JP2002249627A - Elastic roller and rubber composition used for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foaming rubber composition having new constitutions, where a foam rubber molding manufactured by foaming and crosslinking treatments of the composition while being heated achieves consequently low hardness, small surface roughness and, even if being compressed for an extensive period, minimized permanent deformation and permanent strain due to the compression. SOLUTION: The foam rubber composition contains a rubber raw material, a crosslinking agent therefor and a foaming agent therefore. For the major crosslinking agent, an organic peroxide is used, and for the secondary crosslinking agent, sulfur is used in an amount of 0.1-1 pts.mass based on 100 pts.mass of the rubber raw material to give the composition good characteristics for a molding process using a metal mold. The foam rubber molding obtained has low hardness, small permanent compression strain and small surface roughness and is suitable for constituting an elastic layer 12 in an elastic roller 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elastic roller in which a roller layer constituting a roller uses a foamed rubber layer as an elastic layer, and a foamed rubber layer used for producing the same. More specifically, with respect to a suitable rubber composition, more specifically, in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic method, an electrophotographic photosensitive member or an electrostatic recording dielectric is used. When charging the surface of the charged body, such as a charging roller used as a charging member, an elastic roller having a configuration in which the elastic body layer is a low-hardness foamed rubber layer, and under heating that is preferably used for its production, The present invention relates to a rubber composition which is subjected to foaming and crosslinking treatment to form a foamed rubber molded article.

[0002]

2. Description of the Related Art In image forming apparatuses such as electrophotographic apparatuses (copiers, optical printers, etc.), electrostatic recording apparatuses, etc., means for charging the surface of an image carrier such as a photoreceptor, a dielectric, and the like include:
Conventionally, corona discharge devices have been widely used.

A corona discharge device is effective as a means for uniformly charging the surface of a member to be charged, such as an image carrier such as a photosensitive member, to a predetermined potential. However, since it is a non-contact type charger that uses corona discharge, it generates a sufficient corona discharge, requires an expensive high-voltage power supply, and requires the device to maintain the corona discharge at a certain surface density or higher. There is a feature that it becomes large. In addition, during discharge, as a result of generating ozone from oxygen contained in the atmosphere, as a result, when the amount of corona products such as ozone generated increases, various undesired effects on the surface of the photoreceptor, in some cases, There is a problem in that it affects the environment around the device. In particular, the size of the corona discharge device itself or the effects of corona products such as ozone generated when the electrophotographic device itself is further miniaturized or increased in speed are essential as long as the corona discharge method is used. Some problems cannot be solved.

In place of the corona discharge type charging means,
In recent years, a contact charging type has been used. The contact charging method is a method in which a charging member to which a voltage is applied is brought into close proximity to or in contact with the surface of the member to be charged to charge the surface of the member to be charged. Little in principle. Also,
The structure of the charging section also uses only a charging member that comes into contact with the surface of the member to be charged, and has advantages such as downsizing of the device and cost reduction. For example, in the contact charging method, a form (charging roller) in which an elastic roller having a conductive elastic layer provided on a metal core shaft is used as a charging member is generally widely used.

In this charging roller, in order to uniformly charge the photosensitive member, it is necessary to ensure uniform contact with the surface of the photosensitive member in the roller axis direction (general line direction). DC voltage (DC) to AC voltage (AC)
When using by applying a charging bias voltage on which is superimposed, in order to suppress vibration between the charging roller and the photoreceptor due to an alternating voltage (AC) component and a charging noise generated thereby, It is desired to reduce the hardness of the conductive elastic layer used.

However, it has been pointed out that a problem when using a low-hardness elastic roller is that the roller layer is permanently deformed when the photosensitive member is kept in pressure contact with the elastic roller for a long period of time. Permanent deformation of the roller layer causes excessive current from the nip portion, which may cause an abnormal image. In addition, it has been pointed out that the deformed portion can contact the photoconductor surface only unevenly when the roller rotates, resulting in uneven charging potential, resulting in exposure unevenness and image failure.

Furthermore, a minute gap may be formed between the charging roller and the surface of the photoreceptor whose surface flatness is insufficient due to permanent deformation or large surface roughness. When the charging bias voltage is applied in this state, the discharge is concentrated in the gap. In the contact charging method, charging is generally performed by uniform charge injection, but since a discharge current locally flows in a portion where discharge has occurred, etching of the surface of the photosensitive member is caused in that portion, and the photosensitive member is etched. Shorten the lifespan.

[0008] Further, although residual toner is removed by a cleaning device after image formation, a very small amount of toner remains on the photoreceptor surface in many cases. During use while being pressed against the surface of the photoreceptor, transfer and adhesion of the residual toner also occurs on the charging roller. If the surface flatness is not sufficient, the amount of deposited toner increases, and in some cases, uneven charging of the photoconductor may occur. In order to avoid image defects due to this factor, the charging roller is also required to have a small surface roughness.

Conventionally, in producing a charging roller having a small surface roughness and a low hardness, a rubber composition capable of forming a surface as a skin layer in a foamed rubber layer is used.
A rubber composition in which an organic foaming agent and sulfur as a vulcanizing agent (crosslinking agent) are added to raw rubber such as EPDM is used. The unvulcanized rubber composition is extruded into a cylindrical shape around the core by an extruder equipped with a crosshead, and the core and the extruded product are integrated. Further, the extruded body is fixed together with the integrated core metal inside the cylindrical mold having a desired outer diameter, and under heating, foaming and crosslinking are performed to form a foamed crosslinked rubber molded body. It has gained.
The foamed sponge rubber obtained has a surface shape of
It is defined by a cylindrical mold inner wall surface and has a skin layer on the surface. The charging roller manufactured using the rubber composition having the above configuration has a small surface roughness and a low hardness, but even when the elastic roller is kept in pressure contact with the photosensitive member for a long time, the roller may be used. A foam-like sponge rubber in which the compression set is kept small enough to prevent the layer from undergoing permanent deformation has not been obtained.

[0010]

SUMMARY OF THE INVENTION In an elastic roller,
As a technique for achieving a roller having an elastic layer having a low hardness, a small surface roughness and a small compression set, Japanese Patent Application Laid-Open No. 10-202762 discloses a method using urethane rubber. JP-A-244348 proposes a method using silicone rubber. In addition, when applied to an elastic roller that requires conductivity such as a charging roller, for example, in the method using urethane rubber, the polymer itself such as urethane rubber uses a raw material rubber that exhibits conductivity, The desired conductivity can be achieved without using a conductivity-imparting agent. However, the electrical resistance of the obtained rubber molded product greatly depends on the environment such as temperature and humidity, and the resistance of the elastic roller fluctuates depending on the use environment (temperature and humidity). As a result, when such a charging roller having a variable resistance is used for the charging member, there is a problem that the charging potential of the photoconductor often changes greatly depending on the use environment (temperature and humidity).

When a method using silicone rubber is applied to an elastic roller requiring conductivity, such as a charging roller, since silicone rubber itself does not exhibit conductivity, a conductive agent such as carbon is dispersed. To provide the desired conductivity. Therefore, the electrical resistance of the obtained rubber molded body does not essentially show the environmental dependence such as temperature and humidity, and a charging roller having suitable charging performance can be obtained. However,
In order to further reduce the hardness, it is necessary to use a silicone rubber having a higher content ratio of a lower molecular weight component as a raw rubber, and at this time, during the pressing, the lower molecular weight component becomes a liquid. In many cases, the toner oozes out on the roller surface and adheres to or contaminates the photoreceptor surface. As a result, there is a new problem that an image produced by using the contaminated photoconductor causes a partial defect. In addition, silicone rubber itself is an expensive material, and in terms of cost, using less expensive materials, the electrical resistance of the obtained rubber molded body can be reduced to the same degree as the environmental dependence such as temperature and humidity. There is a need for a method of achieving a roller having an elastic layer having low hardness, low surface roughness, and low compression set at the same time.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to obtain a foamable rubber composition having a new structure by subjecting it to foaming and crosslinking under heating. The newly developed elastic roller adopts a foamed rubber layer as an elastic layer, has a low hardness, has a small surface roughness, can suppress a permanent deformation even when subjected to a long-term compression deformation, and has a small compression set. Another object of the present invention is to provide a foamable rubber composition having a new structure used for the production thereof. The object of the present invention, more specifically, as a raw material rubber, instead of urethane rubber or silicone rubber, using a cheaper available, more versatile raw material rubber, such raw material rubber crosslinking treatment conditions, especially By selecting a cross-linking agent to be used, and by adding a new amount of the cross-linking agent, a foamed rubber obtained by performing foaming and cross-linking treatment under heating using a foaming agent added at the same time. The molded body has low hardness, small compression set, and in addition, using a mold,
When subjected to the heat treatment, the surface of the rubber molded body in contact with the mold wall surface can be used as a skin layer, and as a result, the surface roughness thereof can be reduced. Compression set, low hardness, small surface roughness, and can suppress permanent deformation to a small extent even when subjected to compression deformation for a long period of time, provided by using the foamable rubber composition. Another object of the present invention is to provide a new elastic roller having a small size.

[0013]

Means for Solving the Problems The present inventor has made intensive studies and studies in order to solve the above-mentioned problems. Specifically, other than urethane rubber and silicone rubber, inexpensive and more general-purpose materials are available. Using a raw material rubber, a foaming agent and a cross-linking agent for the raw material rubber are added to prepare various rubber compositions. As a cross-linking agent, in addition to sulfur, a commonly used vulcanizing agent, a raw rubber that can be cross-linked by an organic peroxide cross-linking agent (peroxide cross-linking agent) is used. When an organic peroxide cross-linking agent (peroxide cross-linking agent) is used and a small amount of sulfur is used in combination as a secondary cross-linking agent, the rubber obtained by performing foaming and cross-linking treatment under heating Molded body has low hardness and compression set In addition, it was found that the formation of irregularities on the surface due to foaming was also suppressed, and the surface in contact with the mold could be formed on the skin layer, and as a result, a foamed rubber molded product with a small surface roughness was obtained. . At that time,
By adding conductive particles such as carbon commonly used as a conductivity-imparting agent, for example, the range of electric resistance required for the charging roller, and the temperature and humidity in the electric resistance of the obtained rubber molded body It has also been found that the environmental dependence of can be suppressed sufficiently.

Based on this finding, the present inventor further studied the addition ratio of sulfur added as a secondary crosslinking agent to the raw rubber, and as a result, the raw rubber 1
It has been found that the effect of the present invention can be achieved with high reproducibility without depending on the type of raw rubber by selecting the amount of sulfur to be added in a ratio of 0.1 to 1 part by mass per 00 parts by mass, The present invention has been completed.

That is, the rubber composition of the present invention provides a foamed rubber molded article by simultaneously performing foaming with a foaming agent and crosslinking treatment with a crosslinking agent under heating. A rubber composition comprising a crosslinking agent and a foaming agent, wherein the raw rubber is capable of crosslinking with any of an organic peroxide and sulfur, and as the crosslinking agent, an organic peroxide as a main crosslinking agent is used. Oxide and sulfur as a secondary cross-linking agent,
A rubber composition characterized in that the sulfur content per part by mass is selected in the range of 0.1 to 1 part by mass.

The rubber composition of the present invention can be a rubber composition characterized by containing an ethylene / propylene / diene copolymer as a main component of the raw rubber. Further, depending on the type of the foaming agent to be used, it is preferable to use a form of a rubber composition characterized by containing triallyl cyanurate or triallyl isocyanurate as a crosslinking aid in addition to the crosslinking agent.

In addition, the present invention uses the above-described rubber composition of the present invention to prepare an elastic layer made of a foamed rubber molded article, and to construct a roller layer provided on the outer periphery of a cored bar. The invention also provides an invention of an elastic roller having a novel configuration. That is, the elastic roller of the present invention is an elastic roller including a cored bar and a roller layer provided on the outer periphery thereof,
The roller layer is characterized by comprising at least an elastic layer made of a foamed rubber molded product obtained by foaming and cross-linking a rubber composition having any of the above-described configurations. Elastic roller. In this case, the elastic roller of the present invention is such that the elastic layer made of a foamed rubber molded product and the core are integrated, and the integration of the core and the elastic layer is performed by a core member. And a mechanism for holding the core metal member on a concentric axis with the inner surface of the cylindrical mold, the layer of the rubber composition of the present invention having any one of the above-mentioned structures disposed around the axis. In a mold having a lid at both ends, together with the core member, is housed using the holding mechanism, and in the mold, under heating, foaming and cross-linking treatment are performed, and a foamed rubber molded product is formed. By doing so, it is possible to obtain an elastic roller characterized by being integrally molded.
Further, it is preferable that the roller layer has a laminated structure having a surface layer coated on the outer surface of the elastic body layer.

The elastic roller of the present invention is applicable to various types of conductive elastic rollers used in electrophotographic apparatuses, for example, a charging roller, a developing roller, and a transfer roller which are used while being pressed against the surface of a photoreceptor. In this case, each of the layers constituting the roller layer, such as the elastic layer and the surface layer, is formed to have conductivity. For example, the rubber composition of the present invention used for the production of the elastic layer is such that the raw rubber itself does not achieve the desired conductivity, such as an ethylene-propylene-non-conjugated diene copolymer. In some cases, in advance, a conductivity-imparting agent,
For example, by adding a conductive agent such as carbon to such a rubber composition, it is preferable to produce the obtained rubber molded product in a foamed rubber layer having conductivity.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber composition of the present invention is used for molding into a foam using a more widely available raw material rubber other than urethane rubber and silicone rubber, which is inexpensive. A foaming agent and a cross-linking agent for the raw rubber to be used are added, and under heating, foaming and cross-linking are performed to obtain a foamed rubber molded product. In addition to sulfur, a commonly used vulcanizing agent, a raw rubber that can be cross-linked with an organic peroxide cross-linking agent (peroxide cross-linking agent) is selected, and the main cross-linking agent is an organic peroxide cross-linking agent By using (peroxide cross-linking agent) and using a small amount of sulfur as a secondary cross-linking agent, the rubber molded product obtained by subjecting the foaming and the cross-linking treatment under heating to a low- Hardness, small compression set, and Formation of the uneven shape of the surface due to bubbles is suppressed, for example, a surface in contact with the mold may be formed in the skin layer, as a result and gives a rubber molded article of the small foam surface roughness.

More specifically, an organic peroxide crosslinking agent (peroxide crosslinking agent) is used as a main crosslinking agent, but a small amount of sulfur is used in combination as a secondary crosslinking agent. The amount of sulfur added in a small amount is preferably 0.1 to 1 with respect to 100 parts by mass of the raw rubber.
By selecting the range of the parts by mass, the operation according to the configuration of the present invention described below is set in a suitable range.

Hereinafter, the rubber composition of the present invention, and
The elastic roller of the present invention manufactured using the above will be described in more detail.

In general, a rubber molded product obtained by subjecting a crosslinking treatment (peroxide vulcanization) using an organic peroxide crosslinking agent (peroxide crosslinking agent) to a cross-linking using sulfur, which is a commonly used vulcanizing agent, Compared to a rubber molded product obtained by performing treatment (sulfur vulcanization), the same raw rubber is used,
It is known that the compression set is small even when the frequency of cross-link formation is almost the same. Therefore, even if the obtained rubber molded bodies have the same hardness, it is possible to reduce the compression set by using peroxide vulcanization as compared with the case of using sulfur vulcanization.

However, peroxide vulcanization has a problem that the desired frequency of crosslinking cannot be achieved in the presence of oxygen. In peroxide vulcanization, radical species (—O
Using (), a hydrogen atom is extracted from the raw rubber by a radical reaction, and the generated polymer / radical causes a cross-linking reaction to form a desired cross-link. In the presence of molecular oxygen (triplet oxygen), molecular oxygen (triplet oxygen) reacts at the radical point of the generated polymer radical, further causing an oxidative cleavage reaction, resulting in cleavage of the polymer molecule Reaction occurs. Therefore, in the presence of oxygen, the radical points of the generated polymer radicals are consumed in the cleavage reaction of the polymer molecules instead of being used for the crosslinking reaction, and the desired frequency of crosslinking is not achieved. .

Further, even in a state in which the presence of oxygen is excluded and proper peroxide vulcanization is carried out, foaming with a foaming agent is performed together with the crosslinking treatment to form a foamed rubber molded product, so-called sponge rubber. In this case, a phenomenon is observed in which foam moldability is reduced as compared with a method of foaming while performing sulfur vulcanization. This phenomenon is because the crosslinking reaction in peroxide vulcanization proceeds faster than the crosslinking reaction in sulfur vulcanization, so that the reaction rates of the foaming reaction and the crosslinking reaction due to thermal decomposition of the blowing agent are properly balanced. Once the appropriate foaming ratio and bubble diameter are formed, it becomes more difficult to select heating conditions under which the shape is fixed by thermosetting by crosslinking. That is, if the speed of the crosslinking reaction is too fast, foaming becomes insufficient, while if the speed of the foaming reaction is too fast, overfoaming occurs.However, when peroxide vulcanization is used, compared to the case where sulfur vulcanization is used, both The heating temperature width at which the reaction rate of the heating is properly balanced is narrow, and if there is a temperature distribution at the time of heating, due to the temperature difference, insufficient foaming or overfoaming occurs locally, and the formed body is formed. This is considered to be because the deformation of the film easily occurs.

Conventionally, an unvulcanized rubber composition containing only a foaming agent and an organic peroxide crosslinking agent (peroxide crosslinking agent) as a crosslinking agent is prepared. The product is extruded into a cylindrical shape around the core metal by an extruder equipped with a crosshead, and further fixed inside a cylindrical mold having a desired inner diameter larger than the outer diameter of the extruded product, under heating. Foaming and cross-linking treatments have been applied, and a foamed rubber molded article having a skin layer on the surface has been produced by molding. In that case, due to the above phenomenon, while the crosslinking reaction proceeds,
Due to the effect of oxygen remaining in the mold on the surface of the molded body,
Peroxide vulcanization is hindered, and in the vicinity of the surface, the foaming reaction proceeds with insufficient crosslinking and curing, resulting in formation of a large number of recesses and an increase in surface roughness. in addition,
Since the molded article is deformed due to insufficient foaming or over-foaming due to uneven surface temperature distribution, the surface roughness is further increased, which has been a problem in using the surface as a skin layer. .

In the rubber composition of the present invention,
The main cross-linking agents are used to maintain the advantages obtained by using an organic peroxide cross-linking agent (peroxide cross-linking agent) and the feature that even if the hardness is low, the compression set can be reduced. As such, an organic peroxide crosslinking agent (peroxide crosslinking agent) is used. On the other hand, the biggest problem when using an organic peroxide cross-linking agent (peroxide cross-linking agent) as a cross-linking agent is that the speed of the cross-linking reaction in peroxide vulcanization is too high, and that the foaming reaction and the cross-linking reaction are properly performed. The problem of narrowing the conditions to be balanced is that a small amount of added sulfur acts as a retarder in peroxide vulcanization, thereby suppressing the overall crosslinking reaction rate from becoming excessively fast. The problem is solved by avoiding the problem of locally insufficient foaming or overfoaming. In addition, inside the mold,
In particular, the oxygen adsorbed and remaining on the inner wall surface is desorbed when heated to induce a crosslinking reaction, and is a factor that inhibits the vulcanization of peroxide vulcanization. Since it is compensated by the crosslinking reaction with sulfur, it is also possible to avoid the formation of recesses on the surface due to extreme vulcanization inhibition, which is a problem near the surface. That is, in addition to the organic peroxide crosslinking agent (peroxide crosslinking agent) added as a main crosslinking agent, a small amount of sulfur, which is a secondary crosslinking agent, is also added, so that the above-mentioned two actions are achieved. When exerted, it is possible to avoid the occurrence of local insufficient foaming and overfoaming, and furthermore, it is also possible to prevent the formation of concave portions on the surface, and when producing a foamed rubber molded body that forms the surface shape by die molding, A skin layer can be formed on the surface with low surface roughness and good reproducibility.

However, as the addition ratio of sulfur added as a secondary crosslinking agent increases, the effect of inhibiting the reaction to peroxide vulcanization becomes unnecessarily large, and the main crosslinking agent is an organic peroxide crosslinking agent. The advantage of using (peroxide crosslinking agent), the effect of reducing the compression set, is lost. From that point, the addition ratio of sulfur added as a secondary cross-linking agent is set to
The properties of the obtained foamed rubber molded article are maintained at a desired small value of the compression set even at the target low hardness, by keeping the range of not more than 1 part by mass with respect to 0 part by mass. . As a matter of course, in a range where the sulfur addition ratio is extremely low, for example, in a range far less than 0.1 part by mass with respect to 100 parts by mass of the raw rubber, particularly,
In some cases, the influence of oxygen remaining inside the mold cannot be reliably eliminated. Therefore, the addition ratio of sulfur is preferably selected to be at least 0.1 part by mass with respect to 100 parts by mass of the raw rubber. Furthermore, while maintaining the above-mentioned effects of improving moldability and surface properties with higher reproducibility, and maintaining a desired low value of compression set at a desired low hardness, a secondary crosslinking agent is used. It is more preferable to select the addition ratio of sulfur to be added in the range of 0.2 to 0.5 parts by mass with respect to 100 parts by mass of the raw rubber.

The raw rubber used in the rubber composition of the present invention is
As the crosslinking agent, sulfur and an organic peroxide crosslinking agent (peroxide crosslinking agent) can be used. More specifically, it is preferable to use a rubber material having a certain degree of unsaturated bond in the main chain. Rubber materials having a certain degree of unsaturated bond in the main chain include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), ethylene-propylene- Diene terpolymer rubber (EPD
M), epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (CHR) and the like. All of these are relatively inexpensive, and in addition, although many do not themselves exhibit conductivity, they are relatively free of charge by adding a conductive agent such as conductive particles as a conductivity-imparting agent. The desired conductivity can be imparted with high reproducibility even when a foamed rubber molded article having a high foaming rate is obtained.

In addition, when an elastic roller produced by using the rubber composition of the present invention is applied to a charging roller, even if a contact charging method is adopted, it is caused by a discharge phenomenon which is difficult to completely avoid. To prevent deterioration due to a small amount of ozone,
It is preferable to use an insulating polymer for the raw rubber so that the polymer is excellent in ozone resistance, and the conductivity of the polymer itself is not affected and the environmental dependency of electric resistance is not increased. When applied to a charging roller, it is more preferable to use EPDM satisfying all of these requirements.

The organic peroxide cross-linking agent (peroxide cross-linking agent) used as a main cross-linking agent is not particularly limited as long as the raw material rubber used can be peroxide-vulcanized together with foaming. Available to
For example, dicumyl peroxide, benzoyl peroxide, 1,1-bis (t-butylperoxy) 3,3,5
-Trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclododecane, t-butylperoxybenzoate, di-t-butyl peroxide, α, α ′
-Bis (t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne, 2,5-dimethyl-2,5-di (t-
Butylperoxy) hexane and the like. The amount of the organic peroxide crosslinking agent (peroxide crosslinking agent) added as a main crosslinking agent depends on the type of the organic peroxide crosslinking agent (peroxide crosslinking agent) to be used, for example, its molecular weight and the number of effective functional groups. Although it depends on the cross-linking efficiency of the raw rubber, it is usually preferable to select from 0.5 to 10.0 parts by mass with respect to 100 parts by mass of the raw rubber.

In the rubber composition of the present invention, in order to further increase the crosslink density and to further reduce the compression set,
It is preferable to add a crosslinking aid. In the present invention, as a cross-linking aid used for an organic peroxide cross-linking agent (peroxide cross-linking agent) used as a main cross-linking agent, for example, trioxide suitable as a peroxide cross-linking auxiliary for EPDM is used. It is preferable to use allyl cyanurate (TAC) or triallyl isocyanurate (TAIC).

In the rubber composition of the present invention, an appropriate amount of a foaming agent is added as an essential additive component in accordance with the desired expansion ratio in order to obtain a foamed rubber molded product. As available blowing agents, dinitrosopentamethylenetetramine,
Organic foaming agents such as azodicarbonamide, paratoluenesulfonylhydrazine, azobisisobutyronitrile, and 4,4′-oxybisbenzenesulfonylhydrazine, and inorganic foaming agents such as sodium bicarbonate.
In order to further reduce the hardness, a high expansion ratio is used. In this case, in order to obtain a good skin layer on the surface, azodicarponamide (ADCA) and 4,4′-oxybisbenzenesulfonylhydrazine ( OBSH) is preferably used in combination. However, the hydrazine compound OBSH
Has an effect of inhibiting the peroxide vulcanization reaction, so its addition amount is 1 to 100 parts by mass of the raw rubber.
It is preferable to select within the range of 0 parts by mass or less. Also,
In order to obtain a molded article having a sufficient expansion ratio, it is desirable that the foaming reaction due to thermal decomposition of the foaming agent be performed slightly earlier than the crosslinking reaction performed under heating, and for the purpose of lowering the decomposition start temperature of the foaming agent, It is more preferable to add a foaming aid such as urea.

Further, the elastic roller of the present invention will be described in more detail with reference to the drawings. Here, using the case where the elastic roller of the present invention is applied to a charging roller,
As will be described, the usage of the elastic roller of the present invention is not limited to the charging member.

FIG. 1 is a cross-sectional view schematically showing an example in which the elastic roller of the present invention is configured in the form of a charging roller. In the configuration illustrated in FIG. 1, the roller layer of the charging roller adopts a multi-layer configuration, in which a metal core 11, a conductive rubber layer 12 of an elastic body layer on the outer periphery thereof, and a surface layer on the outer surface thereof. The surface coating layer 13 is provided.

The conductive rubber layer 12 uses a non-conductive rubber as a raw rubber itself, and a conductive agent, specifically, conductive particles is added to impart desired conductivity. Therefore, the electric resistance is configured to eliminate the environmental dependence due to the conductivity of the rubber itself due to the added conductive particles. The content of the conductive particles is adjusted so that the charging roller can be used as a charging member so that a charging bias voltage can be applied to the photoconductor.
Is adjusted to be in a range having a semiconductivity of about 1 × 10 ³ to 1 × 10 ⁸ Ω · cm .

As the conductive particles, carbon black,
Graphite, titanium oxide, metal oxides such as tin oxide, metals such as Cu, Ag, and the like, such as particles coated on the particle surface and made conductive, and the like, alone or a plurality of these, as appropriate By adding it in the rubber composition in advance, the desired resistance value can be adjusted. In particular,
Carbon black has a relatively small weight content,
This is preferable in that conductivity in the above range can be imparted. LiClO ₄ , KSCN, N
An ionic electrolyte such as aSCN, LiCF ₃ SO ₃ or the like can be additionally added as long as the environment dependency of the volume resistance of the conductive rubber layer is not increased.

When a substantial amount of a solid additive component such as conductive particles is added, the extrudability of the rubber composition of the present invention used for forming the elastic layer gradually decreases. For the purpose of maintaining the extrusion moldability, it is preferable to add an appropriate amount of a softening agent to the rubber composition of the present invention. As the softener, paraffinic oil, naphthenic oil,
An aromatic oil or the like is used. These softeners are not particularly limited, but it is desirable to select the addition ratio within a range where the softener does not cause contamination of the photoreceptor surface when the charging roller is pressed. In order to prevent the photoconductor surface from being contaminated by the softening agent, it is more preferable to use paraffin oil.

In addition, the rubber composition of the present invention may contain, if necessary, reinforcing agents, fillers, tackifiers, dispersants, extenders, etc., which are generally used as additives to the rubber composition. It can also be added.

The surface layer (surface coating layer) 13 which covers the surface of the conductive rubber layer 12 is such that when a defect such as a pinhole occurs on the photosensitive member to which the charging roller is pressed, the charging current concentrates there. This is to prevent the charging member and the photoconductor from being damaged. Therefore, the surface layer 13
Although it shows conductivity, its resistance value is 1 × 10 ⁶ to
About 1 × 10 ¹⁰ Ω · cm is required. The surface layer 13
Generally, acrylic, polyurethane, polyamide, polyester, polyolefin, silicone and other binder polymers, as a conductive agent, carbon black, graphite, titanium oxide, conductive metal oxides such as tin oxide,
Metals such as Cu and Ag, conductive particles such as particles coated on the particle surface and made conductive, LiClO ₄ , KSC
A conductive film prepared by dispersing an ionic electrolyte such as N, NaSCN, or LiCF ₃ SO _{3 in} an appropriate amount according to a target resistance value and dispersing the ionic electrolyte to prepare a conductive film is used.

The surface layer 13 can be formed by dissolving or dispersing the binder polymer in a solvent and dispersing a conductive agent, for example, a conductive particle in the solvent, by dipping, beam coating, roll coating, or the like. A method of coating the surface of the conductive rubber layer by a coating method, or a method in which a conductive agent is kneaded into the binder polymer, and the resulting mixture is formed into a cylindrical coating material by an extruder or the like. There is a method of coating the surface of the layer 12 and the like.

As described above, the elastic roller of the present invention is used for a charging roller serving as a contact charging type charging member used in an electrophotographic apparatus, and similarly, is brought into contact with the surface of a photoreceptor. Used in the form, both are rollers having conductivity, even when applied to a developing roller or a transfer roller,
It becomes suitable. Specifically, in an electrophotographic apparatus, a developing roller is used in a developing step of attaching a developer to an electrostatic latent image formed on the surface of a photoreceptor and visualizing the image during an image forming step. Generally, the developer is carried on the roller surface in the form of a thin film, and is used in a form in which the developer is pressed against the surface of the photoconductor. When the developer is carried on the roller surface in the form of a thin film, the developer roller also comes into contact with the blade, but in order to supply an appropriate amount of the developer to the surface of the photoconductor, the developing roller also has good contact with the surface of the photoconductor. Need to be maintained,
The elastic roller of the present invention can be suitably used. Further, the transfer roller, in the electrophotographic apparatus, during the image forming process,
The electrostatic latent image is visualized by applying a developer, and is used in a transfer process of transferring an image on the surface of the photoconductor to a transfer paper surface, and the transfer is performed at a gap between the roller surface and the surface of the photoconductor. Used to transfer the image on the photoconductor surface to the transfer paper surface by charging the back surface of the transfer paper in contact with the roller surface, which is charged to a polarity different from that of the photoconductor surface while nipping the paper. . Due to its main purpose, there are many states in which it is in pressure contact with the photoreceptor surface via transfer paper. In addition, maintaining the good contact state is indispensable for avoiding image defects, which is the same as the charging roller. Therefore, the elastic roller of the present invention can be suitably used for the transfer roller.

The developing roller and the transfer roller also have a form in which a conductive surface layer is coated on a conductive elastic layer produced using the rubber composition of the present invention. It is preferable to use it. It is desirable that the material of the surface layer provided with conductivity used in this case be selected in the developing roller in consideration of the holding characteristics of the developer carried on the surface. In the transfer roller,
It is desirable to select the material of the surface layer according to the property and material of the back surface of the transfer paper in contact.

In addition, in the elastic roller of the present invention, the thickness of the elastic layer is appropriately selected according to the contact pressure against the target photoreceptor or the like and the desired nip width. When providing a surface layer for covering the surface, it is a matter of course that the thickness is such that the function and purpose of the surface layer can be achieved, but a low hardness of the elastic layer, which should govern the roller hardness, is selected. It is desirable that the thickness be sufficiently thin to reflect the advantages obtained.

For example, when the elastic roller of the present invention is used for a charging roller, a developing roller, a transfer roller and the like for an electrophotographic apparatus, the thickness of the elastic layer is 1 to 30 mm, preferably 3 to 30 mm. The thickness may be selected in the range of 8 mm, and the thickness of the surface layer covering the surface may be selected in the range of 1 to 200 μm, preferably 5 to 100 μm. In addition, the hardness of the low hardness elastic layer itself is preferably in the range of 20 to 60 °, preferably 30 to 50 ° in the evaluation of ASKER-C.

[0045]

The present invention will be described below more specifically with reference to examples. The illustrated examples are examples of the best mode of the present invention, but the present invention is not limited by these examples. (Example 1) Using a rubber composition described below, an elastic layer was formed on a foamed conductive rubber layer.
A charging roller was prepared by coating with a conductive polyurethane film.

The rubber composition used to form the foamed conductive rubber layer was prepared in the following procedure to prepare a master batch having the composition shown in Table 1, and further foamed into the prepared master batch. Agent, foaming aid, sulfur, peroxide crosslinking agent,
It has a composition obtained by adding a crosslinking aid and mixing uniformly.

The composition and raw material rubber shown in Table 1 are ethylene-propylene-diene terpolymer (EPDM trade name: EPT4045; manufactured by Mitsui Petrochemical Co., Ltd.) 100
Parts, zinc oxide 5 parts, stearic acid 1 part, Ketjen Black as a conductive agent (trade name: Ketjen Black EC
600JD; Mitsubishi Chemical Corporation) 6 parts, S as reinforcing agent
RF carbon 50 parts, paraffin oil 5 as softener
The master batch was prepared by mixing 0 parts of each component at the above ratio in a pressure kneader.

[0048]

[Table 1]

Per 212 parts of the master batch having the composition shown in Table 1, 4 parts of ADCA and 4 parts of OBSH as foaming agents, 2 parts of urea and 0.3 parts of sulfur as foaming aids, and 2,5-dimethyl-2,2 as a peroxide crosslinking agent were used. 5-di (t-butylperoxy) hexane (trade name: Perhexa 25B-40)
15 parts of Nippon Oil & Fats Co., Ltd., triallyl isocyanurate (trade name: TAIC-M60) as a crosslinking aid
8.5 parts of Nippon Kasei Co., Ltd.) were added and mixed with an open roll to prepare an unvulcanized rubber composition for a conductive foamed rubber layer.

The unvulcanized rubber composition thus prepared was simultaneously extruded coaxially and cylindrically around a core metal (diameter 6 mm, length 240 mm) by extrusion molding using a crosshead, and the ends were cut. This was performed to prepare a charged shape. The obtained extruded product of the rubber composition having the charged shape and the core were integrated and fixed inside a cylindrical mold (inner diameter: 12 mm) by the core holding member. Each cylindrical mold was heated for 30 minutes with a heating plate heated to 180 ° C,
Primary vulcanization and foaming were performed. The roller after demolding was further heated at 200 ° C. for 10 minutes in an electric furnace in order to perform secondary vulcanization. A sponge roller having an outer diameter of 12 mm and a thickness of the foamed conductive rubber layer of 3 mm was thus obtained. The hardness of the obtained conductive foamed rubber layer was 42 by ASKER-C.
°. In addition, at this stage, when the properties of the surface of the conductive foamed rubber layer were observed, bubbles generated by the foaming were removed, and no traces of the bubbles remained as minute concave portions were found. There was no unevenness of the surface due to lack, and it was determined that the surface was formed on the skin layer.

Next, a conductive polyurethane film was coated as a surface layer on the surface of the conductive foamed rubber layer by the following procedure.

First, a polyurethane solution dispersed in water was adjusted to pH 5 to 6, and a conductive tin oxide slurry was dispersed in the solution by the electric repulsion at the interface, and the solid content ratio of the polyurethane was 60%. A coating material containing 40% of the conductive tin oxide slurry dispersed therein was prepared. This paint is coated by dipping on the sponge roller previously treated with a silane coupling agent, and the film thickness is about 80%.
A μm film was formed. This film is placed in an electric furnace for 120 minutes.
After ripening and drying at 30 ° C. for 30 minutes, a surface layer was obtained. Finally, both ends were cut to obtain a charging roller having a rubber length of 224 mm.

With respect to this charging roller, 30 minutes from the end
The surface roughness (Rz) was measured at the portion of mm. The charging roller manufactured in this example has an Rz value of 3 μm.
m.

Next, the charging roller was mounted on a process cartridge (coaxially pressed against a photosensitive member having a diameter of 30 mm with a load of 500 g at both ends of the roller), and was charged at 40 ° C. and 95% R.F. H.
(High temperature, high humidity) for 30 days. Thereafter, the charging roller was removed from the cartridge, and the amount of residual distortion immediately after the pressure on the photosensitive member was released was measured using a non-contact laser length measuring machine. The residual strain amount is represented by the difference between the distance from the roller center at the maximum deformation portion at the press contact portion and the roller radius at the time of manufacture, and was 20 μm in the present embodiment.

Further, the charging roller kept in the pressed state for a long time was mounted again on the process cartridge, and the process cartridge was incorporated into an electrophotographic apparatus (Laser Shot LBP-320 manufactured by Canon Inc.) to evaluate the image. As a result, no image defect due to permanent deformation of the charging roller was observed.

(Example 2) An elastic layer was formed on a foamed conductive rubber layer using the following rubber composition, and a conductive polyurethane film was coated as a surface layer. A roller was made.

The rubber composition used to form the foamed conductive rubber layer was prepared by adding the foaming agent, foaming aid, sulfur, It has a composition obtained by adding an oxide crosslinking agent and mixing uniformly.

Per 212 parts of the master batch having the composition shown in Table 1, 4 parts of ADCA and 4 parts of OBSH as foaming agents, 2 parts of urea and 0.3 parts of sulfur as foaming aids, and 2,5-dimethyl-2,2 as a peroxide crosslinking agent were used. 5-di (t-butylperoxy) hexane (trade name: Perhexa 25B-40)
; Nippon Yushi Co., Ltd.) and mixed with an open roll to prepare an unvulcanized rubber composition for a conductive foamed rubber layer.

Using the unvulcanized rubber composition prepared here,
A sponge roller was manufactured in the same manner as in Example 1. Accordingly, a sponge roller having an outer diameter of 12 mm, that is, a foamed conductive rubber layer having a thickness of 3 mm was obtained. The hardness of the obtained conductive foam rubber layer is 40 by ASKER-C.
°. In addition, at this stage, when the properties of the surface of the conductive foamed rubber layer were observed, bubbles generated by the foaming were removed, and no traces of the bubbles remained as minute concave portions were found. There was no unevenness of the surface due to lack, and it was determined that the surface was formed on the skin layer.

Then, the surface of the sponge roller was coated with a surface layer in the same manner as in Example 1. Finally, both ends were cut to obtain a charging roller having a rubber length of 224 mm.

With respect to this charging roller, 30 minutes from the end
The surface roughness (Rz) was measured at the portion of mm. The charging roller manufactured in this example has an Rz value of 5 μm.
Met.

Further, with respect to the charging roller manufactured in the second embodiment, the residual strain was measured and the image was evaluated by the same procedure and method as in the first embodiment. As a result, the residual distortion amount was 40 μm, and no image defect due to permanent distortion of the charging roller was observed.

Example 3 An elastic layer was formed on a foamed conductive rubber layer by using the following rubber composition, and a conductive polyurethane film was coated as a surface layer. A roller was made.

The rubber composition used to form the foamed conductive rubber layer was prepared by preparing a master batch having the composition shown in Table 1 by the following procedure, and further foaming the prepared master batch. Agent, foaming aid, sulfur, peroxide crosslinking agent,
It has a composition obtained by adding a crosslinking aid and mixing uniformly.

Per 212 parts of the master batch having the composition shown in Table 1, 4 parts of ADCA and 4 parts of OBSH as foaming agents, 2 parts of urea and 0.3 parts of sulfur as foaming aids, and 2,5-dimethyl-2,2 as a peroxide crosslinking agent were used. 5-di (t-butylperoxy) hexane (trade name: Perhexa 25B-40)
7.5 parts of Nippon Yushi Co., Ltd., triallyl isocyanurate (trade name: TAIC-M60) as a crosslinking aid
; Nippon Kasei Co., Ltd.) and mixed with an open roll to prepare an unvulcanized rubber composition for a conductive foamed rubber layer.

Using the unvulcanized rubber composition prepared here,
A sponge roller was manufactured in the same manner as in Example 1. Accordingly, a sponge roller having an outer diameter of 12 mm, that is, a foamed conductive rubber layer having a thickness of 3 mm was obtained. The hardness of the obtained conductive foamed rubber layer was 41 by ASKER-C.
°. In addition, at this stage, when the properties of the surface of the conductive foamed rubber layer were observed, bubbles generated by the foaming were removed, and no traces of the bubbles remained as minute concave portions were found. There was no unevenness of the surface due to lack, and it was determined that the surface was formed on the skin layer.

Next, the surface of the sponge roller was coated with a surface layer in the same manner as in Example 1. Finally, both ends were cut to obtain a charging roller having a rubber length of 224 mm.

With respect to this charging roller, 30 minutes from the end
The surface roughness (Rz) was measured at the portion of mm. The charging roller manufactured in this example has an Rz value of 6 μm.
Met.

Further, with respect to the charging roller manufactured in the third embodiment, the residual strain was measured and the image was evaluated by the same procedure and method as in the first embodiment. As a result, the residual distortion amount was 30 μm, and no image defect due to permanent distortion of the charging roller was observed.

(Comparative Example 1) An elastic layer was formed on a foamed conductive rubber layer using the following rubber composition, and a conductive polyurethane film was coated as a surface layer. A roller was made.

The rubber composition used to form the foamed conductive rubber layer was prepared in the following procedure to prepare a master batch having the composition shown in Table 1, and further foamed into the prepared master batch. Agent, sulfur (vulcanizing agent), vulcanization accelerator,
It has a composition obtained by mixing uniformly.

For 212 parts of the master batch having the composition shown in Table 1, 4 parts of ADCA and 4 parts of OBSH as foaming agents, 1 part of sulfur as a vulcanizing agent, and 2-mercaptobenzothiazole as a vulcanization accelerating aid (trade name: Noxeller M; large) 1 part of Uchi Shinko Chemical Industry Co., Ltd., 1 part of tetramethylthiuram disulphide (trade name: Noxeller TT; manufactured by Ouchi Shinko Chemical Co., Ltd.), 1 part of zinc dimethyldithiocarbamate (trade name: Noxeller PZ; large) Uchi Shinko Chemical Industry Co., Ltd.) 1
1 part of zinc dibutyldithiocarbamate (trade name: Noxeller BZ; manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
The mixture was mixed with an open roll to prepare an unvulcanized rubber composition for a conductive foamed rubber layer.

Using the unvulcanized rubber composition prepared here,
A sponge roller was manufactured in the same manner as in Example 1. Accordingly, a sponge roller having an outer diameter of 12 mm, that is, a foamed conductive rubber layer having a thickness of 3 mm was obtained. The hardness of the obtained conductive foam rubber layer is 40 by ASKER-C.
°. In addition, at this stage, when observing the properties of the surface of the conductive foam rubber layer, traces of minute concave portions were not in the apparent range, and local over-foaming, irregularities on the surface due to insufficient foaming were also problematic. Not so much, but it was judged that the surface was formed on the skin layer.

Next, the surface of the sponge roller was coated with a surface layer in the same manner as in Example 1. Finally, both ends were cut to obtain a charging roller having a rubber length of 224 mm.

With respect to this charging roller, 30 minutes from the end
The surface roughness (Rz) was measured at the portion of mm. The charging roller manufactured in this example has an Rz value of 3 μm.
Met.

Further, with respect to the charging roller manufactured in Comparative Example 1, the measurement of residual distortion amount and image evaluation were performed by the same procedure and method as in Example 1. As a result, the residual distortion amount was 80 μm, and accordingly, occurrence of an image defect due to permanent distortion of the charging roller was observed.

Comparative Example 2 An elastic layer was formed on a foamed conductive rubber layer by using the following rubber composition, and a conductive polyurethane film was coated as a surface layer. A roller was made.

The rubber composition used to form the foamed conductive rubber layer was prepared in the following procedure to prepare a master batch having the composition shown in Table 1, and further foamed into the prepared master batch. It has a composition obtained by adding an agent, a foaming aid, a peroxide cross-linking agent, and a cross-linking aid, and uniformly mixing.

For 212 parts of the master batch having the composition shown in Table 1, 4 parts of ADCA and 4 parts of OBSH as foaming agents, 2 parts of urea as foaming aid, and 2.5 parts of peroxide crosslinking agent
-Dimethyl-2,5-di (t-butylperoxy) hexane (trade name: Perhexa 25B-40; manufactured by NOF Corporation), 15 parts, triallyl isocyanurate (trade name: TAIC-M60; 8.5 parts of Nippon Kasei Co., Ltd.) were added and mixed with an open roll to prepare an unvulcanized rubber composition for a conductive foamed rubber layer.

Using the unvulcanized rubber composition prepared here,
A sponge roller was manufactured in the same manner as in Example 1. Accordingly, a sponge roller having an outer diameter of 12 mm, that is, a foamed conductive rubber layer having a thickness of 3 mm was obtained. The hardness of the obtained conductive foamed rubber layer was 41 by ASKER-C.
°. In addition, at this stage, when the properties of the surface of the conductive foam rubber layer were observed, traces of minute recesses were also noticeable,
In addition, apparent surface irregularities were determined at a glance.

Next, the surface of the sponge roller was coated with a surface layer in the same manner as in Example 1. Finally, both ends were cut to obtain a charging roller having a rubber length of 224 mm.

With respect to this charging roller, 30 minutes from the end
The surface roughness (Rz) was measured at the portion of mm. The charging roller manufactured in this example has an Rz value of 21 μm.
m, and this large surface roughness directly reflected the surface properties of the conductive foamed rubber layer.

Further, with respect to the charging roller manufactured in Comparative Example 2, measurement of residual distortion amount and image evaluation were performed by the same procedure and method as in Example 1. As a result, the residual distortion amount was 25 μm, and no image defect was determined, which was determined to be mainly caused by permanent distortion of the charging roller.

Comparative Example 3 An elastic layer was formed on a foamed conductive rubber layer using the following rubber composition, and a conductive polyurethane film was coated as a surface layer. I tried to make a roller.

The rubber composition used to form the foamed conductive rubber layer was prepared in the following procedure to prepare a master batch having the composition shown in Table 1, and further foamed into the prepared master batch. It has a composition obtained by adding an agent, a foaming aid, a peroxide cross-linking agent, and a cross-linking aid, and uniformly mixing.

For 212 parts of the master batch having the composition shown in Table 1, 4 parts of ADCA was used as a foaming agent, and 4 parts of urea were used as a foaming aid.
Part, 2,5-dimethyl- as a peroxide crosslinking agent
2,5-di (t-butylperoxy) hexane (trade name: Perhexa 25B-40; manufactured by NOF Corporation)
7.5 parts, triallyl isocyanurate (trade name: TAIC-M60; manufactured by Nippon Kasei Co., Ltd.) as a crosslinking aid 5
The resulting mixture was mixed with an open roll to prepare an unvulcanized rubber composition for a conductive foamed rubber layer.

Using the unvulcanized rubber composition prepared here,
A sponge roller was manufactured in the same manner as in Example 1. Therefore, an attempt was made to produce a sponge roller having a target outer diameter of 12 mm, that is, a target thickness of the foamed conductive rubber layer of 3 mm. At the stage of primary vulcanization and foaming and demolding, the properties of the obtained foamed rubber layer surface were observed, and fine concave marks were noticeable, and obvious surface irregularities were distinguished at a glance. Was done. The hardness of the conductive foam rubber layer is ASK
ER-C was 41 °. In addition, at this stage, when the properties of the surface of the conductive foamed rubber layer were observed, traces of minute concave portions were noticeable, and apparent surface irregularities were discriminated at a glance.

Further, after the secondary vulcanization was performed, the properties of the surface of the conductive foamed rubber layer and the degree of overall deformation were examined. After the surface layer was coated, fine concave marks were found. Even if filled with a conductive polyurethane coating, the surface unevenness, the degree of overall deformation, the evaluation of the surface roughness, the measurement of the residual strain amount, etc., whether the proper evaluation of the physical properties of the charging roller can be performed Even it was at stake.

At least, if the surface roughness was evaluated, the Rz value of the charging roller of Comparative Example 2 was a value far exceeding 21 μm. The measurement of the residual strain amount, which needs to measure the difference in the layer thickness, has reached a level that cannot be properly performed. Therefore, the evaluation of the physical properties of the finally obtained charging roller was judged to be impossible.

Tables 2 and 3 collectively show the compositions of the rubber compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 3, and the results of evaluation of the charging roller produced using the same.

[0091]

[Table 2]

[0092]

[Table 3]

For the elastic roller used for the charging roller, an elastic layer constituting the roller layer, for example, a conductive foamed rubber layer is required to have low hardness, and the hardness is AS.
Rz value of KER-C is selected at most not more than 50 °, preferably not more than 45 °, and depending on the toner particle diameter used, the surface roughness of the surface coated with the surface layer; Is preferably selected within a range of preferably 10 μm or less, more preferably 5 μm or less. At the same time, it is preferable that the amount of compression set of the roller is at most 50 μm or less, preferably 40 μm or less, in order to avoid occurrence of image defects due to deformation of the charging roller.

In light of the above-mentioned preferable characteristic value criteria,
As shown in Table 2, the charging roller manufactured by using the rubber composition of the present invention has an ASKER-C hardness of 42 ° even at the highest, and thus has a compression set of 45 ° or less. Is at most 40 μm or less, and the surface roughness; Rz value is 10 μm or less, and is approximately 5 μm. That is, good contact with the surface of the photoconductor can be achieved, and the residual strain can be kept in a low range even after being kept in pressure contact with the photoconductor for a long time. As a result, a favorable contact state of the charging roller with respect to the photoreceptor can be maintained, and there is obtained a charging roller having no charging unevenness and causing no image defects.

[0095]

EFFECTS OF THE INVENTION The rubber composition of the present invention is one of the more widely available raw rubbers other than urethane rubber and silicone rubber, which is a widely used vulcanizing agent as a crosslinking agent. In addition, a raw rubber that can be cross-linked with an organic peroxide cross-linking agent (peroxide cross-linking agent) is selected, and a foaming agent and, as a main cross-linking agent, an organic peroxide cross-linking agent (peroxide cross-linking agent) Is used in a form in which a small amount of sulfur is used in combination as a secondary crosslinking agent, and foaming and crosslinking treatment are performed under heating to obtain a foamed rubber molded article. By using an organic peroxide cross-linking agent (peroxide cross-linking agent) as a main cross-linking agent while forming a foam and adjusting the cross-linking density of the raw rubber to be used to achieve the desired low hardness, This makes it possible to produce a foamed rubber layer having a small compression set. In addition, by using a small amount of sulfur as a secondary cross-linking agent, the problem in the cross-linking reaction with the organic peroxide cross-linking agent (peroxide cross-linking agent), In order to prevent peroxide vulcanization, the vulcanization reaction with sulfur compensates for the overall crosslink density, and internally, it acts as a retarder for peroxide vulcanization, causing a reaction between the foaming reaction and the crosslinking reaction. The conditions under which balance is achieved are broadened. As a result, when performing cross-linking by peroxide vulcanization, local unevenness of the expansion ratio is often uneven, or the occurrence of recesses on the surface of the foamed rubber layer is a factor of large surface roughness. However, by compensating for these deteriorating factors by the action of sulfur used together in a small amount, the formation of irregularities on the surface due to foaming is also suppressed.For example, the surface in contact with the mold has a skin layer. Thus, a foamed rubber molded article having a small surface roughness can be obtained. That is, the elastic roller of the present invention produced using the rubber composition having the above advantages has a low hardness, a small compression set, and a small surface roughness. This has the advantage that image defects can be prevented. In addition, the elastic roller of the present invention, like the charging roller, has a good contact state when applied to an elastic roller having various conductivity used in an electrophotographic apparatus, for example, a developing roller and a transfer roller. , It can be maintained even if it is placed in pressure contact for a long time, and to maintain good image quality for a long time,
Both contribute and can be used favorably. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating an example of the configuration of an elastic roller of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Elastic roller (charging roller) 11 Core metal 12 Elastic body layer (conductive foamed rubber layer) 13 Surface layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 5/14 C08K 5/3477 5/3477 F16C 13/00 B F16C 13/00 B29K 9:00 // B29K 9:00 B29C 67/22 F-term (reference) 3J103 AA02 AA13 BA41 GA02 GA52 HA03 HA20 HA53 4F074 AA06 AA08 AA09 AA25 AC03 AD08 AD13 AG20 BA03 BA13 BA14 BA16 BA17 BA18 BA19 CC06X DA24 DA47 DA59 4F212 AA09A03 AG03 AG03 AB03 AD03 UA09 UB01 UB11 UB22 UG05 UN04 UN05 UW06 4J002 AC012 AC032 AC062 AC072 AC082 AC122 BB181 DA046 EK036 EK046 EK056 EQ018 EQ028 ES008 ET008 EU187 EU197 FD146 FD157 FD328 GM00

Claims (6)

[Claims] 1. A foamed rubber molded product is obtained by simultaneously performing foaming with a foaming agent and crosslinking treatment with a crosslinking agent under heating. At least a raw rubber, a crosslinking agent therefor, and a foaming agent are provided. A rubber composition comprising: the raw rubber is capable of being crosslinked by any of an organic peroxide and sulfur; and as the crosslinking agent, an organic peroxide as a main crosslinking agent.
It also contains sulfur as a secondary cross-linking agent, and has a sulfur content of 0.1 per 100 parts by mass of the raw rubber.
A rubber composition selected from the range of 1 to 1 part by mass. 2. The rubber composition according to claim 1, wherein an ethylene / propylene / diene copolymer is contained as a main component of the raw rubber. 3. The rubber composition according to claim 1, further comprising triallyl cyanurate or triallyl isocyanurate as a crosslinking aid in addition to the crosslinking agent. 4. An elastic roller comprising a cored bar and a roller layer provided on the outer periphery thereof, wherein the roller layer is at least the rubber composition according to claim 1. An elastic roller comprising an elastic layer made of a foamed rubber molded product obtained by subjecting a foam to a foaming / crosslinking treatment. 5. The elastic body layer made of a foamed rubber molded article and a core are integrated, and the integration of the core and the elastic layer is performed around a core metal member as an axis, Claims 1-3 arranged on the outer periphery
The layer of the rubber composition according to any one of the above, the core metal member in a mold having a lid body provided at both ends with a mechanism for holding the core metal member on a concentric axis with the inner surface of a cylindrical mold. Along with storing using the holding mechanism, in the mold, under heating, subjected to foaming and cross-linking treatment to form a foamed rubber molded product, characterized by being integrally molded. The elastic roller according to claim 4, wherein 6. The elastic roller according to claim 4, wherein the roller layer has a laminated structure having a surface layer formed on the outer surface of the elastic layer.