JP3056413B2 - Conductive transfer belt - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive transfer belt used for an electrophotographic image forming apparatus such as an electrostatic copying machine, a laser printer, and a facsimile.

[0002]

2. Description of the Related Art In a transfer device of the above-mentioned image forming apparatus, a transfer belt having a function of transferring a toner image formed on the surface of a photoreceptor onto transfer paper and a function of conveying the transfer paper is known. I have. That is, since a charge (transfer bias) is applied to the transfer belt, the transfer paper can be carried and transported electrostatically, and the transfer bias has the opposite polarity to the charge of the toner image. For,
The transfer of the toner image can be performed when the transfer paper is brought into contact with the photoconductor.

In the above transfer apparatus, the quality of a formed image is
It is necessary to transfer the toner image accurately to improve
Is required. Therefore, the electric characteristics of the transfer belt have been
Various studies have been made on the properties, especially the volume resistivity ρ.
You. For example, Japanese Patent Laid-Open Publication No.
Direction volume resistivity ρ is 10 ^Ten-10¹⁴Ω · cm
Forming an anti-layer and contacting the resistive layer with the photoreceptor.
Surface resistance on the side of about 1/10 to 1/100 of the resistance value
A transfer belt set at each time is disclosed.

In Japanese Patent Application Laid-Open Nos. 1-172986 and 2-110586, a high-resistance layer is provided on the side where the transfer belt contacts the photosensitive member, and a low-resistance layer is provided on the side not contacting the photosensitive member. Is disclosed.

[0005]

However, even when the value of the volume resistivity ρ is set within a predetermined range as in the transfer belt disclosed in the above-mentioned publication, unevenness may occur in the formed image. The problem cannot be eliminated.
This is because the rubber used for the transfer belt is generally
This is because conductivity is exhibited by a conductive filler such as carbon black compounded in rubber.

[0006] The conductive filler has the property of being oriented in a certain direction by the action of shear stress during the kneading of rubber or the like. The conductivity of rubber is considered to be manifested by a tunnel effect when the conductive filler or the like comes into contact with (or very close to) the inside of the rubber, and largely depends on the orientation of the conductive filler and rubber molecules. It depends. Therefore, even if the rubber has the same composition, the conductivity greatly varies depending on the processing history of the rubber,
A problem arises in that the conductivity varies in the direction of movement of the transfer belt and in the width direction perpendicular thereto.

On the other hand, Japanese Patent Application Laid-Open No. Hei 7-146594 discloses that by controlling the intensity of the transfer bias, the charge amount of the transfer belt can be kept constant even when the resistivity in the moving direction of the transfer belt changes. A transfer device is disclosed. However, the transfer device described in the above publication cannot control the change in the resistance value in the width direction of the transfer belt, and causes a problem that unevenness occurs in a formed image due to a variation in conductivity in the width direction. It cannot be removed.

The volume resistivity ρ generally indicates a resistance value in the thickness direction of the transfer belt.
It is considered that the current direction and the like differ between the current when measuring the current and the current when the transfer belt is actually used.
Therefore, the correlation between the variation of the volume resistivity ρ in the width direction of the transfer belt and the evaluation of the formed image is low,
Even if the variation in the volume resistivity ρ in the width direction of the conductive belt is small, the unevenness of the formed image cannot be completely removed.

An object of the present invention is to provide a conductive transfer belt that can realize accurate transfer and can form a good image.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the correlation between the molecular orientation angle and the degree of molecular orientation of the conductive layer of the conductive transfer belt and the quality of the formed image. Attention, as a result of intensive research, a conductive transfer belt having at least a conductive layer, on the same line along the width direction of the belt orthogonal to the direction of movement of the belt, (i) of the conductive layer, The average value of the molecular orientation angle θ with respect to the width direction of the belt is in the range of −15 ° to + 15 °, and (ii) the relationship between the average value, the maximum value, and the minimum value of the molecular orientation degree MOR-C of the conductive layer. When the formula (1): (maximum value−minimum value) / average value <0.4 (1), the conductivity that can realize accurate transfer and form a good image can be obtained. Discover the new fact that a transfer belt can be obtained and complete the present invention It came to that.

The molecular orientation angle θ and the degree of molecular orientation MOR
-C is measured using a molecular orientation meter. The molecular orientation meter is a device for examining the orientation state of a molecule, and includes a pair of waveguides (an oscillator and a detector) and a sample holder provided in a gap between the waveguides. When the sample taken out of the conductive layer of the conductive transfer belt is irradiated with microwave polarization, an interaction occurs between the microwave polarization and the dipole moment of the sample. By determining the angle dependence of this interaction, the orientation state of the conductive layer can be examined.

FIG. 1 shows an example of an alignment pattern diagram obtained by measuring the alignment state. Curve 1 in FIG. 1 is a plot of the intensity of microwave polarization detected by the detector of the molecular orientation meter, corresponding to the direction of the plane of polarization. In this orientation pattern diagram, the X axis indicates the moving direction of the transfer belt,
The Y axis indicates the width direction of the transfer belt. That is, the intersection between the curve 1 and the Y axis in FIG.
The intensity of the microwave polarization measured by the detector when the direction corresponding to the width direction of the transfer belt and the polarization plane of the microwave polarization are matched is shown.

The molecular orientation angle θ of the conductive layer in the conductive transfer belt of the present invention with respect to the width direction of the belt is determined by the direction in which the intensity of the microwave polarization transmitted through the sample shows the minimum value and the Y axis (that is, the conductive axis). (The width direction of the transfer belt). The value of the molecular orientation angle θ has a positive value clockwise from the Y axis and a negative value counterclockwise. The smaller the absolute value of the molecular orientation angle θ is, the closer the direction of the dipole moment of the conductive layer is to the Y-axis direction (that is, the width direction of the transfer belt).

The molecular orientation degree MOR-C of the conductive layer in the conductive transfer belt of the present invention is such that the maximum value (indicated by MAX in FIG. 1) of the intensity of microwave polarization is the minimum value (M in FIG. 1).
IN) (indicated by IN), and the thickness is corrected in consideration of the thickness of the sample. The greater the value of the degree of molecular orientation MOR-C, the greater the anisotropy of the dipole moment of the conductive layer. The thickness correction is performed according to the following equation (2).

[0015]

(Equation 1)

(Where t _c represents the corrected thickness (mm) and t _s represents the thickness (mm) of the sample.) The above equation (1) represents the molecular orientation degree in the width direction of the conductive transfer belt. The magnitude of the variation of MOR-C is shown.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive layer in the conductive transfer belt of the present invention is formed by compounding a rubber with a conductive filler, a vulcanizing agent and the like, and vulcanizing and molding. As the rubber used for the conductive layer, conventionally known various rubbers can be used. Specifically, acrylonitrile-butadiene rubber (NB
R), natural rubber (NR), isoprene rubber (IR), chloroprene rubber (CR), styrene-butadiene rubber (SBR), butadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM) ), Silicone rubber, urethane rubber, acrylic rubber, fluoro rubber, butyl rubber (IIR), halogenated butyl rubber, chlorosulfonated polyethylene rubber (CSM), epichlorohydrin rubber (CHR), epichlorohydrin-ethylene oxide copolymer rubber ( CH
C), hydrogenated nitrile rubber (HSM) and the like, and these rubbers can be used alone or as a mixture of two or more.

Examples of the conductive filler compounded in the rubber include metal oxides such as carbon black, tin oxide, and titanium oxide (including those whose surfaces are coated with tin oxide), conductive silica, copper, and the like. Metal powders such as iron, nickel, and aluminum, and carbon fibers can be used. Among the conductive fillers, examples of the carbon black include channel black, furnace black, acetylene black, and the like.
m, especially those in the range of 22 to 90 nm are preferably used.

The amount of the conductive filler is usually determined according to the volume resistivity ρ of the conductive layer. When carbon black is used as the conductive filler, it is suitable to add 50 to 300 parts by weight, preferably 5 to 50 parts by weight, per 100 parts by weight of rubber. If the amount of carbon black exceeds the above range, the volume resistivity ρ of the transfer belt may be too low. In this case, pinholes occur, transfer failure due to reverse charging of toner, leak,
There is a possibility that paper stains or the like may occur. Further, the hardness of the conductive transfer belt may be too high, or the workability may be deteriorated. On the other hand, if the amount of carbon black is less than the above range, the volume resistivity ρ of the transfer belt may be too high. In this case, the transfer efficiency is deteriorated, and may not be suitable for practical use.

As the vulcanizing agent to be added to the rubber, various conventionally known vulcanizing agents such as sulfur, organic sulfur compounds and organic peroxides can be used. Examples of the organic sulfur compound include 2,4,6-trimercapto-S-triazine and N, N′-dithiobismorpholine. Further, as the organic peroxide,
For example, benzoyl peroxide and the like can be mentioned.

The amount of the vulcanizing agent is suitably from 0.3 to 4 parts by weight, preferably from 0.5 to 3 parts by weight, based on 100 parts by weight of the raw rubber. In the rubber used for the conductive layer, in addition to the conductive filler and the vulcanizing agent, for example, a vulcanization accelerator, a vulcanization accelerator, a foaming agent, a filler (reinforcing agent),
Additives such as a softener, a plasticizer, and an antioxidant are added as necessary.

Examples of the vulcanization accelerator include thiurams such as tetramethylthiuram disulfide and tetraethylthiuram disulfide; dithiocarbamic acids such as zinc dibutyldithiocarbamate and zinc diethyldithiocarbamate; 2-mercaptobenzothiazole, N-cyclohexyl-2- In addition to organic accelerators such as thiazoles such as benzothiazole sulfenamide; thioureas such as trimethylthiourea, slaked lime, magnesia (M
gO), litharge (PbO) and the like.

Examples of the vulcanization accelerator include metal oxides such as zinc white, fatty acids such as stearic acid, oleic acid and cottonseed fatty acid, and various other vulcanization accelerators known in the art. The foaming agent is used when foaming rubber for the purpose of lowering the hardness, for example, diaminobenzene, dinitrosopentamethylenetetramine, benzenesulfonylhydrazide, azodicarbonamide,
4,4'-oxybis (benzenesulfonyl hydrazide) and the like. The amount of the foaming agent may be blended in accordance with the desired expansion ratio, and is usually 30 parts by weight or less, preferably 3 to 20 parts by weight, per 100 parts by weight of the raw rubber.

As a filler (reinforcing agent), carbon black is a typical example. However, since carbon black is used for imparting conductivity to rubber, its compounding amount is limited to the above range. . Examples of fillers (reinforcing agents) other than carbon black include calcium carbonate, silica, clay, talc, barium sulfate, diatomaceous earth and the like.

Examples of the softener include fatty acids such as stearic acid and lauric acid, cottonseed oil, tall oil, asphalt substances, paraffin wax and the like. Examples of the plasticizer include phthalic acid compounds such as dimethyl phthalate and dibutyl phthalate, adipic acid compounds such as dioctyl adipate, sebacic acid compounds such as dibutyl sebacate, and benzoic acid compounds.

Examples of the antioxidants include imidazoles such as 2-mercaptobenzimidazole and phenyl-
α-naphthylamine, N, N′-di-β-naphthyl-p
Amines such as phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, di-t-
Examples include phenols such as butyl-p-cresol and styrenated phenol.

The method for forming the conductive layer is as follows. First, the above-mentioned components are blended with the above-described rubber and kneaded with an open roll, a closed kneader or the like to obtain a conductive rubber composition. Next, the conductive rubber composition is formed into a belt having a predetermined shape by a conventionally known molding method such as extrusion molding, injection molding, and the like, and further vulcanization and, if necessary, secondary vulcanization are performed to obtain a desired rubber. A conductive layer is obtained.

In order to obtain a conductive transfer belt capable of forming a good image, the volume resistivity ρ is set in a predetermined range, and the molecular orientation MOR-C and the molecular orientation angle θ are set as described above. What is necessary is just to set to a range. The molecular orientation angle θ and the molecular orientation degree MOR-C of the conductive layer are determined by the extrusion molding,
During molding, such as injection molding, it can be adjusted by changing molding conditions.

For example, when the conductive layer is formed by extrusion molding, the extrusion speed of the conductive rubber composition, the rotation speed of the screw of the extruder, the temperature of the die of the extruder and the like may be adjusted. The higher the extrusion speed or the rotation speed of the screw, or the higher the temperature of the die, the smaller the absolute value of the molecular orientation angle θ of the conductive layer and the greater the degree of molecular orientation MOR-C.

The molecular orientation angle θ and the molecular orientation degree M of the conductive layer
In order to set the OR-C in the above range, generally, the extrusion speed of the conductive rubber composition is set in a range of 0.5 to 4.5 m / min, and the rotation speed of the screw is set in a range of 5 to 25 rpm.
The temperature of the base may be set in the range of 50 to 130 ° C. The molecular orientation angle θ of the conductive layer in the conductive transfer belt of the present invention has an average value on the same line along the width direction of the conductive transfer belt of −15 ° to + 15 °, preferably −5 °.
Suitably, it is in the range of ° to + 5 °. When the average value of the molecular orientation angle θ is less than −15 °, or + 15 °
When the value exceeds, the volume resistivity ρ of the conductive layer apparently becomes too small, and the current flowing from the transfer belt to the photoconductor increases, which causes a problem that image unevenness is likely to occur.
Further, there is also a problem that the tension of the transfer belt is increased and a load is applied to a rotation drive system of the transfer device.

The value of the degree of molecular orientation MOR-C of the conductive layer is usually in the range of 1.4 to 60, preferably 2 to 40. When the degree of molecular orientation MOR-C exceeds 60, the stress relaxation rate of the transfer belt increases, causing a problem that the transfer belt is plastically deformed and the quality of the formed image is deteriorated. Further, the volume resistivity ρ of the transfer belt becomes apparently too large, and image unevenness occurs. Further, there is a problem that the tension of the transfer belt is reduced. On the other hand, when the degree of molecular orientation MOR-C is less than 1.4, the tension of the transfer belt increases, causing a problem that a load is applied to the rotation drive system of the transfer device. Further, the volume resistivity ρ of the transfer belt becomes apparently too small, and image unevenness occurs.

On the same line along the width direction of the conductive transfer belt, a value obtained by dividing the difference between the maximum value and the minimum value of the molecular orientation MOR-C by an average value, that is, the following formula: The value expressed by (minimum value) / average value is suitably less than 0.4, preferably less than 0.3. When the value of the above formula is 0.4 or more, that is, when the above formula (1) is not satisfied, the dispersion of the orientation state of the conductive layer in the width direction of the conductive transfer belt becomes large, and transfer failure may occur. is there.

In the conductive transfer belt of the present invention, the volume resistivity ρ of the conductive layer is defined as “resistivity” of JIS K6911.
Is usually 10 ⁴ to
10 ¹⁰ Ω · cm, preferably 10 ⁵ to 10 ⁹ Ω · cm
It is appropriate to set in the range of cm. When the volume resistivity ρ of the conductive layer is lower than the above range, an excessive current may flow through the photoconductor, and the surface of the photoconductor may be damaged due to generation of pinholes. Further, the toner may be reversely charged to cause a transfer failure, or an image problem such as a leak or a paper stain may occur. On the other hand, the volume resistivity ρ
Is larger than the above range, the current flowing from the conductive transfer belt to the photoreceptor is so small that the toner cannot be attracted to the transfer paper, so that the transfer efficiency is deteriorated and is not suitable for practical use.

The thickness of the conductive layer is set to be in the range of 0.2 to 3 mm, preferably 0.3 to 1.5 mm.
When the thickness of the conductive layer is less than the above range, the tension of the conductive transfer belt decreases, and slip occurs between the drive roller and the conductive transfer belt. On the other hand, when the thickness exceeds the above range, the tension of the conductive transfer belt increases, and a load is applied to the rotation drive system.

The above-mentioned conductive layer can be used as it is as a conductive transfer belt, but it improves the chemical stability of the belt surface, stabilizes the surface resistivity, and prevents the belt surface from being stained by toner adhesion. For the purpose of prevention, a surface layer made of a coating agent such as urethane resin or fluororesin may be formed on the surface. The surface layer is formed by applying the coating agent to the surface of the conductive layer using an electrostatic coating machine or the like. The thickness of the surface layer is
Usually, it is adjusted to be 1 to 10 μm, preferably about 5 μm.

The conductive transfer belt of the present invention may have a structure in which a conductive layer and, if necessary, a surface layer are formed on a support layer, in addition to the above structure. As the support layer, for example, polyethylene terephthalate (PET)
And a woven or non-woven fabric impregnated with a resin.

[0037]

Next, the conductive transfer belt of the present invention will be described with reference to examples and comparative examples. Examples 1 to 3, Comparative Examples 1 to 3 A rubber component, carbon black and various additives were blended in the amounts shown in Table 1 below. The materials used in the examples and comparative examples are as follows. The unit of the compounding amount is parts by weight. Rubber component chloroprene: Neoprene W, manufactured by Showa Denko Dupont
RT EPDM: Mitsui Petrochemical Co., Ltd., EPT4021 Carbon Black Acetylene Black: Denka Black, manufactured by Denki Kagaku Co., Ltd. Diamond Black: Diamond Black LI, manufactured by Mitsubishi Chemical Co., Ltd. Other additives Plasticizer: Idemitsu Kosan Co., Ltd., paraffin oil PW380 Zinc oxide : Zhonghua # 1 silica, manufactured by Shodo Chemical Co., Ltd. Silica: Nipsil ER-R, manufactured by Nippon Silica Co., Ltd. Vulcanizing agent: sulfur Vulcanization accelerator: Noxeller DT, manufactured by Ouchi Shinko Chemical Co., Ltd. The ribbon was removed.
In addition, an extrusion molding machine (Nakada Zoki Co., Ltd., φ60 VAK)
And extruded under the conditions shown in Table 1 to a thickness of 1 m.
m, length in the moving direction (circumferential direction of the belt) is 321 m
m, a belt-shaped conductive layer having a length in the width direction of 360 mm was formed. Next, this conductive layer was heated at 160 ° C. for 30 minutes to perform vulcanization.

Table 1 shows the conditions of the extrusion molding in each of the examples and comparative examples, together with the mixing ratios of the above components.

[0039]

[Table 1]

Next, the length of the conductive layer in the width direction is set to 342 m.
m, and a urethane resin was applied to the surface of the conductive layer with an electrostatic coating machine to form a surface layer having a thickness of 5 μm, thereby obtaining a conductive transfer belt. Actual machine test The conductive transfer belt of each of the above Examples and Comparative Examples was installed in a transfer device of an electrostatic copying machine to perform image formation, and it was visually confirmed whether or not accurate transfer was performed. The quality of was evaluated. Evaluation of Characteristics of Conductive Layer The surface layer of the conductive transfer belt obtained in the above Examples and Comparative Examples was polished and removed, and a belt-shaped conductive layer was taken out.

Next, as shown in FIG. 2, rows at equal intervals from the first row A to the fifth row E are determined in the moving direction X of the transfer belt. A total of 25 measurement positions were determined at five equally spaced intervals. JIS K6 for the above 25 measurement positions
The volume resistivity ρ was measured according to the method described in 911 “Resistance”. In order to evaluate the variation of the volume resistivity ρ in the width direction of the conductive transfer belt, the first transfer resistance shown in FIG.
The maximum value and the minimum value were obtained for each column from column A to the fifth column E, and the difference between the logarithmic values was obtained. The result is Δlo
It is shown in Table 2 below as g ρ.

Next, the conductive layer at each measurement position was 30 mm long.
× 30 mm wide × 0.5 mm thick, molecular orientation angle θ
And the degree of molecular orientation MOR-C was measured according to the method described above. When performing the thickness correction of the degree of molecular orientation, the above equation
The corrected thickness t _C of (2) was 1.08 mm, and the thickness t _{S of the} sample was 0.5 mm. The measurement was performed using a molecular orientation meter (model number MOA-3012A) manufactured by Shin-Oji Paper Co., Ltd., at a microwave (polarization) frequency of 12 GHz.
The rotation speed of the sample was set to one rotation in 12 seconds, and the intensity of the microwave polarization was detected each time the sample rotated 1 °, and the molecular orientation angle θ and molecular orientation were determined from a total of 360 data. The degree MOR-C was calculated.

Molecular orientation angle θ and molecular orientation degree MOR-C
Is the average value of each row from the first row A to the fifth row E (that is, the average value in the width direction of the conductive belt). In addition, in order to evaluate the variation of the molecular orientation MOR-C in each row, the molecular orientation MOR-
The difference between the maximum value and the minimum value of -C was obtained, and the difference was divided by the average value as shown in the above formula (1). The result is Δ
It is shown in Table 2 as MOR-C.

The molecular orientation angle θ and the degree of molecular orientation MOR−
Table 2 shows the results of C, ΔMOR-C and Δlog ρ.

[0045]

[Table 2]

In the conductive transfer belts of Examples 1 to 3, the values of the molecular orientation angle θ and ΔMOR-C of the conductive layer are set within the range of the present invention, and all of them can perform accurate transfer. No unevenness was observed in the formed image. On the other hand, in the conductive transfer belts of Comparative Examples 1 to 3, the molecular orientation angle θ and ΔMOR-C of the conductive layer were out of the range of the present invention, and accurate transfer could not be realized. The image was uneven.

It should be noted that both the examples and the comparative examples have Δl
Although the value of og ρ was small, in the comparative example in which one of the molecular orientation angle θ and ΔMOR-C of the conductive layer was out of the range of the present invention, unevenness occurred in the formed image.
That is, the correlation between the variation in the volume resistivity ρ in the width direction of the transfer belt and the quality of the formed image is low.

[0048]

As described above, according to the conductive transfer belt of the present invention, the formed image is not uneven, accurate transfer can be realized, and good image quality can be obtained.
Therefore, the conductive transfer belt of the present invention is suitably used for an image forming apparatus such as an electrostatic copying machine.

[Brief description of the drawings]

FIG. 1 is an orientation pattern diagram of a conductive layer.

FIG. 2 is a schematic diagram showing a sampling position of a measurement sample on a conductive transfer belt.

[Explanation of symbols]

 X moving direction Y width direction

Claims (4)

(57) [Claims] 1. A conductive transfer belt having at least a conductive layer, wherein on the same line along the width direction of the belt orthogonal to the moving direction of the belt, (i) the conductive layer
The average value of the molecular orientation angle θ with respect to the width direction of the belt is −
(Ii) the relationship between the average value, the maximum value, and the minimum value of the molecular orientation MOR-C of the conductive layer is represented by the following formula (1): (maximum value−minimum value) / A conductive transfer belt having an average value of <0.4 (1). 2. The method according to claim 1, wherein the average value of the molecular orientation MOR-C of the conductive layer is in the range of 1.4 to 60 on the same line along the width direction of the belt perpendicular to the moving direction of the conductive transfer belt. Item 7. The conductive transfer belt according to Item 1. 3. The conductive layer has a volume resistivity ρ of 10 ⁴ to 10.
^2. The conductive transfer belt according to claim 1, which has a resistivity of ¹⁰ Ω · cm. 4. The conductive transfer belt according to claim 1, wherein said conductive layer has a thickness of 0.2 to 3 mm.