Polymer compositions

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This invention relates to novel mixtures of rubbery copolymers having little or no unsaturation with thermoplastic resins.

It relates in particular to microcellular shoe-soling compositions.

Microcellular shoe sole compositions are used as a replacement for crepe soles. These compositions, which are usually based on styrene-butadiene copolymer, have two disadvantages. First, a uniform cure is not obtained in one piece soles when the material is of varying thickness; thus the thicker heel portion tends to be under-cured and as a result the microcellular structure is less dense. Second, after vulcanization, the shoe sole material shrinks approximately 3 5%; It is necessary to preshrink such material by post curing it for a period of 4 - 6 hours.

I have found that these disadvantages may be substantially modified or largely overcame by the use of polymers other than styrene· butadiene copolymer types. In addition, the microcellular shoe-soling compositions based on the polymer blend of the present invention are lighter in weight than crepe soles of the same thickness and do not absorb water nor pick up dirt and grit as readily.

The composition of the present invention is a mixture comprised of (a) a major amount of a rubbery copolymer of two or more polymerized monomers, one of said monomers being a mono-olefin, the other said monomer or monomers being selected from mono-olefins and multi-olefins,and (b) a minor amount of ethylene-vinyl acetate copolymer .

The most preferred rubbery copolymer used in the composition of this invention is butyl rubber. The term butyl rubber is intended to define rubbery copolymers of isobutylene with a diolefin containing 4 to 14 carbon atoms, usually isoprene, but diolefins such as butadiene, dimethyl butadiene and pentadiene may also be used, the copolymers containing about 85 to 99*9 parts by weight of the olefin and about 0.1 to 15 parts by weight of the diolefin. These copolymers

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/2 are normally produced by low temperature polymerization using a solution of a Friedel-Crafts catalyst, such as aluminium chloride, in a solvent, such as methyl or ethyl chloride, at temperatures ranging from -10 to -100°G or lower. The polymer thereby produced usually has a molecular weight between about 200,000 and 600,000. The type of butyl rubber and the amount used are dependent on the properties such as cure rate, resistance to shrinkage and resistance to tear which are required in the final composition.

The preferred rubbery copolymer used in the composition of this invention is ethylene-propylene copolymer. It is usually prepared by copolymerizing the monomers in the presence of Ziegler catalysts at relatively low temperatures and pressures. The copolymer should contain about 20 to 75 mole per cent ethylene and may contain up to 5 mole per cent or more of polymerized diolefin, such as dicyclopentadiene. Butyl rubber and ethylene-propylene copolymer may be used in their halogenated forms.

Examples of other rubbery copolymers which may be used in the composition of this invention include ethylene butene-1 copolymer, ethylene pentene-1 copolymer and propylene butylene dicyclopentadiene copolymer. It is also within the scope of this invention to utilize mixtures of any of the rubbery copolymers described previously.

The ethylene vinyl acetate copolymers used in the composition of this invention may be made in a high pressure polymerization process using a free radical catalyst. Ethylene vinyl acetate copolymers having a copolymerized vinyl acetate content of about 5-45 weight per cent may be used, but a vinyl acetate content of about 20 to 35 weight per cent is preferred. High molecular weight copolymers are most suitable. Such ethylene vinyl acetate copolymers have an inherent viscosity of about 0.5 - 1.1 in toluene at 30°C when 0.25 gnu copolymer is dissolved in 100 mis. toluene. Copolymers which have an inherent viscosity of about 0.7 - 1.0 are preferred. Ethylene vinyl

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acetate copolymers having a melt index of atout 1 to 5θ0 may te used, tut copolymers having a melt Index of atout 2 - 100 gm./l0 minutes are preferred.

The rubbery copolymers previously described are compatible with ethylene vinyl acetate copolymer. A homogeneous mixture of ethylene vinyl acetate copolymer with the rubbery copolymer is readily prepared by blending the polymers on conventional rubber or plastics processing equipment. Such mixtures may contain from about 5 to UO weight per cent of ethylene vinyl acetate copolymer, but a 10 to 30 weight per cent content is preferred.

After blending, the mixture of polymers is cooled to a temperature such that blowing agents do not decompose and vulcanizing agents do not cause scorch, i.e. premature vulcanization, when they are incorporated. The compound, comprising a mixture of the rubbery copolymer, ethylene vinyl acetate copolymer, a blowing agent and a vulcanizing agent, is transferred to a mould prior to vulcanization. The blowing agent decomposes to a gas at vulcanization temperatures of 150 - 170^eC. The gas so generated causes formation of numerous cells in the compound. The gas is trapped In cells, distributed throughout the blown compound and the cells are separated from each other by a cell wall composed of the cured blend of the rubbery copolymer with ethylene vinyl acetate copolymer. This cell structure is referred to as microcellular in describing a specific type of shoe-soling material.

Suitable blowing agents include azodiocarbonamide, azobisisobutyronitrile, ρ,ρ’-oxybis-benzenesulfonylhydrazide, benzene sulfohydrazide, N-azo-di-isobutyronitrile, Ν,Ν’-dinitroso pentamethylene tetramine, N,N'-dimethyl Ν,Ν’-dinitrosoterephthalamide, urea, methyl formate, ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, sodium carbonate and the like. Benzene sulfohydrazide and urea are preferred. The amount of blowing agent used

- 3 842902 is from 0.5 - 15 parts by weight per 100 parts by weight of total polymers.

The rubbery copolymer can be cured with a vulcanizing agent selected from sulfur, ρ-quinone dioxime and phenolic resins and organic peroxides. Accelerators used for vulcanization with sulfur include tetramethylthiuram disulfide, 2-mercaptobenzothiazole, tetraethylthiuram disulfide and the like. Accelerators used for vulcanization with p-quinone dioxime include metal oxides such as zinc oxide and lead oxide. Accelerators used for vulcanization with phenolformaldehyde resin include halogen containing compounds such as stannous chloride dihydrate and chlorosulfonated polyethylene. The amount of vulcanizing agent used is from 0.5 - 10 parts by weight per 100 parts by weight of total polymers.

The processes of vulcanization and blowing are carried out in a mould. Sufficient compound, containing the vulcanizing and blowing agents, is used to completely fill the mould cavity. Gas is generated in the compound by decomposition of the blowing agent at vulcanization temperatures. After vulcanization, the shaped cellular composition is removed. The dual process of blowing and vulcanization is usually completed in 5 - 30 minutes at 150 - 170°C.

The Bhaped vulcanized cellular composition shrinks very gradually unless it is post cured. The shrinkage is believed to be caused by two factors: thermal contraction and gaseous diffusion. Shrinkage due to thermal contraction occurs rapidly as the composition cools from vulcanization temperature to room temperature. The shrinkage believed due to diffusion from the composition of a portion of the gas, formed by decomposition of the blowing agent, occurs extremely slowly. Shrinkage may he accelerated, i.e. the article may he preshrunk, by post curing the composition in air for about 2 hours at 125’C.

The vulcanized microcellular composition of this invention

- 4 842902 is particularly useful as a shoe-soling material. Such compositions usually contain other compounding ingredients, in addition to those described previously, such as reinforcing agents, fillers, plasticizers, antioxidants, colouring pigments and vulcanization activators. Reinforcing agents and fillers such as carbon black, hydrated aluminium silicate, finely divided silica, magnesium silicate, calcium carbonate, aluminium hydroxide, etc. may he used.

In general, any of the plasticizers which are used in rubber compounding may be employed provided they are compatible with the rubbery copolymer; examples of such plasticizers include naphthenic oils, paraffinic oils and esters such as tributoxyethyl phosphate. Zinc oxide and saturated monocarboxylic acids, such as stearic acid, are examples of vulcanization activators which may be used.

The following examples will better illustrate the invention. In these examples, all parts are by weight.

EXAMPLE I

The compound described below was mixed in a Banbury mixer at an initial temperature of 125*0. Butyl rubber and ethylene vinyl acetate were added together; zinc oxide, stearic acid and reinforcing agents, then plasticizers, were added later. The compound was removed from the Banbury at a temperature of 150*C and was sheeted out on a two roll mill.

Compound

Ingredient 1

Butyl Rubber (a) 90.0 Ethylene vinyl acetate copolymer (h) 10.0 Zinc oxide 3·0 Stearic acid 3·0 Precipitated hydrated silica 30·0 Hydrated aluminum silicate clay (c) 60.0 Polyethylene glycol (d) 2.0 Hydrocarbon wax 7*0 Tributoxy ethyl phosphate 2.0

Butyl rubber (a) was a copolymer of isobutylene and isoprene containing about 3.0 mole per cent of copolymerized isoprene

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and. had. a ML-8-212*F Mooney viscosity of about 1+5 · Ethylene vinyl acetate copolymer (b) contained about 28 weight per cent of copolymerized vinyl acetate and had an inherent viscosity of about Ο.85. Hydrated aluminum silicate clay (c) had a specific gravity of 2.6 and

99$ the material could be passed through a 300 mesh sieve. Polyethylene glycol (d) had a molecular weight of about 35θθ and a melting point of 55*C.

Accelerators, blowing agents and a vulcanizing agent were then incorporated in the compound on a mill at a temperature of 100^eF.

I.5 parts of tetramethylthiuram disulfide, 1.0 part of tetraethylthiuram disulfide, 1.0 part of mercaptohenzothiazole, 0-5 parts of urea, 1+.0 parts of benzene sulfohydrazide-paraffinic oil paste (75 weight per cent benzene sulfohydrazide) and 1.75 parts sulfur were added, per 100 parts of butyl rubber plus ethylene vinyl acetate co15 polymer. The final compound was mould cured for 11 minutes at l65*C.

The vulcanizates were post cured in air for 2 hours at 125*C and 1 hour at 100“C before testing.

The vulcanizates were tested for density, shrinkage, split tear strength and crack-growth resistance. The density was calculated after measuring the volume and weight of a test sample. The linear shrinkage of a 1” x 6” test sample was measured after each post cure period. The split tear strength was determined by measuring the load required to increase the split in a test sample by 0.5 inch; a 0.2” x 1 x 3” test sample split half-way between the top and bottom surfaces for a distance of one inch from one end was used. The two tongues” were clamped one in each jaw of a tensile tester and the jaws were pulled apart at a rate of 3 inches per minute. Crack-growth resistance was determined by measuring the growth of a preformed cut in a test sample mounted in a Boss ilex Machine after 25,000 cycles at

-15°C. The cut which was 0.08 inch long was made half-way across and

2.5 inches from one end of a Ο.25 x 1 x 6” test sample which was

- 6 Α-Ί then flexed, through 90* in each of two directions at a rate of 102 cycles per minute.

Vulcanizate properties are presented in Table I.

TABLE I

Compound

Property 1

Density (gm./ml.) 0.69

Shrinkage after 2 hours post cure at 125*C ($) 1.1

Shrinkage after 1 hour post cure at 100*C (¾) 0.8

Split tear (lbs./inch)

a) along grain 18.6

b) across grain 20.1

Crack-growth (inch) Nil

The cellular structure, resilience characteristics and the above properties indicate the compound is suitable for use as a micro15 cellular shoe-soling material.

EXAMPLE II

<td> The following compounds were</td><td> mixed,</td><td colspan="2"> vulcanized and tested</td>

<td> by the procedures described in Example</td><td> I.</td><td></td><td></td>

<td> Ingredient</td><td> 1</td><td> Compound 2</td><td> 3</td>

<td> Butyl rubber (a)</td><td> 9O.O</td><td> 80.0</td><td> 70.0</td>

<td> Ethylene vinyl acetate copolymer (h)</td><td> 10.0</td><td> 20.0</td><td> 30.0</td>

<td> Zinc oxide</td><td> 3.0</td><td> 3.0</td><td> 3.0</td>

<td> Stearic acid</td><td> 3.0</td><td> 3.0</td><td> 3.0</td>

<td> Precipitated hydrated silica</td><td> 48.0</td><td> 48.0</td><td> 48.0</td>

<td> Hydrated aluminum silicate clay (c)</td><td> 42.0</td><td> 42.0</td><td> 42.0</td>

<td> Polyethylene glycol (d)</td><td> 2.0</td><td> 2.0</td><td> 2.0</td>

<td> Hydrocarbon wax</td><td> 7.0</td><td> 7.0</td><td> 7.0</td>

<td> Tributoxyethyl phosphate</td><td> 2.0</td><td> 2.0</td><td> 2.0</td>

<td> Naphthenic oil (e)</td><td> I.5</td><td> 1-5</td><td> I.5</td>

Naphthenic oil (e) had a specific gravity of 0.88 and a viscosity SSU (Saybolt universal seconds) of 47 at 100*C.

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Vulcanizate properties are presented in Table II.

TABLE II

<td> Property</td><td> 1</td><td> Compound 2</td><td> 3</td>

<td> Density (gm./ml.)</td><td> Ο.72</td><td> 0.64</td><td> Ο.54</td>

<td> Shrinkage after 2 hours post cure</td><td> 0.8</td><td> 0.2</td><td> 0.8</td>

<td> at 125*0 ($)</td><td></td><td></td><td></td>

<td> Shrinkage after 1 hour post cure</td><td> 0.4</td><td> 0.8</td><td> 0.8</td>

<td> at 100’C ($)</td><td></td><td></td><td></td>

<td> Split tear (lbs./inch)</td><td></td><td></td><td></td>

<td> a) along grain</td><td> 27.1</td><td> 18.2</td><td> 21.3</td>

<td> b) across grain</td><td> 29.2</td><td> 21.1</td><td> 23-9</td>

<td> Crack-growth (inch)</td><td> Nil</td><td> Nil</td><td> Nil</td>

<td colspan="4"> The cellular structure, resilience characteristics and the</td>

<td colspan="2"> above properties indicate these compounds are</td><td colspan="2"> suitable for use as</td>

<td> microcellular shoe-soling materials.</td><td></td><td></td><td></td>

<td> EXAMPLE III</td><td></td><td></td><td></td>

<td> The following compounds were</td><td> mixed,</td><td> vulcanized</td><td> and tested</td>

<td> by the procedures described in Example</td><td> I.</td><td></td><td></td>

<td></td><td></td><td> Compound</td><td></td>

<td> Ingredient</td><td> 1</td><td> 2</td><td> 3</td>

<td> Butyl rubber (a)</td><td> 9O.O</td><td> 85.Ο</td><td> 80.0</td>

<td> Ethylene vinyl acetate copolymer (f)</td><td> 10.0</td><td> I5.O</td><td> 20.0</td>

<td> Zinc oxide</td><td> 3.0</td><td> 3.O</td><td> 3-0</td>

<td> Stearic acid</td><td> 3.0</td><td> 3.0</td><td> 3.0</td>

<td> Precipitated hydrated silica</td><td> 30.0</td><td> 3O.O</td><td> 30.0</td>

<td> Hydrated aluminum silicate clay (c)</td><td> 60.0</td><td> 6O.O</td><td> 6O.O</td>

<td> Polyethylene glycol (d)</td><td> 2.0</td><td> 2.0</td><td> 2.0</td>

<td> Hydrocarbon wax</td><td> 7.O</td><td> 7.0</td><td> 7.0</td>

<td> Tributoxyethyl phosphate</td><td> 2.0</td><td> 2.0</td><td> 2.0</td>

<td colspan="2"> Ethylene vinyl acetate copolymer (f)</td><td> contained</td><td> about 20</td>

<td colspan="2"> weight per cent of copolymerized vinyl acetate</td><td> and had a</td><td> melt index</td>

of about 2.5 gm./lO minutes.

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<td rowspan="2"> Vulcanizate properties are TABLE III Property</td><td colspan="3"> presented in Table III.</td>

<td> 1</td><td> Compound 2</td><td> 3</td>

<td> Density (gm./ml.)</td><td> 0.6i</td><td> 0.57</td><td> 0.52</td>

<td> Shrinkage after post cure (%)</td><td> 1.0</td><td> 1-5</td><td> 1.2</td>

<td> Shrinkage after 1 hour at 100*0 ($)</td><td> 0.4</td><td> 0.8</td><td> 0.8</td>

<td> Split tear (lbs./inch)</td><td></td><td></td><td></td>

<td> a) along grain</td><td> 18.6</td><td> 18.1</td><td> 18.6</td>

<td> b) across grain</td><td> 19-1</td><td> 20.1</td><td> I8.6</td>

<td> Crack-growth (inch)</td><td> Nil</td><td> Nil</td><td> Nil</td>

The cellular structure, resilience characteristics and the above properties indicate these compounds are suitable for use as microcellular shoe-soling materials.

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The embodiments of the invention in which an exclusive property or privilege