JP2000119449A - Conductive rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a conductive rubber composition which exhibits small fluctuation in electrical resistivity even when its carbon clock content is low and of which the fluctuation in electrical resistivity caused by the change in temperature, humidity, and applied voltage is decresed, by compounding a base rubber exhibiting an excellent ozone resistance and small fluctuation in electrical resistivity due to temperature and humidity with an ionically conductive polymer, an electronically conductive polymer, and a conductive agent. SOLUTION: Based on the total amt. of rubber components, 50-90 wt.% chloroprene rubber exhibiting an excellent ozone resistance and small fluctuation in electrical resistivity due to temperature and humidity, as the base rubber, is compounded with 5-45 wt.% hydrin rubber as the ionically conductive polymer and 5-45 wt.% NBR as the electronically conductive polymer. Based on 100 pts.wt. rubber composition, 10-50 pts.wt. carbon black, as the conductive agent, is added to give a conductive rubber composition having an electrical resistivity of 106-1010 Ω.cm. This composition is compounded and kneaded with suitable amounts of rubber additives, then molded, and crosslinked to give a stable rubber article exhibiting small fluctuation in electrical resistivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a conductive rubber composition, an electrical resistivity of ^{10 6} ~10 10 Ω · cm, change to any of the environmental temperature and humidity and the applied voltage is small, and machining It is suitable for forming a transfer belt used in an electrophotographic apparatus.

[0002]

2. Description of the Related Art A transfer belt used in an electrophotographic apparatus is prepared by blending carbon black as a conductive agent with a simple rubber such as EPDM, CR and NBR, and further comprises a vulcanizing agent, a vulcanization accelerator, a plasticizer and an antioxidant. It is manufactured using a rubber composition containing a compounding agent for rubber such as, and its electrical resistivity is 10 ⁴ to 10 ¹¹ Ω · depending on the type and amount of carbon black.
Adjusted to cm. However, in order to obtain the above electrical resistivity, a large amount of carbon black is required, and the above range is a region where the electrical resistivity greatly changes depending on the amount of the carbon black. In addition, there is a problem that it is not uniform even in the same lot. Further, the electric resistivity varies depending on environmental changes such as temperature and humidity, and also depending on applied voltage, and has so-called environment dependency and voltage dependency. Those with small values tended to be large on the other side.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a conductive rubber composition having a resistivity of about 10 ⁶ Ω · cm to 10 ¹⁰ Ω · cm. The present invention provides a conductive rubber composition suitable for use as a transfer belt in which the variation in resistivity is small and the variation in resistivity with changes in temperature and humidity and the applied voltage are both small.

[0004]

The conductive rubber composition according to the present invention comprises a rubber having excellent ozone resistance and having a small variation in electrical resistivity due to temperature and humidity, comprising an ion conductive polymer and carbon. An electron conductive polymer which becomes a conductor by adding a conductive agent such as black and a conductive agent are added.

[0005] Chloroprene rubber (CR) is an example of a base rubber which is excellent in the above-mentioned ozone resistance and has little change in electric resistivity due to temperature and humidity. In addition, as the ion conductive polymer, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GEC)
O), a hydrin rubber such as an epichlorohydrin-ethylene oxide binary copolymer (ECO) and an epichlorohydrin-allyl glycidyl ether binary copolymer (CO), and the like. They can be used in combination. The electron conductive polymer is a polymer that becomes a conductor by adding a conductive agent such as carbon black.
RBR and EPDM are exemplified. In particular, NBR, especially moisture-resistant NBR, is preferable in that the amount of CB for lowering the resistivity can be smaller than that of EPDM, and the amount of acrylonitrile is preferably 5 to 55%.

Examples of the conductive agent include carbon black, metal oxides, simple metals, and conductive polymers. Carbon black such as channel black, furnace black, and acetylene black is preferred.

The above base rubber (CR), ion conductive polymer (hydrin rubber such as GECO, ECO, CO, etc.)
The preferable compounding amount (constituent ratio) of the electron conductive polymer (NBR, EPDM, etc.) is 50 to 90% by weight of the base rubber, 5 to 45% by weight of the ion conductive polymer and the electron conductive polymer with respect to the total amount of the rubber. It is. The compounding amount of the conductive agent (carbon black) is 10 to 50 parts by weight, especially 1 to 100 parts by weight of the total of the rubber.
5 to 45 parts by weight are preferred. And other compounding agents for rubber, for example, a vulcanizing agent, a vulcanization accelerator, a plasticizer, an antioxidant and the like are appropriately added according to a conventional method.

The rubber composition obtained from the above base rubber, for example, CR, has a small variation in resistivity due to temperature and humidity, and is excellent in ozone resistance and workability, but has a large amount of conductive property to obtain a desired resistivity. Since carbon black is required, the dispersion unevenness becomes large and the homogeneity becomes poor,
In addition, the resistivity is easily changed by the voltage. On the other hand, ion conductive polymers such as hydrin rubber, which have ionic conductivity by themselves, enable the reduction of the carbon black, which is effective for improving the homogeneity of the resistivity, and the fluctuation of the resistivity due to the voltage. Can be reduced, but the resistivity tends to fluctuate depending on the temperature and humidity of the environment. GECO and ECO are ethylene oxide (E
O) Since the resistivity of the polymer itself can be changed by changing the content, it is particularly easy to obtain the desired resistivity. In particular, GECO has the lowest environmental dependency even among hydrin rubbers, and has a resistivity of 10 ⁷ to 10 ⁸ Ω · cm alone,
It is most preferable because it is close to the target resistivity.

Therefore, by mixing the base rubber and the ion-conductive polymer and blending a conductive agent (carbon black) with the mixture, the amount of carbon blended is suppressed to increase the homogeneity and reduce the variation in resistivity. Hold down,
Variations in resistivity due to voltage can be reduced, and good processability and ozone resistance as a rubber composition can be maintained. However, the two-component system composed of the base rubber and the ion-conductive polymer has relatively good conductivity, a resistivity of about 10 ⁷ to 10 ⁹ Ω · cm, and the electron conductivity is reduced by the addition of carbon black. Since the change to the conduction system is abrupt, the electrical characteristics become unstable, and the reproducibility of the resistivity deteriorates.

Therefore, according to the present invention, NBR or EPDM
As described above, the resistance of the rubber itself is higher than that of a mixture of a base rubber and an ion-conductive polymer or a mixture of the ion-conductive polymer and carbon black added to the mixture, and the resistivity of the electron-conductive polymer is particularly small due to temperature and humidity fluctuations. and of being formulated for the adjustment, 10 ^6-1 by selection of the amount
A resistivity in the range of 0 ¹⁰ Ω · cm is easily obtained, and its variation is small, the resistivity is stable with respect to both temperature and humidity and applied voltage, and it has excellent ozone resistance. A conductive rubber composition suitable for production is obtained.

However, the base rubber (C
When the compounding amount of R) is less than 50% by weight, ozone resistance and processability are reduced, and the environmental dependence of resistivity is increased.
If it exceeds 0% by weight, the amount of other polymers is insufficient,
The effect cannot be obtained. On the other hand, if the amount of the ion-conductive polymer (hydrin rubber) is less than 5% by weight, the effect of the addition cannot be obtained. If the amount exceeds 45% by weight, the processability decreases and the resistance value becomes difficult to control. If the amount of the electron conductive polymer (NBR, EPDM) is less than 5% by weight, the effect of addition is not obtained. If the amount exceeds 45% by weight, the ozone resistance becomes insufficient. If the amount of the conductive agent (carbon black) is less than 10 parts by weight with respect to the total amount of rubber, desired conductivity cannot be obtained. If the amount exceeds 50 parts by weight, the electron conductive system is more advantageous than the ion conductive system. A large conduction mechanism, and the variation and the voltage dependency increase.

The above-mentioned base rubber, ion-conductive polymer, electron-conductive polymer and carbon black are kneaded together with rubber additives such as a crosslinking agent, a crosslinking accelerator, a plasticizer and an antioxidant according to a conventional method. Then, it is molded into a desired shape, subjected to a crosslinking treatment, and optionally subjected to a finishing treatment, and then used as a transfer belt or the like.

[0013]

DETAILED DESCRIPTION OF THE INVENTION CR, GECO and NBR are
CR was weighed so as to be 50 to 90% by weight, GECO was 5 to 45% by weight, and NBR was 5 to 45% by weight based on the total amount.
0 parts by weight of carbon black and an appropriate amount of a rubber additive such as a crosslinking agent, a crosslinking accelerator, a plasticizer, an antioxidant, etc. are blended in an appropriate amount, kneaded, and the obtained rubber composition is wound around a mandrel to obtain a desired rubber composition. A cylinder having a diameter is formed, subjected to a cross-linking treatment, then cut into a desired width, and polished to obtain an endless transfer belt. This transfer belt has a resistivity of 10 ⁶ to 10 ¹⁰ Ω ·
In the range of cm, the variation is small, the resistivity is stable with respect to both temperature and humidity and applied voltage, and the ozone resistance is excellent.

[0014]

EXAMPLES The following rubber, polymer, carbon black,
An organic peroxide, a co-crosslinking agent and other rubber compounding agents were prepared. CR: Denka Chloroprene MT-4 manufactured by Denki Kagaku Kogyo Co., Ltd.
0 "GECO-A: Zeklon G310 manufactured by Zeon Corporation
6, EO: about 60% GECO-B: Zeklon G310 manufactured by Zeon Corporation
5 ", EO: about 40% NBR:" Nipol DN401L "manufactured by Zeon Corporation
L "Carbon black: MAF carbon black Organic peroxide:" Perhexa 25B "manufactured by NOF Co-crosslinking agent:" HICROS M "manufactured by Seiko Chemical Co., Ltd.

The above rubber, polymer, carbon black (CB), organic peroxide, co-crosslinking agent and other compounding agents for rubber are kneaded in the compounding ratio (parts by weight) shown in Tables 1-2.
The resulting sheet is wrapped around a mandrel, formed into a cylindrical shape, crosslinked at 160 ° C. for 30 minutes, and then polished to a 0.7 mm thick belt. After that, the electrical resistance was measured under various conditions, and the environmental dependency, the voltage dependency and the variation were compared. The results are shown in Tables 1 and 2. In Tables 1 and 2, the electric resistivity is described as a log value (power index).

Measurement of Electric Resistivity A sample was subjected to a high temperature and high humidity (H / H) condition of a temperature of 28 ° C. and a humidity of 85%, and a normal temperature and a normal humidity (N / N) of a temperature of 22 ° C. and a humidity of 55%.
Under low temperature and low humidity of 15 ° C and 15% humidity (L
/ L), the voltage was set to 500 V, and the electrical resistivity was measured. However, the electric resistivity at a voltage of 100 V was also measured under the conditions of medium temperature and medium humidity (N / N). Then, the resistivity is measured at six points for each sample, and the average value and the variation (difference between the maximum value and the minimum value) are obtained.
Was calculated.

Environmental Dependence The difference between the resistivity of high temperature and high humidity (H / H), 500 V and the resistivity of low temperature, low humidity (L / L), 500 V is calculated, and the environmental dependence is compared. A difference of less than 10 ¹ Ω · cm was evaluated as acceptable.

Voltage Dependency Under the condition of normal temperature and normal humidity (N / N), the difference between the resistivity at 100 V and the resistivity at 500 V was calculated, and the voltage dependency was compared. Less than ¹ Ω · cm was evaluated as acceptable.

Variation Measured at 6 points under the conditions of normal temperature and normal humidity (N / N) and 500 V, and compared the variation with the difference between the maximum value and the minimum value. If this difference was less than 10 ¹ Ω · cm, it passed. Was evaluated.

Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 CR 80 70 60 60 55 GECO-A 10 20 -30 30 GECO-B--20--NBR 10 10 20 10 15 MAF carbon 25 25 30 25 30 Zinc white 5 5 5 5 5 Stearic acid 1 1 1 1 1 Magnesium oxide − − − − − Organic peroxide 5 5 5 5 5 Co-crosslinking agent 3 3 3 3 3 Electric resistivity (Ωcm) A) (H / H, 500 V) 9.98 8.44 7.43 7.09 6.38 B (N / N, 500 V) 10.12 8.64 7.55 7.13 6.55 C (N / N, 100 V) 10.42 8.76 7.96 7.33 6.87 D (L / L, 500 V) 10.45 8.72 7.98 7.56 6.79 Variation (B) 0.23 0.17 0.44 0.56 0.48 Environment dependence (DA) 0.47 0.28 0.55 0.47 0.41 Voltage dependence (CB) 0.30 0.12 0.41 0.20 0.32

Table 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 CR 100 − − 80 80 GECO-A − 100 − 20 20 NBR − − 100 − − MAF carbon 30 − 45 10 30 Zinc white 5 5 5 5 5 Stearic acid 1 1 1 1 1 Magnesium oxide 3 − − 3 3 Organic peroxide 5 7 7 5 5 Co-crosslinking agent 3 1 1 3 3 Electrical resistivity (Ω · cm) A (H / H, 500 V) 8.63 6.29 8.69 7.43 7.69 B (N / N, 500 V) 8.72 7.30 8.92 8.36 8.44 C (N / N, 100 V) 10.09 7.42 10.16 8.42 9.56 D (L / L, 100 V) 9.25 8.16 9.13 9.40 8.58 Variation (B) 0.85 0.02 1.03 0.43 0.32 Environmental dependence (DA) 0.62 1.87 0.44 1.97 0.89 Voltage dependence (CB) 1.37 0.12 1.24 0.06 1.12

As shown in Tables 1 and 2 above, Examples 1 to
Sample No. 4 had an electric resistivity in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, and its variation, environment dependency and voltage dependency were small and less than 10 ^0.6 Ω · cm. On the other hand, in Comparative Example 1, since only CR was used as the rubber and GECO and NBR were omitted, the voltage dependency was excessive and the variation was large. In Comparative Example 2, G was used as the rubber.
Since only ECO was used, CR and NBR were omitted, and no carbon black was added, the variation was extremely small, but the environmental dependency was extremely large. In Comparative Example 3, since only NBR was used for rubber and CR and GECO were omitted, both the variation and the voltage dependency were excessive. Comparative Example 4 is based on rubber NBR.
Was omitted, and the blending amount of carbon black was set to be low. Thus, the ion conduction system was advantageous for hydrin rubber, and the voltage dependency was reduced, but the environment dependency was significantly increased. In Comparative Example 5, the compounding of rubber was the same as that of Comparative Example 4, but the compounding of carbon black was increased as compared with Comparative Example 4, so that the transfer to the CB advantageous electron conduction system was carried out, and the environmental dependency was slightly improved. On the other hand, the voltage dependency became excessive.

[0023]

As described above, the conductive rubber composition according to the first aspect has a base rubber which is excellent in ozone resistance and has little change in electric resistivity due to temperature and humidity. Since the ion-conductive polymer, the electron-conductive polymer and the conductive agent are respectively added, the electric resistivity can be reduced to 10 by appropriately setting the compounding amount.
^It is set in the range of ⁶ to 10 ¹⁰ Ω · cm, and its dispersion, environment dependency and voltage dependency can be reduced to 10 ¹ Ω · cm or less, respectively, and it has excellent ozone resistance. It is suitable for belts.

In particular, the invention of claim 2 limits the base rubber, the ion conductive polymer, the electron conductive polymer and the conductive agent to CR, hydrin rubber, NBR and carbon black, respectively. Variations in resistivity, environmental dependence and voltage dependence can be more easily balanced. Claim 3
In the invention described in the above, since the amount of each of CR, hydrin rubber, NBR and carbon black is limited,
The manufacturing of the transfer belt is further facilitated, and the manufacturing cost can be reduced.

Claims (3)

[Claims] 1. A base rubber made of rubber having excellent ozone resistance and little change in electrical resistivity due to temperature and humidity, and a conductive agent such as an ion conductive polymer or carbon black added to the base rubber to form an electronic conductor. A conductive rubber composition, wherein a conductive polymer and a conductive agent are added respectively. 2. The conductive rubber composition according to claim 1, wherein the base rubber is chloroprene rubber, the ionic conductive polymer is hydrin rubber, the electron conductive polymer is NBR, and the conductive agent is carbon black. 3. The compounding amount of chloroprene rubber is 50 to 90% by weight, the hydrin rubber is 5 to 45% by weight and the NBR is 5 to 45% by weight based on the total amount of rubber. The conductive rubber composition according to claim 2, wherein the amount is 10 to 50 parts by weight.