JPH0517635A - Polyethylene-based polymer composition - Google Patents

Abstract

PURPOSE:To obtain a composition which can give a vulcanizate excellent in strength properties by mixing a specified PE-based polymer with a metal salt of an ethylenically unsaturated carboxylic acid and an organic peroxide in a specified ratio. CONSTITUTION:This composition comprises 100 pts.wt. PE-based polymer (e.g. ethylene/propylene copolymer) having a Mooney viscosity (ML1+4, 100 deg.C) of 10-70 and containing at least 75mol% ethylene units, 15-80 pts.wt. metal salt of an ethylenically unsaturated carboxylic acid (e.g. zinc dimethacrylate) and 0.2-10 pts.wt. organic peroxide [e.g. alpha,alpha'-bis(t-butylperoxy-m-isopropyl)benzene].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene-based polymer composition, and more particularly to a polyethylene-based polymer composition which gives a vulcanized product having excellent strength properties.

[0002]

BACKGROUND OF THE INVENTION Rubber used for automobile tires, belts, hoses, etc. is styrene-butadiene copolymer rubber (SB
R), butadiene rubber (BR), chloroprene rubber (C
R), isoprene rubber (IR), natural rubber (NR) and the like. These general-purpose rubbers are usually reinforced with carbon black, and the upper limit of the tensile strength of compounded rubber (vulcanized product) reaches 300 kg / cm ² or more.

On the other hand, ethylene-propylene rubber (EPM), which is a saturated rubber, and ethylene-containing a partially unsaturated bond,
Propylene-diene rubber (EPDM) has ozone resistance,
A rubber with excellent weather resistance and heat resistance. However, EP
M and EPDM are compared with the above-mentioned general diene rubber,
The reinforcing effect of carbon black is extremely small, and the upper limit of the tensile strength of the compounded rubber is up to about 200 kg / cm ² , which limits the development of applications in fields requiring high strength. For example, when a bicycle tire is made by using EPM or EPDM as a raw material rubber, cracks due to ozone deterioration do not occur, but cracks due to insufficient strength easily occur.
The life will be extremely short.

Although attempts to reinforce EPDM have hitherto been made mainly on polymer alloys, high strength rubbers comparable to general diene rubbers have not yet been obtained.

By the way, it is known that a metal salt of an ethylenically unsaturated carboxylic acid such as zinc dimethacrylate is blended with various rubbers as a reinforcing agent in place of carbon black.

For example, JP-A-63-270753 discloses that a partially hydrogenated acrylonitrile-butadiene copolymer rubber (NBR) is blended with an organic peroxide and a metal salt of an ethylenically unsaturated carboxylic acid to obtain strength characteristics. It is disclosed that an improved rubber composition is obtained. Further, JP-A-1-306440 discloses that partially hydrogenated NBR.
It is disclosed that a vulcanized rubber having a tensile strength of more than 500 kg / cm ² can be obtained by blending an organic peroxide and a finely powdered zinc salt of methacrylic acid with the above. JP-A-5
No. 2-121653, a polybutadiene rubber and an ethylenically unsaturated carboxylic acid are blended with a divalent metal compound and an organic peroxide to obtain a rubber article with improved abrasion resistance. It is disclosed.

However, even if EPM or EPDM is mixed with a metal salt of an ethylenically unsaturated carboxylic acid and vulcanized with an organic peroxide, the strength characteristics are not so improved.

[0008] For example, British Patent No. 1,091,818 proposes a vulcanizable composition in which EPM or EPDM is mixed with an organic peroxide and a metal salt of (meth) acrylic acid. For example, the vulcanizate has a tensile strength of 2370p.
Only those up to si (170 kg / cm ² ) are shown. Also, U.S. Pat. No. 4,713,409 and U.S. Pat. No. 4,192,790 disclose EPM and EPDM.
It has been disclosed that a zinc salt of methacrylic acid and an organic peroxide are blended alone or in a blend with a diene rubber, but the vulcanizate has a tensile strength of 200 kg / cm ^2.
Only up to the level obtained, there is no great difference from the case of blending carbon black.

As described above, EPM and EPDM have little reinforcing effect by a reinforcing agent, and conventionally, no effective means for significantly improving the strength of a polymer containing an ethylene unit as a copolymer composition has been found. Is.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyethylene-based polymer composition in which the vulcanizate has significantly improved strength characteristics. The present inventors have combined EPM and E by combining a metal salt of an ethylenically unsaturated carboxylic acid such as zinc dimethacrylate as a reinforcing agent with an organic peroxide.
When an experiment for compounding with PDM was conducted, a high-strength vulcanizate was obtained with a polymer having a copolymerization composition ratio (ethylene composition of about 40 to 60% by weight, about 70 mol% or less) which is usually used for rubber. I couldn't.

However, a polyethylene-based polymer having a composition ratio of 75 mol% or more of ethylene units and a specific Mooney viscosity range is used, in which a metal salt of an ethylenically unsaturated carboxylic acid and an organic peroxide are used. It was surprisingly found that vulcanizates having markedly improved tensile strength can be obtained by blending in a specific ratio.

General-purpose EPM and EP with low ethylene composition ratio
In DM, the strength was not improved because the dispersibility of metal salts such as zinc dimethacrylate was poor, but in the case of a polyethylene-based polymer having a higher ethylene composition ratio and a Mooney viscosity in an appropriate range than in the past. It is presumed that the metal salt of ethylenically unsaturated carboxylic acid such as zinc dimethacrylate is finely dispersed, and as a result, the strength characteristics are significantly improved. The composition of the present invention may be 250 kg / cm ² or more, preferably 300, though it depends on the formulation and the like.
A tensile strength of kg / cm ² or more can be achieved.

Further, when carbon black is used as the reinforcing agent, the color tone of the compounded rubber is black, but when the metal salt is used, a bright color compounding is possible. The present invention has been completed based on these findings.

[0014]

Thus, according to the present invention, (A) Mooney viscosity (ML _{1 + 4} , 100 ° C.) 10 to
70, 100 parts by weight of a polyethylene-based polymer containing 75 mol% or more of ethylene units, (B) 15 to 80 parts by weight of a metal salt of an ethylenically unsaturated carboxylic acid, and (C).
There is provided a polyethylene-based polymer composition comprising 0.2 to 10 parts by weight of an organic peroxide.

The present invention will be described in detail below. (Polyethylene-based polymer) The polyethylene-based polymer used in the present invention is a homopolymer or copolymer having a Mooney viscosity of 10 to 70 and an ethylene unit content of 75 mol% or more, or a blend thereof.

Examples of the copolymer include a copolymer of ethylene and at least one α-monoolefin having 3 to 6 carbon atoms. Examples of the α-monoolefin include propylene, 1-butene, 1-pentene, 1-hexene and the like. These α-monoolefins have a copolymerization composition ratio of 25 mol% or less.

Further, a copolymer having a double bond introduced may be used. Specifically, there is a terpolymer in which a part of the α-olefin is replaced with a non-conjugated diene monomer having a double bond as a third component. As the non-conjugated diene monomer, 5-ethylidene-2-norbornene (EN
B), dicyclopentadiene, 1,4-hexadiene and the like. These non-conjugated diene monomers are usually used in the range of 10 mol% or less.

Therefore, specific examples of the polyethylene-based polymer used in the present invention include, for example, ultra high molecular weight polyethylene, linear low density polyethylene (LLDPE),
Examples thereof include an ethylene-propylene copolymer, an ethylene-1-butene copolymer, an ethylene-propylene-ENB terpolymer, and a blend thereof. A small amount of other copolymerizable monomer such as acrylate may be copolymerized within a range not impairing the object of the present invention.

The polyethylene-based polymer used in the present invention must have an ethylene unit (ethylene composition ratio) of 75 mol% or more. When the ethylene unit is less than 75 mol%, a vulcanizate having high strength cannot be obtained even if a metal salt of ethylenically unsaturated carboxylic acid is added.

The polyethylene polymer used in the present invention must have a Mooney viscosity in the range of 10 to 70, and a vulcanized product with high strength cannot be obtained outside this range.

(Metal salt of ethylenically unsaturated carboxylic acid)
Examples of the metal salt of an ethylenically unsaturated carboxylic acid used in the present invention include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid and 3-butenoic acid; maleic acid, fumaric acid, itaconic acid and the like. Unsaturated dicarboxylic acids; monoesters of unsaturated dicarboxylic acids such as monomethyl maleate, monoethyl maleate and monoethyl itaconate, unsaturated polycarboxylic acids other than the above and unsaturated polycarboxylic acids having at least a monovalent free carboxyl group It is at least one metal salt such as an ester of a carboxylic acid.

The metal is not particularly limited as long as it forms a salt with the above-mentioned ethylenically unsaturated carboxylic acid, but zinc, magnesium, calcium and aluminum are particularly suitable.

The metal salt of these ethylenically unsaturated carboxylic acids may be blended as the metal salt. However, the polyethylene-based polymer may be mixed with an ethylenically unsaturated carboxylic acid and an oxide, hydroxide or carbonate of the above metal. It is also possible to add a metal compound such as the above and react them in the polymer during the production of the composition of the present invention to generate a metal salt in situ. However, when these compounds or metal salts are used, coarse particles are removed, that is, classification is performed by an air classifier, etc., and the content of particles having a particle diameter of 20 μm or more is 5%.
The following are preferable.

Among these metal salts of ethylenically unsaturated carboxylic acid, zinc salt of methacrylic acid is particularly preferable because of its physical properties and availability. When a zinc salt of methacrylic acid is used, 0.5 to 3.2 mol of a zinc compound such as zinc oxide or zinc carbonate is used per 1 mol of methacrylic acid.
It is desirable that the product is obtained by reacting within the range of 0.5 to 2 mol.

The amount of the metal salt of ethylenically unsaturated carboxylic acid used is 15 to 80 parts by weight, preferably 20 to 80 parts by weight, based on 100 parts by weight of the polyethylene polymer.
It is more preferably 25 to 70 parts by weight. This ratio is 1
If it is less than 5 parts by weight, the desired strength cannot be obtained, and if it exceeds 80 parts by weight, kneading becomes difficult.

(Organic Peroxide) The organic peroxide used in the present invention may be the one used in ordinary peroxide vulcanization of rubber. Specific examples include dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl oxide, benzoyl peroxide,
2,5-Dimethyl-2,5-di (t-butylperoxy) hexyne-3,2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-
2,5-mono (t-butylperoxy) -hexane,
Examples include α, α′-bis (t-butylperoxy-m-isopropyl) benzene and the like. These organic peroxides may be used alone or in combination of two or more. It is preferable to use an organic peroxide having a decomposition temperature as high as possible so that scorch does not occur during kneading.

The amount of the organic peroxide used is 0.2 to 10 parts by weight, preferably 0.4 to 8 parts by weight, based on 100 parts by weight of the polyethylene polymer. If this proportion is less than 0.2 parts by weight or exceeds 10 parts by weight, a high-strength vulcanizate cannot be obtained.

(Other Additives) In the polyethylene-based polymer composition of the present invention, a reinforcing agent such as carbon black and silica; a filler such as calcium carbonate and talc; Various agents such as a cross-linking aid such as methylol propane trimethacrylate and m-phenylene bismaleimide; a stabilizer, a colorant and the like can be appropriately blended and used as necessary.

The composition of the present invention comprises a roll, Banbury,
It can be produced by kneading the respective components using an ordinary mixer such as a kneader. The polyethylene-based polymer used in the present invention has a large proportion of ethylene units and is a general-purpose EP.
It is preferable to heat to about 120 to 130 ° C. at the time of kneading, because it tends to crystallize and become harder than M or EPDM. If the heating temperature is too high, scorch tends to occur during kneading, and if it is too low, kneading becomes difficult.

[0030]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The methods for measuring the physical properties are as follows. <Moonie viscosity> The Mooney viscosity of the polymer is JIS
Measured according to K 6300 at ML _{1 + 4} , 100 ° C.

<Physical Properties of Vulcanized Products> Hardness, Tensile Stress M
₁₀₀ (100% modulus), tensile strength, and elongation were measured according to JIS K6301.

[Examples 1 to 10 and Comparative Examples 1 to 8] As the polymers, various polymers having the compositions shown in Table 1 were used. However, the polymer B is a combination of the polymer A and the polymer I.
It is a blend of 0:50 (weight ratio). Also,
Polymer E is LLDPE (Showa Denko KK trade name Shorex 720EF) and ultra-high molecular weight polyethylene (Showa Denko KK trade name 5551Z) 70:
Blended at 30 (weight ratio) (note that LL
DPE is a copolymer of ethylene and a small amount of α-olefin, but since it is conventionally called polyethylene,
The ethylene unit of polymer E was shown as 100 mol%).

As the metal salt of ethylenically unsaturated carboxylic acid, zinc dimethacrylate is pulverized to a size of several μm,
A product obtained by classifying with an air classifier to remove coarse particles of 20 μm or more was used. However, in Example 4, classification is performed to 20 μm.
15 parts by weight of zinc oxide excluding coarse particles of m or more and 20 parts by weight of methacrylic acid were mixed at the time of kneading and reacted in a polymer to form a zinc salt of methacrylic acid.

As the organic peroxide, α, α'-bis (t-butylperoxy-m-isopropyl) benzene was used.

A composition was prepared according to the formulation shown in Table 2. Specifically, first, the polymer is wound around a 6-inch roll whose surface temperature is set to 120 ° C., then zinc dimethacrylate powder (or zinc oxide and methacrylic acid) is kneaded, and then an organic peroxide is added. Kneaded and kneaded. The kneaded product was vulcanized by a press at 170 ° C. for 20 minutes to obtain a vulcanized sheet having a thickness of 2 mm.

In Comparative Example 1, carbon black was used as a reinforcing agent, and in Comparative Examples 6 to 7, no reinforcing agent was used. The results are shown in Table 1.

[0038]

[Table 1] Note (* 1) 5-ethylidene-2-norbornene

[0039]

[Table 2] Note (* 2) α, α'-bis (t-butylperoxy-m-isopropyl) benzene (* 3) Zinc oxide 15 parts by weight and methacrylic acid 20 parts by weight

As is clear from Table 2, the use of the composition of the present invention makes it possible to obtain a vulcanized product having excellent strength characteristics. In Examples 1 to 10, tensile strengths of 250 kg / cm ² or more, and in many cases 300 kg / cm ² or more are achieved.

On the other hand, when no reinforcing agent was added (Comparative Examples 6 to 7), only vulcanizates having low strength were obtained,
Even if carbon black is blended (Comparative Example 1), the tensile strength does not increase so much. When the composition ratio of the ethylene unit and the Mooney viscosity are out of the ranges of the present invention (Comparative Examples 2 to 5), even if zinc dimethacrylate is blended, a high-strength vulcanized product cannot be obtained. Furthermore, even when the blending ratio of zinc dimethacrylate is small (Comparative Example 8), the strength characteristics cannot be improved.

[0042]

According to the present invention, there is provided a polyethylene-based polymer composition which gives a vulcanizate of high strength. The composition of the present invention can be applied to many applications which cannot be applied to conventional EPMs and EPDMs due to insufficient strength, for example, belts, rolls, anti-vibration rubbers and tires requiring high strength.

Claims (1)

Claims (A) Mooney viscosity (ML _{1 + 4} , 100)
C) 10-70, 100 parts by weight of a polyethylene-based polymer containing 75 mol% or more of ethylene units, (B) 15-80 parts by weight of a metal salt of an ethylenically unsaturated carboxylic acid, and (C) an organic peroxide 0 The polyethylene-based polymer composition is characterized by containing 2 to 10 parts by weight.