JPH07309974A - Rubber composition - Google Patents

Abstract

PURPOSE:To obtain a rubber composition being highly anisotropic and reduced in fatigue and heat buildup. CONSTITUTION:This composition is one comprising 100 pts.wt. at least one rubber component selected from the group consisting of a natural rubber and a synthetic diene rubber, 1-100 pts.wt. fiber made of a thermoplastic amide elastomer, 1-100 pts.wt. olefin resin and 1-10 pts.wt. unsaturated fatty acid having at least two C-C double bonds in the molecule, wherein the mixing ratio of the fiber made of the thermoplastic amide elastomer to the olefin resin is 3/7 to 7/3, and unsaturated fatty acid contains at least 10wt.% conjugated dienoic acid having at least one pair of conjugated double bonds in the molecule.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition having high anisotropy, fatigue resistance and low heat buildup.

[0002]

2. Description of the Related Art In recent years, various kinds of rubber products such as automobile tires, conveyor belts, hoses, etc. are required to have higher performance, and fatigue properties and low heat generation properties are required to be compatible with each other. .

Conventionally, in order to obtain a rubber composition having excellent processability and excellent strength and modulus of a vulcanized product, it has been known to mix short fibers such as nylon, polyester and vinylon into a vulcanizable rubber. Has been. For example, JP-A-59-43041 discloses a reinforced rubber composition in which rubber and nylon fibers embedded therein are graft-bonded through an initial condensation product of a novolac type phenol formaldehyde resin. . However, in this rubber composition, a kneaded product of rubber and nylon fibers is mixed with a resin curing agent and cured in the rubber, so that it is difficult to control the graft bond between the nylon fibers and the rubber, and the usable rubber is also Only rubber compositions having a limited and low nylon fiber content could be obtained.

To solve this problem, Japanese Patent Publication No. 3-499
No. 32 discloses a rubber composition in which short fibers and a resin are reinforced by kneading aromatic polyamide pulp short fibers and a phenol resin into a rubber, and thereby a high elastic modulus can be obtained. However, in this rubber composition, since rubber molecules and aromatic polyamide pulp short fibers are not directly bonded, the reinforcing efficiency is low, and the short fibers themselves act as fracture nuclei in the rubber, resulting in fatigue durability of the rubber. And has the drawback of significantly lowering the creep property, and also
Since the pulp-like fibers are dispersed in the rubber using a kneading machine such as a Banbury mixer, the dispersion level is extremely low,
If the amount exceeds a certain amount, the reinforcing effect on the blending amount of the short fibers decreases, and if the amount is further increased, there is a drawback that kneading and extrusion become extremely difficult.

Further, in order to obtain a desired elastic modulus, it is conceivable to add carbon black and a novolac type phenol resin to a rubber containing short fibers, but by adding carbon black or a novolac type phenol resin,
The viscosity of the rubber increases significantly, and in each process such as kneading, sheeting, heating, and extrusion, not only the work becomes extremely difficult, but it becomes difficult to arrange the short fibers in the desired direction. It had a drawback that the effect of blending was significantly reduced.

Further, from the viewpoint of improving workability and processability of rubber, when a conventional softening agent such as oil or resin is used, the viscosity is lowered by softening,
Although short fibers can be easily arranged in a desired manner, it is unavoidable that the elastic modulus is decreased and the heat generation is deteriorated by the addition of a softening agent like the conventional rubber, and therefore a rubber composition having desired physical properties can be obtained. There is a problem that can not be done.

On the other hand, the applicant of the present invention has filed Japanese Patent Application Laid-Open No. 4-18985.
No. 0, the specific unsaturated fatty acid, that is, a carbon-carbon double bond containing 5% by weight or more of a conjugated dienoic acid containing at least one pair of two carbon-carbon double bonds in a conjugated relationship in the molecule. It proposes a rubber composition having improved static mechanical strength by blending an organic unsaturated fatty acid containing two or more bonds as a vulcanization accelerator.

This rubber composition and the present application have some common points in that they use a specific unsaturated fatty acid.
No. 189850 aims at the static mechanical strength of rubber products such as tires and conveyor belts, while the present application makes it possible for the above-mentioned specific unsaturated fatty acid to significantly improve anisotropy and processability. While discovering that
Further research has been conducted on the basis of the novel action of this specific unsaturated fatty acid as a basic idea, and the rubber composition has high anisotropy and is excellent in fatigue resistance and low heat buildup.
It is different from the publication No. 0 in its purpose, structure and effect.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention solves these problems, and provides a rubber composition having high anisotropy, fatigue resistance and low heat buildup. The purpose is to do.

[0010]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor
By blending a specific resin and a specific unsaturated fatty acid with a diene rubber component, it was possible to obtain the above rubber composition which could not be achieved by fiber reinforcement alone, and to complete the present invention. It has arrived. That is, the rubber composition of the present invention contains fibers 1 to 100 made of a thermoplastic elastomer having an amide group with respect to 100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene synthetic rubber. Parts by weight and olefin resin 1-1
00 parts by weight and 1 to 10 parts by weight of an unsaturated fatty acid having two or more carbon-carbon double bonds in the molecule, and a fiber comprising the amide group-containing thermoplastic elastomer and an olefin resin Mixing ratio with 3/7 to 7/3
And the unsaturated fatty acid contains 10% by weight or more of a conjugated diene-based acid having one or more sets of conjugated double bonds in the molecule. It is preferable that the fiber made of the thermoplastic elastomer is made of nylon 6 and the olefin resin is made of polypropylene. Further, the average diameter of the fiber made of the thermoplastic elastomer is 0.1 to
1.0 μm, ratio (L / D) of average length L and average diameter D is 8
The above is preferable. The melting point of the olefin resin is preferably 130 to 200 ° C. The final kneading temperature in the kneading stage containing no vulcanization accelerator or vulcanizing agent is preferably 3 ° C. or more higher than the melting point of the olefin resin.

[0011]

The rubber composition of the present invention comprises fibers made of a thermoplastic elastomer having an amide group with respect to 100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene synthetic rubber. An olefin resin and an unsaturated fatty acid are each formed by mixing in a specific amount, and a fiber made of a thermoplastic elastomer having these amide groups, the olefin resin and the unsaturated fatty acid are synergistic with each other. It is based on the new fact that the anisotropy can be significantly improved and a rubber composition excellent in fatigue resistance and low heat buildup can be obtained, and even if each of the conditions is partially satisfied. The object of the present invention is not achieved (this point will be described in more detail in Examples and the like).

The contents of the present invention will be described below. Examples of rubber components that can be preferably used in the present invention include natural rubber (NR), synthetic polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), butyl rubber (IIR), chloroprene. Examples thereof include rubber (CR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR) and ethylene-propylene rubber (EPDM), and these rubbers can be used alone or in combination of two or more kinds.

In the present invention, the "conjugated diene-based acid" means at least one pair of carbon-carbon double bonds having a conjugated relationship in the molecule (for example, -CH = CH-CH = CH).
-) An unsaturated monocarboxylic acid containing

The unsaturated fatty acid containing two or more carbon-carbon double bonds in the molecule containing 10% by weight or more of the conjugated diene-based acid (hereinafter, simply referred to as "organic unsaturated fatty acid") is, of course, the conjugated diene-based. Although it contains an acid, the other organic unsaturated fatty acids contain two or more carbon-carbon double bonds, but are different in that they are in a non-conjugated relationship with each other. The unsaturated fatty acid is preferably within the range of a fatty acid having a carbon number of 10 to 22 which is a conventionally used vulcanization accelerator, including conjugated diene acids.

The content of the conjugated diene-based acid in the unsaturated fatty acid must be 10% by weight or more, preferably 25% by weight or more, and 100% by weight, that is, the unsaturated fatty acids are all conjugated diene-based acids. May be. If the content of the conjugated diene-based acid is less than 10% by weight, the vulcanized rubber cannot have a sufficient elastic modulus and the effect of improving breaking strength cannot be obtained.

Examples of the conjugated diene-based acid include 2,4
-Pentadienoic acid, 2,4-hexadienoic acid, 2,4-
Decadienoic acid, 2,4-dodecadienoic acid, 9,11-octadecadienoic acid, eriostearic acid, 9,11,1
3,15-octadecatetraenoic acid, 9,11,13-
Examples thereof include octadecatrienoic acid, which are used alone, in a mixture, or in a form contained in the unsaturated fatty acid.

A preferred example of the organic unsaturated fatty acid used in the present invention is dehydrated castor oil fatty acid. This dehydrated castor oil fatty acid is obtained by dehydrating castor oil. The content of the conjugated dienoic acid can be changed depending on the dehydration method, and for example, 35% by weight and 50% by weight can be obtained. In the case of the dehydrated castor oil fatty acid, the conjugated diene-based acid is mainly 9,11-octadecadienoic acid, and the other organic unsaturated fatty acids are mainly non-conjugated octadecadienoic acid. Examples of the non-conjugated unsaturated fatty acid also include linoleic acid and linoleic acid.

The amount of the organic unsaturated fatty acid used in the present invention is 1 to 10 parts by weight based on 100 parts by weight of the rubber component.
It is preferably 3 to 6 parts by weight. When the organic unsaturated fatty acid is blended in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the rubber component, workability and anisotropy can be significantly improved. When the amount of the organic unsaturated fatty acid compounded exceeds 10 parts by weight, or when it is less than 1 part by weight, a sufficient elastic modulus of the rubber cannot be obtained. No improvement effect can be obtained. Furthermore, in the rubber composition of the present invention, it is more preferable to use, in addition to the above-mentioned organic unsaturated fatty acid, a conventionally used fatty acid represented by stearic acid.

Examples of the amide group-containing thermoplastic elastomer (hereinafter referred to as "polyamide") used in the present invention include nylon 6, nylon 11, nylon 12, nylon 610, nylon 611 and nylon 61.
2, polyamides including copolymerization of nylon 6/66, and mixed polyamides of two or more of these may be mentioned. The molecular weight of the polyamide used is preferably 8,000 or more, and the melting point thereof is preferably in the range of 170 to 240 ° C. in consideration of the temperature of kneading when preparing a masterbatch. The blending amount of this polyamide can be appropriately adjusted by, for example, further kneading a diene rubber with a reinforcing rubber of a polyamide as a masterbatch and an olefin resin described later. Further, in the rubber composition of the present invention, the polyamide is contained in the form of short fibers, and from the viewpoint of physical properties and processed surface, it is necessary to consider the amount of polyamide as short fibers, and the amount thereof is the above diene type. 1 to 100 parts by weight, preferably 2.5 to 50 parts by weight, and more preferably 5 to 3 parts by weight with respect to 100 parts by weight of the rubber component.
0 parts by weight. If the blending amount of polyamide is less than 1 part by weight, the effect of the present invention cannot be exhibited, and 10
If it exceeds 0 parts by weight, the workability is remarkably lowered and the workability becomes difficult, which is not preferable.

The polyamide in the rubber composition of the present invention may be in any bonding state with rubber molecules, but is preferably chemically bonded such as graft bonding. This polyamide has a circular cross section or a shape similar thereto, and has an average diameter D of 0.1 to 1.0 μm, preferably 0.1 to 0.8 μm, and more preferably 90% by weight or more. Is 1.0 μm or less, the average fiber length L is 10 μm or more, and 90% by weight thereof.
The above is preferably 1000 μm or less. If the average diameter D exceeds 1.0 μm, the stress concentration at the fiber ends causes the fatigue durability to decrease. Further, the larger the ratio (L / D) of the average length L and the average diameter D of the polyamide, the easier the orientation and the effect of increasing the anisotropy. Therefore, the ideal characteristics of polyamide are small diameter,
It can be said that it is preferable to increase L / D. Therefore,
L / D is required to be 8 or more, preferably 50 to
It is 5000. When L / D is less than 8, anisotropy cannot be increased, which is not preferable. Since the polyamide used in the present invention is melt-stretched in rubber, it is an extremely microfiber, and can significantly improve fatigue durability.

Examples of the olefin resin used in the present invention include low density polyethylene (L-PE), high density polyethylene (H-PE), polypropylene (P).
P) and the like. The melting point of olefin resin is 13
It is 0 to 200 ° C, preferably 150 to 170 ° C. If the melting point is less than 130 ° C, the exothermic property, which is a physical property of rubber after vulcanization, cannot be lowered, and the melting point is 200 ° C.
If it exceeds, the workability will deteriorate and it will not dissolve when kneading rubber,
Not preferable.

The amount of the olefin resin blended can be adjusted as appropriate by further kneading the diene rubber with the reinforced rubber of the masterbatch olefin resin and the above polyamide, and 100 weight parts of the diene rubber component. 1 to 100 parts by weight, preferably 2.5 to 5 parts by weight
The amount is 0 parts by weight, more preferably 5 to 30 parts by weight. If the blending amount of the olefin resin is less than 1 part by weight, the effect of the present invention cannot be exhibited, and if it exceeds 100 parts by weight, the workability is remarkably lowered and the workability becomes difficult, which is not preferable. Furthermore, the compounding ratio of the polyamide and the olefin resin is 3/7 to 7/3, preferably 4 /
When it is 6 to 6/4 and the compounding ratio is less than 3/7,
Anisotropy and fatigue resistance are reduced, which is not preferable, and when the compounding ratio exceeds 7/3, heat generation is increased, which is not preferable.

Next, an example of the method for producing the rubber composition according to the present invention will be described. The materials and their amounts used here are as described above. First, a diene rubber and an amine anti-aging agent are kneaded for about 1 to 3 minutes, and then a polyamide and an olefin resin are added and kneaded to raise the temperature to a temperature equal to or higher than the melting points of the polyamide and the olefin resin and melt them. . Then, if necessary, a coupling agent such as a phenol resin oligomer is added and further kneaded to obtain a masterbatch. Then, this masterbatch is extruded by an extruder and stretched to obtain a rubber composition reinforced with a polyamide fiber / olefin resin.

Further, to the obtained masterbatch (the diene rubber is reinforced by polyamide and olefin resin by graft bonding), the diene rubber is added in order to adjust the polyamide and olefin resin in the blend to a desired amount. Rubber is appropriately added, and the organic unsaturated fatty acid is added in a predetermined amount, and carbon black usually used in the rubber industry, sulfur, a vulcanizing agent, a vulcanization accelerator, a vulcanization accelerating aid, an antioxidant, In addition to carbon black, for example, a filler such as silica, a novolac type phenol resin, a process oil and the like are appropriately added and kneaded with a Banbury mixer, a kneader or the like to obtain a desired rubber composition. This kneading is carried out for 30 seconds to 10 minutes in a kneading stage containing no vulcanization accelerator or vulcanizing agent so that the final kneading temperature is 3 ° C. or more higher than the melting point of the olefin resin. The final kneading temperature after the above kneading is set to a temperature higher than the melting point of the olefin resin by 3 ° C. or more in order to completely melt the olefin resin and promote good dispersion of the olefin resin and fusion with the polyamide. Is. In addition,
The vulcanization temperature is preferably set at 3 ° C. or higher than the melting point of the olefin resin. This is because if the temperature is raised to 3 ° C. or higher, the olefin resin is easily dispersed and fused to the polyamide.

In the rubber composition of the present invention, the diene rubber and the polyamide are chemically bonded together, and the olefin resin is fused to the polyamide, and the polyamide has the characteristics of break resistance, It is possible to significantly improve the anisotropy by improving the fatigue property and improving the anisotropy, which is a characteristic of the olefin resin, and by using the organic unsaturated fatty acid. It becomes a thing. Therefore, by appropriately adjusting the compounding amounts of polyamide, olefin resin, carbon black, sulfur, vulcanization accelerator, etc. to the desired physical properties, belts, carcasses, tire internal members such as beads, treads, sidewalls, etc. It can be suitably used as a tire external member or in various rubber products such as conveyor belts and hoses.

[0026]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and the like.

In the present examples and the like, the polyamide fiber used is nylon 6, and the olefin resin is polypropylene (PP). The melting point was measured by the following method. (Measurement of melting point) Suggested thermal analyzer DS by Seiko Instruments Inc.
Using C200, the temperature rise rate is 10 ° C / min.
The temperature was raised in the temperature range up to 50 ° C., and the melting point temperature was measured from the obtained endothermic peak.

Examples 1 to 4 and Comparative Examples 1 to 6 100 parts by weight of natural rubber and N- (3-methacryloyloxy-2)
-Hydroxypropyl) -N'-phenyl-P-phenylenediamine [trade name "Nocrac G-1", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.] 1.0 part by weight, and then a molecular weight of 3
50 parts by weight of 6-nylon resin having a melting point of 220.degree.
-Nylon was melted, 2 parts by weight of novolak-type phenol formaldehyde initial condensate was added, and 0.2 part by weight of hexamethylenetetramine was further added to obtain a masterbatch. Then, the master batch was stretched by an extruder to obtain a short fiber polyamide / olefin resin reinforced rubber master batch. In addition, this master batch is
By further kneading with a diene rubber in a Banbury mixer, the compounding amounts of polyamide (6-nylon) and olefin resin (polypropylene) can be adjusted appropriately. Further, by changing the average particle size of the polyamide powder used, the average diameter (D) and length (L) of the polyamide (6-nylon) in the masterbatch were obtained as shown in Table 1. Moreover, the olefin resin of the melting point shown in Table 1 was used.

Next, the reinforcing rubber masterbatch was compounded with the compounding agents shown in Table 1 below in a Banbury mixer to prepare various rubber compositions, which were vulcanized to have an orientation direction of 50%.
The modulus (M _50p ), the 50% modulus in the direction perpendicular to the orientation (M _50V ), and the anisotropy (M _50p / M _50V ) were evaluated. The fiber orientation direction is p, and the direction perpendicular to the fiber orientation direction is v.
Display as. The results are shown in Table 1 below.

The above 50% modulus (M _50p , M _50V ) was measured by the following method. JIS K 630
According to 1, the dumbbell No. 3 was measured as a sample.

[0031]

[Table 1]

[Discussion of Table 1] As a general view, Examples 1 to 4 which are within the scope of the present invention have anisotropy (M _{50p) as} compared with Comparative Examples 1 to 6 which are outside the scope of the present invention. / M _50V ) was found to be significantly improved. When examined individually, in Example 1, the composition of the polyamide and the olefin resin was the same amount (15 parts by weight), and the dehydrated castor oil fatty acid having the conjugated diene acid content of 35% by weight was compounded. Yes, it was found that the anisotropy could be significantly improved. On the other hand, Comparative Example 1 is a case where only dehydrated castor oil fatty acid is not blended, Comparative Example 2 is a case where only olefin resin is not blended, and Comparative Example 3 is a case where only polyamide is not blended. In the case of, the anisotropy was lower than that of Example 1, and particularly in Comparative Example 3, it was found that the anisotropy was significantly reduced, which was not preferable.

In Example 2, the blending composition of the polyamide and the olefin resin was the same amount (15 parts by weight), and the blending amount of dehydrated castor oil fatty acid having a conjugated diene acid content of 35% by weight was doubled as compared with Example 1. In the case of Example 3, when the conjugated diene-based acid content is 15% by weight and the compounding amount is 4 parts by weight, in Example 4, the compounding amounts of the polyamide and the olefin resin are both higher than those in Example 1. It was 50 parts by weight and the blending amount of carbon black was 15 parts by weight, and it was found that the anisotropy was significantly improved even in these cases. On the other hand, Comparative Example 4 is a case where a process oil is blended in place of the dehydrated castor oil fatty acid, and Comparative Example 5 is a case where the conjugated diene-based acid content is 8% by weight. In these cases, It was found that the anisotropy was significantly reduced, which was not preferable. Further, Comparative Example 6 is a case where the dehydrated castor oil fatty acid was not blended, as compared with Example 4, and in this case, it was found that the anisotropy was significantly reduced.

[0034]

According to the present invention, the diene rubber and the fiber made of the thermoplastic elastomer having an amide group are chemically bonded to each other and the olefin resin is fused to the polyamide. To improve the anisotropy further by compounding an organic unsaturated fatty acid, as well as to improve the fracture resistance and fatigue properties of the polyamide fiber and the anisotropy of the olefin resin. Therefore, the anisotropy can be greatly improved,
And, it becomes excellent in fatigue resistance and low heat generation, therefore, tire internal members such as belts, carcass and beads,
Provided is a rubber composition that can be suitably used for a tire as a tire external member such as a tread or a sidewall, or various rubber products such as a conveyor belt or a hose.

Claims (5)

[Claims] 1. 100 parts by weight of at least one rubber component selected from the group consisting of natural rubber and diene synthetic rubber, and 1 to 100 parts by weight of a fiber made of a thermoplastic elastomer having an amide group, and an olefin. Resins 1-1
00 parts by weight and 1 to 10 parts by weight of an unsaturated fatty acid having two or more carbon-carbon double bonds in the molecule, and a fiber comprising the amide group-containing thermoplastic elastomer and an olefin resin Mixing ratio with 3/7 to 7/3
And a rubber composition in which the unsaturated fatty acid contains 10% by weight or more of a conjugated diene-based acid having one or more sets of conjugated double bonds in the molecule. 2. The rubber composition according to claim 1, wherein the fiber made of a thermoplastic elastomer is nylon 6, and the olefin resin is polypropylene. 3. The average diameter D of the fiber made of a thermoplastic elastomer is 0.1 to 1.0 μm, and the ratio (L / D) of the average length L and the average diameter D is 8 or more. Rubber composition. 4. The melting point of the olefin resin is 130 to 20.
The rubber composition according to claim 1, which has a temperature of 0 ° C. 5. The rubber composition according to claim 1, wherein the final kneading temperature in the kneading stage containing no vulcanization accelerator or vulcanizing agent is 3 ° C. or more higher than the melting point of the olefin resin.