JPH08297423A - Electrophotographic process and electrophotographic device - Google Patents

Abstract

PURPOSE: To provide an electrophotographic process and an electrophotographic device capable of suppressing the abraded amount of a photoreceptor by the durability, capable of suppressing the increase of remaining potential, excellent in durability and stability, and capable of obtaining a good image. CONSTITUTION: In this electrophotographic process, a primary electrifier means and a transferring and electrifying means are arranged in contact with each other, and the electrophotographic device is electrified by impressing only a direct voltage to the photoreceptor from an electrifier member at both time of primary electrification and transferring electrification. The relation among a current value Z(μA) per 10cm of a transfer electrifier, a process speed (x)(mm/ sec) and the peripheral length (y)(mm) of the photoreceptor satisfies expressions (1) Z<=7.28×10<-4> ×x×y-0.687 and (2) Z>=1.46×10<-4> ×x×y--0.137.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic process for charging an electrophotographic apparatus by placing a charging means in contact with an electrophotographic photosensitive member and applying only a DC voltage from the charging means to the photosensitive member. And an electrophotographic apparatus using the same.

[0002]

2. Description of the Related Art In an electrophotographic method, for example, selenium,
Charge, expose, and develop electrophotographic photoreceptors such as cadmium sulfide, zinc chloride, amorphous silicon, and organic photoconductors.
When an image is obtained by performing basic processes such as transfer, fixing, and cleaning, the charging process is conventionally performed by applying a high voltage (DC 5 to 8 kV) to a metal wire and charging by a corona generated. However, in this method, when corona occurs, corona products such as ozone and NOx deteriorate the surface of the photoconductor to cause image blurring and deterioration, and wire stains affect image quality, resulting in white spots and black streaks. There was such a problem. In particular, the electrophotographic photosensitive member whose photosensitive layer is mainly composed of an organic photoconductor,
It has lower chemical stability than other selenium photoconductors and amorphous silicon photoconductors, and when exposed to corona products, a chemical reaction (mainly an oxidation reaction) occurs and tends to deteriorate. Therefore, when it is repeatedly used under corona charging, image blurring due to the above-mentioned deterioration and low copy density due to reduction in sensitivity tend to occur, and the printing durability life tends to be short.

In the case of corona charging, the electric current flowing to the photoconductor is only 5 to 30% in terms of electric power, and most of them flow to the shield plate and are inefficient as charging means.

In order to make up for such a problem, without using a corona discharger, Japanese Patent Laid-Open No. 57-178267 has been proposed.
JP-A-56-104351, JP-A-58-405
As proposed in Japanese Patent Laid-Open No. 66, Japanese Patent Application Laid-Open No. 58-139156, Japanese Patent Application Laid-Open No. 58-150975, etc., a method of contact charging has been studied.

Specifically, the surface of the photoconductor is charged to a predetermined potential by contacting the surface of the photoconductor with a charging member such as a conductive elastic roller to which a direct current voltage of about 1 to 2 kV is applied from the outside. .

However, although there are many proposals for the direct charging method, there is almost no market record. The reasons for this are the non-uniform charging and the occurrence of discharge dielectric breakdown of the photoconductor due to direct application of voltage.

In order to solve the above problems and improve the uniformity of charging, a method of superimposing an AC voltage on a DC voltage and applying it to a charging member has been proposed (JP-A-63-63).
149668). This charging method uses a DC voltage (V
_A pulsating current voltage is applied by superimposing an _AC voltage (VAC) on ( _DC ) to perform uniform charging.

However, by superposing the AC voltage,
There is also a problem that the damage to the photosensitive layer is large and the durability performance is significantly reduced.

FIG. 1 shows a schematic view of the image forming apparatus.

Reference numeral 1 is a body to be charged. In this example, it is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive member). The photoreceptor 1 of this example is a conductive support 1b such as aluminum.
And the photosensitive layer 1a formed on the outer surface thereof are the basic constituent layers.

Reference numeral 2 is a charging member. This example is a roller type (hereinafter referred to as a charging roller). The charging roller 2 is composed of a central cored bar 2c, a conductive layer 2b formed on the outer periphery thereof, and a resistance layer 2a formed on the outer periphery thereof.

The charging roller 2 has both ends of a cored bar 2c rotatably supported by bearing members (not shown), which are arranged in parallel with the drum type photoconductor 1 and are attached to the surface of the photoconductor 1 by pressing means (not shown). The photoconductor 1 is pressed against it with a predetermined pressing force, and is driven to rotate as the photoconductor 1 is rotationally driven. It is also possible to attach a gear or the like and transmit the driving force from the motor for forced rotation driving.

Reference numeral 3 denotes a bias applying power source for the charging roller 2. The power source 3 and the core metal 2c of the charging roller 2 are electrically connected, and a predetermined bias is applied to the charging roller 2 by the power source 3.

When the photosensitive member 1 as the member to be charged is rotationally driven, the photosensitive member 1 is pressed by the photosensitive member 1 and is charged by the charging roller 2 as a charging member to which a bias voltage is applied.
The outer peripheral surface is charged with a predetermined polarity and potential.

As shown in FIG. 1, around and around the photosensitive member 1,
In addition to the charging roller 2 as the charging means, the exposing means 1
0, developing means 11, transfer means 12, cleaning means 1
3, necessary image forming process equipment such as the pre-exposure means 15 and the image fixing means are arranged to constitute an image forming mechanism, and the image formation is executed on the transfer material 14.

[0016]

In the image forming apparatus as described above, the outer peripheral surface of the photoconductor is scraped by the cleaning blade of the cleaning means or the developer as the number of times of image formation increases. Then, as the thickness (layer thickness, film thickness) of the photoconductor is reduced, the charging characteristic changes due to the change in equivalent capacity.

In particular, when the charging means applies a contact type DC voltage, it is greatly affected by the change in the capacity of the photoconductor.
That is, when the number of times image formation is used increases and the film thickness of the photoconductor decreases, the direct current flowing through the charging roller increases and the surface potential of the outer peripheral surface of the photoconductor rises. Further, when the film thickness of the photoconductor is decreased and the surface potential is increased, the development contrast is increased and the development image density is increased, and at the same time, sufficient reverse contrast cannot be obtained with respect to the potential of the white image. However, there was a problem in that it was thinly developed and became a "fog" image. Further, in the reversal development system, there was an obstacle of "low density".

That is, when the film thickness of the photoconductor is reduced, the surface potential is increased and the bright portion potential of the surface potential is also increased accordingly. Further, due to the endurance, an increase in residual potential is also recognized, which increases the bright potential.

An object of the present invention is to eliminate the above problems.

[0020]

Means and Action for Solving the Problems The present inventors have
As a result of repeated studies on the above-mentioned problems, it has been found that the electrophotographic process can be improved to solve the above problems by applying only a DC voltage when contact charging the photoconductor from a charging member. It was

That is, according to the present invention, a primary charging unit and a transfer charging unit are arranged in contact with an electrophotographic photosensitive member, and only a DC voltage is applied to the photosensitive member from the charging member for both primary charging and transfer charging. In the electrophotographic process for charging the device, the current value Z per 10 cm of the transfer charger
(ΜA), the process speed x (mm / sec), and the peripheral length y (mm) of the photoconductor are expressed by the following equations (1) and (2) Z ≦ 7.28 × 10 ⁻⁴ × x × y− 0.687 (1) Z ≧ 1.46 × 10 ⁻⁴ × x−y−0.137 (2) An electrophotographic process characterized by the following.

Further, the present invention has an electrophotographic photosensitive member, a primary charging member and a transfer charging member which are disposed in contact with the photosensitive member, and the photosensitive member is subjected to a DC voltage for both primary charging and transfer charging. In the electrophotographic apparatus which is charged by applying only the current, the current value Z per 10 cm of the transfer charger
(ΜA), the process speed x (mm / sec), and the peripheral length y (mm) of the photoconductor are expressed by the following equations (1) and (2) Z ≦ 7.28 × 10 ⁻⁴ × x × y− 0.687 (1) Z ≧ 1.46 × 10 ⁻⁴ × x−y−0.137 (2) The electrophotographic apparatus is characterized by the following.

The present invention will be described in detail below.

The direct charging method, in which a charging member is brought into contact with an electrophotographic photosensitive member to perform charging, is carried out in a minute space near the contact portion between the photosensitive member and the charging member by void breaking discharge according to Paschen's law. Due to the nature of such a charging mechanism, the surface potential greatly depends on the electrostatic capacity of the photoconductor. Similarly, the surface potential also depends on the electrostatic capacity of the photoconductor in corona discharge, which has been widely used in the past, but unlike DC direct charging, when the electrostatic capacity is large, the dark potential is low and the electrostatic capacity is low. When is small, the dark potential is high. On the contrary, when a commonly used charge generation layer is used, the bright potential is high when the electrostatic capacity is large, and the bright potential is low when the electrostatic capacity is large.

However, in the DC direct charging system, the dark potential is higher as the electrostatic capacity is larger, and vice versa when the capacitance is smaller.

Regarding the sensitivity, the bright potential is such that the difference between the dark potentials is further amplified. The larger the electrostatic capacity, the higher the bright potential, and conversely, the smaller the electrostatic potential, the lower the bright potential.

That is, as the surface layer of the photoconductor is shaved, both the dark potential and the bright potential become higher, and the durability potential stability is lost, resulting in problems such as direct image fog in the positive development and low density in the reverse development. Become.

That is, it is understood that the larger the abrasion amount of the photosensitive layer due to the durability, the more the problem.

The present inventors have found that the amount of abrasion of the DC direct charging system largely depends on the current value flowing from the transfer charger to the surface of the photosensitive layer due to transfer.

On the other hand, in the case of superimposing AC on the primary charging, the amount of current due to AC has a large digit difference, so that the amount of abrasion depends on the amount of primary current and hardly depends on the transfer current.

Further, it was also found that the rise of the residual potential of the photosensitive member largely depends on the current value flowing from the transfer charger to the surface of the photosensitive layer.

That is, by controlling the transfer current as shown in the formula (1), the abrasion amount of the photosensitive layer can be reduced and the increase of the residual potential can be suppressed, and the durability stability can be improved.
A good image can be obtained.

On the contrary, when the expression (2) is not satisfied,
Transfer of toner to the transfer paper is not performed sufficiently,
The concentration becomes thin.

This tendency was the same in both the positive development system (having the same primary and transfer polarities) and the reverse development system (having the opposite primary and transfer polarities).

As the shape of the charging member 1 used in the present invention,
In addition to the rollers shown in FIG. 1, blades and belts
You can take any shape, depending on the specifications of the electrophotographic device and
It can be selected according to the form. In addition, this charging member
Materials include metals such as aluminum, iron and copper, and poly
Conductivity of acetylene, polypyrrole, polythiophene, etc.
Conductive treatment by dispersing conductive polymer, carbon, metal, etc.
Treated rubber or artificial fiber, or polycarbonate, poly
The surface of insulating materials such as vinyl and polyester should be
Do not use those coated with other conductive materials.
You can The volume resistance value of the charging member is 10⁰ ~
10¹²Ω · cm is preferred, especially 10 ² -10¹²Ω ・
cm is preferred.

Examples of the organic photoconductor include those using an organic photoconductive polymer such as polyvinylcarbazole, and those containing a low molecular weight organic photoconductive substance in a binder resin.

The electrophotographic photosensitive member of FIG. 2 has a conductive support 2
0 is provided with a photosensitive layer 21, and the photosensitive layer 21
Is a laminated structure of a charge generating layer 23 containing a charge generating material (not shown) dispersed in a binder resin and a charge transporting layer 24 containing a charge transporting material (not shown). in this case,
The charge transport layer 24 is laminated on the charge generation layer 23.

In the electrophotographic photosensitive member of FIG. 3, unlike the case of FIG. 2, the charge transport layer 24 is laminated below the charge generation layer 23. In this case, the charge generation layer 23 may contain a charge transport material.

The electrophotographic photosensitive member of FIG. 4 has a conductive support 2
0 is provided with a photosensitive layer 21, and the photosensitive layer 21
Includes a charge generation material 22 and a charge transport material (not shown) in the binder resin.

Further, an overcoat layer may be applied in addition to the structure shown in FIGS.

As the conductive support 20, a metal such as aluminum or stainless steel, a cylindrical cylinder such as paper or plastic, a sheet or a film is used. Further, these cylindrical cylinders, sheets or films may have a conductive polymer layer or a resin layer containing conductive particles such as tin oxide, titanium oxide and silver particles, if necessary.

An undercoat layer (adhesive layer) having a barrier function and an undercoat function may be provided between the conductive support and the photosensitive layer.

The subbing layer improves the adhesion of the photosensitive layer, the coating property, the protection of the support, the coating of defects on the support, the improvement of the charge injection property from the support, the protection of the photosensitive layer against electric breakdown, etc. Formed for. The film thickness is about 0.2 to 2 μm.

As the charge generating material, use is made of pyrylium, thiopyrylium dye, phthalocyanine pigment, anthanthrone pigment, dibenzpyrenequinone pigment, pyratron pigment, azo pigment, indigo pigment, quinacridone pigment, asymmetric quinocyanine, quinocyanine, etc. You can

The charge generating layer 23 includes a homogenizer, an ultrasonic wave, a ball mill, a vibrating ball mill, a sand mill, an attritor, a roll mill, etc., together with a binder resin in an amount of 0.3 to 4 times the amount of the charge generating material and a solvent. It is formed by being well dispersed by a method, applied and dried. Its thickness is 5 μm
In the following, the range of 0.01 to 1 μm is particularly preferable.

The charge transport layer 24 is generally formed by dissolving the above charge transport material and the binder resin in a solvent and coating the solution. The mixing ratio of the charge transport material and the binder resin is 2: 1 to
It is about 1: 2. As the solvent, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, chlorinated hydrocarbons such as chlorobenzene, chloroform and carbon tetrachloride are used. To be When applying this solution, a coating method such as a dip coating method, a spray coating method or a spinner coating method can be used, and drying is performed at 10 ° C to 200 ° C.
It can be carried out at a temperature in the range of 20 ° C. to 150 ° C. for 5 minutes to 5 hours, preferably 10 minutes to 2 hours under blast drying or static drying.

As the binder resin used for forming the charge transport layer 24, acrylic resin, styrene resin,
A resin selected from polyester, polycarbonate resin, polyarylate, polysulfone, polyphenylene oxide, epoxy resin, polyurethane resin, alkyd resin, unsaturated resin and the like is preferable. Particularly preferred resins include polymethylmethacrylate, polystyrene,
Examples thereof include a styrene-acrylonitrile copolymer, a polycarbonate resin or a diallyl phthalate resin.

The charge generating layer or the charge transporting layer may contain various additives such as an antioxidant, an ultraviolet absorber and a lubricant. Further, in order to improve the lubricity and wear resistance of the surface layer, it is possible to disperse a fluororesin powder, add a silicone oil, and further apply a protective layer on the photosensitive layer.

The electrophotographic photoreceptor of the present invention can be used not only in electrophotographic copying machines but also in laser beam printers, C
RT printer, LED printer, liquid crystal printer,
It can be widely used in electrophotographic application fields such as laser plate making.

[0050]

The present invention will be described below with reference to examples. [Example 1] An aluminum cylinder having a diameter of 30 mm x 357.5 mm was used as a support, and 5% by weight of a polyamide resin (trade name: Amilan CM8000, manufactured by Toray Industries) was added thereto.
A methanol solution was applied by a dipping method to form an undercoat layer having a thickness of 0.5 μm.

Next, the following structural formula

[0052]

Embedded image 2 parts (parts by weight, the same applies hereinafter), 1 part of the resin (a) represented by the following structural formula and

[0053]

Embedded image 100 parts of cyclohexanone was dispersed for 20 hours by a sand mill device using φ1 mm glass beads. Tetrahydrofuran (100 parts) was added to this dispersion, and the solution was coated on the undercoat layer.

Then, 10 parts of the compound of the following structural formula

[0055]

Embedded image And bisphenol Z type polycarbonate (trade name: Z
10 parts (-200, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was dissolved in 100 parts of monochlorobenzene. This solution was applied on the charge generation layer and dried in hot air at 120 ° C. for 1 hour to form a 25 μm charge transport layer.

The electrophotographic apparatus is Canon NP-603.
0 was used. This device has both primary charging and transfer charging.
A contact or charging method is used in which only a DC voltage is applied to a charging member arranged in contact with the photoconductor to charge the photoconductor.

The process speed of this device is 20.
0 (mm / sec), the length of the transfer roller is 30
It is 7 (mm).

The transfer voltage was applied from the outside, modified so that the current value could be monitored, and set so that a 35 μA current would flow.

For confirmation, equations (1) and (2) are applied.

Z = 35 ÷ 307 × 100 = 1.40 Formula (1) right side 7.28 × 10 ⁻⁴ × x × y −0.687
= 7.28 × 10 ⁻⁴ × 200 × 30 × 3.14−0.6
87 = 13.03 Formula (2) right side 1.46 × 10 ⁻⁴ × x × y −0.137
= 1.46 × 10 ⁻⁴ × 200 × 30 × 3.14−0.1
37 = 2.61 It is understood that the formulas (1) and (2) are satisfied.

[Example 2] The same procedure as in Example 1 was carried out except that the transfer current was set to 25 µA.

[Embodiment 3] NP6030 manufactured by Canon was modified in Embodiment 1 so that the process speed was 100%.
(Mm / sec) and the transfer current was 15 (μA), and the same procedure as in Example 1 was performed.

[Embodiment 4] A cartridge of NP6030 manufactured by Canon was modified in Embodiment 1 to obtain a diameter of 24 (m).
m) photosensitive drum, process speed 100
(Mm / sec) and the transfer current was set to 14 (μA).

[Embodiment 5] In addition to the solution for the charge transport layer in Embodiment 1, fluororesin powder (trade name: Lubron L-
(2, manufactured by Daikin Industries, Ltd.) 2 parts by weight of the mixture was added to 10 parts by weight of monochlorobenzene in a sand mill to prepare a solution for charge transport layer. To stabilize the dispersion of the fluororesin powder, 0.12 part of a dispersion aid (trade name: GF-300, manufactured by Toagosei) was added. This solution was applied onto the charge generation layer and dried in hot air at 120 ° C. for 1 hour to form a charge transport layer having a thickness of 25 μm.

[Comparative Example 1] The procedure of Example 1 was repeated except that the transfer current was changed to 50 μA.

[Comparative Example 2] The procedure of Example 1 was repeated except that the transfer current was changed to 70 μA.

[Comparative Example 3] The procedure of Example 1 was repeated except that the transfer current was changed to 5 μA.

[Comparative Example 4] The procedure of Example 3 was repeated except that the transfer current was changed to 30 μA.

[Comparative Example 5] The procedure of Example 4 was repeated except that the transfer current was changed to 30 μA.

[Comparative Example 6] The procedure of Example 5 was repeated except that the transfer current was changed to 50 μA.

The abrasion amount was evaluated by using the above-mentioned apparatus to endure 10,000 sheets intermittently with A4 sheet passing durability and measure the film thickness difference before and after the durability to obtain the abrasion amount. The evaluation of the increase in the residual potential was made by using the above-mentioned apparatus and continuously using A4 paper feed 1,000 times.
The sheet was durable and the residual potential before and after the durability was measured. The results are shown in Table 1.
Shown in

[0072]

[Table 1]

[0073]

As described above, according to the present invention,
If the transfer current is set to satisfy the conditions (1) and (2), damage to the photoconductor can be reduced, the amount of abrasion of the photoconductor can be suppressed, and the increase in residual potential can also be suppressed. And an excellent image can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration example of an electrophotographic apparatus of the present invention.

FIG. 2 is a diagram showing an example of the layer structure of a photoreceptor used in the present invention.

FIG. 3 is a diagram showing an example of the layer structure of a photoconductor used in the present invention.

FIG. 4 is a diagram showing an example of the layer structure of a photoreceptor used in the present invention.

Claims (2)

[Claims] 1. An electrophotographic apparatus is charged by arranging a primary charging unit and a transfer charging unit in contact with an electrophotographic photosensitive member, and applying only a DC voltage to the photosensitive member from the charging member for both primary charging and transfer charging. In the electrophotographic process, the current value Z (μA) per 10 cm of the transfer charger, the process speed x (mm / sec), and the peripheral length y (m of the photoreceptor)
m) is expressed by the following equations (1) and (2) Z ≦ 7.28 × 10 ⁻⁴ × x × y−0.687 (1) Z ≧ 1.46 × 10 ⁻⁴ × x × y− An electrophotographic process characterized by satisfying 0.137 (2). 2. An electrophotographic photosensitive member, and a primary charging member and a transfer charging member which are disposed in contact with the photosensitive member, and only a DC voltage is applied to the photosensitive member from the charging member for both primary charging and transfer charging. In the electrophotographic apparatus charged by the above, the current value Z (μA) per 10 cm of the transfer charger, the process speed x (mm / sec), and the peripheral length y (m of the photoconductor are
m) is expressed by the following equations (1) and (2) Z ≦ 7.28 × 10 ⁻⁴ × x × y−0.687 (1) Z ≧ 1.46 × 10 ⁻⁴ × x × y− An electrophotographic device characterized by satisfying 0.137 (2).