JPH08302075A - Electroconductive rubber composition - Google Patents

Abstract

PURPOSE: To obtain a stable electroconductive rubber composition low in the lot-to-lot variation of electrical resistance and voltage dependency, by blending a base rubber with each specified amount of a metal salt-doped ether linkage- contg. ester-based plasticizer and carbon black. CONSTITUTION: This electroconductive rubber composition excellent in stability with time and having the above-mentioned advantages is obtained by blending 100 pts.wt. of a base rubber (e.g. styrene-butadiene copolymer rubber) with 5-100 pts.wt. of an ester-based plasticizer doped with a metal salt such as lithium chloride, expressed by the formula (X is a 2-8C alkylene, divalent aromatic group or divalent alicyclic group; R<1> and R<2> are each a 3-15C alkyl; A<1> and A<2> are each a 2-4C alkylene; (m) and (n) are each an integer of 1-7) and having at least one ether linkage in the molecule and <=70 pts.wt. of carbon black followed by kneading the resultant blend using an open roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive rubber composition.

[0002]

2. Description of the Related Art In order to impart conductivity to a rubber composition, it is usual to blend a conductive carbon black into a base rubber.
In such a conventional conductive rubber composition, the electric resistance value greatly varies between the production lots and within the production lots, the electric resistance value greatly changes depending on the applied voltage (the voltage dependence is large), or the electric resistance value Has a problem that it becomes unstable over time.

This is because in the conventional conductive rubber composition, the rubber composition is electrically conductive mainly by a so-called electron conduction mechanism in which π electrons on the surface of carbon black compounded in the base rubber move. This was due to the imparting of sex. That is, in the conventional conductive rubber composition, as described above, the contribution to conductivity is very small.
Since it is an electron and its mechanism of exhibiting conductivity is not clear and it is difficult to control, it causes various problems as described above.

Further, since the above-mentioned conventional conductive rubber composition contains a large amount of carbon black, there is also a problem that a color other than black (particularly a light color such as white) cannot be obtained. The object of the present invention is to reduce variations in electric resistance values due to manufacturing lots and the like, voltage dependency, etc., and to have excellent stability over time. To provide a rubber composition.

[0005]

In order to solve the above-mentioned problems, the inventors of the present invention have been less dependent on carbon black because of the addition of a new component which can impart conductivity to the rubber composition instead of carbon black. It was considered to produce a conductive rubber composition that does not. As a result, it is known that when compounded in a rubber composition, it exhibits conductivity even though it is insufficient. Doping with a metal salt into an ester plasticizer having at least one ether bond in the molecule Then, because the metal ions in the metal salt dissociate and move, so-called ion conduction occurs, and sufficient conductivity can be imparted to the rubber composition, so that the amount of carbon black blended should be smaller than before. It has been found that a conductive rubber composition having sufficient conductivity can be obtained without adding any carbon black.

Further, the above-mentioned ester-based plasticizer doped with a metal salt does not show a black color like carbon black itself, but shows a light-colored color such as white depending on the kind of the metal salt. It has also been found that a conductive rubber composition having a free tint other than black can be obtained by using the above-mentioned system containing only the plasticizer, which does not contain carbon black. Therefore, the conductive rubber composition of the present invention is a conductive rubber composition in which at least a plasticizer of a plasticizer and carbon black is mixed in the base rubber, and as the plasticizer,
An ester plasticizer doped with a metal salt and having at least one ether bond in the molecule is used,
The compounding amount of the ester plasticizer with respect to 100 parts by weight of the base rubber is in the range of 5 to 100 parts by weight, and the compounding amount of carbon black is 70 parts by weight or less.

The present invention will be described below. The conductive rubber composition of the present invention is a composition in which at least a plasticizer among ester black plasticizers doped with a metal salt and carbon black is mixed with the base rubber as described above. That is, the conductive rubber composition of the present invention includes a system in which a plasticizer and carbon black are used in combination and a system in which only the plasticizer is used.

The base rubber is not limited to this, but includes, for example, natural rubber (NR) and chloroprene rubber (C).
R), ethylene-propylene-diene copolymer rubber (EP
DM), chlorosulfonated polyethylene rubber (CS
M), epichlorohydrin-ethylene oxide copolymer rubber (CHC), epichlorohydrin homopolymer rubber (CH)
R), styrene-butadiene copolymer rubber (SBR), nitrile rubber (NBR), butadiene rubber (BR), acrylic rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether ternary copolymer rubber, epichlorohydrin-propylene oxide-allyl glycidyl ether ternary Examples include original copolymer rubber. Such base rubbers can be used alone or in combination of two or more.

Particularly, in the case of a light-colored conductive rubber composition, NBR, CR, SBR, BR, CS among the above
Light-colored base rubbers such as M, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer rubber, and epichlorohydrin-propylene oxide-allyl glycidyl ether terpolymer rubber are preferably used.

Of these, 3 of NBR, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer rubber, and epichlorohydrin-propylene oxide-allyl glycidyl ether terpolymer rubber are particularly preferable.
The base rubber of the seed itself has a volume resistivity of 10 ¹⁰ Ω · cm.
Since it has the following high conductivity, it is suitable for use in a system using only a plasticizer to obtain a rubber composition having a light color and high conductivity.

Regarding the base rubber having a volume resistivity of more than 10 ¹⁰ Ω · cm, a system in which a plasticizer and carbon black are used in combination for the purpose of resistance adjustment, hardness adjustment, elongation / workability adjustment, and a plasticizer Can be used in any of the systems used alone. The plasticizer to be added to the base rubber is known to have at least one ether bond in its molecule and to exhibit electrical conductivity, though insufficient, when added to the rubber composition. Any of various known ester plasticizers known in the art can be used.

Specific examples of the ester-based plasticizer include, but are not limited to, general formula (1):

[0013]

Embedded image

[In the formula, X represents an alkylene group having 2 to 8 carbon atoms, a divalent aromatic group, or a divalent alicyclic group,
R ¹ and R ² are the same or different and represent an alkyl group having 3 to 15 carbon atoms, and A ¹ and A ² are the same or different and represent an alkylene group having 2 to 4 carbon atoms. m and n each independently represent an integer of 1 to 7. ] Is included.

Examples of the metal salt to be added to the ester-based plasticizer include organic or inorganic compounds that are prone to cause dissociation of metal ions as described above. Is preferable, and a metal salt having a small dissociation energy, that is, easily becoming an ion and generating a cation with high mobility is preferable.

Examples of such a cation include L
Alkali metal cations such as i ⁺ , Na ⁺ and K ⁺ , or alkaline earth metal cations such as Mg ²⁺ and Ca ²⁺ are preferable. Specific examples of the metal salt containing the above cation include, for example, Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , PF whose anion site that constitutes the metal salt together with the cation is.
_{^{6 -, ClO 4 -, NO}} 2 -, CO 3 - , etc. inorganic metal salt and a, or comprises the cationic in the molecule, various ionic surfactants, such as alkyl phosphate ester salts, polyoxyethylene alkyl (Or phenyl) ether phosphate salt, salt of polyoxyethylene-polyoxypropylene block copolymer, polyoxyethylene alkylamine salt, quaternary ammonium salt and the like.

The amount of the metal salt doped into the plasticizer is not particularly limited, but it is preferable to dope 0.5 to 5 parts by weight of the metal salt with respect to 100 parts by weight of the plasticizer. When the doping amount of the metal salt is less than the above range, the action of the above-mentioned ion conduction due to the metal ions in the metal salt may not be sufficiently obtained, and when the amount exceeds the above range, the metal salt is May be precipitated.

Specific examples of the ester-based plasticizer doped with the above metal salt include, but are not limited to, for example, trade name US-70 manufactured by Sanken Kako Co., Ltd. (volume resistivity 10 ⁷ Ω · cm). ) And the product name LV8 manufactured by Asahi Denka Co., Ltd.
08 (volume resistivity 10 ⁵ Ω · cm) and the like. The compounding amount of the ester-based plasticizer doped with the metal salt with respect to the base rubber is limited to 5 to 100 parts by weight with respect to 100 parts by weight of the base rubber.

When the compounding amount of the plasticizer is less than the above range, the effect of imparting conductivity to the rubber composition cannot be obtained. On the other hand, if the compounding amount of the plasticizer exceeds the above range, it becomes difficult to process the rubber composition. In consideration of prevention of bleeding of the plasticizer from the rubber composition and the like, the blending amount of the plasticizer is preferably 5 to 50 parts by weight even within the above range.

As the carbon black that may be compounded in the base rubber together with the above-mentioned plasticizer, various conventionally known grades of carbon black can be used. However, in this invention, conductivity is imparted to the rubber composition mainly by the plasticizer, and carbon black has a secondary function of conductivity (for example, adjustment of volume resistivity).
Therefore, it is not necessary to select a grade having excellent conductivity. Rather, it is preferable to use carbon black which is excellent in the function of reinforcing and increasing the amount of the rubber composition, and the function of assisting the moldability of the rubber composition. As such carbon black,
Examples include GPF and FEF.

In the present invention, carbon black is a component which may or may not be blended, and particularly in the case of a light-colored rubber composition such as white as described above, or its own volume resistance. In the case of a base rubber having a rate of 10 ¹⁰ Ω · cm or less, it is preferable not to mix. Also, when blending carbon black for the purpose of adjusting the volume resistivity,
The blending amount must be 70 parts by weight or less with respect to 100 parts by weight of the base rubber. When the blending amount of carbon black exceeds the above range, the influence of electron conduction of the carbon black becomes large, and as described above,
There arises a problem that variations in electric resistance values due to manufacturing lots, voltage dependence, or the like becomes large, or electric resistance values become unstable over time.

When carbon black is blended, the lower limit of the blending amount is not particularly limited,
It is preferable to add 5 parts by weight or more of carbon black to 100 parts by weight of the base rubber. If the blending amount of carbon black is smaller than this, the effect of addition is not sufficiently obtained, and there is a possibility that it will be almost the same as when it is not blended.

The conductive rubber composition of the present invention comprising the above-mentioned components is further supplemented with a filler such as silica, clay, talc, etc., a flame retardant, a vulcanizing agent, a vulcanization accelerator, and Various conventionally known additives such as a sulfur retardation agent, a vulcanization acceleration aid, and an antiaging agent may be blended in appropriate proportions, if necessary. The conductive rubber composition of the present invention is produced by kneading the above components using, for example, an open roll or a closed kneader.

The electroconductive rubber composition of the present invention can be used for electroconductive rollers, conveyor belts and the like in electrophotographic devices such as electrostatic copying machines, laser printers and plain paper facsimile machines. It can also be used for flooring materials, mats, footwear, etc. that require an antistatic function. In particular, the above flooring materials, mats, footwear, etc., had a problem in terms of appearance because only black ones could be obtained by using the conventional conductive rubber composition, but the conductive rubber composition of the present invention was used. Of these, if a system that does not contain carbon black is adopted in particular, it is possible to produce products with various shades, so that aesthetic problems can be solved.

The conductive range of the conductive rubber composition is not particularly limited, and the optimum conductive range is selected according to the application of the conductive rubber. For example, in the case of the above-mentioned conductive roller or conveyor belt, the electric resistance value of the conductive rubber composition is 10 ⁴ to 10 ¹⁵ Ω in terms of volume resistivity.
・ It is preferably about cm, particularly 10 ⁷ to 10 ⁹
More preferably, it is about Ω · cm. Also, for flooring materials, mats, footwear, etc. that require antistatic function, 1
There is no problem if it is about 0 ⁷ to 10 ⁸ Ω · cm or less.

In order to mold the conductive rubber composition of the present invention into the above various shapes, various conventionally known molding methods such as extrusion molding and injection molding can be adopted.

[0027]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Examples 1 to 4 and Comparative Example 1 Base material rubber CR (volume resistivity 10 ¹¹ Ω · cm) 10
To 0 parts by weight, 30 parts by weight of carbon black FEF, the above-mentioned trade name US-70 manufactured by Sanken Kako Co., Ltd., and each of the following additives were blended, and kneaded using an open roll to give electroconductivity. A rubber composition was produced. The above-mentioned US-7
The compounding amount of 0 was set to Example 1 → 5 parts by weight, Example 2 → 30 parts by weight, Example 3 → 50 parts by weight, Example 4 → 100 parts by weight, and Comparative Example 1 → 150 parts by weight.

[0028] The conductive rubber composition of each of the above Examples and Comparative Examples was extruded into a sheet shape, and then press-vulcanized at 160 ° C. for 30 minutes to obtain a sample sheet having a thickness of 2 mm. Each sheet was manufactured, and the following tests were performed using the sheets to evaluate the characteristics. Since the conductive rubber composition of Comparative Example 1 had poor processability and a sample sheet could not be prepared by the above work, the electrical characteristic test was abandoned. Electrical Property Test I The volume resistivity (Ω · cm) at an applied voltage of 150 V of four sample sheets prepared from the conductive rubber compositions of each Example and Comparative Example was measured by Advantest Corporation digital ultra high resistance. Micro Ammeter R-8340 / 8340
The volume resistivity R (Ω · cm) of the conductive rubber compositions of Examples and Comparative Examples was measured using A.

From the maximum value R _max and the minimum value R _min among the measured values of the four sample sheets, the volume resistivity can be obtained by the following equation (1): ΔlogR ₁ = logR _max −logR _min (1) Then, the magnitude of the variation within the manufacturing lot was evaluated. The above ΔlogR ₁ is ΔlogR ₁ =
When 0, there is no variation in volume resistivity, indicating that the volume resistivity of each sample is all the same, and conversely ΔlogR ₁
It is shown that the larger the value, the greater the variation in the volume resistivity among the samples. Electrical Property Test II Volume resistivity R at an applied voltage of 10 V of one of the sample sheets prepared from the conductive rubber compositions of Examples and Comparative Examples
_10V (Ω · cm) and volume resistivity R _150V (Ω · cm) at an applied voltage of 150V were measured using the above-mentioned digital ultra-high resistance micro ammeter. And from the above both measured values,
Following formula (2): ΔlogR by _{2 = logR 10V -logR 150V ... (} 2), the volume resistivity was evaluated voltage dependence of the size. The above ΔlogR ₂ has no voltage dependence when ΔlogR ₂ = 0 and shows that the volume resistivity is always constant. On the contrary, the larger ΔlogR ₂ shows that the volume dependency of the voltage becomes larger. ing. Electrical Property Test III The volume resistivity (Ω · cm) of one of the sample sheets prepared from the conductive rubber compositions of each Example and Comparative Example at the applied voltage of 150 V was measured by the digital ultra-high resistance microcurrent described above. Using a meter, under the conditions of temperature 23.5 ° C and humidity 55% RH,
It was measured continuously for 30 days. Then, from the maximum value R _MAX and the minimum value R _MIN among them, the temporal stability of the volume resistivity was evaluated by the following formula (3): ΔlogR ₃ = logR _MAX −logR _MIN (3). The above ΔlogR ₃ shows that when ΔlogR ₃ = 0, there is no change with time and the volume resistivity is stable, and conversely, the larger ΔlogR ₃ is, the larger the change in volume resistivity with time is and the stable. It shows that the sex is reduced.

The above results are shown in Table 1.

[0031]

[Table 1]

From Table 1, the compounding amount of US-70 is 5-10.
It has been found that when the content is within the range of 0 parts by weight, a conductive rubber composition having a small variation in the electric resistance value due to the manufacturing lot and the like, a voltage dependency, etc., and an excellent stability over time can be obtained. . Further, when visually observing the sample sheets produced from the conductive rubber composition of each example, there was no problem in Examples 1 to 3, but the sample sheet of Example 4 had US-70 on its surface. Slight bleeding was observed. From this, it was confirmed that the compounding amount of US-70 is particularly preferably 5 to 50 parts by weight within the above range. Example 5 A conductive rubber composition was produced in the same manner as in Example 2 except that carbon black was not added. Example 6, Comparative Example 2 Instead of carbon black FEF, carbon black G
A conductive rubber composition was produced in the same manner as in Example 2 except that 70 parts by weight (Example 6) or 100 parts by weight (Comparative Example 2) of PF was blended.

The above-mentioned respective tests were conducted on the above-mentioned respective Examples and Comparative Examples, and the characteristics thereof were evaluated. Table 2 shows the results.

[0034]

[Table 2]

From Table 2, the amount of carbon black compounded is 7
It was found that when the content is within the range of 0 parts by weight or less, a conductive rubber composition having a small variation in the electric resistance value due to the manufacturing lot and the like, a voltage dependence, etc., and an excellent stability over time can be obtained. It was In addition, among the two examples, Example 5 in which carbon black was not blended was white, and it was confirmed that it could be colored in any desired shade. Examples 7 to 10 and Comparative Example 3 Conductivity was the same as Examples 1 to 4 and Comparative Example 1 except that the above-mentioned Asahi Denka Co., Ltd. trade name LV808 was used instead of US-70. A rubber composition was produced. The compounding amount of the LV808 was as follows: Example 7 → 5 parts by weight,
Example 8 → 30 parts by weight, Example 9 → 50 parts by weight, Example 10 → 100 parts by weight, and Comparative Example 3 → 150 parts by weight.

The above-mentioned respective tests were carried out on the above-mentioned respective Examples and Comparative Examples, and the characteristics thereof were evaluated. The results are shown in Table 3. Since the conductive rubber composition of Comparative Example 3 had poor processability and a sample sheet could not be prepared by the above work, the electrical characteristic test was abandoned.

[0037]

[Table 3]

From Table 3, the compounding amount of LV808 is 5-10.
It has been found that when the content is within the range of 0 parts by weight, a conductive rubber composition having a small variation in the electric resistance value due to the manufacturing lot and the like, a voltage dependency, etc., and an excellent stability over time can be obtained. . Further, when visually observing the sample sheet made from the conductive rubber composition of each example, there was no problem in Examples 1 to 3, but the sample sheet of Example 4 had LV808 slightly on its surface. Bleeding was observed. From this, it was confirmed that the compounding amount of LV808 is particularly preferably 5 to 50 parts by weight within the above range. Comparative Example 4 Instead of US-70, an ester-based plasticizer that was not doped with a metal salt and did not have an ether bond in the molecule (trade name: Reofos 65 manufactured by Ajinomoto Co., Inc., volume resistivity 10 ^12). A conductive rubber composition was produced in the same manner as in Example 2 except that 30 parts by weight of Ω · cm) was used and the amount of carbon black FEF was 100 parts by weight. Comparative Example 5 In place of US-70, 30 parts by weight of dibutyl phthalate (volume resistivity of 10 ¹² Ω · cm or more) not doped with a metal salt and not of an ester type was used, and carbon black FEF was added. A conductive rubber composition was produced in the same manner as in Example 2 except that the amount was 100 parts by weight. Comparative Example 6 In place of US-70, 30 parts by weight of paraffin oil (volume resistivity 10 ¹² Ω · cm) which was not doped with a metal salt and was not an ester system was used.
A conductive rubber composition was produced in the same manner as in Example 2 except that the blending amount of carbon black FEF was 100 parts by weight.

The above-mentioned respective tests were carried out for each of the above-mentioned comparative examples, and the characteristics thereof were evaluated. The results are shown in Table 4.

[0040]

[Table 4]

From Table 4, it is necessary to use a large amount of carbon black in excess of 70 parts by weight to obtain the same volume resistivity as in the present invention with other plasticizers. As a result,
It was found that it is not possible to obtain a conductive rubber composition having a small variation in electric resistance value due to manufacturing lots, voltage dependence, etc., and excellent stability over time. Example 11 NBR (volume resistivity 10 ¹⁰ Ω · cm) 1 which is a base rubber
30 parts by weight of US-70 and 100 parts by weight of each of the following additives were mixed and kneaded using an open roll to produce a conductive rubber composition.

[0042] Example 12 In addition to the above components, 30 parts by weight of carbon black F was added.
A conductive rubber composition was produced in the same manner as in Example 11 except that EF was blended. Example 13 100 parts by weight of epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer rubber (volume resistivity 10 ⁸ Ω · cm) as a base rubber, and 30 parts by weight of US
-70 and the following additives were blended and kneaded using an open roll to produce a conductive rubber composition.

[0043] Example 14 30 parts by weight of carbon black F was added to the above components.
A conductive rubber composition was produced in the same manner as in Example 13 except that EF was blended. Example 15 100 parts by weight of epichlorohydrin-propylene oxide-allyl glycidyl ether terpolymer rubber (volume resistivity 10 ⁹ Ω · cm) as a base rubber, and 30 parts by weight of U
S-70 and the following additives were blended and kneaded using an open roll to produce a conductive rubber composition.

[0044] Example 16 30 parts by weight of carbon black F was added to each of the above components.
A conductive rubber composition was produced in the same manner as in Example 15 except that EF was blended. Example 17 EPDM (volume resistivity 10 ¹⁵ Ω · cm) which is a base rubber
50 parts by weight of US-70 and 100 parts by weight of each of the following additives were mixed and kneaded using an open roll,
A conductive rubber composition was produced.

[0045] Example 18 In addition to the above components, 30 parts by weight of carbon black F was added.
A conductive rubber composition was produced in the same manner as in Example 17 except that EF was blended. Example 19 SBR (volume resistivity 10 ¹⁴ Ω · cm) 1 which is a base rubber
50 parts by weight of US-70 and each of the following additives were mixed with 00 parts by weight and kneaded using an open roll to produce a conductive rubber composition.

[0046] Example 20 In addition to the above components, 30 parts by weight of carbon black F was added.
A conductive rubber composition was produced in the same manner as in Example 19 except that EF was blended.

For each of the above-mentioned examples, the above-mentioned respective tests were conducted and the characteristics thereof were evaluated. The results are shown in Tables 5-9.

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

[Table 9]

From the above tables, NBR, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer rubber, epichlorohydrin-propylene oxide-allyl glycidyl ether terpolymer rubber, EPDM and SBR were used as base rubbers, respectively. , US-70 alone, a conductive rubber composition having a small variation in electric resistance due to manufacturing lots, voltage dependence, etc., and excellent stability over time can be obtained. Since the material rubber is a light-colored material such as white, it has been found that these systems are preferable as the light-colored conductive rubber composition. Among these systems, the system using the former three base rubbers is suitable for US-70 alone because the volume resistivity of the rubber itself is small. It was found that the voltage dependence of the rate may increase.

[0054]

As described above in detail, according to the present invention, at least 1 is present in a molecule doped with a metal salt.
With an ester-based plasticizer having individual ether bonds,
Since conductivity is imparted to the rubber composition, a conductive rubber composition having sufficient conductivity can be obtained even if the compounding amount of carbon black is smaller than ever, or even if carbon black is not compounded at all. To be Therefore, the conductive rubber composition of the present invention has less variation in electrical resistance, voltage dependence, etc. due to manufacturing lots, etc., as compared with the conventional composition in which conductivity is imparted by carbon black, and It also has excellent stability. Moreover, when carbon black is not added at all, it is possible to obtain a product having a free color tone.

Claims (2)

[Claims] 1. A conductive rubber composition in which at least a plasticizer of a plasticizer and carbon black is mixed in a base rubber, wherein a metal salt is doped as the plasticizer in at least one molecule. An ester-based plasticizer having one ether bond is used, and the compounding amount of the ester-based plasticizer with respect to 100 parts by weight of the base rubber is 5 to 100.
A conductive rubber composition, characterized in that the content of carbon black is within the range of 70 parts by weight and the content of carbon black is 70 parts by weight or less. 2. The conductive rubber composition according to claim 1, wherein the compounding amount of the ester plasticizer is 5 to 50 parts by weight with respect to 100 parts by weight of the base rubber.