JPH03164762A - Color image forming device with wet type development - Google Patents

Abstract

PURPOSE:To surely transfer a toner image on a transfer sheet without degrading the quality of an image by wetting the transfer sheet with a liquid reducing the surface tension of a color liquid developer before the toner image is transferred. CONSTITUTION:An electrostatic latent image formed on a photosensitive body 10 based on color resolving information is developed with each complementary color liquid developer. When an excess developer is removed, and then the toner image is superimposed and transferred on the transfer sheet S sequentially the transfer sheet S is wet with the liquid reducing the surface tension of the color liquid developer before the toner image is transferred. Thus, in the gap between the photosensitive body 10 and a reverse roller 144, that is, in the gap that the quantity of the developer is extremely less between the photosensitive body 10 and the transfer sheet S, it is uniformly wet by the affection of a liquid reducing surface tension such as silicone oil, and a faithful transfer is performed without changing the quality of an image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to color image formation by electrophotography, and more particularly to a color image formation method using wet development in which developed images formed by liquid developers of different colors are transferred in a superimposed manner. .

[Conventional technology]

There are two methods for forming color images using electrophotography: dry color electrophotography, in which a dry developer is applied to an electrostatic latent image formed based on color separation information, and wet color, in which a liquid developer is applied. There is an electrophotographic method, but the latter wet method has an extremely small toner particle size compared to the dry method (dry method approximately 10
micrometer (wet type: approximately 1 micrometer or less), it has excellent resolution, toner transparency, etc., and high-quality color images can be obtained.

However, this high-definition toner image can only be obtained when the image is directly formed on the photoreceptor.

It is difficult to faithfully transfer a wet toner image onto transfer paper, so in the color image forming method proposed in US Pat. No. 4,600,669, a thermoplastic dielectric layer is provided on the surface. After drying, a full-color toner image is obtained directly on the photoreceptor, and then a transfer paper is placed on top of the image and passed through a hot pressure roll to transfer the entire thermoplastic dielectric layer. That is, one cycle of [charging→exposure→development→drying] is applied to a photoconductor on which a thermoplastic dielectric layer is provided via a release layer, and this cycle is repeated for a multicolor developer. A full-color dried wet toner image is obtained, and a transfer paper is placed on top of this and passed through a hot pressure roll to peel it off from the release layer and transfer the entire thermoplastic dielectric layer to obtain a color image.

Another method is disclosed in Japanese Patent Application Laid-Open No. 61-205954, in which a full-color toner image is directly obtained on a surface-removable photoreceptor, dried, and then a resin liquid is applied onto the toner image or transfer paper. The toner image is transferred using the adhesive strength of the resin. That is, an electrographic multicolor toner image is formed on a photoreceptor having a releasable surface by repeating the cycle of [charging → exposure → development → drying] using a multicolor developer to form a full-color dried wet toner image on the photoreceptor. Then, by overlaying a transfer paper coated with a resin agent, or by overlaying a transfer paper coated with a resin liquid, it is peeled off and transferred from the releasable surface,
The toner image is encapsulated in the resin layer on the transfer paper.

The color image forming method disclosed in US Pat. No. 4,600,669 has the drawback that the photoreceptor cannot be used repeatedly and is consumed each time. In the color image forming method disclosed in JP-A-61-205954, the photoreceptor can be used repeatedly, but since a resin liquid for transfer is used in addition to the developer, the apparatus becomes complicated and the resin liquid becomes sticky. There are many problems with its operability and equipment maintenance.

U.S. Pat. No. 4,547,061 discloses a full-color recording method in which the cycle of [latent image formation → development → transfer paper pre-wetting → transfer → drying] is repeated for each of three to four color recordings. Although it is.

Because each color is wetted and then dried, a large amount of solvent is consumed, and drying causes dimensional changes in the transfer paper, which tends to cause color shift.As the toners of each color are not compatible, it is similar to the case with dry toner. However, there are problems in terms of image quality and complexity of the device, such as poor color reproducibility and the need for overcoating with resin liquid to improve fixing and color reproducibility.

Therefore, the electrostatic latent images formed on the photoreceptor based on the color separation information are developed with color liquid developers of complementary colors, and after removing the excess developer, the toner images are sequentially transferred onto transfer paper in an overlapping manner. A color image forming method using wet development to obtain a color image has been proposed. The principle of transferring the toner image is that the toner particles are electrophoresed in the liquid carrier by the transfer (or development) electric field, similar to the case of development. must be filled with an appropriate amount of carrier liquid; if this is insufficient, partial transfer loss or image disturbance will occur; if there is too much,
Not only is the amount of developer discharged after being transferred to the transfer paper uneconomical, but the toner image is also crushed due to the electrostatic and mechanical pressure applied during transfer.

Therefore, in order to transfer a wet toner image using the wet method, the excess developer on the photoconductor must be removed to minimize the amount of developer consumed, which causes image quality deterioration such as running and bleeding.
Furthermore, it is necessary to optimize the image quality so as not to cause deterioration in image quality. In particular, when obtaining a color image by overlapping toner images, even if the first color can be optimized, the quality of the transferred images from the second color onwards will deteriorate, making it difficult to obtain a high-quality color image. there were.

This is due to the difference in the degree of wetting of the surface of the transfer paper with the developer. When the first color is transferred, the transfer paper is not yet wetted by the developer, but for the second and subsequent colors, the surface of the transfer paper is not wetted by the developer. The developer transferred during the cycle remains, and this creates an overabundance of developer for the transfer of the second and subsequent colors, leading to deterioration in image quality.

Therefore, since the amount of developer transferred onto the transfer paper depends on the amount of developer on the photoreceptor, the present inventors proposed the use of a reverse roller to control this (Japanese Patent Laid-Open No. 63-2577
Publication No. 72). The amount of developer attached to the transfer paper changes depending on the gap between the photoreceptor and the reverse roller, as shown in Figure 6, and the amount of developer attached to the transfer paper changes depending on the rotation speed of the reverse roller, as shown in Figure 7. Since the amount of liquid applied changes, in order to balance the first color and subsequent colors,
The amount of developer of each color applied to the transfer paper is adjusted using a reverse roller so that there are relatively many colors and the second and subsequent colors are narrowed down as much as possible.
Prevents image quality deterioration due to excessive developer solution for colors below.

[Problem to be solved by the invention]

Since the gap between the photoreceptor and the reverse roller is extremely small,
The adjustment mechanism performs extremely high-precision adjustment, which increases the cost of each mechanism and requires labor for the adjustment work.

The present invention relates to an improvement in a method for faithfully transferring a toner image onto a transfer paper by liquid development that does not require a transfer resin liquid. The first purpose is to transfer the color to a transfer paper, and the second purpose is to improve color reproducibility.

[Means to solve the problem]

In the first aspect of the present invention, electrostatic latent images formed on a photoreceptor based on color separation information are developed with color liquid developers of complementary colors, and after removing excess developer, the toner images are transferred. A wet development color image forming method for obtaining a color image by successive overlapping transfers onto paper is characterized in that, prior to the transfer of the toner image, the transfer paper is bulked up with a liquid that reduces the surface tension of the color liquid developer.

One method for pre-wetting transfer paper is to pre-wet the transfer paper with a liquid that reduces surface tension, such as silicone oil, and then feed the paper to the transfer unit. Therefore, in a preferred embodiment of the present invention, a developer containing toner particles is used as the pre-wet liquid, and it is difficult to adjust the amount of pre-wet and transport the wet transfer paper. Wet liquid is supplied to the transfer paper via the photoreceptor.

The specific method of pre-wetting the photoreceptor using this developer varies depending on whether the image forming system is regular development or reversal development, but for example, (A) In the regular development system, the photoreceptor is removed using a static eliminator. After completely eliminating static electricity, without charging or image exposure, a developer containing silicone oil as a carrier liquid is used to operate the developing electrode with ground or reverse bias applied to prevent toner particles from adhering to the photoreceptor. After performing so-called "full development" and adjusting the amount of carrier liquid remaining on the photoreceptor using a reverse roller, a transfer electric field is applied at the transfer section to maintain the adhesion between the photoreceptor and the transfer paper, and the carrier on the photoreceptor is Prewet the liquid film by uniformly transferring it to the transfer paper. Also,
(B) In a reversal development system, a developer containing silicone oil is used to uniformly charge the photoreceptor without image exposure.
Similar to A), under development conditions that do not cause toner particle migration,
After complete development and adjusting the amount of carrier liquid on the photoreceptor using a reverse roller, the image is uniformly transferred to transfer paper and pre-wet.

The surface tension of conventional developer carrier liquid is 2 at room temperature.
It is low at 0 to 25 dyne/am and has the property of easily wetting transfer paper, etc., but silicone oil has a low level of about 15 dyne/am.
This is because it has a further wettability property of ne/cm.

Silicone oil is contained as part of the carrier liquid, and by pre-wetting it, a liquid film is simply formed on the photoconductor, and this liquid film wets the transfer paper extremely uniformly, making pre-wetting easy. Moreover, this pre-wet liquid on the transfer paper promotes the transfer characteristics of the toner image from the first color, so even if the amount of carrier liquid on the photoreceptor is kept to a minimum from the time of development of the first color, high fidelity can be achieved. It became possible to obtain a transfer image.

The method of adding silicone oil to the developer can be applied equally to each color, but it is effective in terms of developer cost to include it in at least one type of developer and use it for pre-wet. It is.

In addition, if we take Shin-Etsu Silicone Co., Ltd. as an example of applicable silicone oil, KF which is dimethyl silicone
96L O,65,1,2,5cs, phenylmethyl silicone niF-56,-58, and cyclic dimethyl silicone KF-994, -995 are suitable, and these can be used alone or in combination for development. The content of the carrier liquid is 5% or more, preferably 1% or more, based on the carrier liquid.
It is in the range of 0 to 60%.

In the second aspect of the present invention, electrostatic latent images formed on the photoreceptor based on color separation information are developed with color liquid developers of complementary colors, and after removing excess developer, the toner images are transferred. In a wet development color image forming method in which a color image is obtained by sequentially overlapping transfer onto paper, the carrier liquid of at least one color liquid developer contains a liquid that reduces the surface tension of the toner, and the toner image has been transferred. The transfer paper is heat-fixed with this carrier liquid present in the toner image.

This is based on the discovery that the transfer method has a large effect on image quality.
As a result of drying and removing the carrier liquid and heating it under the same conditions, there was almost no improvement in image quality in ■, but in ■ the gloss of the toner image increased, especially due to the overlapping of toner images. In the case of the obtained color images, it was observed that the transparency increased and the reproduced colors changed vividly. In order to investigate this change in more detail, we compared and observed the changes in the toner images of ■ and ■ on a hot plate, and found that in the case of ■, the toner was slightly melted and deformed, whereas in the case of ■, the toner image appeared to be boiling. The liquid carrier gas is evaporated while repeating micro-vibration.
We have observed that the surface of the toner image becomes smooth and transparent when this carrier gas generation stops, so by leaving even a small amount of liquid carrier on the toner image, when it evaporates as carrier gas, The toner particles are disturbed like boiling, and the toner layers of each color, which were superimposed in multiple layers, are almost uniformly mixed and rearranged, so the transparency of the toner layer 1 The surface smoothness changes, resulting in color reproduction. This is considered to be due to improved quality and image density.

These phenomena vary greatly depending on the composition of the liquid developer, and the toner composition contains polyolefin resins and wax-like substances that have a relatively low softening point below the boiling point of the liquid carrier and can be miscible with the carrier when heated. Furthermore, it has been found that it is particularly effective to use a carrier liquid containing silicone oil or the like, which reduces the surface tension of the carrier liquid. This is probably due to the polyolefin thread-conducting low softening point resin being melted and liquefied by heating, becoming completely compatible with the liquid carrier, increasing the amount of apparent liquid carrier in the toner image, and further lowering the viscosity. This is to promote the disturbance and rearrangement of toner particles.

Wetting properties are improved by including a low surface tension solvent such as silicone oil as a liquid carrier.

It is believed that the toner particles uniformly adhere to the transfer paper and further smoothen the surface of the toner layer.

The low softening point resins used as components of these developers include paraffin hooks, which have a softening point of 60 to 80°C, and
116°C low molecular weight polyethylene, polypropylene, etc. are suitable, and petroleum-based hydrocarbon solvents (for example, Isopar H: surface tension 22.6
Dimethyl silicone oil (KF-96
L 0.65cs, 1cg+2cs, 5cs) + Phenylmethyl silicone oil (KF -56, -58)
, cyclic dimethylpolysiloxane (F-994, -
995), all of which have a surface tension of 15 to 16 dyne/c.
m, manufactured by Shin-Etsu Silicone Co., Ltd., are preferred, and these are included alone or in combination in at least one developer of each color developer.

Its content is 5% or more, preferably 10 to 60% by volume, based on the carrier liquid.

[Effect]

According to the above-described first aspect of the present invention, the surface tension is reduced even in the gap between the photoconductor and the reverse roller where transfer omission would normally occur, that is, in the gap between the photoconductor and the transfer paper where the amount of developer is extremely small. The effect of the liquid, such as silicone oil, evenly wets the transfer paper, resulting in faithful transfer without any change in image quality.

According to the second aspect of the present invention, the same effects as the first aspect can be obtained, and at the same time, the resin contained in the toner is melted and liquefied by heating during heat fixing, and a liquid with a low surface tension is formed. It is completely compatible with the liquid carrier contained in it, increases the amount of the apparent liquid carrier in the toner image, takes a form with a lower viscosity, and promotes the disturbance and rearrangement of toner particles, improving color reproducibility.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

FIG. 1 shows the main parts of an example of a color image forming apparatus embodying the present invention. In FIG. 1, a neutral number IO is a drum-shaped photoreceptor which can be rotated in the direction of arrow AR1. A charger 12 is placed around the photoreceptor lO. Developing unit 14. Transfer drum 16.
Static eliminator 20. A cleaning unit 24 is arranged as shown in the figure.

Image exposure is performed between the charger 12 and the developing unit 14 by the exposure unit L. This image exposure may be performed by optical projection of the original image, but it may also be performed using an LED array, LCS array, LD, etc. This is performed by a known light spot scanning writing unit.

The developing unit 14 includes four developing devices 14Y.

14M, 14C, and 14B, and these four developing devices develop an electrostatic latent image using yellow, magenta, cyan, and black developers, respectively.

The functions of these developing devices will be explained using the developing device 14M as an example, but other developing devices also function in exactly the same manner.

As shown in FIG. 2, the developing device 14M includes a pump 141
．． Nozzle 142. Developing roller 143. It has a reverse roller 144 for squeezing, and during development, the pump 141 sucks up the developer 145, and the nozzle 142
The liquid is uniformly supplied to the surface of the developing roller 143 through the developer roller 143.

The developing roller 143 moves in the same direction as the photoreceptor 10 (in the opposite direction of rotation) and attaches the supplied developer to the electrostatic latent image for development. Excess developer on the photoreceptor after development is removed by moving the squeeze reverse roller 144 at high speed in the opposite direction to the photoreceptor (the rotational direction is the same).

The toner image on the photoreceptor from which the excess developer has been removed in this way is transported in the direction of arrow A in FIG. . This transfer drum 18 has a conductive rubber on the inner circumferential surface of a dielectric film, and by applying a bias voltage of opposite polarity to the developer toner charge to this conductive rubber, the toner image on the photoreceptor is transferred. The image is transferred to transfer paper S.

After the transfer, the photoreceptor 10 is neutralized by a static eliminator 20, cleaned by a cleaning unit 24, and subjected to the next cycle.

By repeating the cycle for the second and subsequent colors in the same manner, the transfer paper S on which the full-color toner image has been transferred is separated from the transfer drum 18 by the separation claw 19 and conveyed in the direction of arrow B shown in FIG. be discharged.

Next, the wet color electrophotographic method according to the first aspect of the present invention will be described in detail based on FIG.

First, in the developing device 14Y, petroleum hydrocarbon (isopar H2 viscosity 1.72cs, surface tension 22cs) is used as a carrier liquid.
．． 6 dyne/aa: manufactured by Exxon) and dimethyl silicone oil (KF96L-1,5 viscosity 1.5 cs
, surface tension 15.9 dyne/cm (manufactured by Shin-Etsu Silicone Co., Ltd.) in a ratio of 1:1, and a developer in which a resin-containing toner was dispersed was supplied.

Prior to image formation, while the photoreceptor 10 is rotated in the direction of arrow AR1, a charger 12 is used to inject 167
The developing unit 1 is charged with 0V and without image exposure.
4Y was operated at a developing bias Ov to perform dry development, and after adjusting the liquid film on the surface of the photoreceptor drum 10 using a reverse roller, the liquid film was transferred onto the transfer paper S by bias transfer (pre-wet). The gap was 40 μm with respect to the photoreceptor drum IO, and the rotation speed was 150 rpm. Transfer bias is +1.
At 4 KV', 40 mg/A4 of carrier liquid adhered to the transfer paper.

Next, the photosensitive drum 10 was neutralized by an AC charger static eliminator 20 superimposed with a direct current having a polarity opposite to that of the charger 12, and a slight amount of remaining carrier liquid was cleaned by a cleaning unit 24, and image formation was started. That is, while rotating the photoreceptor lO in the direction of arrow AR1, the charger 12 applies a charge of -670V to the surface of the photoreceptor, and then a yellow toner latent image is written and formed.

The obtained electrostatic latent image is developed with a developing device 14Y at a developing bias of -450V, and after removing excess developer with a reverse roller (compatible with 144), the yellow toner image is transferred to the previously prewet transfer paper S. Bias transfer was performed on top at +1.6v. The reverse roller gap was 40 μm and the rotation speed was 150 rpm, as in the pre-wet process, and the amount of carrier liquid deposited on the transfer paper S was 40 mg/A4.

Subsequently, the photoreceptor 10 was cleaned after being neutralized by an AC corona charge static eliminator 20 applied with a DC voltage of a positive polarity opposite to that of the charger 12, and then the next cycle was started.

Similarly to the above yellow toner image formation, -670V is applied to the photoreceptor.
After performing charging and forming a magenta electrostatic latent image using a writing device, the developing device 14M was operated to perform development and transfer. In the case of this magenta toner image formation, the carrier liquid of the developing solution in the developing device 14M is only petroleum hydrocarbon (Isopar H), the gap of the reverse roller is exactly the same as in the case of yellow development, and the transfer bias is applied using only magenta developer. The test was conducted at +1.8 KV and the amount of carrier liquid adhered to the transfer paper S was 40 a+g/A4.

Following charge removal and cleaning, an electrostatic latent image for cyan is formed, and developed with a cyan developer consisting of a carrier liquid of only Isopar H, similar to the case of magenta, with the same reverse roller conditions, and a transfer bias of +2. ．． At OKV,
The amount of carrier liquid deposited was 40 mg/A4.

Further, black toner was developed in the same manner, and the transfer bias was set to +2.2.
After the transfer was performed using the KV, the transfer paper S on which the four-color toner images had been transferred was separated by the separation claw 19 and taken out. As a result, there was no image quality deterioration such as missing transfer or one image collapse, and the photosensitive A high-density, high-definition color image in which the toner image on the body was faithfully transferred was obtained.

For comparison, a color image was created by repeating the same cycle as above with the other conditions being exactly the same, except that the carrier liquid for the first color yellow developer was only Isopar H and the above-mentioned Briwet was not used. When created, the color image was dotted with unevenness, which was thought to be due to poor transfer of the yellow toner image.

According to the above-described first aspect, (1) the low surface tension silicone oil improves the wetting characteristics of the transfer paper, thereby providing extremely faithful transferability from the first color toner image. (2)
Since the silicone oil maintains good transferability not only for the first color but also for the second and subsequent colors, a good transferred image is always obtained even if the toner is transferred many times. (3
) Since the carrier liquid containing silicone oil is extremely wettable, even a very small amount of this liquid film on the photoreceptor is easily transferred to the transfer paper as a uniform liquid film, making the pre-wetting operation itself easy. (4) Similar to (3), the amount of carrier liquid consumed in Briwet and the amount of carrier liquid required during toner image transfer is small, and a good transferred image can be obtained, so there is an economical effect.

(5) Since the pre-wet liquid is used as the developer, there is no need for a separate container or pre-wet device.

The device can be simplified and costs can be reduced.

Next, a second aspect of the present invention will be explained. In the copying machine shown in FIGS. 1 and 2, the toner of each color developer contains a polyolefin resin for thermally fusing the toner to the transfer paper.

While rotating the photoreceptor 10 in the direction of the arrow AR1, the charger 1
A charge of -670V is applied to the surface of the photoreceptor by 2, and then a latent image for yellow toner is written and formed, and the obtained electrostatic latent image is developed by the developer 14Y, and the reverse roller (compatible with 144) is applied. After removing the excess developer, the yellow toner image is bias-transferred onto the transfer paper S. In this case, the carrier liquid of the developing solution in the developing device 14Y is petroleum hydrocarbon (Isopar H9 viscosity 1.72cs+
Surface tension 22.6 dyne/cm: manufactured by Exxon)
and dimethyl silicone oil (KF96L-1,5 viscosity 1.5 cs, surface tension 15.9 dyne/cm:
A 1:1 mixture with Shin-Etsu Silicone Co., Ltd. 1!1), and a reverse roller gap of 40 μm.

Assuming that the rotation speed is 15 Orpm, the transfer bias is +1.6
With KV, the amount of carrier liquid attached to the transfer paper S is 40mg/
The condition was A4.

Subsequently, the photoreceptor 10 was cleaned after being neutralized by an AC corona charge static eliminator 20 applied with a DC voltage of a positive polarity opposite to that of the charger 12, and then the first cycle was started.

Similarly to the above yellow toner image formation, -670V is applied to the photoreceptor.
After performing charging and forming a magenta electrostatic latent image using a writing device, the developing device 14M was operated to perform development and transfer. In the case of this magenta toner image formation, the carrier liquid of the developing solution in the developing device 14M is only petroleum hydrocarbon (Isopar H), the gap of the reverse roller is exactly the same as in the case of yellow development, and the transfer bias is applied using only magenta developer. The test was carried out under the conditions that the voltage was +1.8 KV and the amount of carrier liquid adhering to the transfer paper S was 40 mg/A4.

Following charge removal and cleaning, an electrostatic latent image for cyan is formed, and developed with a cyan developer consisting of a carrier liquid of only Isopar H, similar to the case of magenta, with the same reverse roller conditions, and a transfer bias of +2. ．． At OKV,
The amount of carrier liquid deposited was 40a+g/A4.

Further, black toner was developed in the same manner, and the transfer bias was set to +2.2.
After the transfer was performed using the KV, the transfer paper S on which the four-color toner images had been transferred was separated by the separation claw 19 and taken out. As a result, there was no image quality deterioration such as transfer omission or image collapse, and the photosensitive A high-density, high-definition color image in which the toner image on the body was faithfully transferred was obtained.

The transferred color toner images obtained in this way were transferred using a hot plate type heat fixing device shown in FIG. The results of heating and fixing the dried product are shown in Table 1 below. In the second embodiment of the present invention, the image density and gloss were significantly improved, and the reproduced colors were vivid.

Me Nibble-2 ■: Red, VC Nigeleen.

TMC Niblack.

*1: The manuscript is a Kodak force patch.

*2: Density is a value measured with a Macbeth RD-915 reflection densitometer. () is the Kodak Wratten filter number.

*3: Glossiness indicates the light reflectance (%) at an incident angle of 60' using a Japan aG-2P-Dm gloss meter.

In both the examples of the present invention and the comparative examples shown in Table 1, immediately after the transfer is completed, different color toners are layered and the toners are wet with the carrier liquid, as shown in FIGS. 4a and 5a, for example. state. In the example of the present invention, since the toner is heated in a wet state using the hot plate type fixing device shown in FIG. At this time, as shown in Figure 5b, the different color toners that have been stacked are disturbed by the vaporization of the carrier liquid and mix, forming an upper layer to fill the gaps between the toners. The toner mixes with the toner in the lower layer.

The thermal adhesive then adheres to the transfer paper, and as shown in FIG. 4c, a relatively smooth toner layer with toner distributed at high density is formed, resulting in smoothness and improved gloss. On the contrary,
If the carrier liquid is dried after transfer as in the comparative example, the 5th b.
As shown in the figure, even if the toner maintains the stacked state at the time of transfer and is similarly heat-fixed, it becomes a little flat due to the melting of the heat-fusing agent, but as shown in Figure 5c, the toner Although the particles are slightly deformed, the density of one image does not change and the gloss does not change either.

The entrance guide roller 29, fixing roller 33, and exit guide roller 35 of the fixing device shown in FIG. It is. The fixing hot plate 30 is heated by the heaters 31 and 32 to heat the transfer paper S from the back side. As described above, toner particles containing a low softening point resin are developed with a liquid developer containing silicone oil.

By heating and fixing the transferred toner image with the carrier liquid remaining, the transparency of the toner increases, the surface of the toner image on the transfer paper becomes smooth, and a color image with improved image density and two-color reproducibility is obtained. High-definition color images can be achieved without the need for complicated and expensive equipment as in the prior art.

According to the second aspect described above, (6) the low surface tension silicone oil improves the wetting characteristics of the transfer paper, thereby providing faithful transferability. (7) During heat fixing, the thermal adhesive melted into the carrier liquid containing silicone oil is compatible with the carrier liquid, and the carrier liquid evaporates to mix different color toners to fill the gaps between toner particles, increasing the toner density. The height increases and the toner layer becomes flat. (8) Since it is not necessary to apply an overcoat resin after transfer, the image quality is not impaired, and a separate container or overcoat device is not required, so that the device can be simplified and the cost can be reduced.

〔Effect of the invention〕

According to the first aspect of the present invention, toner transferability is improved;
According to the second aspect of the present invention, the surface of the toner image on the transfer paper is smoothed, and the image density is improved.

Color images with improved color reproducibility can be obtained, and high-definition color images can be achieved without the need for complicated and expensive equipment as in the prior art.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the configuration of an apparatus for carrying out the present invention, and FIG. 2 shows a developing unit 1 shown in FIG.
FIG. 4 is an enlarged block diagram showing details of a part of FIG. FIG. 3 is a block diagram showing the configuration of a fixing device that heat-fixes the transfer paper S shown in FIG. 1. FIG. 4a is an enlarged sectional view schematically showing a toner layer formed on a transfer paper according to the present invention immediately after transfer, and FIG. 4b is an enlarged sectional view schematically showing a toner layer during heat fixing. FIG. 4c is an enlarged sectional view schematically showing the toner layer after the heat fixing process. FIG. 5a is an enlarged cross-sectional view schematically showing a toner layer formed on a transfer paper immediately after transfer, and FIG. 5b is an enlarged cross-sectional view schematically showing a toner layer in which the carrier liquid has been dried after transfer. FIG. 5c is an enlarged sectional view schematically showing the toner layer after the dry toner layer has been subjected to heat fixing treatment. FIG. 6 shows the photoreceptor 10 and reverse roller 1 shown in FIG.
7 is a graph showing the relationship between the gap between the reverse rollers 144 and the amount of developer applied to the transfer paper, and FIG. 7 is a graph showing the relationship between the rotational speed of the reverse roller 144 and the amount of developer. IO: Photoreceptor 12: Charger 14: Developing unit 14Y to 14B: Each color developer 16:
Corona discharger 18: Transfer drum 19: Separation claw 20: Static eliminator 24: Cleaning unit S: Transfer paper L: Exposure for latent image formation 27:
Transfer toner layer 28.29: Entry guide roller 30: Fixing hot plate 31.32: Heater 33: Fixing roller 34.35: Outlet guide roller 141: Bump 142
: Nozzle 143: Developing roller 144: Reverse roller

Claims (4)

[Claims] (1) The electrostatic latent images formed on the photoreceptor based on the color separation information are developed with color liquid developers of complementary colors, and after removing the excess developer, the toner images are sequentially transferred onto transfer paper in an overlapping manner. 1. A wet development color image forming method for obtaining a color image by wetting a transfer paper with a liquid that reduces the surface tension of a color liquid developer prior to transferring a toner image. (2) The carrier liquid of at least one color liquid developer contains a liquid that reduces the surface tension of the color liquid developer, and prior to toner image transfer, the photoreceptor surface is wetted with the color liquid developer without forming an electrostatic latent image. A color image forming method using wet development as claimed in claim 1, characterized in that this is transferred to a transfer paper and the transfer paper is wetted. (3) The electrostatic latent images formed on the photoreceptor based on the color separation information are developed with color liquid developers of complementary colors, and after removing the excess developer, the toner images are sequentially transferred onto transfer paper in an overlapping manner. In a color image forming method using wet development to obtain a color image, the carrier liquid of at least one color liquid developer contains a liquid that reduces the surface tension of the liquid developer, and the transfer paper after the toner image transfer is transferred to the carrier liquid. A method for forming a color image using wet development, characterized in that a heat fixing process is carried out in a state where is present in a toner image. (4) A color image forming method using wet development according to claim 1, 2, or 3, wherein the liquid that reduces the surface tension of the color liquid developer is silicone oil. .