JPS5952178B2 - Thermoplastic elastomer composition with improved oil resistance and abrasion resistance - Google Patents

Description

Detailed Description of the Invention The present invention relates to a conjugated diolefin-vinyl aromatic hydrocarbon block copolymer (hereinafter referred to as block copolymer), which is a thermoplastic elastomer, and an ethylene-organic acid vinyl alcohol ester copolymer. (hereinafter abbreviated as ethylene-organic acid vinyl copolymer), has dramatically improved wear resistance, excellent oil resistance, and maintains bending resistance, slip resistance, and permanent set to a level that does not pose any practical problems. The present invention relates to a thermoplastic elastomer composition for footwear materials.

BACKGROUND ART Conventionally, vulcanized products of synthetic rubber and natural rubber have been mainly used for sole materials of cloth bags such as canvas shoes and materials for boots.

However, these have the disadvantage that it is very difficult to mechanize and save labor in the molding stage, and the molding cost is high.

Therefore, in recent years, injection moldable soft polyvinyl chloride compositions and thermoplastic elastomer conjugated diolefin-vinyl aromatic hydrocarbon block copolymer compositions have been used as shoe sole materials instead. It has reached this point. However, soft polyvinyl chloride compositions inherently lack rubber-like properties, and specifically have drawbacks such as low rebound elasticity, poor slip resistance, and poor low-temperature properties. is a far from ideal material.

In addition, since block copolymer compositions have properties similar to vulcanized rubber in their unvulcanized state, they have excellent rubber elasticity, high slip resistance, and good low-temperature properties. Can be used as shoe sole material.

However, it has the disadvantage of insufficient wear resistance and poor oil resistance, so it is used in fields where there is a lot of movement and severe wear, or where oil resistance is particularly important, such as when machine oil is used. There are limits to its use in environmental work shoes, etc. For this reason, various attempts have been made to obtain block copolymer compositions with good abrasion resistance, but no practical examples have yet been found.

Various attempts have also been made to improve the oil resistance of the book copolymer itself or its composition.

For example, Japanese Patent Publication No. 42-18326 discloses an example in which a block copolymer of a vinyl-substituted nitrogen-containing compound and a conjugated diolefin is used, but the cost of producing the polymer is high and it is not practical at present. Cheap and
One possible method for easily improving oil resistance is to blend a resin with excellent oil resistance into a block copolymer.

However, these blends generally reduce the degree of oil swelling after the composition comes into contact with oil, and the most practical measure of oil resistance is the tensile strength retained after oil swelling. Improvements in strength cannot be achieved, and other important properties,
For example, this resulted in a decrease in rubber elasticity, bending resistance, etc. The present invention maintains the rubber properties (flexibility, rubber elasticity, slip resistance, etc.) originally possessed by PROC copolymers, while essentially improving oil resistance and improving abrasion resistance. As a result of our research to obtain an excellent block copolymer composition, we found that
60 to 150 parts, preferably 80 to 14 parts of the specific ethylene-organic acid vinyl copolymer to 100 parts by weight of the specific block copolymer (hereinafter, all parts are by weight).
The block copolymer is mixed in a discontinuous phase (
It has been discovered that the objects of the present invention can only be achieved in a composition having a specific solid phase structure in which the ethylene-organic acid vinyl copolymer forms a continuous phase (so-called sea structure).

Compositions of block copolymers and ethylene-organic acid vinyl copolymers are already known. For example, U.S. Patent 356
No. 2356 discloses a composition of a conjugated diolefin-vinyl aromatic hydrocarbon block copolymer and an engineered ethylene copolymer containing an ethylene-vinyl organic acid copolymer.

However, in this patent, the preferred amount of ethylene copolymer mixed with 100 parts of PROC copolymer is 25 to 75 parts, and in the examples, ethylene copolymer is mixed with 100 parts of PROC copolymer. As can be seen from the fact that only examples are shown in which the amount of the copolymer mixed is up to 50 parts, for the block copolymer,
Only a technique has been disclosed in which a small amount of ethylene copolymer is mixed as a modifier to improve physical properties with a focus on improving bending resistance. On the other hand, in the present invention, a composition having a specific solid phase structure is produced by using a very limited specific block copolymer and a specific ethylene-organic acid vinyl copolymer in a specific range of composition ratios. It was discovered for the first time that a composition for footwear material having excellent abrasion resistance and substantially improved oil resistance could be obtained.

The specific block copolymer used in the present invention is
General formula (A-B)l or (B-A)l-B or (A
-B) m-A or (A-B) RlX (where B is substantially a conjugated diolefin polymer block, A is substantially an aromatic vinyl polymer block, and ' is an integer from 2 to 5) , m represents an integer of 1 to 5, X is a polyfunctional compound to which n polymer chains are bonded, and n represents an integer of 3 to 7.

) is a conjugated diolefin-vinyl aromatic multiblock copolymer. Its molecular weight is from 100,000 to 500,000, preferably from 150,000 to 300,000. molecular weight is 10
If it is less than 10,000 yen, it is difficult to form a specific solid two-phase structure, which is an essential requirement of the present invention, within the limited range of the mixing ratio of the two types of polymers by a normal mixing method. It has the disadvantage that only low-level properties can be obtained in terms of strength properties such as tensile strength after swelling and abrasion resistance. If the molecular weight exceeds 500,000, the molding processability of the composition will be poor, and this is not preferred. The vinyl aromatic hydrocarbon content in the block copolymer used is from 30% by weight to 50% by weight.

30 weight? If it is less than that, the level of physical properties retained after oil swelling of the composition of the present invention is low, and the bending resistance is also poor, so it is not preferable.

On the contrary, 50 weight? If it exceeds this range, the resulting composition has the disadvantage of reduced flexibility and slip resistance. The conjugated diolefin used here has a carbon number of 4 to 6.
straight-chain and branched-chain conjugated diolefins of up to
For example, 1,3-butadiene, 1,3-bentadiene,
Examples include 1,3-hexadiene and isoprene.

In addition, examples of vinyl aromatic hydrocarbon compounds include:
Examples include styrene, vinyltoluene, α-methylstyrene, and the like.

Various production methods are known for the conjugated diolefin-vinyl aromatic hydrocarbon block copolymer, but the production method is not particularly limited in the present invention.

The specific ethylene-organic acid vinyl copolymer used in the present invention is a copolymer of ethylene and an organic acid vinyl alcohol ester monomer that can be copolymerized with ethylene.

The content of organic acid vinyl alcohol in the copolymer used is 20% to 30% by weight.
Compositions using copolymers with a content of less than 20% by weight will only result in extremely low bending resistance, while those containing more than 30% by weight will result in poor strength properties such as tensile strength. This is not preferable because the oil resistance of the composition decreases, and as a result, the oil resistance of the composition decreases. The melt index (ASTM-Dl238, E conditions) of the copolymer is 0.5.
to 10) preferably within the range of 1 to 5 (y/10 minutes).

If it is less than 0.5, it will be difficult to form a specific solid two-phase structure, which is an essential requirement of the present invention, within the limited range of the mixing ratio of the two types of polymers by ordinary mixing methods, and oil resistance will become essential. There is no improvement in certain aspects.

It also has the disadvantage that the molding processability of the composition is also reduced. On the other hand, if it exceeds 10, the strength properties such as tensile strength, abrasion resistance, and even bending resistance of the composition will be significantly reduced, which is not preferable. Examples of organic acid vinyl monomers that can be copolymerized with ethylene include vinyl acetate, vinyl propionate, vinyl dioxylate, and vinyl benzoate, among which vinyl acetate is most preferred.

The mixing ratio of the ethylene-organic acid vinyl copolymer to 100 parts of the block copolymer is limited to 60 to 150 parts, preferably 80 to 140 parts. If it is less than 60 parts, even if the above-mentioned specific polymer is used, in the present invention, the ethylene-organic acid vinyl copolymer forms a continuous phase (so-called sea structure) and the block copolymer forms a discontinuous phase (so-called island structure). It is not desirable to have a specific solid phase structure that is essential, and as a result, the level of physical properties such as tensile strength maintained after oil swelling becomes low.

In other words, as is clear from the examples, although the apparent oil resistance, that is, the degree of oil swelling of the composition after contact with oil, decreases, the tensile strength maintained after oil swelling, which is the most substantial measure of oil resistance, decreases. Improvements in strength, etc. cannot be measured. If the amount exceeds 150 parts, the above-mentioned bending resistance and slip resistance will be markedly reduced, and the permanent deformation (permanent elongation, etc.) of the composition will be excessive, which will significantly impair commercial value, which is not preferable.

In the present invention, of the two constituent components, the block copolymer forms a discontinuous phase (so-called island structure), and the other ethylene-organic acid vinyl copolymer forms a continuous phase (so-called sea structure). It is necessary to do so.

In this case, the term "block copolymer forming a discontinuous phase (so-called island structure)" means a dispersion in which preferably 80% by weight of the block copolymer has an average particle size in the range of 0.5 microns to 3 microns. This means that it exists as a phase.

Furthermore, when the ethylene-organic acid vinyl copolymer forms a continuous phase (a so-called sea structure), it means that the copolymer exists in a continuous form surrounding the discontinuous phase of the block copolymer. means. The method of mixing to obtain such a dispersion involves controlling the kneading time and the shearing force applied at this time in a temperature range of 80°C to 140°C, preferably 90°C to 120°C, so that the block copolymer The method may be appropriately selected and carried out so as to achieve dispersion with a specific average particle diameter.

Under such crosstalk conditions, the block copolymer will form a discontinuous phase, regardless of the order in which polymers and other additives are added.
A composition having a solid phase structure in which the ethylene-organic acid vinyl copolymer is a continuous phase is obtained.

As the mixing method used here, for example, a method using a mixing roll, a method using a Banbury mixer, a method using various extruders, etc. are used. In this way, a specific conjugated diolefin-vinyl aromatic block copolymer and a specific ethylene-organic acid vinyl copolymer are mixed within a very limited range to form a composition having a specific solid phase structure. As a result, the abrasion resistance of the composition has been dramatically improved, and oil resistance has been substantially improved, while maintaining good bending resistance, slip resistance, and small permanent set, etc., for footwear. An ideal composition can be obtained.

Various commonly used fillers can be added to the composition of the present invention, mainly for the purpose of reducing costs.

Furthermore, in order to obtain a good color tone depending on the application, commonly used pigments and the like may be added. Examples of these fillers and pigments include calcium carbonate, clay,
Finely powdered solids such as silica and titanium dioxide may be mentioned.

Furthermore, the composition of the present invention contains polystyrene resins (general polystyrene, impact polystyrene, low molecular weight polystyrene, etc.) in order to adjust hardness, improve heat distortion temperature, and improve moldability. ) or AB
Styrene copolymers such as S, AS resins, and polyolefin polymers such as polyethylene and polypropylene can be added as necessary.

Additionally, commonly used processing oils can be added to the compositions of the present invention in order to improve their moldability, adjust their hardness to desirable levels, and reduce costs.

Among these process oils, paraffin oils,
Naphthenic oils are preferably used. The composition thus obtained is suitably used for the soles of cloth shoes, such as canvas shoes, or boots, which are directly molded by injection molding.

It can also be used for various molded products that require oil resistance, abrasion resistance, rubber elasticity, etc. Hereinafter, some examples will be given to illustrate embodiments of the present invention, but these are intended to explain the gist of the present invention more specifically, and are not intended to limit the present invention.

Example 1, Comparative Example 1 Various compositions were prepared by varying the composition ratio of the conjugated diolefin-vinyl aromatic hydrocarbon block copolymer and the ethylene-organic acid vinyl copolymer, and their physical properties were evaluated.

The block copolymer used was a styrene-butadiene radial type block copolymer (A-B)4Si (where A represents polystyrene block and B represents polybutadiene block.

), its molecular weight was approximately 200,000, and the styrene content in the copolymer was 40% by weight. Ethylene-mono-vinyl acetate copolymer (EVA resin) was used as the ethylene-vinyl organic acid copolymer, and the vinyl acetate content in the copolymer was 25% by weight. The melt flow index (ASTM-Dl238, E conditions) was 2.

Naphthenic oil was used as the process oil.

This naphthenic oil contained 10% or less of aromatic substances. The composition was mixed on a mixing roll at a roll temperature of about 100°C according to the following recipe.

Composition ratio PROTSU copolymer 100 parts by weight Ethylene monovinyl acetate copolymer Variable naphthenic process oil 90 parts by weight Light calcium carbonate 50 parts by weight Titanium oxide
The results obtained using 10 parts by weight are shown in Table 1 as Comparative Examples and Examples.

Comparative Example 2 The physical properties of a composition of a block copolymer and polystyrene (general purpose polystyrene) similar to those used in Example 1, and a flexible polyvinyl chloride composition were evaluated and shown in Table 1.

The formulation of these two compositions is as follows. Block Copolymer/Polystyrene Composition Block Copolymer
100 parts by weight Polystyrene (general grade) 60 parts by weight Naphthenic process oil 9
0 parts by weight Light calcium carbonate 50 parts by weight Titanium oxide 10 parts by weight Soft PVC composition Soft grade vinyl chloride polymer 100 parts by weight Plasticizer (DOP) 100 parts by weight Light calcium carbonate 20 parts by weight Stabilizer
3 parts by weight Example 2, Comparative Example 3 Compositions were produced using various ethylene-vinyl acetate copolymers with varying vinyl acetate content and melt flow index in the copolymer, and their physical properties were evaluated. .

The block copolymer and process oil used were exactly the same as in Example 1.

The composition was mixed in the same manner as in Example 1 according to the following recipe. Composition blending ratio PROTSU copolymer 100 parts by weight Various ethylene H pre-acid bicarbonate copolymers 120 parts by weight Naphthenic process oil 90 parts by weight Soft calcium carbonate 50 parts by weight Titanium oxide 10 parts by weight The obtained results are shown in a comparative example. , are shown in Table 2 as examples.

Example 3, Comparative Example 4 Various compositions were prepared using block copolymers whose molecular weight, styrene content, and block structure were tabulated, and their physical properties were evaluated.

The other ethylene-organic acid vinyl copolymer and process oil used were the same as those used in Example 1.

The composition was prepared in the same manner as in Example 2, and the mixing method was also substantially the same as in Example 1.

The results obtained are shown in Table 3.

Claims (1)

[Claims] 1 (I) Conjugated diolefin-vinyl aromatic hydrocarbon block conjugate which is a thermoplastic elastomer with a molecular weight of 100,000 to 500,000 and a vinyl aromatic hydrocarbon content in the range of 30% to 50% by weight. 100 parts by weight of polymer and (
II) Organic acid vinyl alcohol ester content is 20% to 30% by weight, melt index (AST)
M-D1238, E conditions) from 0.5 to 10 (g/10
60-150 parts by weight of ethylene-organic acid vinyl alcohol ester copolymer in the range of
The block copolymer has a discontinuous phase (so-called island structure), (
A thermoplastic elastomer composition having improved oil resistance and abrasion resistance and having a solid phase structure in which the ethylene-organic acid vinyl alcohol ester copolymer of II) forms a continuous phase (so-called sea structure).