JP3185285B2 - Method for producing foamed conductive roll - 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 roll used for electrophotography, such as a developing roll, a charging roll, a charge removing roll and a transfer roll, and a method for producing the same. And its manufacturing method.

[0002]

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

[0003] Among them, the method (1) has a problem in that it requires an ingenuity to prevent the elution of the plasticizer due to an extremely high oil-resistant film, and lacks long-term reliability. Adopting is advantageous in that the hardness range can be controlled widely.

Conventionally, such foamed conductive rolls include:
A urethane foam which has been subjected to continuous foam treatment 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 uniformly apply the conductivity-imparting agent, the cell diameter of the urethane foam is 1 mm or more, and the larger the cell diameter, the better. Therefore, it is not suitable for a case where low surface roughness of the roll is required, such as for charging and static elimination. Furthermore, since the conductive path is formed on the outer surface of the urethane skeleton, when compression deformation and the like are repeated for a long time,
There is also a risk of peeling. For this reason, the conductivity imparting agent tends to be coated thicker, and the volume resistivity of the foamed conductive roll to be produced is as low as 10 ⁻² to 10 ³ Ω · cm (high conductivity). Difficult to make. In addition, a method of blending the conductive powder in the urethane prepolymer is also considered,
In this method, the type of powder (the oil absorption is as small as possible) and the upper limit of the compounding amount are limited due to the increase in viscosity, and the volume resistivity of the foamed conductive roll to be produced is usually 10 ⁶ to 1.
At 0 ¹² Ω · cm, only those having a semiconductive region can be manufactured.

[0005] In addition to the urethane foam, foams that can form a roll include thermoplastic resins such as polypropylene and polyethylene, and thermoplastic elastomers such as olefin, styrene, ester, and vinyl chloride. It is conceivable that such a thermoplastic resin or thermoplastic elastomer foam has a large compression set (30 to 80% according to JIS K6301), and is not suitable for a roll material requiring durability and dimensional accuracy. is there.

[0006]

Therefore, it has elasticity,
Low compression set (5 to 30 in JIS K6301)
%) It is considered optimal to use a vulcanized rubber foam as a roll material. However, conventionally, a block-shaped unvulcanized rubber is foamed in two stages (for example, at 140 ° C. for 20 minutes, followed by 20 minutes). (170 ° C, 15 minutes)
Cutting from this block-shaped foam (rectangular parallelepiped) → drilling →
The operation is very complicated because it is necessary to produce a foamed roll through the steps of core metal penetration → 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 increase the productivity.However, in actuality, heat generation due to the rotation of the screw causes early foaming and early vulcanization, and the shape,
There is a problem that satisfactory cell diameter distribution, hardness distribution and the like cannot be obtained.

The present invention has been made in view of the above circumstances, and even if extrusion molding or injection molding with high productivity is employed, early foaming and early vulcanization are unlikely to occur, and there is little risk of plasticizer elution. Provided are 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, and a method for producing the same. The purpose is to:

[0008]

That is, the present inventor has conceived that the above object can be achieved by reducing the viscosity of the unvulcanized rubber, and as a result of intensive studies, it has been found that the main polymer can be crosslinked. A liquid rubber having an average molecular weight of 5,000 or more is compounded as a softening agent, and a Mooney viscosity ML _{1 + 4} (13
(0 ° C.) by foaming an unvulcanized rubber having a particle size of 25 or less with a foaming agent, thereby increasing the productivity, reducing the risk of dissolution of the plasticizer, having a uniform cell diameter distribution and hardness, and having a low hardness.
Furthermore, a foamed conductive roll that can be manufactured over a wide range of volume resistivity of 10 ⁻² to 10 ¹² Ω · cm is obtained. When this foamed conductive roll is manufactured by injection molding, heat is easily generated during molding. The present inventors have found that early foaming and early vulcanization can be prevented from being easily performed, and the present invention has been accomplished.

Therefore, according to the present invention, a core metal is arranged in a mold, and a main polymer, a liquid rubber having an average molecular weight of 5,000 or more crosslinkable with the main polymer as a softening agent, and a conductive material are placed in the mold. Mooney viscosity including ML
_A method for producing a foamed conductive roll, comprising: injecting a rubber composition having a _{1 + 4} (130 ° C.) of 25 or less, foaming and vulcanizing, and integrally molding the foamed vulcanizate with the core metal. To provide.

Hereinafter, the present invention will be described in more detail. 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), fluoro rubber (FFKM, FKM), polysulfide rubber (OT, EOT) and the like. Among them, diene-based polymers have good compatibility with conductive substances such as carbon black and the like, and are themselves non-polar, so they have a small amount of moisture absorption, high temperature and high humidity (32.5 ° C., 85%) or low temperature. This is preferable because the change in volume resistivity under low humidity (15 ° C., 10%) is small. 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 It is desirable to avoid the use of volume resistivity under high temperature and high humidity or low temperature and low humidity because the range of variation tends to be large. That is, in the printing method using the electrophotographic method, since the toner is electrostatically controlled on the roll, if the fluctuation range of the volume resistivity of the roll material is large, a compensating circuit is required correspondingly, and the design of the device is difficult. Disadvantageous. The main polymer used is preferably a low Mooney product. Specifically, those having a Mooney viscosity ML _{1 + 4} (100 ° C.) in the range of 20 to 40 are preferably used.

An average molecular weight of 5 capable of crosslinking with the above main polymer.
Examples of the liquid rubber of 000 or more 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 adhesion to the Banbury mixer and rolls are small, and the mold release during vulcanization is good. A combination of butadiene rubber and liquid isoprene rubber is preferred. However, as the amount of liquid rubber increases, the viscosity of the rubber increases,
Workability such as sheeting with a roll is deteriorated. For this reason, the compounding ratio of the main polymer and the liquid rubber is 9: 1 by weight.
To 4: 6, particularly preferably 8: 2 to 6: 4.

The conductive material used in the present invention includes conductive carbon such as Ketjen Black EC and acetylene black, SAF, ISAF, HAF, FEF, GPF, and the like.
Rubber carbon such as SRF, FT, MT, etc., carbon for color (ink) which has been oxidized, etc., pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, nickel, copper, silver, germanium, etc. And conductive polymers such as polyaniline, polypyrrole, and polyacetylene. Among them, carbon, graphite, and conductive polymers are inexpensive and easy to control the volume resistivity with a small amount. The roll of the present invention has a volume resistivity of 10
^Since the conductive material can be formed over a wide range from a conductivity of ⁻² to 10 ¹² Ω · cm to a semiconductive property, a conductive material 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 too large, it tends to generate heat during extrusion molding and injection molding, and thus it is easy to foam and vulcanize early, so that the object of the present invention cannot be achieved.

The composition may contain a vulcanizing agent, a vulcanization accelerator, an antioxidant and the like, and a foaming agent and a foaming aid for foaming.

In this case, examples of the foaming agent include inorganic foaming agents such as sodium bicarbonate, ammonium bicarbonate and sodium borohydride, azodicarbonamide (ADCA), azobisisobutyronitrile (AIBN), and barium azodicarboxy. And organic blowing agents such as dinitropentamethylenetetramine (DPT), P, P-oxybis (benzenesulfonylhydrazide) (OBSH), and paratoluenesulfonylhydrazide (TSH). Among them, the change with time of the foaming agent itself is small, the decomposition temperature is high (180 to 200 ° C), the decomposition temperature is easily controlled by a decomposition aid such as urea (130 to 190 ° C), and the vulcanization accelerator and the like are used. Azodicarbonamide is preferred in that the decomposition temperature is unlikely to decrease.

In the kneading step of the rubber composition, the main polymer, the liquid rubber, the conductive substance, the antioxidant, the foaming agent, the foaming assistant, and the vulcanizing agent are mixed in a kneading machine such as an ordinary Banbury mixer or a kneader. A method in which an accelerator, a vulcanizing agent, and the like are charged and kneaded, and the unvulcanized rubber composition is sheeted with a roll may be employed.

As a method of molding the rubber composition, the unvulcanized rubber sheeted is wound around a core metal, and then, a mold,
Alternatively, foam vulcanization can be performed in a vulcanization can,
It is preferable to employ extrusion molding and injection molding from the viewpoint of productivity.

As a method of the extrusion molding, a method of extruding into a tube, followed by foaming and vulcanization with hot air or a microwave as it is, and inserting a core metal, or a method of unvulcanized rubber in a direction perpendicular to the core metal is used. A method of extruding into a roll shape, and foaming and vulcanizing this with a vulcanizer or a press machine can be employed.

When a pressing machine is used, if the amount of rubber filling in the mold is small (for example, 70%), the cell diameter tends to be non-uniform, so it is preferable to fill 100% or more. Further, vulcanization degree as is desired expansion ratio at the time about 90% (corresponding to T ₉₀ in curastometer tester), slightly open gap of the split mold,
Further, it is preferable to fix the cell diameter by vulcanizing while keeping the gap open until 100% vulcanization is achieved. The amount of the gap is 12 mm in diameter, 3 mm in rubber thickness, and expansion ratio (expansion ratio = ((true specific gravity / apparent specific gravity) -1) × 100) 80
% Of the foamed rubber roll is about 3 mm.

Here, foam vulcanization by hot air or microwaves without pressure tends to increase the cell diameter, and microwaves have a volume resistivity of 10 ⁴ Ω · cm or more, and have a semi-conductive to insulating property. Only things can be vulcanized and foamed. For this reason, a vulcanizer using steam pressure (about 10 kg at 180 ° C.)
/ Cm ² ) or a press machine. This is because when the pressure is applied, the decomposition gas is hardly connected to each other before the crosslinking, and the cell diameter is hardly increased.
This is because a foam having a fine cell diameter of μm is easily obtained, and this method reduces the surface roughness of the roll.
Suitable for rolls for charging, discharging, etc. in contact with the photoreceptor.

On the other hand, as a method of injection molding, a method in which a core metal is placed in a split mold for a roll and an unvulcanized rubber is extruded into a roll-shaped mold by an injection molding machine can be adopted. It is preferable to open the gap of the mold by dividing the sulfur degree by 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 and prevention of contamination of the photoreceptor are required, thermoplastic resins such as nylon, olefin, ester, and ether, or olefin, styrene, ester, and urethane are used. A thin-film coating of a thermoplastic elastomer such as a vinyl chloride-based resin or an extruded tube of a thin film may be covered with a roll.
When the outer layer needs to have conductivity, the above-described conductive substance may be kneaded with a resin or an elastomer.

[0024]

EXAMPLES The present invention will be described below in detail with reference to 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 the main polymer, and a liquid polyisoprene rubber LIR- manufactured by Kuraray Co., Ltd. was used as the liquid rubber.
No. 30 was kneaded with the composition shown in Table 1 using Ketjen Black EC, a conductive carbon manufactured by Ketjen Black International Co., Ltd., or carbon # 2300 for ink manufactured by Mitsubishi Kasei Kogyo Co., Ltd. as a conductive substance. did.

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

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

The temperature in the screw was set to 80 ° C. and the heating temperature of the split mold was set to 165 ° C.
Was injection molded. And vulcanization degree 90%,
Specifically in time T ₉₀ of Kyurasuto test to 3mm open gap of the split mold. 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, early foaming and early vulcanization occurred in the middle of the runner, and rubber did not enter the mold. Furthermore, the temperature, the injection speed, and the like were variously examined, and under moderate conditions, although rubber entered the mold, foaming was not uniform because early foaming and early vulcanization had already occurred.

Next, the foamed roll was taken out of the mold, the surface was polished until the thickness of the rubber portion became 3 mm, and the hardness was measured with the roll shape. ° or less, it was soft and elastic.

Table 1 shows the results of the expansion ratio.
The expansion ratio was calculated by cutting a rubber piece from a foam roll and measuring the specific gravity. Similarly, the volume resistivity was measured by cutting a rubber piece, and using a resistivity meter (Loresta AP, Hiresta IP) manufactured by Mitsubishi Yuka Co., Ltd. at low temperature and low humidity (15 ° C., 10%), normal temperature and normal humidity (25%). ℃, 50%), high temperature and high humidity (35 ℃, 90%)
Was measured under each environment. The results are shown in FIG. Example 1
No. 4 has a small variation range of the electric resistance within one digit under each environment, which is very advantageous in equipment design.

In the above composition, the volume resistivity is 10 ^1.
From 10 ⁹ Ω · cm was manufactured, but by examining the type and blending amount of the conductive substance, it was further 10 ^-2-
A foam roll having a wide range of volume resistivity of 10 ¹² Ω · cm can be manufactured.

[0032]

[Table 1]

[0033]

As described above, according to the present invention,
A liquid rubber having an average molecular weight of 5,000 or more crosslinkable with the main polymer is compounded as a softening agent, and the Mooney viscosity ML _{1 + 4} (1
By foaming an unvulcanized rubber composition having a temperature of 30 ° C. or less with a foaming agent, the productivity is high, the risk of dissolution of the plasticizer is small, the cell diameter distribution and hardness are uniform, the hardness is low, and A foamed conductive roll that can be manufactured over a wide range of volume resistivity of 10 ⁻² to 10 ¹² Ω · cm can be manufactured.

Further, if the foamed conductive roll of the present invention is used for development, charging, charge elimination, transfer, etc. rolls used for electrophotography, the speed of the apparatus can be increased and the image quality can be improved.
The industrial value of the present invention is very high.

[Brief description of the drawings]

FIG. 1 shows a low-temperature low-humidity (L /
L) is a graph showing volume resistivity under normal temperature and normal humidity (N / N) and high temperature and high humidity (H / H).

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B29K 105: 04 105: 24 C08L 9:00 (56) References JP-A-5-59206 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) C08J 9/06 B29D 31/00 F16C 13/00 G03G 15/09

Claims (2)

(57) [Claims] 1. A core metal is placed in a mold, and a Mooney viscosity ML containing a main polymer, a liquid rubber having an average molecular weight of 5,000 or more capable of crosslinking with the main polymer as a softening agent, and a conductive material in the mold. _{1 + 4} (130 ° C) is 25
A method for producing a foamed conductive roll, comprising injecting the following rubber composition, foaming and vulcanizing, and integrally molding the foamed vulcanized product with the core metal. 2. The method according to claim 1, wherein the main polymer is a butadiene rubber, and the liquid rubber is a liquid isoprene rubber.
The manufacturing method as described.