part by weight and dichloroethane 89
50 parts by weight of a solution consisting of 100 parts by weight of blue-violet particles is fluidly applied. Next, add water to 10 parts by weight of polymer electrolyte quaternary ammonium salt ECR-34 (manufactured by Dow Chemical Company).
To a solution of 90 parts by weight and thoroughly mixed, 100 parts by weight of the colored particles obtained above were added and separately spray-dried for conductive treatment. The specific resistance of the particles is approximately
It was 10 ⁷ Ω・cm. The particles thus obtained were classified into 25 to 35 μm. When the transmission spectrum of these particles was measured using a microspectrophotometer, the spectrum was as shown in FIG. The particle size of the measured particles is approximately
It is 30 μm. In the figure, R-1 and R-2 are red solutions.
1. Spectra of red particles-1 and red particles-2 obtained from red solution-2;
B-1 and B-2 are green solution-1 and green solution-, respectively.
2. Green particles-1, green particles-2, blue-violet particles-1, blue-violet particles obtained from blue-violet solution-1 and blue-violet solution-2
This is the spectrum of 2. Red particles-1, green particles-1, and blue-violet particles-1 are mixed in equal amounts to form color particles-1. Red particles-2, green particles-2, and blue-violet particles-2 are mixed in equal amounts to obtain color particles-2. These color particles-1 and 2 were mixed at the mixing ratio shown in Table 2. When an image was formed using the mixed particles shown in Table 2 by the process described below, an image as shown in Table 2 was obtained. As a comparative example, a case where only Color Particle-2 was used was also described. The image forming process is as follows. A conventional panchromatically sensitized zinc oxide photoreceptor is uniformly charged in a dark place using a corona charger that applies a voltage of -6KV. Next, the mixed particles are sprinkled onto the photoreceptor in a dark place, and the photoreceptor is lightly vibrated to remove excessively attached particles.
The particles are electrostatically deposited on the photoreceptor in a uniform layer. Next, the color transparent original is image-exposed for 10 seconds with a 500W tungsten lamp, and after the image exposure, the photoreceptor is vibrated, and the image-forming particles that have been exposed to the light and whose electrostatic adhesion to the photoreceptor is weakened or removed fall off. , a color-separated particle image is obtained on the photoreceptor. Next, after optically attenuating the electrostatic latent image remaining on the photoreceptor, the clay layer side of the clay paper is brought into close contact with the particle image, and a voltage of +300V is applied from the back side of the clay paper to transfer the particle image to the clay paper. Transcribe. Transferred clay paper
It is heated to 180 to 250 degrees Celsius to sublimate the colorless sublimable dye to develop color in the clay layer, and the particles are removed with a cleaning brush to obtain a positive color image on the original.

[Table] As mentioned above, Color Particle-2 alone has approx.
The tone reproduction range that was 1.1 has expanded to about 1.5. That is, the color particles -2 mainly remained in the highlight portions of the original, and as the density of the original became higher, the proportion of particles -1 increased and the tone reproduction range expanded. This is because the spectrum of the particles changed as shown in FIG. 4 by changing the amount of colored dye. Furthermore, since black density and white background density hardly change, fog and uniformity of development are not impaired. Example 3 First, two doses each of red, green, and blue-purple solutions were prepared according to the following recipe.
Each type was prepared. (1) Red solution - 1 SBR resin binder (Nogatatex 2752 from Sumitomo Naugatatsu Co., Ltd., the same hereinafter) ...100 parts by weight Silica (Snowtex N from Nissan Chemical Co., Ltd., the same below) ...80 parts by weight CI Pigment Red 5...2.6 parts by weight CI Pigment Orange 21115...5.3 parts by weight Anionic active agent...1.0 parts by weight Water...130 parts by weight Sublimation color former: 3,7-bis-diethylamino-10-trichloroacetyl- Phenoxazine...8 parts by weight (2) Green solution-1 SBR resin binder...100 parts by weight Silica (Snowtex N)...80 parts by weight CI Pigment Green 36...5.4 parts by weight CI Battuyero 20...0.8 parts by weight Part β-type copper phthalocyanine...2.2 parts by weight Anionic activator...0.3 part by weight Nonionic activator...0.46 part by weight Water...160 parts by weight Sublimation color former: 4-(5-chloro-1,
3,3-trimethyl-indolino)methyl-7
-(N-methyl-N-phenyl)amino-5'-
Chloro-1',3',3'-trimethyl-spiro[2H
-1-benzopyran-(2H)-indole]
...3 parts by weight (3) Blue-violet solution-1 SBR resin binder ...100 parts by weight Silica (Snowtex N) ...80 parts by weight CI Pigment Blue 15 ...3 parts by weight Dioxazine Violet ...0.5 parts by weight Methyl violet lake...0.5 parts by weight Anionic activator...0.3 parts by weight Sublimation color former: N-(1,2-dimethyl-3-yl)methylidene-2,4-dimethoxyaniline...5 parts by weight ( 4) Red solution-2 SBR resin binder...100 parts by weight Silica (Snowtex N)...80 parts by weight CI Pigment Red 5...2.6 parts by weight CI Pigment Orange 2115...5.3 parts by weight Anionic activator... ...1.0 parts by weight BaSO ₄ (particle size 0.02-0.1 μm) ...60 parts by weight Water ...130 parts by weight Sublimation color former: 3,7-bis-diethylamino-10-trichloroacetyl-phenoxazine ...8 parts by weight (5 ) Green solution-2 SBR resin binder ……100 parts by weight Silica (Snowtex N) ……80 parts by weight CI Pigment Green 36 ……5.4 parts by weight CI Batsuto Yellow 20 ……0.8 parts by weight β-type copper phthalocyanine ……2.2 parts by weight Part anionic activator: 0.3 parts by weight Nonionic activator: 0.46 parts by weight BaSO ₄ (particle size: 0.02 to 0.1 μm) 50 parts by weight Water: 160 parts Sublimable color former: 4-(5-chloro) -1,
3,3-trimethyl-indolino)methyl-7
-(N-methyl-N-phenyl)amino-5'-
Chloro-1',3',3'-trimethyl-spiro[2H
-1-benzopyran-(2H)-indole]
...3 parts by weight (6) Blue-violet solution-2 SBR resin binder ...100 parts by weight Silica (Snowtex N) ...80 parts by weight CI Pigment Blue 15 ...3 parts by weight Dioxazine Violet ...0.5 parts by weight Methyl violet lake ...0.5 parts by weight Anionic activator ...0.3 parts by weight BaSO ₄ (particle size 0.02-0.1 μm) ...45 parts by weight Sublimation color former: N-(1,2-dimethyl-3-yl) Methylidene-2,4-dimethoxyaniline...5 parts by weight After dispersing the above six types of solutions separately in a ball mill for 3 hours, they were granulated separately by spray drying, resulting in particles with a particle size of 3 to 60 μm. Spherical particles were obtained. Next, 200 parts by weight of a copper iodide solution having the following formulation was separately fluid-coated to 100 parts by weight of the particles obtained above. After that, 15~
When classified to 25 μm, the specific resistance of the particles was approximately
It was 10 ⁵ Ω・cm. Copper iodide solution treatment Copper iodide ... 2 parts by weight Polyvinyl acetate ... 0.2 parts by weight Acetonitrile ... 100 parts by weight The transmission spectrum of the particles thus obtained was measured with a microspectrophotometer, and the results were as shown in Figure 5. It was a spectrum like that. The particle size of the measured particles is approximately 25μ.
It is m. In the figure, R-1 and R-2 are the spectra of red particles-1 and red particles-2 obtained from red solution-1 and red solution-2, and the same goes for G-1, G-2, B-
1 and B-2 are green solution-1, green solution-2, and
Green particles obtained from blue-violet solution-1 and blue-violet solution-2
1. Spectra of green particles-2, blue-violet particles-1, and blue-violet particles-2. Red particles-1, green particles-1, and blue-violet particles-1 are mixed in equal amounts to form color particles-3. Red particles-2, green particles-2, and blue-violet particles-2 are mixed in equal amounts to form color particles-4. These color particles-3 and 4 were mixed at the mixing ratio shown in Table 3. When an image was formed using this mixed particle in the same process as in Example 3, the images shown in Table 4 were obtained. As a comparative example, a case where only Color Particle-3 was used was also described.

[Table] As shown above, Color Particle-3 alone has approx.
The tone reproduction range that was 1.2 has expanded to about 1.5. That is, color particles -4 mainly remained in the highlight portions of the document, and as the density of the document became higher, the proportion of particles -3 increased and the tone reproduction range expanded. This is because the addition of the white pigment BaSO ₄ changed the transmittance of the particles as shown in FIG. Furthermore, since black density and white background density hardly change, fog and uniformity of development are not impaired. Although the image forming processes of Examples 1 to 4 have been described using vibration development, almost the same results can be obtained using electrostatic development. In addition, in Examples 1 to 4, two types of particles with different spectral shapes were explained, but the same effect can be obtained even if three or more types of particles are mixed, and moreover, as the number of types increases, the tone reproduction range expands and the intermediate The tone reproduction also improves. Therefore, the features of the present invention include the following points. (1) The tone reproduction range can be expanded by a simple method of mixing particles with different spectral shapes or transmittances. (2) The tone reproduction range can be controlled by adjusting the mixing ratio of particles with different spectral shapes or transmittances. (3) By increasing the types of particles with different spectral shapes or transmittances, it is possible to further expand the tone reproduction range and improve reproduction of intermediate tones. (4) Even if the particle size distribution is relatively sharp, the tone reproduction range can be expanded, so uniform development can be achieved regardless of the development method. (5) Since particles with a relatively sharp particle size distribution can be applied and uniform development can be achieved, there are no negative effects such as fogging or a decrease in print density. (6) The spectral shape of each particle can be easily adjusted because it can be controlled, for example, in a casting film or in a solution state before granulation. Effects of the Invention According to the image forming method of the present invention, there is an effect that the tone reproduction range can be expanded very easily.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional side views of important parts for explaining problems during development that occur when the tone reproduction range is expanded in the prior art. 3 to 5 are transmission spectra of the particles described in Examples 1 to 3 measured with a microspectrophotometer. FIG. 6 is a schematic diagram illustrating one embodiment of the light-transmitting particles used in the present invention, and FIG. 7 is a schematic diagram illustrating the relationship between document density and print density in the present invention and conventional image forming methods. It is a diagram. DESCRIPTION OF SYMBOLS 1... Support, 2... Photoconductive material, 3... Photoconductive support, 4... Vibrator, 9... Dielectric material.

Claims (1)

[Scope of Claims] 1. A charging step of charging a photoconductive support, a scattering step of scattering light-transmitting particles containing a sublimable dye onto the support, and a step of selectively charging the support through the particles. an exposure step of exposing the particles to light, a developing step of removing the particles from the support according to the residual charge on the support corresponding to the exposure step, and obtaining a particle image of the particles remaining on the support; a coloring step of heating the particles forming a particle image to transfer and color the sublimable dye contained in the particles from the particles; An image forming method characterized in that a plurality of particle groups each having different diameters and different transmittances exist. 2. The image forming method according to claim 1, wherein the light-transmitting particles have selective spectral transmittance.