JP2003307945A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance efficiency in transferring toner from a latent image carrier to a transfer body, and also, to reduce image-flowing and a missing of an image, as for an image forming apparatus using liquid developer. <P>SOLUTION: As for the image forming apparatus provided with a latent image forming means for forming an electrostatic latent image on the latent image carrier, a means for supplying the liquid developer to the electrostatic latent image and visualizing the image and a means for offset-transferring the visible image on the latent image carrier to the transfer body by pressure, the storage elastic modulus of the toner in the liquid developer at a transfer temperature is controlled to be 10<SP>3</SP>to 10<SP>6</SP>Pa, and the storage elastic modulus of a backup roller arranged behind the transfer body is controlled to be ≥10<SP>4</SP>Pa. <P>COPYRIGHT: (C)2004,JPO

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 An electrophotographic apparatus using a liquid developer has an advantage that cannot be realized by dry electrophotography.
Its value is being reviewed. That is, the main advantages of wet electrophotography over dry electrophotography are that since very fine toner of submicron size can be used, high image quality can be realized and sufficient image density can be obtained with a small amount of toner, which is economical. In addition, it is possible to realize a texture equivalent to that of printing (for example, offset printing), and to realize energy saving because toner can be fixed on a sheet at a relatively low temperature.

However, the conventional wet electrophotographic technique using a liquid toner includes some essential problems. First, since a fine liquid toner is used, the toner adherence to the latent image carrier is strong, and the toner transfer efficiency from the latent image carrier to the transfer medium is not always sufficient.

Particularly, in the case of electric field transfer in which toner is transferred from a latent image carrier to a transfer medium by using an electric field, this transfer process is basically a liquid existing in a gap between the latent image carrier and the transfer medium. The transfer is performed by using the electrophoresis of toner particles in the developer, but at this time, the electrophoretic force is not sufficiently strong as compared with the adhesive force of the fine liquid toner to the latent image carrier. Therefore, it is difficult to obtain good toner transferability.

Further, in the electric field transfer, the transfer performance is easily affected by the external environment such as temperature and humidity, and the phenomenon of hollow image in the fine line image is likely to occur, thus deteriorating the image quality.

On the other hand, there is known a so-called offset transfer system in which toner is transferred from a latent image carrier to a transfer medium by using heat or pressure. In the case of this offset transfer method, the toner transfer efficiency itself is improved as compared with the electric field transfer,
Even so, it has been difficult to achieve a toner transfer efficiency close to 100%.

Further, in the case of the liquid developing method, when the amount of the solvent remaining on the latent image holding member before the transfer is large, there is also a problem of so-called image deletion, in which the end portion of the toner image transferred to the transferred member is blurred. is there. In order to solve this problem, excess solvent is squeezed out after development, but it is difficult to significantly reduce image deletion.

Further, when the efficiency of toner transfer from the latent image carrier to the transfer medium is low, the cleaning means for removing the toner remaining on the latent image carrier needs to be more powerful. However, in such a case, the latent image carrier is not a little damaged by the cleaning means, and as a result, the life of the latent image carrier is shortened.

Further, as a method for transferring an image developed on a photoconductor by a liquid developing system to a transfer target such as paper,
Although there is a method of performing transfer via an intermediate transfer medium instead of directly transferring from the photoconductor to the transfer target, not only is the transfer mechanism complicated and adjustment becomes difficult, but it is not possible to obtain high image quality. There was a problem that the medium had to be selected from among the given materials.

[0010]

As described above, in the electrophotographic apparatus using the conventional liquid developing technique, the efficiency of toner transfer from the latent image carrier to the transferred material is insufficient,
Further, there is a problem that image deletion due to the liquid developing system is likely to occur.

The present invention has been made under the above circumstances, and the transferability of the toner from the latent image carrier to the transfer medium is good, and
It is an object of the present invention to provide a liquid development type electrophotographic apparatus with less image deletion.

Another object of the present invention is to provide an image forming apparatus which is not affected by temperature and humidity and the like, the transfer state of which does not easily change depending on environmental conditions, and which enables transfer without requiring high mechanical precision. is there.

[0013]

Since a wet type image forming apparatus using a liquid developer uses finer toner particles than a dry type image forming apparatus, the toner adheres strongly to the latent image holding member. Also in this case, it is important that the toner is satisfactorily transferred from the latent image holding member to the transfer target member. It is also important to minimize the image deletion due to the residual solvent peculiar to the liquid developing system.

The present inventors have paid attention to the physical properties of the surface layer of the latent image carrier, particularly the contact angle of the solvent of the liquid developer, and have made earnest studies on the relationship between this contact angle and the transferability of toner and image deletion. As a result, when the contact angle becomes larger than the predetermined value (lower limit value),
It has been found that the toner transferability is improved, and the wettability between the surface layer of the latent image carrier and the solvent is significantly reduced particularly in the non-image area, whereby the image deletion due to the residual solvent can be reduced. It was

On the other hand, when the contact angle exceeds a predetermined value (upper limit value), the repulsive force between the surface layer of the latent image holding member and the liquid toner becomes remarkable, and a liquid developer missing area is generated in the image area. I found that. That is, it was confirmed that the contact angle has an upper limit in order to obtain a good image.

Based on these facts, the present inventors have
It was found that the above problems can be solved by forming the surface layer of the latent image holding member so that the contact angle of the liquid developer with the solvent falls within a predetermined range, and to complete the first invention. I arrived.

That is, the first invention comprises a latent image forming means for forming an electrostatic latent image on a latent image holding member, and a means for supplying a liquid developer to the electrostatic latent image to form a visible image. In the image forming apparatus having the above, the contact angle θ of the solvent of the liquid developer with respect to the surface of the latent image holding member is 20 ° <θ <110 °.

In such an image forming apparatus, the contact angle θ of the solvent of the liquid developer with respect to the surface of the latent image carrier.
Is preferably 20 ° <θ <90 °. In addition,
The contact angle is a value measured at room temperature.

In order to keep the contact angle θ of the solvent of the liquid developer with respect to the surface of the latent image carrier within the above range, a surface layer made of a material selected so as to obtain the contact angle within the above range is latently formed. It can be formed on the surface of the image carrier.

Examples of such materials include silicone resins, fluorosilicone resins, fluororesins, and mixtures of two or more of these, and by selecting these appropriately, the blending ratio of these resins is adjusted appropriately. By doing so, a desired contact angle can be obtained. Alternatively, the surface of the latent image carrier, that is, the photosensitive layer itself may contain a contact angle adjusting component selected so as to obtain a contact angle in the above range.

Regarding the adhesion between the surface of the latent image carrier and the solvent, the surface energies of both may be taken into consideration. However, the surface energy is a physical property value peculiar to the substance. The adhesiveness between the surface of the holder and the solvent depends on various surface conditions such as unevenness of the surfaces of both, and if only the surface energy is specified, good transfer efficiency and high-quality images can be obtained. I can't. Therefore, the present inventors have focused on the contact angle, not the surface energy.

Further, the present inventors need to set the storage elastic modulus at the temperature at the time of transfer of the toner within a predetermined range in order to perform the transfer for obtaining a high quality image, However, it has been found that the value of the storage elastic modulus of the backup roller arranged on the back surface of the transfer target at the transfer position is also important.

A second aspect of the invention is based on such knowledge, and supplies latent image forming means for forming an electrostatic latent image on a latent image holding member and a liquid developer to the electrostatic latent image. In an image forming apparatus having means for making a visible image and means for offset-transferring a visible image on the latent image carrier to a transfer medium by pressure, at a temperature at the time of transferring the toner in the liquid developer. Has a storage elastic modulus of 10 ³ to 10 ⁶ Pa, and the backup roller arranged on the back surface of the transfer target has a storage elastic modulus of 1
Provided is an image forming apparatus having a pressure of 0 ⁴ Pa or more.

In such an image forming apparatus,
It is desirable that the average surface roughness Rz of the backup roller be equal to or smaller than the minimum pixel.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing the configuration of an electrophotographic apparatus according to an embodiment of the present invention. In FIG. 1, the latent image carrier 1 is a photosensitive drum in which an organic or inorganic photosensitive layer such as amorphous Si is provided on a conductive substrate. The latent image carrier 1 is uniformly charged by a first charger 2a composed of a well-known corona charger (corotron charger or scorotron charger), and then image-modulated laser or LE.
Upon receiving the first exposure beam 3a of D or the like, an electrostatic latent image is formed on the surface.

Thereafter, the electrostatic latent image is visualized by the first developing device 4a containing the liquid developer. The liquid developer or toner adhered to the electrostatic latent image may be directly transferred to the transfer step and transferred to the sheet by the transfer device, but here, the second charger 2b and the second exposure beam 3b are continuously used. A second electrostatic latent image is formed and developed by a second developing device 4b that contains a second developer of a color different from the liquid developer contained in the first developing device 4a. Therefore, after the second development, two color toner images are formed on the latent image carrier 1.

Similarly, the third charger 2c, the third exposure beam 3c, the third developing device 4c, and the fourth charger 2 are provided.
The third and fourth charging / exposure / development are performed by d, the fourth exposure beam 3d, and the fourth developing device 4d, and a full-color toner image is formed on the latent image carrier 1.

This toner image is transferred to the paper by the transfer device 5, but at that time, it may be directly transferred to the paper, or as shown in FIG. It may be transferred to 9.

In the transfer from the latent image carrier 1 to the intermediate transfer medium 6 and the transfer from the intermediate transfer medium 6 to the sheet 9, either transfer by electric field or transfer by heat and pressure may be used. it can. In general, many liquid developers can be fixed on a sheet at room temperature, but the pressure roller 7 or the like may be heated to perform fixing by heat.

On the other hand, the latent image holder 1 which has completed the transfer of the full-color toner image is cleaned by the cleaner 8.
The residual toner on the top is removed. Such an image forming process is disclosed in, for example, US Pat. No. 5,57073 and is a conventionally known process.

In the image forming apparatus using such a liquid developing technique, the present inventors improve the efficiency of toner transfer from the latent image carrier 1 to the transferred material (intermediate transfer medium 6 or paper 9). We examined the method and the method of reducing image deletion. Particularly, in the liquid developing method, from the viewpoint that the solvent contained in the liquid developer will greatly affect the toner transfer property and the image quality, the contact angle θ of the solvent with respect to the latent image holding member and the toner transfer property and We investigated the relationship with image deletion.

As a result, when the contact angle θ is larger than 20 °, the toner transfer efficiency is improved, and the amount of the residual solvent on the latent image holding member, especially the residual solvent in the non-image area is remarkably reduced. It was confirmed that the image deletion was reduced. However, it is not so good that the contact angle θ is larger than 20 °, and it has been found that there is an upper limit value (θ to 110 °) in order to obtain good image quality.

This is based on the fact that when the contact angle θ is 110 ° or more, the repulsive force between the latent image carrier 1 and the liquid toner increases, and a liquid developer lacking portion occurs in the image area. It was confirmed that the image quality remarkably deteriorates due to this missing phenomenon.

Thus, the contact angle θ is 20 ° <θ
In the case of <110 °, it was revealed that a good toner transfer property and a good image without image deletion or image loss can be obtained.

Here, the surface layer material of the latent image carrier is not particularly limited as long as the contact angle θ is in the range of 20 ° <θ <110 °. For example, silicone. Resins, fluorosilicone resins, fluororesins and the like can be preferably used.

Among these materials, the silicone resin is
The contact angle θ is smaller than other materials,
It works in the direction of increasing the contact angle θ as compared with other materials. Fluorosilicone resins are in between. Therefore, a desired contact angle θ can be obtained by appropriately mixing these materials. The contact angle θ with the toner of the photoconductor itself is quite small and does not fall within the range of 20 ° <θ <110 °. Therefore, in the present invention, a surface layer is generally provided.

The thickness of the surface layer is preferably about 0.5 to 3 μm from the viewpoint of not significantly deteriorating the electrostatic characteristics of the photosensitive layer and ensuring the wear resistance of the surface layer. When a sufficient thickness cannot be obtained, such as when using a fluororesin alone, it may be mixed with another material (for example, a silicone resin).

Fine particles such as silica may be mixed in order to improve the wear resistance of the surface layer. Alternatively, a method of mixing a component (contact angle adjusting component) having a contact angle within the above range into the photosensitive layer of the latent image carrier may be used.

On the other hand, the solvent for the liquid developer is preferably petroleum-based insulating solvent such as Isopar L or Norper 12. The contact angle is determined by the combination of these surface layer materials and the solvent, but the solvent used for the liquid developer may be limited in kind to some extent, and the contact angle is rather than the kind of the solvent. It can be said that it often depends on the surface layer material.

Next, a second embodiment of the present invention will be described.
Reveal That is, the present inventors have made a transfer to obtain a high quality image.
To do this, the storage elastic modulus at the temperature when transferring the toner
10 ^Three-10⁶Find out that it is necessary to be in Pa
did. In the case of liquid development method, transfer the toner by heating
There are times when this is done, and the temperature when the machine is running
Sometimes done in degrees. Tona in any case
Storage elastic modulus is 10 ^Three-10⁶Be within the range of Pa
Is important, and if the storage modulus is higher than this, the toner
It is in a so-called rigid state and can be deformed by the pressure during transfer.
No, it is not transferred to the transferred material. Also lower than this range
If it becomes too soft and does not leave the surface of the photoreceptor,
Is greatly deformed, and high image quality cannot be maintained.

The toner usually contains 5 pigments for coloring.
These pigments are added in a range of ˜50 wt%, and usually have a high elastic modulus, and when added to the toner resin, they have an effect of increasing the elastic modulus of the toner. In addition, some charge control agents such as metal soaps added in a small amount (1 to 50 wt% with respect to the nonvolatile content) harden the resin and increase the elastic modulus. Therefore, it is necessary to disperse the pigment, add a predetermined amount of the charge control agent, and make the elastic modulus of the toner in a predetermined range.

However, sufficient transfer cannot be achieved only by setting such a toner in such a range of the elastic modulus. In order to achieve sufficient transfer, the storage elastic modulus of the backup roller arranged on the back surface of the transfer target becomes important at the transfer position. The storage elastic modulus of this backup roller needs to be 10 ⁴ Pa or more. This is because if the elastic modulus is smaller than this, sufficient pressure cannot be applied to the toner and the image cannot be transferred to the transfer target.

The surface roughness of the backup roller is also an important point, and unless the surface roughness represented by Rz (10-point average roughness) is less than or equal to pixels, pressure cannot be applied to all pixels forming an image. , High quality images cannot be obtained.

The surface roughness Rz is measured according to JIS B0601, and the minimum pixel indicates the minimum image point of the image. For example, for a system with a resolution of 600 dpi,
In the case of 42 μm 200 dpi, it is 21 μm. The resolution is expressed in the main scanning direction of normal exposure, but if the value differs from the sub-scanning direction, the one with higher resolution (600 dpi × 1200)
If it is dpi, it is desirable to adjust to 1200 dpi).

The reference length and the evaluation length for obtaining Rz are also measured according to JIS B0601 and depend on the range of Rz. When the surface roughness is expressed by Rz, it is generally expressed by using a standard number sequence, but a value actually measured by using a surface roughness meter such as Thalistep manufactured by Rank Taylor Hobson may be used.

The backup roller preferably rotates in the direction of the width of the photoconductor and rotates at the same linear velocity as the photoconductor, but in order to further improve the transfer efficiency,
The linear velocities may be varied within the range of 10%.

A sufficient pressure must be applied to the backup roller to transfer the toner, and the pressure causes a nip in a certain width in the roller in the region where the elastic modulus is relatively low. Therefore, the pressure per unit area changes, but normally this area is not taken into consideration, and the unit distance of the portion where the photoconductor and the roller contact each other is taken as the pressure. That is, 20k on a roller with a length of 20cm
If a pressure of g is applied, the pressure becomes 1 kg / cm even if a nip due to deformation occurs.

According to the invention, this pressure is 0.01 kg.
The range from / cm to 20 kg / cm is preferred. Although not usually required, this roller is made conductive (10 ³
~10 ¹³ Ω · cm) transfer bias voltage (100 to 20
00V) can be applied to further increase the efficiency of transfer by pressure alone.

When the toner is heated to reach the above-mentioned storage elastic modulus range, the backup roller may be provided with a heating mechanism and energized for heating.

The photoreceptor on which a latent image is formed and which is developed with toner is usually formed on a substantially rigid metal drum, but the present invention is not limited to this. For example, a metal is vapor-deposited. It may be formed on the resin film. When such a photoconductor is used, it is desirable to dispose a roller, which is a substantially rigid body, on the back surface of the photoconductor so as to face the backup roller.

[0051]

EXAMPLES Hereinafter, the present invention will be described more specifically by showing Examples and Comparative Examples of the present invention.

Embodiment 1 FIG. 2 shows a state diagram of the developing toner on the latent image carrier according to the first embodiment of the present invention. This figure shows the state of the developing toner before the liquid developer is developed and transferred to the transfer target.

A petroleum-based insulating solvent, Isopar L (manufactured by Exxon Chemical Co., Ltd.) was used as a solvent for the liquid developer, and submicron level fine toner was dispersed in this solvent. The latent image carrier 10 is composed of a substrate 11, a conductive layer 12, a photosensitive layer 13 and a surface layer 14. Note that a conductive substrate in which the substrate and the conductive layer are integrated may be used. The photosensitive layer 13 is an organic photosensitive layer in which a phthalocyanine-based pigment is dispersed in a polycarbonate binder resin.

The surface layer 14 was formed by the following procedure. First, the surface of the photosensitive layer was washed with 2-propanol and blown with high-pressure nitrogen gas to dry it. In this example, Tosgard 510 (manufactured by Toshiba Silicone), which is a silicone hard coating agent, was used as the surface layer material. This Tosgard 510 was diluted 1.5 times with 2-propanol, filled in a glass container, and applied on the surface of the photosensitive layer 13 by a dip coating method to form a coating film. The pulling rate during dip coating was 5 cm / min.

After air-drying for 5 minutes in a room temperature atmosphere,
The surface layer 14 is formed by applying heat curing at 90 ° C. for 1 hour.
Was formed. The film thickness of the surface layer 14 after curing was about 1 μm. Further, a droplet of Isopar L was dropped on the surface layer 14 after curing, and the contact angle θ was measured by a droplet method using a contact angle meter (CA-DT • A type, manufactured by Kyowa Interface Science). θ = 25 °.

A visible image was formed using a liquid developer on the latent image carrier 10 produced by the above procedure, and heat / pressure transfer (offset transfer) was performed to an intermediate transfer medium made of urethane rubber. The heating temperature was 80 ° C. on the side of the intermediate transfer medium, and the latent image carrier side was kept at room temperature without any heating means. The pressure is 50k including the weight of the intermediate transfer medium.
A weight of g was added. As a result, a toner transfer efficiency of 97% was obtained.

On the other hand, in order to quantitatively grasp the degree of image deletion, the image transferred onto the intermediate transfer medium was read by using a scanner and the area was calculated by the area area calculation software. Then, with respect to the original image, the degree of spread of the image due to the image deletion was calculated. As a result, in this embodiment, with respect to the area 100 (normalized value) of the original image,
The area of the transferred image was 102, and it was confirmed that the image deletion was sufficiently small.

As described above, the reason why the image deletion is reduced is
Surface layer 14 of latent image carrier 10 and solvent 15 of liquid developer
By selecting the surface layer material and the solvent so that the contact angle θ with is in the range of 20 ° <θ <110 °, FIG.
It is considered that this is due to the reduction in the amount of the residual solvent 15 in the non-image area, as shown in FIG.

Example 2 CYTOP (CTL) which is a fluororesin as a surface layer material
A latent image carrier 10 similar to that of Example 1 was prepared except that 107M, manufactured by Asahi Glass Co., Ltd. was used. In this example, the surface layer 14 was formed by the following procedure. First, the surface of the photosensitive layer 13 was washed with 2-propanol and dried by blowing high-pressure nitrogen gas. Then, the Cytop was not diluted and was filled as it was into a glass container, and a coating film was formed by a dip coating method. The pulling rate during dip coating was 5 cm / min.

After air-drying for 5 minutes at room temperature in the atmosphere,
The surface layer 1 is formed by heat-curing at 100 ° C. for 1 hour.
4 was formed. The thickness of the surface layer 14 after curing is about 1.2μ
It was m. Also, the cured surface layer 14 and Isopar L
The contact angle θ with was θ = 40 °.

Therefore, when heat / pressure transfer (offset transfer) was performed to the intermediate transfer medium made of urethane rubber under the same conditions as in Example 1, the toner transfer efficiency was 98%, which is higher than that in Example 1. It was also found that the toner transferability was further improved.

Further, when a quantitative evaluation of the degree of image blur was performed by the same method as in Example 1, in this Example,
The area of the transferred image was 101 with respect to the area of the original image of 100 (normalized value), and it was confirmed that the image deletion was further reduced as compared with the case of Example 1.

As described above, in this embodiment, the first embodiment
It is considered that the toner transferability was improved and the image deletion was reduced more than in the case of 1. because the contact angle θ is larger than in the case of the first embodiment.

Comparative Example 1 FIG. 3 shows a state diagram of the developing toner on the latent image carrier according to the comparative example of the present invention. This figure also shows the state of the developing toner before the liquid developer is developed and transferred to the transfer target.

The same liquid developer as in Example 1 was used. That is, Isopar L is used as the solvent. The latent image carrier 16 includes a substrate 17, a conductive layer 18 and a photosensitive layer 1.
It is composed of nine. Note that a conductive substrate in which the substrate and the conductive layer are integrated may be used. The photosensitive layer 19 is an organic photosensitive layer in which a phthalocyanine-based pigment is dispersed in a polycarbonate binder resin. The difference from Example 1 is that the surface layer is not formed. In this case, the latent image holder 1
The contact angle θ between the surface of 6 (photosensitive layer) and Isopar L is θ =
It was 8 °.

Under the same conditions as in Example 1, thermal and pressure transfer (offset transfer) was carried out on the intermediate transfer medium made of urethane rubber, and the toner transfer efficiency was 75%.

Further, when the quantitative evaluation of the degree of image deletion was performed by the same method as in Example 1, in this comparative example,
The area of the transferred image was 112 with respect to the area of the original image 100 (normalized value), and it was confirmed that a large image deletion occurred. This is considered to be due to the presence of a large amount of residual solvent 20, especially in the non-image area, as shown in FIG.

Comparative Example 2 FIG. 4 shows a state diagram of the developing toner on the latent image carrier according to another comparative example of the present invention. This figure also develops liquid developer,
The state of the developing toner before being transferred to the transfer target is shown.

The same liquid developer as in Example 1 was used. That is, Isopar L is used as the solvent. The latent image carrier 21 is composed of a substrate 22, a conductive layer 23, a photosensitive layer 24 and a surface layer 25. Note that a conductive substrate in which the substrate and the conductive layer are integrated may be used. The photosensitive layer 24 is an organic photosensitive layer in which a phthalocyanine-based pigment is dispersed in a polycarbonate binder resin.

The surface layer 25 was formed by the following procedure. First, the surface of the photosensitive layer was washed with 2-propanol and dried by blowing high-pressure nitrogen gas. In this comparative example, fluorinated monoalkyl phosphoric acid was used as the surface layer material. The surface layer 25 was formed by immersing in an ethanol solution containing 2 wt% of this fluorinated monoalkylphosphoric acid at room temperature for 24 hours. The thickness of this surface layer is about 0.8 μm
Met. Further, the contact angle θ between the surface layer 25 and the Isopar L was θ = 120 °.

Under the same conditions as in Example 1, thermal and pressure transfer (offset transfer) was performed on an intermediate transfer medium made of urethane rubber, and a high toner transfer efficiency of 99% was obtained. However, in this comparative example,
As shown in FIG. 4, a liquid developer lacking region 27 was generated in the image forming region, and a good image was not obtained. It is considered that the occurrence of the missing area is caused by the repulsive force of the surface layer of the latent image holding member and the liquid toner being too large.

Example 3 and Comparative Example 3 shown below relate to the second invention.

Example 3 In an electrophotographic apparatus using an organic photoconductor formed on an aluminum drum (thickness: 2 mm) having a diameter of 100 mm, a highly insulating liquid (ISOPAR L, manufactured by Exxon Chemical Co.) had a nonvolatile content of 1 wt. A developer in which a cyan toner is dispersed so that the content of the toner is 100% is used.

Phthalocyanine blue was used as the cyan pigment, and was added to the resin in an amount of 20 wt%. Zirconium naphthenate is used as the charge control agent, and it is 1w with respect to the nonvolatile content.
t% was added. 25 ° C. of the toner manufactured in this way
The storage elastic modulus of was 5 × 10 ⁴ Pa. The storage elastic modulus is 3H using a viscoelasticity measuring device manufactured by Rheometrics.
It was measured at the frequency of z.

The latent image on the photosensitive member was developed with a developing solution in which such toner particles were dispersed, and transferred to a high-quality paper having a basis weight of 80 g / m ^{2 at} a transfer speed of 240 mm / s. The roller on the back side of the paper was fitted with a core metal having a diameter of 45 mm, a silicone rubber having a storage elastic modulus of 10 ⁵ Pa (Rz = 12 μm, measured by Tallystep manufactured by Rank Taylor Hobson) having a thickness of 5 mm without play and looseness. It was used as a backup roller.

The photosensitive member, the paper, and the backup roller are moved at substantially the same linear velocity, and the pressure is 0.3 kg / cm.
And The latent image was formed on the photoconductor with an LED, and the resolution was 1200 dpi. The image transferred onto the paper by such a method had a transfer efficiency of 100% and had an extremely high image quality.

Comparative Example 3 In an electrophotographic apparatus using an organic photoconductor formed on an aluminum drum (thickness: 2 mm) having a diameter of 100 mm, a highly insulating liquid (ISOPAR L, manufactured by Exxon Chemical Co.) had a nonvolatile content of 1 wt. A developer in which a cyan toner is dispersed so that the content of the toner is 100% is used.

Phthalocyanine blue was used for the cyan pigment, and unlike Example 3, the storage elastic modulus at 25 ° C. was 2 ×.
A resin of 10 ⁸ Pa was used. 20% pigment for resin
wt% was added. Zirconium naphthenate was used as the charge control agent, and 1 wt% was added to the nonvolatile content. Storage elastic modulus, using a rheometrics viscoelasticity measuring device,
It was measured at a frequency of 3 Hz.

A latent image on the photosensitive member was developed with a developing solution in which the toner particles are dispersed, and transferred to a high-quality paper having a basis weight of 80 g / m ^{2 at} a transfer speed of 240 mm / s. The roller on the back of the paper has a core metal with a diameter of 45 mm and a storage elastic modulus of 10 with a thickness of 5 mm.
A silicone rubber of ³ Pa (Rz = 30 μm, measured by Turley Step manufactured by Rank Taylor Hobson) was attached without play and looseness to form a backup roller.

The photosensitive member, the paper, and the backup roller are moved at substantially the same linear velocity, and the pressure is 0.3 kg / cm.
And The latent image was formed on the photoconductor with an LED, and the resolution was 1200 dpi. In such a method, the toner is hardly transferred to the paper and the transfer efficiency is 1
It was 0% or less.

[0081]

As described above in detail, according to the first aspect of the invention, the contact angle of the solvent of the liquid developer with respect to the surface layer of the latent image carrier is regulated within a predetermined range. It is possible to obtain a liquid-developing image forming apparatus which has good toner transferability from an image carrier to a transfer medium and does not cause image deletion or image loss.

Further, according to the second invention, the storage elastic modulus at the temperature at the time of transfer of the toner in the liquid developer and the storage elastic modulus of the backup roller arranged on the back surface of the transfer target are:
By defining the liquid content in a predetermined range, it is possible to obtain a liquid developing type image forming apparatus capable of forming a high quality image with high transfer efficiency.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an electrophotographic apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state of developing toner on a latent image holding body after development and before transfer according to the first embodiment.

FIG. 3 is a cross-sectional view showing a state of developing toner on a latent image holding body after development and before transfer according to Comparative Example 1.

FIG. 4 is a cross-sectional view showing a state of developing toner on a latent image holding body after development and before transfer according to Comparative Example 2.

[Explanation of symbols]

1, 10, 16, 21 ... Latent image holders 2a, 2b, 2c,
2d ... Charger, 3a, 3b, 3c, 3d ... Exposure beam,
4a, 4b, 4c, 4d ... Developing device, 5 ... Transfer device, 6
... Intermediate transfer medium, 7 ... Pressure roller, 8 ... Cleaner, 9 ...
Paper, 11, 17, 22 ... Substrate, 12, 18, 23 ... Conductive layer, 13, 19, 24 ... Photosensitive layer, 14, 25 ... Surface layer, 15, 20, 26 ... Residual solvent, 27 ... Liquid developer Missing area.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuka Yamaguchi             70, Yanagimachi, Saiwai-ku, Kawasaki City, Kanagawa Prefecture             Ku Co., Ltd. (72) Inventor Yasushi Masatsune             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center (72) Inventor Seiichi Ooka             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F-term (reference) 2H069 DA06                 2H074 AA03 EE07                 2H200 FA16 FA19 GA04 GA16 GA18                       GA23 GA33 GA43 GA47 GA50                       HA02 HB12 HB22 JA02 JA07                       JA08 JA25 JA27 JB10 JC02                       JC15 LA18 LA19 LA40 MA03                       MA04 MA20 MC03 MC06

Claims (2)

[Claims] 1. A latent image forming means for forming an electrostatic latent image on a latent image holding member, a means for supplying a liquid developer to the electrostatic latent image to form a visible image, and the latent image holding member. In the image forming apparatus having a means for offset-transferring the above visible image to a transfer medium by pressure, the storage elastic modulus at the temperature of the transfer of the toner in the liquid developer is 10 ³ to 10 ⁶ Pa. The image forming apparatus is characterized in that the storage elastic modulus of the backup roller arranged on the back surface of the transfer target is 10 ⁴ Pa or more. 2. The average surface roughness Rz of the backup roller is less than or equal to a minimum pixel.
The image forming apparatus according to item 1.