JP4841986B2 - Method for controlling electrical resistance of rubber composition - Google Patents

Description

  The present invention relates to a method for controlling the electrical resistance of a rubber composition, in which the aggregation of carbon black blended in the rubber composition is released and the electrical resistance of the rubber composition is easily controlled.

Conventionally, as a material of conductive rubber members (development roll, charging roll, intermediate transfer roll, intermediate transfer belt, layer forming blade, etc.) used in office automation equipment such as copying machines, printers, facsimiles, etc., for example, acrylonitrile butadiene rubber A rubber material such as carbon black or the like, a conductive agent such as carbon black, a vulcanizing agent such as sulfur, or a plasticizer such as oil is blended (for example, see Patent Document 1). The conductive rubber member such as the developing roll is set to an electric resistance (semi-conductive) in the middle resistance region so as to be suitable for its use by imparting conductivity.
JP-A-2005-350496

  However, if the electrical resistance of the rubber composition is controlled to the target intermediate resistance range by blending carbon black, the electrical resistance will change rapidly depending on the amount of carbon black added. It is difficult to perform such control. For example, low-polar rubber such as natural rubber (rubber that has almost no polar group) has a low affinity with carbon black, so that it is difficult to uniformly disperse carbon black in the rubber polymer. Even when the rubber composition is kneaded by various methods such as the above, the carbon black and the rubber polymer are separated with time, and reaggregation of the carbon black is likely to occur. When such non-uniform dispersion and re-aggregation of carbon black occurs, carbon black particles are brought into contact with each other and it becomes easy to form a new conductive path. A sudden change in electrical resistance with quantity occurs. In addition, when general-purpose carbon black mainly used as a reinforcing material is used, the amount of carbon black added is excessive, which is not preferable.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for controlling the electrical resistance of a rubber composition that makes it easier to control the electrical resistance of the rubber composition, particularly in the middle resistance region.

To achieve the above object, the electric resistance control method of the rubber composition of the present invention, the rubber composition is carbon black which has been pulverized together with antioxidant by mill, the volume resistivity of the rubber composition Is controlled to the middle resistance region.

That is, the present inventor has intensively studied to solve the above problems. In the course of the research, a method for obtaining carbon black having an extremely fine particle size that can deagglomerate carbon black and suppress the formation of reaggregation was examined. As a result of recalling the use of a pulverizer to break up the agglomeration and as a result of trying various pulverizers , when carbon black is pulverized together with an antioxidant by a mill such as a planetary mill, the aggregate structure of carbon black is It has been found that an extremely fine carbon black that can be satisfactorily solved and also prevented from reaggregating can be obtained. Then, when the carbon black thus modified is contained in the rubber composition, the dispersibility of the carbon black is improved, so that the formation of a conductive path due to the contact between the carbon blacks is suppressed and the carbon black is suppressed. An abrupt change in electrical resistance due to an increase in the amount of added is suppressed. As a result, the change in electrical resistance is moderate with respect to the amount of carbon black added (the change in electrical resistance due to the amount of carbon black added becomes small), so that it is particularly easy to control the electrical resistance in the middle resistance region. As a result, the present invention has been reached.

  In the present invention, carbon black pulverized by a mill is contained in the rubber composition, and the volume resistivity of the rubber composition is controlled in the middle resistance region. By blending carbon black modified by such a pulverization treatment, variation in electrical resistance is reduced, and the change in electrical resistance with respect to the blended amount becomes gradual. Control in the resistance region is easy to implement. Therefore, it is easy to adjust the resistance when manufacturing rubber members that require electrical resistance (semi-conductive) in the middle resistance region, such as conductive rolls (developing rolls, charging rolls, etc.) used in OA equipment. Can be. On the other hand, by using such refined and modified carbon black, it is possible to uniformly disperse the carbon black in the rubber composition and to separate the carbon black and the rubber polymer that occur with time. In addition, since reaggregation of carbon black can be suppressed, a high-quality rubber member can be produced by the electrical resistance control method for a rubber composition of the present invention. On the other hand, due to the above miniaturization, even if the blending amount of carbon black is larger than usual, there is no sudden change in electrical resistance, and it is possible to achieve high hardness of rubber members by blending a large amount thereof. It can also be applied to fields such as anti-vibration rubber.

In particular, since the pulverization of the carbon black is performed by adding an anti-aging agent together with the carbon black to the mill, the treated carbon black is less likely to aggregate in the rubber composition . Therefore , controlling the volume specific resistance of the rubber composition in the middle resistance region has an effect that it is easier to implement.

  Moreover, it becomes more excellent in the aggregation improvement effect of the said processed carbon black in a rubber composition as the said anti-aging agent is a phenol type anti-aging agent.

  Next, an embodiment of the present invention will be described.

The present invention relates to a rubber composition, by incorporating a carbon black which has been pulverized together with antioxidant by mill is a method of controlling a medium resistance region volume resistivity of the rubber composition. By including the carbon black modified by such a pulverization treatment, variation in electric resistance is reduced, and the change in volume resistivity of the rubber composition with respect to the blending amount becomes gradual. Control of volume resistivity (control in the range of 1 × 10 ² to 1 × 10 ¹³ Ω · cm) is facilitated. In the present invention, control in the middle resistance region (range of 1 × 10 ⁵ to 1 × 10 ⁹ Ω · cm), which has been difficult in the past, can be easily performed. The measured value of the volume resistivity of the rubber composition is a value measured according to JIS K6271.

  The main component of the rubber composition is not particularly limited, and examples thereof include natural rubber (NR), acrylonitrile-butadiene rubber (NBR), epichlorohydrin rubber (ECO), chloroprene rubber (CR), and NBR. Polyvinyl chloride (PVC) blend rubber (NBR-PVC), hydrogenated NBR (H-NBR), acrylic rubber (ACM), ethylene acrylic rubber (AEM), chlorosulfonated polyethylene (CSM), chlorinated polyethylene rubber ( Examples thereof include rubbers (raw rubber) such as CPE), ethylene-propylene-diene rubber (EPDM), butyl rubber (IIR), isoprene rubber (IR), ethylene-propylene rubber (EPM), and silicone rubber (Q). These may be used alone or in combination of two or more. Among them, low polarity rubbers such as ethylene-propylene-diene rubber (EPDM), butyl rubber (IIR), natural rubber (NR), isoprene rubber (IR), ethylene-propylene rubber (EPM), and silicone rubber (Q) are carbon black. Therefore, essentially, it was difficult to uniformly disperse carbon black in the rubber composition. However, according to the present invention, such a problem is solved. Become. The rubber composition may be only the main component rubber and the pulverized carbon black, and if necessary, a vulcanizing agent, a vulcanization accelerator, a vulcanization aid, and a processing aid. An agent, a foaming agent, a softening agent, a filler such as calcium carbonate, and the like may be appropriately blended.

  As the carbon black to be the object to be pulverized, conductive carbon black such as furnace black, acetylene black, channel black or the like is used. These may be used alone or in combination of two or more.

  The mill used for the carbon black pulverization process is not particularly limited. For example, a planetary mill, a stirring mill, and a vibration mill can be advantageously used in the present invention because dry processing can be performed. Especially, since a planetary mill can be processed in a short time, it can be used more preferably in the present invention.

  The planetary mill is composed of a revolving mill body and a mill pot that rotates in the same direction and in the opposite direction. In the rotating mill pot, beads serving as a grinding medium and an object to be ground (carbon black in the present invention) , And the beads are driven by the centrifugal force generated at the time of revolution or rotation and pulverized. As described above, the mill pot is called a planetary mill because it rotates and revolves, that is, operates in a planet. Specifically, there is a batch type high-speed planetary mill “Kurimoto Hygie” BX384E manufactured by Kurimoto Iron Works.

  The beads that are the grinding media for the planetary mill are not particularly limited, but metal balls such as stainless steel balls are preferably used. A diameter of about 1 to 4 mm is preferably used, and a diameter of 2 to 3 mm is particularly preferably used.

  As the grinding treatment conditions by the planetary mill, it is preferable to set the centrifugal acceleration in a range of 10 to 150 G, more preferably 100 to 150 G with respect to beads as a grinding medium. Furthermore, the pulverization time by the pulverizer is preferably set to 1 to 30 minutes, more preferably 3 to 15 minutes. That is, if the centrifugal acceleration is less than 10G, the carbon black is not aggregated and finer pulverization is not performed, and it is difficult to obtain the desired carbon black. Conversely, if it exceeds 150G, there is a possibility that the durability of the equipment itself may be problematic. Because there is. Further, if the pulverization time is out of the above-mentioned specific range, for example, more than 30 minutes and is too long, the processing cost is increased. On the other hand, if the pulverization time is too short in less than 1 minute, the treatment effect is not sufficiently exhibited.

  The carbon black obtained in this manner is extremely fine because it is unagglomerated, and the Stokes diameter obtained by dispersing in a mixed solvent of water / ethanol / surfactant and determined by centrifugal sedimentation is in the range of 60 nm to 130 nm. And this thing has suppressed re-aggregation.

Furthermore, in the present invention, during the grinding process of the carbon black, anti-aging agent is formulated with carbon black. Thus, by blending the anti-aging agent at the same time, the anti-aging agent is adsorbed on the surface of the carbon black, and when the treated carbon black is kneaded into the rubber material in the characteristics after the pulverization treatment of the carbon black, As a result, it becomes difficult for carbon black to have an agglomerated structure, and as a result, controlling the volume resistivity of the rubber composition in the middle resistance region has the effect of being easier to implement. The anti-aging agent is not particularly limited, but it is more preferable to use a phenol-based anti-aging agent because it is more excellent due to the above-described effects.

  Examples of the phenol-based antiaging agent include 2,6-di-tert-butyl-4-methylphenol, 2,2′-methylenebis (4-methyl-6-tert-butylphenol (MBMTB), 2,5- Examples thereof include di-tert-butylhydroquinone (DBHQ), 2-tert-butyl-6 (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylene acrylate, etc. Particularly, the modification effect is high. From a remarkable point of view, 2,6-di-tert-butyl-4-methylphenol is preferably used, and these phenolic antioxidants may be used alone or in combination of two or more.

And when mix | blending the said anti-aging agent simultaneously, it is preferable at the point which maintains the reinforcement effect of carbon black that the compounding quantity is set as follows. That is, it is preferable to set the ratio of carbon black: anti-aging agent = 9.5: 0.5 to 8: 2 in terms of weight ratio with respect to carbon black.

  The blending ratio of the carbon black after the pulverization treatment to the raw rubber is particularly limited as long as it is a blending ratio so that the volume specific resistance of the rubber composition is controlled to a target medium resistance region. Although it is not a thing, normally, it mix | blends in the range of 20-100 parts with respect to 100 weight part (henceforth "part") of the said raw rubber, and controls the volume specific resistance of a rubber composition. Thus, since the blending ratio of carbon black can be taken in a wide range, it becomes easy to carry out control in the middle resistance region, which has been difficult in the past.

  A desired rubber composition can be obtained by kneading these materials with a kneader such as a kneader, roll or mixer. Next, the rubber composition thus prepared is extruded, etc., and then heat vulcanized or press vulcanized to form a desired shape, thereby achieving the desired conductivity. A rubber member can be manufactured. In addition, the heating conditions at the time of the vulcanization molding are not particularly limited, and are appropriately set depending on the size of the product to be manufactured, the rubber to be used, and the like.

  The conductive rubber member thus obtained is not particularly limited as long as the conductivity is required by dispersion of carbon black. For example, the conductive rubber member used in OA equipment such as a copying machine, a printer, and a facsimile is used. For example, a developing rubber member (developing roll, charging roll, intermediate transfer roll, intermediate transfer belt, layer forming blade). On the other hand, since the carbon black is made finer, even if the amount of carbon black is larger than usual, there is no sudden change in electrical resistance, and a high hardness of the rubber member can be achieved by the large amount of carbon black. It can also be applied to the field of anti-vibration rubber for automobiles, etc. Further, when applied in this field, the rubber mixed with the carbon black treated according to the present invention has a high electric resistance, so that different metals are bonded. It can also be used as a high-hardness rubber member or a high-hardness rubber member that requires electrical insulation. Here, the said high hardness means the thing of 65 or more measured with a type A durometer based on JISK6253.

  Next, the present invention will be described in detail based on examples. However, the present invention is not limited to these examples.

  First, prior to the examples and comparative examples, the following materials were prepared.

[NR]
Natural rubber

[Carbon black (A)]
Talker Black # 5500, manufactured by Tokai Carbon

[Carbon black (B)]
Seast SO, manufactured by Tokai Carbon

[Anti-aging agent (i)]
NOCRACK NS-6, manufactured by Ouchi Shinsei Chemical Co., Ltd.

[Anti-aging agent (ii)]
NOCRACK 200, manufactured by Ouchi Shinsei Chemical Co., Ltd.

[Zinc oxide]
Two types of zinc oxide, manufactured by Mitsui Mining & Mining

〔stearic acid〕
LUNAC S30, manufactured by Kao

[Vulcanization accelerator]
Noxeller CZ-G, manufactured by Ouchi Shinsei Chemical Co., Ltd.

〔sulfur〕
Sulfax 200S, manufactured by Tsurumi Chemical Co.

[Preparation of treated carbon blacks (a) to (e)]
Using the carbon blacks (A) and (B) and the anti-aging agents (i) and (ii), the beads having the bead diameters (particle diameters) shown in the same table in the proportions shown in Table 1 below. At the same time, it was put into a planetary mill (batch type high-speed planetary mill “Kurimoto Hygie” BX384E manufactured by Kurimoto Iron Works Co., Ltd.) (charged to account for 30% of the total input volume). Thereafter, the planetary mill was used to pulverize carbon black under the conditions (centrifugal acceleration, treatment time) shown in Table 1 below. Thus, treated carbon blacks (a) to (e) were produced.

[Examples 1 to 4, Comparative Example 1]
100 parts of NR, 20 to 60 parts of treated carbon black (a), 5 parts of zinc oxide, and 1 part of stearic acid were used in a closed type small kneader (Toyo Seiki Seisakusho, Labo Plast Mill, capacity 100 cc). And kneaded. Thereafter, the above kneaded product, and 1 part of vulcanization accelerator, sulfur 2.5 parts, and kneaded using a roll to prepare a conductive rubber composition. This was designated as Example 1.

  In Example 2, 30 parts of treated carbon black (c) was blended in place of the treated carbon black (a). Other than that was carried out similarly to Example 1, and prepared the conductive rubber composition.

  In Example 3, in place of the treated carbon black (a), 30 parts of treated carbon black (d) was blended. Other than that was carried out similarly to Example 1, and prepared the conductive rubber composition.

  In Example 4, 30 parts of treated carbon black (e) was blended in place of the treated carbon black (a). Other than that was carried out similarly to Example 1, and prepared the conductive rubber composition.

In Comparative Example 1, carbon black (A) 5 to 40 parts were blended in place of the treated carbon black (a). Other than that was carried out similarly to Example 1, and prepared the conductive rubber composition.

  Using the rubber composition thus obtained, the volume resistivity of the rubber composition was measured according to JIS K6271. These results are shown in Tables 2 and 3 below.

From the above results, the sample using carbon black as an example product subjected to pulverization treatment is more specific to the volume depending on the amount of carbon black added than the one using untreated carbon black as in the comparative example product. It can be seen that the rate of decrease in resistance is small. That is, since the volume resistivity of the example product is higher, it can be seen that the example product has better carbon black dispersion. Moreover, the fluctuation state of the volume resistivity of the rubber composition accompanying the increase in the amount of carbon black added in Example 1 and Comparative Example 1 based on Table 2 and Table 3 is shown in the graph of FIG. As shown, compared to Comparative Example 1, in Example 1, it can be seen that there is no sudden change in electrical resistance due to the amount of carbon black added in the middle resistance region. Since the electrical resistance of the example product is higher, it can be seen that the dispersion of carbon black is better in the example product.

[Example 5, Comparative Example 2]
Using the NR100 parts, and 4 5-95 parts carbon black (b), zinc oxide 5 parts, 1 part of stearic acid, a sealed type small kneader (manufactured by Toyo Seiki Seisaku, Laboplastomill, volume 100 cc) and And kneaded. Thereafter, 1 part of the vulcanization accelerator and 2.5 parts of sulfur were kneaded with the kneaded material using a roll to prepare a conductive rubber composition. This was designated as Example 5.

In Comparative Example 2, 5-95 parts of carbon black (B) 2 was blended in place of the treated carbon black (b). Otherwise, a conductive rubber composition was prepared in the same manner as in Example 5.

  Using the rubber composition thus obtained, the volume resistivity of the rubber composition was measured according to JIS K6271. These results are shown in Tables 4 and 5 below.

  From the above results, the sample using carbon black as an example product subjected to pulverization treatment is more specific to the volume depending on the amount of carbon black added than the one using untreated carbon black as in the comparative example product. It can be seen that the decrease rate of resistance is small. That is, since the volume resistivity of the example product is higher, it can be seen that the example product has better carbon black dispersion. Moreover, the fluctuation state of the volume specific resistance of the rubber composition according to the increase in the amount of carbon black in Example 5 and Comparative Example 2 based on Table 4 and Table 5 is shown in the graph of FIG. As shown, compared to Comparative Example 2, in Example 5, it can be seen that there is no sudden change in electrical resistance due to the amount of carbon black added in the middle resistance region.

  In addition, the present inventor confirmed that the dispersion of carbon black is improved in the case of using other rubbers such as ECO, NBR, and EPDM instead of the NR of the examples as in the other examples. Confirmed by experiment.

  The method of controlling the electrical resistance of the rubber composition of the present invention is a manufacturing field of rubber members (developing rolls, charging rolls, intermediate transfer rolls, etc.) that are required to control the volume resistivity in the middle resistance range by dispersing carbon black Can be used effectively. On the other hand, in the above method, even if the amount of carbon black is larger than usual due to the refinement of carbon black, there is no sudden change in electrical resistance, and high hardness of the rubber member is achieved by the large amount of carbon black. Therefore, it can also be applied to the field of anti-vibration rubber for automobiles and the like. Further, in application in this field, since the electric resistance of rubber kneaded with carbon black treated according to the present invention is high, It can also be used as a high-hardness rubber member for bonding metals or a high-hardness rubber member that requires electrical insulation.

It is a graph which shows the relationship between carbon black addition amount and the volume specific resistance of a rubber composition with respect to Example 1 and Comparative Example 1. It is a graph which shows the relationship between carbon black addition amount and the volume specific resistance of a rubber composition with respect to Example 5 and Comparative Example 2.

Claims (5)

The rubber composition is carbon black which has been pulverized together with antioxidant by milling, the electrical resistance method for controlling a rubber composition characterized by controlling the medium-resistance region volume resistivity of the rubber composition.   The method for controlling electrical resistance of a rubber composition according to claim 1, wherein the carbon black is pulverized by a planetary mill. The method for controlling electrical resistance of a rubber composition according to claim 1 or 2, wherein the volume resistivity of the medium resistance region is in the range of 1 x 10 ⁶ to 1 x 10 ⁹ Ω · cm. The method for controlling electrical resistance of a rubber composition according to any one of claims 1 to 3, wherein the anti-aging agent is a phenol-based anti-aging agent. Pulverization of the carbon black, the carbon black and antioxidant, by weight, of carbon black: Antioxidant = 9.5: 0.5 to 8: claim 1 performed by introducing in a ratio of 2 The electrical resistance control method of the rubber composition as described in any one of -4 .

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