JP2003043621A - Image forming method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a liquid ink advantageous to energy saving and environmental protection and to achieve functionality comparable to that of an electrophotographic system in a use in which target images vary in sequence. SOLUTION: An image forming material layer 1 consisting of an image forming material which suffers a discoloration reaction under a photocatalytic action is uniformly formed on the image forming face 3 of an image carrier 2. Writing is carried out by selectively irradiating a photocatalyst layer 4 formed on the surface of the image carrier with excitation light to partially cause the discoloration reaction in the image forming material layer, and a visible image is formed according to the presence/absence of the discoloration reaction in the image forming material layer. In particular, the photocatalyst layer is previously made hydrophilic by irradiation with excitation light and then a water-base ink solution consisting of an image forming material is applied to the image forming face of the surface of the photocatalyst layer to form the image forming material layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image formation in which an image is formed by an image forming material on an image carrier by performing a required writing process, and the image is transferred to a recording medium such as recording paper to form an image. The present invention relates to a method and an image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic system which is often used for image formation, powder toner is generally used as a developer for visualizing an electrostatic latent image. This powder toner is fixed on a recording paper. In order to do so, it is necessary to apply heat and pressure, which consumes a large amount of electric power and generates a large amount of heat, which causes a problem in energy saving. Further, in order to achieve higher resolution with powder toner, it is necessary to reduce the particle diameter of the powder toner, but if this powder toner becomes finer, it becomes technically difficult to suppress the release to the outside of the device. However, since it becomes a factor of deteriorating the environment, there is a disadvantage that high resolution is restricted.

On the other hand, a wet developing method has been proposed which develops with liquid toner and does not require a fixing step. However, electrophoresis of developing particles is used to selectively attach the toner to the photoconductor. Therefore, a low-viscosity liquid is handled, which has a disadvantage that the apparatus becomes complicated and maintenance is complicated.

On the other hand, in recent years, various methods have been proposed in which an image can be formed with a liquid ink by paying attention to the superhydrophilicity of a photocatalyst material (see Japanese Patent Laid-Open No. 2000-126606). In this method, a writing process of selectively irradiating the photocatalyst material layer with excitation light according to required image information is performed, thereby forming an image by forming regions having different ink adhesion properties on the surface of the photocatalyst material layer. I am trying.

However, such a method of changing the surface characteristics of the photocatalyst material layer by irradiating the excitation light requires a long time to change the surface characteristics to the required surface characteristics, so that the same image is repeatedly printed. However, it is not suitable for applications in which images to be printed change one after another. On the other hand, although a method of improving the writing processing speed has been proposed (see Japanese Patent Laid-Open No. 2000-317312),
In addition to complicating the device structure, there are manufacturing restrictions such as limited materials, and there are various problems in achieving a function equivalent to that of the electrophotographic method with a simple configuration.

[0006]

Therefore, according to the present invention,
Provided are an image forming method and an image forming apparatus which can use liquid ink from the viewpoint of energy saving and environmental protection, and can realize the same functionality as an electrophotographic method in applications where a target image changes one after another. The purpose is to do.

[0007]

In order to achieve such an object, in the present invention, as described in claim 1, an image forming material layer made of an image forming material which causes a color change reaction by a photocatalytic action is provided on an image carrier. Formed uniformly on the image forming surface of
The photocatalyst material uniformly distributed along this image forming surface is subjected to a writing process to selectively irradiate excitation light to cause a partial color change reaction in the image forming material layer, and the color change reaction in the image forming material layer is performed. A visible image was obtained with or without.

According to this, an image is formed depending on the presence or absence of discoloration of the image forming material itself, and since the image forming surface of the image bearing member is not changed by the writing process, the image forming material layer on the image bearing member is recorded on the recording paper. When the image is transferred to a recording medium such as, it is possible to immediately start forming a different image. In this case, titanium dioxide or a photocatalyst material in which a required composition is combined may be used, and such a photocatalyst material is irradiated with an excitation light having an intensity exceeding the band gap to excite it, whereby the surrounding substances are oxidized and reduced. A photocatalytic action that causes a reaction is developed, and the photocatalytic action causes a color change reaction in the image forming material.

Furthermore, it is possible to use an ink liquid having a constitution in which an image forming material is dispersed in the liquid, and it is possible to avoid the inconvenience in terms of energy saving and environmental protection that occurs when powder toner is used. Moreover, since a high-viscosity ink can be used, handling is easy, the device configuration is simple, and maintenance is easy. It should be noted that a configuration in which the image forming material layer is formed of powder of the image forming material is also possible,
In order to cause an appropriate color change reaction in the image forming material by the photocatalytic action, it is desirable to use an ink liquid having a structure in which the image forming material is dispersed.

Further, in the writing process of irradiating the exciting light, the exciting light may be scanned in accordance with the image information to be formed, and at this time, it is possible to cope with high resolution by narrowing the diameter of the exciting light. is there. It is also possible to arrange a film on which a desired image is recorded on the image forming material layer and uniformly irradiate the entire surface with excitation light with a light source such as a xenon lamp.

In the image forming method, as described in claim 2, the discoloring reaction can be a fading reaction for changing the image forming material to a colorless side. According to this, a required image is formed in a portion that escapes the fading reaction in the image forming material layer, and an unbleached portion that appears as this image shows the initial color of the image forming material and has a constant color tone. High image quality can be obtained. In this case, when a leuco dye is used as the image forming material, a fading reaction due to reduction is caused to make the material colorless. It is also possible to use a method of forming a desired image on the portion where the fading reaction has occurred.

In the image forming method, as described in claim 3, the photocatalyst material forms a photocatalyst layer on the surface of the image carrier, and the surface of the photocatalyst layer serves as an image forming surface, and the image forming material layer is formed thereon. It can be configured to be formed. According to this, by forming the image forming material layer on the surface of the photocatalyst layer,
The photocatalyst material can be made to act uniformly on the image forming material in the image forming material layer, and a uniform discoloration reaction can be caused in the image forming material in the region irradiated with the excitation light. In this case, the photocatalyst layer may be formed on the image carrier by vapor deposition or the like.

In the image forming method, as described in claim 4, the photocatalyst layer is preliminarily subjected to a hydrophilic treatment by irradiating with excitation light, and then the image forming surface on the surface of the photocatalyst layer is made of an image forming material. It is possible to adopt a configuration in which an aqueous ink liquid is applied to form the image forming material layer. According to this, since a uniform and thin image forming material layer (ink layer) can be formed on the image forming surface of the image carrier, high image quality can be obtained.

In the image forming method, as described in claim 5, the image carrier is formed of a material capable of transmitting excitation light, and the surface of the photocatalyst layer provided on the image carrier is formed. It is possible to adopt a configuration in which the excitation light is emitted from the side opposite to the image material layer. According to this, the excitation light is not obstructed by the image forming material layer, and the attenuation of the excitation light can be suppressed.

In the image forming method, as described in claim 6, the photocatalyst material is finely powdered and uniformly dispersed in the ink liquid containing the image forming material forming the image forming material layer. Can be taken. According to this, since the photocatalytic material uniformly dispersed in the ink layer (image forming material layer) acts on the image forming material in the vicinity thereof, avoiding non-uniform color change reaction in the thickness direction within the layer, The image quality can be improved. In this case, if it is possible to form the image forming material layer on the image forming surface of the image carrier with required uniformity by various surface treatments suitable for the ink liquid used,
Although the photocatalyst layer is not always necessary, it is desirable to utilize the superhydrophilic property of the photocatalyst layer in order to form a uniform image forming material layer using a water-based ink. A synergistic effect of the photocatalyst material and the photocatalyst layer mixed in can be expected.

In the image forming method, as described in claim 7, the photocatalyst material may be irradiated with excitation light from the image forming material layer side on the image forming surface. According to this, when the image carrier is composed of a cylindrical drum or an endless belt for performing continuous image forming work, a light source for irradiating the image forming surface of its outer periphery with excitation light,
It becomes easy to arrange an optical system device such as a lens for guiding this to the image forming surface on the outer periphery. This structure is suitable when the attenuation of the excitation light in the image forming material layer is small or when the photocatalyst fine powder is dispersed in the ink liquid containing the image forming material.

In the image forming method, as described in claim 8, the image forming material layer on the image carrier is transferred to the recording medium when the image forming material layer on which the image forming surface is written is transferred. It is possible to adopt a configuration in which it is once transferred to another intermediate transfer member and then transferred to a recording medium. According to this, damage caused by direct contact of the image forming surface of the image carrier on which the image forming material layer is formed with a recording medium such as recording paper can be avoided, and a particularly uniform image forming material layer is formed. Therefore, it is possible to avoid the disadvantage that the function of the photocatalyst layer subjected to the hydrophilic treatment is impaired.

In the image forming method, as described in claim 9, when the transfer from the intermediate transfer member to the recording medium is completed, the surface of the intermediate transfer member can be cleaned. According to this, it is possible to prevent the image transferred next from the image carrier to the intermediate transfer body from being contaminated by the image forming material remaining on the intermediate transfer body.

According to the tenth aspect of the invention, in the image forming method.
As shown in, it is possible to adopt a configuration using ultraviolet laser light as the excitation light. According to this, the photocatalytic material is irradiated with high-energy ultraviolet rays, whereby a strong photocatalytic action is exhibited, and a reliable discoloration reaction can be caused in the image forming material. Moreover, high resolution can be achieved by adjusting the beam diameter of the laser. In this case, a photocatalytic material containing titanium oxide (TiO ₂ ) as a main component, which exhibits a photocatalytic action with ultraviolet rays of 400 nm or less, may be used. In this case, a laser oscillator using Nd: YAG as the laser medium may be adopted. According to this, an appropriate oscillation wavelength near 300 nm can be obtained, and since it is a solid-state laser, it is easy to maintain and has a high output. And it can be miniaturized.

According to the eleventh aspect of the invention, in the image forming method.
As shown in FIG. 3, a writing process is performed on the image forming material layers by using different image carriers for each of the image forming materials of a plurality of colors, and then these image forming material layers are superposed to obtain a composite image. be able to. According to this, a multicolor image can be obtained by using the image forming materials of a plurality of colors.

The image forming method according to claim 12
As shown in, the image forming material layers on the image carrier for each of a plurality of colors are sequentially transferred to the intermediate transfer body, and the image forming material layers are superposed on the intermediate transfer body. It is possible to adopt a configuration in which the composite image forming material layer is transferred to a recording medium.
Further, as described in claim 13, the image forming material layer on the image carrier for each of a plurality of colors may be sequentially transferred to the surface of the recording medium and the image forming material layers may be superposed on the recording medium. it can.

According to a fourteenth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier having a photocatalyst layer formed of a photocatalyst material on its surface; and an image forming material which causes a color change reaction by a photocatalytic action. An ink layer forming means for uniformly applying an aqueous ink liquid to the image forming surface on the surface of the photocatalyst layer, and a light irradiating means for performing a writing process for selectively irradiating the photocatalyst layer with excitation light according to image information to be formed. And a desired image is formed depending on the presence or absence of a color change reaction occurring in the image forming material layer by the writing process by the light irradiation means. According to this, since an image can be formed with the aqueous ink liquid, it is possible to avoid inconveniences in energy saving and environmental protection that occur when the powder toner is used. Since there is no change in the image forming surface of the image bearing member during the writing process, the next different image can be immediately formed. In this case, it is assumed that the photocatalyst layer of the image carrier is previously subjected to hydrophilic treatment by irradiating excitation light, and then the aqueous ink liquid is applied to the surface of the photocatalyst layer.

According to another aspect of the invention, in the image forming apparatus.
As shown in FIG. 3, an image forming unit including an image carrier and an ink layer forming unit is provided for each of a plurality of colors, and the image forming material layers individually written by the plurality of image forming units are sequentially superimposed and combined. It is possible to adopt a configuration in which an image is obtained. According to this, a multicolor image can be obtained using a plurality of ink liquids having different colors.

In the image forming apparatus, the image forming apparatus according to claim 16
As shown in, the light irradiation means is an ultraviolet laser oscillator,
An optical system device that guides the laser light emitted from this to the image forming surface on which the image forming material layer is formed can be employed.
According to this, the photocatalytic material is irradiated with high-energy ultraviolet rays, whereby a strong photocatalytic action is exhibited, and a reliable discoloration reaction can be caused in the image forming material. Moreover, high resolution can be achieved by adjusting the beam diameter of the laser light with an optical system device.

[0025]

DETAILED DESCRIPTION OF THE INVENTION The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic view showing the steps of the image forming method according to the present invention step by step. Here, first,
As shown in (A), the image forming material layer 1 is uniformly formed on the image forming surface 3 of the image carrier 2 (image forming material layer forming step), and then as shown in FIG. The photocatalyst layer 4 forming the image plane 3 is subjected to a writing process of selectively irradiating the excitation light from the light source 5 according to the image information to be formed,
A fading reaction is selectively caused in the image forming material layer 1 on the image forming surface 3 (writing process), and a desired image is formed on the image forming material layer 1 depending on the presence or absence of the fading reaction. Excitation light is lens 6
The photocatalyst layer 4 is irradiated with light after focusing on. Next, as shown in FIG. 1C, the image forming material layer 1 on the image carrier 2 on which the writing process has been performed is once transferred to the intermediate transfer body 7 (first transfer step), 1D, the image forming material layer 1 on the intermediate transfer body 7 is transferred to the recording medium 8 (second transfer step), whereby the image forming material layer 1 on the recording medium 8 is required by the image forming material layer 1. An image is formed.

The image forming material layer 1 is composed of an image forming material which causes a fading reaction (color change reaction) by a photocatalytic action. For example, an aqueous ink liquid in which a required image forming material is dispersed in water is used. In this case, Then, the photocatalyst layer 4 is irradiated with excitation light in advance, and a hydrophilic treatment for bringing the image forming surface 3 into a superhydrophilic state is performed.
As a result, a uniform and thin ink layer (imaging material layer) is obtained. It is also possible to use an ink liquid in which fine powder (for example, titanium oxide fine powder) made of a photocatalytic material is dispersed together with the image forming material.

FIG. 2 is a plan view showing an example of an image obtained by the image forming method shown in FIG. Here, the image forming material layer 1 is transferred onto the recording medium 8, and the image forming material layer 1 is transferred.
In this area, a fading area 21 that has become colorless due to a fading reaction due to the writing process and an unbleached area 22 that has escaped the fading reaction are formed, and a desired image is formed in the unbleached area 22.

FIG. 3 is a sectional view showing another example of the image forming method according to the present invention. Here, the image forming material layer 1 is formed on the image forming surface 32 of the image carrier 31 formed of a material that transmits excitation light, and the image forming material is formed on the photocatalyst layer 33 forming the image forming surface 32. Excitation light is emitted from the surface opposite to the layer 1 by the light source 5 and the lens 6. The image forming material layer 1 on the image carrier 2 as in the example shown in FIG.
When irradiating the excitation light from the side, the excitation light passes through the image forming material layer 1 and reaches the photocatalyst layer 4, whereas the excitation light does not pass through the image forming material layer 1, so that the excitation light is excited. The attenuation of light can be suppressed.

FIG. 4 is a perspective view schematically showing an example of the image forming apparatus according to the present invention. Here, a titanium oxide thin film (photocatalyst layer) is formed on the outer peripheral surface, and the surface thereof is used as an image forming surface 41.
The image forming surface 41 of the drum (image carrier) 42 and the ink liquid made of the image forming material that causes a color change reaction by the photocatalytic action.
An ink coating roller (ink layer forming means) 44 for uniformly and thinly coating to form an ink layer (image forming material layer) 43,
A light irradiation unit (light irradiation means) 45 that selectively irradiates the image formation surface 41 with excitation light according to image information to be formed.

The light irradiator 45 includes an ultraviolet laser oscillator 46.
And a lens 47 for narrowing the focus of the laser light emitted from the ultraviolet laser oscillator 46 as an optical system device for guiding the laser light (excitation light) emitted from this to the image forming surface 41 of the drum 42, and passed through this lens 47. A polygon mirror 48 that rotates the laser light at high speed to scan in the axial direction of the drum 42, and an fθ lens 49 that corrects the focal length of the laser light.
And has a predetermined beam diameter on the image forming surface 41 of the drum 42.

FIG. 5 is a schematic sectional view of the image forming apparatus shown in FIG. A desired image is formed on the ink layer 43, which has been subjected to the writing process by the laser beam on the image forming surface 41 of the drum 42, depending on the presence or absence of the fading reaction.
Is once transferred onto a transfer roller (intermediate transfer member) 51 and then transferred onto a recording paper (recording medium) 52, whereby a desired image is formed on the recording paper 52. Transfer roller 51
When the upper ink layer 43 is transferred to the recording paper 52, pressure is applied from the back surface of the recording paper 52 by the pressure roller 53. Further, here, when the transfer from the transfer roller 51 to the recording paper 52 is completed, the ink remaining on the transfer roller 51 is removed by the cleaning roller 54 (cleaning step).

FIG. 6 is a perspective view showing an example of a multicolor image forming apparatus to which the present invention is applied. Here, 2 with different colors
A pair of ink layers (image forming material layers) that have image forming units 61a and 61b for each type of ink and are individually written by the pair of image forming units 61a and 61b.
62a and 62b are sequentially overlapped to obtain a composite image, and the image forming units 61a and 61b for the first color and the second color are respectively arranged on the drum (image carrier) 63a.
63b and application roller (ink layer forming means) 64a
4b, which are provided side by side in the circumferential direction of the transfer roller (intermediate transfer member) 65, and the ink layers 62a and 62b on which the writing process has been performed on the drums 63a and 63b are combined on the transfer roller 65. An image of two colors is formed on the recording paper 52 by transferring the synthetic ink layer 66 on the transfer roller 65 to the recording paper 52.

The image forming units 61a and 61b are respectively provided with light irradiating parts (light irradiating means) 67a and 67b having the same structure as shown in FIG. 4, and the drums 63a and 63b.
The writing process is individually performed on the upper ink layers 62a and 62b. In addition, the synthetic ink layer 6 on the transfer roller 65
A pressure roller 68 that applies a pressure when transferring 6 to the recording paper 52 is provided, and a cleaning roller 69 that removes ink remaining on the transfer roller 65 is provided.
With this configuration, the transfer roller 6 accurately positioned and fixed
5, the ink layers 62a and 62b of the respective colors are combined, so that the deviation of the images of the respective colors can be suppressed.

FIG. 7 is a perspective view showing another example of a multicolor image forming apparatus to which the present invention is applied. Here, in FIG.
Similar to the example shown in FIG. 3, the image forming units 71a and 71b for each of two types of ink having different colors are provided, and the pair of ink layers 72a and 71b are individually written by the pair of image forming units 71a and 71b. The image forming units 71a and 71b for the first and second colors respectively include drums (image carrier) 73a and 73b and coating rollers (ink layer). Forming means) 74a and 74b and transfer roller (intermediate transfer member) 7
5a and 75b, which are provided side by side in the transport direction of the recording paper 52, and the ink layers 72a and 72b on which the writing processing is performed on the respective drums 73a and 73b are the recording paper (recording medium)
An image of two colors is formed on the recording paper 52 by being combined on the recording paper 52 by the combined ink layer 76. Also, the image forming unit 71a
71b are provided with light irradiators (light irradiators) 77a and 77b having the same configuration as that shown in FIG. 4, and pressure rollers 78a and 78b and cleaning rollers 79a and 79b are provided in the image forming unit 71a. -It is provided for each 71b.

In the example shown in FIGS. 6 and 7,
Although two types of ink are used, it is also possible to use a large number of types of ink that exceed this amount. In that case, a plurality of image forming units are provided side by side along the transfer surface of the intermediate transfer member, as described above. Alternatively, it may be configured such that they are provided side by side in the recording paper conveyance direction.

[0037]

As described above, according to the present invention, since the liquid ink can be used, the fixing process as in the case of using the powder toner is not necessary, and the power consumption and the heat generation are reduced. It is possible to contribute to energy saving, and since there is no problem of toner scattering into the atmosphere, a great effect can be obtained in terms of environmental protection. In addition, since the image forming surface of the image carrier does not change due to the writing process, it is possible to immediately move to the next different image forming work, and with the same functionality as the electrophotographic method, small-volume multi-product printing and on-demand printing. It can support printing.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing stepwise the procedure of an image forming method according to the present invention.

FIG. 2 is a plan view showing an example of an image obtained by the image forming method shown in FIG.

FIG. 3 is a sectional view showing another example of the image forming method according to the present invention.

FIG. 4 is a perspective view schematically showing an example of an image forming apparatus according to the present invention.

5 is a schematic cross-sectional view of the image forming apparatus shown in FIG.

FIG. 6 is a perspective view showing an example of a multicolor image forming apparatus to which the present invention is applied.

FIG. 7 is a perspective view showing another example of a multicolor image forming apparatus to which the present invention is applied.

[Explanation of symbols]

1 image forming material layer 2 ・ 31 image carrier 3 ・ 32 ・ 41 image forming surface 4 ・ 33 photocatalyst layer 5 light source 6 lens 7 intermediate transfer member 8 recording medium 21 faded area 22 unbleached area 42 ・ 63a ・ 63b ・ 73a ・73b Drum (image bearing member) 43, 62a, 62b, 72a, 72b Ink layer (imaging material layer) 44, 64a, 64b, 74a, 74b Ink application roller (ink layer forming means) 45, 67a, 67b, 77a. 77b Light irradiation unit (light irradiation means) 46 Ultraviolet laser oscillator 47 Lens 48 Polygon mirror 49 fθ lens 51, 65, 75a, 75b Transfer roller (intermediate transfer member) 52 Recording paper (recording medium) 53, 68, 78a, 78b Addition Pressure roller 54/69 / 79a / 79b Cleaning roller 61a / 61b / 71a / 71b Image forming unit 66/76 Synthetic ink

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H123 AE00 AE11 BA00 BA03 BA40                       BA70 BC00 BC11 BC18 CA00                       CA20 CA22 CC00 FA00 FA21                       FA22                 4G069 AA02 BA04A BA04B BA48A                       CD10 EA07

Claims (16)

[Claims] 1. A photocatalytic material in which an image forming material layer made of an image forming material which causes a color change reaction by a photocatalytic action is uniformly formed on an image forming surface of an image carrier and is evenly distributed along the image forming surface. A writing process of selectively irradiating excitation light onto the image forming material layer to partially cause a color changing reaction, and a visible image is obtained by the presence or absence of the color changing reaction in the image forming material layer. Image forming method. 2. The image forming method according to claim 1, wherein the color change reaction is a color fading reaction that changes the image forming material to a colorless side. 3. The photocatalyst material forms a photocatalyst layer on the surface of the image carrier, and the surface of the photocatalyst layer serves as the image forming surface, and the image forming material layer is formed thereon. Item 2. The image forming method according to Item 1. 4. The photocatalyst layer is preliminarily subjected to a hydrophilizing treatment by irradiating with excitation light, and then the image forming surface on the surface of the photocatalyst layer is coated with an aqueous ink liquid containing the image forming material. The image forming method according to claim 3, wherein an image material layer is formed. 5. The image carrier is formed of a material that can transmit the excitation light, and the surface of the photocatalyst layer provided on the image carrier is opposite to the image forming material layer. The image forming method according to claim 3, wherein the excitation light is irradiated. 6. The image according to claim 1, wherein the photocatalytic material is finely powdered and uniformly dispersed in the ink liquid formed of the image forming material forming the image forming material layer. Forming method. 7. The image forming method according to claim 1, wherein the photocatalytic material is irradiated with the excitation light from the side of the image forming material layer on the image forming surface. 8. The image forming material layer on the image bearing member is temporarily transferred to another intermediate transfer member in transferring the image forming material layer subjected to the writing processing on the image forming surface to a recording medium. The image forming method according to claim 1, further comprising the step of transferring the image onto the recording medium. 9. The image forming method according to claim 8, wherein when the transfer from the intermediate transfer body to the recording medium is completed, the surface of the intermediate transfer body is cleaned. 10. The image forming method according to claim 1, wherein an ultraviolet laser beam is used as the excitation light. 11. A composite image is obtained by performing a writing process on the image forming material layers by using different image carriers for each of the image forming materials of a plurality of colors and then superimposing the image forming material layers. The image forming method according to claim 1, wherein: 12. The image forming material layer for each of a plurality of colors is sequentially transferred to an intermediate transfer member, the image forming material layers are superposed on the intermediate transfer member, and then the intermediate transfer member is transferred. The image forming method according to claim 11, wherein the synthetic image forming material layer on the body is transferred to a recording medium. 13. The image forming material layer on the image bearing member for each of a plurality of colors is sequentially transferred to the surface of a recording medium, and the image forming material layer is superposed on the recording medium. 11. The image forming method according to item 11. 14. An image carrier on which a photocatalyst layer made of a photocatalyst material is formed, and an aqueous ink liquid made of an image-forming material that causes a color change reaction by a photocatalytic action are uniformly applied to the image-forming surface on the surface of the photocatalyst layer. An ink layer forming means for applying and a light irradiating means for performing a writing process for selectively irradiating the photocatalyst layer with excitation light according to image information to be formed, and the image forming by the writing process by the light irradiating means. An image forming apparatus, wherein a required image is formed depending on the presence or absence of a color change reaction occurring in a material layer. 15. An image forming unit comprising the image carrier and an ink layer forming means is provided for each of a plurality of colors, and the image forming material layers individually subjected to the writing processing are successively superposed on each other. The image forming apparatus according to claim 14, wherein a combined image is also obtained. 16. The image forming apparatus according to claim 14, wherein the light irradiation unit includes an ultraviolet laser oscillator and an optical system device that guides laser light emitted by the ultraviolet laser to the image forming surface.