KR20030075890A - Composition for overcoat layer of organic electrophotographic photoreceptor and organic photoreceptor employing the overcoat layer formed therefrom - Google Patents

Abstract

PURPOSE: An overcoat layer forming composition for an organic photosensitizer and an organic photosensitizer employing the overcoat layer formed from the composition are provided, to enhance the lifetime of an organic photosensitizer by improving the abrasion resistance, reducing the electrostatic potential and releasing the increase of residual potential. CONSTITUTION: The overcoat layer forming composition comprises 50-99.9 wt% of an acrylate-based polymer based on the solid content of the composition; 0.1-50 wt% of polyvinyl butyral based on the solid content of the composition; and an alcohol-based solvent. Preferably the acrylate-based polymer is the methyl methacrylate-methacrylic acid copolymer represented by the formula 1, wherein m is 10-50 mol% and n is 50-90 mol%; and the polyvinyl butyral is represented by the formula 2, wherein a is 60-90 mol%, b is 0-10 mol% and c is 0-40 mol%. Preferably the alcohol-based solvent is at least one selected from the group consisting of ethanol, butanol, methanol and isopropanol.

Description

Composition for overcoat layer of organic electrophotographic photoreceptor and organic photoreceptor employing the overcoat layer formed therefrom}

The present invention relates to a composition for forming an overcoat for an organic photoconductor and an organic photoconductor employing the overcoat layer formed therefrom, and more particularly, to a composition for forming an overcoat layer constituting an outermost layer of an organic photoconductor for electrophotographic image formation. By employing an overcoat layer formed therefrom, the present invention relates to an organic photoconductor having excellent electrical properties and improved adhesion.

In electrophotography, the organic photoconductor is formed by forming a photosensitive layer on a conductive support, and has a plate, disk, sheet, belt or drum form. Looking at the method of forming an image electrophotographically using such an organic photosensitive member is as follows.

First, the surface of the photoconductor is electrostatically uniformly charged, and then the charged surface is irradiated with a laser beam. In the portion to which the laser beam is irradiated, positive and negative charges are generated and move to the surface, and as the electric charges charged on the surface are neutralized, the surface potential is changed to form a latent image.

Then, when liquid or solid toner is developed in this latent image area, an image is formed on the surface of the organic photoconductor. The image thus formed is transferred to a receptor surface such as paper. This image forming process is repeated a plurality of times.

The photosensitive layer has a single layer or a plurality of layers. When the photosensitive layer is in the form of a single layer, the charge transport material and the charge generating material are combined with the polymer binder to be formed on the conductive support. In the case where the photosensitive layer has a plurality of layers, a separate layer is formed by using a charge transport material and a charge generating material, and is selectively bonded with a polymer binder to be applied on a conductive support.

The charge transport layer and the charge generating layer have the following two arrangements. According to the first arrangement (dual layer arrangement), the charge generating layer is applied on the conductive support and the charge transport layer is formed on the charge generating layer. According to the second arrangement (inverted dual layer arrangement), the above-described stacking order of the charge transport layer and the charge generation layer is reversed.

In single and multilayer photosensitive layers, the charge generating material functions to generate charge carriers (holes or electrons) upon exposure. The charge transport material serves to receive the charge carriers and to move them through the charge transport layer to release charges on the photosensitive layer surface.

However, the photoreceptor is easily worn by friction with the toner, the roller or the cleaning blade during the image forming process. This reduces the thickness and shortens its lifespan. In order to solve this problem, an overcoat layer is formed on the organic photoconductor.

It is known that the overcoat layer of the organic photoconductor as described above is formed using an acrylate polymer.

However, since the overcoat layer has a problem in that the adhesive force to the photoreceptor is weak and easily peels off or wears out, an adhesive layer must be formed thereon in order to improve this problem.

However, when the adhesive layer is formed in this way, there is a problem that the electrical characteristics of the organic photoconductor are lowered.

The technical problem to be achieved by the present invention is to provide an organic photoreceptor employing the composition for forming an overcoat layer capable of forming an organic photoreceptor having excellent electrical properties while improving the wear resistance and adhesion by solving the above problems and an organic photoreceptor employing the overcoat layer formed therefrom. .

In order to achieve the above technical problem, the present invention provides an composition for forming an overcoat layer for an organic photoconductor comprising an acrylate polymer, polyvinyl butyral and an alcohol solvent.

The acrylate-based polymer is a methyl methacrylate-methacrylic acid copolymer represented by Formula 1, and the content thereof is 50 to 99.9 parts by weight based on 100 parts by weight of the solid content of the composition for forming an overcoat layer.

[Formula 1]

Wherein m is 10-50 mol% and n is 50-90 mol%.

The polyvinyl butyral is represented by the formula (2), the content is preferably from 0.1 to 50 parts by weight based on 100 parts by weight of solids of the composition for forming an overcoat layer.

[Formula 2]

Wherein a is 60 to 90 mol%, b is 0 to 10 mol% and c is 0 to 40 mol%.

The alcohol solvent is at least one selected from the group consisting of ethanol, butanol, methanol, and isopropanol, and the content thereof is suitably 80 to 99 parts by weight based on 100 parts by weight of the composition for forming an overcoat layer.

The weight average molecular weight of the acrylate polymer is 2,000 to 30,000, the weight average molecular weight of the polyvinyl butyral is preferably 40,000 to 160,000.

Another technical problem of the present invention is a conductive support;

A photosensitive layer formed on the conductive support;

An electrophotographic organic photoconductor comprising an overcoat layer formed by coating and drying the above-described composition for forming an overcoat layer on the photosensitive layer.

The photosensitive layer has a single layer structure including a charge generating material and a charge transporting material, or a two-layer stacked structure including a charge generating layer including a charge generating material and a charge transporting layer including a charge transporting material.

The organic photoconductor is used for forming an electrophotographic image using dry or liquid toner.

The present invention is characterized by using an acrylate-based polymer, in particular, methyl methacrylate-methacrylic acid copolymer and polyvinyl butyral when forming an overcoat layer. When the two materials are used together to form the overcoat layer, the primer or adhesive layer coating process, which is necessary due to the weak adhesion of the overcoat layer, can be removed, thereby simplifying the process, and the organic photoconductor due to the additional layer It is possible to prevent the characteristic from deteriorating.

The methyl methacrylate-methacrylic acid copolymer constituting the overcoat layer of the present invention is represented by the following formula (1).

<Formula 1>

Wherein m is 10-50 mol% and n is 50-90 mol%.

The weight average molecular weight of the methyl methacrylate-methacrylic acid copolymer is preferably 2,000 to 30,000. If the weight average molecular weight of the methyl methacrylate-methacrylic acid copolymer is out of the above range, it is difficult to coat the composition for forming an overcoat layer and the solubility characteristics of the methyl methacrylate-methacrylic acid copolymer in an alcohol solvent. Not preferred in terms of

The content of the methyl methacrylate-methacrylic acid copolymer is preferably 50 to 99.9 parts by weight, and particularly preferably 70 to 99 parts by weight based on 100 parts by weight of the solid content of the composition for forming an overcoat layer. If the content of the methyl methacrylate-methacrylic acid copolymer is less than 50 parts by weight, the advantages of the wear resistance and electrical properties of the methyl methacrylate-methacrylic acid copolymer cannot be utilized. The adhesion of the overcoat layer is lowered.

The polyvinyl butyral is represented by the following formula (2).

<Formula 2>

Wherein a is 60 to 90 mol%, b is 0 to 10 mol% and c is 0 to 40 mol%.

The weight average molecular weight of the polyvinyl butyral is preferably 40,000 to 160,000. If the weight average molecular weight of the polyvinyl butyral is out of the above range, it is difficult to coat the composition for forming an overcoat layer and may cause a problem in compatibility with the methyl methacrylate-methacrylic acid copolymer, and an alcohol solvent. It is not preferable in view of the solubility characteristics of polyvinyl butyral in.

Herein, the content of polyvinyl butyral is preferably 0.1 to 50 parts by weight, more preferably 1 to 30 parts by weight based on 100 parts by weight of the solid content of the overcoat layer-forming composition. If the content of the polyvinyl butyral is less than 0.1 parts by weight, the adhesive strength of the overcoat layer is lowered. If the content of the polyvinyl butyral is more than 50 parts by weight, the characteristics such as wear resistance and electrical properties of the overcoat layer are deteriorated.

In the present invention, the alcohol solvent is capable of dissolving the acrylate polymer and polyvinyl butyral, and specific examples thereof include one or more selected from the group consisting of ethanol, butanol, methanol, and isopropanol. The content of the alcohol solvent is 400 to 9,900 parts by weight based on 100 parts by weight of the solid content of the composition for forming an overcoat layer (ie, the total of polyvinyl butyral and methyl methacrylate-methacrylic acid copolymer). When the content of the solvent exceeds the above range, not only is not preferable in terms of coating properties of the composition, but is too thinly coated to function properly as an overcoat layer, and when the solvent is below the above range, the polyvinyl butyral and acrylate polymers It is not preferable in terms of solubility.

Hereinafter, a method of manufacturing an electrophotographic organic photoconductor using the composition for forming an overcoat layer of the present invention will be described.

First, a photosensitive layer is formed on a conductive support. In this case, the photosensitive layer may be formed by sequentially stacking the charge transport layer including the charge transport material and the charge generating layer including the charge generating material or in the reverse order. Alternatively, a single photosensitive layer containing a charge transport material and a charge generating material may be formed.

The charge transport layer is formed by coating and drying a composition including a charge transport material, a binder, and an organic solvent, and the charge generating layer is formed by coating and drying a composition including a charge generating material, a binder, and an organic solvent.

The charge transport material (pyrazoline derivatives, fluorene derivatives, oxadiazole derivatives, stilbene derivatives, hydrazone derivatives, carbazole hydrazone derivatives, polyvinyl carbazole, polyvinylpyrene (polyvinylpyrene) or polyacenaphthylene, and the like, as the charge generating material, metal free phthalocyanine (eg, Progen 1x-form metal free phthalocyanine, Zeneca Inc.), titanium phthalocyanine, copper phthalocyanine, oxytitanium phthalocyanine, A metal phthalocyanine such as hydroxygallium phthalocyanine is used, and its content is a conventional level, and the content of the charge transport material is 35 to 65 parts by weight based on 100 parts by weight of the composition for forming the charge transport layer, and the content of the charge generating material. 55 to 85 based on 100 parts by weight of the solids of the composition for forming a silver charge generating layer Use the volume part.

The binder may dissolve or disperse the charge transport material or the charge generating material, and specific examples thereof include polyvinyl butyral, polycarbonate, polystyrene-Co-butadiene, modified acrylic polymer, polyvinylacetate, styrene-alkyd resin, Soya-alkyl resin, polyvinylchloride, polyvinylidene chloride, polyacrylonitrile, polycarbonate, polyacrylic acid, polyacrylate, polymethacrylate, styrene polymer, alkyd resin, polyamide, polyurethane, polyester, poly Sulfones, polyethers) and combinations thereof, in particular the polyvinyl butyral and polycarbonates used in the present invention. The content of the binder is 15 to 65 parts by weight based on 100 parts by weight of the solids of the composition for charge generation layer formation or the composition for charge transport layer formation.

Tetrahydrofuran, methylene chloride, chloroform, dichloroethane, trichloroethane, chlorobenzene, an acetate solvent, alcohols, and the like are used as a solvent constituting the composition for forming a charge transport layer and the composition for forming a charge generating layer. The content is 70 to 99 parts by weight based on 100 parts by weight of the composition for charge generation layer formation or the composition for charge transport layer formation.

The method for forming the charge generating layer and the method for forming the charge transport layer is not particularly limited, but in the case where the conductive support has a drum form, a ring coating method or a dip coating method may be used. It is more preferable.

As described above, after the photosensitive layer is formed on the conductive support, the electrophotographic photosensitive member of the present invention is completed by coating and drying the composition for forming an overcoat layer of the present invention on the photosensitive layer to form an overcoat layer. It is preferable that a drying temperature is 80-120 degreeC here.

As the coating method of the composition for forming the overcoat layer, a spin coating method, a dip coating method, a ring coating method, or the like may be used. When the conductive support has a drum form, it is preferable to use a ring coating method or a dip coating method. .

The total thickness of the photosensitive layer in the organic photoreceptor of the present invention is 5.1 to 26 mu m. Among them, the thickness of the charge generating layer is 0.1 to 1.04 mu m, the thickness of the charge transport layer is 5 to 25 mu m, and the conductive support, particularly the drum substrate, generally has a thickness of 0.5 to 2 mm. And the overcoat layer has a thickness of 0.1 to 10㎛. If the thickness of the overcoat layer is less than 0.10 mu m, the protective function of the lower layer is weak. If the thickness of the over coat layer exceeds 10 mu m, the electrical properties are deteriorated such that the exposure potential is increased, which is not preferable.

The organic photoreceptor of the present invention may further include an additional layer. Such layers are well known and further include, for example, charge blocking layers and the like. Here, the charge blocking layer is formed between the conductive support and the charge transport layer to improve the adhesion.

When an image is formed electrophotographically using the organic photoconductor described above, a dry or liquid toner can be used.

In the electrophotographic method using a liquid toner, when the organic photoconductor for a dry toner according to the prior art is applied to a liquid toner as it is, it is in contact with a paraffin solvent, which is a main component of the liquid toner, causing cracking or crazing. Or some component of the organic photoconductor is eluted.

On the other hand, the organic photoconductor of the present invention can be very usefully used in an electrophotographic image forming process using a liquid toner, and can prevent the above-described problems in advance.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

<Example 1>

A mixture of 0.475 g of methyl methacrylate-methacrylic acid copolymer in a 25:75 mixing molar ratio, 0.025 g of BM-S (Sekisui, Japan) (polyvinyl butyral) and 2.5 g of ethanol were sufficiently mixed to form an overcoat layer in a transparent solution state. The composition was obtained.

The composition was ring-coated on an auxiliary photosensitive drum (Samsung Electric Co., Ltd.) using a ring coater, and then dried at 100 ° C. for 10 minutes to form an overcoat layer to complete an organic photoconductor. At this time, the coating speed was about 100 mm / min.

<Example 2>

The overcoat layer was formed in the same manner as in Example 1, except that the content of the methyl methacrylate-methacrylic acid copolymer and BM-S in a 25:75 mixed mole ratio was 0.45 g and 0.05 g, respectively. To complete the organic photoconductor.

<Example 3>

Except that the methyl methacrylate-methacrylic acid copolymer and BM-S content of 0.495g and 0.005g, respectively, was carried out in the same manner as in Example 1 to form an overcoat layer to complete the organic photoconductor .

<Example 3>

Except that the methyl methacrylate-methacrylic acid copolymer and BM-S content of 0.488g and 0.013g, respectively, was carried out in the same manner as in Example 1 to form an overcoat layer to complete the organic photoconductor .

Comparative Example 1

An organic photosensitive member was completed in the same manner as in Example 1 except that no overcoat layer was formed on the auxiliary photoconductive drum (Samsung Electric Co., Ltd.).

Comparative Example 2

The overcoat layer was prepared in the same manner as in Example 1, except that 0.5 g of methyl methacrylate-methacrylic acid copolymer and 9.5 g of ethanol were sufficiently mixed to prepare a composition for forming an overcoat layer in a transparent solution. To form an organic photoconductor.

The film state of the organic photoconductor having the overcoat layer prepared according to Example 1-3 and Comparative Example 1-2, the bonding force and the electrostatic characteristics of the overcoat layer was evaluated according to the following method, the evaluation results are shown in Table 1 and same.

(1) the film state of the organic photoconductor

Visually evaluate the presence of cracks.

(2) bonding strength of the overcoat layer

It evaluates using a 180 degree peel tester.

(3) electrical characteristics

The electrical properties of the photoconductor before and after coating of the composition for forming the overcoat layer and after 48 hours of deposition on Norpar 12 were evaluated using PDT2000 (QEA) (cycles of charge-exposure-antistatic were repeated 100 times). do.)

Evaluation item Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Coating weight (g / ㎠) 1.05 1.02 1.06 1.07 - 1.04 Before coating Charge potential (V) change 697-29 699-19 729-29 707-24 758-28 735-30 Exposure potential (V) change amount 48 + 1 49 + 1 49 + 1 48 + 3 50 + 8 38 + 9 After coating Charge potential (V) change 715-24 719-18 754-40 723-43 - 750-22 Exposure potential (V) change amount 54 + 3 55 + 3 37 + 6 51 + 5 - 33 + 5 After deposition Charge potential (V) change 711-20 704-15 718-24 698-7 705-15 733-29 Exposure potential (V) change amount 52 + 7 50 + 8 50 + 9 50 + 11 47 + 12 48 + 7 Adhesion - Good Good Good Good - Bad crack - none none none none Badly none

As can be seen from Table 1, when the organic photoconductor of Comparative Example 1 was examined, the cracks were severely generated after the haze 12 deposition, the charge potential was severely reduced, and the organic photoconductor of Comparative Example 2 had exposure and charge potential characteristics. Showed similar results to other examples and cracks were not found, but were easily peeled off due to the poor adhesion of the overcoat layer to the photosensitive layer.

On the contrary, in the organic photoconductor of Example 1-4, the adhesion of the overcoat layer was better than that of Comparative Example 1-2, and the film state was also excellent. In addition, cracks did not occur after the deposition on the old woman 12, and the electrical properties were not significantly changed.

According to the present invention, the following effects are obtained.

First, it is excellent in wear resistance can improve the life of the electrophotographic organic photoconductor.

Secondly, primer or adhesive layer coating, which was essentially required for adhesion improvement when using an acrylate polymer, is unnecessary, thereby simplifying the coating process and reducing the additional layer formation cost.

Third, in electrophotographic image formation, the reduction of the charging potential and the increase of the residual potential can be alleviated to improve the life of the organic photoconductor.

Fourth, it can be usefully used as an organic photoconductor for liquid toner having excellent durability against liquid toners, especially paraffin solvents.

Claims (9)

A composition for forming an overcoat layer for an organic photoconductor comprising an acrylate polymer, polyvinyl butyral and an alcohol solvent. The method of claim 1, wherein the acrylate-based polymer is a methyl methacrylate-methacrylic acid copolymer represented by the formula (1), The composition for forming an overcoat layer for an organic photoconductor, characterized in that the content is 50 to 99.9 parts by weight based on 100 parts by weight of the solid content of the composition for forming an overcoat layer. <Formula 1> Wherein m is 10-50 mol% and n is 50-90 mol%. The method of claim 1, wherein the polyvinyl butyral is represented by the formula (2), The composition for forming an overcoat layer for an organic photoconductor, characterized in that the content of polyvinyl butyral is 0.1 to 50 parts by weight based on 100 parts by weight of the solid content of the composition for forming an overcoat layer. <Formula 2> Wherein a is 60 to 90 mol%, b is 0 to 10 mol% and c is 0 to 40 mol%. The method of claim 1, wherein the alcohol solvent is at least one selected from the group consisting of ethanol, butanol, methanol, isopropanol, The composition for forming an overcoat layer for an organic photoconductor, characterized in that the content is 80 to 99 parts by weight based on 100 parts by weight of the composition for forming an overcoat layer. The composition for forming an overcoat layer for an organic photoconductor according to claim 1, wherein the weight average molecular weight of the acrylate polymer is 2,000 to 30,000, and the weight average molecular weight of the polyvinyl butyral is 40,000 to 160,000. Conductive support; A photosensitive layer formed on the conductive support; An organophotoreceptor comprising an overcoat layer formed by coating and drying the composition for forming an overcoat layer according to any one of claims 1 to 5 on the photosensitive layer. 7. An organic photoconductor according to claim 6, wherein the overcoat layer has a thickness of 0.1 to 10 mu m. The method of claim 6, wherein the photosensitive layer has a single layer structure including a charge generating material and a charge transporting material, or includes a charge transporting layer including a charge generating material and a charge generating layer including a charge generating material. An organic photoconductor which has a layer laminated structure. 7. An organic photoconductor according to claim 6, which is used for electrophotographic image formation using dry or liquid toner.