JPH05117434A - Foamed conductive roll - Google Patents

Abstract

PURPOSE:To produce a roll which hardly allows the extraction of a plasticizer and is almost free from premature foaming and premature vulcanization even when molded by extrusion or injection molding, each being a method with a high productivity, by molding a rubber compsn. contg. a polymer, a specific liq. rubber, and a conductive material into a roll and vulcanizing the resulting molded article. CONSTITUTION:A foamed conductive roll comprising a foamed vulcanizate of a rubber compsn. which has a Mooney viscosity ML1+4 (130 deg.C) of 25 or lower and comprises a main polymer, a softener consisting of a liq. rubber which can form cross-links with the main polymer and has an average mol.wt. of 5,000 or higher, and a conductive material is provided. A Mooney viscosity higher than 25 tends to result in heat buildup, leading to premature foaming and premature vulcanization. The foamed vulcanizate has a uniform cell structure and a uniform and low hardness, and can be given a vol. resistivity selected from a wide range of 10<-2>-10<12>OMEGA.cm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive roll used for electrophotography, such as for development, charging, charge removal, and transfer.
In particular, it relates to a foamed conductive roll having a core of a metal shaft having a good conductor.

[0002]

2. Description of the Related Art Conductive rolls used for electrophotography, such as developing rolls, charging rolls, charge erasing rolls, and transfer rolls, have a lower hardness (specifically, in order to respond to high-speed equipment and high image quality). Is 60 ° or less in Asker C hardness).
Conventionally, the methods for reducing the hardness are roughly classified into the following two methods. (1) A large amount of plasticizer is mixed in the matrix polymer. (2) A foam such as urethane foam is used.

Of these, the method (1) requires a device for preventing the elution of the plasticizer with a film having extremely high oil resistance, and has a problem of lacking long-term reliability. Therefore, the foam of (2) is used. It is more advantageous to adopt the above because the hardness range can be widely controlled.

Conventionally, as such a foamed conductive roll,
It is known that a continuous foam-treated urethane foam is impregnated with a dispersion containing a conductivity-imparting agent such as carbon and then dried (Japanese Patent Publication No. 57-7176). However, in order to apply the conductivity-imparting agent uniformly, it is preferable that the cell diameter of the urethane foam is 1 mm or more, and the larger it is. For this reason, it is not suitable when a low roll surface roughness is required as seen in charging, discharging, etc. Furthermore, since the conductive path is formed on the outer surface of the urethane skeleton, if compressive deformation is repeated for a long time,
There is also a risk of peeling. For this reason, the conductivity-imparting agent tends to be coated thickly, and the foamed conductive roll produced has only a low volume resistivity of 10 ⁻² to 10 ³ Ω · cm (high conductivity). Difficult to make. Also, a method of blending a conductive powder into the urethane prepolymer can be considered,
In this method, the type of powder (such as oil absorption is as small as possible) and the upper limit of the blending amount are limited due to the increase in viscosity, and the volume resistivity of the foamed conductive roll produced is usually 10 ⁶ to 1
Only those with a semi-conductive region of 0 ¹² Ω · cm can be produced.

In addition to urethane foams, as foams capable of forming rolls, thermoplastic resins such as polypropylene and polyethylene, or thermoplastic elastomers such as olefin series, styrene series, ester series and vinyl chloride series are also available. It is conceivable that such a thermoplastic resin or thermoplastic elastomer foam has a large compression set (30 to 80% in JIS K6301), which makes it unsuitable for roll materials that require durability and dimensional accuracy. is there.

[0006]

Therefore, it has elasticity,
Small compression set (JIS K6301 5-30
%) It is considered optimal to use a vulcanized rubber foam as the roll material, but conventionally, block-shaped unvulcanized rubber was two-stage foamed (for example, 140 ° C., 20 minutes, then Rolls are made at 170 ° C for 15 minutes,
Cutting from this block-shaped foam (rectangular solid) → drilling →
The operation is very complicated because it is necessary to prepare a foamed roll through the steps of penetrating the core metal → adhesion (core metal and foam) → polishing. In this case, it is considered that the foaming roll may be produced by extrusion molding or injection molding in order to improve productivity, but in reality, due to heat generated by the rotation of the screw, early foaming and early vulcanization occur, and the shape,
There is a problem that a satisfactory cell diameter distribution, hardness distribution, etc. cannot be obtained.

The present invention has been made in view of the above circumstances, and even if highly productive extrusion molding or injection molding is adopted, early foaming and early vulcanization are unlikely to occur, and there is little risk of plasticizer elution, and An object of the present invention is to provide a foamed conductive roll using a rubber material having a uniform diameter distribution and hardness, a low hardness, and a volume resistivity of 10 ^-2 to 10 ¹² Ω · cm, which can be produced over a wide range. To do.

[0008]

Means for Solving the Problems That is, the present inventor has conceived that the above object can be achieved by lowering the viscosity of unvulcanized rubber, and as a result of earnest studies, it was possible to crosslink with the main polymer. Liquid rubber having an average molecular weight of 5,000 or more is blended as a softening agent, and the Mooney viscosity ML _{1 + 4} (13
By foaming an unvulcanized rubber (0 ° C.) of 25 or less with a foaming agent, productivity is high, there is little risk of elution of a plasticizer, cell size distribution and hardness are uniform, and hardness is low.
Further, they have found that a foamed conductive roll that can be produced over a wide range of volume resistivity of 10 ⁻² to 10 ¹² Ω · cm can be obtained, and completed the present invention.

Accordingly, the present invention provides a main polymer and an average molecular weight of 5000 which is crosslinkable with the main polymer as a softening agent.
Mooney viscosity M containing the above liquid rubber and a conductive substance
It is intended to provide a foamed conductive roll made of a foamed vulcanized product of a rubber composition having L _{1 + 4} (130 ° C.) of 25 or less.

The present invention will be described in more detail below. The main polymer used in the present invention is a diene-based natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber. (CR), acrylonitrile butadiene rubber (NBR, NIR, NBIR), non-diene butyl rubber (IIR), ethylene propylene rubber (EPM, EP
DM), silicone rubber, chlorosulfonated polyethylene (CSM), chlorinated polyethylene (CM), acrylic rubber (ACM, ANM), epichlorohydrin rubber (C
O, ECO), fluororubber (FFKM, FKM), polysulfide rubber (OT, EOT) and the like. Among them, the diene-based polymer has good compatibility with a conductive substance such as carbon black, and since it is nonpolar in itself, it has a small moisture absorption amount, and thus has high temperature and high humidity (32.5 ° C, 85%) or low temperature. It is preferable because there is little variation in volume resistivity under low humidity (15 ° C, 10%). In this case, chlorosulfonated polyethylene having chlorine in the side chain, chlorinated polyethylene, epichlorohydrin rubber or urethane rubber having an ether bond in the main chain, epichlorohydrin rubber, etc. are all polar polymers, and these polymers are Since there is a tendency that the fluctuation range of volume resistivity under high temperature and high humidity or low temperature and low humidity tends to be large, it is desirable to avoid its use. That is, since the electrophotographic printing method electrostatically tries to control the toner on the roll, if the fluctuation range of the volume resistivity of the roll material is large, a compensating circuit is required accordingly, and the device design It is a disadvantage. The main polymer used is preferably a low Mooney product. Specifically, those having a Mooney viscosity ML _{1 + 4} (100 ° C.) of 20 to 40 are preferably used.

Average molecular weight 5 crosslinkable with the main polymer
Examples of the 000 or more liquid rubber include liquid isoprene rubber (LIR), liquid butadiene rubber (LBR), liquid chloroprene rubber (LCR), liquid polydimethylsiloxane, and liquid polysulfide rubber.

Various combinations of the main polymer and the liquid rubber are conceivable. However, even if a large amount of the liquid rubber is blended, adhesion and sticking to a Banbury mixer or a roll are small, and mold release during vulcanization is good. A combination of butadiene rubber and liquid isoprene rubber is preferred. However, when the amount of liquid rubber increases, the adhesiveness of rubber increases,
Workability such as sheeting on rolls deteriorates. Therefore, the compounding ratio of the main polymer and the liquid rubber is 9: 1 by weight.
˜4: 6, particularly preferably 8: 2 to 6: 4.

As the conductive material used in the present invention, conductive carbon such as Ketjenblack EC and acetylene black, SAF, ISAF, HAF, FEF, GPF,
Carbon for rubber such as SRF, FT, MT, carbon for oxidation (color) (ink), pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, nickel, copper, silver, germanium, etc. And conductive oxides such as polyaniline, polypyrrole, and polyacetylene. Among them, carbon, graphite, and conductive polymers are inexpensive and whose volume resistivity can be easily controlled with a small amount. The roll of the present invention has a volume resistivity of 10
^Since a wide range of conductivity from ⁻² to 10 ¹² Ω · cm to semiconductivity can be produced, a conductive substance is appropriately selected.

The foamed conductive roll of the present invention is obtained by foaming and vulcanizing a rubber composition containing the above components and having a Mooney viscosity ML _{1 + 4} (130 ° C.) of 25 or less. If it is large, heat is likely to be generated during extrusion molding and injection molding, and as a result, early foaming and early vulcanization are likely to occur, so that the object of the present invention cannot be achieved.

A vulcanizing agent, a vulcanization accelerator, an antioxidant and the like may be added to the above composition, and a foaming agent and a foaming auxiliary agent are added for foaming.

In this case, as the foaming agent, an inorganic foaming agent such as sodium bicarbonate, ammonium bicarbonate, sodium borohydride, azodicarbonamide (ADCA), azobisisobutyronitrile (AIBN), barium azodicarboxyl. Examples of the organic foaming agent include rate, dinitropentamethylenetetramine (DPT), P, P-oxybis (benzenesulfonylhydrazide) (OBSH), and paratoluenesulfonylhydrazide (TSH). Among these, the foaming agent itself has little change with time, its decomposition temperature is high (180 to 200 ° C.), its decomposition temperature can be easily controlled by a decomposition auxiliary agent such as urea (130 to 190 ° C.), and it can be controlled by a vulcanization accelerator or the like. Azodicarbonamide is preferred because the decomposition temperature is less likely to decrease.

In the kneading step of the above rubber composition, the above-mentioned main polymer, liquid rubber, conductive substance, antioxidant, foaming agent, foaming aid and vulcanization are carried out in a kneading machine such as an ordinary Banbury mixer or kneader. A method of adding an accelerator, a vulcanizing agent, etc., kneading, and sheeting the unvulcanized rubber composition with a roll can be adopted.

As a method for molding the rubber composition, the sheet-formed unvulcanized rubber is wound around a core metal, and then a mold,
Alternatively, foam vulcanization can be performed in a vulcanizer,
From the viewpoint of productivity, it is preferable to employ extrusion molding or injection molding.

As a method of extrusion molding, after extruding into a tubular shape, it is foamed and vulcanized by hot air or microwave and the core metal is inserted, or unvulcanized rubber is perpendicular to the core metal. It is possible to employ a method in which the material is extruded into a roll shape and foamed and vulcanized by a vulcanization can or a press.

When using a pressing machine, if the amount of rubber filled in the mold is small (for example, 70%), the cell diameter tends to be nonuniform, so it is preferable to fill 100% or more. In addition, the gap of the split mold is slightly opened so that the desired expansion ratio is obtained in a time when the vulcanization degree is about 90% (corresponding to T ₉₀ in the curast meter tester),
Further, it is preferable that the cell diameter is fixed by vulcanizing while leaving the gap open until 100% vulcanization. The amount of the gap is as follows: diameter 12 mm, rubber thickness 3 mm, foaming ratio (foaming ratio = ((true specific gravity / apparent specific gravity) -1) × 100) 80
% Foamed rubber roll is about 3 mm.

Here, the foaming vulcanization by hot air or microwave without pressure tends to increase the cell diameter, and the microwave has a volume resistivity of 10 ⁴ Ω · cm or more from semiconductive to insulating properties. Only things that can be vulcanized and foamed. For this reason, a vulcanization can with steam pressure (about 10 kg at 180 ° C)
/ Cm ² ) or a press is preferably used. When the pressure is applied, it is more difficult for the decomposed gas to be connected to each other before the cross-linking and the cell diameter is not increased.
This is because it is easy to obtain a foam having a fine cell diameter of μm, and since this method reduces the surface roughness of the roll,
Suitable for charging and discharging rolls that come into contact with the photoconductor.

On the other hand, as an injection molding method, a method of placing a core metal in a split mold for rolls and extruding unvulcanized rubber into a roll-shaped mold by an injection molding machine can be adopted. It is preferable to open the gap between the split molds at a time when the degree of sulfurization is about 90%. next,
The foamed conductive roll can be completed by removing the foamed roll from the mold and polishing the surface.

When surface smoothness or prevention of contamination of the photoconductor is required, a thermoplastic resin such as a nylon resin, an olefin resin, an ester resin, an ether resin, or an olefin resin, a styrene resin, an ester resin, or a urethane resin. System, a thin film coating of a thermoplastic elastomer such as vinyl chloride, or a thin film extrusion tube may be covered on the roll.
Further, when the outer skin layer is required to have conductivity, the above-mentioned conductive substance may be kneaded with a resin or an elastomer.

[0024]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example] A butadiene rubber BR02LL manufactured by Nippon Synthetic Rubber Co., Ltd. was used as a main polymer, and a liquid polyisoprene rubber LIR manufactured by Kuraray Co., Ltd. was used as a liquid rubber.
Kneading No. 30 using Ketjen Black EC, which is conductive carbon manufactured by Ketjen Black International Co., Ltd., or carbon # 2300 for ink, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. did.

The above rubber composition was subjected to a curastometer test and a Mooney scorch test as unvulcanized rubber tests. The results are shown in Table 1. As a result, the values of Mooney viscosity ML _{1 + 4} (130 ° C.) of Examples 1 to 4 were all 20.
It was below, and that of Comparative Example 1 was 27.8.

Next, foaming vulcanization was performed using an injection molding machine and a split mold for rolls. Here, the core metal is designed to have a diameter of 6 mm and a length of 260 mm, and the mold is designed to have a diameter of 12 mm including the rubber portion and a length of the rubber portion of 240 mm. The rubber portion has a thickness of 3 mm.

The temperature inside the screw was set to 80 ° C., the heating temperature of the split mold was set to 165 ° C., and Examples 1 to 4 and Comparative Example 1 were set.
Of unvulcanized rubber was injection molded. And vulcanization degree 90%,
Specifically, the gap of the split mold was opened by 3 mm at the time T ₉₀ of the curast test. As a result, Examples 1-4
In each case, rubber could be injected into the mold and foaming was uniform. On the other hand, in Comparative Example 1, premature foaming and premature vulcanization occurred in the middle of the runner, and the rubber did not enter the mold. Furthermore, when various conditions such as temperature and injection speed were studied and the conditions were made mild, rubber was introduced into the mold, but premature foaming and vulcanization had already occurred, and thus foaming was non-uniform.

Next, the foaming roll was taken out of the mold, the surface was ground until the thickness of the rubber portion became 3 mm, and the hardness was measured with the roll shape. In Examples 1 to 4, the Asker C hardness was 50. It was soft and elastic below °.

Table 1 shows the results of the expansion ratio.
The expansion ratio was calculated by cutting a rubber piece from a foaming roll and measuring the specific gravity. Similarly, for volume resistivity, rubber pieces were cut, and a resistivity meter (Loresta AP, Hiresta IP) manufactured by Mitsubishi Petrochemical Co., Ltd. was used. ℃, 50%), high temperature and high humidity (35 ℃, 90%)
Was measured under each environment. The results are shown in Figure 1. Example 1
In No. 4, in each environment, the fluctuation range of the electric resistance is as small as one digit or less, which is very advantageous in designing the device.

In the above formulation, the volume resistivity is 10 ¹
From was produced foam roll 10 ⁹ Omega · cm, to examine the type and compounding amount of the conductive material further 10 ^-2 to
Foam rolls having a wide range of volume resistivity of 10 ¹² Ω · cm can be produced.

[0032]

[Table 1]

[0033]

As described above, according to the present invention,
A Mooney viscosity ML _{1 + 4} (1
By foaming an unvulcanized rubber composition having a temperature of 30 ° C. or less of 25 with a foaming agent, the productivity is high, the plasticizer is less likely to be eluted, the cell diameter distribution and hardness are uniform, and the hardness is low. It is possible to produce a foamed conductive roll that can be produced over a wide range of volume resistivity of 10 ⁻² to 10 ¹² Ω · cm.

Further, if the foamed conductive roll of the present invention is used for developing, charging, discharging, transfer, etc. rolls used in electrophotography, the apparatus can be operated at high speed and the image quality can be improved.
The industrial value of the present invention is very high.

[Brief description of drawings]

FIG. 1 shows the low temperature and low humidity (L / L) of the foamed conductive roll of each example.
L), normal temperature and normal humidity (N / N), and high temperature and high humidity (H / H) are graphs showing volume resistivity.

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Claims (1)

[Claims] 1. A Mooney viscosity ML _{1 + 4} (130) containing a main polymer, a liquid rubber having an average molecular weight of 5000 or more capable of crosslinking with the main polymer as a softening agent, and a conductive substance.
A foamed conductive roll made of a foamed vulcanizate of a rubber composition having a temperature of 25 ° C. or less.