JP2727670B2 - Method for producing crosslinked molded article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a crosslinked molded article having heat resistance and excellent flexibility, and also having flame retardancy and useful as an electric wire insulating material. It relates to a manufacturing method.

[Prior Art] Chlorinated polyethylene is produced by partially replacing a hydrogen atom of polyethylene with a chlorine atom, and is generally produced by a suspension chlorination method of polyethylene by a medium-low pressure method. It is.

Depending on the structure, molecular weight, etc. of polyethylene as a raw material,
Depending on the chlorine content, the distribution of bound chlorine, and the presence or absence of remaining crystals, a wide range of physical properties ranging from hard plastic to rubber can be obtained.

In addition, because it is a halogen-based polymer having no double bond in the main chain, it has weather resistance, ozone resistance, flame retardancy, impact resistance,
It has many excellent properties such as chemical resistance and oil resistance.

For this reason, chlorinated polyethylene has attracted attention as a material for electric wires and cables, and is often used as an alternative to polychloroprene rubber or chlorosulfonated polyethylene as a sheath material due to its electrical characteristics. It is used effectively as a material.

Furthermore, when viewed as a flame-retardant material, it exhibits excellent flame-retardant properties due to the halogen content, and is promising as a material that can be used in various flame-retardant tests required for recent wire and cable materials. Have been.

On the other hand, ethylene vinyl acetate copolymer is produced by the high pressure radical polymerization method like other ethylene copolymers,
Two types of apparatuses for this purpose are known, an autoclave and a tubular reactor. Such a method for producing an ethylene copolymer using a high-pressure polymerization method was first announced by ICI in 1938.

The primary purpose of copolymerizing ethylene with another vinyl monomer is to introduce the disadvantages of polyethylene being non-polar by introducing materials with these polarities, such as transparency, flexibility, as well as printability and adhesiveness. The same applies to the case of ethylene vinyl acetate because it is intended to impart physical properties.

However, the yield point of the ethylene-vinyl acetate copolymer is not clear like PVC and rubber. This is a characteristic of the polymer having a high entropic elasticity, and this tendency increases with an increase in the copolymerization amount of the comonomer, so that the polymer has properties that are rich in flexibility and excellent in toughness.

For this reason, even in the low-temperature characteristics, the glass transition temperature is -30 to -50 ° C, and the material has good low-temperature flexibility and low brittleness. The electrical properties tend to slightly decrease as the vinyl acetate content increases, but they can be said to be generally excellent. However, from the viewpoint of flame retardancy, there is a disadvantage that it is considerably inferior to the chlorinated polyethylene described above.

Therefore, by blending the two by taking advantage of the above-mentioned excellent properties of both, and by cross-linking the blend, it is possible to obtain a material having good properties as both an insulating material and a sheath material. It is possible to obtain a material which is very flexible and has flame retardancy, oil resistance, heat resistance and good electrical properties.

[Problems to be Solved by the Invention] The crosslinked product of the blend of chlorinated polyethylene and ethylene-vinyl acetate copolymer described above does not have a generally defined continuous use temperature, but it is about 105 ° C. Electric wires using this material as a coating material have been widely used as lead wires for motors, vehicles, and the like.

However, due to the recent trend of miniaturization and precision of equipment, the temperature rise due to dense wiring of wires or the allowable temperature of the atmosphere in which equipment is used has become remarkable, and higher heat resistance than the above temperature range is required. It has come to be.

To address these higher heat resistance requirements,
Up to now, addition of an antioxidant or blending or copolymerization with a heat-resistant polymer (for example, silicone rubber) has been studied.

However, measures against the antioxidant have their own limits, and when they are compounded in a multiplexed manner, cross-linking inhibition occurs and a so-called bloom phenomenon that precipitates on the surface during use is not preferable.

In addition, although a method of blending silicone rubber or the like is effective in improving heat resistance by simple blending, there is a problem that mechanical properties are significantly reduced, and thus expected properties are not always obtained.

An object of the present invention is to provide a novel chlorinated polyethylene and ethylene vinyl acetate which can solve the above-mentioned problems of the prior art and can effectively improve heat resistance without adversely affecting other properties such as mechanical properties. An object of the present invention is to provide a method for producing a crosslinked molded article made of a copolymer.

[Means for Solving the Problems] The method for producing a crosslinked molded article of the present invention comprises a polymer blend 100 comprising 20 to 60% by weight of a silane-grafted chlorinated polyethylene and 80 to 40% by weight of a silane-grafted ethylene-vinyl acetate copolymer. A total of 10 to 100 parts by weight of a two-component silicone rubber capable of addition and cross-linking in the presence of a platinum compound is blended with respect to parts by weight, and the polymer blend is cross-linked by contacting with water in the presence of a silanol condensation catalyst. At the same time, the two-component silicone rubber is crosslinked by heating.

In chlorinated polyethylene, chlorine content, the presence or absence of crystals,
There are various grades depending on the molecular weight, molecular weight distribution and the like, but the grade is not particularly limited in the present invention.

Similar to chlorinated polyethylene, ethylene vinyl acetate copolymer also has various grades depending on the molecular weight, molecular weight distribution, vinyl acetate content, and the arrangement on the molecular chain.
Although not specified, the vinyl acetate content is preferably in the range of 10 to 45% by weight.

The blending ratio of these is 20 to 60% by weight of chlorinated polyethylene and 80 to 80% of ethylene vinyl acetate copolymer.
When the blend amount of the chlorinated polyethylene is 20% by weight or less, the flame retardancy is poor, and when it is 60% by weight or more, sufficient flexibility cannot be obtained.

The blend of these two polymers is crosslinked by a silane grafting method that can cause a crosslinking reaction by contact with moisture in the presence of a silanol condensation catalyst (eg, dibutyltin dilaurate). Examples of the silane compound to be grafted on the polymer include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, vinyltriacetoxysilane, and γ-methacryloxypropyltrimethoxysilane. These can be grafted to the polymer with a peroxide such as dicumyl peroxide.

The two-component liquid silicone rubber has a skeleton of dimethylsiloxane, methylphenylsiloxane, diphenylsiloxane, etc., and an addition reaction between a component having a hydrogen group at a terminal or a side chain and a component having a vinyl group in the presence of a platinum compound. This is a type of cross-linking. These two components generally have approximately the same viscosity and are often mixed at a ratio of 1: 1. The viscosity, that is, the molecular weight, can be variously changed depending on the purpose.

The reason that the mixing amount of the two-component liquid silicone rubber is limited to the range of 10 to 100 parts by weight with respect to 100 parts by weight of the polymer blend is that the desired heat resistance cannot be imparted at 10 parts by weight or less. If the content exceeds 100 parts by weight, the tear strength decreases.

In addition to the above components, stabilizers, antioxidants, lubricants, flame retardants, fillers, reinforcing agents, coloring agents, and the like can be added.

[Action] A predetermined amount of a two-component liquid silicone rubber is blended with a polymer blend composed of a silane-grafted chlorinated polyethylene and a silane-grafted ethylene-vinyl acetate copolymer, and the polymer blend is mixed with water in the presence of a silanol condensation catalyst. And the two-component silicone rubber is cross-linked by an addition reaction, whereby the cross-linking reaction of the polymer blend and the cross-linking reaction of the silicone rubber are performed separately, and the cross-linked product of the polymer blend and the silicone rubber are A polymer network structure in which the crosslinked body and the crosslinked body interpenetrate is formed, whereby the tear strength and the tensile properties are improved, and at the same time, the effect of improving the heat resistance is exhibited.

[Example] Hereinafter, the present invention will be described with reference to examples.

A test material having the composition shown in each of Examples and Comparative Examples in Table 1 was kneaded with a B-type Banbury mixer for about 10 minutes, and then formed into a sheet having a thickness of about 1 mm with a 6-inch roll.
The sheet was pressed for 10 minutes by a press maintained at a temperature of 10 ° C. to form a sheet having a thickness of 1 mm. During the pressing, the two-component liquid silicone rubber was crosslinked (addition reaction of liquid silicone).

Further, after lightly applying dibutyltin dilaurate to the sheet surface, wrap it lightly in aluminum foil, and hold it in a suitable container filled with water at the bottom so that it is not directly immersed in water.
For 24 hours to crosslink the blend of chlorinated polyethylene and ethylene-vinyl acetate copolymer to prepare a crosslinked sheet.

About the crosslinked sheet produced in the examples and comparative examples,
Heat resistance, oxygen index (flame retardancy), tensile properties, flexibility (100
% Modulus) and tear strength, and the results are shown in the lower column of Table 1. Each evaluation method is as follows.

Heat resistance: Using an aging tester of JIS type maintained at 180 ° C., a graph was prepared by plotting the elongation and time at several points over time, and the time to reach 50% elongation was determined from this graph.

Oxygen index (flame retardancy): Measured in accordance with JIS K7201 Tensile properties: Measured at a constant temperature of 20 ° C. for one day, then punched out with a dumbbell No. 3, and measured at a speed of 500 mm / min using a Shopper type tensile tester.

Flexibility: 100% modulus in the above tensile properties was measured. A value of 0.5 kg / mm ² or less was used as a measure of flexibility.

Tear strength: Measured at a speed of 500 mm / min with a shopper type tensile tester similar to the above using a B-type sample in accordance with JIS K6301.

(1) 2% vinyltrimethoxysilane graft on Eraslen 401A (Showa Denko) (2) 2% vinyltrimethoxysilane graft on Eraslen 351A (Showa Denko) (3) Evaflex 260 (Mitsui DuPont Chemical) 100
(4) Hydrogen-terminated dimethylsiloxane: viscosity 3,100 poise (at 100 ° C) (5) Vinyl-terminated dimethylsiloxane: viscosity 2,400 poise (at 100 ° C) (containing platinum compound) (6) Teibakis [methylene-3] manufactured by Ciba-Geigy Corporation
(3,5-di-t-butyl-4-hydroxy-phenyl)
Propionate] methane The heat resistance of the conventional chlorinated polyethylene / ethylene-vinyl acetate copolymer blend is about 60 hours, as shown in Comparative Example 1, while the heat resistance is shown in Examples.
All of the samples No. 1 to No. 4 exhibit excellent heat resistance and at the same time, have substantially the same tensile properties as those of the silicone rubber non-blend system shown in Comparative Example 1.
This is probably because the blend and the silicone rubber were separately crosslinked to form an interpenetrating polymer network structure. On the other hand, when looking at the comparative examples, it can be seen that chlorinated polyethylene No. 2 in which the chlorinated polyethylene exceeds the range specified by the present invention is inferior in flexibility. Further, in No. 3 in which chlorinated polyethylene was not blended, the oxygen index indicating the measure of flame retardancy was low, and the self-extinguishing property was lost. Further, in No. 4, the amount of the liquid silicone rubber added exceeded the range of the present invention, and as a result, the tear strength was significantly reduced.

[Effects of the Invention] As described above, according to the present invention, a cross-linked molded article capable of maintaining flexibility and significantly improving heat resistance without reducing mechanical properties such as tensile strength and tear strength. The present invention can further enhance the industrial utility of wire and cable coating materials that are increasingly used at high temperatures.

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Claims (1)

(57) [Claims] 1. A silane-grafted chlorinated polyethylene 20 to 60.
Weight percent and silane-grafted ethylene vinyl acetate copolymer 80
For 100 parts by weight of a polymer blend consisting of ~ 40% by weight,
A total of 10 to 100 parts by weight of a two-component silicone rubber capable of addition and crosslinking in the presence of a platinum compound is blended, the two-component silicone rubber is crosslinked by an addition reaction, and then the polymer blend is subjected to the presence of a silanol condensation catalyst. A method for producing a crosslinked molded article, wherein the crosslinked article is crosslinked by contacting with moisture underneath.