JP2000267448A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always obtain a satisfactory transfer characteristic and the output of an image of high image quality by applying a resin layer which is substantially transparent or whose color does not exert adverse effect on the recognition of a visible image substantially, to the visible image prior to transfer. SOLUTION: To a color image formed on a latent-image holder 1 after a four-color image forming process, a transparent resin layer is applied by a resin application device 9. In the resin application device 9, so-called transparent developer 10 composed of components which are the same as liquid developers, except coloring agents, stored in respective developing devices 4a-4d, or a solvent whose composition is approximate to it and a solid component is stored. In this case, the composition of the materials except the coloring agents may not be the same as that of the color developers. However, it is preferable that the electrification characteristic and the viscoelastic characteristic of the resin component, etc., be approximate to the characteristics of the color developers. When a transparent resin layer is applied to a toner layer, the transparent resin layer deforms along the recesses and projections of the surface of plain paper and is able to contact with the recesses and projections of the plain paper as well, therefore satisfactory transfer can be obtained even on the plain paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a liquid developer.

[0002]

2. Description of the Related Art A wet image forming apparatus such as an electrophotographic recording apparatus or an electrostatic recording apparatus using a liquid developer has advantages that cannot be realized by a dry image forming apparatus, and its value is recently being reviewed. . That is, it is possible to use a very fine toner having a submicron size, so that high image quality can be realized, and a sufficient image density can be obtained with a small amount of toner, so that it is economical and at the same level as printing (for example, offset printing). The main advantages of the wet image forming apparatus over the dry image forming apparatus are that the texture can be realized and the toner can be fixed on the paper at a relatively low temperature, so that energy can be saved.

On the other hand, the conventional liquid image forming apparatus using a liquid toner has some essential problems, and for a long time, has allowed the sole use of dry technology. One of the problems of these wet image forming apparatuses is a problem in transfer means.

[0004] The first problem in transfer is deterioration of image quality. That is, conventionally, the developer adhered on the latent image holding member is directly transferred to the paper by the action of the electric field by the transfer means, so that the transfer unevenness due to the electric field fluctuation according to the unevenness of the paper surface has occurred. In addition, transfer failure was likely to occur due to variations in the electrical characteristics of the paper and environmental dependence. These problems have significantly degraded the quality of the transferred image.

In order to solve such a problem, there has been proposed an apparatus for temporarily transferring the image from the latent image holding member to an intermediate transfer medium and then transferring the image to a sheet. US Patent 5,148,
No. 222, 5,166,734, 5,208,63
No. 7 and the like disclose an apparatus for transferring an image from a latent image carrier to an intermediate transfer medium by an electric field, and thereafter transferring the image to a sheet by pressure (and heat).

Further, Japanese Patent Publication No. 46-41679 and Japanese Patent Application Laid-Open No. 62-280882 disclose an apparatus using pressure (and heat) for both transfer to an intermediate transfer medium and transfer to paper without using electric field transfer. Is disclosed. Since it is relatively easy to configure the intermediate transfer medium from a material with a smooth surface and little variation or fluctuation in electrical resistance, the image quality degradation due to transfer is dramatically faster than when performing electric field transfer directly to paper. Be improved.

[0007] Even when the image is transferred to the intermediate transfer medium by pressure and heat, the deterioration of the image quality is remarkably suppressed. In addition, in these proposals, since transfer is performed on paper by heat and pressure, uneven transfer due to electric field fluctuations due to unevenness of the paper surface, such as seen in the case of electric field transfer, and variations in the electrical characteristics of the paper. There is no problem such as poor transfer due to environmental or environmental dependence.

However, these proposals still have the following problems in practical use. First, providing an intermediate transfer medium complicates the process. In addition, the image quality fluctuates with the deterioration of the intermediate transfer medium, which lowers the reliability of the system. Since the intermediate transfer medium generally requires elasticity and release properties, a medium in which a silicone-based or fluorine-based release layer is provided on the surface of an elastic layer such as rubber is often used. It is inferior to the component parts.

Furthermore, when transferring a toner image from an intermediate transfer medium to a sheet, it is difficult to maintain 100% transfer efficiency, and a cleaner for removing toner remaining on the intermediate transfer medium after transfer is required. And the system becomes more complex, and its durability is further shortened by the damage caused by the cleaner.

In order to solve such a problem relating to the intermediate transfer medium, there has been proposed an apparatus for directly transferring a toner image from a latent image holding member to an image carrier (paper) by heat and pressure. U.S. Pat. No. 5,608,507 discloses an apparatus for directly transferring an image by a liquid toner from a latent image holding member having a release layer on the surface to a sheet by heat and pressure.

In the invention disclosed in this patent document, the liquid toner image attached to the latent image on the surface of the photoreceptor is completely dried (dry out) and then transferred to the sheet, so that the solvent adheres to the sheet. Harmful solvent vapor can be prevented from being discharged outside the device.

However, according to the follow-up test conducted by the present inventors,
It became clear that the following problems also existed in this device. First, it is extremely difficult to transfer a toner image onto paper with pressure (and heat) in a state where the solvent is completely dried. As described in detail in the patent, it is necessary to improve transfer efficiency. It is necessary to form the photoreceptor layer on the elastic backing layer and to improve the adhesion between the paper surface and the toner by utilizing the elastic deformation.

In this case, since the photoconductor layer is repeatedly deformed with the deformation of the elastic body under the pressure of the pressing member pressing the back surface of the sheet, the binder resin constituting the photoconductor undergoes fatigue destruction, and The problem has been found that the life of the body is significantly reduced. Since the photoreceptor needs to have flexibility, a metal-based photoreceptor such as amorphous silicon or selenium cannot be used, and a binder-based photoreceptor such as an organic photoreceptor must be used. It is difficult to improve the life.

Further, in order to obtain good transfer efficiency, the surface layer of the photoreceptor must be made of a material having a remarkably high releasability, and it has been extremely difficult to achieve both high photosensitivity and a high releasability layer. Further, in order to obtain a transfer efficiency close to 100%, the photoconductor layer and the pressure member (backup roller) are
It is necessary to heat the paper to 0 ° C. or higher to melt the toner sufficiently, and at the same time press the paper against the photoreceptor with a high pressure. Brought problems.

[0015]

[0007] The transfer unevenness due to the electric field fluctuation according to the irregularities on the paper surface has occurred. In addition, in a conventional wet image forming apparatus, if a good transfer efficiency is to be obtained in a conventional wet image forming apparatus, a short transfer of the photosensitive member and a selection of a material are not performed. Many problems such as difficulty, waste of heat energy, increase of driving torque, etc. have been caused.

The present invention has been made under such circumstances,
An object of the present invention is to provide an image forming apparatus capable of always realizing good transfer characteristics and high-quality image output in wet image formation.

[0017]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to obtain good transfer characteristics and high-quality image output in wet image formation. It has been found that these problems can be solved by increasing the thickness of the solid component (resin component) or the apparent thickness. The present invention is based on such findings.

That is, a first invention is a latent image forming means for forming an electrostatic latent image on a latent image holding member, and a liquid developer is supplied to the electrostatic latent image to form the electrostatic latent image. In an image forming apparatus including a developing unit that develops and forms a visible image, and a transfer unit that transfers the visible image to an image carrier, substantially prior to the transfer by the transfer unit, substantially An image forming apparatus provided with a resin applying means for applying a resin layer of a color which is transparent or has substantially no adverse effect on the recognition of the visible image.

In the image forming apparatus according to the first aspect, the resin applying unit can be provided between the developing unit and the transfer unit. Alternatively, it can be provided before the developing means.

The resin layer may be formed only in the visible image area, or only in the visible image area and its neighboring area.
It can be applied to both the image area and the background area of the visible image.

As the transfer means, a direct transfer method in which a visible image provided with a resin layer is directly transferred to an image carrier can be employed. Alternatively, it is also possible to adopt an indirect transfer method in which the image is temporarily transferred to an intermediate transfer medium and then transferred to an image carrier.

In the transfer by the transfer means, the visible image provided with the resin layer is transferred by pressure or by pressure and heat.
The transfer can be performed by transferring the image to an image carrier. In this case, the transfer unit may include a pressing roller pressed against the latent image holding member via the image carrier, and a load per unit length in the axial direction of the pressing roller may be 0.3 kg / cm to 15 kg.
means for pressing the pressure roller against the latent image holding member such that the pressure becomes kg / cm.

The resin layer has a thickness of 0.1 to 20 μm
It is desirable to be provided to the visible image so that Further, as the resin layer, a coating liquid containing a solid resin component and a solvent component can be used and applied to the image carrier by an electric field effect. In this case, the ratio of the solid component contained in the coating liquid is desirably 1 to 40 wt%.

It is desirable that the visible image provided with the resin is heated to a temperature of 30 to 150 ° C. by a heating means. Further, the amount of the solvent component is adjusted by the squeezing means so that the developer and the resin layer which form the visible image are combined, and the solid content of 25 to 100% and the solvent component of 0 to 75% are included. It is desirable.

According to a second aspect of the present invention, there is provided a latent image forming means for forming an electrostatic latent image on a latent image holding member, and developing the electrostatic latent image by supplying a liquid developer to the electrostatic latent image. In an image forming apparatus including a developing unit for forming a visible image and a transfer unit for transferring the visible image to an image carrier, the thickness of the developer layer for forming the visible image has a minimum value of 0. An image forming apparatus characterized by being not less than 1 μm and not more than a maximum value of 20 μm.

In the second aspect of the invention, the thickness of the developer layer for forming a visible image can be set to 8 to 20 μm.

According to the image forming apparatus of the present invention configured as described above, the thickness of the developer layer for forming a visible image,
Or, by increasing the apparent thickness of the developer layer by providing a resin layer, in the wet image formation,
It has become possible to always achieve good transfer characteristics and high-quality image output.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a wet image forming apparatus according to an embodiment of the present invention. In FIG. 1, a latent image holding member 1 is a photosensitive drum in which a photosensitive layer of an organic or amorphous silicon type is provided on the surface of a cylindrical conductive substrate. The latent image carrier 1 is uniformly charged by a well-known corona charger or scorotron charger 2a, and then is exposed to an image-modulated laser beam 3a to form an electrostatic latent image on the surface. Thereafter, the electrostatic latent image is visualized by the developing device 4a that stores the liquid developer.

The liquid developer or toner particles (solid components) adhering to the electrostatic latent image may directly reach the transfer means and be transferred to the sheet by the transfer device 6, but here, the second charger 2b And a second laser exposure 3b to form a second electrostatic latent image, and a second developing device for storing a second developer of a different color from the liquid developer stored in the first developing device 4a. This is developed by the device 4b.

Therefore, after the second development, a two-color toner image is formed on the latent image holding member 1. Similarly, the third charger 2c, the third laser exposure 3c, the third developing device 4c, the fourth charger 2d, the fourth laser exposure 3
d, The third and fourth charging, exposure, and development are performed by the fourth developing device 4d, and a full-color toner image is formed on the latent image holding member 1.

The toner image formed on the latent image holding member 1 is
The toner image is transferred onto the sheet 8 by the transfer roller 6, and at this time, a predetermined pressure is applied to the toner image by the transfer roller 6. At the same time, for example, a heating source is provided inside the transfer roller 6 or the latent image holding drum 1 to heat the toner image, thereby improving transferability.

In the conventional wet image forming apparatus, the thickness of the toner image formed on the surface of the latent image holding member 1 by the developing means is at most about 0.4 μm, and is less than 0.1 μm in the low density image area. It was not uncommon to be. Therefore, when these toner images are transferred to plain paper having irregularities of several tens of μm on the surface, how to bring the toner particles into contact with the paper surface has been an important issue.

In the conventional electric field transfer, a sufficient amount of solvent is supplied to the paper and the solvent is allowed to penetrate into the concave portions of the paper, so that toner particles adhere to the concave portions of the paper by electrophoresis (= transfer). Was possible, but as a result,
The paper was ejected outside the machine while absorbing a large amount of solvent, which caused environmental problems due to solvent vapor.

In the transfer by pressure (and heat), the toner can be transferred to the paper after the solvent has been sufficiently removed in advance.
An extremely thin toner layer having a thickness of about 1 μm must be adhered to a paper recess having a depth of several tens of μm. for that reason,
It has been an essential condition that the latent image holding member and the intermediate transfer medium are made of an elastic body, and the elastic body is deformed under a high pressure so that the toner comes into contact with the concave portion of the paper.
This request has caused problems relating to durability and stability of the latent image holding member and the intermediate transfer medium as described above.

The present inventors have conducted intensive studies to solve these problems, and as a result, have obtained the following findings. That is, even in the wet image forming process, if the thickness of the toner image transferred to the paper is in the range of 0.3 μm to 20 μm, more preferably in the range of 1 μm to 10 μm,
It has been found that even when the surface of the latent image holding member or the intermediate transfer member is made of a rigid or low-flexibility material, good transfer to plain paper can be realized.

Here, the first embodiment will be described in detail with reference to FIG. A transparent resin layer is applied to the color image formed on the latent image holding member 1 through the four-color image forming process as described above by the resin application device 9. In the resin application device 9, a liquid developer contained in the developing devices 4 a to 4 d and a component obtained by removing a colorant, or a solvent and a solid component having compositions similar to the components, that is, a “transparent developer” 10 Is stored.

Of course, the material composition excluding the colorant may not be the same as the color developer, but it is desirable that the charging characteristics and the viscoelastic characteristics of the resin component are close to those of the color developer. The specific composition of the “transparent developer” is as follows: as a solvent, an insulating solvent such as Isopar G, L, M or Norpar 12 (trade name, Exxon), or as a solid resin having a glass transition point of −50 ° C. Acrylic resins in the range of 50 ° C., including those to which a metal soap for charge control is added, are exemplified.

In this embodiment, a transparent resin is applied to a toner image by the action of an electric field using such a transparent developer. For example, by disposing a metal resin applying roller 11 having an outer diameter of 30 mm with a gap of 150 μm relative to the latent image holding member 1 and rotating in the same direction or the opposite direction to the latent image holding member, the transparent developer 10 can be supplied to the toner image.

When reversal development is performed in the developing devices 4a to 4d under the conditions of a charging potential of 700 V and an exposure portion potential of 100 V, a latent image holding member 1 is used. Since the potential of the toner image formed on the toner image is usually 200 V or less, the transparent resin adhering means applies a voltage in the range of 300 V to 1500 V, more preferably 500 V to 1000 V, to the toner applying roller 11 so that the toner image is transparent. A resin layer can be provided.

FIG. 2 shows a case where only the toner layer (image) 22 is transferred to the plain paper 21 (a), and a transparent resin layer 24 is provided before the transfer of the toner layer 23. A cross-sectional view of the case (b) in which the toner layer 23 is transferred is schematically shown. In the example shown in FIG. 2, from the visible image formed by the liquid development, the solvent component is increased by a well-known solvent recovery device 5 (for example, a reverse squeezing roller, an elastic contact roller, an air knife, etc.) or a drying unit (a hot roller, etc.). It shows the case where the part is removed and the paper is transferred almost without getting wet,
The transfer is performed by pressure (and heat) without using the electric field effect.

The thickness of the toner layer formed on the latent image holding member by liquid development is usually 0.5 μm or less, which is extremely thin as compared with the case of dry toner. The toner particle size of the liquid developer is usually 1/10 or less (submicron size) of the particle size of the dry toner, and the colorant component in the toner particles is large. Is obtained.

Therefore, as shown in FIG. 2 (a), when the toner layer 22 is transferred to the plain paper 21 having a surface having irregularities of about 10 to 50 μm, the toner layer 22 and the plain paper 21 are transferred.
It is extremely difficult to obtain physical contact between the concave portions, and it is extremely difficult to obtain good transfer efficiency.

On the other hand, as shown in FIG. 2B, when the transparent resin layer 24 is applied to the toner layer 23, the transparent resin layer 24 is deformed along irregularities on the surface of the plain paper 25, and
5 can be contacted, so that good transfer can be obtained even on plain paper 25. It is desirable that the thickness of the transparent resin layer 24 be equal to or greater than the surface roughness of the sheet. However, even when the thickness is smaller than this, the sheet is strongly pressed against the surface of the latent image By elastically deforming, it is possible to temporarily reduce the paper surface roughness at the transfer position, so that good transfer can be obtained.

When using paper having a small surface roughness such as coated paper, even if the transparent resin layer is made thinner,
Needless to say, the toner can be transferred. Further, in order for the toner layer to be transferred to the paper together with the transparent resin layer, the adhesive force between the transparent resin layer and the toner needs to be higher than the adhesive force between the toner and the surface of the latent image holding member. Therefore, practically, the release layer 26 is provided on the surface of the latent image holding member,
It is desirable to use a transparent resin having high adhesion to the toner at the same time as enhancing the toner releasability, and more preferably to use a transparent resin having the same or similar composition as the resin constituting the toner.

Here, the transparent resin refers to a resin which has a small optical absorption in a visible light wavelength region and is substantially transparent to human eyes, and may have an absorption in an infrared region or an ultraviolet region. Absent.

In the first embodiment of the present invention described above, the transparent resin layer is provided after forming the toner image on the latent image holding member. However, as shown in FIG. 3, the toner image is formed. A transparent resin may be provided before. That is, in the second embodiment of the present invention shown in FIG. 3, the transparent resin is applied to the surface of the latent image holding member 1 by the resin applying roller 33 before the latent image holding member 1 reaches the position of the corona charger 34. Thereafter, exposure by the exposure beam 35 and development by the developing device 36 are performed to form a toner image on the transparent resin.
The expression "applying a resin layer to a visible image" also includes such a configuration.

The transparent resin may be applied only to the position where the toner image exists, that is, the image area, or may be applied to both the background area and the image area, that is, the entire surface of the latent image holding member. To make the latent image adhere to the entire surface, the entire surface is developed using a transparent developer in a state where the spatial variation of the latent image potential is reduced.

For example, in the embodiment shown in FIG. 3, after the surface potential of the latent image holding member is made uniform by the neutralization lamp 31 so that the surface potential becomes about 20 V, 5
By applying a voltage of 00 V to 1000 V, positively charged transparent resin particles can be uniformly adhered to the whole by the same principle as that of ordinary liquid development. Subsequently, the latent image holding member 1 is placed on the transparent resin layer with the corona charger 34 from 500 to
It is charged to 800 V, and the image is exposed by the exposing means 35 to form an electrostatic latent image. At this time, the thickness of the transparent resin layer is 0.1
When the thickness is within the range of 5 μm, transferability to paper can be improved without adversely affecting the formation of a latent image.

When development is performed by the developing device 36, a toner image is formed on the transparent resin layer. The transfer may be performed as it is, or as shown in FIG. 1, the transfer may be performed after the development is further repeated. When the toner image thus formed is directly transferred to paper together with the transparent resin layer, the transparent resin layer is present on the outermost surface of the transferred image. As a result, a glossy high-quality image can be obtained.

This effect can be obtained substantially similarly when the transparent resin layer is adhered to the entire latent image holding member after development as shown in FIG. However, in this case, since the latent image is not formed after the transparent resin layer is attached, the transparent resin layer can be made even thicker, thereby significantly improving the transferability.

It is desirable that the thickness of the transparent resin layer be in the range of 0.1 to 20 μm. If the thickness is larger than this, problems such as collapse of an image at the time of transfer, loss of flexibility of a sheet after transfer, and an increase in printing cost will occur. Methods for increasing the thickness include increasing the electric field, increasing the rotation speed of the resin application roller,
Increasing the diameter of the resin application roller, increasing the particle diameter of the transparent resin, lowering the charge amount of the transparent resin, filling the dish-like container with the transparent developer, and immersing the latent image holding body in the transparent developer to thereby clear the developer To increase the contact time between the toner and the latent image holding member, and to increase the ratio of the transparent resin particle component in the transparent developer.

Among these methods, the method of increasing the ratio of the transparent resin particle component during the transparent development is particularly effective.
The ratio of the solid component contained in the transparent developer is 1 wt% to 40
When the content is in the range of wt%, more preferably in the range of 2 wt% to 10 wt%, a transparent resin layer having a thickness sufficient to perform transfer and having a thickness small enough not to cause image collapse is obtained.

The solvent content per unit volume of the developer and the transparent developer adhering to the surface of the photoreceptor is 0 g / cm ^3.
The range is preferably ⁴ g / cm ^{3 to 4} g / cm ³ . In addition, in the examples shown in FIGS. 1 to 3, the transparent resin is applied according to the same principle as that of liquid development, but other coating techniques can be used. For example, a device for applying with a brush roller, a device for carrying and applying a foam such as an elastic foam, a device for conveying and applying a transparent paint containing a high concentration of solids with a roller, a device for applying by spraying, and the like. is there. When these means are used, it is not always necessary to charge the solid content in advance.

Next, by applying the transparent resin layer only to the toner-attached portion, the consumption of the transparent resin can be reduced, and the printing cost can be reduced. Also in this case, there are a method of applying before development and a method of applying after development.

According to the method of applying before development, an electrostatic latent image corresponding to an output image is formed, and a resin layer is applied thereto by the principle of liquid development. When a color image is output by the process shown in FIG. 1, it is necessary to form a latent image using data of a final image obtained by superimposing color separation images. After the resin layer is formed as in the process shown in FIG. 3, toner development is performed on the resin layer.

In the case where a resin layer is applied to the toner-attached portion after development, the method of forming an electrostatic latent image at a position where a toner image exists by charging and exposure as described above can be applied. However, by using the following method,
The apparatus can be simplified.

First, after the development, the surface of the latent image holding member is once uniformly charged by a corona charger or the like, and then the entire surface is exposed. When the entire surface is exposed with light having a wavelength range in which the photoconductor has sensitivity and a wavelength that is absorbed by the toner image, the charge is not attenuated in the toner-attached portion, and the non-toner-attached portion is attenuated. Therefore, if development is performed with a transparent developer containing transparent resin particles charged to a polarity opposite to the charging polarity of the toner attached portion, the transparent resin can be applied only to the toner attached portion.

This eliminates the need for image exposure to apply the resin layer, and eliminates the need for an exposure optical system, an image processing circuit, and a positioning mechanism for reliably exposing the toner image to the toner image. Thus, a simple resin applying means can be realized. Typical potential conditions are as follows: +300 to +800 V for the toner attached portion, and 0 to ++ for the non-toner attached portion.
The condition is 200 V, and the transparent developing bias is a voltage between these two voltages, for example, +300 to +600 V.

It is also effective to provide an opening in the shield case of the corona charger and perform the above-described overall exposure, that is, a method of performing simultaneous charge exposure, thereby further simplifying the process. Become.

In a single-color image forming process in which development is performed only once, by performing development with a transparent developer subsequent to development with a colored developer, the transparent developer can be applied only to the image area. This is because in normal liquid development, the potential increase in the exposed area due to toner adhesion is several tens of volts, and the electrostatic latent image is retained even after development.

The effect of providing the transparent resin is most remarkable when the visible image is directly transferred to the image carrier (paper) by pressure (and heat) in the transfer means. However, even in an apparatus that directly transfers to paper by an electric field, the transparent resin layer flexibly enters the concave portion of the paper surface, so that an excessive amount of solvent does not adhere to the paper,
The effect that a highly efficient transfer can be obtained is obtained.

In the case where the visible image to which the transparent resin is applied is once transferred to the intermediate transfer medium and then transferred to the image carrier, the transfer characteristics from the intermediate transfer medium to the paper are affected by the adhesion of the transparent resin. Of course, it can be improved.

By providing a release layer made of a silicone or fluorine-based material on the surface of the latent image holding member, the transfer characteristics are further improved. In particular, when a transparent resin layer is provided on the entire surface of the latent image holding member, it is necessary to reduce the total adhesive force between the resin layer and the latent image holding member as much as possible and to improve the releasability of the paper. Layer is important.

It is important that the transparent resin be deformed at the transfer position in accordance with the surface shape of the sheet, and be able to come into contact with concave portions on the sheet surface. To this end, it is important to heat the visible image and the transparent resin layer at the transfer position to a temperature in the range of 30 ° C. or more and 150 ° C. or less to soften the resin. Excessive heating is not preferable from the viewpoint of energy saving.

When the visible image and the transparent resin reach the transfer position in a state where 3% to 50% of the total weight of the transparent resin is used as a solvent component, the swelling action of the solvent causes the same flexibility as during heating. Is obtained. Therefore, it is also effective to provide a throttle means for adjusting the amount of the solvent in such a range. When the solvent component is extremely small, flexibility is lost, and when the solvent component is extremely large, environmental problems occur.

Further, in order to obtain good transfer, as a transfer device, a pressure roller pressed against a latent image holding member via an image carrier, and a pressure roller per unit length in the axial direction of the pressure roller are used. It is desirable to use a device having means for pressing the pressure roller against the latent image holding member so that the load is in the range of 0.3 kg / cm or more and 15 kg / cm or less. If the load is less than this range, the transfer efficiency is reduced. If the load is beyond this range, the paper may be wrinkled or the driving torque of the pressure roller or the like may become excessively large.

In the embodiment described above, the transparent resin is used. However, the resin is not necessarily required to be transparent, and does not adversely affect the recognition of the toner image such as making the recognition of the toner image difficult. Alternatively, it is also possible to use a color having little adverse effect, for example, a resin having the same color as the paper. When the paper is white, the effect of the present invention can be obtained by applying a white resin without any adverse effect on the toner image.

In the example described above, the transferability is improved by increasing the thickness of the toner layer by using a resin. However, if the thickness of the toner image itself can be increased, a resin layer is provided. Without this, the same effect can be obtained. According to the experiments of the present inventors, if the minimum value of the thickness of the toner image is 0.1 μm or more and the maximum value is in the range of 20 μm or less, even in direct pressure transfer and indirect pressure transfer, Good transfer efficiency is obtained. Particularly, when the thickness of the toner image is 8 to 20 μm, particularly good transfer efficiency can be obtained.

To obtain a toner image having such a thickness, the ratio of the solid component in the liquid developer is increased, for example, to 3 wt.
% To 30 wt% is effective. Further, a method of increasing the particle size of the toner, a method of increasing the developing electric field, a method of increasing the rotation speed of the developing roller, and a method of increasing the contact time between the developer and the latent image holding member are also applicable.

In any of the methods, the thickness of the toner layer is 0.1 μm in the highlight area (low density area) of the image.
It is important that the settings are made as described above. Further, the ratio of the colorant component in the toner particles is reduced to, for example, 1 wt%.
When the amount is within the range of 15% by weight, a desired optical density can be obtained even when a large amount of toner adheres.

[0071]

As described above, according to the first aspect, the apparent thickness of the developer layer is increased by providing the resin layer. For example, since the thickness of the developer layer for forming a visible image is increased, a visible image formed of a liquid developer can be transferred from the latent image holding member to the image carrier with high efficiency. In addition, it is possible to reduce the adhesion of the solvent to the paper, to form a high-quality image, and to obtain an environment-friendly image forming apparatus.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a comparison of transfer between an image forming apparatus according to an embodiment of the present invention and a conventional image forming apparatus.

FIG. 3 is a sectional view showing a main part of an image forming apparatus according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Latent image holding body 2a, 2b, 2c, 2d ... Charger 3a, 3b, 3c, 3d ... Laser exposure 4a, 4b, 4c, 4d ... Developing device 5 ... Solvent recovery device 6 ... Transfer (pressure) roller 8 ... Paper (image carrier) 9 ... Resin applying device 10 ... Transparent developer 11 ... Resin applying roller 22,23 ... Toner layer 21,25 ... Paper 24 ... Transparent resin layer 26 ... Release layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasushi Maneshiro 1st Kosuka Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Inventor Seika Ooka, Sachi-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 Muko Toshiba Town F-term in Toshiba R & D Center (reference) 2H032 AA14 AA15 BA01 BA02 BA04 2H074 AA03 BB44 BB46 BB68 BB72 EE07 EE09

Claims (9)

[Claims] 1. A latent image forming means for forming an electrostatic latent image on a latent image holding member, and developing the electrostatic latent image by supplying a liquid developer to the electrostatic latent image to form a visible image And an image forming apparatus including a transfer unit configured to transfer the visible image to an image carrier. Prior to the transfer by the transfer unit, the image forming apparatus is substantially transparent to the visible image, or An image forming apparatus comprising: a resin applying unit that applies a resin layer having a color that does not substantially affect the recognition of a visible image. 2. The image according to claim 1, wherein the resin layer is provided only on the image area of the visible image, or only on the image area of the visible image and an area in the vicinity thereof. Forming equipment. 3. The method according to claim 1, wherein the transparent resin layer is provided on an image area and a background area of the visible image.
An image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 1, wherein the transfer unit directly transfers the visible image provided with the resin layer to the image carrier. 5. The image forming apparatus according to claim 1, wherein the transfer unit transfers the visible image provided with the resin layer to the image carrier using pressure. 6. The resin layer has a thickness of 0.1 to 2
The image forming apparatus according to claim 1, wherein the image is provided to the visible image so as to have a thickness of 0 μm. 7. The resin layer comprises a solvent and a solid component dispersed in the solvent, wherein the ratio of the solid component is 1 to 4
2. The image forming apparatus according to claim 1, wherein a coating liquid of 0 wt% is applied. 8. A latent image forming means for forming an electrostatic latent image on a latent image holding member, and developing the electrostatic latent image by supplying a liquid developer to the electrostatic latent image to form a visible image. And a transfer unit for transferring the visible image to an image carrier, wherein the thickness of the developer layer for forming the visible image has a minimum value of 0.1.
An image forming apparatus having a size of not less than μm and not more than a maximum value of 20 μm. 9. The developer layer forming the visible image has a thickness of:
The image forming apparatus according to claim 10, wherein the thickness is 8 to 20 μm.