JP2012237901A - Semiconductive belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductive belt that prevents a resistance value from being changed with time from immediately after manufacturing to installation in an image forming device.SOLUTION: The semiconductive belt includes an elastic layer made of semiconductive rubber and a surface layer having lubricity. The elastic layer contains ethylene-propylene rubber as a rubber raw material, and contains 30-70 pts.wt. of conductive carbon black with respect to 100 pts.wt. of the ethylene-propylene rubber. When the resistance value to be obtained immediately after manufacturing is R, and the resistance value to be obtained 30 days after is R, 100[(logR)-(logR)]/(logR)≤6(%) is satisfied.

Description

  The present invention relates to a transfer belt and a transfer conveyor belt in an image forming apparatus such as a plain paper copier, a color copier, a laser beam printer, a facsimile, and an OA apparatus having a combined function of these using the basic principle of electrophotography. In particular, the present invention relates to a semiconductive belt that can be used in the same manner and a method of manufacturing the same.

  Semiconductive belts such as transfer belts, transfer conveying belts, and intermediate transfer belts used in electrophotographic image forming apparatuses are known, and such semiconductive belts can be used as a conductive additive for rubber materials. Or at least the surface of the elastic layer to which the filler is added is provided with a surface layer which is a lubricating layer (Patent Documents 1 to 5, etc.).

  The invention disclosed in the above-mentioned Patent Document 1 can be used for a semiconductive belt, etc., has a small volume resistivity change in a medium resistance region, is excellent in mass production stability, and has excellent workability and ozone resistance. Also, the rubber for the elastic layer is excellent, and is characterized in that carbon black having an average particle diameter of 80 nm or more and carbon black having an average particle diameter of 30 nm or less are blended in the raw rubber. The invention disclosed in Patent Document 2 is substantially free from unevenness in resistance in the belt circumferential direction, variation in resistance with time, and variation in resistance value at the time of manufacture, and good transferability in a low temperature, low humidity environment, high temperature and high humidity environment, and The present invention relates to a transfer / conveying belt that can ensure the transportability, and has a three-layer structure, and the intermediate layer is an ion conductive elastic layer.

The invention disclosed in Patent Document 3 satisfies characteristics required for a transfer belt such as ozone resistance, flame retardancy, and prevention of deterioration, is free from bleed and bloom, and has little fluctuation in electrical resistance over time. It relates to a transfer belt that can stably obtain a good transfer image. The raw rubber is composed of chloroprene rubber and ethylene / propylene / non-conjugated diene terpolymer, and chloroprene rubber is an essential component. is there.

The belt disclosed in Patent Document 4 can follow the rubber layer satisfactorily, can easily adjust the resistance, and can satisfy functions such as prevention of contamination of the photosensitive member, prevention of toner adhesion, and reduction of the friction coefficient. The skin layer is formed using a polyolefin-based urethane resin as a main material.

The invention disclosed in Patent Document 5 has a coating layer (surface layer) that follows the elastic deformation of an elastic layer made of rubber or the like and has good durability against ozone and nitrogen oxides, This is related to a belt that is an intermediate transfer member that can stably obtain a good image over a long period of time without deteriorating transfer performance even in long-term use. An intermediate transfer is performed by forming a coating layer made of a resin on an elastic layer. When a member is obtained, a urethane resin having excellent conformability to elastic deformation is used as a base resin for forming a coating layer, and an oxide of a metal selected from aluminum, zinc, magnesium, and calcium is used as the urethane resin. Alternatively, a hydroxide is contained.

JP-A-8-127675 JP-A-8-292648 JP-A-9-179414 Japanese Patent Laid-Open No. 11-45015 JP 2000-19855 A

  As the semiconductive rubber constituting the elastic layer, Patent Document 1 lists all known raw rubbers without specifying the raw rubber in the detailed description of the invention, and in the examples, ethylene propylene rubber mainly composed of natural rubber. (Hereinafter referred to as EPDM) is used together, and in Patent Document 2, the elastic layer is exemplified by one or more of hydrin rubber, chloroprene rubber, urethane rubber, and EPDM as raw material rubber, and contains an ion conductive additive. . The raw material rubber constituting the semiconductive rubber of Patent Document 3 is a blend rubber of chloroprene rubber (CR) and EPDM. In Patent Documents 4 and 5, the material of the elastic layer is particularly characterized because it is characterized by the structure of the skin layer. There is no limitation, and the raw rubber used in the examples is chloroprene rubber (Patent Document 4), a combined rubber of nitrile rubber and EPDM (Patent Document 5).

  However, the ion conductive rubber used in Patent Document 2 has a problem that the resistance value is easily influenced by humidity, and the present invention is a belt coated on both sides in order to suppress the influence of humidity. Yes. Furthermore, Patent Document 2 points out the problem of using conductive carbon. The conductivity of rubber compounded with conductive carbon black is electronic conduction through carbon black, and has a completely different conduction mechanism from ionic conduction.

A blended rubber of chloroprene rubber (CR) and EPDM disclosed in Patent Documents 3 to 5, chloroprene rubber, a combined rubber of nitrile rubber and EPDM is used as a raw rubber, and a lubricating surface layer is provided on an elastic layer to which conductive carbon black is added. When a lubricating paint to be formed is applied and dried to form a semiconductive belt such as a transfer belt or a transfer and transport belt, there is a problem that the resistance value increases with time, and the increase varies. For this reason, in order to obtain a belt that is within the standard value set by the image forming apparatus when it is actually mounted on the image forming apparatus, the resistance value of the belt must be set and manufactured by taking into account the rise and variation caused by changes over time. Don't be. In addition, due to variations in the resistance value, the occurrence of non-standard resistance value belts at the time of delivery is unavoidable, and improvements have been demanded from the viewpoint of reducing the defect rate and ensuring the stability of quality.

  An object of the present invention is to provide a semiconductive belt having a small change in resistance over time from immediately after manufacture to when an image forming apparatus is mounted.

The semiconductive belt of the present invention has an elastic layer made of semiconductive rubber and a surface layer having lubricity,
The elastic layer contains ethylene propylene rubber as a raw rubber component, and contains 30 to 70 parts by weight of conductive carbon black with respect to 100 parts by weight of the ethylene propylene rubber. The resistance value immediately after production is R ₀ , 30 days. 100 [(log R _f ) − (log R ₀ )] / (log R ₀ ) ≦ 6 (%), where R _f is the resistance value after that (surface resistance value: unit Ω / □)
It is characterized by being.

The semiconductive belt having such a configuration has a small change in resistance value with time from immediately after manufacture to when the image forming apparatus is mounted. 100 _[(logR f) - (logR _0)] / (logR ₀₎ is preferably not more than 5%, and more preferably 4% or less. If the change in resistance value with time is small, the belt resistance value has a stable resistance value variation since the change (variation) in the resistance value of the belt in use is small after the image forming apparatus is mounted.

  Although it is not clear why the change in the resistance value over time from the time immediately after manufacture of the belt of the present invention to when the image forming apparatus is mounted is small, chloroprene rubber (CR) or nitrile rubber (NBR) is used alone or as EPDM. When used in combination, it is presumed that the influence of these polar rubbers may affect the change in belt resistance with time. In the case of ionic conductivity, it is difficult to set the adjustment range of the resistance value as wide as that of the conductive carbon black, and the resistance value is likely to fluctuate due to the influence of humidity.

Another aspect of the present invention is a method for producing a semiconductive belt having an elastic layer made of semiconductive rubber and a surface layer having lubricity,
Having a manufacturing process of the elastic layer and a coating process of forming a surface layer;
In the elastic layer manufacturing process, ethylene propylene rubber is used as a raw rubber component, and 30 to 70 parts by weight of conductive carbon black is added to and kneaded with 100 parts by weight of the ethylene propylene rubber to manufacture an unvulcanized rubber composition. A kneading step, an extrusion molding step in which the unvulcanized rubber composition is molded into a belt shape to form an unvulcanized belt, and a vulcanization step in which the unvulcanized belt is molded into an elastic layer,
100 [(logR _f ) − (logR ₀ )] / (logR ₀ ) ≦ 6 (%) where R _{0 is} the resistance value immediately after the coating process and R _f is the resistance value after 30 days.
It is characterized by being.

  According to the manufacturing method having such a configuration, it is possible to manufacture a semiconductive belt having a small change in resistance value with time from immediately after manufacturing to when the image forming apparatus is mounted, thereby achieving a reduction in defect rate and an improvement in quality stability. it can.

Nonpolar ethylene propylene rubber is used as the rubber material constituting the elastic layer of the semiconductive belt of the present invention (volume resistivity range 10 ⁵ to 10 ¹¹ Ω · cm). The raw rubber used in Patent Document 1 is EPDM and natural rubber, and the ratio of natural rubber is 15% or more (in the claims, “15% or more”, but the error is only 15% or less in Examples) Not described), and EPDM-only examples are not disclosed. The belt disclosed in Patent Document 2 does not use conductive carbon black. The belt disclosed in Patent Document 3 uses chloroprene rubber as an essential raw rubber component, and the belt disclosed in Patent Documents 4 and 5 is not limited as an elastic layer-constituting raw material rubber, and almost all known rubbers are disclosed. In the examples, nitrile rubber is used in combination. Natural rubber has a high Mooney viscosity, and a large amount of process oil must be used for extrusion processing, resulting in contamination problems.

  While EPDM is a highly ozone-resistant rubber, it has a problem with flame retardancy. Used to improve ozone resistance. An electronic device such as a copying machine equipped with an image forming apparatus is required to have flame retardancy. For this reason, patent documents use components that increase flame retardancy such as chloroprene, but the present invention has a problem of ozone resistance. This is not a matter of course, but only a change with time of the resistance value without pursuing flame retardancy.

In the present invention, the ethylene propylene rubber used as the raw rubber preferably has a Mooney viscosity (ML _{1 + 4} : 125 ° C.) of 50 or less. When the Mooney viscosity exceeds 50, non-uniform internal strain is generated when extruding the rubber composition after kneading with an extruder to form a cylindrical belt, particularly when forming a belt having a thickness of 1 mm or less. Is not preferable. As the EPDM, a commercially available EPDM having a Mooney viscosity of 50 or less may be used alone, or 50 or more EPDM and 50 or less EPDM may be mixed to be 50 or less. When two types of EPDM having different Mooney viscosities are used, the difference in Mooney viscosity is preferably 30 or more.

  As the conductive carbon black used in the present invention, a known carbon black that can be obtained by adding conductivity to rubber can be used without limitation, and acetylene black is particularly preferable.

  In the semiconductive belt of the present invention and the production method thereof, it is preferable to add a process oil (plasticizer) to EPDM, and the process oil is a paraffinic process oil such as PW-380 (Idemitsu Kosan). It is preferable. The amount of process oil added is preferably 40 parts by weight or less and more preferably 30 parts by weight or less with respect to 100 parts by weight of EPDM. When the amount of process oil added is large, problems such as contamination of the photoreceptor due to bleeding and adhesion to the belt drive roll may occur.

  Silica and aluminum hydroxide are preferably added to the rubber constituting the elastic layer of the semiconductive belt of the present invention. The compounding ratio of silica is 10 parts by weight or less with respect to 100 parts by weight of the raw rubber, and may be omitted. The compounding amount of aluminum hydroxide is 40 parts by weight or less. Other known rubber compounding agents can be added to the rubber constituting the elastic layer of the semiconductive belt of the present invention.

  The surface layer is made of a material having lubricity. Such a lubricating material is preferably a material formed by applying and drying a water-based lubricating paint composed of polytetrafluoroethylene fine powder and a binder resin or a mixed paint of the water-based lubricating paint and water-based polyurethane resin. The binder constituting the water-based lubricating paint is preferably a polyurethane resin, an acrylic resin, or a mixed resin thereof. The binder resin may be a non-crosslinked type or may be crosslinked using a crosslinking agent. The content of polytetrafluoroethylene in the water-based lubricating paint after drying is preferably 10 to 80% by weight, more preferably 30 to 70% by weight, and further preferably 40 to 65% by weight. preferable. If the content of polytetrafluoroethylene is too small, the lubricity of the surface layer is lowered, and if it is too large, cracks are likely to occur due to stretching. As such a water-based lubricating paint, a commercially available paint can be used, such as Emuralon 345 (Henkel Japan). All of these commercially available paints are water-based lubricating paints that can be diluted with water, and are composed of a main agent and a curing agent, and are mixed at the time of use.

  The polyol compound that constitutes the water-based polyurethane resin that can be added to the water-based lubricating paint is not particularly limited to polyether-based, polyester-based, etc., but is mainly polyether-based, especially PTMG from the viewpoint of excellent durability of the surface layer ( It is more preferable to use a polyurethane resin as a polyol component (90 mol% or more of all polyol compounds). A commercially available product can be used as the water-based polyurethane resin, and one having an elongation of the coating film after drying of 500 to 1500%, preferably 600 to 1300% is selected.

  It is a preferred embodiment to provide an intermediate layer or primer layer between the elastic layer and the surface layer to strengthen the adhesion between the elastic layer and the surface layer. Examples of the intermediate layer constituting material include polyurethane resins and halogenated polyolefins (see JP-A-11-352787).

  The method for producing a semiconductive belt of the present invention includes an elastic layer production step and a coating step for forming a surface layer. The elastic layer production step uses ethylene propylene rubber as a raw rubber component, and 100 parts by weight of the ethylene propylene rubber. 30 to 70 parts by weight of conductive carbon black is added to and kneaded to produce an unvulcanized rubber composition, and the unvulcanized rubber composition is formed into a belt shape to form an unvulcanized belt. An extrusion molding step and a vulcanization step of forming an unvulcanized belt to form an elastic layer are provided. A polishing step for making the belt a predetermined thickness may be provided after the vulcanization step.

  The kneading step is performed by a method well known in the technical field of rubber. When two types of EPDM are used, a primary kneading may be performed using only one of the EPDMs, and a two-stage method in which the obtained master batch and the remaining EPDM are secondarily kneaded may be used. A one-stage method of kneading may be used. When two types of EPDM having a Mooney viscosity difference of 30 or more are used, it is preferable to perform primary kneading using EPDM having a high Mooney viscosity. In this case, all of process oil in the primary kneading is used. It is preferable to use 70% or more of the addition amount, more preferably 75% or more, and still more preferably 80% or more.

(Examples and comparative examples)
An unvulcanized rubber composition was prepared according to the formulation shown in the upper part of Table 1. The unvulcanized rubber composition was kneaded by a two-stage method. First, esprene 505, process oil (using 75 to 90% of the total amount of process oil added), carbon black and stearic acid are kneaded with a Banbury mixer in the primary kneading to make a primary masterbatch, and then secondary kneading after cooling The primary masterbatch, EP33, components excluding sulfur, zinc oxide, and vulcanization accelerator, and the remaining amount of process oil were kneaded with a kneader to obtain a secondary masterbatch. After cooling the secondary masterbatch, zinc oxide, sulfur and a vulcanization accelerator were kneaded using a kneader to obtain an unvulcanized rubber composition. The belt was formed by an extrusion method. Molding is performed by supplying a metal mandrel having an outer diameter of 40 mm and a length of 400 mm using a vent type extruder equipped with a cross head, and forming an elastic layer having a thickness of 0.8 mm on the outer peripheral surface of the mandrel. Heat vulcanization was performed, and after cooling, a polishing finish was performed to a thickness of 0.5 mm to obtain an elastic layer. A water-based lubricating paint (Emuralon 345 clear) was applied to the elastic layer and dried to form a surface layer.

(Evaluation)
Within 24 hours after forming the surface layer, the electrical resistance value of the semiconductive belt was measured to obtain an initial resistance value _R0, and the resistance value after 30 days was measured to be _Rf . The value of 100 [(logR _f ) − (logR ₀ )] / (logR ₀ ) (%) is shown in the lower part of Table 1. The electrical resistance value (unit: Ω / □) was measured under the following conditions by setting a belt between the counter electrode and the probe, applying an applied voltage of 500 V for 10 seconds, and reading the resistance value.
Measuring device: Hiresta UP MCP-HT450 (Mitsubishi Chemical)
Probe: 2-pin probe (type UA)
Counter electrode: Polytetrafluoroethylene sheet laminated insulation board Measurement environment: Temperature 25 ° C; Humidity 60% RH

  From the above results, it can be seen that the semiconductive belt obtained by the present invention has a small change in resistance value with time and is stable, and naturally has a small variation in resistance value with time. In contrast, a semiconductive belt using chloroprene rubber, which is a polar rubber, has a large change in resistance over time.

Claims (5)

A semiconductive belt having an elastic layer made of semiconductive rubber and a surface layer having lubricity,
The elastic layer contains ethylene propylene rubber as a raw rubber component, and contains 30 to 70 parts by weight of conductive carbon black with respect to 100 parts by weight of the ethylene propylene rubber. The resistance value immediately after production is R ₀ , 30 days. [(LogR _f ) − (logR ₀ )] / (logR ₀ ) ≦ 6%, where R _f is the subsequent resistance value
A semiconductive belt characterized in that. The semiconductive belt according to claim 1, wherein the ethylene propylene rubber has a Mooney viscosity (ML _{1 + 4} : 125 ° C.) of 50 or less. 3. The surface layer is formed of a water-based lubricating paint containing polytetrafluoroethylene resin fine powder and a binder resin or a mixture paint of the water-based lubricating paint and a water-based polyurethane resin. Semi-conductive belt. A method for producing a semiconductive belt having an elastic layer made of semiconductive rubber and a surface layer having lubricity,
Having a manufacturing process of the elastic layer and a coating process of forming a surface layer;
In the elastic layer manufacturing process, ethylene propylene rubber is used as a raw rubber component, and 30 to 70 parts by weight of conductive carbon black is added to and kneaded with 100 parts by weight of the ethylene propylene rubber to manufacture an unvulcanized rubber composition. A kneading step, an extrusion molding step in which the unvulcanized rubber composition is molded into a belt shape to form an unvulcanized belt, and a vulcanization step in which the unvulcanized belt is molded into an elastic layer,
100 [(logR _f ) − (logR ₀ )] / (logR ₀ ) ≦ 6 (%) where R _{0 is} the resistance value immediately after the coating process and R _f is the resistance value after 30 days.
A process for producing a semiconductive belt, characterized in that 5. The method for producing a semiconductive belt according to claim 4, wherein EPDM having a Mooney viscosity (ML _{1 + 4} : 125 ° C.) of 50 or less is used as the ethylene propylene rubber.