JPH06348043A - Image holding member - Google Patents

Abstract

PURPOSE:To enhance the printing durability of the image holding member which can store image information by one time of image exposure and is used for copying of many sheets by enhancing the durability of the image holding member. CONSTITUTION:The image holding member 1 is constituted by coating the surface of the base body 2 with a conductive layer 3 and successively providing the surface thereof with a charge generating layer 4, a thermally softening layer 5 and a conductive particle dispersion layer 7. This conductive particle dispersion layer 7 is formed by dispersing conductive particles 6 into a thermally softening resin of the mol.wt. higher than the mol.wt. of the thermally softening resin forming the thermally softening layer 5. The thermally softening resin on the thermally softening layer side has preferably 5000 to 40000 weight average mol.wt. and about 3000 to 20000 number average mol.wt. and the thermally softening resin of the conductive particle dispersion layer side has preferably about 20000 to 100000 weight average mol.wt. and about 10000 to 50000 number average mol.wt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image holding member capable of storing image information by moving conductive particles in a thermosoftening resin, and more particularly to an image holding member having improved durability. .

[0002]

2. Description of the Related Art In the conventional electrophotographic copying method, after uniformly charging the surface of an electrophotographic photosensitive member, imagewise exposure is performed to attenuate the surface potential in an imagewise manner, then toner development is performed, and the image is transferred onto paper. The Carlson method is widely applied as a general method. However, in this method, each time one image is copied, exposure must be performed once. Therefore, in high-speed copying, there is a problem that the device becomes complicated and becomes large in size. In order to improve this point, the present inventor previously disclosed in Japanese Patent Application No. 3-69442 that image information is stored in an image holding member in which conductive particles are embedded in the vicinity of the surface of a heat-softening layer, and image exposure is performed. We have proposed an image holding member and an electrophotographic method capable of making continuous copying of a large number of sheets only once. When a copied image is obtained using this image holding member, first, the electrically conductive particles are moved in the thermal softening layer by charging, image exposure and heating to store the image information.
Then, the surface of the image holding member in which this image information is stored is charged to form an electrostatic image, which is developed with a developer, transferred to a sheet, and heated and fixed to form a copy image. . This electrophotographic method has an advantage of being able to continuously obtain copied images because it can be repeatedly performed without performing image exposure after image information is stored. When an image is obtained by repeating continuous copying using the image holding member, if the surface layer of the image holding member is formed of a material that easily deteriorates due to abrasion or the like, the number of copies is limited. Further, in Japanese Patent Application No. 4-257570, an electrophotographic method using an image holding member in a copy mode and a print mode was proposed, but if the durability is poor when used in the copy mode, an image can be stored in due time. There is a risk of disappearing.

[0003]

Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to be able to store information in an image by one image exposure and to copy a large number of sheets. Another object is to increase the durability of the image holding member used for printing and to increase the printing durability.

[0004]

Means for Solving the Problems The present inventor has conducted extensive studies to improve the durability of an image holding member, and as a result, has found that the heat-softening resin on the conductive particle dispersion layer side is better than the heat-softening resin on the heat-softening layer side. The inventors have found that the durability of the image holding member can be improved and the printing durability can be improved by increasing the molecular weight of (1), and have completed the present invention. That is, the image holding member of the present invention,
A charge generation layer, a heat softening layer, and a conductive particle dispersion layer are sequentially provided on the conductive surface of a substrate, wherein the conductive particle dispersion layer is formed from a heat softening resin that forms a heat softening layer together with a charge transport material. Is characterized in that conductive particles are dispersed in a high-molecular-weight thermosoftening resin.

The present invention will be described in detail below. FIG. 1 is a vertical sectional view of an image holding member of the present invention. An image holding member 1 has a conductive layer 3 formed on a substrate 2, and a charge generation layer 4 is laminated thereon. An undercoat layer may be formed between the conductive layer 3 and the charge generation layer 4. Further, on the charge generation layer 4, a heat softening layer 5 made of a heat softening resin that is softened by heat and a charge transport material is laminated.
Near the surface of the thermal softening layer 5, a conductive particle dispersion layer 7 in which conductive particles 6 are dispersed is laminated.

In the present invention, as the substrate, for example, a plastic film, paper, metal foil, glass or the like can be used as long as it can be used in an electrophotographic photoreceptor. The shape is not particularly limited, and any shape can be used. The substrate must have at least a conductive surface.
The conductive surface may be formed by separately coating a conductive layer. The conductive layer may be made of any material as long as the charge can flow freely, for example, a metal film is formed by a method such as a vapor deposition method, a sputtering method, a plasma CVD method, a plating method, or a metal or a metal oxide having a low resistance is used. It may be formed by applying a conductive coating material in which conductive particles such as substances are dispersed in a resin.
Further, when the substrate is conductive, it is not necessary to form the conductive layer.

An undercoat layer may be formed on the conductive surface, if necessary, in order to improve adhesiveness, chargeability, image quality and the like. The undercoat layer can be formed by applying a coating liquid for forming the undercoat layer. Examples of the resin constituting the coating liquid include polyvinyl alcohol, polyvinylpyrrolidone, polyvinylpyridine, cellulose ethers, cellulose esters, polyamide, polyurethane, casein, polyglutamic acid, starch, starch acetate, amino starch, polyacrylic acid, Examples include polyacrylamide and the like. Among them, the type 8-described in JP-A-56-21129
Nylon and polyamide-based resins such as copolymerized nylon described in JP-A-52-7242 disclose adhesion to metal, solvent resistance to a charge generating layer as an overcoat layer, and stability of coating solution. It is a material with excellent properties.

The undercoat layer may be formed of the above resin alone, but powder may be dispersed in order to scatter coherent light such as laser light and prevent the generation of interference fringes. Examples of such powder include organic powders such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polyester, polystyrene, Teflon, and silicone resin, and titanium oxide, zinc oxide, silica, alumina, barium sulfate, calcium sulfate. , Kaolin, calcium silicate, calcium carbonate, white lead, magnesium carbonate, lithopone, magnesium oxide, zirconium oxide,
Inorganic powder such as cerium oxide may be used. These may be used alone or in combination of two or more. In addition,
It is not preferable to use the conductive particles described below because they have charge injection properties. In addition to the above components, the coating liquid for forming the undercoat layer further contains a conductive polymer, an electron-donating or accepting substance, a carboxylic acid compound, a sulfonic acid compound, and a quaternary ammonium in order to reduce the resistivity. You may add salt etc. Also, in order to improve the dispersibility of the powder,
Various kinds of surfactants, silane or titanate coupling agents, etc. may be added.

As a method of dispersing each of the above components, for example,
A known method of dispersing with a device such as a ball mill, a sand mill or a roll mill can be used. Coating solution has a film thickness of 0.5
It is applied to have a thickness of ˜5 μm. If the thickness of the undercoat layer is too thick, residual charges may be accumulated, which is not preferable. When powder is dispersed in the coating liquid, the surface of the undercoat layer becomes rough. The roughness Ra is 0.1 to 0.1.
It is preferably 0.5 μm and Rmax is about 0.3 to 1 μm.
When the roughness becomes large, it causes troubles such as the image quality becoming rough.

In the present invention, the charge generation layer is formed on the conductive layer or the undercoat layer. As the charge generation layer, the same charge generation substance as that used when forming the charge generation layer in a general function-separated electrophotographic photoreceptor is used. As the charge generating substance, a phthalocyanine pigment such as a metal or metal-free phthalocyanine, a squarylium compound, an azurenium compound, a perylene pigment, an indigo pigment, a quinacridone pigment, anthanthrone, a brominated anthanthrone, pyranthrone, a polycyclic quinone such as flavanthrone, Examples include cyanine dyes and xanthene dyes. Further, highly sensitive charge generating substances such as titanyl phthalocyanine and azo pigments having various crystal structures can be used. These charge-generating substances can be used together with charge-transporting substances as required. The charge generation layer is prepared by dispersing the above materials together with an appropriate binder resin and a solvent by a conventional method to prepare a coating solution, and then coating the conductive layer or the undercoat layer on the coating layer and drying to remove the solvent. Is formed by. The thickness of the charge generation layer is usually 0.1 to
A range of 2 μm is suitable.

A thermal softening layer is then formed on the charge generation layer. The heat softening layer can be formed by applying a coating liquid containing a charge transport substance and a heat softening resin. As the charge-transporting substance, the same material as that used for forming the charge-transporting layer in the electrophotographic photoreceptor can be used. For example, anthracene-based, pyrene-based, phenanthrene-based and other polycyclic aromatic compounds, indole-based, carbazole-based, imidazole-based, and pyrazoline-based compounds having a nitrogen-containing heterocycle, hydrazone-based compounds, triphenylmethane-based compounds, and triphenylmethane-based compounds Examples thereof include phenylamine compounds, stilbene compounds, benzidine compounds and the like.

As the thermosoftening resin, a thermoplastic resin having a glass transition point (Tg) of 30 to 90 ° C. and a viscosity at a temperature of Tg or higher of 10 to 10 ⁵ Pa · sec is preferably used. . For example, polyethylene, vinyl chloride resin, polypropylene, styrene resin, ABS resin, polyvinyl alcohol, acrylic resin, acrylonitrile-styrene resin, vinylidene chloride resin, AAS
(ASA) resin, AES resin, fibrin derivative resin, thermoplastic polyurethane, polyvinyl butyral, polyisopentene, poly n-butene, rosin ester resin and the like. Among them, a styrene-acrylic acid ester copolymer and a styrene-acrylic acid ester-acrylic acid terpolymer are preferable.

The coating solution prepared by dissolving the above components in a suitable solvent is usually applied so that the film thickness of the heat softening layer is in the range of 3 to 15 μm. The coating method may be the same as the method for forming the charge generation layer, but since the film thickness is thicker than the charge generation layer, the coating conditions are appropriately changed or a coating method different from that for the charge generation layer is adopted. be able to.

In the present invention, a conductive particle dispersion liquid containing conductive particles is applied onto the heat-softening layer, and the vicinity of the surface of the heat-softening layer is within a few times the diameter of the conductive particles from the surface of the image holding member. A conductive particle dispersion layer containing conductive particles in the range is formed. As the conductive particles, in addition to carbon black, copper iodide, silver iodide, zinc sulfide, silicon carbide, etc., granular materials such as metal oxides are preferably used. In particular, metal oxides containing oxygen defects and metal oxides containing a small amount of different atoms forming donors are preferable because they have high conductivity, that is, they contain many electron-hole pairs. Specific examples of the metal oxide include ZnO, TiO ₂ , SnO ₂ and In ₂ O.
₃ , MoO _{3 and the} like or composite oxides of these. As an example containing a heteroatom, A for ZnO
l, In, etc., TiO ₂ , Nb, Ta, etc., SnO
Examples of ₂ include metal oxides containing different atoms such as Sb, Nb, In and halogen elements. The addition amount of these hetero atoms is appropriately in the range of 0.01 to 30 mol%, preferably 0.1 to 10 mol%.

The particle size of the conductive particles is preferably in the range of 0.05 to 1 μm. If the particle size of the conductive particles is too large, it becomes difficult for the conductive particles to move. On the other hand, if the particle size is too small, it becomes difficult to charge, so the above range is appropriate. Moreover, when the shape of the conductive particles is a thin film, it is difficult to move the conductive particles, which is not preferable. The thickness of the conductive particle dispersion layer is preferably about 2 to 5 times the particle diameter of the conductive particles, and the ratio of the conductive particles in the dispersion layer is 2 to 20% by volume.
A degree is preferable. When the ratio of the conductive particles is too high, the particles come into contact with each other, and the surface resistance decreases, which hinders image formation.

Next, an image forming method for storing image information in the image holding member of the present invention will be described with reference to FIGS. As shown in FIG. 2, the corona charger 8 is moved relative to the image holding member 1 to negatively charge the surface. As a result, the conductive particles 6 embedded near the surface of the thermal softening layer 5 have electron-hole pairs at room temperature,
Immediately, holes are released to the negative charge on the surface, and the surface charge is neutralized through the charge transport material. Then, negative charges remain on the conductive particles 6. At this time, when the surface potential is measured, it is 80 to 95 when the conductive particles 6 do not exist.
It is about%.

Next, as shown in FIG. 3, the image holding member 1
Is irradiated with light to expose the charge generation layer 4 to light to perform image exposure. The light passes through the sufficiently thin conductive particle dispersion layer 7 and most of the light reaches the charge generation layer 4. In the case of laser diode light, the light is modulated by an electronic means in an image-wise manner to be exposed, and in that case, the light may be applied to the portion to which the developer is attached. As a result, positive charges are injected from the charge generation layer 4 into the thermal softening layer 5 and are transported through the thermal softening layer 5 to neutralize the negative charges of the conductive particles 6. On the other hand, the negative charges remain in the conductive particles 6 in the portions not irradiated with light.

Thereafter, as shown in FIG. 4, the image holding member 1
Is heated by heat. As a heating method, any method such as a method of passing through a heating roller, a method of putting in a heating container, a method of heating with a heating wire, or the like can be adopted, and heating is performed at a temperature of Tg or higher for several seconds. As a result, the conductive particles 6 in which the negative charges have remained move to the side of the base body 2 serving as an electrode in the thermosoftening layer 5 which has been softened and whose viscosity has been reduced by electrostatic force. On the other hand, due to the heating, the electric resistance of the thermal softening layer 5 is lowered, and the electric charge of the conductive particles 6 is abruptly spontaneously discharged. Therefore, the conductive particles 6 do not all move to the electrode side,
Due to variations in the charge density, etc., they are sparsely distributed in the thermal softening layer 5 and stop. In this way, a portion containing the conductive particles that have moved (moving particles 6a) and the conductive particles that have not moved (non-moving particles 6b) is formed. Then
When the image holding member 1 is returned to room temperature, an image holding member 1'having image information stored therein can be obtained.

An electrophotographic method for obtaining a copy by using the image holding member in which the image information is stored as described above will be described. As shown in FIG. 5, the charger 8 is moved with respect to the image holding member 1 ′ in which the image information is stored, and the entire surface thereof is negatively charged. As a result, in the portion where the non-migrating particles 6b are present, as in the case shown in FIG. 2, negative charges remain in the conductive particles, and the surface potential is 85 when the conductive particles do not exist.
It will be about 95%. On the other hand, in the portion where the moving particles 6a are present, positive charges are successively injected from the particles closer to the electrode to neutralize the negative charges on the surface side, and as a result, the surface potential is such that conductive particles are present. When it is not done, it becomes very low, 0-20%. Therefore, a latent image having an electrostatic contrast corresponding to the image is formed only by uniform negative charging on the entire surface.
Next, the formed latent image is developed using a positively chargeable developer. As a result, the latent image is visualized, and a copy can be obtained by transferring the latent image on a transfer sheet by a conventional method. After that, a latent image can be formed by charging again. Therefore, copying can be continuously performed without performing image exposure. It should be noted that after the copying, cleaning can be performed if necessary.

When copying image information using the image holding member of the present invention, the image holding member is cleaned,
Its durability, specifically wear resistance of the conductive particle dispersion layer, is important. If the surface layer is made of a material that easily wears,
The latent image gradually deteriorates because the charging characteristics change as the surface gradually wears. In particular, when the image holding member is used in the copy mode, when the surface layer is worn, the conductive particles are depleted, and there is a concern that the image holding member cannot be used in the print mode. In order to prevent abrasion of the surface layer, the binder resin in the surface layer may be hardened, but a polycarbonate resin cannot be used like the OPC drum, and the resin has a heat softening property. I have to do it. Therefore, as a preferable binder resin, a thermo-softening resin used in the conductive particle dispersion layer having a higher molecular weight is used. That is, in the present invention, the heat-softening layer on the inner side, which is free from the risk of wear, uses a heat-softening resin having a relatively low molecular weight in consideration of the ease of movement of particles as a first priority. The heat-softening resin having a higher molecular weight is used for the functional particle dispersion layer in consideration of wear resistance. Specifically, the heat-softening resin on the heat-softening layer side has a weight average molecular weight of 5,000 to 40,000 and a number-average molecular weight of about 3,000 to 20,000. The heat-softening resin on the conductive particle dispersion layer side has a weight average molecular weight. 20 in molecular weight
000 to 100,000, number average molecular weight of 10,000 to 5
Those of about 0000 are preferable.

The two monomer components may be different, but the same monomer component is preferable because the boundary between the two layers is not clearly formed and the particles easily move. In this case, even if the molecular weight of the heat-softening resin on the conductive particle dispersion layer side is increased, there is no effect on the dispersibility of particles or the coatability at the time of coating. Further, even when the image holding member is heated to move the conductive particles, since the conductive particle dispersion layer has a very thin film thickness, even if the particles become slightly hard to move due to the high molecular weight of the resin, it is Compared with the total film thickness, it has only a slight effect. Therefore, according to the present invention, it is possible to improve only durability without causing any problem in use of the image holding member, and it is possible to improve printing durability during printing.

[0022]

The present invention will be described in more detail with reference to the following examples. Example A polyvinyl butyral resin (S-REC BM-1, manufactured by Sekisui Chemical Co., Ltd.) was dissolved in advance at a ratio of 19 parts by weight of cyclohexanone to 1 part by weight. 8 parts by weight of this solution was mixed with 1.6 parts by weight of x-type metal-free phthalocyanine and 12.8 parts by weight of cyclohexanone, and dispersed by a sand mill using glass beads having a diameter of about 1 mm as a dispersion medium to form a charge generation layer. A dispersion was prepared. On the other hand, as the heat softening resin, 62 parts by weight of styrene and 3 parts of ethyl acrylate
A terpolymer was prepared by using 6 parts by weight and 2 parts by weight of acrylic acid as raw materials and synthesized in a toluene solvent. This polymer has a weight average molecular weight of about 8,000 and a Tg of 48 ° C.
And the viscosity at 110 ° C. was 28,000 poise. 78 parts by weight of this terpolymer and N, N'-diphenyl-N, N'-bis- (m- used as a charge transport material
Tolyl) benzidine (22 parts by weight) was dissolved in toluene (600 parts by weight) to prepare a heat-softening layer forming solution. In addition, a polymer was prepared by further increasing the polymerization time during the production of the terpolymer. The weight average molecular weight of this polymer is about 45.
And was higher than the former. Then, 6 parts by weight of the higher polymerized terpolymer, 1 part by weight of indium oxide-tin oxide (ITO) powder, 2 parts by weight of the charge transport material, 50 parts by weight of toluene and 50 parts of butanol.
The mixture consisting of parts by weight was treated with a sand mill to obtain a conductive particle dispersion liquid.

Then, an image holding member was manufactured by a web coater using a polyester film having a thickness of 50 μm and having evaporated aluminum as a conductive layer as a substrate.
That is, the charge generation layer forming dispersion liquid was applied onto a polyester film at a speed of 50 cm / sec to give a film thickness of 0.33 μm.
m charge generating layer was formed. A solution for forming a heat-softening layer was applied thereon at a rate of 50 cm / sec to form a heat-softening layer having a film thickness of 8 μm. Furthermore, also by the web coater,
The conductive particle dispersion liquid was applied onto the heat-softening layer at a speed of 50 cm / sec to form a conductive particle dispersion layer having a film thickness of 0.5 μm. The image holding member of the present invention was produced as described above.

Comparative Example Instead of the terpolymer having a weight average molecular weight of about 45,000 as the thermosoftening resin component of the conductive particle dispersion liquid, the same weight average molecular weight as that of the heat softening resin component of the heat softening layer forming solution was used. 8
An image holding member was produced in the same manner as in the example except that 3,000 terpolymers were used.

The image holding members produced in Examples and Comparative Examples were mounted on the electrophotographic copying machine shown in FIG. 6, and copying was first carried out by the Carlson method in the following copy mode. The image holding member 1 was wound around an 84 mmφ × 320 mm aluminum pipe to form a photosensitive drum. The surface was negatively charged by the charger 8. As a result, the negative charge is IT
After moving to O particles, the surface potential became −570V. Then, the black portion (character portion) of the original was extinguished, and the white background of the original was lit so that it was image-wise modulated by a diode laser 10 and exposed at an intensity of 12 ergs / cm ² . The potential of the exposed portion was -100V. After that, development was performed by the developing device 11 in which a positively chargeable developer was enclosed, and the image was transferred onto the paper 12, whereby a copy image could be obtained. At this time, the copy speed was 4 sheets of A4 size paper per minute.

On the other hand, a continuous copying test was conducted in a print mode based on the image storage system. That is, after the image holding member 1 is charged by the charger 8 under the condition of −600V, the image is exposed by modulating with the diode laser 10 so that the black part of the document emits light and the white background part of the document disappears. I went. Then, in a dark place, it was passed through a heat roll (not shown) kept at 115 ° C. for a heating time of 5 seconds to perform heat treatment. As a result, the ITO particles in the unexposed portion moved to the substrate side.
In this way, the storage by writing the image is completed.
The image holding member 1'in which image information was stored was wound around the aluminum pipe 9 similar to the above, and a print test was conducted. That is, it was charged by the corona charger 8. As a result, the exposed portion (the portion where the conductive particles did not move) became −570V and the non-exposed portion (the portion where the conductive particles moved) became −80V. In that state, development was performed with a positively chargeable developer in the same manner as described above, and then the image was transferred to the paper 12 to obtain a print image. In this print mode, it is not necessary to perform image exposure, so the print speed was 100 sheets per minute.

The durability of the image holding member was compared between the copy mode and the print mode.

[Table 1] The image holding member of the comparative example is an example in which the binder resin of the conductive particle dispersion layer is the same as that of the thermal softening layer, but in both copy mode and print mode, durability is high. The result was inferior to that of the example.

[0028]

INDUSTRIAL APPLICABILITY According to the present invention, the heat-softening resin as the binder resin for the conductive particle dispersion layer has a larger molecular weight than the heat-softening resin forming the heat-softening layer.
It is possible to improve the durability of the conductive particle dispersion layer, and thus the durability of use of the image holding member. As a result, the printing durability of the image holding member can be improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an image holding member of the present invention.

FIG. 2 is an explanatory diagram of a process of charging an image holding member.

FIG. 3 is an explanatory diagram of a process of writing an image on an image holding member.

FIG. 4 is an explanatory diagram of a process of heating an image holding member to store an image.

FIG. 5 is an explanatory diagram of a process of charging an image holding member on which an image is written.

FIG. 6 is a sectional view of an electrophotographic copying machine using an image holding member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image holding member, 1 '... Image holding member that stores image information, 2 ... Substrate, 3 ... Conductive layer, 4 ... Charge generation layer, 5 ... Thermal softening layer, 6 ... Conductive particles, 6a ... Moving particles, 6b ... Non-migrating particles, 7 ... Conductive particle dispersion layer, 8 ... Charger.

Claims (2)

[Claims] 1. In an image holding member in which a charge generation layer, a heat softening layer and a conductive particle dispersion layer are sequentially provided on a conductive surface of a substrate, the conductive particle dispersion layer forms a heat softening layer together with a charge transport substance. An image holding member formed by dispersing conductive particles in a heat softening resin having a higher molecular weight than that of the heat softening resin. 2. The image holding member according to claim 1, wherein the monomer components of the thermosoftening resin in the thermosoftening layer and the thermosoftening resin in the conductive particle dispersion layer are the same.