JP3593402B2 - Semi-conductive rubber - Google Patents

Description

【００２１】
［実施例２］
また比較例１の配合（１−３）の未加硫半導電性ゴム基材（加硫物の体積抵抗率４×１０^１０Ω・ｃｍのもの）を用いた以外は実施例１と同様にして以下の表２に示す結果を得た。
【表２】

【００２２】
［比較例２］
常法による半導電性ゴムの調製と試験
以下の配合による以外は、比較例１と同様の手順で、３個の試験シート片を作製し、体積抵抗率を測定した。
配 合 （重量部） （２−１）
エピクロマーＣＧ（東洋ソーダ） １００
Ｓｐａｎ＃６０（三共化成） ２
二塩基性亜燐酸鉛 ３
ＤＣＰ−４０ｃ^１） ３．５
ＣａＣＯ_３ （炭カルＰＣ） ２０
１）ＤＣＰ成分を４０重量％含有
試験シート片の体積抵抗率は、２×１０^８ Ω・ｃｍ、３×１０^９ Ω・ｃｍ及び７×１０^９ Ω・ｃｍであった。
【００２３】
［実施例３］
半導電性ゴムの調製及び体積抵抗率の測定
実施例１で調製した粒子（ａ）（体積抵抗率５×１０^２ Ω・ｃｍのもの）及び粒子（ｂ）（体積抵抗率６×１０^１４Ω・ｃｍのもの）を比較例２の配合（２−１）の未加硫半導電性ゴム基材（加硫物の体積抵抗率２×１０^８ Ω・ｃｍのもの）に表３に示す容積比率（ｖｏｌ％）で配合し、比較例１と同様の条件で加熱成形し、試験用シート片を得、体積抵抗率（Ω・ｃｍ）を測定した。表３に体積抵抗率の実測値を目標値と対比して示す。

【００２４】
【発明の効果】
上記実施例及び比較例に示す結果から明らかな通り、半導電性ゴム基材（Ｉ）が１×１０^４Ω・ｃｍ〜９×１０^１２Ω・ｃｍの範囲内の体積抵抗率を有するものであれば、導電性付与剤を含む（比較例１の配合）か含まない（比較例２の配合）かに係わりなく、１×１０^３Ω・ｃｍ以下の体積抵抗率を有する架橋、半架橋又は非架橋状態のゴム又はプラスチックの粒子（ａ）を単独に又は１×１０^１３Ω・ｃｍ以上の体積抵抗率を有する粒子（ｂ）と組み合わせて配合することにより、１×１０^３Ω・ｃｍ〜９×１０^１３Ω・ｃｍの範囲の体積抵抗率を有する半導電性ゴムを高い再現性で得ることができる。[0001]
[Industrial applications]
The present invention relates to a semiconductive rubber and a method for producing the same, and a semiconductive roll suitable for use as a charging roll, a developing roll, a transfer roll and the like in an electrophotographic system.
[0002]
[Prior art]
In the electrophotographic system, charging of the photoconductor, transfer of toner to plain paper, and elimination of residual toner have been generally performed by corona discharge method, that is, a thin wire such as tungsten stretched about 1 cm away from the surface of the photoconductor. A method has been adopted in which a high DC voltage of 4 to 10 kV is applied as a discharge electrode and a photoconductor base electrode as a counter electrode to cause a corona discharge between the two electrodes to charge the photoconductor. As is well known, corona discharge inevitably involves the generation of ozone. However, there has been no particular problem in the past because the equipment was small and low speed and the amount of generated ozone was small. However, in recent years, as the size and speed of devices have been increased, the amount of ozone generated has increased significantly, leading to environmental health problems.
[0003]
As a means for addressing this problem, a DC high voltage of about 1 kV is applied between a semiconductive rubber roll (hereinafter referred to as a charging roll) and a photoconductor base electrode which are brought into pressure contact with each other so as to form a rubber nip on the photoconductor surface. And a method of injecting charges from the charging roll to the photoreceptor (layer), that is, a so-called contact-type charging roll system has been proposed and partially adopted. However, in this method, the charge amount of the photoreceptor depends on the volume resistivity of the semiconductive rubber forming the charging roll. There is the problem that significant unacceptable fluctuations occur in the quality of the resulting image.
In order to keep the variation in image quality within an acceptable range, the variation range of the volume resistivity between lots is within two digits in units of Ω · cm, that is, 1 × 10 ^x Ω · cm to 1 × 10 ^{x + 2} Ω · cm (here, 3 ≦ X ≦ 11). However, with the conventional semiconductive rubber compounding technology, it is difficult to suppress the variation range of the volume resistivity between lots within four digits. there were.
[0004]
The semiconductive rubber is made of a conductive substance such as Ketjen black, acetylene black, conductive titanium oxide, zinc white, metal powder (tin, silver, copper, nickel), graphite, carbon fiber, metal fiber, whisker, conductive It is manufactured by compounding a rubber with ceramics, a powder having particle surfaces coated with a conductive substance, an organic conductive substance (pyrrole, anthracene compound, etc., and an ammonium salt as an ionic conductive substance).
[0005]
In particular, conductive carbon black such as Ketjen EC-600 (Ketjen Black International), Asahi HS-500 (Asahi Carbon), Vulcan XC-72 (Cabot), and electrified acetylene black (Denki Kagaku Kogyo) is used as the conductive substance. It is widely used.
These conductive carbon blacks give a conductive rubber having a volume resistivity in the semiconductive region at a loading of less than 10 phr, but this has been pointed out to be related to the high structure-forming ability of the conductive carbon black. ing. Presumably, this high ability to form structures results in large variations in product volume resistivity as a result of slight variations in processing conditions.
[0006]
Further, carbon blacks such as HAF, SRF, SRAF, FT, and MT, which are widely used as rubber reinforcing agents, have a low structure-forming ability and do not cause problems due to a high structure-forming ability. For this purpose, it must be blended in a large amount (for example, 40 parts to 120 parts), thereby deteriorating the processability of rubber and giving a product having a hardness that is too high for use in a charging roll. Incidentally, it is said that the semiconductive rubber used for the charging roll preferably has a low hardness of about 30 ° to 35 ° according to JISA so as to obtain a sufficient nip width.
[0007]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to have a volume resistivity in the range of 1 × 10 ³ Ω · cm to 9 × 10 ¹³ Ω · cm, in which the lot-to-lot variation of the volume resistivity is within two digits in Ω · cm units. An object of the present invention is to provide a semiconductive rubber, a method for producing the same, and a roll made of the semiconductive rubber.
[0008]
[Means for Solving the Problems]
The present invention, first (I) 1 × semiconductive rubber substrate was prepared having a volume resistivity in the range of ^{10 4 Ω · cm~ 9 × 10} 12 Ω · cm, which in (II) 1 × 10 ³ Crosslinked, semi-crosslinked or non-crosslinked rubber or plastic particles (a) having a volume resistivity of Ω · cm or less, alone or with the particles (a) having a volume resistivity of 1 × 10 ¹³ Ω · cm or more A semiconductive rubber having a volume resistivity in the range of 1 × 10 ³ Ω · cm to 9 × 10 ¹³ Ω · cm with high reproducibility is obtained by combining the particles with the particles (b) of the substance.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Semiconductive rubber substrate (I)
As the rubber used in the practice of the present invention, urethane rubber, epichlorohydrin rubber, nitrile rubber, acrylic rubber, polynorbornene rubber, chloroprene rubber, fluorine rubber, fluorosilicone rubber, silicone rubber, styrene-butadiene rubber, ethylene-propylene rubber, etc. Although there is no particular limitation, epichlorohydrin rubber, silicone rubber and ethylene-propylene rubber (including EPDM) having excellent weather resistance are preferred.
In order to obtain a semiconductive rubber substrate (I) having a volume resistivity in the range of 1 × 10 ⁴ Ω · cm to 9 × 10 ¹² Ω · cm from these rubbers, an appropriate amount of conductive carbon black is blended. Generally, other conductive substances such as conductive fibers, whiskers, and metal powders can be used. The mixing ratio of the conductive substance to the rubber varies depending on the type of the conductive substance and the rubber. For example, in the case of Ketjen EC-600, about 5 parts for epichlorohydrin rubber and about 7 to 10 for ethylene-propylene rubber. Parts.
In addition, as shown in Comparative Example 2 and Example 3 described later, the blending of a conductive substance such as conductive carbon black is not always necessary.
[0010]
Particle (a)
Particles (a) having a volume resistivity of 1 × 10 ³ Ω · cm or less can be obtained, for example, by blending 20 parts or more of Ketjen EC-600 with ethylene-propylene rubber by an ordinary method, and forming the resulting compound as described below. It is obtained by pulverizing by a suitable method. When the rubber is epichlorohydrin rubber, a compounding amount of Ketjen EC-600 of 10 parts or more is sufficient.
[0011]
Particle (b)
Particles (b) having a volume resistivity of 1 × 10 ¹³ Ω · cm or more are obtained by, for example, mixing ethylene-propylene rubber with reinforcing carbon black such as HAF and SRF within 5 parts and pulverizing the mixture. Obtained by: Further, silica, calcium carbonate, talc, or the like can be used instead of carbon black.
In the case of epichlorohydrin rubber, the volume resistivity of itself is low. To obtain a composition having a volume resistivity of 1 × 10 ¹³ Ω · cm or more, a non-conductive filler such as calcium carbonate, mica, talc, silica, etc. You can add However, silicone rubber is generally used to obtain rubber particles of 1 × 10 ¹³ Ω · cm or more.
[0012]
Use of resin in preparation of particles (a) and (b) In preparing particles (a) and (b), resins can be used instead of rubber. For example, polycarbonate, polyamide, polyimide, fluorine resin, silicone resin, polyester resin, polyether resin and the like can be used. However, these resins have a high hardness at room temperature and tend to increase the hardness of the resulting semiconductive rubber. Therefore, the amount of the resin to the semiconductive rubber substrate is limited.
[0013]
Powdering the formulation for the preparation of particles (a) and particles (b) Particles (a) and (b) are generally prepared by converting a formulation having a given volume resistivity into liquid nitrogen. And can be easily obtained by a freeze-pulverization method at -160 ° C or lower. Grinding or other powdering means can also be used. The obtained particles change into spherical, ellipsoidal, or acicular shapes by means of powdering, and any shape can be used. Although the particle size distribution is also various, in general, particles having a range of 0.1 to 750 μm are obtained. The particle size is most preferably 50 ± 25 μm, and a powder having a desired particle size can be obtained by classifying the powdered product.
The compound to be powdered may be in a cross-linked state, a semi-cross-linked state, or an uncross-linked state.
[0014]
Mixing of particles (a) and (b) with the semiconductive rubber substrate (I) The volume resistivity of the semiconductive rubber is such that the particles (a) and (b) are mixed with the semiconductive rubber substrate (I). It depends on the blending amount (outer volume ratio) of (b). The blending amount of the particles (a) is in the range of 1 to 60 vol%. If the amount exceeds 60 vol%, the processability of the rubber becomes extremely poor, and a semiconductive rubber having a desired volume resistivity cannot be obtained with high reproducibility.
The amount of particles (b) is 3 5 vol% or less. If the amount of the particles (b) is more than 3 5 vol%, the particles also increases the amount of (a) (of course, within a range not extremely worsen the workability), 9 × following ^{10 13 Ω} · cm It is difficult to obtain a semiconductive rubber having a volume resistivity.
The obtained semiconductive rubber can be molded by any method, and can be cross-linked by any cross-linking means according to the properties of the rubber.
The particles (a) and (b) may be deformed or melted during compounding and kneading with the semiconductive rubber substrate or during the molding process, and lose the original shape. In such a state, it becomes difficult to obtain a product having a desired volume resistivity with good reproducibility, so that sufficient consideration must be given to the composition, processing conditions, and the like.
[0015]
Semiconductive rubber roll The semiconductive rubber of the present invention obtained according to the above procedure is suitable for producing a semiconductive rubber roll, particularly a semiconductive roll used as a charging roll in an electrophotographic system. For the semiconductive rubber layer of the roll to be manufactured, a solid body is generally used.However, using a foaming agent, elution of the mixed soluble powder, mixing of micro-balloons, etc. It may be a so-called sponge body having a generated closed or open cell structure.
In general, semi-conductive rubber rolls are formed by compression molding (press molding), but other means such as compression molding, injection molding, powder compression molding, and casting of liquid compounds, depending on the characteristics of the compound. It can also be. This type of roll is generally formed integrally with a core held in a mold, but it is also possible to insert the core into a separately formed tubular rubber roll. The formed roll is usually finished to a predetermined outer diameter by polishing.
The core metal of the rubber roll is generally made of metal, particularly steel, but may be made of ceramics or plastics. The rubber roll layer is usually fixed to the core with an adhesive, but the core is inserted in a state in which the tubular rubber roll layer is heated and expanded, and the shrink fit method is used in which the rubber roll layer is fixed to the core by cooling and shrinking the rubber roll layer. You can also.
[0016]
The semiconductive rubber roll finished to a predetermined outer diameter then improves the medium resistivity layer as a resistivity adjusting layer and the stain resistance, toner resistance, insulation resistance, sliding properties or abrasion resistance as desired. Multi-layer rolls can be finished by coating a protective layer.
As the coating material, depending on the purpose, a fluororesin, a urethane resin, a nylon resin, a polyolefin resin, a rubber-based polymer, a thermoplastic elastomer, various ceramics, or the like with or without a filler such as carbon or ceramic powder is used. . Although the thickness of the coating layer is not particularly limited, the thickness of the medium resistivity layer is usually 100 to 300 μm, the thickness of the protective layer is usually 5 to 30 μm, and a three-layer structure is generally used. The protective layer may be provided by a thin tubular film coating.
[0017]
The semiconductive rubber roll of the present invention exhibits excellent image reproducibility when used as a charging roll in an electrophotographic system (a uniform image can be obtained even if the roll is manufactured in different lots), and also has a high quality. Since there is almost no variation, it shows excellent performance as a developing roll, a transfer roll, a paper feed roll, a hot-press fixing roll, and a backup roll.
As described above, the semiconductive rubber roll has been described, but the semiconductive rubber of the present invention can be suitably used as another rubber member which is required to be semiconductive or non-chargeable. Would be self-evident.
[0018]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Comparative Examples and Examples.
[Comparative Example 1]
Preparation and test of semi-conductive rubber by conventional method Three kinds of semi-conductive rubber having different target volume resistivity by the following three kinds of compounds (only the amount of conductive Ketjen EC-600 is different). A conductive rubber sheet was prepared, and the volume resistivity was measured.
Combination (parts by weight) (1-1) (1-2) (1-3)
Mitsui 3045 ETP ¹⁾ 100 100 100
ZnO 5 5 5
Stearic acid 1 1 1
DCP ²⁾ 1.5 1.5 1.5
TAIC ³⁾ 2.0 2.0 2.0 2.0
CaCO ₃ (charcoal PC) 20 20 20
Process oil 35 35 35
Ketjen EC-600 ⁴⁾ 10 7 5
1) Ethylene-propylene rubber (Mitsui Petrochemical Industries)
2) Dicumyl peroxide 3) Triallyl isocyanurate 4) Conductive carbon black (Ketchen Black International)
The compound was prepared by kneading the rubber and the compounding components by a conventional method, and press-cured at 150 ° C. for 30 minutes to obtain a test sheet piece of 120 mm × 120 mm × 2 mm. The preparation of the compound and the preparation of test sheet pieces were repeated three times for each compounding. The measurement of the volume resistivity was performed using the following equipment.
Volume resistivity range of 10 ⁶ to 10 ¹⁶ Ω · cm: insulation resistance meter type 4329A (Yokogawa / Hewlett-Packard)
Volume resistivity range of 10 ⁻² to 10 ⁷ Ω · cm: Loresta AP (manufactured by Mitsubishi Yuka)
The measurement results (volume resistivity Ω · cm) were as shown below.
Combination (1-1) (1-2) (1-3)
Target value 1 × 10 ⁶ 1 × 10 ⁹ 1 × 10 ¹¹
Actual measurement value 1 2 × 10 ⁵ 9 × 10 ⁷ 5 × 10 ⁹
Measured value 24 × 10 ⁶ 4 × 10 ⁸ 1 × 10 ¹⁰
Measured value 37 × 10 ⁸ 2 × 10 ¹¹ 3 × 10 ¹²
From the above results, it can be understood that it is extremely difficult to stop the variation of the volume resistivity within two digits by the conventional method.
[0019]
[Example 1]
Preparation of particles (a) and particles (b) Two kinds of rubber sheets having different volume resistivity were prepared by the same procedure as in Comparative Example 1 under the following blending and vulcanization conditions, and Was measured. The preparation of the compound and the preparation of test sheet pieces were repeated three times for each compounding.
Mixing (parts by weight) (1-a) (1-b)
TSE3452HCR ¹⁾ 100
Mitsui 3045EPT 100
DCP 1.5 1.5
ZnO 5
Stearic acid 1
TAIC 2.0
CaCO ₃ (charcoal PC) 40
Process oil 35
1) Silicone rubber (Toshiba Silicone)
The compound of Formula (1-a) was press-cured at 160 ° C. for 20 minutes, and then subjected to secondary vulcanization at 200 ° C. for 4 hours to obtain a sheet having the same dimensions as Comparative Example 1. The compound of the compound (1-b) was press-cured at 150 ° C. for 30 minutes, and then subjected to secondary vulcanization at 155 ° C. for 3 hours to obtain a test sheet piece having the same dimensions as Comparative Example 1.
The measurement results (volume resistivity Ω · cm) were as shown below.
Combination (1-a) (1-b)
Target value <1 × 10 ³ > 1 × 10 ¹³
Measured value 1 3.0 × 10 ² 6 × 10 ¹⁴
Measured value 2 5.5 × 10 ² 8 × 10 ¹⁴
Measured 3 5.0 × 10 ² 1 × 10 ¹⁵
The above results show that the target volume resistivity of 10 ³ Ω · cm or less and the target volume resistivity of 10 ¹³ Ω · cm or more were both obtained with good reproducibility.
Next, these rubber sheet pieces were cooled and pulverized with liquid nitrogen and classified to obtain particles (a) and particles (b) having a particle size of 25 to 100 μm (75 μm on average).
[0020]
Preparation of semiconductive rubber and measurement of volume resistivity Particles (a) (having a volume resistivity of 5 × 10 ² Ω · cm) and particles (b) (volume resistivity of 6) prepared by the above method. × 10 ¹⁴ Ω · cm) to the unvulcanized semiconductive rubber base material (vulcanized material having a volume resistivity of 4 × 10 ⁴ Ω · cm) of the composition (1-1) of Comparative Example 1. The mixture was blended at the volume ratio (vol%) shown in No. 1 and heat-molded under the same conditions as in Comparative Example 1 to obtain a test sheet piece, and the volume resistivity (Ω · cm) was measured. Table 1 shows the measured values of the volume resistivity in comparison with the target values.
[Table 1]

[0021]
[Example 2]
In addition, the same procedure as in Example 1 was carried out except that the unvulcanized semiconductive rubber substrate (having a volume resistivity of the vulcanized product of 4 × 10 ¹⁰ Ω · cm) of the composition (1-3) of Comparative Example 1 was used. The results shown in Table 2 below were obtained.
[Table 2]

[0022]
[Comparative Example 2]
Preparation and Test of Semiconductive Rubber by Conventional Method Three test sheet pieces were prepared in the same procedure as in Comparative Example 1 except that the following compounding was performed, and the volume resistivity was measured.
Mixing (parts by weight) (2-1)
Epichromer CG (Toyo Soda) 100
Span # 60 (Sankyo Kasei) 2
Dibasic lead phosphite 3
DCP-40c ¹⁾ 3.5
CaCO ₃ (charcoal PC) 20
1) The volume resistivity of a test sheet piece containing 40% by weight of the DCP component was 2 × 10 ⁸ Ω · cm, 3 × 10 ⁹ Ω · cm, and 7 × 10 ⁹ Ω · cm.
[0023]
[Example 3]
Preparation of semiconductive rubber and measurement of volume resistivity Particles (a) (having a volume resistivity of 5 × 10 ² Ω · cm) and particles (b) (volume resistivity of 6) prepared in Example 1 were prepared. × 10 ¹⁴ Ω · cm) to the unvulcanized semiconductive rubber base material (vulcanized material having a volume resistivity of 2 × 10 ⁸ Ω · cm) of the composition (2-1) of Comparative Example 2. 3, and heat-molded under the same conditions as in Comparative Example 1 to obtain a test sheet piece and measure its volume resistivity (Ω · cm). Table 3 shows the measured values of the volume resistivity in comparison with the target values.

[0024]
【The invention's effect】
As is clear from the results shown in the above Examples and Comparative Examples, the semiconductive rubber substrate (I) has a volume resistivity in the range of 1 × 10 ⁴ Ω · cm to 9 × 10 ¹² Ω · cm. If present, regardless of whether the composition contains a conductivity-imparting agent (composition of Comparative Example 1) or not (composition of Comparative Example 2), it has a cross-linking, semi-cross-linking or a volume resistivity of 1 × 10 ³ Ω · cm or less. By mixing the non-crosslinked rubber or plastic particles (a) alone or in combination with the particles (b) having a volume resistivity of 1 × 10 ¹³ Ω · cm or more, 1 × 10 ³ Ω · cm to A semiconductive rubber having a volume resistivity in the range of 9 × 10 ¹³ Ω · cm can be obtained with high reproducibility.

Claims (14)

In a semiconductive rubber having a volume resistivity in the range of 1 × 10 ³ Ω · cm to 9 × 10 ¹³ Ω · cm,
(I) A semiconductive rubber base material having a volume resistivity in the range of 1 × 10 ⁴ Ω · cm to 9 × 10 ¹² Ω · cm has (II) a volume resistivity of 1 × 10 ³ Ω · cm or less. Crosslinked, semi-crosslinked or non-crosslinked rubber or plastic particles (a) alone or in combination with particles (a) and particles (b) of a substance having a volume resistivity of 1 × 10 ¹³ Ω · cm or more A semi-conductive rubber characterized by being compounded with a rubber. Based on the semiconductive rubber substrate (I), a is 1 ~ 6 0 vol% proportion of the particles (a), semiconducting of claim 1 proportion of particles (b) is 3 5 vol% or less Rubber. Particles (a) and particles (b) is a semi-conductive rubber according to claim 1 or 2 have an average particle diameter of 1 ~ 7 50 [mu] m. 4. The semiconductive rubber according to claim 1, wherein the particles (b) are rubber particles or plastic particles, ceramic particles or metal particles in a crosslinked, semicrosslinked or non-crosslinked state. The semiconductive rubber according to claim 1, wherein the rubber is a crosslinkable rubber, a thermoplastic rubber, or a mixture thereof. (I) A semiconductive rubber base material having a volume resistivity in the range of 1 × 10 ⁴ Ω · cm to 9 × 10 ¹² Ω · cm has (II) a volume resistivity of 1 × 10 ³ Ω · cm or less. Crosslinked, semi-crosslinked or non-crosslinked rubber or plastic particles (a) alone or in combination with particles (a) and particles (b) of a substance having a volume resistivity of 1 × 10 ¹³ Ω · cm or more A method for producing a semiconductive rubber having a volume resistivity in the range of 1 × 10 ³ Ω · cm to 9 × 10 ¹³ Ω · cm. The semiconductive rubber substrate based on the particles are the 1 ~ 6 0 vol% blend ratio of (a), the semi-conductive rubber according to claim 6 blend ratio of the particles (b) is 3 5 vol% or less Production method. Particles (a) and particles (b) is 1 ~ 7 50 [mu] m average method of manufacturing semi-conductive rubber according to claim 6 or 7 and has a particle size of. 9. The method according to claim 6, wherein the particles (b) are crosslinked, semicrosslinked or non-crosslinked rubber or plastic particles, ceramic particles or metal particles. 7. The method according to claim 6, wherein the rubber is a crosslinkable rubber, a thermoplastic rubber, or a mixture thereof. (I) A semiconductive rubber base material having a volume resistivity in the range of 1 × 10 ⁴ Ω · cm to 9 × 10 ¹² Ω · cm has (II) a volume resistivity of 1 × 10 ³ Ω · cm or less. Crosslinked, semi-crosslinked or non-crosslinked rubber or plastic particles (a) alone or in combination with particles (a) and particles (b) of a substance having a volume resistivity of 1 × 10 ¹³ Ω · cm or more A semiconductive single-layer or multi-layer, comprising a semiconductive rubber having a volume resistivity in the range of 1 × 10 ³ Ω · cm to 9 × 10 ¹³ Ω · cm obtained by mixing roll. The roll according to claim 11, which is coated with resin or rubber. The roll of claim 11, wherein the semiconductive rubber is non-porous or porous. The roll according to claim 11, which is a charging roll, a developing roll, a transfer roll, a paper feed roll, a heat and pressure fixing roll, and / or a backup roll in an electrophotographic system.