WO2003097736A1

WO2003097736A1 - Rubber composition

Info

Publication number: WO2003097736A1
Application number: PCT/JP2003/005886
Authority: WO
Inventors: Shinichi Toyosawa; Mituaki Maeda; Sei Aoki; Hideo Takeichi
Original assignee: Bridgestone Corporation
Priority date: 2002-05-16
Filing date: 2003-05-12
Publication date: 2003-11-27
Also published as: AU2003235937A1

Abstract

A rubber composition, characterized by comprising a rubber as the base material and at least one filler selected from among vapor-phase-produced carbon fibers which are oxidized, vapor-phase-produced carbon fibers which have mean aspect ratios of less than 10, and vapor-phase-produced carbon fibers which are surface-coated with resins.

Description

Description Rubber composition Technical field

The present invention relates to a rubber composition (hereinafter, also simply referred to as “composition”), and more particularly, to a rubber composition having good mechanical properties and the like, and having excellent heat conductivity and electric conductivity. Background art

For various products such as electric and electronic parts, tires, and belts, rubber compositions based on various natural rubbers and various synthetic rubbers are used according to their characteristics. The performance and functions of such products are greatly affected by auxiliary materials such as various fillers and vulcanization conditions as well as the rubber material as the base material.

For example, carbon black and silica are widely known as fillers for obtaining the effect of capturing natural rubber, and alumina / boron nitride is used to increase thermal conductivity. In order to achieve this, methods such as compounding metal powders such as copper and nickel, and highly conductive fibrous fillers such as conductive carbon and carbon fiber (hereinafter sometimes abbreviated as “CF j”) are used. However, in the conventionally known fillers, the only way to obtain a high effect is to increase the compounding amount, and as a result, it is not possible to obtain a uniform dispersion of the fillers, and the performance varies. In addition, there are disadvantages such as exudation, increase in viscosity and decrease in physical properties, resulting in deterioration of moldability, and deterioration of mechanical properties of the obtained rubber article, making it unpractical. It was.

As a method of solving these problems, the research group of the present inventors has developed a high effect even with a relatively small amount of addition, and as a filler that does not adversely affect other performances such as mechanical properties. We discovered vapor-grown carbon fibers and developed a rubber composition in which these fillers were blended with a rubber material as a base material. Disclosure of the invention

An object of the present invention is to provide a rubber composition containing the above-mentioned vapor-grown carbon fiber, which further improves its mechanical properties, and specifically, has a dynamic viscoelasticity, a modulus, and a thermal conductivity in a wide temperature range. The rubber composition containing the vapor-grown carbon fiber can be used for many purposes by improving the breaking property at 80 ° C or higher while maintaining low loss property while improving the loss rate. It is.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by oxidizing the vapor-grown carbon fiber used in the rubber composition, The effect of improving thermal conductivity and electrical conductivity is impaired by reducing the average aspect ratio to less than 10 and further by resin-coating the surface of the vapor-grown carbon fiber used in the rubber composition. It has been found that the mechanical properties can be improved without the need, and the present invention has been completed. BEST MODE FOR CARRYING OUT THE INVENTION

According to the present invention, a vapor-grown carbon fiber oxidized as a filler using a rubber material as a base material, and a resin-coated surface and a vapor-grown carbon fiber having an average aspect ratio of less than 10 It is characterized by blending at least one selected from vapor grown carbon fibers.

Rubber materials include natural rubber, general-purpose synthetic rubber, for example, emulsion-polymerized styrene-butadiene rubber, solution-polymerized styrene-butadiene rubber, high cis-1,4 polybutadiene rubber, low cis-1,4 polybutadiene rubber, high cis-1,4 (4) Polyisoprene rubber, etc., gen-based special rubbers, such as nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, etc., olefin-based special rubbers, such as ethylene-propylene rubber, petinole rubber, No., butyl butyl rubber, acrylinole rubber, chlorosnolephone And other special rubbers such as hydrin rubber, fluoro rubber, polysulfurized rubber, polyurethane rubber, and the like. From the standpoint of cost and performance, natural rubber or general-purpose synthetic rubber is preferred.

The rubber material according to the present invention is preferably used after vulcanization. Examples of the crosslinking method include a method of adding iodine, a peroxide, a metal oxide, and the like, and crosslinking by heating, A method in which a photopolymerization initiator is added and crosslinking is performed by irradiation with light, a method in which crosslinking is performed by irradiating an electron beam or radiation, and the like.

Vapor-grown carbon fiber according to the present invention is generally of carbon fibers (CF) (average diameter 5 mu m to, the length 1 0 0 mu about m) of 1 0 ^{_ 2} to 1 0 - ¹ times of the order Since it is a fine fibrous structure, there is an advantage that a problem such as dispersibility does not easily occur as compared with the case where carbon fiber is added, and a similar performance improving effect can be obtained. In the present invention, by using the vapor-grown carbon fiber as a filler for the rubber composition, an excellent effect of improving various properties can be obtained with a small amount of addition. In the oxidized vapor-grown carbon fiber of the present invention, the method of the oxidizing treatment is not particularly limited as long as the object of the present invention can be achieved, and it may be a chemical treatment or a physical treatment. Is also good.

As the chemical treatment, a method of treating with nitric acid, sulfuric acid, perchloric acid or a mixture of these acids is preferable from the viewpoint that it can be easily performed. The conditions of these acid treatments are as follows: from the viewpoint that the treatment can be carried out effectively, which can be appropriately selected according to the kind of the acid, etc., the treatment temperature is about 20 to 80 ° C, and the pH is about 0 to 2 Is preferred.

Further, treatment with an oxidizing gas can also be suitably performed. Here, the oxidizing gas may be any gas having the ability to oxidize the vapor grown carbon fiber, and specifically includes ozone, nitric acid gas, nitrous acid gas, sulfuric acid gas, sulfurous acid gas, and the like. These oxidizing gases can be used alone or in combination of two or more.

When using ozone as the oxidizing gas, the concentration of ozone generated using a commercially available ozone generator is sufficient. When nitric acid gas or sulfuric acid gas is used, commercially available gas supplied from a standard gas cylinder such as NOX or SOX can be used, and the processing temperature is from room temperature to about 250 ° C. I can do it.

Examples of the physical treatment include corona discharge treatment, plasma treatment, and the like.Each condition can be appropriately selected, but in each case, the reaction components are effectively brought into contact with the surface of the vapor-grown carbon fiber. In addition, do not allow the vapor-grown carbon fiber to be too thick under the condition where it is allowed to stand still, or apply a large amount of current when introducing the vapor-grown carbon fiber to the place where discharge or plasma is generated and react. Be careful not to I do.

Next, the method of resin coating on the vapor-grown carbon fiber whose surface is coated with a resin according to the present invention is not particularly limited as long as the method can achieve the object of the present invention. A method of impregnating the vapor-grown carbon fiber with a solution dissolved in a solvent or an aqueous solvent is preferable.

As the organic solvent, toluene, xylene, hexane, acetone, ethanol, as tetrahydrofuran and the like, and are fist up and mixtures thereof, as long as the resin is soluble is _water: There is optionally an organic solvent And an aqueous additive to which a surfactant or the like is added. The temperature conditions for the impregnation are not limited, but it is preferable that the temperature is lower than the boiling point of the solution to be used and the viscosity is as low as possible.

The resin used in the present invention is not particularly limited as long as it can achieve the effects of the present invention, but preferably has a polar portion. In particular, a resin obtained by copolymerizing a monomer having a polar group or a resin modified by a substance having a polar group is preferable, and examples thereof include polyethylene copolymerized with maleic acid.

The vapor-grown carbon fiber in the present invention can be treated with a coupling agent in addition to the oxidation treatment and / or the resin coating treatment. Examples of the coupling agent include titanate-based, aluminum-based, and silane-based coupling agents. The coupling agent is dissolved in a solvent, and treated by a method such as impregnating the vapor-grown carbon fiber. can do.

In the case of performing the oxidation treatment and / or the resin coating treatment, the vapor-grown carbon fiber to be subjected to these treatments is not particularly limited, and the fiber diameter, the fiber length, and the length according to the required performance as appropriate. It is preferable that the force average diameter is in the range of 0.4 to 0.4 μππ, more preferably in the range of 0.05 to 0.3 m, especially 0. A range of 0.7 to 0.3 μπι is preferred. Further, those having an average length in a range of 0.5 to 50 / im are preferable, and those having an average length in a range of:! To 30 μιη, and particularly in a range of 1.5 to 25 m. Is preferred. The specific surface area of ^{^{5~ 5 0 m 2/7 g}} , especially in the range of 8 ~ 3 O m ² Z g It is preferable to use a certain one. Specifically, as a commercially available product, for example, vapor-grown carbon fiber VGCF (registered trademark) manufactured by Showa Denko KK can be used. In the present invention, a rubber composition containing a rubber material as a base material and a vapor-grown carbon fiber having an average aspect ratio of less than 10 as a filler is also included in the scope of the present invention. As long as the average aspect ratio is less than 10, there are no particular restrictions on the shape, and the method for producing the vapor-grown carbon fiber having a low aspect ratio is not particularly limited. For example, there is a method in which a long fiber produced by a usual method is pulverized into a short length to reduce an aspect ratio. Specifically, there are a method of mechanically pulverizing using a pole mill mixer or a mortar, a method of dispersing in an aqueous or organic solvent and pulverizing by applying ultrasonic waves, and sieving these. Vapor-phase grown carbon fibers with a cut ratio of less than 10 can be obtained.

The average diameter of the vapor-grown carbon fiber according to the present invention is not particularly limited as long as the average aspect ratio is less than 10, but the average diameter is preferably in the range of 0.04 to 0.4 πι. Is preferably in the range of 0.05 to 0.3 m, particularly preferably in the range of 0.07 to 0.3 m. The length is not particularly limited, and may have a range in which the average aspect ratio is less than 10, depending on the average diameter. Furthermore, specific surface area of 5 to 50 m ² Zg, and particularly preferably in the range of 8~30 m ² / g. Further, there is no particular limitation on the shape of the vapor-grown carbon fiber of the long fiber which is a raw material of the vapor-grown carbon fiber having an average aspect ratio of less than 10 according to the present invention. For example, a commercially available product, Showa Denko KK ) Can be used.

The vapor-grown carbon fiber having an average aspect ratio of less than 10 can be subjected to oxidation treatment and / or resin coating on the surface, and the treatment method and conditions are the same as described above. . Further, in addition to acid treatment and Z or surface resin coating, a force coupling agent treatment can also be performed.

The compounding amount of the vapor grown carbon fiber of the present invention is preferably in the range of 0.1 to 20% by volume based on the total amount of the rubber composition. If the compounding amount is within this range, the desired performance can be sufficiently obtained, and the workability in mixing, molding and the like becomes good. In addition, from the same viewpoint, the range may be further set to 0.2 to 15 volume%. preferable.

Further, the rubber composition of the present invention preferably has a Young's modulus in a range of 0.5 to 1 OMPa. When the Young's modulus is in this range, the rubber properties such as creep property and strength are good, and the rubber elasticity is preferable. Also, the JISA hardness is preferably in the range of 30 to 90.

In the composition of the present invention, various fillers other than the vapor-grown carbon fiber can be blended, and the blending amount is 1 to 60% by volume, particularly 1 to 40% by volume based on the total amount of the rubber composition. A range of volume% is preferred. Various fillers can be selected as needed, but it is preferable to contain carbon black and / or silica. When the composition contains an appropriate amount of carbon black and Z or silicium, a higher reinforcing effect can be obtained as compared with the case where only the vapor-grown carbon fiber is added. As the carbon black, known ones such as HAF class carbon black can be used. The method of mixing and molding the rubber composition can be a known method used for ordinary mixing and molding of rubber, and is not particularly limited.

The rubber composition of the present invention is characterized in that, by blending a small amount of vapor-grown carbon fiber, it does not significantly change other physical properties and does not impair molding processability, and has thermal conductivity, electrical conductivity, etc. Since the characteristics can be greatly improved, it can be widely used for electrical and electronic parts, tires, belts, and other various products. The rubber and the composition of the present invention may contain additives generally used in the rubber industry, such as vulcanizing agents, vulcanization accelerators, reinforcing materials, antioxidants, and softening agents. Additives can be used as appropriate.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Physical property evaluation method)

The following physical properties were evaluated for the rubber sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 6.

(1) Dynamic viscoelasticity

Use a viscoelasticity tester (Toyo Seiki Co., Ltd., Rheograph Solid L-1R type) to form a rubber sheet 60. Hysteresis loss (tan S) at C was measured. (2) Thermal conductivity

Thermal conductivity was evaluated based on the thermal conductivity measured using a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Co., Ltd.

(3) Mechanical properties

The modulus at the time of pulling at 100 ° C. was measured in accordance with JIS K6253—1993, and the value at the time of pulling at 300% was evaluated.

Example 1

40 g of vapor grown carbon fiber (“VGCF” (registered trademark) manufactured by Showa Denko KK) is placed in a 2 L beaker, and 500 cc of concentrated nitric acid is gently poured into the beaker and slowly mixed so as to be evenly mixed. And stirred. After standing for 5 days with occasional stirring, excess nitric acid was washed off with water. As a washing method, decantation was performed until the pH of water reached 6, and suction filtration was performed. Thereafter, suction washing was performed with 100 cc of ethanol. The obtained VGCF cake was dried in a vacuum dryer at 60 ° C. until the weight became constant, to obtain an acid-treated V GCF.

The acid-treated VG CF and various additives were blended with natural rubber (NR) as a rubber material in the composition shown in Table 1, and the vulcanized rubber was mixed according to the kneading conditions and sheet preparation conditions shown below. A sheet of the composition was made. The amounts in Table 1 all indicate parts by weight. Table 1 shows the results of various physical property evaluations.

Kneading conditions

Using a Labo Plastomill (manufactured by Toyo Seiki Co., Ltd.), masticate the NR at 70 rpm for 3 minutes at 50 rpm, and then add the vulcanization accelerators shown in Table 1 and the additives except sulfur. Then, the mixture was further mixed at 70 ° C. at 30 rpm (non-pro mixture). The resulting mixture was taken out, cooled and weighed, the remaining vulcanization accelerator and sulfur were added, and the mixture was mixed again at 50 ° C at 30 rpm using a pravender (Pro Mix) .

Sheet preparation conditions

The mixture was kneaded with a vulcanization at 0.99 ° Cxl 5 minutes using a hot press to prepare a vulcanized rubber sheet lm _m thick.

Example 2 A vulcanized rubber sheet was produced in the same manner as in Example 1 except that the vapor-grown carbon fiber was subjected to a corner treatment instead of the nitric acid treatment. Corona treatment was performed as follows. 10 g of the vapor-grown carbon fiber was placed in a glass petri dish and placed in a glass low-pressure plasma generator chamber. After the inside of the chamber was replaced with argon, oxygen was introduced at a concentration of 1 torr, and a plasma was generated by operating with an electrostatic power of 100 W to modify the surface of the vapor grown carbon fiber. The processing time was 15 minutes. Table 1 shows the evaluation results.

Example 3

A vulcanized rubber sheet was produced in the same manner as in Example 1 except that the vapor-grown carbon fiber was treated with ozone instead of nitric acid. Ozone treatment was performed as follows. Vapor-grown carbon fibers were placed in a tray treated with enamel so as to have a thickness of about 2 cm, and the tray was placed in a glass desiccator. Ozone generated at the maximum capacity (0.7 g / hour of ozone generation) of an ozone generator (SO-03 manufactured by Tokyu Corporation) was introduced into the desiccator and treated at room temperature for 24 hours. Table 1 shows the evaluation results. .

Comparative Example 1

A vulcanized rubber sheet was produced in the same manner as in Example 1 except that the vapor-grown carbon fiber was used without being oxidized. Table 1 shows the evaluation results.

Comparative Example 2

A natural rubber (NR) as a rubber material and various additives were mixed with the content shown in Table 1 without using vapor-grown carbon fiber, and a vulcanized rubber composition was prepared in the same manner as in Example 1. A sheet of the product was produced. Table 1 shows the evaluation results.

Table 1

1) Vapor-grown carbon fiber (VGCF (registered trademark)) manufactured by Showa Denko KK (fiber diameter 0.15 wm, fiber length 10-20 μm)

2) H A F grade carbon black

3) N— (1,3-dimethylbutyl) 1 N, 1 f P-phenylene

4) N-Cyclohexyl 2-benzothiazyl sulfenamide Example 4

Vapor-grown carbon fiber (VGCF (registered trademark)) (fiber diameter 0.15μιτα, fiber length 10-20 μπι) manufactured by Showa Denko Co., Ltd. is pulverized and sieved to obtain an average aspect ratio of 3 Was obtained. Natural rubber (NR) as a rubber material, the above-mentioned vapor-grown carbon fiber having an average aspect ratio of 3 and various additives were mixed according to the blending contents shown in Table 1, and the kneading conditions and the following conditions were used. A sheet of the vulcanized rubber composition was prepared according to the sheet preparation conditions. The amounts in Table 1 all indicate parts by weight. Table 2 shows the evaluation results. The kneading conditions and sheet preparation conditions are the same as those described in Example 1. Comparative Example 3

A vulcanized rubber sheet was produced in the same manner as in Example 4, except that a vapor-grown carbon fiber having an average aspect ratio of 100 was used. Table 2 shows the evaluation results.

Comparative Example 4

The natural rubber (NR) as the rubber material and various additives were mixed with the compounding content shown in Table 2 without using the vapor-grown carbon fiber, and vulcanized rubber was formed in the same manner as in Example 4. A sheet of the product was produced. Table 2 shows the evaluation results. Table 2

Example 5

Into a 2 L beaker, 40 g of vapor grown carbon fiber (“VGC F” (registered trademark) manufactured by Showa Denko KK) was added, and about 0.3 g of maleic acid copolymerized polyethylene (Ducrel) was dissolved. Toluene (50 Oml) was gently poured and stirred gently so as to mix uniformly. Leave for about 3 hours with occasional stirring, then place in a vacuum dryer at 60 ° C. And dried until the weight became constant to obtain a resin coating VGCF.

The VGC F used had a wire diameter of 150 nm, a length of 15 μπι (aspect ratio of 100), and a surface area of 7.10 X 1 CI- ⁸ cm ² (specific surface area). 14 m ² / g), the volume was 2.65 × ^10-13 cm ³ , and the weight was 5.3 × ^10-13 g. Assuming that a resin having a specific gravity of 1 covers the VGCF surface by 5 nm, the required resin amount was calculated to be 0.007 g / g (0.28 g of resin / 40 g of VGCF).

The coating treatment VGCF and various additives were blended with natural rubber (NR) as a rubber material according to the blending content shown in Table 3, and the vulcanized rubber was mixed according to the kneading conditions and sheet preparation conditions shown below. A sheet of the composition was made. ] ¾, all amounts in Table 3 represent parts by weight. Table 3 shows the results of various physical property evaluations.

The kneading conditions and sheet preparation conditions are the same as those described in Example 1. Example 6

A vulcanized rubber sheet was produced in the same manner as in Example 5, except that unmodified polyethylene was used instead of maleic acid-modified polyethylene. Table 3 shows the evaluation results. Comparative Example 5

A vulcanized rubber sheet was produced in the same manner as in Example 5, except that a vapor-grown carbon fiber without resin coating was used. Table 3 shows the evaluation results.

Comparative Example 6

A vulcanized rubber was produced in the same manner as in Example 5 except that the vapor-grown carbon fiber was not used and the mixing ratio shown in Table 3 was used. Table 3 shows the evaluation results.

Table 3

Industrial applicability

According to the rubber composition of the present invention, even when added in a small amount, properties such as thermal conductivity and electrical conductivity are not significantly changed without significantly changing other physical properties, and without impairing moldability. The ta η δ value can be reduced while maintaining particularly high thermal conductivity and high modulus in a high-temperature region. Therefore, the vulcanized rubber composition of the present invention can be widely used for electric and electronic parts, tires, belts, and other various products.

Claims

The scope of the claims

1. Oxidized vapor-grown carbon fiber with rubber material as base material, vapor-grown carbon fiber with average aspect ratio less than 10 and vapor-grown carbon fiber with resin-coated surface A rubber composition comprising at least one compound selected from the group consisting of:

2. The rubber composition according to claim 1, wherein the oxidation treatment is a treatment with nitric acid, sulfuric acid, perchloric acid, or a mixture thereof.

3. The rubber composition according to claim 1, wherein the oxidizing treatment is a treatment with an oxidizing gas.

4. The rubber composition according to claim 3, wherein the oxidizing gas is at least one selected from the group consisting of ozone, nitric acid gas, nitrous acid gas, sulfuric acid gas, and sulfurous acid gas.

5. The rubber composition according to claim 1, wherein the oxidation treatment is a physical oxidation treatment.

6. The rubber composition according to claim 5, wherein the physical oxidation treatment is at least one selected from corona discharge treatment and plasma treatment.

7. The rubber composition according to claim 1, wherein the resin coating is performed by impregnating a solution obtained by dissolving a resin in an organic solvent or an aqueous solvent with vapor-grown carbon fibers.

8. The rubber composition according to claim 1, wherein the resin is a resin having a polar part.

9. The rubber set according to claim 8, wherein the resin having a polar portion is a resin obtained by copolymerizing a monomer having a polar group or a resin modified with a substance having a polar group. Adult.

10. The rubber composition according to any one of claims 1 to 9, wherein the amount of the vapor-grown carbon fiber is 0.1 to 20% by volume based on the total amount of the rubber composition.

1 1. The vapor-grown carbon fiber has a diameter of 0.04 to 0.0.

11. The rubber composition according to any one of 10.

12. The rubber composition according to any one of claims 1 to 11, wherein the vapor-grown carbon fiber has a length of 0.5 to 50 x m.

13. The rubber composition according to any one of claims 1 to 12, wherein the JISA hardness is 30 to 90.

14. The rubber composition according to any one of claims 1 to 14, wherein a filler other than the vapor-grown carbon fiber is blended in an amount of 1 to 60% by volume based on the total amount of the rubber composition.

15. The rubber composition according to claim 14, wherein the filler other than the vapor grown carbon fiber is carbon black and Z or silica.