JPH0474375B2 - - Google Patents

Description

[Detailed description of the invention]

"Field of Industrial Application" The present invention relates to a crosslinked foam composition of ethylene-vinyl acetate copolymer using an organic peroxide and a blowing agent, which has low specific gravity (high foaming), high hardness,
Ethylene with high tear strength, impact resistance, and elasticity
It is possible to produce crosslinked vinyl acetate copolymer foams in a short time. ``Prior art'' Ethylene is used as a crosslinked foam with rubber elasticity.
Crosslinked foams using vinyl acetate copolymer (EVA), natural rubber, synthetic rubber, etc. are known. Among these, crosslinked foams using natural rubber and synthetic rubber have difficulty achieving a high expansion ratio, and also suffer from large shrinkage after crosslinking, resulting in poor dimensional accuracy. Furthermore, it has the disadvantage of poor mold flowability. On the other hand, EVA cross-linked foams using EVA are generally known to be able to obtain foams with a high expansion ratio without shrinkage problems with only one step of cross-linking, such as the midsole, outer sole, and inner sole of sports shoe It is widely used in applications that require weight reduction. However, in order to reduce the weight of EVA cross-linked foam,
Although it is essential to increase the expansion ratio to 3 times or more, the hardness, tear strength, and tensile strength of the resulting foam decrease, resulting in deformation, tearing, cracking, etc. of the molded product.
In addition, in order to reduce the weight, a large amount of blowing agent is used, and the crosslinking time becomes long, which causes problems in productivity. However, in recent years, there has been an increasing trend toward weight reduction, and there has been a growing demand for a high expansion ratio of 5 times or more, making it even more desirable to solve the above problem. The hardness, tear strength, and impact resistance of the foam are particularly important properties for the sole material of sports shoes, along with the adhesive strength, and if a foam with low hardness and impact resistance is used as the sole material, it may sag during use. Foams with low tear strength can cause abnormal phenomena such as deformation (deformation), and breakage phenomena such as cracking during production and actual use (running), which poses a major problem in use and reduces commercial value. In addition, in pursuit of high foaming and high functionality, the conventional manufacturing method for EVA crosslinked foam requires a large amount of crosslinking agent and foaming agent, and takes a long time for crosslinking, resulting in a high product cost. "Problems to be Solved by the Invention" The inventors have conducted various studies to solve the above problems, and as a result, by adding a specific amount of 1,2-polybutadiene (hereinafter abbreviated as 1,2PBD) to EVA, With only one stage of cross-linking, it is highly elastic and extremely lightweight (specific gravity
We have discovered a composition that can produce a highly productive EVA-based crosslinked foam that can be obtained in a short time with a small amount of crosslinking agent, and has excellent hardness, impact resistance, and tear strength (0.2 or less). Based on this knowledge, we were able to complete this invention. "Means for Solving the Problems" That is, the present invention consists of (A) an ethylene-vinyl acetate copolymer of 98 to 60% by weight, and (B) a vinyl bond content of 70%.
1,2 with a crystallinity of 5% or more and an intrinsic viscosity [η] (measured at 30℃ in toluene) of 0.5dl/g or more.
- 100 parts by weight of a mixture consisting of 2 to 30% by weight of polybutadiene and (C) 0 to 30% by weight of natural rubber or diene-based synthetic rubber, (D) 0.05 to 5 parts by weight of organic peroxide, and (E) 0.5 to 0.5 parts by weight of a blowing agent. 30 parts by weight of an ethylene-vinyl acetate copolymer composition for a crosslinked foam. The present invention will be explained in more detail below. The EVA (A) used in the present invention has high foaming, high hardness,
To obtain a crosslinked foam with high tear strength, impact resistance, and elasticity, the vinyl acetate bond content should be 5 to 45%, preferably 10 to 30%, and the melt flow index (190
℃, 2160g) 0.2~50g/10min preferably 0.5~
20g/10min is preferable. It should be noted that if the vinyl acetate bond content is less than 5%, the flexibility and tear resistance of the sponge will be impaired, and the crosslinking agent will be consumed to a large extent, resulting in an increase in cost, which is not preferable. If the vinyl acetate bond content is 46% or more, the hardness of the crosslinked foam decreases, which is not preferable. Melt flow index (hereinafter abbreviated as MI) is 0.2
If it is less than g/10 min, processability and foamability will be impaired due to insufficient fluidity, which is not preferable. 51g/
If it is longer than 10 min, the tear strength decreases and troubles in kneading processing occur due to excessive fluidity, which is not preferable. In the composition of the present invention, the content of EVA (A) is 98 to 60% by weight, preferably 97 to 65% by weight, and more preferably 95 to 70% by weight. (A) is 98% by weight
Exceeding this is not preferable because the elasticity and resistance to set will be impaired and the amount of crosslinking agent will need to be significantly increased in order to achieve sufficient crosslinking. If it is less than 65% by weight, the hardness, specific gravity, and appearance (cracks) of the molded product will be out of the desired range, which is not preferable. 1 of (B) blended with EVA in the present invention,
2PBD plays extremely important roles, such as achieving high foaming, maintaining hardness, crosslinking activity, reducing the amount of crosslinking agent, and shortening crosslinking time, leading to significant cost reductions. 1,2 PBD has a vinyl bond content of 70
% or more, preferably 85% or more, and 1,2PB with a crystallinity of 5% or more, preferably 10 to 40%. Furthermore, when the vinyl bond content is less than 70%,
Adversely affects the strength of the foam, with a crystallinity of 5%
If it is less than that, the hardness of the foam will be impaired. Although the molecular weight can be selected over a wide range, in order to obtain a crosslinked rubber composition, which is the object of the present invention, the intrinsic viscosity [η] (measured in toluene at 30°C) must be 0.5 dl/g or more. is necessary. [η] is more preferably 1.0 to 3.0 dl/g. The blending amount of 1,2PBD in (B) is 2 to 30% by weight, preferably 3 to 25% by weight, more preferably 5 to 25% by weight.
It is 20% by weight. The amount of 1,2PBD in B is 2% by weight
If it is less than that, it is impossible to achieve crosslinking activity, that is, to reduce the amount of crosslinking agent and shorten crosslinking time. In addition, elasticity and resistance to fatigue are impaired, which is undesirable. If the amount exceeds 30 parts by weight, the crosslinked foam may crack or the balance between specific gravity, hardness and tear strength may be lost, making it impossible to obtain the desired crosslinked foam. (C) Natural rubber or diene-based synthetic rubber is mainly used to prevent cracking during high foaming and to make foam cells uniform. Typical rubbers are the natural rubber (NR) mentioned above,
Examples include diene-based synthetic rubbers such as cis-polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), and chloroprene rubber (CR). Among these, preferred rubbers are NR and IR. The blending amount of (C) is 0 to 30% by weight, preferably 0 to 25% by weight, and more preferably 0 to 20% by weight. If the amount of (C) exceeds 30% by weight, the hardness of the crosslinked foam decreases and the desired product cannot be obtained, which is not preferable. The organic peroxides (D) used in the present invention are those having an -O-O- bond in the molecule, and specifically include ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide. These include oxide, diacyl peroxide, peroxy carbonate, peroxy ester, etc. Among these, dialkyl peroxide is preferred from the viewpoint of workability and processing decomposition temperature. The amount of organic peroxide required to obtain the effects of the present invention is based on 100 parts by weight of [(A) + (B) + (C)].
The amount is 0.05 to 5 parts by weight, preferably 0.1 to 1 part by weight. If the amount of organic peroxide added is less than 0.05 part by weight, the degree of crosslinking will be too low, resulting in loss of compressive deformation and mechanical strength, which is not preferable. If it exceeds 5 parts by weight, the degree of crosslinking will be too high, resulting in a brittle material with poor elasticity. These have poor foamability and even if they foam, they exhibit abnormal foaming accompanied by material destruction. Crosslinking using an organic peroxide has the advantage of superior crosslinking properties for EVA and excellent color clarity compared to crosslinking using sulfur. As the blowing agent (E) used in the present invention, any known inorganic or organic blowing agent can be used. Specific examples of blowing agents include sodium bicarbonate, ammonium bicarbonate, sodium carbonate, ammonium carbonate, azodicarbonamide, dinitrosopentamethylenetetramine, dinitrosoterephthalamide, azobisisobutyronitrile, barium azodicarboxylate, and sulfonyl. Examples include hydrazide, toluenesulfonyl hydrazide, and the like.
These blowing agents may be used in combination with known blowing agents such as urea and urea derivatives. The amount of blowing agent used is 0.5 to 30 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the mixture [(A)+(B)+(C)]. Foaming agent is 30
If the amount is more than 1 part by weight, the amount of gas generated by the decomposition of the blowing agent will increase, and the gas pressure will become abnormally high, which may cause cracks in the resulting foam. If the amount of the blowing agent is less than 0.5 part by weight, it will be difficult to obtain the desired highly foamed product. In addition to the above-mentioned (A) to (E), the crosslinked foam of the present invention may also contain other compounding agents that are blended into general rubber compositions, such as reinforcing agents, fillers, activators, anti-aging agents, and processing aids. , a softener, a toning agent, etc. may be added as appropriate. There are no particular restrictions on the method of mixing the above (A) to (E) and other compounding agents, and any mixing method used for general rubber compounds such as a Banbury mixer, pressure kneader, or open roll may be used at 70 to 140°C. Preferably, the mixing is carried out at a temperature in the range of . The mixture thus obtained is fed into a mold and heated under pressure, preferably from 130 to 200
C., more preferably 140 to 180.degree. C., and at a temperature higher than the decomposition temperature of the organic peroxide and the blowing agent to crosslink the compound and decompose the blowing agent. The clamping pressure of the mold needs to be a pressure that substantially suppresses the expansion of gas generated by decomposition of the blowing agent, and is preferably 80 kg/cm ² or more. Conventional EVA foam is an uneconomical material that requires a large amount of cross-linking agent (0.6 PHR or more) to obtain the desired cross-linked product, and requires cross-linking time of 30 minutes or more in a 17 mm thick mold. In addition, the physical properties lack elasticity,
The EVA foam material has poor fatigue resistance and low tear strength, and when taken together, EVA foam material is by no means a satisfactory foam material. The present invention relates to a crosslinked composition with low specific gravity (high foaming), high hardness, high tear strength, impact resistance, and elasticity that can be produced in a short time in the presence of a small amount of crosslinking agent. The difference with foam materials is clear. The crosslinked foam produced according to the present invention is suitably used for industrial goods, automobile parts, footwear materials (outsoles, midsoles, innersoles, sandals), cushioning materials, sound absorbing materials for automobiles and buildings, packaging materials, and the like. Among these, it is particularly suitable for footwear materials, especially for its midsoles. Furthermore, the crosslinked foam produced by the present invention has excellent dimensional accuracy, durability, and cushioning properties, and can be applied to thermoformed sponges. "Examples" Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. In the Examples and Comparative Examples, tensile strength and elongation were measured according to JISK-6301, sponge interlayer tear strength was measured according to ASTMD1564, and hardness was measured using Lava Tester Type C (Kobunshi Keiki sponge hardness tester). Specific gravity was measured by the buoyancy method. Impact resistance (settling) is measured by applying a 20 kg weight (a disc with a larger area than the sample) to 5 cm.
The permanent strain was measured after impacting a 60φmm x 20mm sponge sample 100,000 times at a frequency of 80 times/minute from a height of . Settling (%) = T ₀ - T ₁ / T ₀ × 100 T ₀ : Sample thickness before test (mm) T ₁ : After sample 〃 (〃) Examples 1 to 3 Vinyl acetate content, melt flow index different EVA ((Toyo Soda Co., Ltd. 540, 631, 633)),
1,2PBD (JSR820 manufactured by Japan Synthetic Rubber Co., Ltd. Vinyl bond content 92%, crystallinity 24.5% [η] Toluene 30℃
= 1.25), blowing agent AC# 3 ((Eiwa Kasei Co., Ltd.) azodicarbonamide decomposition temperature 205℃, amount of gas generated 220c.c./g
)), crosslinking agent ((Nippon Oil & Fats Corporation) Permil D (98%),
dicumyl peroxide)) and magnesium carbonate ((
Tokuyama Soda Co., Ltd.'s MgCO ₃ -TT)), titanium oxide (Ishihara Sangyo Co., Ltd.'s Anatase)), and transparent zinc white (Sakai Chemical Industry Co., Ltd.'s ZnCO ₃ ) are listed in Table 1. were mixed in a pressure kneader and crosslinked under the conditions shown in Table 1.The results are shown in Table 1. Examples 4 to 6 The systems of Examples 1 to 3 were mixed by IR (Japanese Made by Synthetic Rubber Co., Ltd.
It was obtained in the same manner as Examples 1 to 3 except that JSR IR2200)) was added. The results are shown in Table 1. The results of Examples 1 to 6 are compared to the comparative examples.Amount of crosslinking agent (DCP is expensive at 2500 to 3000 yen/Kg, and from a cost perspective, less than 5 parts by weight was judged as ○, and more than 5 parts by weight was judged as ×) Crosslinking Time (This has a large impact on production volume and cost, so less than 30 minutes was judged as ○, and 30 minutes or more was judged as ×) Molded product cracking (No cracks appear in the molded product when the crosslinked foam is removed from the mold) ○,
Items with cracks were judged as ×) Specific gravity (0.1 to 0.2 were judged as ○ based on the standards of major sports shoe manufacturers, and those outside this were judged as ×) Hardness (50 based on the standards of major sports shoe manufacturers) ~60 was judged as ○, outside of this was judged as ×) Impact wear (an important indicator for measuring the durability of sports shoes; less than 15% was judged as ○, and 15% or more was judged as ×)
) Tensile strength (20Kg/cm ² or more was judged as ○, less than 20Kg/cm ² was judged as ×) Elongation (200% or more was judged as ○, less than 200% was judged as ×) Overall judgment (～ was judged as All ○ items ◎,
Those with an x mark of 5 or less were judged as x, and those with an x mark of more than 5 were judged as xx.) It can be seen that the results of the above ~ and overall judgments are excellent. In particular, when 1,2PBD is added to EVA, the crosslinking activity is significantly improved, and the amount of crosslinking agent and crosslinking time can be reduced. Furthermore, since it satisfies physical properties including hardness even with a low specific gravity, it has the great advantage of reducing the weight of the sole material for sports shoes, which is a long-awaited goal, and allowing manufacturers to use more material when making shoes than with sponge. Comparative Examples 1 to 8 Crosslinked foams were obtained in the same manner as in Examples according to the formulations shown in Table 1. The results are shown in Table 1.
The comparative example is a system outside the scope of the claims, and its performance is not satisfactory as expressed in the comprehensive evaluation. Specifically, Comparative Examples 1 and 2 have a crosslinking agent amount, Comparative Examples 3, 4, and 5 have a 1,2 PBD, Comparative Examples 6 and 7 have a blowing agent amount, and Comparative Example 8 has an IR that exceeds the scope of the claims. It can be seen that these are all inferior to the examples. Comparative Example 9 shows the results obtained by sulfur vulcanization. EVA cannot be vulcanized with sulfur, and when taken out after a predetermined vulcanization time, it presents a dangerous situation of foaming and molten material scattering, and is inferior to the examples within the scope of the present invention. Comparative Examples 5-1, 5-2, and 5-3 are inferior to Examples because two or three of the 1,2 PBD amount, crosslinking agent amount, and crosslinking time are outside the scope of the present invention. I understand that.

【table】

[Table] Manufactured by Gyo Co., Ltd.

【table】

[Table] "Effects of the Invention" As is clear from the above, the ethylene-vinyl acetate copolymer crosslinked foam composition of the present invention has a high expansion ratio (low specific gravity) and moderate hardness that could not be obtained conventionally. It is possible to obtain a crosslinked foam with excellent tear strength, durability against repeated stress, and crosslinking activity (reduced amount of crosslinking agent, shortened crosslinking time).Using these excellent characteristics, it can be used as a material for footwear soles (outer soles,
Inner soles, midsoles, beach sandals (especially midsoles), industrial supplies, cushioning materials,
Suitable for use in packaging materials, sealing materials, automobile parts, sound absorbing materials, etc. The crosslinked foam obtained from the composition of the present invention has excellent dimensional accuracy, durability, cushioning properties, and fluidity, so it can be used as an integrally molded sponge, thermoformed sponge, etc. in which the outsole and midsole of Shoes are crosslinked and molded at the same time. It can be used suitably.

Claims (1)

[Scope of Claims] 1 (A) ethylene-vinyl acetate copolymer 98 to 60% by weight, (B) vinyl bond content of 70% or more, crystallinity of 5% or more, and intrinsic viscosity [η] (toluene 100 parts by weight of a mixture consisting of 2-30% by weight of 1,2-polybutadiene (measured at 30°C) of 0.5 dl/g or more and (C) 0-30% by weight of natural rubber or diene-based synthetic rubber (D)
0.05 to 5 parts by weight of organic peroxide and (E) 0.5 parts by weight of blowing agent
A composition for a crosslinked foam based on ethylene-vinyl acetate copolymer, characterized in that the composition contains 30 parts by weight of ethylene-vinyl acetate copolymer.