JPH04255738A - Insulating composition and production thereof - Google Patents

Abstract

PURPOSE:To provide a method for producing an insulating polyolefin composition having good mechanical characteristics and not depositing on the surface of an insulated article, improved in heat resistance without accompanying the deposition of the composition on the surface of the insulated article and the lowering of the mechanical characteristics. CONSTITUTION:An insulating composition comprises (1) 100 pts.wt. of a polyolefin and (2) 5-100 pts.wt. of a cross-linked silicone rubber whose cross- linking reaction has been carried out in the polyolefin. A method for producing the insulating composition comprising the polyolefin and the cross-linked silicon rubber is characterized by mixing the polyolefin with the first and second components capable of forming the cross-linked silicone rubber, respectively, before their contact, and subsequently bringing both the components into contact with each other to form the cross-linked silicon rubber by the addition reaction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating composition and a method for producing the same, and more particularly to an insulating composition made of polyolefin with improved heat resistance and a method for producing the same.

0002

BACKGROUND OF THE INVENTION Polyolefins such as polyethylene and ethylene/acrylic acid copolymers have excellent mechanical and electrical properties and are therefore useful as materials for sheaths and insulators of cables and the like. Crosslinked polyolefins have also been used to improve the heat resistance of insulating materials. As an indicator of the heat resistance of insulating materials, the continuous use temperature is determined for each material. For example, polyethylene is 75 degrees Celsius.
, crosslinked polyethylene is said to be 90°C.

As will be described later, there is a need to improve the heat resistance of this type of insulated wire. A major problem regarding the heat resistance of polyolefins is that they undergo oxidative deterioration at high temperatures, and in order to prevent this oxidative deterioration, antioxidants are added. As the antioxidant, amine compounds, phenol compounds, sulfur compounds, etc. are used. On the other hand, blending or copolymerization with heat-resistant polymers such as silicone rubber is also being considered.

0004

[Problems to be Solved by the Invention] The heat resistance of conventional cross-linked polyethylene, which is approximately 90°C, cannot withstand the increase in wiring density due to the recent miniaturization of equipment and the rise in the allowable temperature of the atmosphere in which equipment is used. , is insufficient, and further improvement of heat resistance is required.

However, when polyolefins are used at high temperatures, they deteriorate due to oxidation due to oxygen in the atmosphere, resulting in decreased flexibility and brittleness, as well as decreased mechanical strength and electrical properties. The higher the temperature, the more significant the deterioration.

Conventionally, the addition of antioxidants to prevent oxidative deterioration has limited effectiveness, and when added in large amounts, crosslinking of polyolefins may be inhibited or the antioxidants may precipitate on the surface of insulators. , a so-called bleed (or bloom) phenomenon occurs. On the other hand, mere blending with a heat-resistant polymer for the purpose of improving heat resistance significantly reduces mechanical properties. Copolymerization with heat-resistant polymers has technical limitations and cannot be said to be a panacea.

[0007] Therefore, an object of the present invention is to improve the heat resistance of an insulating composition made of polyolefin without deterioration of mechanical properties or precipitation on the surface of the insulating material. Another object of the present invention is to realize a method for producing an insulating composition made of polyolefin, which has improved heat resistance, good mechanical properties, and does not involve precipitation on the surface of the insulator.

[0008]

[Means for Solving the Problems] In the insulating composition of the present invention, in order to improve the heat resistance of the insulating composition made of polyolefin without precipitation on the surface of the insulator or deterioration of mechanical properties, 100 parts by weight of polyolefin;
Insulating compositions were comprised of 5 parts by weight to 100 parts by weight of crosslinked silicone rubber in which the substantial crosslinking took place in the polyolefin.

[0009] The method for producing an insulating composition of the present invention is a method for producing an insulating composition made of polyolefin, which has improved heat resistance, good mechanical properties, and does not cause precipitation on the surface of an insulating material. In order to realize this, a first component and a second component (usually referred to as the first and second components of a two-component liquid silicone rubber) capable of forming a crosslinked silicone rubber are hereinafter simply referred to as the first component and the second component, respectively, for convenience. The second component) is mixed with the polyolefin before contacting them, and the first and second components are brought into contact in the presence of the polyolefin to form a crosslinked silicone rubber through an addition reaction. An insulating composition made of crosslinked silicone rubber was obtained. Divide the polyolefin raw material into two parts, add the first component to the first part and the second component to the second part, mix, and then mix each part with each other to form this three-component mixture. A crosslinked silicone rubber is formed by addition reaction of the first component and the second component under appropriate temperature and pressure, or the first component and the second component are mixed with the polyolefin,
It is preferable to further add a silicone graft acid-modified acrylic ester polymer to the mixture of these three components, and form a crosslinked silicone rubber by an addition reaction between the first component and the second component in the four-component mixture. Crosslinking of the first and second components takes place in the polyolefin by an addition reaction. When dividing the polyolefin into two parts, the division ratio is not limited to 1:1, but can be any suitable ratio such as 2:1.

In the present invention, polyolefin includes not only olefin homopolymers and copolymers, but also copolymers with other monomers that can be copolymerized with olefins. For example, polyethylene, polypropylene, ethylene
Propylene copolymer, ethylene propylene diene terpolymer, ethylene butene copolymer, ethylene butene diene terpolymer, ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, These are ethylene/ethyl acrylate copolymer and ethylene/methyl methacrylate copolymer. These can also be used in combination of two or more types. The polyolefin may be crosslinked to increase heat resistance.

[0011] In order to crosslink the polyolefin, a silane grafting method (also known as a silane water crosslinking method) is suitable, in which the polyolefin is grafted with silane and the silane grafted product is subjected to a crosslinking reaction in the presence of a catalyst. This reaction requires the presence of water (the silane graft is subjected to a silanol condensation reaction with water and crosslinked). Examples of the silane compounds used for silane grafting of each polymer include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, vinyltriacetoxysilane, and (γ-methacryloxypropyl)trimethoxysilane. Can be used. These can be grafted onto the polymer with peroxides such as dicumyl peroxide. In the case of diene polyolefin, methods such as sulfur crosslinking can be used.

As mentioned above, the first and second components capable of forming a crosslinked silicone rubber are usually called the first and second components of a two-component liquid silicone rubber. Generally, in two-component liquid silicone rubber, the first liquid component (the first component in the present invention) has a skeleton of siloxanes such as dimethylsiloxane, methylphenylsiloxane, diphenylsiloxane, etc., and has a hydrogen group at the terminal or side chain. a component of the second liquid (second component in the present invention)
is a compound having a vinyl group, and when the first liquid and the second liquid are brought into contact, a crosslinked silicone rubber is formed by an addition reaction between the first component and the second component. The first liquid and the second liquid are usually liquids having similar viscosities, and are often used as a mixture at a ratio of 1:1. The viscosity is determined by the molecular weight, and is adjusted to an appropriate viscosity depending on the purpose. The above addition reaction is usually carried out in the presence of a catalyst such as platinum, and the catalyst is usually included in the second component.

When polyolefin is crosslinked by the silane grafting method, the polyolefin is grafted with silane, the first component and the second component are added to the uncrosslinked state, the silicone rubber is crosslinked, and then the polyolefin is crosslinked. Crosslinking may also be performed. When adding the first and second components to the silane-grafted polyolefin, the silane-grafted polyolefin may be divided into two parts and the first and second components may be mixed (separately) into each part; The division ratio can be set to an appropriate ratio such as 1:1 or 2:1.

The amount of the two-component liquid silicone rubber (the total of the first component and the second component) is 5 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the polyolefin. If the amount is less than 5 parts by weight, sufficient heat resistance cannot be obtained. By controlling the amount to 100 parts by weight or less per 100 parts by weight of polyolefin, the mechanical properties of the coexisting polyolefin can be maintained.

The silicone-grafted acid-modified acrylic ester polymer is preferably one synthesized by the macromonomer method, and the amount added is based on the amount of the two-component liquid silicone rubber (total of the first and second components). The amount is preferably 1/100 or more by weight. If the amount is less than this, tensile properties such as tensile strength and elongation will deteriorate.

In addition to the above-mentioned components, the insulating composition of the present invention may also contain stabilizers, antioxidants, lubricants, flame retardants, fillers, reinforcing agents, colorants, and the like.

[0017]

[Function] In the insulating composition of the present invention, since the crosslinked silicone rubber is substantially crosslinked in the polyolefin, the crosslinked silicone rubber exists in an extremely finely dispersed state in the polyolefin, which improves mechanical properties. Improved heat resistance can be obtained without impairing electrical characteristics.

In the method for producing an insulating composition of the present invention, the first component and the second component capable of forming a crosslinked silicone rubber are mixed into the polyolefin before they come into contact with each other.
Crosslinked silicone rubber is dispersed extremely finely and uniformly in the polyolefin, thereby
An insulating composition with improved heat resistance can be produced without sacrificing mechanical or electrical properties. In one embodiment of the method for producing an insulating composition of the present invention, crosslinking of silicone rubber is performed independently prior to crosslinking of polyolefin, so that the resulting composition is not a co-crosslinked product of polyolefin and silicone rubber, but a blend. It is a polymer and probably has a polymeric network structure in which the molecular chains interpenetrate. Due to this structure, it is believed that improved heat resistance is achieved without deterioration of mechanical properties or precipitation of one component on the surface.

In another embodiment of the method for producing an insulating composition of the present invention, a silicone-grafted acid-modified acrylic ester polymer is added to a three-component mixture of a polyolefin, a first component, and a second component, and the comb-shaped In order to form a crosslinked silicone rubber by carrying out an addition reaction between the first component and the second component in the polyolefin in the presence of a polymer with a molecular structure, the first component and the second component have a compatibilizing effect in the polyolefin. The presence of the above-mentioned polymer with the above-mentioned properties allows for uniform dissolution or dispersion of the crosslinked silicone rubber, thereby creating an insulating composition with improved heat resistance without sacrificing mechanical or electrical properties. can be manufactured.

[0020] Examples are shown below to provide a more detailed explanation of the present invention.

[0021]

[Examples 1 to 4] Example 1 of the insulating composition of the present invention contains 100 parts by weight of an ethylene/vinyl acetate copolymer (vinyl acetate content: 28% by weight) crosslinked by a silane grafting method,
20 parts by weight of silicone rubber crosslinked in the coexistence of
1 part by weight of antioxidant, 1 part by weight of stearic acid, 2 parts by weight of talc
0 parts by weight, and 2 parts by weight of carbon black. Example 2 differs from Example 1 in that the crosslinked silicone rubber is
The amount was increased to 0 parts by weight. Example 3 is an ethylene/ethyl acrylate copolymer (ethyl acrylate content: 15% by weight) crosslinked by a silane grafting method.
0 parts by weight and silicone rubber crosslinked in the coexistence of 2
0 parts by weight and other additives as in Example 1. Example 2 differs from Example 1 in that the crosslinked silicone rubber is
The amount was increased to 0 parts by weight.

For example, the insulating composition of Example 1 is manufactured by the method described below. First, a base polymer was prepared according to the steps shown in the figure. In detail, using a Banbury mixer, a silane-grafted ethylene/vinyl acetate copolymer (vinyl acetate content: 28% by weight) 50
Parts by weight and two-component liquid silicone rubber liquid A were kneaded and further pelletized using a twin-screw kneader. This is called pellet A. Similarly, 50 parts by weight of silane grafted ethylene/vinyl acetate copolymer and 1 part of two-component liquid silicone rubber B solution
0 parts by weight is kneaded and pelletized, and this is made into pellet B.
shall be. Pellets A and B are further kneaded using a twin-screw kneader to form a base polymer. The two-component liquid silicone rubber solution A contains vinyl-terminated dimethylsiloxane and a platinum catalyst, and has a viscosity of 3100 ps (temperature 100 ps).
The two-component liquid silicone rubber solution B is a mixture of vinyl-terminated dimethylsiloxane and hydrogen-terminated dimethylsiloxane with a platinum catalyst added, and has a viscosity of 2600 ps (temperature 100°C).

[0023] 120 parts by weight of the base polymer, 1 part by weight of the antioxidant Irganox 1010 (trade name of Ciba Geigy, Switzerland), 1 part by weight of stearic acid, and 20 parts by weight of talc ("Mistron Vapa Talc", a product of Nippon Mistron). , 2 parts by weight of FEF carbon black was added, 80
Roll kneading was performed for about 10 minutes using 6-inch rolls maintained at a temperature of 110 to 110°C. After kneading, 100 kg/c
m2 to form a sheet with a thickness of 1 mm. This causes crosslinking of the silicone rubber. A thin layer of dibutyltin dilaurate is applied to the surface of the cross-linked silicone rubber sheet, wrapped loosely in aluminum foil, and held in a suitable container with water at the bottom so as not to come into direct contact with water. It was left at a temperature of 80°C for 24 hours. This results in
The ethylene/vinyl acetate copolymer is crosslinked. Example 2
Insulating compositions No. 4 to 4 were also prepared according to Example 1. Table 1 shows the components used to prepare the base polymer of each example (numbers are in parts by weight).

[0024]

Regarding the obtained sheet-like sample, heat resistance,
Flame retardancy and mechanical properties were evaluated by the following methods. As for mechanical properties, tensile strength, elongation, flexibility, and tear strength were measured. (1) Heat Resistance Using an aging tester according to JIS, samples are taken over time at a temperature of 180° C., and the time to reach 50% elongation is determined from a graph of changes in elongation with respect to time. (2) Tensile properties After being left in a constant temperature room at 20° C. for one day, it was punched out using a No. 3 dumbbell, and the tensile strength and elongation rate were measured using a Schopper tensile tester at a tensile speed of 500 mm/min. (3) Tear strength Measured according to JIS K7201 using a B-type sample using the same Schopper tensile tester as above at a tensile speed of 500 mm/min.

The evaluation results are shown in Table 2.

[0027]

[0028] As shown in Table 2, the insulating composition of the present invention has excellent heat resistance, as indicated by the time required to reach 50% elongation at a temperature of 180°C, exceeding 80 hours. Strength is 1.8kg/mm2 or more, elongation rate is 50
0% or more, tear strength is 50 kg/cm or more, and exhibits excellent mechanical properties. In addition, no bleeding was observed in either case.

[0029]

[Comparative Example 1] In Example 4, the amounts of liquid A and B of the two-component liquid silicone rubber were increased to 75 parts by weight each, and in the same manner as in Example 4, except for the preparation and evaluation of an insulating composition. I did it. The composition of the base polymer in this case is shown in Table 3 (
The evaluation results are shown in Table 4 (units are parts by weight). In addition, Table 4
The results of Example 4 are also shown at the same time.

[0030]

[0031]

As shown in Table 4, Comparative Example 1, in which the total amount of liquid A and B of the two-component liquid silicone rubber exceeds 100 parts by weight, has excellent heat resistance, but has poor tear strength. It has decreased considerably, and the tensile strength and elongation rate have also decreased slightly.

[0033]

[Comparative Examples 2 to 4] Comparative Example 2 is an insulation composition made only of ethylene/vinyl acetate copolymer crosslinked by a conventional silane grafting method, and Comparative Examples 3 and 4 are insulating compositions made of ethylene/vinyl acetate copolymer crosslinked with silane grafting. Conventional insulation compositions were prepared by blending already crosslinked silicone rubber with the polymer and the silane-grafted ethylene/ethyl acrylate copolymer, and crosslinking the olefin copolymer, and the compositions were prepared in Examples 1 to 4. It was evaluated using the same method. The composition of the base polymer is shown in Table 5, and the evaluation results are shown in Table 6.

[0034]

[0035]

As shown in Table 6, the heat resistance of Comparative Example 2, which is made of a crosslinked ethylene/vinyl acetate copolymer and does not contain silicone rubber, is significantly inferior. In addition, in Comparative Example 3, which was conducted using the conventional method of blending already crosslinked silicone rubber with the silane-grafted ethylene/vinyl acetate copolymer and crosslinking the olefin copolymer, the tensile strength and elongation rate decreased, Heat resistance is also considerably reduced. Comparative Example 4 is a conventional insulation composition made by blending silicone rubber with a silane-grafted ethylene/ethyl acrylate copolymer and crosslinking the former, but its heat resistance is not so good and its mechanical properties are poor. Significantly low.

[0037]

[Examples 5 to 8] The ingredients shown in Table 7 (numbers are in parts by weight) were mixed, kneaded for about 10 minutes in a Brabender kept at a temperature of 100°C and rotating at 50 revolutions per minute, and then rolled into a 6-inch roll. It was made into a sheet with a thickness of about 1 mm, and was heated to 100 kg/cm for about 10 minutes using a steam heating press heated to 180°C.
m2 to form a sheet with a thickness of 1 mm. This causes crosslinking of the silicone rubber. Silang-grafted EVA in Table 7 is a silane-grafted ethylene/vinyl acetate copolymer obtained by grafting 2% by weight of vinyltrimethoxysilane onto the same Evaflex 260 used in Example 1, and silane-grafted EEA is Example 3. Silane-grafted ethylene, which was made by grafting 2% by weight of vinyltrimethoxysilane to the same Lexron 1150A used in
The ethyl acrylate copolymer and the two-component liquid silicone rubber liquid A and B were the same as those used in Examples 1 to 4, and the silicone grafted acid-modified ethyl acrylate was Reseda GP-700 (Toagosei Kagaku Co., Ltd.) merchandise)
The antioxidant is Irganox 1010 (trade name of Ciba Geigy, Switzerland. The chemical structure is tetra[3-(3,5-
di-t-butyl-4-hydroxyphenyl)propionoxymethyl]methane).

[0038]

A thin layer of dibutyltin dilaurate was applied to the surface of the crosslinked silicone rubber sheet, and the mixture was wrapped loosely in aluminum foil and placed in a suitable container with water at the bottom.
It was kept at a temperature of 80° C. for 24 hours without coming into direct contact with water. As a result, the ethylene/vinyl acetate copolymer or the ethylene/ethyl acrylate copolymer is crosslinked.

[0040] Regarding the obtained sheet material, heat resistance,
Flame retardancy and mechanical properties were evaluated using the same methods as Examples 1-4. The evaluation results are shown in Table 8.

[0041]

As shown in Table 8, the insulating composition of the present invention has excellent heat resistance, as measured by the time required to reach 50% elongation at a temperature of 180°C, which is 80 hours or more. Strength is 1.8kg/mm2 or more, elongation rate is 50
0% or more, tear strength is 50 kg/cm or more, and exhibits excellent mechanical properties.

[0043]

[Comparative Examples 5-8] For comparison, mixtures having the compositions shown in Table 9 were treated in the same manner as in Examples 5-8. Comparative Example 5 uses a silane grafted product of ethylene/vinyl acetate copolymer, and omits both the two-component liquid silicone rubber and the silicone grafted acid-modified acrylic ester polymer;
Comparative Example 6 omitted the silicone-grafted acid-modified acrylic ester polymer, and Comparative Example 7 omitted the silicone-grafted acid-modified acrylic ester polymer, and Comparative Example 7 omitted the weight ratio of the silane-grafted ethylene/ethyl acrylate copolymer to the sum of the two-component liquid silicone rubber components A and B. 40:
60, and Comparative Example 8 had this ratio as 30:70, which is outside the scope of the present invention. Among these, Comparative Example 5 is a conventional insulation composition containing no crosslinked silicone rubber, in which an ethylene/vinyl acetate copolymer is co-crosslinked by a silane grafting method.

[0044]

Regarding the obtained sheet-like sample, heat resistance,
Flame retardancy and mechanical properties were evaluated using the same methods as Examples 1-4. The evaluation results are shown in Table 10.

[0046]

As shown in Table 10, the conventional insulation composition containing no crosslinked silicone rubber of Comparative Example 5 had a heat resistance of less than 50 hours, as measured by the time it takes to reach an elongation rate of 50% at a temperature of 180°C. , poor heat resistance. Comparative Example 6, which had almost the same composition as Example 6 (see Table 7) but omitted the silicone-grafted acid-modified acrylic ester polymer, had slightly higher tensile strength and elongation than Examples 5 or 6 (see Table 8). It is declining. Comparative Examples 7 and 8, in which the weight ratio of the silane-grafted polyolefin to the sum of the two-component liquid silicone rubber components A and B, are outside the invention range, have tensile strength and elongation percentage that are lower than those of Example 7 (see Table 8). The tear strength is also clearly lower. In particular, Comparative Example 8 in which the silicone-grafted acid-modified acrylic ester polymer was omitted.
has inferior tear strength.

From the above Examples and Comparative Examples, it is clear that the insulating composition of the present invention has excellent heat resistance and mechanical properties.

[0049]

According to the present invention, the heat resistance of an insulating composition made of polyolefin can be improved without deterioration of mechanical properties or precipitation on the surface of an insulating material.

Furthermore, according to the method for producing an insulating composition of the present invention, an insulating composition made of polyolefin that has improved heat resistance, good mechanical properties, and does not cause precipitation on the surface of an insulator can be produced. be able to.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a base polymer preparation process in an example of the present invention.

Claims (7)

[Claims] Claim 1: 100 parts by weight of polyolefin;
An insulating composition comprising from parts by weight to 100 parts by weight of a crosslinked silicone rubber in which substantial crosslinking has taken place in a polyolefin. 2. The insulating composition of claim 1, wherein the polyolefin is crosslinked. 3. In a method for producing an insulating composition comprising a polyolefin and a crosslinked silicone rubber, a first component and a second component capable of forming a crosslinked silicone rubber are each mixed with the polyolefin before contacting them, and the polyolefin is A method for producing an insulating composition, comprising bringing the first component and the second component into contact with each other in the presence of each other to form a crosslinked silicone rubber through an addition reaction. 4. A method for producing an insulating composition comprising a crosslinked polyolefin and a crosslinked silicone rubber, wherein a first component and a second component capable of forming a crosslinked silicone rubber are each mixed into an uncrosslinked polyolefin before contacting them. The first component and the second component are brought into contact with each other in the presence of the polyolefin to form a crosslinked silicone rubber through an addition reaction, and after the formation of the crosslinked silicone rubber, the polyolefin is crosslinked. A method for producing an insulating composition. 5. The insulating composition according to claim 3 or 4, wherein the total amount of the first component and the second component is 5 parts by weight to 100 parts by weight based on 100 parts by weight of the polyolefin. Production method. 6. Dividing the polyolefin into two parts, separately mixing the first component and the second component in each part, and mixing the separate mixtures with each other to bring the first component and the second component into contact. The method for producing an insulating composition according to any one of claims 3 to 5. 7. A method for producing an insulating composition comprising a crosslinked polyolefin and a crosslinked silicone rubber, wherein a total amount of 5 to 10 parts by weight is added to 100 parts by weight of the polyolefin.
0 parts by weight of a first component and a second component capable of forming a crosslinked silicone rubber are mixed, and the mixture of the polyolefin and the first component and the second component is further mixed with the first component and the second component. A silicone graft acid-modified acrylic ester polymer is added in an amount of 1/100 or more by weight of the total, and the first component and the second component are brought into contact in the presence of a polyolefin to form a crosslinked silicone rubber by an addition reaction. After forming and forming cross-linked silicone rubber,
A method for producing an insulating composition, comprising crosslinking the polyolefin.