JPH0551484A - Rubber composition - Google Patents

Abstract

PURPOSE:To obtain a rubber composition having improved abrasion resistance and low heat-generation by compounding a natural rubber and/or a synthetic diene rubber with carbon black, silica, a silane coupling agent and a silylation agent. CONSTITUTION:The objective rubber composition is produced by compounding and kneading (A) 100 pts.wt. of a natural rubber and/or a synthetic diene rubber with (B) 10-60 pts.wt. of carbon black (preferably ISAF, HAF, etc.), (C) 5-50 pts.wt. of silica (preferably fine powder of synthetic anhydrous silicic acid), (D) 2-15wt.% (based on the component C) of a silane coupling agent, preferably one or more compounds selected from formula I, formula II (R is methyl or ethyl; n is integer of 1-8; m is integer of 1-6 ; X is mercapto or amino group), formula III and formula IV and (E) 2-45wt.% (based on the component C) of a silylation agent, preferably one or more compounds selected from the compounds of formula V to formula VIII. The obtained composition has an abrasion resistance comparable or superior to a composition containing the component B as the exclusive additive and has low heat-generation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition used for tires, hoses, conveyor belts, etc., which has improved reinforcing properties, particularly abrasion resistance and low heat buildup.

[0002]

2. Description of the Related Art In rubber compositions such as truck and bus tires, which require considerably high durability and low heat buildup,
Although carbon black having a high reinforcing property such as ISAF has been conventionally used, it is recognized that carbon black as a filler has excellent wear resistance. However, in order to improve wear resistance, the amount of carbon black must be increased. If it is increased, the exothermic property deteriorates. As the market demand for economy has increased in recent years, obtaining lower heat generation and fuel economy has become important points in determining product value.

For this purpose, carbon black alone has a limit as a filler. Therefore, as a conventional method for improving the low heat buildup, the blending amount is changed such that the blending amount of carbon black is decreased and the blending amount of silica is increased.

In the case of reinforcing the filler of rubber, fine particles having high surface activity, such as reinforcing carbon black, having a developed structure have a large interfacial adhesive force between the particle surface and the rubber, so that the tension sharing in the molecular chain is shared. It is also possible to micro-average, but for fillers with low surface activity, before taking on the tension share for stress averaging,
It causes an interfacial failure between the particle surface and the rubber molecule and does not show a reinforcing effect.

Adhesion of rubber molecules to the surface of particles and further chemical bonding have an advantageous effect on enhancement of tensile stress, reinforcement of tear strength, abrasion resistance and the like, and in order to provide high reinforcement. The chemical bond with the rubber molecule on the particle surface is an important factor, and the existence and kind of the functional group involved in such chemical bond on the particle surface must be carefully considered.

It is known that the surface of carbon black particles has a functional group capable of chemically bonding with a rubber molecule, and many studies have shown that a carboxyl group, a hydroxyl group, a ketone group, an ester group and an aldehyde group are present. Are recognized. Has been confirmed.

Since the silanol group has a hydrophilic --OH group, it has a poor wettability with a rubber molecule and a poor dispersion effect. Therefore, so-called silane coupling such as γ-mercaptopropyltrimethoxysilane is involved. Depending on the agent, one end of the molecular chain is bonded to the silanol group of the silica particles by a condensation reaction by hydrolysis of the trimethoxysilane group, that is, bonded to the silica surface, and the other end is mechanically cut during kneading. The functional group (-SH) reacts with the produced elastomer radical of the rubber, and the remaining hydrogen radicals are terminated by the elastomer radical and stabilized. Thus, it is known that the so-called bound rubber around the silane particles, which is insoluble in a solvent such as benzene, increases by a factor of 1.5 as compared with the case where no silane is added. It is known that such a rubber layer has a so-called dense structure having a higher density than the uncrosslinked rubber molecule portion which is easy to move, and this increases the elastic modulus and also functions to equalize and reinforce the stress.

However, even by a means of improving the reinforcing property of silica by using such a silane coupling agent in combination with silica, the effect of the silane coupling agent is aluminum, which is an impurity in silica, and the effect is not good. descend.
There is also a group in which two -OH are attached to Si, which is also one of the causes of the decrease in coupling efficiency. Therefore, there is a problem that even if a silane coupling agent is used in combination with silica, it does not reach the reinforcing property of carbon black.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to replace a part of carbon black compounded in natural rubber and / or diene-based synthetic rubber with silica so as to have low heat buildup and to provide a filler containing only carbon black. It is to provide a rubber composition for a tire, a conveyor belt or the like, which has abrasion resistance equal to or higher than that of the case.

[0010]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that by combining a silane coupling agent with a silylating agent, silica can be effectively used. As a result of finding possible solutions, the present invention has been completed.

That is, the present invention is based on 100 parts by weight of natural rubber and / or diene-based synthetic rubber; %, And a silylating agent in an amount of 2 to 45% by weight based on the amount of silica compounded and kneaded.

The rubber composition according to the above item, wherein the silylating agent is at least one selected from the group consisting of compounds of [Chemical Formula 1], [Chemical Formula 2], [Chemical Formula 3] and [Chemical Formula 4]. ..

Silica is 25 to 35 parts by weight, and the silane coupling agent is represented by the following chemical formula [Chemical Formula 5] [Chemical Formula 6] (wherein R is a methyl group or an ethyl group, n is an integer of 1 to 8, and m is 1 to
An integer of 6, X is a mercapto group or an amino group),
The rubber composition according to the above item, which is at least one selected from the group consisting of [Chemical formula 7] and [Chemical formula 8].

As the rubber component in the present invention, natural rubber or synthetic rubber can be used alone or in a blend thereof. Examples of this synthetic rubber include synthetic polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber. As carbon black, I
SAF, HAF and the like can be preferably used, but are not particularly limited. As the silica, synthetic anhydrous fine silicic acid can be preferably used, but it is not particularly limited.

A large number of silanol groups are present on the surface of silica, although the degree varies depending on the type. The silanol group is hydrophilic and has poor wettability with rubber as described above,
Interaction with rubber is weak. It is the role of the silane coupling agent that acts on both the silanol group and the rubber polymer to improve the reinforcing property, as described above. However, this silane coupling agent is not compatible with aluminum, which is an impurity in silica. This is also one of the causes of the decrease in coupling efficiency.

The silylating agent of the present invention changes the terminal --OH, which reduces the coupling efficiency, into a form called Si--OR by the following reaction.

[Chemical 9]

[Chemical 10] This reaction modifies the hydrophilic silica surface. When the silane coupling agent represented by [Chemical Formula 5], [Chemical Formula 6], [Chemical Formula 7] or [Chemical Formula 8] is used, there is a particularly synergistic effect. Therefore, by using this silica as a filler, the rubber is changed to carbon. It is possible to make the heat generation lower than that when only black is filled, and it is possible to maintain abrasion resistance equal to or higher than that when only carbon black is filled.

If the amount of carbon black used is less than 10 parts by weight, the reinforcing effect is not sufficient, and if it exceeds 60 parts by weight, not only high heat build-up but also abrasion resistance deteriorates.
When the amount of silica used is less than 5 parts by weight, the merit of low exothermicity due to substitution is small, and when it exceeds 50 parts by weight, workability is deteriorated. Silica is preferably 25 to 35 parts by weight.

When the amount of the silane coupling agent used is less than 2% by weight based on the weight of silica, the coupling effect is small, and when it exceeds 15% by weight, gelation of the polymer occurs.
When the amount of silylating agent used is less than 2% by weight based on the amount of silica used, the effect of using the silylating agent is not observed, and when it exceeds 45% by weight, the effect of the coupling agent is obstructed.

The rubber composition of the present invention contains compounding agents usually used in the rubber industry, such as other reinforcing fillers, vulcanizing agents, vulcanization accelerators, antioxidants and softening agents. It goes without saying that they can be appropriately mixed.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Rubber physical property measuring method) (1) Abrasion resistance The abrasion resistance index, which represents abrasion resistance, was calculated by the following equation by measuring the amount of abrasion loss using a Lambourn tester. The larger this index, the better the wear resistance.

(2) Exothermicity The tan δ value representing the exothermicity was measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co.
The measurement was performed under the conditions of a frequency of 50 Hz and 25 ° C. As the test piece, a slab sheet having a thickness of 2 mm and a width of 5 mm was used, and the initial load was 100 g with the distance between the samples being 2 cm. It is expressed by an index in comparison with the control product, and the lower the index value, the lower the heat buildup. (Measured Values) The measured values of the compositions of Examples and Comparative Examples shown in Tables 1 and 2 are shown in the lower columns of Tables 1 and 2.

[0022]

[Table 1]

[Table 2]

In Tables 1 and 2, * 1 Styrene-butadiene copolymer rubber manufactured by Nippon Synthetic Rubber Co., Ltd. * 2 Nipsil AQ manufactured by Nippon Silica Co., Ltd. * 3 Silane coupling agent Si manufactured by Degussa, West Germany
69

[Chemical 11] * 4 Shin-Etsu Chemical Co., Ltd. mercaptosilane

[Chemical formula 12] * 5

[Chemical 13] * 6 N-phenyl-N'-isopropyl-P-phenylenediamine * 7 N-oxydiethylene-2-benzothiazolesulfenamide * 8 Larger is better * 9 Smaller is better

Examples 1, 2 and Comparative Examples 1, 2 are SBR
In the combination of 65 parts by weight and 35 parts by weight of natural rubber, Example 1 is 3 out of 45 parts of carbon black of Comparative Example.
Substituting 0 part of silica with silane coupling agent (10% silica), silylating agent (30% silica)
%) Added. Example 2 is an example in which a silane coupling agent (vs. 3.3% silica) and a silylating agent (vs. 10% silica) were added in Example 1. Comparative Example 1 is an example in which 45 parts by weight of carbon black alone is blended with the same rubber component as in Examples 1 and 2 and neither silica, silane coupling agent nor silylating agent is added. Comparative Example 2 is the same as Comparative Example 1 except for 45 parts of carbon black.
Example of replacing 30 parts by silica

In Example 3 and Comparative Examples 3 and 4, SBR5
0 parts by weight and 50 parts by weight of natural rubber are mixed, and in Example 3, 15 parts by weight of carbon black and 30 parts of silica are used.
Parts by weight, silane coupling agent (based on 3.3% silica),
Example in which a silylating agent (based on silica 10%) was added. Comparative Example 3 is an example in which the silylating agent was not added in Example 3. Comparative Example 4 is an example in which the silane coupling agent was not added in Example 3 but only the silylating agent (10% to silica) was added.

In Example 4 and Comparative Example 5, 15 parts by weight of carbon black and 30 parts by weight of silica were used in the composition of 35 parts by weight of SBR and 65 parts by weight of natural rubber. In Example 4, the silane coupling agent (15 parts by weight of silica) was used. %) Example in which a silylating agent (based on silica 16.7% by weight) is added. Comparative Example 5 is an example in which a silane coupling agent (based on silica: 33.3% by weight, not included in the present invention) and a silylating agent (based on silica, 10% by weight) were added.

In Example 5 and Comparative Example 6, 30 parts by weight of SBR and 70 parts by weight of natural rubber are mixed. In Example 5, 15 parts by weight of carbon black and 30 parts by weight of silica are used, and a silane coupling agent (versus silica) is used. 3.3
Wt%) Example in which a silylating agent (10 wt% to silica) was added. Comparative Example 6 is Example 5 and is an example in which 45 parts by weight of carbon black is blended without silica. As is clear from Tables 1 and 2, the rubber composition of the present invention has wear resistance equal to or higher than that of the comparative example, while exhibiting low heat buildup. In Example 4 and Comparative Example 5, when the silane coupling agent is blended beyond the range of the present invention, the tan δ also decreases, but the wear resistance also deteriorates. Example 5 and Comparative Example 6 show that in Comparative Example 6, when silane coupling agent or silylating agent is added without adding silica, tan δ is lowered, but wear resistance is also deteriorated.

[0028]

EFFECT OF THE INVENTION A rubber composition prepared by substituting silica for a part of carbon black blended in the natural rubber and / or diene synthetic rubber of the present invention and blending a silane coupling agent and especially a silylating agent is added. The heat resistance of the sulfide can be reduced while maintaining the wear resistance at the same level or higher as compared with the case where the carbon black alone is blended. Therefore, when low fuel consumption aiming at energy saving is demanded in recent years, it can greatly contribute to the performance improvement of the product.

Claims (3)

[Claims] 1. Carbon black 10 to 60 relative to 100 parts by weight of natural rubber and / or diene-based synthetic rubber.
A rubber composition obtained by mixing and kneading 5 parts by weight, 5 to 50 parts by weight of silica, 2 to 15% by weight of a silane coupling agent with respect to the amount of silica, and 2 to 45% by weight of a silylating agent with respect to the amount of silica. 2. The rubber composition according to claim 1, wherein the silylating agent is at least one selected from the group consisting of compounds of the following [Chemical formula 1], [Chemical formula 2], [Chemical formula 3] and [Chemical formula 4]. [Chemical 1] [Chemical 2] [Chemical 3] [Chemical 4] 3. 25 to 35 parts by weight of silica, and the silane coupling agent is represented by the following chemical formula [Chemical formula 5] [Chemical formula 6] (wherein R is a methyl group or an ethyl group, n is an integer of 1 to 8 and m is 1 to 1). 6
, X is a mercapto group or an amino group),
The rubber composition according to claim 2, which is at least one selected from the group consisting of [Chemical formula 7] and [Chemical formula 8]. [Chemical 5] [Chemical 6] [Chemical 7] [Chemical 8]