JP2003295527A - Method for image forming by using organic photosensitive body of positive charging type - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent a transfer memory without adjusting a transfer current value. <P>SOLUTION: In a method for forming an image by using the organic photosensitive body of a positive charging type and by utilizing an inversion development system and a transfer bias potential, a relation between the thickness of a photosensitive layer and a potential difference on the surface of a photosensitive body in the case of main charging generated by the transfer memory is previously measured about each transfer current value in transferring about the photosensitive body. From the obtained relation between the thickness of a photosensitive layer and the potential difference, transfer current which shows a potential difference within ±10 V in an area where a thickness difference is not smaller than 15 μm is generated for performing transferring by applying the transfer bias potential. <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 method using a positive charging type organic photoconductor, and more specifically, it applies development by a reversal development method and transfer bias potential by a transfer roller. And an image forming method for transferring the toner image.

[0002]

2. Description of the Related Art As a developing method adopted in an image forming apparatus using an electrophotographic method such as a copying machine, a facsimile and a printer, a reversal developing method is currently the mainstream as a digital machine spreads. Also, since almost no discharge products such as ozone are generated, a positive charging type organic photoconductor is used as the photoconductor, and the toner image formed on the photoconductor surface is transferred onto a predetermined paper (transfer paper). As a transfer means for this purpose, a method of applying a transfer bias potential using a transfer roller is widely adopted.

That is, in the image forming apparatus as described above, image formation is generally performed as follows. A photosensitive member (positively charged organic photosensitive member) is uniformly and main-charged to a positive polarity, and imagewise exposed by light irradiation based on predetermined image information to form an electrostatic latent image. In this case, the light irradiation part becomes the image part, and the part not irradiated with light becomes the background part of the image. The electrostatic latent image formed as described above is developed by a reversal development method with a developing bias voltage applied to form a toner image on the surface of the photoconductor. That is, the toner powder used as the developer is charged to the same positive polarity as the charging polarity of the photoconductor, and the toner adheres to the portion where the potential is lowered by the light irradiation. The toner image thus formed on the surface of the photoconductor is transferred to the transfer paper by applying a transfer bias potential using the transfer roller. This transfer bias potential is such that the transfer roller has a higher potential than the potential of the toner image on the surface of the photoconductor. The transfer paper on which the toner image is transferred is introduced into a fixing device, and the toner image is fixed on the surface of the transfer paper by heat and pressure. on the other hand,
After the transfer is completed, the toner remaining on the surface of the photoconductor is cleaned, and if necessary, static elimination (irradiation of static elimination light) is performed, whereby one cycle of the image forming process is completed and the next image forming is performed. Be seen.

[0004]

However, when an image is formed by using the positive charging type organic photoconductor as described above and utilizing the reversal development system and the transfer bias potential,
There is a problem that a so-called transfer memory is produced. That is, at the time of transfer, since a negative potential having a polarity opposite to the main charging polarity is applied to the photoconductor as a bias potential, after the transfer, negative charge flows into the photoconductor as a transfer current,
This causes a partial potential difference when main charging is performed in the next image forming process, and the potential difference is reflected in the obtained image as a transfer memory, resulting in uneven image density and image blurring. Occurs. Such a transfer memory becomes remarkable especially when reproducing a halftone image such as a gray image.

By the way, in the organic photoreceptor, a single-layer photosensitive layer containing a charge generating agent and a charge transporting agent is formed on a conductive substrate, a charge generating layer containing a charge generating agent and a charge transporting layer. There is a laminate type photosensitive layer formed by laminating a charge transporting layer containing an agent, and any type of charge transporting agent usually contains a hole transporting agent and an electron transporting agent. Is used. That is, electric charge is generated by the charge generating agent by light irradiation, but in the positive charging type organic photoreceptor,
The electron transfer agent transfers a negative charge to the surface of the photosensitive layer to neutralize the charged charge (positive charge) existing on the surface, while the positive charge is transferred to the surface of the conductive substrate side by the hole transfer agent,
Removed from the substrate. Thus, the electrostatic latent image is formed by the light irradiation by the image exposure. As described above, in the positive charge type organic photoreceptor containing the electron transfer agent and the hole transfer agent as the charge transfer agent, the negative charges flowing by the transfer current are removed by removing the charge after the transfer. However, there are very few electron-transporting materials whose charge-transporting properties have reached a practical level. Recently, those having excellent electron-transporting properties have been developed, but their performance is still inferior to that of hole-transporting agents. It is not possible to sufficiently remove the charges (which is naturally not removed unless the charge is removed), which is a factor of the transfer memory.

Therefore, in order to prevent the above-mentioned transfer memory, in actual image formation, the charge is removed after the transfer, and the transfer bias current is applied by controlling the transfer current flowing into the surface of the photosensitive member during the transfer. The degree of this transfer memory changes depending on the thickness of the photosensitive layer. For this reason,
It was necessary to adjust the transfer current value as the photosensitive layer was abraded by repeating the image forming process.

That is, an object of the present invention is to provide an image forming method in which a positive charging type organic photoconductor is used and an image is formed by utilizing a reversal development method and a transfer bias potential, without adjusting a transfer current value. It is to provide a method capable of effectively preventing a transfer memory.

[0008]

According to the present invention, a positively chargeable organic photoreceptor containing a hole-transporting agent and an electron-transporting agent in a photosensitive layer is used, and the photoreceptor is mainly positively charged. Then, image exposure is performed to form an electrostatic latent image on the surface of the photoconductor, the electrostatic latent image is developed by a reversal development method to form a toner image, and a transfer bias potential using a transfer roller is used. The toner image is transferred to the surface of the transfer sheet by applying a voltage, a transfer bias potential is applied, and the image forming process is repeated by cleaning the toner remaining on the surface of the photoconductor. As an organic photoreceptor, the following general formula (1):

[Chemical 8] In the formula, R ¹ is an alkyl group or an aryl group, and R 1
² is an alkyl group, an aryl group, or a formula: -OR
³ (R ³ is a group represented by an alkyl group or an aryl group) containing a naphthoquinone compound represented by the following as an electron transfer agent is used. For each value, the relationship between the thickness of the photosensitive layer and the potential difference on the surface of the photoconductor at the time of main charging caused by the transfer memory was measured, and from the relationship between the thickness of the photosensitive layer and the potential difference obtained above, a region where the thickness difference was 15 μm or more At ± 1
There is provided an image forming method characterized in that a transfer bias potential is applied so that a transfer current having a potential difference of 0 V or less is applied to perform transfer.

The present invention relates to a positive charging type organic photoconductor in which a specific electron transferring material is used in combination with a hole transferring material, when the transfer current value is a constant value, the photosensitive member at the time of main charging generated by a transfer memory. The surface potential difference (hereinafter simply referred to as the potential difference due to the transfer memory) does not depend on the thickness of the photosensitive layer, and there is a region showing a substantially constant transfer memory, and that transfer can be effectively performed in such a region. , Based on the new finding that it exhibits extremely specific properties. That is, FIG. 1 showing the experimental results of Examples described later.
3 shows the relationship between the potential difference due to the transfer memory and the film thickness of the photosensitive layer, for each transfer current value, for the positively charged organic photoreceptor containing the naphthoquinone compound represented by the general formula (1) as an electron transfer agent. Is a curve plotted (transfer memory-film thickness curve). As is clear from these figures, the curve generally has a downwardly convex 2 curve when the transfer current value is small.
It becomes the following curve, and when the transfer current value is large, 2
It becomes the next curve. Therefore, it is understood that as the transfer current value is changed, the potential difference due to the transfer memory does not change much depending on the film thickness, and there is a region where the curve becomes substantially linear. In such a region, even when the film thickness difference changes by about 15 μm, the potential difference due to the transfer memory does not change so much and is within ± 10 V. Therefore, the transfer bias potential is generated by generating such a transfer current. By applying, it is possible to effectively prevent the transfer memory without changing the transfer current value depending on the film thickness, and moreover, it is possible to perform the transfer effectively without causing the transfer failure.

In the positively chargeable organic photoconductor used in the present invention, the hole transfer agent used in combination with the naphthoquinone compound (electron transfer agent) represented by the above general formula (1) is particularly represented by the following general formula ( 2a), (2b), (2c), (2
It is preferable to use the stilbene compound represented by d), (2e) or (2f). That is, when these stilbene compounds are combined as a hole transporting agent, the linearity of the transfer memory-film thickness curve in the above region is high, and the potential difference change due to the transfer memory is extremely small over the film thickness difference of 15 μm or more. From (the slope of the line is close to zero).

[0011]

[Chemical 9] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 4.

[0012]

[Chemical 10] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 4.

[0013]

[Chemical 11] In the formula, R may be the same or different and represents an alkyl group, n and p are integers of 0 to 5, and m and q
Is a number from 0 to 3, and o is an integer from 0 to 4.

[0014]

[Chemical 12] In the formula, R may be the same or different and represents an alkyl group, and m, n, p and q are integers of 0-5.

[0015]

[Chemical 13] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 6.

[0016]

[Chemical 14] In the formula, R may be the same or different and represents an alkyl group, and m, n, p and q are integers of 0-5. o
Is an integer of 0 to 6.

According to the present invention, from the above-mentioned transfer memory-film thickness curve, the transfer bias potential is set so that the transfer current is such that the potential difference is within ± 10 V in the region where the thickness difference of the photosensitive layer exceeds 15 μm. Is applied, it is possible to reliably prevent the transfer memory without adjusting the transfer current value until the thickness of the photosensitive layer is worn by at least about 15 μm by repeating the image forming process. Further, in the positive charging type organic photoconductor used in the present invention,
At the transfer current value set at the beginning, since the linearity of the transfer memory-film thickness curve is high and the fluctuation of the potential difference due to the transfer memory is small, for example, the initial thickness of the photosensitive layer of the photoconductor is set to 25 μm or more. Until the layer thickness reaches 10 μm, the transfer can be continuously performed as it is without adjusting the transfer current value under the transfer conditions set above.

In the present invention, the transfer memory can be effectively prevented even when the next image forming step is performed without removing the charge after transfer. Further, in the present invention, it is most preferable that the positive charging type organic photoconductor is a single-layer organic photoconductor.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION [Positively Charged Organic Photoreceptor] The positively charged organic photoreceptor used in the present invention contains an electron transfer agent and a hole transfer agent in combination as a charge transfer agent (CTM),
In particular, it contains a specific naphthoquinone compound as an electron transfer agent. A single-dispersion type single-layer photoreceptor containing such a charge transport material (CTM) and a charge generation material (CGM) in a single photosensitive layer is preferable, but the charge generation layer (CGL) and charge transport material are preferable. It may be a laminated type photoreceptor including a layer (CTL). The composition of the photoreceptor will be described below.

(Charge Transporting Agent / Electron Transporting Agent) In the positive charging type organic photoreceptor used in the present invention, the electron transporting agent is
The following general formula (1):

[Chemical 15] The naphthoquinone compound represented by is used.

In the above general formula (1), R ¹ is an alkyl group or an aryl group, R ² is an alkyl group, an aryl group, or a formula: —OR ³ (R ³ is an alkyl group or an aryl group) Is a group represented by. As the alkyl group for R ^{1 to} R ³ , those having 6 or less carbon atoms,
For example, methyl group, ethyl group, n-propyl group, iso
-Propyl group, n-butyl group, isobutyl group, sec-
Examples thereof include a butyl group, a tert-butyl group, a pentyl group and a hexyl group. Further, in these alkyl groups, a part of hydrogen atoms may be substituted with a halogen atom or the following aryl group. Examples of the aryl group for R ^{1 to} R ³ include a phenyl group, a tolyl group, a xylyl group, a biphenyl group, an o-terphenyl group, a naphthyl group, an anthryl group and a phenanthryl group. In these aryl groups, some hydrogen atoms are
It may be substituted with the aforementioned alkyl group or halogen atom.

Such a naphthoquinone compound represented by the general formula (1) is known from, for example, Japanese Patent Application Laid-Open No. 09-151157, but in the present invention, among them,
The R ² group is preferably an —OR ³ group, most preferably R ¹ is a phenyl group or a methyl group and R ³ is t.
It is preferably an ert-butyl group or a benzyl group. In the present invention, the photoreceptor containing the naphthoquinone compound as an electron transfer agent, when the transfer current value shows a specific value, the potential difference caused by the transfer memory becomes almost independent of the photosensitive layer thickness, the potential difference ± It shows a unique property that it hardly fluctuates within the range of 10 V, and prevents transfer memory even when transfer is performed under a constant transfer condition for a long period without controlling the transfer current value.
The transfer can be effectively performed. In addition, as long as the specific properties as described above are not impaired,
The above nephtoquinone compound may be used in combination with an electron accepting substance known as an electron transferring material.

(Charge Transporting Agent / Hole Transporting Agent) (Hole Transporting Agent) In the present invention, the above-mentioned naphthoquinone compound is contained as an electron transporting agent. In combination with these, a hole transporting agent known per se is used. Is used. Although the photosensitivity can be further improved by the combined use of such hole transport agents, in the present invention, the specific relationship regarding the relationship between the potential difference caused by the transfer memory at the above-mentioned specific transfer current value and the photosensitive layer thickness is used. The following general formula (from the viewpoint that the transfer memory-thickness curve linearity in the region exhibiting such peculiar property is enhanced and the potential difference change due to the transfer memory becomes extremely small, It is preferable to use a stilbene compound represented by 2a), (2b), (2c), (2d), (2e) or (2f).

[0024]

[Chemical 16] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 4.

[0025]

[Chemical 17] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 4.

[0026]

[Chemical 18] In the formula, R may be the same or different and represents an alkyl group, n and p are integers of 0 to 5, and m and q
Is a number from 0 to 3, and o is an integer from 0 to 4.

[0027]

[Chemical 19] In the formula, R may be the same or different and represents an alkyl group, and m, n, p and q are integers of 0-5.

[0028]

[Chemical 20] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 6.

[0029]

[Chemical 21] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 6.

In the above general formulas (2a) to (2f), the alkyl group R which can be bonded to the benzene ring or the naphthene ring as a substituent has a carbon number of 6 or less, for example, a methyl group or an ethyl group. , N-propyl group, i
so-propyl group, n-butyl group, isobutyl group, se
Examples thereof include a c-butyl group, a tert-butyl group, a pentyl group and a hexyl group, and among them, the number of carbon atoms is 4
The following are optimal: Further, in these alkyl groups, some hydrogen atoms may be replaced with halogen atoms.

(Charge Generating Agent) Examples of the charge generating agent include selenium, selenium-tellurium, amorphous silicon,
Pyrylium salts, azo pigments, disazo pigments, anthanthrone pigments, phthalocyanine pigments, indico pigments, slene pigments, toluidine pigments, pyrazoline pigments, perylene pigments, quinacridone pigments, etc. are exemplified and desired. One kind or a mixture of two or more kinds is used so as to have an absorption wavelength range in a region.

Particularly preferable examples include the following phthalocyanine pigments, perylene pigments, and bisazo pigments. The phthalocyanine pigments include metal-free phthalocyanine, aluminium phthalocyanine, vanadium phthalocyanine, cadmium phthalocyanine, antimony phthalocyanine, chromium phthalocyanine, copper 4-phthalocyanine, germanium phthalocyanine, iron phthalocyanine, chloroaluminum phthalocyanine, oxotitanyl phthalocyanine, chloroindium phthalocyanine, chlorogallium. Examples thereof include phthalocyanine, magnesium phthalocyanine, dialkyl phthalocyanine, tetramethyl phthalocyanine and tetraphenyl phthalocyanine. Further, the crystal form is also α type, β type, γ type, δ type,
Any of ε type, σ type, x type, τ type and the like can be used.

As the perylene pigment, particularly, the general formula (3),

[Chemical formula 22] In the formula, R ₄ And R ₅ Each is a substituted or unsubstituted alkyl group having 18 or less carbon atoms, a cycloalkyl group, an aryl group, an alkaryl group, or an aralkyl group,
Can be mentioned. Examples of the alkyl group include an ethyl group, propyl group, butyl group, and 2-ethylhexyl group, examples of the cycloalkyl group include a cyclohexyl group, and examples of the aryl group include a phenyl group and a naphthyl group. Examples of the alkaryl group include a tolyl group, a xylyl group, and an ethylphenyl group, and examples of the aralkyl group include a benzyl group and a phenethyl group. Examples of the substituent include an alkoxy group and a halogen atom.

As the bisazo pigment, especially the following formula (4)

[Chemical formula 23] In the formula, Y is a divalent aromatic group which may contain a heterocyclic group, and Cp is a coupler residue. Examples of the divalent aromatic group include divalent groups derived from benzene, naphthalene, anthracene, phenanthrene, chrysene, anthraquinone, biphenol, bisphenol, a heterocycle or a combination thereof. Examples of the heterocyclic group include a monocyclic or polycyclic saturated or unsaturated heterocycle containing nitrogen, oxygen, sulfur or a combination thereof in the ring, and specifically, pyrrole, pyrazole,
Examples thereof include thiophene, furan, imidazoline, pyrimidine, pyrazoline, pyran, pyridine, pyrimidine, benzofuran, benzimidazoline, benzoxazole, indoline, quinoline, chromene, carbazole, dibenzofuran, xanthene and thioxanthene. These divalent groups may be unsubstituted or substituted, and examples of the substituent include an alkyl group, an aryl group and a heterocyclic group. Here, examples of the alkyl group include methyl, ethyl, propyl, butyl, amyl group and the like, examples of the aryl group include phenyl, naphthyl, biphenyl, anthryl, phenanthryl, fluorenyl group and the like, and examples of the heterocyclic group include: Monocyclic or polycyclic saturated or unsaturated heterocyclic groups containing nitrogen, oxygen, sulfur or a combination thereof in the ring, for example, thienyl group, furyl group, imidazolyl group, pyrrolyl group, pyrimidinyl group, imidazole group, pyrazinyl Group, pyrazolinyl group, pyrrolidinyl group, pyranyl group, piperidyl group, piperazinyl group, morpholyl group, pyridyl group, pyrimidyl group, pyrrolidinyl group, pyrrolinyl group, benzofuryl group, benzimidazolyl group, benzofuranyl group, indolyl group, quinolyl group, carbazolyl group, Dibenzofuranyl Etc. The. On the other hand, as the coupler residue in the formula (4),
Any residue may be used as long as it is a residue of a coupler (azo coupling component) used in this type of azo pigment, for example, substituted or unsubstituted phenols, naphthols, or hydroxyl group-containing heterocyclic compounds. As the substituent, a halogen atom such as a lower alkyl group, a lower alkoxy group, an aryl group, an acyloxy group and chlor, a hydroxyl group, a nitrile group, a nitro group, an amino group, an amide group, an acyloxy group, a carboxyl group and the like can be mentioned. Can be mentioned.

(Binder Resin) As the resin medium in which the charge generating agent and the charge transporting agent are dispersed, various resins can be used. For example, a styrene polymer, an acrylic polymer, a styrene-acrylic polymer, ethylene. -Vinyl acetate copolymer,
Olefin polymers such as polypropylene and ionomer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone Resin, polyvinyl butyral resin,
Examples include various polymers such as polyether resins, phenol resins, and photocurable resins such as epoxy acrylate. These binder resins may be used alone or in combination of two or more. Suitable resins include styrene polymers, acrylic polymers, styrene-acrylic polymers,
Examples include polyester resins, alkyd resins, polycarbonates, polyarylates, and the like.

Particularly preferable resins are polycarbonate, Panlite manufactured by Teijin Chemicals, PCZ manufactured by Mitsubishi Gas Chemical Co., Ltd., and the following general formula (5):

[Chemical formula 24] In the formula, R ₁₂ and R ₁₃ are a hydrogen atom or a lower alkyl group, and R ₁₂ and R ₁₃ may be linked to each other to form a cyclo ring such as a cyclohexane ring together with the bonding carbon atom. Is a polycarbonate derived from bisphenols and phosgene.

(Single Layer Photoreceptor) In the present invention, in the monodisperse type photoreceptor, which is particularly preferably used, that is, the single layer type photoreceptor, the charge generating agent (CGM) is 1 to 1 per solid content.
It may be contained in the photosensitive layer in an amount in the range of 0% by weight, particularly 3 to 5% by weight, while the naphthoquinone compound used as an electron transfer agent may be contained in an amount of 3 to 100% by weight, particularly 50% by weight, based on the solid content. It is preferable that it is contained in the photosensitive layer in an amount ranging from 80 to 80% by weight. Further, the naphthoquinone compound,
That is, the electron transfer material (ET) and the hole transfer material (HT) are
The weight ratio is best in the range of ET: HT = 10: 1 to 1:10, especially 1: 5 to 1: 1. In such a single-layer photoreceptor, it is preferable that the photosensitive layer has an initial thickness of generally 25 to 100 μm, particularly 30 to 50 μm from the viewpoint of electrophotographic characteristics and durable life.

(Layered Photoreceptor) In the present invention, a layered photoreceptor may be used. In this case, the charge generating agent (CGM) is used as the resin solid content 1 in the charge generating layer (CGL).
The naphthoquinone compound (electron transfer agent) may be contained in an amount of 5 to 1000 parts by weight, particularly 30 to 500 parts by weight, per 100 parts by weight, while the naphthoquinone compound (electron transfer agent) may be included in the charge transport layer (CT).
It is preferably contained in an amount of 0.1 to 40 parts by weight, particularly 0.5 to 20 parts by weight, based on 100 parts by weight of the resin solid content of L). In case of substrate / CGL / CTL photoreceptor, CGL is
Generally, the range is 0.01 to 5 μm, preferably 0.1 to 3 μm, and the CTL is 2 to 100 μm, especially 5
To 50 μm, and in any case, the initial thickness of the photosensitive layer (total thickness of the charge generation layer and the charge transport layer) is generally 25 to 100 μm, and particularly 30 to 50 μm. Is good.

(Preparation of Photoreceptor) The composition for forming a photosensitive layer used for forming the above-mentioned photosensitive layer contains various compounding agents known per se, for example, an oxidizing agent, within a range that does not adversely affect electrophotographic characteristics. Inhibitors, radical scavengers, singlet quenchers, UV absorbers, softeners, surface modifiers, defoamers, extenders, thickeners, dispersion stabilizers, waxes, acceptors, donors, etc. it can.

When at least an upper layer of the photosensitive layer is blended with 0.1 to 50% by weight based on the total solid content of a sterically hindered phenolic antioxidant, electrophotographic characteristics are not adversely affected and the photosensitive layer is not adversely affected. The durability can be remarkably improved.

As the conductive substrate on which the photosensitive layer is provided, various conductive materials can be used, for example, aluminum, copper, tin, platinum, gold, silver, vanadium, molybdenum,
Chromium, cadmium, titanium, nickel, indium,
Examples include simple metals such as stainless steel and brass, plastic materials in which the above metals are vapor-deposited or laminated, and glass covered with aluminum iodide, tin oxide, indium oxide and the like. In the photoconductor of the present invention, a normal aluminum tube, especially an anodized tube having a film thickness of 1 to 50 μm can be preferably used.

Conventionally, in order to form a photoreceptor, a combination of a charge generating agent, an electron transporting agent and a binder resin, a combination of a charge generating agent and a binder resin, or a combination of an electron transporting agent and a binder resin has been used. A known method, for example, a roll mill,
A coating composition may be prepared using a ball mill, an attritor, a paint shaker, an ultrasonic disperser, or the like, coated by a conventionally known coating means, laminated if necessary, and dried.

As the solvent used to form the coating solution, various organic solvents can be used, and alcohols such as methanol, ethanol, isopropanol, butanol,
Aliphatic hydrocarbons such as n-hexane, octane and cyclohexane, aromatic hydrocarbons such as benzene, toluene and xylene, halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon tetrachloride and chlorobenzene, dimethyl ether, diethyl ether, tetrahydrofuran, Ethylene glycol dimethyl ether, ethers such as diethylene glycol dimethyl ether, acetone, methyl ethyl ketone, ketones such as cyclohexanone, ethyl acetate, esters such as methyl acetate, dimethylformamide, dimethyl sulfoxide, etc. Used as a mixture. The solid content concentration of the coating liquid is generally preferably 5 to 50%.

The above-mentioned single-layer or laminated-type photosensitive layer may be formed directly on the conductive substrate, but may be formed via an undercoat layer. As such an undercoat layer, casein, polyvinyl alcohol, polyvinyl acetal, polyamide, melamine, cellulose,
Examples thereof include polymer films of polythiophene, polypyrrole, polyaniline, polyester, polyacrylate, polystyrene and the like. The thickness of the undercoat layer is 0.01
The range of μm to 20 μm is preferable. In order to impart conductivity to the undercoat layer, metal powder such as gold, silver and aluminum, metal oxide powder such as titanium oxide and tin oxide, and conductive fine powder such as carbon black can be dispersed.

[Image Forming Process] The image forming method using the above-mentioned positive charging type organic photoconductor is carried out as follows.

First, the main body of the photosensitive member is uniformly uniformly charged to the positive polarity and then imagewise exposed to form an electrostatic latent image. The main charging of the photoconductor can be performed by positive corona charging, contact charging using a conductor roller, or the like, and the surface potential is generally +2.
It is performed to the extent that it is in the range of 00V to + 1000V. The image exposure is performed by irradiating light such as laser light based on predetermined image information. By this light irradiation, the potential of the portion irradiated with light is lowered, and an electrostatic latent image is formed.

Next, the electrostatic latent image formed on the surface of the photoconductor is developed by a reversal development method using a developer containing a toner charged to a positive polarity to form a toner image on the surface of the photoconductor. . That is, the toner image is formed by the positively charged toner adhering to the portion where the potential is lowered by the irradiation of light.
As the developer, a one-component developer composed of a non-magnetic or magnetic toner, or a two-component developer composed of a non-magnetic or magnetic toner and a magnetic carrier (such as iron powder or ferrite) is used. The development may be carried out by contact development or non-contact development. In developing, a developing bias potential of about 50 to 400 V is generally applied.

The toner image formed as described above is
A transfer bias potential is applied by using a transfer roller, the transfer paper is passed between the transfer roller and the transfer roller, and an electric field generated between the surface of the photoconductor and the transfer roller causes transfer to the surface of the transfer paper. In the present invention, the transfer bias potential is
A transfer bias potential is applied to the above-described photoreceptor based on a transfer current value set based on a transfer memory-film thickness curve measured in advance for each transfer current value. That is, in the region where the thickness difference of the photosensitive layer is 15 μm or more, ±
A transfer bias potential showing a transfer current showing a potential difference within 10 V is applied. If the transfer is performed according to the transfer conditions set in this way, it is obvious that no transfer failure occurs until the photosensitive layer thickness is worn by at least about 15 μm by repeating the image forming process, and the transfer current value is adjusted. The transfer memory can be surely prevented without performing the above. Further, in such a transfer current value region, the linearity of the transfer memory-film thickness curve is high,
Further, since the potential difference due to the transfer memory is small, for example, the initial thickness of the photosensitive layer of the photosensitive member is set to 25 μm or more, and the transfer current value is not adjusted until the photosensitive layer thickness reaches 10 μm. The transfer can be continuously performed under the condition of. This is the greatest advantage of the present invention.

After the above-mentioned transfer is completed, the transfer paper on which the toner image is transferred is introduced into a fixing device known per se, and the toner image is fixed on the surface of the transfer paper by heat and pressure. On the other hand, the photoconductor after the transfer is cleaned by a cleaning blade or the like to remove the toner remaining on the surface of the photoconductor, and further, if necessary, the charge is removed by irradiation of the charge removing light. The cycle is completed and the next image forming process is performed.

In the present invention, since the transfer conditions are set as described above, when the main charging is performed in the next image forming process, the potential difference between the portion where the transfer memory is generated and the portion where the transfer memory is not generated is different. Remarkably small (± 1
Within 0 V), the transfer memory is effectively prevented, and for example, even when a gray image or the like is reproduced, a clear image without density unevenness or blurring can be obtained. Moreover, such a prevention effect of the transfer memory is effectively exhibited for a long period of time without adjusting the transfer current value. Furthermore, in the present invention, the effect of preventing the transfer memory as described above occurs even if the charge is not removed after the transfer. Therefore, it is possible to omit the static elimination step in the image forming process.

[0051]

The present invention will be described in the following experimental examples.

[Preparation of Photoreceptor] In the following experimental example,
The following were used as the charge generating agent and the charge transporting agent (electron transporting agent and hole transporting agent).

Charge generating agent: Metal-free phthalocyanine

Electron transport agent: Formula (1a) below:

[Chemical 25] A naphthoquinone compound represented by the following formula (b):

[Chemical formula 26] A diphenoquinone compound represented by

Hole transport material: The following formula (2b '):

[Chemical 27] Stilbene compound represented by the following formula (2e ′):

[Chemical 28] Stilbene compound represented by the following formula (2f ′):

[Chemical 29] Stilbene compound represented by

As a binder resin, a polycarbonate resin (TS2050 / RV) manufactured by Teijin Chemicals Ltd. is used, and the charge generating agent, the electron transfer agent and the hole transfer agent are combined in a solvent as shown in Table 1 to form a solvent. A coating liquid was prepared by dissolving or dispersing, the coating liquid was coated on an aluminum tube having a diameter of 30 mm, and dried to prepare positively charged single-layer organic photoreceptors having photosensitive layers of various thicknesses. . The compounding amount of each compounding agent is 3 parts by weight per 100 parts by weight of the binder resin.
2 parts by weight, 50 parts by weight of the hole transferring material, 35 parts by weight of PNQbz and 5 parts by weight of DADN were used as the electron transferring material.

The single-layer type organic photoconductor prepared above was mounted on a remodeled laser beam printer FS-1100 manufactured by Kyocera, main charged to 400 V, reverse development (developing bias potential: 300 V) was performed, and transfer current was applied. Transfer is performed under various transfer conditions, and the potential difference due to the transfer memory (potential difference between the portion where the transfer memory occurs and the portion where the transfer memory does not occur at the next main charging) is measured for each transfer current, and the results are shown in Table 1. And shown in FIGS. In the above measurement, static electricity was not removed.

Further, with respect to each of the photoconductors used above, the thickness of each photoconductive layer is set to about 30 μm, and the transfer current value (proper transfer current Value), a gray image was continuously reproduced until the thickness of the photosensitive layer reached about 15 μm, and the presence or absence of the transfer memory was visually observed, and the results are shown in Table 1. At the same time, it was also observed whether or not the transfer was effectively performed, and the results are also shown in Table 1.

[0058]

[Table 1]

[0059]

According to the present invention, a positive charging type organic photoconductor containing a specific electron transfer material is used, and by utilizing its unique property, a reversal development method and a transfer bias potential are utilized. In the image forming method of forming an image by using the transfer memory, the transfer memory is effectively prevented even if the transfer current value is not adjusted and the transfer is continuously performed under a constant transfer condition for a long period of time. , It became possible to perform the transfer effectively.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a potential difference due to a transfer memory for each transfer current and a photosensitive layer thickness of a photosensitive member used in the present invention.

FIG. 2 is a diagram showing a relationship between a potential difference due to a transfer memory for each transfer current and a photosensitive layer thickness of another photosensitive member used in the present invention.

FIG. 3 is a diagram showing a relationship between a potential difference due to a transfer memory for each transfer current and a photosensitive layer thickness of still another photosensitive member used in the present invention.

FIG. 4 is a diagram showing a relationship between a potential difference due to a transfer memory for each transfer current and a photosensitive layer thickness of a photosensitive member of a comparative example.

FIG. 5 is a diagram showing a relationship between a potential difference due to a transfer memory for each transfer current and a photosensitive layer thickness, with respect to a photoconductor of another comparative example.

FIG. 6 is a diagram showing the relationship between the potential difference due to a transfer memory for each transfer current and the thickness of the photosensitive layer in the photoconductor of still another comparative example.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 5/06 322 G03G 5/06 322 15/16 103 15/16 103 F term (reference) 2H068 AA20 AA31 BA13 BA14 BA22 BA63 BA64 FC02 FC08 FC11 2H171 FA09 FA13 FA15 GA01 GA15 QA08 QA17 QB49 QC11 TB02 UA02 UA03 UA04 UA05 UA06 UA07 VA01 VA03 VA05 2H200 FA01 FA02 FA05 FA18 GA13 GA23 GA34 JA02 NA02 JA04 NA02 JA02 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA29 HA29 HA22 HA29 HA22 HA22 HA29 HA22 HA29 HA22 HA22 HA29 HA22 HA22 HA29 HA22 HA22 HA22 HA29 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 HA22 PA10 PA20 PA23 PA30 PB02 PB04 PB25 PB40

Claims (5)

[Claims] 1. A positively chargeable organic photoreceptor containing a hole-transporting agent and an electron-transporting agent in a photosensitive layer is used, the photoreceptor is main-charged to a positive polarity, and then imagewise exposure is carried out. An electrostatic latent image is formed on the surface of the photoconductor, the electrostatic latent image is developed by a reversal development method to form a toner image, and the toner image is transferred by applying a transfer bias potential using a transfer roller. In the method of forming an image by repeating the image forming process of transferring the toner to the surface and cleaning the toner remaining on the surface of the photoreceptor, the following general formula (1): In the formula, R ¹ is an alkyl group or an aryl group, and R 1
² is an alkyl group, an aryl group, or a formula: -OR
³ (R ³ is a group represented by an alkyl group or an aryl group) containing a naphthoquinone compound represented by the following as an electron transfer agent is used. For each value, the relationship between the thickness of the photosensitive layer and the potential difference on the surface of the photoconductor at the time of main charging caused by the transfer memory was measured, and from the relationship between the thickness of the photosensitive layer and the potential difference obtained above, a region where the thickness difference was 15 μm or more At ± 1
An image forming method comprising applying a transfer bias potential so that a transfer current having a potential difference of 0 V or less is applied to perform transfer. 2. The initial thickness of the photosensitive layer of the photoconductor is 25 μm.
m or more, until the thickness of the photosensitive layer reaches 10 μm,
The image forming method according to claim 1, wherein the transfer is continuously performed under the transfer conditions set in the above. 3. The positive charging type organic photoconductor is defined by the following general formulas (2a), (2b), (2c), (2d) and (2).
The image forming method according to claim 1 or 2, wherein a compound containing a stilbene compound represented by e) or (2f) is used as a hole transport material. In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer from 0 to 4, &nbsp; In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer from 0 to 4, In the formula, R may be the same or different and represents an alkyl group, n and p are integers of 0 to 5, and m and q
Is a number from 0 to 3, and o is an integer from 0 to 4. [Chemical 5] In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers of 0 to 5; In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 6, In the formula, R may be the same or different and each represents an alkyl group, m, n, p and q are integers from 0 to 5, o
Is an integer of 0 to 6. 4. The image forming method according to claim 1, wherein the next image forming step is performed after the transfer without removing the charge. 5. The image forming method according to claim 1, wherein the positively chargeable organic photoconductor is a single-layer organic photoconductor.