JPH026778B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a butadiene-isoprene copolymer composition. More specifically, butadiene, whose glass transition temperature is above a certain temperature,
The present invention relates to a composition containing an isoprene copolymer as a rubber component. Conventionally, many types of polymers have been known as polymers of conjugated diene compounds, and in particular, isoprene polymers and butadiene polymers synthesized using so-called Ziegler catalysts, and polymers synthesized using organolithium catalysts. Butadiene polymers and the like are used as synthetic rubbers for various purposes. These polymers are characterized by their microbonding mode and are generally known to be polymers with high cis content or high cis and trans content. Compositions containing these polymers as rubber components are characterized by low dynamic heat generation, especially when used in automobile tires, but have poor braking properties, which is another important performance of tires. In particular, it is significantly lacking in wet skid resistance, which means braking performance on wet road surfaces. In order to compensate for this, a method has been adopted that uses a rubber composition containing, for example, styrene-butadiene copolymer rubber (SBR) in an appropriate ratio. However, according to this method, although the wet skid resistance performance is improved, the dynamic heat generation property increases and the rolling resistance value of the tire increases. Even after investigating various rubbers, there has been no rubber available that has wet skid resistance performance comparable to that of styrene-butadiene copolymer rubber, yet exhibits a dynamic heat build-up as low as that of high-cis polybutadiene rubber. The current situation in the industry is that the two are unavoidably blended in appropriate ratios and used in rubber compositions that are unsatisfactory in both of these properties. In recent years, due to the development of expressway networks and the soaring price of gasoline, greater emphasis has been placed on driving safety and fuel efficiency of automobiles than ever before, and the road surface grip and low rolling resistance of tires are becoming more important than ever. increasingly demanded. The characteristics of these tires vary depending on the structure of the tire and the characteristics of the raw material, but in particular dynamic characteristics such as road grip and energy loss due to dynamic heat generation are greatly influenced by the characteristics of the raw rubber composition. . For these reasons, there is a strong demand for rubber compositions that have high wet skid resistance and low dynamic heat build-up. In view of this technical background, the inventors of the present invention have conducted extensive studies with the aim of developing a rubber composition that improves both wet skid resistance performance and dynamic heat generation property, and as a result, they have discovered that glass The fact that a rubber composition whose rubber component is a butadiene-isoprene copolymer whose transition temperature is above a certain value and whose average molecular weight exhibits a Mooney viscosity within a certain range satisfies these objectives is demonstrated. This discovery led to the present invention. The butadiene-isoprene copolymer composition of the present invention contains 30 to 70 parts of butadiene per 100 parts by weight of rubber.
A copolymer composition obtained by copolymerizing parts by weight of isoprene and 70 to 30 parts by weight of isoprene, the glass transition temperature of the copolymer being -50°C or higher, and the copolymer composition measured at 121°C. Mooney viscosity of coalescence is 20 to 120
This is a butadiene/isoprene copolymer composition characterized by having a trans bond content of 20 to 29% in the butadiene moiety. Furthermore, the composition of the present invention refers to such butadiene.
A rubber composition obtained by blending ordinary rubber additives such as carbon black, sulfur, a vulcanization accelerator, and an anti-aging agent with an isoprene polymer, and an amount of extender oil that does not impair the purpose of the present invention. This also includes those that contain. The butadiene-isoprene polymer composition of the present invention will be explained in more detail below. Generally, the glass transition temperature of a polymer obtained by polymerizing a conjugated diene compound is influenced by the content of microbonds. For example, the glass transition temperature of currently commercially available high-cis polyisoprene is around -75°C, and
That of high cis polybutadiene is around -108°C. On the other hand, as the content of 1,2 bonds or 3,4 bonds in the isoprene polymer or butadiene polymer increases, the glass transition temperature increases. The glass transition temperature of the butadiene-isoprene copolymer, which is the rubber component of the composition of the present invention, is -50°C or higher, and such a copolymer has a content of 1,2 bonds and/or 3,4 bonds. obtained through control. To control these microstructures, it is effective to employ a known polymerization method called living anionic polymerization method. i.e. hexane, heptane, cyclohexane,
Using an alkali metal such as sodium or potassium or an organometallic compound thereof as an initiator in a nonpolar hydrocarbon solvent such as benzene, or using lithium metal or an organometallic compound thereof and a Lewis base such as an ether or a tertiary amine. This is a method of copolymerizing butadiene and isoprene using an initiator system in combination with a chemical compound. In particular, it is preferable to use an initiator system consisting of a combination of lithium metal or an organolithium compound and a Lewis basic compound from the viewpoint of stability of the polymerization reaction. In this case, as the ratio of Lewis basic compound to lithium metal or organolithium compound increases, 1,
The content of 2 bonds and 3,4 bonds increases, and the glass transition temperature of the copolymer increases. Although the bonding ratio between butadiene and isoprene can be arbitrarily selected, the higher the ratio of isoprene, the higher the polymerization reaction rate and the higher the glass transition temperature of the resulting copolymer tends to be. When copolymerizing butadiene and isoprene using such a polymerization initiator system, if both monomers are simultaneously added to the polymerization system, butadiene will be preferentially polymerized first due to the difference in copolymerization reactivity ratio, and the remaining monomers will be polymerized first. It is known that a so-called tapered copolymer is formed in which the bond composition of isoprene gradually increases as the concentration ratio changes, and in order to prevent this, butadiene is divided or the polymerization system is continuously It is also known that non-tapered copolymers can be obtained by adding monomers to is also possible, and the obtained copolymer can be used as the rubber component of the composition of the present invention.The polymerization reaction temperature for obtaining such a copolymer ranges from the same temperature range as that of a normal solution polymerization system. However, in this case, it is necessary to pay attention to the relationship between the polymerization temperature and the microbond content of the resulting copolymer. In other words, when using a catalyst system that combines a Lewis basic compound and a lithium-based initiator, if the ratio of these additions is the same, 1,2 bonds and 3,4 bonds will increase as the polymerization temperature increases. The content of bonds tends to decrease. Therefore, in order to obtain a butadiene-isoprene polymer having the desired glass transition temperature, it is necessary to consider both the addition ratio of these catalyst systems and the polymerization temperature, and then add the monomers of butadiene and isoprene. It is preferable to select it by considering the amount ratio. As in the present invention, in a rubber composition containing a butadiene-isoprene copolymer having a glass transition temperature of -50°C or higher as a rubber component, the dynamic heat generation property is as low as that of a high-cis polybutadiene rubber composition, and the wet skid It exhibits excellent resistance performance, with resistance performance comparable to or higher than that of styrene-butadiene copolymer (SBR). On the other hand, compositions of butadiene-isoprene copolymers with glass transition temperatures lower than -50 DEG C. have low wet skid resistance and are unsuitable for use as compositions for the purpose of the present invention. Furthermore, the molecular weight of the butadiene-isoprene copolymer used as the rubber component of the composition of the present invention is 121
Mooney viscosity measured at °C between 20 and
It's like falling in the 120 range. If the Mooney viscosity of the copolymer is less than 20, the dynamic exothermic property will increase;
If it exceeds 120, it may be difficult to feed the additive to the processing machine when producing the composition, or the mixing condition may deteriorate, making it difficult to obtain the composition desired by the present invention. I can't. The composition of the present invention comprises a butadiene-isoprene polymer having the glass transition temperature and Mooney viscosity as described above, carbon black, process oil, sulfur,
It is obtained by mixing it with ordinary rubber additives such as vulcanization accelerators and anti-aging agents in ordinary rubber kneading processing machines. Further, the rubber composition of the present invention can be made into a vulcanizate using a conventional vulcanization device. The content of the present invention will be explained below with reference to Examples, but the present invention is not limited thereto in any way. Examples 1 to 4 100 parts of butadiene-isoprene copolymer with a glass transition temperature of -50°C or higher, 60 parts of carbon black, 20 parts of aroma oil, 5 parts of zinc white, 2 parts of stearic acid, 2 parts of vulcanization accelerator and 1.6 parts of sulfur were mixed using an 8-inch mixing roll to obtain a composition. These compositions were press-vulcanized at 150°C using a 150-ton steam press, and the following physical property values were measured for test pieces obtained. In addition,
Butadiene-isoprene copolymers having different glass transition temperatures were synthesized by polymerizing isoprene in an n-hexane solvent using a catalyst system with varying ratios of n-butyllithium and tetrahydrofuran. (Table 1) Mooney Viscosity For unblended raw rubber, the torque value was read at 4 minutes after preheating for 1 minute using a Mooney viscometer set at 121°C. (ML1+4,121°C) Glass transition temperature Measured using a DuPont differential scanning calorimeter (D, S, C) from -100°C to +20°C at a heating rate of 20°C/min. The transition temperature was determined from the position of the transition endothermic peak. Microbond Content and Copolymer Composition The infrared absorption spectrum of the polymer was measured by the rock salt plate method using a spectrophotometer manufactured by Hitachi, Ltd. The ratio of bond amounts and the micro bond content in the butadiene and isoprene copolymer were calculated according to the method of Coffman et al. [VLKofman et al.
Polymer Sci.USSR, (Coffman et al., Polymer Science USSR) 21 (7),
1676 (1979)] Wet skid resistance performance A 6.5 mm thick sheet obtained by press vulcanization of the composition was measured using a portable skid resistance tester manufactured by Stanley. An asphalt surface sprayed with water at a temperature of 20°C was selected as the contact road surface. Dynamic exothermic property Measured on the above vulcanizate using an automatic Gutsudritsu flexometer under the following conditions: static load 20 lb, frequency 1800 cpm, temperature 75°C, stroke 02''.
The degree of temperature rise after 14 minutes was recorded. These measured values are shown in Table 2. The composition of the present invention has excellent properties such as high skid resistance and low dynamic heat build-up. Comparative Examples 1 to 3 Compositions similar to those in Examples were prepared using butadiene-isoprene copolymers having a glass transition temperature lower than -50°C, and the physical properties of the vulcanized products were measured in the same manner. The results are shown in Table 2. It is clear that compositions of copolymers with low glass transition temperatures have poor skid resistance performance. Examples 5 and 6 An example of a composition containing as a rubber component a butadiene-isoprene copolymer having a glass transition temperature of about -40°C and a Mooney viscosity of 20 to 120, synthesized using the same formulation as in Examples 1 to 4. The same study as in 1 to 4 was conducted. The results are shown in Table 3. These compositions are the compositions of the present invention and have the advantageous characteristics of high wet skid resistance performance and low dynamic exotherm. Comparative Example 4 Unlike the composition of the present invention, the Mooney viscosity was 18
The same studies as in Examples 1 to 4 were carried out on the butadiene-isoprene copolymer composition. The results are shown in Table 3. This composition has a high dynamic exothermic property and is unsuitable as a composition for the purpose of the present invention. Comparative Examples 5, 6 Commercially available styrene butadiene rubber (SBR#1500)
Similar studies were conducted on compositions containing cis-1,4-polybutadiene rubber and high-cis polyisoprene compositions. The results are shown in Table 3. These compositions either have high dynamic exothermic properties or low wet skid resistance, and are unsuitable as compositions for the purpose of the present invention. As shown in the examples above, the butadiene-isoprene copolymer composition of the present invention has improved characteristics in both wet skid resistance and dynamic heat generation properties.

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Claims (1)

[Claims] 1 A copolymer composition obtained by copolymerizing 30 to 70 parts by weight of butadiene and 70 to 30 parts by weight of isoprene per 100 parts by weight of rubber, the copolymer having a glass transition temperature of -50°C or higher. and the Mooney viscosity of the copolymer measured at 121°C is
In the range of 20 to 120, the trans bond content of the butadiene moiety is 20 to 29%, and the 1 and 2 bond content is 45
% or more, and the sum of the 1,2 bond content and the 3,4 bond content of the isoprene moiety is 36% or more.