JPS58217527A - Vulcanizable and foamable rubber composition - Google Patents

Abstract

PURPOSE:A vulcanizable and foamable rubber composition which shows no heat shrinkage and provides foams excellent in processability and performances and suitable for soles, etc., prepared by mixing a crystalline diene rubber with a liquid diene rubber, a vulcanizing agent and a blowing agent. CONSTITUTION:A crystalline diene rubber (A) with m.p. of 50-110 deg.C (e.g., trans- 1,4-polyisoprene rubber or 1,2-polybutadiene rubber) is mixed with a liquid diene rubber (B) having below 35% vinyl bond and an MW of 6,000-100,000 (e.g., liquid polyisoprene rubber or liquid isoprene/butadiene copolymer rubber) in amounts such that the weight ratio of component A to component B can be within the range of about 97/3-40/60. Then, about 0.1-20pts.wt. vulcanizing agent (e.g., sulfur) and about 0.05-20pts.wt. blowing agent (e.g., sodium bicarbonate) per 100pts.wt. total of components A and B are added to obtain the purpose vulcanizable and foamable rubber composition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vulcanized foam rubber composition comprising a crystalline diene rubber, a liquid diene rubber, a vulcanizing agent, and a blowing agent.

Conventionally, in the rubber industry, particularly in the footwear industry, materials made by foaming rubber have been used for various purposes. By foaming rubber, it has become possible to add several new functions such as weight reduction and cushioning, and it is now being used to take advantage of these functions.

Conventionally, as raw materials (base materials) for such foams, rubbers such as natural rubber, styrene-butadiene copolymer rubber, and ethylene-vinyl acetate copolymer have been mainly used. However, the production of foams using these rubbers has the disadvantages that the processing is complicated and the resulting foams have poor weather resistance, and when ethylene-vinyl acetate copolymer is used, However, the foam has disadvantages such as insufficient elasticity and abrasion resistance.

On the other hand, it was found that by using 1,2-polybutadiene eutectic diene rubber as the raw material (base material) for foams, it was possible to obtain foams with excellent processability, and it became widely used. It's starting to look like this. However, even in such excellent foams, some drawbacks are recognized. The drawback is that the foam undergoes significant shrinkage due to heating after vulcanization molding. Due to large shrinkage, dimensional stability deteriorates, making it impossible to obtain products with high precision. For example, when used in footwear, large shrinkage when bonding the sole and upper portions of the foam results in deformation and distortion of the resulting footwear product, leading to a high incidence of defective products.

The inventors of the present invention have completed the present invention as a result of intensive research into solving the above-mentioned drawbacks in order to take advantage of the characteristics of foams made of crystalline diene rubber.

That is, according to the present invention, by mixing a crystalline diene rubber, a liquid diene rubber, a vulcanizing agent, and a blowing agent, it has excellent processability and excellent performance when formed into a foam.
In addition, a vulcanized foam rubber composition with little shrinkage due to heating can be obtained.

The crystalline diene rubber used in the present invention is a crystalline diene polymer such as butadiene, isoprene, pentadiene, octadiene, etc., and examples thereof include trans-1
, 4-polyisoprene, 3,4-polyisoprene, trans-1,4-polybutadiene, 1,2-polybutadiene, trans-1,4-polybentadiene, and 1,4-polyoctadiene. Among them, considering the workability and performance of the foam, Towonu 1
．． 4-polyisoprene and 1,2-polybutadiene are preferred.

The crystalline diene rubber mentioned above preferably has a melting point of 50 to 110°C. When the melting point is lower than 50°C, kneading workability is poor. If the temperature is higher than 110°C, the kneading operation must be carried out at a high temperature, which will cause problems such as scorch and poor foaming, and the fluidity during molding will be insufficient, which may affect the properties of the resulting foam. Lose. In addition, the melting point here is commonly referred to in the polymer chemical industry, and specifically means the value obtained by measurement using a differential calorimeter. Also, the degree of crystallinity is at least 5
It is preferable that the amount is at least 5%, preferably 5 to 50%.

The molecular weight of the crystalline diene rubber is 60.000 to 40.
0.000, particularly preferably in the range 100,000 to 300.000. If the molecular weight is too small, the viscosity of the composition will be too low, resulting in poor workability and poor moldability when unvulcanized. On the other hand, if the molecular weight is too large, the fluidity of the composition will deteriorate, resulting in a decrease in moldability and poor foaming of the foam, which is not preferable.

The liquid diene rubber used in the present invention is a low molecular weight polymer or copolymer of a diene compound such as butadiene, isoprene, 1,3-pentadiene, etc. Examples thereof include liquid polyisoprene rubber, liquid polyester rubber, etc. Butadiene rubber, liquid pentadiene com, liquid butadiene-isof0
Examples include ethylene copolymer rubber, liquid butadiene-pentadiene copolymer rubber, and liquid isoprene-pentadiene copolymer rubber. Among these, from the viewpoint of processability and physical properties of the foam,
Liquid rubbers containing at least 10 mol % of isoprene, such as liquid polyisofluorene rubber and liquid butadiene-isoprene copolymer rubber, are preferred. These liquid diene rubbers may be copolymerized with a small amount of a vinyl compound such as styrene or acrylic acid as long as the spirit of the present invention is not completely impaired. Furthermore, a compound having a functional group such as a canonboxyl group, an acid anhydride group, a hydroxyl group, an incyanate group, or an epoxy group may be added to the molecular chain or at the end thereof.

The above-mentioned liquid diene rubber has a vinyl bond content of 35% or less, but if it exceeds 35% gold, processability deteriorates and the performance of the final foam deteriorates. Preferably 2
More preferably, it is 0% or less. Note that the vinyl bond amount or Sinu 1.4 bond amount herein refers to all amounts measured by infrared absorption spectroscopy.

Further, the liquid diene rubber has a molecular weight of 6.000 to 6.000.
100,000. In particular, those having a molecular weight of 15,000 to 60,000 are used. If the molecular weight is too small, the physical properties of the foamed rubber composition after foaming and vulcanization will deteriorate; if the molecular weight is too large, the composition will have poor fluidity, and when formed into a foam, it will prevent shrinkage due to heating. I become unable to do so. In addition, the molecular weight here means the viscosity average molecular weight.

Such liquid diene rubber can be manufactured by various methods, but preferably by an anionic polymerization method. Among these, living polymerization using a lithium-based catalyst such as metallic lithium or organolithium such as methyllithium, propullithium, butyllithium, or distyrenyllithium produces a microstructure with easy control of molecular weight and a small amount of vinyl bonds. Therefore, since the copolymer can be easily produced, it is preferably employed. The polymerization solvent is preferably an inert hydrocarbon such as n-butane, impentane, n-hexane, n-hebutane, benzene, toluene or xylene because it is easy to control the polymerization. However, depending on the situation, there is no problem even if it is not used.

The mixing ratio of the crystalline diene rubber and the liquid diene rubber is preferably in the range of 9715 to 40/6 in weight ratio of crystalline diene rubber/liquid diene rubber. Especially considering workability, it is preferably in the range of 9515 to 5015o.

As the vulcanizing agent used in the present invention, those commonly used in the rubber industry, such as sulfur, peroxide, or quinone dioxime, are used.

Among them, sulfur is preferably used. The amount of the vulcanizing agent to be used is not particularly limited and is used within the range normally used in the rubber industry, but considering the performance of the foam obtained from the composition of the present invention, the amount of the vulcanizing agent The amount is 0.1 to 20 parts by weight, particularly 0.5 parts by weight, based on 100 parts by weight of the total amount of crystalline diene rubber and liquid diene rubber.
Preferably, the amount is in the range of 10 to 10 parts by weight.

The blowing agent used in the present invention may be any one commonly used in the rubber industry; typical examples include inorganic blowing agents such as sodium bicarbonate or ammonium carbonate; Examples include organic blowing agents such as bentamethylenetethumine, azodicarbonamide, and benzenesulfonyl hydrazide, and preparations containing these as main ingredients. In addition to these foaming agents, it is also possible to use foaming aids such as salicylic acid and urea compounds. The amount of the blowing agent to be used is not particularly limited and is determined depending on the expansion ratio of the desired vulcanized foam rubber composition. 0 per 100 parts by weight total
．． It is preferably used in an amount of 0.05 to 20 M parts, particularly 0.1 to 10 parts by weight.

The vulcanized foam rubber composition of the present invention is prepared by mixing a crystalline diene tetraprotic rubber, a liquid diene rubber, a vulcanizing agent, and a blowing agent using a suitable mixer. For mixing, natural rubber, cis-1,4-polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, etc. Solid rubber, thermoplastic polymers such as styrene-isoprene copolymer, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, etc. may be blended, and fillers used in ordinary rubber compounding,
There is no problem in adding rubber compounding bacteria such as activators, tackifying resins, zinc white, stearic acid, anti-aging agents, and vulcanization accelerators.

The vulcanized foam rubber composition of the present invention is made into a foam by vulcanization accompanied by foaming (for example, fullless vulcanization). The foam thus obtained is suitable for use in footwear such as shoe soles, as well as in cushioning materials, vibration-proofing materials, sound-absorbing materials, heat-insulating materials, backing materials, sealing materials, buoyancy materials, and the like.

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 and Comparative Example 1 Liquid polyisoprene rubber with a molecular weight of 47.000 and a vinyl bond content of 12% and trans-1°4-polyisoprene (rubber) with a melting point of 60°C were used according to the formulation shown in Table 1. Kneading was carried out using a Sibanbury mixer. Incidentally, among the compounding ingredients, the vulcanization accelerator, foaming agent, foaming aid, and rubber component were kneaded in a Banbury mixer, and then added using an open roll.

The thus obtained (vulcanized and foamed) rubber composition was
Press vulcanization was performed at 0°C for 20 minutes to obtain a vulcanized foam.

The obtained vulcanized foam has a length of 10, a width of 5, and a thickness of 1.
A test piece of ty* was cut out, heated at 70°C for 2 hours, and the shrinkage rate ((length in the longitudinal direction after heating) x 100 /(Length in longitudinal direction before heating)) was determined.

For comparison, a foam was obtained from a composition prepared without containing liquid polyisogrene rubber in the same manner as above. When the shrinkage rate of the obtained foam was determined in the same manner as the above method, the results shown in Table 1 were obtained.

Table 1) Dibenzothiadyldisa A/7 ide 2) Tetofmethylthiufumisotylphide 5) Azodicarbonamide mixture (Vinihole AK#2: Hydration chemical ■) 4) Diethylene glycol 5) 2. 6-di-t-buty/l/-4-methylphenol As shown in Table 1, the vulcanized foam of Example 1 was composed of liquid polyisoprene rubber, trans-1,4-polyisoprene rubber, sulfur, and a blowing agent. The foam obtained from the rubber composition has significantly smaller shrinkage after heating than the foam according to Comparative Example 1 which does not contain liquid polyiso7°lene rubber from the above formulation.

Example 2 and Comparative Example 2 Molecular weight 29. Using ODD, liquid polyisoprene rubber with a vinyl bond content of 14%, and 1,2-polybutadiene with a melting point of 80°C, a vulcanized foam rubber composition was prepared in the same manner as in Example 1 according to the formulation shown in Table 2. Obtained. The composition was press-cured at 150°C for 15 minutes to obtain a foam. Example 1
The shrinkage rate of the foam due to heating was determined in the same manner as above, and the results shown in Table 2 were obtained.

On the other hand, for comparison, a composition was prepared in which the above formulation did not contain liquid polyisogrene rubber.

A foam was obtained in the same manner. Table 2 shows the shrinkage rate of the foam upon heating.

The following margin @2 Table 1) Azodicarbonamide mixture (Vinihole AK#2: Hydration Chemical ■) 2) Diethylene glycol 3) 2.6-di-t-butyl-4-methylphenol As shown in Table 2 Compared to the foam of Comparative Example 2, the foam of Example 2 has a significantly smaller shrinkage rate upon heating.

Patent applicant Rira Shi Co., Ltd. Agent Patent attorney civil engineering ratio Ken

Claims (5)

[Claims] (1) A vulcanized foam rubber composition comprising a crystalline diene rubber, a liquid diene rubber, a vulcanizing agent, and a blowing agent. (2) The vulcanized foam rubber composition according to claim (1), wherein the crystalline diene rubber is a polymer having a melting point of 50 to 110°C. (3) M quality diene rubber is trans-1/4-
The vulcanized foam rubber composition according to claim 1, which is polyisoprene rubber or 1,2-polybutadiene rubber. (4) The vulcanized foam rubber composition according to claim (1), wherein the liquid diene rubber is a polymer having 35% or less of vinyl bonds and a molecular weight of 6,000 to 100,000. . (5) The vulcanized foam rubber composition according to claim (1), wherein the liquid diene rubber is liquid polyisoprene rubber or liquid isogrene-butadiene copolymer rubber.