JPS6223786B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a rubber vulcanizate having excellent processability, thermal stability and elasticity. More specifically, the present invention relates to a method for producing a rubber vulcanizate using a low molecular weight isoprene-butadiene block copolymer rubber as a rubber component. In recent years, various types of sealants have been actually used in various fields such as architecture, civil engineering, and the automobile industry. Sealants have various performance requirements depending on their intended use, but the basic performance is that they can be applied to the required areas using a caulking gun or spatula at room temperature or a temperature close to it, and after installation, It is required to have a sealing function. For this purpose, it is most preferable to use a low-molecular-weight polymer that is liquid or has sufficient fluidity at room temperature and can have appropriate strength through curing reactions such as vulcanization. In addition, sealants generally require the function of absorbing vibrations and strains between adhered materials, and they also need to have rubber elasticity.For this purpose, diene-based polymers are required to be vulcanized. The sealing material thus obtained exhibits excellent elasticity, and this elasticity hardly changes over a wide temperature range from low temperatures to relatively high temperatures, making it the most suitable sealing material. However, among sealants, automobiles,
Seam seals in aircraft, ships, etc., seals in tank manufacturing, etc. are often subjected to harsh thermal conditions, such as being exposed to quite high temperatures after applying the sealant due to baking paint. The heat resistance of a material essentially depends on the heat resistance of the base polymer, so it is necessary to use a polymer with excellent heat resistance, but conventional diene rubbers with excellent elasticity etc. are not heat resistant. It had insufficient properties and deteriorated due to softening or hardening due to heat, and lost its rubber elasticity. That is, polyisoprene, polybutadiene, or their vulcanized products soften or harden and deteriorate when heated, and their mixtures or their vulcanizates soften or harden and deteriorate depending on the mixing ratio, resulting in superior performance. It could not demonstrate thermal stability. In view of the above-mentioned problems, the present inventors have made extensive studies to obtain an excellent diene rubber vulcanizate, and have found that by using a specific isoprene-butadiene block copolymer, it has excellent processability and heat resistance. It was discovered that a rubber vulcanizate with excellent stability and elasticity can be obtained, and the present invention was completed. That is, in the present invention, when the isoprene-butadiene block copolymer rubber is mixed with a vulcanizing agent and optionally other additives and vulcanized, the isoprene-butadiene block copolymer rubber has a viscosity average molecular weight of 7,000 to 70,000. Yes, the weight composition ratio of (isoprene/butadiene) in the copolymer rubber is
25/75 to 85/15, and has the general formula (B-I) _o B or (B-I) _o+1 (wherein B is a polybutadiene block, I is a polyisoprene block, and n is 1 to 10 The present invention relates to a method for producing a rubber vulcanizate characterized by using an isoprene-butadiene block copolymer rubber having a structure represented by (representing an integer of ). The viscosity average molecular weight (hereinafter simply referred to as molecular weight) of the isoprene-butadiene block copolymer rubber used in the present invention must be in the range of 7,000 to 70,000. The molecular weight (Mv) is measured at 30℃ in toluene.
The formula [η] is determined by the intrinsic viscosity ([η]) measured at
= 1.21×10 ^-4 Mv ^0.77 is defined as ^the value calculated. If the molecular weight is lower than the above range, the physical properties of the vulcanizate, such as mechanical strength, will be insufficient and it will not be versatile, and the vulcanizate mixed with other elastomers will show oozing. On the other hand, if the viscosity is high, the viscosity will be quite high and the workability and processability will be significantly reduced, which is unsuitable. Furthermore, the weight composition ratio of isoprene/butadiene in the isoprene-butadiene block copolymer rubber used in the present invention must be in the range of 25/75 to 85/15, more preferably 35/65 to 75/25. . If the amount of isoprene is greater than the above range, the resulting copolymer rubber will undergo softening deterioration due to heating, while if the amount of butadiene is large, conversely, curing deterioration will be significant, and in either case, thermal stability will be poor. Further, the isoprene-butadiene block copolymer rubber used in the present invention must have the structure (B-I) _o B or (B-I) _o+1 .
Note that B is a polybutadiene block, I is a polyisoprene block, and n is 1 to 10, preferably 1 to 4.
is an integer. Surprisingly, block copolymer rubber with such a structure maintains a well-balanced structure without exhibiting the preferential characteristics of that component, even when one component occupies a much larger amount than the other. Shows excellent thermal stability.
On the other hand, in block copolymer rubbers having a structure of B-I or I-B-I, similar to a mixture of polyisoprene rubber and polyisoprene rubber, the quantitatively preferential properties of the components are dominant, resulting in softening or hardening. Indicates significant deterioration of any of the following. On the other hand, if n exceeds 10, the molecular weight per block of B or I will be too small, making it impossible to exhibit balanced thermal stability. From this point of view, n is a number that can take a value such that the degree of polymerization of the polymer per block is at least about 20 or more, preferably 4 or less. Further, at this time, it is preferable that the viscosity average molecular weight of the polymer of each block is at most 70,000 or less. Such isoprene-butadiene block copolymer rubber can be easily obtained by a living polymerization method using an anionic initiator, and by this method, the molecular weight and the isoprene/butadiene weight ratio can be easily controlled. As the anionic initiator, it is preferable to use a lithium-based catalyst which has better thermal stability and can generate more organic 1,4 bonds, particularly cis-1,4 bonds, in rubber elasticity. Examples of lithium-based catalysts include metallic lithium,
Alkyl lithium such as propyl lithium and butyl lithium, cycloalkyl lithium such as cyclohexyl lithium and cyclopentyl lithium, aryl lithium such as phenyl lithium, organomonolithium such as aralkyl lithium such as phenyl methyl lithium and phenyl cyclohexyl lithium, naphthalene Examples include organodilithium such as dilithium and tetraphenyldilithium. Although polymerization is carried out in the presence or absence of a polymerization solvent, it is generally more preferable to use a solvent in order to remove polymerization heat, homogenize the polymerization system, and the like.
As the solvent that can be used, inert hydrocarbons that do not act as chain transfer agents are used, and butane, pentane, hexane, cyclohexane, cyclooctane, benzene, etc. are preferably used. As an example of a polymerization method using organomonolithium as a catalyst, a predetermined amount of butadiene monomer is added to a reactor containing a catalyst, and the butadiene monomer is completely polymerized and the resulting polymer still has polymerization activity. Add a predetermined amount of isoprene monomer to the B-I-B, B-I-B-
A method for producing a block copolymer having the structure I,...(B-I) _o B, (B-I) _o+1. After obtaining the polymer B-I, for example, dibromide is added in an active state. Examples include a method of producing a B-I-B copolymer by coupling with a coupling agent such as benzene. When organodilithium is used, a method may be employed in which isoprene is first polymerized, and then butadiene is added and polymerized to obtain a B-I-B copolymer. The polymerization temperature is not particularly specified, but if the polymerization temperature is too low, the reaction rate will be extremely slow, and if it is too high, undesirable side effects such as decomposition of the catalyst or coloring of the copolymer produced may occur. There is a risk of a reaction occurring, so generally 20 to 70℃
It is preferable to polymerize with The isoprene-butadiene block copolymer rubber produced using a lithium catalyst in this manner contains at least 75% of 1,4 bonds in both the polyisoprene block and the polybutadiene block, and has a high degree of unsaturation in the molecular chain. vulcanization with sulfur or peroxide. It should be noted that the block copolymer rubber used in the present invention may have a functional group such as a hydroxyl group or a carboxyl group added to the end or in the molecule thereof without any problem. The vulcanizate obtained in the present invention contains the above-mentioned specific isoprene-butadiene block copolymer rubber, a vulcanizing agent or accelerator such as sulfur or peroxide, a filler such as carbon black, calcium carbonate, or clay, and zinc. It is obtained by blending activators such as hydrangea, stearic acid, and chemicals such as anti-aging agents and heating the mixture. The vulcanizate obtained in the present invention is obtained by preparing a mixture of isoprene-butadiene block copolymer rubber and a vulcanizing agent, filling the area to be sealed, and heating the mixture. Examples of such uses include sealing materials that require heat resistance due to their excellent thermal stability. Natural rubber, synthetic cis-
1,4-polyisoprene, polybutadiene, styrene-butadiene copolymer, chloroprene rubber,
Solid synthetic rubber such as acrylonitrile-butadiene copolymer is mixed with isoprene-butadiene block copolymer rubber along with a rubber vulcanizing agent and rubber compounding chemicals using a kneading machine such as a Banbury mixer or kneader, followed by a press vulcanizer. , obtained by vulcanization molding in a hot air vulcanizer or steam vulcanizer. Examples of such uses include tires, belts, etc. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 Dehydrated cyclohexane was placed in the reactor of 3.
Add 500CC and add sec-butyllithium to it.
Add 10 mmo and heat to 40℃. Next, 70 g of a sufficiently dehydrated butadiene monomer was gradually added to this system and polymerized. After all 70g of monomer has been added, hold the temperature at 40°C for another 30 minutes to complete polymerization, sample the gas phase in the reactor, and confirm that no butadiene monomer remains by gas chromatography analysis. 170 g of dehydrated isoprene monomer was gradually added and polymerized. After all isoprene monomer has been added, heat for an additional 30 minutes to complete polymerization.
After confirming that no isoprene monomer remained, 70 g of butadiene monomer was added again. After all of the butadiene monomer had been polymerized, the reaction mixture was cooled and poured into a large amount of methanol to recover the polymer. The yield of the polymer was 99.8%, which confirms that the added butadiene and isoprene monomers were all polymerized in the form of B-I-B. The molecular weight of the polymer was 40,500. A compound of the isoprene-butadiene block copolymer rubber thus obtained was prepared according to the formulation shown in Table 1. Approximately 5 g of this compound was taken and placed in a hemispherical shape on an iron plate with a spatula at 150°C for 20 minutes. Vulcanization was achieved by heating for minutes. After vulcanization, further 30 at 175℃
The mixture was heated for 1 minute to evaluate thermal stability. As is clear from the results shown in Table 1, it exhibits excellent thermal stability. Example 2 B was prepared in the same manner as in Example 1, except that dehydrated n-hexane was used as the solvent, 7 mmo of n-butyllithium was used as the catalyst, and the monomers were added in the order of 45 g of butadiene, 105 g of isoprene, 45 g of butadiene, and 105 g of isoprene. A block copolymer having the structure -I-B-I was obtained. The yield was 99.7%, confirming that it had the structure B-I-B-I. The molecular weight was 62,300. The thermal stability of the vulcanizate of this isoprene-butadiene block copolymer rubber was evaluated in the same manner as in Example 1. The thermal stability of this vulcanizate was excellent. Example 3 10 mmol of naphthalene dilithium obtained by shaking a lithium dispersion and naphthalene in tetrahydrofuran at room temperature for 48 hours, removing unreacted materials, and distilling off tetrahydrofuran
Disperse it in dehydrated benzene in a reactor and heat it to 50℃. Add 100g of isoprene monomer to this system and polymerize, and then add 100g of butadiene monomer.
was added and polymerized. Completion of polymerization was confirmed by gas chromatography analysis in the same manner as in Example 1. The yield of the polymer was 99.8%, and it had a structure of B-I-B,
Its molecular weight was 27,500. This block copolymer rubber was made into a vulcanizate in the same manner as in Example 1, and the thermal stability of the vulcanizate was evaluated. As can be seen from Table 1, this vulcanizate has excellent thermal stability. Example 4 Using dehydrated hexane as a solvent, as a catalyst
Using 16 mmo of sec-butyllithium, add monomers 180 g of butadiene and 120 g of isoprene in order to polymerize a block copolymer called B-I,
Dehydrated dibromobenzene is added to this system without stopping the polymerization to cause a coupling reaction,
The yield of a B-I-B block copolymer was 99.6%, and the molecular weight was 49,800. A vulcanizate of this block copolymer was obtained in the same manner as in Example 1. When the thermal stability of the vulcanizate was evaluated, it showed excellent thermal stability. Comparative Example 1 Polyisoprene (homopolymer) with a molecular weight of 62,000 and 80% of cis-1,4 bonds and a molecular weight of
59500 polybutadiene (homopolymer) was obtained. Using the polyisoprene and polybutadiene, a compound was prepared according to the formulation shown in Table 1, and a vulcanizate thereof was prepared in the same manner as in Example 1. When examining the thermal stability of these vulcanizates, it was found that when polyisoprene was used, the vulcanizates became soft and sticky, while when polybutadiene was used, they hardened and fell apart, resulting in poor thermal stability.

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Claims (1)

[Claims] 1. When vulcanizing the isoprene-butadiene block copolymer rubber by mixing it with a vulcanizing agent and optionally other various additives, the isoprene-butadiene block copolymer rubber has a viscosity average molecular weight of 7,000 to 70,000; The weight composition ratio of (isoprene/butadiene) in the copolymer rubber is 25/75 to 8
5/15, and general formula (B-I) _o B or (B
-I) _o+1 (where B is a polybutadiene block, I is a polyisoprene block, and n is an integer from 1 to 10). Characteristic method for producing rubber vulcanizate.