JPH0625279B2 - Rubber composition for tire tread - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention significantly improves the frictional resistance on snow or iced road surfaces, maintains its excellent athletic performance for a long time, and further eliminates volatile components in the tire manufacturing process. The present invention relates to a rubber composition for a tire tread, which can be dramatically reduced and the working environment can be improved.

[Prior art]

Of the road conditions on which a car runs, icy road conditions are the most slippery and dangerous. Therefore, in cold regions where the vehicle frequently travels on an icy road surface, automobile tires in which a metal spike is driven into the tire tread portion or a chain is attached are widely used. However, even in cold regions, roads are rarely frozen in the winter, and in most of the winter, the roads are not frozen. With the development of automobile traffic, automobiles equipped with spiked or chain-tired tires frequently come and go on uniced roads in cold regions.Today, spikes and chains damage roads. As a result, social problems are becoming apparent, in which dust pollution is induced and repair of damaged roads requires a great deal of money. In order to deal with this problem, there is a demand for the development of a tire that can be safely driven on a frozen road surface without using spikes or chains. One of the methods for obtaining such a tire is to develop a rubber material for a tread having a large frictional resistance on an icy road surface.

The main factor that determines the friction characteristics of the rubber material is the raw rubber (elastomer) component, and under general road surface conditions such as dry road surface and wet road surface, the glass transition temperature such as styrene-butadiene copolymer rubber (SBR). When a raw material rubber having a relatively high (Tg) is used, the frictional resistance becomes large. on the other hand,
On the icy road surface, the opposite is true, and when a raw material rubber having a low Tg such as natural rubber (NR) or polybutadiene rubber (BR) is used, the friction resistance increases. BR has a greater effect of increasing frictional resistance as the temperature of ice decreases, and is widely used as a raw material rubber for tread rubber of winter tires, but the frictional resistance on general road surfaces, particularly wet road surfaces, is significantly reduced. Therefore, the amount of use is limited. As described above, the frictional resistance on the icy road surface and the frictional resistance on the wet road surface are generally considered as contradictory characteristics, and the frictional resistance on the icy road surface is significantly reduced without significantly reducing the frictional resistance on the wet road surface. It was difficult to improve.

As a method of increasing the frictional resistance on wet road surfaces, Japanese Patent Publication Sho 58-
It is proposed in the 7662 publication to use a particular process oil. However, the degree of improvement of the frictional resistance on the icy road surface is insufficient as compared with the effect of the spikes or chains attached to the tire, and further, the frictional resistance on the icy road surface is required to be improved. Further, as a raw material for increasing the frictional resistance on an icy road surface, JP-A-59-126443 discloses a low-temperature plasticizer such as dioctyl sebacate (DOS), and JP-A-59-206209 discloses an oleic acid derivative. It is disclosed that each of the synthetic plasticizers is used. However, such synthetic plasticizers have a problem that plasticizer vapor is generated in the tire manufacturing process, particularly in the mixing and vulcanization processes, and the working environment is deteriorated and the physical properties are deteriorated. In a tire with a rubber temperature of 60 to 120 ° C. and a service life of several years, the softening agent gradually evaporates from the tire surface due to the high temperature (heating), and the physical properties may change over time. It is difficult or difficult to maintain a high frictional resistance on an icy road surface for a long period of time. Therefore, a softening agent having a small volatilization amount by heating is desired.

[Object of the Invention]

The present invention provides a rubber composition for a tire tread capable of significantly increasing frictional resistance on an icy road surface, maintaining its kinetic performance for a long period of time, and dramatically reducing volatile components in a tire manufacturing process to improve a working environment. The purpose is to provide things. This rubber composition can be used particularly as a rubber material for a tread of a winter tire or an all-season tire.

[Structure of Invention]

Therefore, the present invention, natural rubber, polyisoprene rubber,
And 100 parts by weight of one or more rubbers selected from the group consisting of polybutadiene rubber, 40 to 100 parts by weight of carbon black, 2 to 35 parts by weight of neopentyl polyol ester represented by the following formula, and petroleum-based A rubber composition for a tire tread is characterized in that 0 to 60 parts by weight of a softening agent is blended.

(In the formula, R is a hydrogen atom, a hydroxyl group, a methyl group or a general formula. (In the formula, R ′ represents a hydrocarbon group having 3 to 21 carbon atoms)
Which may be the same or different, but at least two of R are general formulas. Is a monocarboxylic acid residue. n is a number from 0 to 2) Hereinafter, the configuration of the present invention will be described in detail.

(1) Raw rubber.

1 selected from the group consisting of natural rubber (NR), polyisoprene rubber (IR) and polybutadiene rubber (BR)
One type or two or more types of rubber are used. It is preferable to use a blend of these rubbers, and the blending ratio is such that NR or IR is
It is preferable that 100 to 0 parts by weight and BR to be 0 to 75 parts by weight.
For example, for the purpose of significantly increasing the frictional resistance on an icy road surface, NR or IR or BR (low vinyl BR) having a 1.2-bond unit content of 20% or less is used as a raw rubber component. However, low vinyl BR has a remarkable effect of increasing the frictional resistance on the icy road surface as the temperature decreases, but it may decrease the frictional resistance on the icy road surface near the melting point of ice, and at the same time, on the wet road surface. It significantly reduces the frictional resistance in the
It is preferable to keep it to 75% by weight or less.

(2) Carbon black.

It may be of the type normally used for tire treads.

(3) Neopentyl type polyol ester.

In the present invention, one or two or more neopentyl type polyol esters represented by the above formula are blended with the above-mentioned raw material rubber in order to improve the friction resistance on the frozen road surface. Preferable examples of such neopentyl type polyol ester are compounds represented by the following general formulas (1) to (3). In the formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are alkyl groups or alkenyl groups having 3 to 21 carbon atoms and may be the same or different.

Examples of the polyhydric alcohol that constitutes the neopentyl type polyol ester include neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. The acid constituting the neopentyl type polyol ester is a monocarboxylic acid, and examples thereof include C _{4 to} C ₂₂ saturated fatty acids and unsaturated fatty acids, and examples thereof include butyric acid, valeric acid, caproic acid, enanthic acid, and capryl. Acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, isostearic acid, nonadecanoic acid, heneicoic acid, lauroleic acid, tzuic acid, ficetrain acid , Fatty acids such as myristic acid, zoumaric acid, palmitoleic acid, petrosenoic acid, vaccenic acid, gadolenic acid, oleic acid, linoleic acid, linolenic acid, and mixed fatty acids thereof.

(4) Petroleum-based softener The petroleum-based softener has a viscosity specific gravity constant (VGC) of 0.80 to
A paraffinic process oil, a naphthenic process oil, and an aromatic process oil consisting of 1.00. Petroleum softener,
A part or the whole amount thereof may be impregnated into the raw rubber as an extending oil in advance during the production of the raw rubber.

(5) The rubber composition of the present invention, relative to 100 parts by weight of the raw material rubber, 40 to 100 parts by weight of the carbon black, 2 to 35 parts by weight of the neopentyl type polyol ester, and 0 to 60 parts by weight of the petroleum softener. It is a mixture of parts.

If the blending amount of carbon black is less than 40 parts by weight, the abrasion resistance is lowered, and if it exceeds 100 parts by weight, the productivity is lowered, which is not preferable.

Also, the amount of neopentyl-type polyol ester blended is 2
If it is less than part by weight, the frictional resistance on the icy road surface cannot be sufficiently increased, and if it is more than 35 parts by weight, the abrasion resistance is remarkably reduced, which is not preferable.

The neopentyl-type polyol ester may be used alone, but the petroleum-based softening agent may be used in an amount of 60 parts by weight, preferably 50 parts by weight or less, based on 100 parts by weight of the raw rubber.
When the neopentyl type polyol ester is used alone, the frictional resistance on the icy road surface can be significantly increased. It is possible to obtain a frictional resistance on an icy road surface which is almost the same as that when the type polyol ester is used alone. The petroleum-based softening agent is added in order to suppress a decrease in frictional resistance on a wet road surface, and if it exceeds 60 parts by weight, abrasion resistance is deteriorated, which is not preferable. When the neopentyl type polyol ester and the petroleum-based softening agent are used in combination, it is preferable that the total amount of the softening agent contains 20 to 80% by weight of the neopentyl type polyol ester.

When the neopentyl type polyol ester which is a softening agent and the petroleum softening agent are used in combination in the present invention, the compounding amount thereof is preferably 10 to 90 parts by weight based on 100 parts by weight of the raw rubber. Therefore, as described above, the amount of the neopentyl type polyol ester added is 2 to 3 with respect to 100 parts by weight of the raw rubber.
Since it is 5 parts by weight, the blending amount of the petroleum softener may be a value obtained by subtracting 2 to 35 parts by weight from the combined amount (10 to 90 parts by weight), that is, 8 to 55 parts by weight. Therefore, the blending amount of the petroleum softener is 8 to 60 parts by weight,
It is preferably 8 to 55 parts by weight, preferably 8 to 50 parts by weight. If the combined amount is less than 10 parts by weight, the frictional resistance on ice cannot be sufficiently increased, and if it exceeds 90 parts by weight, the wear resistance is significantly deteriorated, which is not preferable.

In the rubber composition for a tire tread of the present invention, in addition to the above-mentioned compounding agents, compounding agents such as zinc oxide, stearic acid, an antioxidant, a vulcanization accelerator, and sulfur are arbitrarily mixed in appropriate amounts.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Examples 1 to 6 and Comparative Examples 1 to 4 A raw material rubber and various compounding agents were kneaded by a usual method in a composition (parts by weight) shown in Table 1 below to prepare a rubber composition. This rubber composition was press-vulcanized at 160 ° C. for 15 minutes to prepare samples for measuring volatilization amount (heat loss amount), abrasion amount (pico abrasion), and friction resistance.

The weight loss by heating was to leave the unvulcanized rubber for 2 hours and the vulcanized rubber for 24 hours in an oven at 150 ± 2 ° C for test pieces with a thickness of 2.5 ± 0.5 mm, a width and a length of 70 mm, and then remove them. It was cooled in a desiccator, the mass was measured, and the weight loss on heating was determined. The results are shown as an index with the weight loss on heating in Comparative Example 1 as 100. The smaller the value, the smaller the loss on heating and the better.

The wear test is expressed as an index with the wear amount of Comparative Example 1 obtained by measuring the wear loss (cc) using a Goodrich pico wear tester as 100, and the larger the index, the better.

Friction resistance on icy and wet road surfaces was measured with a British Portable Skid Tester (ASTM E303). The British portable skid tester is a tester developed for the purpose of evaluating the frictional characteristics of roads, and is a suitable tester for measuring the frictional resistance of tire tread materials on various road surfaces. In the measurement of the frictional resistance, an ice disk at −8 ° C. was used as the ice-bound road surface, and a flooded safety walk (manufactured by 3M, outdoor type B) was used as the wet road surface. The frictional resistance of the frozen road surface was measured on a blank sample immediately after vulcanization and a sample left in an oven at 70 ° C for 10 days. The frictional resistance of Comparative Example 1 is expressed as an index, and the frictional resistance of the frozen road surface is shown in Comparative Example 1
The value was expressed as an index with the friction resistance of the sample before being heat-treated as 100. The larger the frictional resistance index, the larger the frictional resistance, and the better.

In Table 1, Comparative Example 1 uses a paraffinic process oil having a small VGC (viscosity constant) as a softening agent, which is conventionally considered to be suitable for increasing the frictional resistance of the tread rubber material on the icy road surface. It is a rubber compound. As shown in Table 1, in Examples 1 to 6 in which the neopentyl type polyol ester was blended as the softening agent, the volatilization amount in the unvulcanized and vulcanized rubber was significantly reduced. When the neopentyl type polyol ester is used in combination with the petroleum-based softener, the higher the content of the neopentyl type polyol ester, the smaller the volatilization amount.

Further, in Examples 1 to 6 in which the neopentyl type polyol ester was blended, the frictional resistance on the frozen road surface was significantly improved. Since the volatilization of the softening agent due to simultaneous heating is small, there is an advantage that the physical properties after heat treatment, that is, the frictional resistance on the icy road surface also has little change, and high exercise performance during tire manufacturing can be exhibited for a long period of time. .

On the other hand, Comparative Example 2 containing an oleic acid derivative (eg: butyl oleate) and Comparative Example 3 containing a sebacic acid derivative (eg: dioctyl sebacate) also have improved friction resistance as compared with petroleum softeners. Since the volatilization of the softening agent due to heating is large, the frictional resistance after the heat treatment is reduced, and the initial high frictional resistance cannot be maintained. Further, in the oleic acid derivative and the sebacic acid derivative, the unvulcanized rubber has a large amount of heat loss, and the softening agent is volatilized during tire production, which deteriorates the working environment.

Although Table 1 does not show the case of using polyisoprene rubber, since polyisoprene rubber has a chemical structure similar to that of polybutadiene rubber and has a similar chemical structure, polybutadiene rubber shown in Table 1 is used. Similar results will be obtained by using polyisoprene rubber instead.

〔The invention's effect〕

As described above, according to the present invention, by using a neopentyl type polyol ester or a mixture of a neopentyl type polyol ester and a petroleum-based softening agent as a softening agent for a rubber composition for a tire tread, friction resistance on an icy road surface can be improved. It is possible to significantly improve and maintain the high exercise performance for a long period of time. At the same time, volatile components in the tire manufacturing process can be greatly reduced, and the working environment can be improved.

The rubber composition of the present invention having such an effect is not only suitable as a tread material for a winter tire running on an icy road surface, but also has the above-mentioned characteristics, so that it can be used for both general road surfaces and snow, and icy road surfaces. It can also be used as a tread material for all-season tires.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Umemura 904-76 East, Miyashiro-cho, Minami-Saitama-gun, Saitama Prefecture

Claims (2)

[Claims] 1. Carbon black 40 to 100 relative to 100 parts by weight of one or more rubbers selected from the group consisting of natural rubber, polyisoprene rubber, and polybutadiene rubber.
A rubber composition for a tire tread, characterized in that 2 to 35 parts by weight of a neopentyl type polyol ester represented by the following formula is blended. (In the formula, R is a hydrogen atom, a hydroxyl group, a methyl group or a general formula. (In the formula, R ′ represents a hydrocarbon group having 3 to 21 carbon atoms)
Which may be the same or different, but at least two of R are general formulas. Is a monocarboxylic acid residue. (n is a number from 0 to 2) 2. Carbon black 40 to 100 relative to 100 parts by weight of one or more rubbers selected from the group consisting of natural rubber, polyisoprene rubber, and polybutadiene rubber.
A rubber composition for a tire tread, characterized in that 2 to 35 parts by weight of a neopentyl type polyol ester represented by the following formula and 8 to 60 parts by weight of a petroleum-based softening agent are blended. (In the formula, R is a hydrogen atom, a hydroxyl group, a methyl group or a general formula. (In the formula, R ′ represents a hydrocarbon group having 3 to 21 carbon atoms)
Which may be the same or different, but at least two of R are general formulas. Is a monocarboxylic acid residue. (n is a number from 0 to 2)