JPH0527550A - Electrophotographic electrifier and electrophotographic device using this device - Google Patents

Abstract

PURPOSE:To stably assure semiconductivity at a low cost and to prevent flawing of a contact party by using a specific resin compsn. to constitute a contact electrifying part. CONSTITUTION:The conductive resin compsn. compounded with zinc oxide whiskers is used for a semiconductive cylindrical molding 8 constituting the contact electrifying part of an electrifying roller (electrifier) and further, a light source 11 for irradiating the surface of this conductive roller 2 is provided. The illuminance and light spectra of this light source 11 is preferably made variable. The zinc oxide whiskers can be arbitrarily stabilized between 10<5> to 10<10>OMEGA by taking the intrinsic resistance value and sizes of the whiskers and the compounding ratio thereof into consideration if such whiskers are compounded as an electrical conductivity imparting material with the resin. Since the molding can be produced by infection molding extrusion molding, compression molding, etc., the molding have high mass productivity and can be produced at a low cost. The oxide whiskers are soft packing materials and, therefore, hardly flaw the photosensitive body. The surface resistance value of the electrifying roller can be varied by the light source and is adjustable to an optimum electrifying state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic charger and an electrophotographic apparatus using the same, and more particularly to an improvement of a conductive material in a contact charging type charger and an electrophotographic apparatus having a structure corresponding thereto. is there.

[0002]

2. Description of the Related Art Conventionally, as a charging device type in an electrophotographic apparatus, a non-contact charging type corona discharge charging device, a contact charging type conductive brush charging device and a conductive roller charging device have been known.

In particular, a conductive roller charger that does not use corona discharge causes less damage to the photosensitive member because it produces less ozone, and has a low voltage (for example, 0.4 to 1K).
Since it is charged with V), it has many advantages such as high safety and low power supply cost, and various technical developments have been devised so far.

In the contact charging type electrophotographic apparatus, as shown in FIG. 4, a charging roller 2 as a charging device, an exposure light source 3, a developing device 4, a transfer portion 5, a charge eliminating portion 6 and A cleaning blade 7 is arranged to uniformly charge the photoconductor 1 and then expose it to develop the formed electrostatic latent image, transfer it to a sheet at a transfer portion, and then remove residual charges of the photoconductor 1. Then, the residual toner on the photoconductor 1 is removed.

A material having a semi-conductivity (a resistance value between the roller surface and the roller core is 10 ⁵ to 10 ⁹ Ω) is particularly suitable as a material forming the charging roller 2, and a conductive material obtained by kneading carbon black into rubber. Rubber rollers and ceramic rollers have been proposed.

That is, V. E. STRAUGHAN, et al. (Pro.Nat. Electronics Conf., 13, 959-96)
8 (1957)) and JP-A-56-104346, a conductive rubber roller is disclosed.
The publication discloses a semiconductive ceramic roller.

Further, conventionally, there has been proposed a technique of changing the temperature of the roller to change the conductivity of the conductive roller.

[0008]

However, the conventional conductive contact charging member has the following problems.

First, the material obtained by kneading carbon black into rubber has a low resistance value of carbon black itself (10
^{Since it is 3} Ω-cm or less, it is semi-conductive (eg 10 ⁵ to 10 ^9).
Ω) is extremely difficult to stabilize, and it appears as deterioration of reliability of characteristics and product variations, and a means for stabilizing with semiconductivity has been strongly desired.

On the other hand, as for the semiconductive ceramic roller, the materials that can stably secure the semiconductive property are limited, and the cost is high, the mass productivity is poor, and the cost is inevitably high, and the roller itself is hard. Therefore, the photoconductor (xerographic photoconductor) of the contact partner is easily scratched, and the roller itself is fragile and the impact strength is weak, so there is a problem in durability.

Further, the heating type resistance variable roller is
Since the variable response is poor and the influence of heat on the photoconductor occurs, further preferable technical development has been desired.

In view of the above-mentioned conventional problems, the present invention provides a contact charging type electrophotographic charger which can secure semiconductivity stably at a low cost and does not damage the contact partner, and a charger for the same. The purpose of the present invention is to provide an electrophotographic device.

[0013]

In the charger for electrophotography of the present invention, the contact charging section is formed by using a resin composition containing at least zinc oxide whiskers.

Further, the electrophotographic apparatus of the present invention comprises a charging roller composed of a resin composition containing at least zinc oxide whiskers, and a light source for irradiating the surface of the charging roller. The light spectrum is variable.

[0015]

According to the present invention, the resistance value of the contact charging portion can be easily stabilized with semiconductivity (10 ⁵ to 10 ⁹ Ω) and the mass productivity is excellent, so that the cost can be reduced.

More specifically, the intrinsic resistance value inside the zinc oxide whisker crystal is considered to be quite low. However, the aggregate of whisker powder in a powder compacted by pressure or in a state of being compounded in a resin is shown. The resistance value is considerably high, and is about 10 ⁵ Ω-cm or more. In other words, zinc oxide whiskers are small needle-shaped complete single crystals, and their conductivity depends on the properties of the n-type semiconductor of zinc oxide. Therefore, the contact interface between single crystals is explained by a double Schottky barrier. There is a high resistance interface that is created. Therefore, the zinc oxide whisker powder compact and the resin composition have a high electric resistance and are stabilized at a high resistance. This phenomenon is in contrast to the case where metal powder or carbon (both of which have a low specific resistance value) is used and stabilized with low resistance (for example, 10 ^-2 to 10 ³ Ω-cm).

When this zinc oxide whisker is blended with a resin as a conductivity-imparting material, by considering the specific resistance value and size of this whisker and the blending amount,
It can be arbitrarily stabilized between 0 ^{5 and} 10 ¹⁰ Ω.

Further, when this resin composition is used, a charging device in the form of a charging roller or the like can be produced by injection molding, extrusion molding, compression molding or the like, so that mass production is excellent and production at low cost becomes possible. Further, since the resin composition is highly filled with zinc oxide whiskers, it is possible to perform precise molding and is suitable for a charger that comes into precise contact with the photoconductor. Further, the charger made of the whisker-reinforced resin is excellent in abrasion resistance on the contact surface and high in impact resistance because the resin is micro-reinforced by the whiskers, and thus is also excellent in durability. On the other hand, since zinc oxide whiskers have a Mohs hardness of 4 and are a soft filler, it is also a great feature that a charging device that does not easily damage the photoconductor of the other material is realized. In addition, zinc oxide whiskers have a high specific gravity (5.8), and the resin in which the whiskers are highly filled has a high specific gravity, so the inertia during rotation is large,
Further, it is possible to realize a charging device (charging roller) capable of maintaining close contact even under high speed rotation.

Next, by providing a light source for irradiating the surface of the charging roller, the surface resistance value of the charging roller can be varied and the charging state can be adjusted to an optimum state. Moreover, this method is superior in response as compared with the heating method, and has no thermal effect on the photoconductor.

According to this principle, since zinc oxide whiskers are a photoconductive material, the surface resistance value of the charging roller can be changed by changing the illuminance or spectrum of light (visible light, ultraviolet light, etc.).

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

In the present invention, particularly preferable results can be obtained by using a tetrapot-shaped zinc oxide whisker (an electron micrograph of which is shown in FIG. 3), but a simple needle-shaped zinc oxide whisker is used. However, the same effect can be obtained.

This tetrapot-shaped zinc oxide whisker contains a molten metal of zinc at 700 to 1100 ° C., preferably 800 to 100 ° C. in an atmosphere containing oxygen with an oxygen concentration of several percent or less.
It can be generated by heat treatment at 1050 ° C.
However, the generation method is not limited to the so-called molten metal method.

The obtained zinc oxide whiskers usually have an apparent bulk specific gravity of 0.02 to 0.5, and have a high yield of 70% by weight or more, and are extremely highly producible.

When the X-ray diffraction pattern of this zinc oxide whisker was taken, it usually showed all the peaks of zinc oxide. On the other hand, the electron diffraction results also showed single crystallinity with few transitions and lattice defects.

Further, the content of impurities was also small, and as a result of atomic absorption analysis, zinc oxide was 99.9%.

Incidentally, the needle-shaped crystal part of the zinc oxide whisker may be a mixture of triaxial, biaxial or uniaxial ones in addition to the four axial ones. Is. It is also recognized that zinc oxide in the form of plate crystals is mixed.

Among the tetrapod-shaped zinc oxide whiskers, the length from the base to the tip of the needle-shaped crystal part is 3 μm.
Whiskers having an aspect ratio (length / diameter of the base portion) of 3 or more at m or more are preferable from the viewpoint of imparting conductivity. Here, the base portion is a portion connected to the core portion of each needle-shaped crystal portion with the central portion where the axes of the needle-shaped crystals extending in the four-axis directions are gathered as the core portion.

Further, it is more preferable to use a whisker having a needle-shaped crystal portion with a length of 10 μm or more and an aspect ratio of 5 or more because the conductivity is further improved.

On the other hand, from the viewpoint of uniformly kneading into the resin to obtain stable conductivity, the length of about 200 μm or less is preferable, and the length of 150 μm or less is optimal.

From the viewpoint of breakage of whiskers, the aspect ratio is preferably 1000 or less, and particularly 50 or less gives good results.

By the way, the resistance value of the zinc oxide whiskers used in the present invention is preferably in the range of 10 ⁵ to ¹⁰ 10 Ω-cm, and whiskers of 10 ⁷ to 10 ⁹ Ω-cm are particularly suitable.

The method for measuring the resistance value of the zinc oxide whisker used in the present invention is as follows. First, 0.5 g of zinc oxide whiskers is sampled and evenly sandwiched between a pair of flat plate electrodes having a diameter of 20 mm, and a pressure of 5 kg / cm ² is uniformly applied to the sample. Next, the resistance between the pair of flat plate electrodes is measured by a super insulation resistance tester (HP,
Read using a High Resistance Meter 4329A) at a measuring voltage of 25V. Next, take out a dust sample of zinc oxide whiskers, measure the sample thickness with a caliper, and calculate from the sample thickness, the sample area (3.14 cm ² ) and the resistance value obtained earlier by the following formula. Then, the volume resistance value P is obtained.

P [Ω-cm] = R · S / t where R [Ω]: resistance value S [cm ² ]: sample area t [cm]: sample thickness Next, zinc oxide whiskers in resin The mixing ratio of is 20
It is preferably not less than wt% and not more than 80 wt%. If it is less than 20 wt%, sufficiently stable conductivity is not imparted, and if it exceeds 80 wt%, the composite becomes extremely brittle, which is not preferable. 40 wt% to 70 wt% is particularly preferred to obtain a balanced composite.

Next, as the type of resin used, either thermosetting resin or thermoplastic resin can be used.

The thermosetting resin may be, but is not limited to, an epoxy resin, a silicone resin, an unsaturated polyester resin, or the like.

As the thermoplastic resin, either a crystalline resin or an amorphous resin can be used, but a resin having a large amount of crystalline components is particularly suitable.

The thermoplastic resin used is not limited, but polypropylene, polyethylene, chlorinated polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyamide, polysulfone, polyetherimide, polyether sulfone, polyphenylene sulfone, polyphenylene sulfide, poly Ether ketone, polyether ether ketone, ABS resin, polybutadiene, polymethylmethacrylate, polyacrylonitrile, polyacetal, polycarbonate, ethylene-vinyl acetate copolymer, polyvinyl acetate, ethylene-
Tetrafluoroethylene copolymer, aromatic polyester,
Polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene chloride, "Teflon" (fluorine resin manufactured by DuPont), polyarylate, polyvinyl chloride, grafted polyphenylene ether (modified PPE resin), polystyrene, etc. either alone or together Resin made of polymer and 2 of such resin
Alloys and mixtures of more than one species are applied.

As the crystalline thermoplastic resin giving more preferable results, polypropylene, polybutylene terephthalate, polyethylene terephthalate, polyamide (for example, PA-6, PA-66, PA-610, PA-) is used.
11, PA-12, PA-46), polyphenylene sulfide, polyether ether ketone, polyacetal, various liquid crystal polymers (fully aromatic liquid crystal polyester, semiaromatic liquid crystal polyester, etc.) and the like are suitable.

Among these, polypropylene and polybutylene terephthalate are particularly preferable. Besides, various rubbers and elastomers (for example, NBR, EPDM, chloroprene, etc.) are used.

Next, for mixing and kneading the resin and the zinc oxide whiskers, various devices conventionally used for kneading this kind of composite material are used. That is, the use of a single-screw type or multi-screw type extruder gives good results, and a screw rotary blade type container fixed type such as a ribbon blender or a super mixer (Hensiel mixer), or a horizontal cylindrical type or an inclined cylindrical type. Alternatively, a container rotary type mixer such as a V-type tumble mixer is used.

Next, injection molding, extrusion molding, compression molding or the like can be used to mold the charger member using these resin compositions.

On the other hand, zinc oxide whiskers surface-treated with a coupling agent are used in order to obtain a resin composition having stable electrical conductivity and mechanical properties. As the coupling agent,
A silane-based, chromium-based or titanium-based coupling agent, a silyl peroxide-based agent, and an organic phosphoric acid-based agent can be used, and the silane coupling agent is particularly effective.

In the resin composition used in the present invention, conductive fillers which have been conventionally used, that is, silver, copper, gold,
Metals such as aluminum, nickel, palladium, iron, and stainless steel; metal oxides such as tin oxide, antimony-doped tin oxide, conductive potassium titanate, indium oxide, and lead oxide; silicon carbide, zirconium carbide, and carbonization. Insulating or low-conductivity-based materials such as carbon-based powders such as titanium, or carbon-based powders such as highly conductive carbon, graphite, and acetylene black, flakes, beads, fibers, or the above powder materials such as antimony-doped tin oxide. Needless to say, it is possible to improve the conductivity and other physical properties by blending powder, flakes, beads, and a fiber material with an appropriate amount of a conductive filler coated by various methods.

On the other hand, powders and flakes of organic conductive polymers such as polyacetylene, polypyrrole, polythiophene, polyaniline, and TCNQ may be used together as a conductive filler in an appropriate amount, or high alcohol, quaternary ammonium salt, potassium salt or sodium may be used. Salt-type amphoteric cation
There is no problem in adding an appropriate amount of anionic antistatic agent.

In addition to the above, various fillers and flame retardants conventionally used (for example, for the purpose of improving various mechanical properties, reducing total cost, or making flame retardant within a range not significantly impairing the overall conductivity) (for example, , Glass fiber, glass flakes, glass beads, talc, mica, calcium carbonate, clay, barium sulfate, aluminum hydroxide, alumina, titanium oxide, silica, white carbon, diatomaceous earth, molybdenum disulfide, carbon black, graphite, wood Powders, phosphagen compounds, phosphoric acid esters, etc.), and colorants such as titanium oxide, zinc oxide, red iron oxide, etc., various stabilizers, deterioration inhibitors, etc. may be blended in appropriate amounts.

Next, the present invention can be widely applied to various contact charging type charger members.

That is, although not particularly limited, it can be applied to, for example, a charging roller or a charging brush. Needless to say, the same idea can be extended to a charge eliminating roller, a cleaning roller and the like.

Further, the resistance value (ASTM-D257) of the resin composition used in the present invention is preferably 10 ⁵ to 10 ¹⁰ Ω-cm, and particularly preferably 10 ⁷ to 10 ⁹ Ω-cm.

Next, the light source used in the present invention may have any shape as long as the irradiated portion is uniformly irradiated, and a rod-shaped or non-shaped light source is preferable.

The light source is preferably in the visible to ultraviolet region, and the optimum charged state can be obtained by changing the illuminance or spectrum and changing the resistance value of the charger.

The illuminance is adjusted by providing a slit, changing the amount of light, and changing the irradiation distance.
A method of changing the optical spectrum by utilizing the optical spectrum dependence of the surface resistance of the resin composition is also very effective.

On the other hand, in the present invention, since a white charger can be formed, the reflected light can be utilized to effectively detect the degree of contamination by toner or the like. Further, even if the charging roller is of a plural type, there is no problem.

Example 1 The aspect ratio is 3 or more, the length from the base to the tip is 3 to 30 μm, and the resistance value is 3 × 1.
Prepare a tetrapot-shaped zinc oxide whisker of 0 ⁸ Ω-cm and use polypropylene (Mitsubishi Yuka Co., Ltd .: product number BC1E).
Then, the mixture was kneaded using a ruder, extruded, and pelletized using a pelletizer. At this time, the kneading temperature is 180 to 19
At 0 ° C., the zinc oxide whisker content was 60% by weight (% by weight based on the total resin composition).

The pellets (specific gravity: 1.8) were injection-molded by a usual method to form a semi-conductive cylindrical molded body 8 to be a contact charging portion in the charging roller 2 shown in FIG.
The semiconductive tubular molded body 8 had an outer diameter of 50 mm, an inner diameter of 30 mm, and a length of 400 mm, and the mold temperature during molding was 50 ° C. Next, the roller core 9 made of stainless steel, which exactly matches the inner diameter of the semi-conductive tubular body 8, was inserted to form the charging roller 2 as a charger. When the resistance values on the surfaces (pin points) of the roller core 9 and the semiconductive tubular molded body 8 were measured, the average value was 6 × 10 ⁸ Ω at 500 VDC, and the variation was extremely small.

As shown in FIG. 1, the charging roller (charging device) 2 was brought into contact with the photosensitive member 1 and mounted on an electrophotographic apparatus. The semi-conductive tubular molded body 8 was white, had a smooth surface, and had extremely excellent adhesion to the photoreceptor 1. 10 is a cleaning blade of the charging roller 2. When the charging roller 2 was operated with an applied voltage of 700 V, it was found that an electrophotographic image with good image quality could be obtained. That is, the charging roller 2 follows well even when the photosensitive member 1 rotates at high speed, which is the basis for obtaining high image quality. Further, from the result of the durability test, it was found that the charging roller 2 rarely scratches the xerographic photoreceptor 1, and the charging roller 2 itself has extremely high abrasion resistance.

(Second Embodiment) In addition to the apparatus of the first embodiment,
As shown in FIG. 2, a light source (ultraviolet germicidal lamp 15W) 11 is added. The light source 11 is covered with a cover 13 except for a portion facing the charging roller 2, and a slit 12 provided in a portion facing the charging roller 2 is adjusted to change the irradiation light amount to the charging roller 2. Is configured to get.

When the electrophotographic apparatus was operated with this apparatus, it was found that the charged state could be optimized by adjusting the width of the slit 12 and the image quality could be improved.

[0059]

EFFECTS OF THE INVENTION According to the present invention, since the contact charging section is formed by using the resin composition containing the zinc oxide whisker as described above, it is possible to stably obtain an appropriate conductivity, It is possible to realize a contact charging method that has not been widely used because conductive materials could not be procured, it can be driven at low voltage, it is highly safe, and it is excellent in downsizing and cost reduction.
Furthermore, it is possible to suppress the generation of ozone and remove the damage to the photoconductor, and by providing a light source and varying the surface resistance value, it is possible to adjust to an optimum charged state. It has excellent response and has no effect on heat on the photoconductor. Its application range is not limited to copiers, but it can be applied to all devices that apply electrophotography, such as facsimiles and printers, and is industrially large. Be effective.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a main part of an electrophotographic apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of a main part of an electrophotographic apparatus according to a second embodiment of the present invention.

FIG. 3 is an electron micrograph of zinc oxide whiskers.

FIG. 4 is a sectional view showing a schematic configuration of an electrophotographic apparatus.

[Explanation of symbols]

1 photoconductor 2 Charging roller (charging device) 8 Semi-conductive tubular molding (contact charging part) 11 light source 12 slits

Claims (10)

[Claims] 1. A charger for electrophotography, comprising a contact charging section formed by using a resin composition containing at least zinc oxide whiskers. Wherein the resistance value of the zinc oxide whisker 10 ^5-1
The charger for electrophotography according to claim 1, which has a resistance of ⁰⁹ Ω-cm. 3. The charger for electrophotography according to claim 1, wherein the length from the base to the tip of the zinc oxide whisker is 3 to 200 μm. 4. The charger for electrophotography according to claim 1, wherein the zinc oxide whiskers have an aspect ratio of 3 or more. 5. The resin composition containing zinc oxide whiskers in an amount of 20 to 20.
The electrification device for electrophotography according to claim 1, wherein 80% by weight is blended. 6. The resin composition has a resistance value of 10 ⁵ to 10 ⁹ Ω.
The charger for electrophotography according to claim 1, wherein the charger is -cm. 7. The charger for electrophotography according to claim 1, wherein the charger comprises a charging roller. 8. The charger for electrophotography according to claim 1, wherein the zinc oxide whiskers are in a tetrapot shape having a core portion and needle-shaped crystal portions extending from the core portion in different four-axis directions. 9. An electrophotographic apparatus comprising: a charging roller made of a resin composition containing at least zinc oxide whiskers, and a light source for irradiating the surface of the charging roller. 10. The electrophotographic apparatus according to claim 9, wherein the light source is configured such that its illuminance or light spectrum is variable.