JPH08283465A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE: To obtain a rubber composition capable of raising the abrasion resistance while retaining characteristics such as viscoelastic ones. CONSTITUTION: This composition is obtained by blending (i) SBR having <=-40 deg.C Tg , (ii) SBR and/or BR, incompatible with the SBR of the component (i) and having a lower Tg than that of the SBR of the component (i) by >=10 deg.C with a copolymer having (A) a block comprising (iii) SBR and/or IR, compatible with the SBR of the component (i) and incompatible with the SBR or BR of the component (ii) and (B) a block comprising SBR or BR, compatible with the SBR or BR of the component (ii) and incompatible with the SBR of the component (i) in an amount of 1-20 pts.wt. based on 100 pts.wt. sum total of the components (i), (ii) and (iii).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for a tire tread capable of improving abrasion resistance without changing viscoelastic properties.

[0002]

2. Description of the Related Art In recent years, improvements in various performances have been demanded for rubber compositions for tires of automobiles and the like. Therefore, it is necessary to blend a plurality of polymers in rubbers for tire treads or the like (for example, Blending SBR having a high glass transition temperature Tg and SBR or BR having a low Tg) to improve grip and low temperature embrittlement), but when these polymers are incompatible with each other, There is a phase separation interface. In many cases, this interface serves as a starting point of fracture and adversely affects tensile strength, tear strength, wear resistance, and the like. However, conventionally, in rubber products such as tires, rubber /
The problem of the phase-separated interface of the rubber blend has not been sufficiently investigated, and a solution to this problem has not been found.

Conventionally, a decrease in breaking strength based on the incompatibility of a diene rubber blend by blending a block polymer has not been sufficiently studied, and a natural rubber (NR) / polybutadiene rubber (BR) blend system is Polybutadiene (B
R) and polyisoprene (IR) in a small amount can be blended in accordance with J. Apply. Polym. S
ci. 49 (1993) and RCT. 66 (199
It is only described in 3). However, in these documents, only a block polymer having an isoprene copolymer block and a butadiene copolymer block in the NR / BR system is studied, and the SBR which is often used for tire treads. / SBR (or /
And BR) based incompatible blends, there is no unified study on the more industrially useful block polymers with SBR blocks.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention eliminates the above-mentioned problems of the prior art and improves the wear resistance while maintaining the tire characteristics such as viscoelastic characteristics. An object is to provide a rubber composition.

[0005]

According to the present invention, (i)
Styrene-butadiene copolymer rubber (SBR) having a glass transition point (Tg) of −40 ° C. or higher, and (ii) Tg is incompatible with the SBR of the component (i) and has a Tg higher than that of the SBR of the component (i). A styrene-butadiene copolymer (SBR) and / or polybutadiene rubber (BR) having a Tg lower than 10 ° C. is compatible with the SBR of the component (ii) and / or the BR of the component (ii) and the SBR of the component (i). Incompatible styrene-butadiene copolymer (SBR) or polyisoprene (I
Block A consisting of R) and SBR or B of component (ii)
Styrene which is compatible with R and incompatible with SBR of component (i)
Butadiene copolymer (SBR) or polybutadiene (B
A rubber composition for a tire tread, which comprises 1 to 20 parts by weight of a block copolymer having blocks A and B of block B consisting of R) per 100 parts by weight of the total amount of components (i), (ii) and (iii). Things are offered.

According to the present invention, (i) an SBR having a Tg of -40 ° C or higher, and (ii) an incompatible (ie, tan) SBR.
Tg is 1 when the temperature dispersion curve of δ becomes bimodal or the phase separation can be confirmed by observation with a transmission electron microscope.
In SBR or a blended rubber system of BR lower than 0 ° C., it is compatible with SBR of component (i) and SBR of component (ii)
And / or SBR or IR block A incompatible with BR
And SBR of component (ii) and / or block B of SBR compatible with SBR and incompatible with SBR of component (i) or BR
A specific block copolymer consisting of components (i), (ii)
By blending 1 to 20 parts by weight per 100 parts by weight of the total amount of (iii), the wear resistance can be improved without substantially changing the viscoelastic properties and the like.
The SBR of (i) or the SBR or BR of (ii) may be a mixture of two or more kinds of mutually compatible rubbers, in which case the Tg of (i) and (ii) is Tg as a mixture. Is.

The SBR compounded as the component (i) in the rubber composition according to the present invention has a Tg of -40 ° C. or higher, preferably −35 to 0 ° C., and any SBR conventionally used for various rubber applications. It can be SBR.

As described above, the SBR or BR compounded as the component (ii) in the rubber composition according to the present invention is incompatible with the rubber component comprising the SBR of the component (i) and has a Tg of the component (i). Any SBR and / or BR conventionally used as a rubber component in various rubber applications as long as it has a Tg lower than that of the SBR of 10) by 10 ° C or more.
Can be The blending ratio of component (i) / component (ii) can be selected according to the performance required for the rubber composition and the like. Those skilled in the art can appropriately make such selection, but preferably component (i) / component (i
The i) ratio can be a weight ratio of 90/10 to 10/90.

According to the present invention, the above object of the present invention can be achieved by blending a specific block copolymer with the above-mentioned blend system. If the content of this block copolymer is too large, the viscoelasticity of the block polymer itself will appear, so the rubber blend physical properties of components (i) and (ii) are the viscoelastic properties such as grip performance and fuel efficiency. It is not preferable because the characteristics and the like are lost. On the other hand, if the amount is too small, the desired improvement effect is reduced. From this viewpoint, the block copolymer used in the present invention has 1 to 20 parts by weight, preferably 3 parts by weight, of the block copolymer based on 100 parts by weight of all polymer components (including the block copolymer) as described above.
-18 parts by weight, more preferably 3-15 parts by weight.

As described above, the block copolymer used in the present invention is SBR which is compatible with the rubber component composed of SBR (i) and is incompatible with the rubber component composed of SBR or BR of component (ii). Block A of IR and block B of SBR or BR which is compatible with the rubber component of SBR or BR of component (ii) and incompatible with the rubber component of SBR of component (i)
It consists of and. Here, compatible and incompatible means that a 50/50 ratio blend of the copolymer constituting each block and the rubber component (i) or (ii) is prepared, and its tan δ temperature dispersion curve is measured. When the shape is bimodal, it is incompatible, and when it is monomodal, it is compatible. However, even if it is partially monomodal, it may be incompatible when viewed microscopically, so DSC
When two Tg's are observed by confirming the Tg's by the above, it is incompatible. Further, when the Tg of the polymer is close to the above-mentioned method and the judgment cannot be made by the above method, it is necessary to examine whether or not phase separation is observed by observation with a transmission electron microscope.

The block copolymer used in the present invention is a known polymer, and is generally a catalyst such as styrene and butadiene in an organic solvent such as hexane using an organic alkali metal compound catalyst such as butyllithium, or Block A can be produced by polymerizing isoprene to produce block A, and styrene and butadiene, or butadiene can be added to this block in the terminal living state. The desired block copolymer can be obtained by appropriately selecting the conditions and the like. The block polymers may be coupled with, for example, tin tetrachloride or silicon tetrachloride in order to suppress the tackiness, cold flow property and the like of the block polymer and to facilitate industrial handling.

Alternatively, the block A and the block B may be produced by a conventional method, and the block A and the block B may be produced by coupling them with a coupling agent such as tin tetrachloride or silicon tetrachloride. You can also The block copolymer may be, for example, a cyclic amine, a compound having a bond of -CN (= M) = (M represents an O atom or an S atom), such as an amide compound, an imide compound, a lactam compound, a urea compound. The end-modified block may be produced by adding an appropriate modifier in the living state after completion of the copolymerization of the block copolymer.

As described above, it is necessary that the components (i) and (ii) and the composition of each block A and B of the block copolymer to be added have a specific compatible or incompatible relationship. , A,
B need not have the same composition as components (i) and (ii), respectively. The composition of A and B is determined within a certain range if the components (i) and (ii) are determined. To determine this range,
As described above, for (i), (ii) and A and B, it is necessary to prepare a phase diagram by measuring Tg by tan δ temperature dispersion DSC, observing the phase separation structure by a transmission electron microscope, etc. is there. Therefore, it is important to determine the block polymer components A and B which are easily manufactured industrially and can be applied to other polymer blend components.

In the rubber composition of the present invention, carbon black 10 to 1 is added to 100 parts by weight of the rubber component, if necessary.
00 parts by weight, preferably 20 to 90 parts by weight and / or 10 to 100 parts by weight of silica, preferably 20 to 90 parts by weight can be added. As the carbon black and silica, any of those generally used in conventional rubber compositions can be used.

In the rubber composition of the present invention, in addition to the above-mentioned respective components, a crosslinking chemical containing sulfur, a vulcanization accelerator, etc., an antioxidant, a filler, a softening agent, a plasticizer, etc. Various additives that are generally blended with the rubber composition can be blended, and the blend can be vulcanized by a common method. The compounding amount of these additives may be a general amount. For example, the amount of sulfur blended is preferably 0.5 parts by weight or more, more preferably 0.8 to 3.0 parts by weight, per 100 parts by weight of the rubber component. Vulcanization conditions are also in the general range.

[0016]

The present invention will be further described below with reference to examples, but it goes without saying that the scope of the present invention is not limited to these examples. The physical properties in the following examples were measured by the following methods.

Wet skid resistance : Using a British portable skid tester at room temperature (23
° C). A safety walk made by Sumitomo 3M was used as the road surface, and the room temperature (23 ° C) water was sprayed on the road surface for measurement.

Tan δ: Using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho, static strain = 10%, dynamic strain = ± 2
%, Frequency = 20Hz (sample width 5mm, 60 ° C)

Embrittlement temperature: It was carried out based on the low temperature impact embrittlement test method defined in JIS K6301.

Abrasion resistance test: Measured using a Lambourn abrasion tester under the conditions of a slip ratio of 25% and a load of 5 kg. The results are shown by an index (wear resistance index) with the rubber of the standard example of Comparative Example 1 being 100, and the larger the number, the better the wear resistance.

Examples 1 to 3 and Comparative Examples 1 to 3 The ingredients (parts by weight) shown in Table I were blended, and a vulcanization accelerator, raw material rubber excluding sulfur, and a blending agent were added in 1.7 liters of bamba. After mixing for 5 minutes with a remixer, the mixture was mixed with a vulcanization accelerator and sulfur using an 8-inch test kneading roll machine.
Kneading was performed for a minute to obtain a rubber composition. These rubber compositions were press-vulcanized at 160 ° C. for 20 minutes to prepare target test pieces, various tests were conducted, and their physical properties were measured. The physical properties of the obtained vulcanizate are shown in Table I.

[0022]

[Table 1]

Examples 4 to 6 and Comparative Example 4 The ingredients (parts by weight) shown in Table II were blended, and the vulcanization accelerator, the raw rubber excluding sulfur and the blending agent were mixed in a 1.7 liter Banbury mixer. After mixing for 5 minutes, the mixture was mixed with vulcanization accelerator and sulfur using an 8-inch test mill roll machine.
Kneading was performed for a minute to obtain a rubber composition. These rubber compositions were press-vulcanized at 160 ° C. for 20 minutes to prepare target test pieces, various tests were conducted, and their physical properties were measured. The physical properties of the obtained vulcanizate are shown in Table II.

[0024]

[Table 2]

Examples 7 to 9 and Comparative Example 5 The ingredients (parts by weight) shown in Table III were blended, and the vulcanization accelerator, the raw rubber excluding sulfur and the blending agent were mixed in a 1.7 liter Banbury mixer. After mixing for 5 minutes, a vulcanization accelerator and sulfur were kneaded with this mixture for 4 minutes with an 8-inch test kneading roll machine to obtain a rubber composition. These rubber compositions were press-vulcanized at 160 ° C. for 20 minutes to prepare target test pieces, various tests were conducted, and their physical properties were measured. The physical properties of the obtained vulcanizate are as shown in Table III.

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

As described above, according to the present invention, wet skid resistance and low fuel consumption (tan)
It is possible to obtain a rubber composition excellent in abrasion resistance (the larger the abrasion resistance index of Tables I to III is), without lowering the low temperature embrittlement resistance and the lower δ (60 ° C.). it can.

Claims (2)

[Claims] 1. (i) Glass transition point (Tg) is -40 ° C.
The above styrene-butadiene copolymer rubber (SBR) and (ii) Styrene-butadiene which is incompatible with the SBR of the component (i) and has a Tg lower than the Tg of the SBR of the component (i) by 10 ° C. or more. Styrene-butadiene copolymer which is compatible with the SBR of the component (i) and is incompatible with the SBR of the component (ii) and / or BR in the copolymer (SBR) and / or the polybutadiene rubber (BR). (SBR) or polyisoprene (IR) block A and component (i
Block copolymer having blocks A and B of block B consisting of styrene-butadiene copolymer (SBR) or polybutadiene (BR) which is compatible with SBR of i) and is incompatible with SBR of component (i) The components (i) (ii)
And 1 to 20 parts by weight per 100 parts by weight of the total amount of (iii), a rubber composition for a tire tread. 2. The weight average molecular weight of the block copolymer having blocks A and B is 30,000 or more.
The rubber composition for a tire tread described in.