JPH1095874A - Rubber composition for reinforced rubber products - Google Patents

Abstract

(57) [Problem] To provide a reinforced rubber product excellent in a reinforcing effect and fatigue property and a short fiber-containing rubber composition therefor. SOLUTION: A short fiber having a hollow or irregular cross-sectional shape, wherein the short fiber has a split fiber of 70% or more and a rubber composition for a reinforced rubber product comprising an unvulcanized rubber. This rubber composition can be obtained by kneading a short fiber having a hollow or irregular cross section and an unvulcanized rubber, and splitting 70% or more of the short fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a rubber composition for a reinforced rubber product and a reinforced rubber product. More specifically, it relates to a rubber composition and a reinforced rubber product of a reinforced rubber product for use as an industrial material such as a belt, a hose, and a tire.

[0002]

2. Description of the Related Art At present, in order to improve mechanical properties such as strength and elastic modulus of rubber products such as belts, hoses and tires,
It has been studied to mix and reinforce short fibers, but in order to obtain a sufficient reinforcing effect, it is effective to increase the aspect ratio (short fiber length / short fiber cross-sectional area) of the short fibers as much as possible. However, to increase the aspect ratio,
First, it is conceivable to increase the short fiber length, but if it is too long, when kneading with rubber, the short fibers are not sufficiently dispersed, the short fibers are entangled with each other, a fiber ball state is formed, and not only the reinforcing effect is not exhibited. This becomes a defect in the rubber and causes a reduction in fatigue. As a countermeasure, various studies have been made on a method of performing surface treatment processing on short fibers, a kneading method, and an improvement in dispersibility by improving kneading equipment, but these methods are not yet satisfactory. In order to increase the aspect ratio, it is conceivable to reduce the cross-sectional area of the short fiber, but if it is too small, the production becomes difficult. For this reason, short fibers that have good dispersibility and can maintain a large aspect ratio even after rubber kneading are desired.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a rubber composition for a reinforced rubber product having an excellent reinforcing effect and excellent fatigue properties.

[0004]

Means for Solving the Problems The present inventors have conducted research to achieve the above object, and found that short fibers which are easy to split are compounded in unvulcanized rubber and kneaded. As a result, the short fibers are split, and the anchor effect and the aspect ratio are increased, whereby the reinforcing effect and the fatigue property are improved.

According to the present invention, there is provided a staple fiber having a hollow or irregular cross-sectional shape, wherein the staple fiber comprises 70% or more of split short fibers and unvulcanized rubber. A rubber composition is provided. Further, according to the present invention, a rubber composition for a reinforced rubber product obtained by kneading a short fiber having a hollow or irregular cross section and an unvulcanized rubber and splitting at least 70% of the short fiber. Things are provided. Hereinafter, the present invention will be described in more detail.

The rubber composition for a reinforced rubber product of the present invention is most conveniently prepared by kneading short fibers having a hollow or irregular cross section with unvulcanized rubber and splitting the short fibers by shearing force. Obtainable. Therefore, it is required that the short fibers blended in the rubber composition of the present invention have a cross-sectional shape that splits when kneaded with rubber.
Therefore, it is not desirable that the cross-sectional shape is circular, and it is hollow or irregular.

In the case of a hollow fiber having a hollow cross section, the hollow ratio is 30% or more, preferably 35 to 50%. Here, the hollow ratio is a ratio (%) of the area of the hollow portion to the cross-sectional area including the hollow portion calculated from the outer periphery of the fiber. When the hollow ratio is less than 30%, splitting is difficult even when kneaded, which is not preferable. On the other hand, the shape of the irregular cross section may be any shape that is non-circular and easy to split, and generally includes three folds (triangles) or four (triangular threads). In the case of an irregular cross section, those having a flatness of 3.5 or more, preferably 3.5 to 5 are preferred because they are easy to split. Here, the flattening ratio is represented by a ratio of a maximum diameter of a cross section / a minimum diameter of a cross section of the cross section of the fiber.

The short fibers to be blended with the unvulcanized rubber advantageously have a fineness before splitting of 1 to 10 De, preferably 2 to 8 De. The strength is suitably at least 5 g / De, preferably at least 8 g / De, and the upper limit is generally about 20 g / De. The fiber length of the short fibers is in the range of 0.3 to 10 mm, preferably 0.5 to 7 mm. When the fiber length is less than 0.3 mm, the reinforcing effect is insufficient. On the other hand, when the fiber length is more than 10 mm, entanglement between short fibers tends to occur, and dispersion in rubber tends to be poor.

As the polymer forming the short fibers, those having a rubber reinforcing effect are preferable. For example, polyester fibers such as polyethylene terephthalate and polyethylene naphthalate, polyamide fibers such as nylon 6, 66 and 46, paraphenylene terephthalamide, And aramid fibers typified by copolymers with aromatic ethers are preferred, but other polyaromatic fibers such as wholly aromatic polyester fibers, vinylon fibers, rayon fibers, ultra-high-molecular-weight polyethylene, polyoxymethylene fibers, paraphenylene sal Sulfone-based fibers such as phone and polysulfone;
Polyetheretherketone fibers, polyetherimide fibers, carbon fibers, etc., and in some cases, inorganic fibers such as glass fibers, ceramic fibers, and metal fibers may be used in combination.

[0010] The fiber may contain various additives usually used for improving productivity or characteristics in the production and processing steps of the raw yarn. For example, heat stabilizers,
It may contain an antioxidant, a light stabilizer, a leveling agent, a plasticizer, a thickener, a pigment, a glossing agent, a flame retardant, and the like. Further, a surface treatment agent for improving dispersibility and adhesion may be applied.

[0011] Among the various short fibers described above, polyethylene terephthalate short fibers and polyethylene naphthalate short fibers are preferred, and polyethylene-2,6-
Naphthalate short fibers are preferred for their high tenacity. The polyethylene-2,6-naphthalate has at least 90 mol%, preferably at least 95 mol% of the total repeat units.
It is preferred that the mole% is ethylene-2,6-naphthalate unit and the intrinsic viscosity is 0.6 or more, particularly 0.7 to 1.0. Here, the intrinsic viscosity is a value calculated from the viscosity measured at 35 ° C. by dissolving the fiber in a mixed solvent of phenol and orthochlorobenzene (volume ratio 6: 4).

The rubber which forms the rubber composition of the present invention may be any one which is generally used as a raw material for fiber-reinforced rubber products as an industrial material such as belts, hoses and tires, and may be natural rubber or synthetic rubber. Any of rubber may be used. Examples of the synthetic rubber include isoprene rubber, SB rubber, butadiene rubber, EP rubber, and the like, and two or more of these can be used in combination.

The rubber composition of the present invention is obtained by blending the short fibers and the unvulcanized rubber as described above, and then kneading the mixture.
It is obtained by splitting short fibers by applying a shearing force.
This kneading is desirably performed so that the short fibers and the rubber are uniformly mixed, the short fibers are well dispersed, and 70% or more, preferably 80% or more of the short fibers are split. The ratio of the split fibers indicates the ratio (%) of split short fibers to all short fibers. Specifically, the composition after kneading is dissolved and removed with a rubber solvent to remove short fibers. A micrograph is taken and the number of split fibers in the cross section of the short fiber is calculated to determine the split ratio.

The mixing ratio of the short fibers in the rubber composition of the present invention is in the range of 1 to 10% by weight, preferably 3 to 7%. The composition of the short fiber and the unvulcanized rubber in the present invention is obtained by subjecting the composition to a usual molding method known per se.
Rubber products can be obtained by vulcanizing and molding by heating.

[0015]

According to the present invention, there can be obtained a rubber composition which can be processed into a reinforced rubber product having excellent reinforcing effect and fatigue property.

[0016]

The present invention will be described more specifically with reference to the following examples. In addition, each physical property value is measured by the following method. (1) Splitting ratio of short fibers After dissolving and removing the rubber after kneading with a solvent, a microscopic photograph of the short fibers was taken, and the number of splits in the cross section of the short fibers was counted to obtain the splitting ratio. (2) Hollowness ratio It was calculated by measuring the cross-sectional area ratio with a planimeter from the microscopic cross-sectional photograph. (2) Flatness Calculated from the ratio of the maximum diameter of the cross section to the minimum diameter of the cross section. (3) Tensile strength at yield point and elongation at break of reinforced rubber product This shows the reinforcing effect and elongation of a rubber product reinforced with short fibers. The value obtained by dividing the yield point load at the time of cutting by the cross-sectional area of the test piece is defined as the tensile strength at the yield point, and the elongation between the marked lines at the time of cutting is defined as the elongation at break. (4) Bending fatigue life of reinforced rubber product It is an index for judging the fatigue property of rubber product reinforced with short fibers, using a Demachia bending fatigue tester of Toyo Seiki Co., Ltd.
The No. 3 dumbbell-shaped test piece was bent by 25% at a cycle of 5 Hz in an atmosphere of 80 ° C. and indicated by the number of times until a crack was generated.

Example 1 An ethylene-2,6-naphthalate chip having an intrinsic viscosity of 0.7 was prepared at a temperature of 310.degree. C. at a temperature of 310.degree. Discharged more. The discharge amount was adjusted so that the single yarn fineness after spinning and drawing became 4 De. The discharged yarn passes through a zone heated and maintained at 300 ° C. over a length of 100 mm, and then a cooling air having a temperature of 25 ° C. and a wind speed of 0.3 m / sec is blown out to a length of 33 mm.
After spraying and cooling and solidifying over 0 mm, and applying an oil agent with an oiling roller, it was wound up at a speed of 700 m / min. Next, the undrawn yarn is subjected to first-stage drawing (magnification: 5.0) between a heat-supplying roll at 160 ° C. and the first-stage drawing roll, and subsequently, between the first-stage drawing roll and the two-stage drawing roll. After performing the second-stage stretching (1.1 magnification) in a 320 ° C. dry heat bath, the film was passed through a 320 ° C. dry heat bath without relaxation (1.0 magnification), and wound at a speed of 300 m / min. . The obtained drawn yarn had a single fiber fineness of 4.0 De, a hollow fiber ratio of 36%, and a strength of 8.0 g / De.

The obtained drawn yarn is guillotine-cuttered for 3.
Cut to a length of 0 mm to obtain short fibers. 5% by weight of this short fiber is blended into an unvulcanized rubber mainly composed of a mixture of natural rubber and styrene butadiene (SB rubber).
Using an S-type pressure kneader (DS3-10MHHS Moriyama Seisakusho Co., Ltd.), the mixture was kneaded for 3 minutes. Sheeting was performed to an appropriate thickness so that the short fibers were oriented, a rubber sheet was prepared by press vulcanization, and a sample was cut out in the orientation direction of the short fibers to evaluate performance.

Example 2 Example 2 was carried out in the same manner as in Example 1 except that a short fiber was used in a die having a flat cross section and the short fiber flatness was 3.7.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the base was changed and the short fiber cross section was round. Comparative Examples 2 and 3 The same operation as in Example 1 was performed except that the spinning conditions were adjusted and the hollow ratio and the flattening ratio were changed. The results are as shown in Table 1. By setting the short fibers to have a high hollow ratio and a high flatness, the rubber kneading was easily divided at the time of kneading, and the reinforcing effect and the excellent fatigue effect were obtained.

[0021]

[Table 1]

Claims (3)

[Claims] 1. A rubber composition for a reinforced rubber product comprising short fibers having a hollow or irregular cross-sectional shape, wherein the short fibers are split fibers of at least 70% and unvulcanized rubber. 2. A rubber composition for a reinforced rubber product obtained by kneading a short fiber having a hollow or irregular cross-sectional shape with an unvulcanized rubber and splitting at least 70% of the short fiber. 3. The rubber composition according to claim 1 or 2,
A reinforced rubber product obtained by heating and vulcanizing.