JPH03212441A - Fluororesin composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition capable of preventing stickiness in an uncrosslinked state, excellent in strength after crosslinking and suitable for a heat-shrinkable tubing by blending a flexible fluororesin composition composed of fluororubbers and fluororesins with a specified amount of a specified silicone powder. CONSTITUTION:With 100 pts.wt. composition prepared by blending (A) one or more fluororubbers selected from vinylidene fluoride-hexafluoropropylene based copolymer rubbers, vinylidene fluoride-hexafluoropropylene- tetrafluoroethylene-based copolymer rubbers, etc., with (B) one or more fluororesins selected from polyvinylidene fluoride and copolymers of vinylidene fluoride and another fluoroolefin and having >=60 deg.C melting point in (1:1) to (4:1) weight ratio, (C) a powdery silicone mainly composed of polydimethylsiloxane and having <=5wt.% weight loss on heating at 400 deg.C is blended in an amount of 0.1-10 pts.wt., preferably 0.5-7 pts.wt.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a fluororesin composition that has excellent heat resistance and oil resistance and is non-adhesive. The present invention relates to a fluororesin composition having the following properties, which prevents stickiness in an uncrosslinked state and has excellent strength after crosslinking.

The fluororesin composition of the present invention is particularly useful as a heat-shrinkable tube.

[Prior Art] Fluororesin and fluororubber have excellent heat resistance and oil resistance, and are indispensable materials in the automobile and aircraft fields, which require high reliability under harsh conditions. Heat-shrinkable tubes used for various purposes such as protecting the terminals of electric wires are also in demand in these fields, and products made of fluorine-based polymers are already being used. Heat-shrinkable tubes made of such materials have been put into practical use.

In addition, if the flexibility of the heat-shrinkable tube made of such fluororesin is insufficient, a fluororesin composition that is a blend of fluororubber such as tetrafluoroethylene-propylene copolymer rubber and polyvinylidene fluoride resin may be used. It has been proposed to obtain a heat-shrinkable tube with excellent flexibility by forming a tube into a tube, crosslinking it, and then expanding it in the radial direction (Japanese Patent Laid-Open No. 61-25
Publication No. 8727).

However, the fluororesin composition, which is a blend of fluororubber and polyvinylidene fluoride resin, is sticky in an uncrosslinked state, and the pellets of the composition may stick together during storage, or the inner surfaces of extruded tubes may stick together. is so strong that it cannot be easily peeled off by external pressure (there are problems such as adhesion), making it virtually impossible to manufacture heat-shrinkable tubes.

As a method to prevent this stickiness, the present inventor has already developed
A method of adding a perfluoroalkyl sulfonate or a perfluoroalkyl carboxylate to a fluororesin composition has been proposed (Japanese Patent Application No. 1-7650).

According to this method, it is possible to prevent stickiness without impairing properties such as heat resistance and oil resistance, but if the amount added is large (the tensile strength tends to decrease, and high strength is required) There was a problem that the performance was not sufficient for use in the field.

[Problem to be solved by the invention]

An object of the present invention is to provide a flexible fluororesin composition made of fluororubber and fluororesin, which prevents stickiness in an uncrosslinked state and maintains the heat resistance and oil resistance inherent to the fluororesin composition. At the same time, the strength (tensile strength) of the crosslinked material
An object of the present invention is to provide a fluororesin composition with excellent properties.

As a result of intensive research to overcome the problems of the prior art, the present inventors have discovered that silicon powder with a thermal weight loss of 5% by weight or less at 400°C has been added to a flexible fluororesin composition consisting of fluororubber and fluororesin. It has been discovered that by blending a specific amount of , it is possible to prevent or significantly reduce tackiness when uncrosslinked, and to obtain a crosslinked molded product with excellent strength without reducing the tensile strength after crosslinking. .

The present invention has been completed based on these findings.

[Means for Solving the Problems] That is, according to the present invention, (A) vinylidene fluoride-hexafluoropropylene copolymer rubber, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer rubber, and at least one fluororubber selected from tetrafluoroethylene-propylene copolymer rubber; (B) polyvinylidene fluoride and a copolymer of vinylidene fluoride and other fluorinated olefin;
At least one type of fluororesin having a melting point of at least
100 parts by weight of a fluororesin composition blended in the range of ~4:1, containing (C) polydimethylsiloxane as the main component, and heated at 400°C.
Silicon powder with a thermal weight loss of 5% by weight or less in
．． There is provided a fluororesin composition characterized in that it contains 1 to 10 parts by weight.

The present invention will be explained in detail below.

[Fluororubber (A)] The fluororubber used in the present invention is a vinylidene fluoride-based rubber such as vinylidene fluoride-hexafluoropropylene copolymer rubber or vinylidene fluoride-hexafluoropropylene tetrafluoroethylene copolymer rubber. At least one fluororubber selected from rubber and tetrafluoroethylene-propylene copolymer rubber.

Typical vinylidene fluoride rubber is an elastomer in which monomer units are randomly bonded, obtained by emulsification or suspension polymerization of vinylidene fluoride and hexafluoropropylene, or with the addition of tetrafluoroethylene, using a radical initiator. It is readily available as a commercial product.

Tetrafluoroethylene-propylene copolymer rubber is typically obtained by low-temperature emulsion copolymerization of tetrafluoroethylene and propylene, and contains a copolymerizable monomer such as ethylene as the third component. , isobutylene, acrylic acid and its alkyl esters,
It may contain an appropriate amount of one or more of methacrylic acid and its alkyl esters, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, chloroethyl vinyl ether, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, and the like.

This tetrafluoroethylene-propylene copolymer rubber is also generally known and readily available as a commercial product.

[Fluororesin (B) 1 The fluororesin used in the present invention is a polyvinylidene fluoride-based resin such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and another fluorinated olefin,
It is a polymer with a melting point of ℃ or higher.

As other fluorinated olefins, tetrafluoroethylene and hexafluoropropylene are preferred from the viewpoint of processability, and the copolymerization ratio is usually 1 to 20 mol% in the copolymer.

When these vinylidene fluoride resins are used as a heat-shrinkable dupe, it is necessary to maintain the expanded diameter at room temperature, so it is necessary that the melting point is 60° C. or higher. A fluororesin having a melting point of less than 60° C. is not preferable because when the composition with fluororubber is made into a heat-shrinkable tube, natural shrinkage in diameter may occur at room temperature.

(Fluororesin composition) In the present invention, the at least one fluororubber (A)
and at least one type of fluororesin (B) in a weight ratio (A:B) of 1:1 to 4:1 to obtain a fluororesin composition.

In the resin composition, the proportion of fluororubber was 50% by weight (1:1
) By doing so, a crosslinked molded product with excellent flexibility can be obtained. However, if the proportion of fluororesin exceeds 80% by weight (4:L), the flexibility will be very excellent, but if the proportion of fluororesin is less than 20% by weight, it will not be possible to mold it into a heat-shrinkable tube. , there is a problem that heat setting becomes insufficient.

Silicon powder having the following specific physical properties is added to the fluororesin composition of the present invention in a specific proportion.

[Silicon powder (C)]

The silicon powder used in the present invention is a silicon powder whose main component is polydimethylsiloxane and whose thermal weight loss at 400°C is 5% by weight or less. By adding this silicon powder, the inherent heat resistance of the fluororesin composition is improved. Can prevent tackiness without adversely affecting oil resistance. moreover,
There is no initial decrease in tensile strength.

If the thermal weight loss at 400°C exceeds 5% by weight, an anti-adhesive effect can be obtained, but the initial tensile strength and 250°C
Tensile strength decreases after heat aging test. The preferable range of thermogravimetric loss at 400° C. is 3% by weight or less.

The amount of silicon powder added is 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the fluororesin composition.
7 parts by weight.

If it is less than 0.1 part by weight, the fluororesin composition will not have a sufficient anti-tackiness effect, and if it exceeds 10 parts by weight, properties such as heat resistance will tend to deteriorate.

Note that thermogravimetric loss in the present invention refers to thermogravimetric analysis (
It is the weight loss rate [(x-y)8 x too] of the weight (y) at 400°C with respect to the initial weight (x) measured at a heating rate of 15°C/min under a nitrogen atmosphere.

(Crosslinking method, additives, etc.) As a crosslinking method for the fluororesin composition of the present invention, there are methods using chemical crosslinking agents and methods using ionizing radiation. It is advantageous to crosslink by means of energetic ionizing radiation.

In order to increase the crosslinking efficiency, a polyfunctional monomer such as triallyl cyanurate or triallyl isocyanurate may be added as a crosslinking promoter to the fluororesin composition of the present invention. Further, in order to capture hydrogen fluoride generated when exposed to high temperatures, an acid scavenger such as zinc oxide, magnesium oxide, or lead oxide may be added and used. Furthermore, various general-purpose additives such as colorants and other inorganic fillers may be added as desired.

(Applications) The fluororesin composition of the present invention can be used in various applications such as heat-shrinkable tubes, gaskets, backings, and hoses by taking advantage of its excellent properties such as heat resistance, oil resistance, and chemical resistance. I can do it. Among these, it can be particularly suitably used as a heat-shrinkable duplex used for insulation purposes.

In particular, since the fluororesin composition of the present invention has excellent tensile strength, it can be used satisfactorily even in fields where high strength is required.

[Example 1] Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited only to these Examples.

[Examples 1 to 3] Each component was mixed according to the formulation of Examples 1 to 3 shown in Table 1 to form a pellet.

The thermal weight loss of the silicon powder used in the examples was 2% by weight.

Stack these pellets to a thickness of 30 cm and heat to 40°C.
When I left it for 24 hours, no blocking of the beret occurred at all.

Next, this pellet was formed into a tube with an inner diameter of 20 mm and a wall thickness of 1.5 mm using an extruder, and then 10 kg
/crr? Forcibly crushed with pressure.

The inner surfaces of the tubes were kept in complete contact with each other for 10 minutes. When the crushed tube was taken out and the degree of adhesion on the inner surface was examined, it was found that there was almost no adhesion and that it could be easily restored to its original cylindrical shape.

Furthermore, after crosslinking this tube by irradiating it with an electron beam of 10 Mrad, the tensile strength was measured, and the result was 1.
5kg/mrr? The results were very good.

Furthermore, when the tensile strength retention rate was examined when heat aging was performed at 250° C. for 168 hours, the retention rate was all 80% or more in the tubes of Examples 1 to 3, and the heat resistance was good.

[Comparative Examples 1 to 4] In the same manner as Examples 1 to 3, pellets were prepared using the formulations of Comparative Examples 1 to 4 based on the formulations shown in Table 1, and the state of blocking was examined in the same manner. However, the lower layer of the pellet of Comparative Example 1 to which no silicon powder was added was completely blocked, and could not be fed to the extruder as it was.

Furthermore, tubes with the compositions of Comparative Examples 1 to 4 (inner diameter 2
0 mm and wall thickness of 1.5 mm), and the adhesion of the inner surface was examined in the same manner as in the example.

The inner surface of the tube of Comparative Example 1 was in close contact with each other, and it was difficult to restore the tube to its original cylindrical shape.

Silicon powder with a thermal weight loss of 45% by weight at 400℃ (
Comparative Example 2), perfluoroalkyl carboxylate (Comparative Example 3), and perfluoroalkyl sulfonate (Comparative Example 4) were added to the fluororesin composition, and almost no blocking of the pellet or adhesion to the inner surface of the tube occurred. However, after crosslinking these tubes with a 10 Mrad electron beam, the tensile strength is 1.0 to 1.3 kg/mry? It was about 20% or more lower than that of the example.

From the above results, the fluororesin composition of the present invention is excellent in the blocking resistance of pellets and the effect of preventing inner surface adhesion of tubes, and has no decrease in tensile strength after crosslinking. It can be seen that when silicon powder, perfluoroalkyl carboxylate, or perfluoroalkyl sulfonate which is outside the scope of the invention is added, although there is an effect of preventing tackiness, the tensile strength after crosslinking is not sufficient.

Table 1 shows the formulation, blocking resistance, and heat aging test results.

(The following is a blank space) [Effects of the Invention] According to the present invention, it is possible to obtain a flexible fluororesin composition that prevents or significantly reduces tackiness when uncrosslinked without reducing the tensile strength after crosslinking. can.

The fluororesin composition of the present invention can be used in fields requiring high strength, and can be particularly suitably used as heat-shrinkable tubes.

Claims (1)

[Claims] (1) (A) selected from vinylidene fluoride-hexafluoropropylene copolymer rubber, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer rubber, and tetrafluoroethylene-propylene copolymer rubber at least one fluororubber; (B) selected from polyvinylidene fluoride and copolymers of vinylidene fluoride and other fluorinated olefins;
At least one type of fluororesin having a melting point of ℃ or higher, and the weight ratio of fluororubber (A) to fluororesin (B) is 1:1.
100 parts by weight of a fluororesin composition blended in the range of ~4:1, containing (C) polydimethylsiloxane as the main component, and heated at 400°C.
Silicon powder with a thermal weight loss of 5% by weight or less in
．． A fluororesin composition comprising 1 to 10 parts by weight.