JPS63278955A - Production of crosslinked molding of fluorine-containing elastomer - Google Patents

Abstract

PURPOSE:To produce the title molding excellent in mechanical strengths and flexibility, by molding a mixture of two specified copolymers both of which contain fluorine and crosslinking the obtained molding by irradiation with an ionizing radiation. CONSTITUTION:A mixture of a copolymer of tetrafluoroethylene with a 2-4C alpha-olefin (e.g., tetrafluoroethylene/propylene copolymer) with a copolymer of crystallinity >=5%, prepared by copolymerizing vinylidene fluoride with a fluoromonomer (e.g., vinylidene fluoride/fluoroethylene copolymer), is molded into a predetermined shape, and the obtained molding is crosslinked by irradiation with an ionizing radiation. A decrease in the mechanical strengths and heat resistance due to irradiation with an ionizing radiation can be prevented, so that a crosslinked molding of a fluorine-containing elastomer excellent in mechanical strengths and flexibility can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to tetrafluoroethylene and a
- It relates to a method for producing a crosslinked fluorine-containing elastomer molded product mainly composed of a copolymer with an olefin.

[Prior art] A copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms, especially a tetrafluoroethylene-propylene copolymer, has properties such as heat resistance, oil resistance, chemical resistance, electrical insulation, etc. Because of its excellent properties, it is a material that is highly expected to be applied to hoses, tubes, heat-shrinkable tubes, gaskets, gaskets, diaphragms, sheets, electrical insulation coatings, etc.

Crosslinking of this copolymer is usually carried out by adding a chemical crosslinking agent, molding it into a predetermined shape, and then holding it in a heated atmosphere, but this poses problems in terms of production efficiency because the crosslinking time is relatively long. be.

For this reason, crosslinking by irradiation with ionizing radiation such as electron beams is being considered.

[Problems to be Solved by the Invention] However, there is a problem in that the crosslinked molded product obtained by irradiation with ionizing radiation does not have sufficient mechanical properties such as tensile strength and heat resistance.

An object of the present invention is to provide a method for producing a crosslinked fluorine-containing elastomer molded article that can suppress deterioration in mechanical strength and heat resistance due to irradiation with ionizing radiation.

[Means for solving the problems] The method for producing a crosslinked fluorine-containing elastomer molded article of the present invention includes:
A copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms, vinylidene fluoride, and at least a fluoromonomer selected from fluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, hexafluoroisobutylene, etc. It is characterized in that a mixture containing a copolymer with a degree of crystallinity of 5% or more is formed into a predetermined shape, and then crosslinked by irradiation with ionizing radiation.

In the present invention, the α-olefin having 2 to 4 carbon atoms that exhibits elastomeric properties by copolymerizing with tetrafluoroethylene includes propylene and butene-1 alone, and two types selected from ethylene, propylene, butene-1, and isobutyne. Although the above combinations are exemplified, propylene is preferred in order to achieve the purpose of the present invention.

Tetrafluoroethylene-propylene copolymers can be crosslinked by the action of a peroxide crosslinking agent with little ionic impurity remaining after crosslinking, and have excellent dielectric properties. The tetrafluoroethylene-propylene copolymer includes, in addition to the main components tetrafluoroethylene and propylene, components copolymerizable with these,
For example, ethylene, butene-11 isobutyne, acrylic acid and its alkyl esters, methacrylic acid and its alkyl esters, vinyl butylene, vinylidene butyrate, hexafluoropropene, chloroethyl vinyl ether, glycidyl vinyl ether, chlorotrifluoroethylene, perfluoroalkyl It may also contain vinyl ether or the like as appropriate.

The tetrafluoroethylene-propylene copolymer is desirably selected from the viewpoint of heat resistance, moldability, etc., with a molar ratio of tetrafluoroethylene/propylene in the range of 9515 to 30/70, particularly preferably 90/10. ~4
It is 5155. Further, the content of components other than the main component, which may be added as appropriate, is desirably selected from a range of 50 mol% or less, particularly 30 mol% or less.

The number average molecular weight of the tetrafluoroethylene-propylene copolymer is preferably from 20,000 to 150,000 in terms of extrudability and mechanical strength; if the number average molecular weight is too large, cracks will easily occur in the molded product. On the other hand, if it is too small, the mechanical strength tends to be insufficient. In this case, the number molecular weight can be adjusted directly by manipulating copolymerization reaction conditions such as monomer concentration, polymerization initiator concentration, monomer to polymerization initiator ratio, polymerization temperature, and use of chain transfer agents. This can be carried out by adjusting the molecular weight, or by producing a high molecular weight copolymer during the copolymerization reaction, and reducing the molecular weight by heating the copolymer in the presence of oxygen.

In the present invention, the copolymer of vinylidene buttride and fluoromonomer must have a degree of crystallinity of 5% or more, and if it is less than 5%, the effect of improving strength will be small. The amount of fluoromonomer to make the degree of crystallinity less than 5% is usually in the range of 2 to 10 mol%. Specific examples of fluoromonomers include fluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and hexafluoroisobutylene.

The content weight ratio of tetrafluoroethylene-α-olefin copolymer/vinylidene fluoride-fluoromonomer copolymer is selected from the range of 9515 to 40/60, considering the mechanical strength and flexibility of the resulting molded product. It is preferable that the content of the vinylidene buttomide-fluoromonomer copolymer is too small, and the effect of improving mechanical strength will be small.
If the amount is too large, heat resistance tends to be impaired.

Melt blending of the tetrafluoroethylene-α-olefin copolymer and the vinylidene fluoride-fluoromonomer copolymer is performed by adding a powder of the latter to the former at a temperature below its melting point, e.g.
100. The mixture may be kneaded with rolls or a panburi mixer at a temperature of 0.9C, and then molded at a temperature higher than the melting point of the latter, or may be kneaded in advance using a roll, panburi mixer, extruder, etc. at a temperature higher than the melting point of the latter.

In the present invention, it is preferable to add a crosslinking aid to increase crosslinking reactivity. Examples of crosslinking aids include allyl-type compounds, sulfur, organic amines, maleimides, methacrylates, divinyl compounds, polybutadiene, etc. Allyl-type compounds represented by triallyl isocyanurate and triallyl cyanurate are particularly useful. preferable.

In the present invention, in addition to the above components, calcium oxide,
Metal oxides such as magnesium oxide and lead oxide; metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide; metal carbonates such as calcium carbonate, lead carbonate, and aluminum carbonate; Various inorganic fillers such as carbon black, aluminum silicate, and silicic anhydride, and other additives such as stabilizers, pigments, antioxidants, and plasticizers can be blended.

[Embodiments of the invention] Various ingredients were mixed according to the formulations shown on each side of Table 1.
A mixture was prepared by kneading for 10 minutes with a roll set to .

This mixture was heated using a press at 200°C with a cage pressure of 15%.
A crosslinked sheet was produced by forming a sheet with a thickness of 1 mm under the conditions of 01 cg/Cm2 and irradiating it with an electron beam of 3 Mrad.

The results of measuring the tensile strength of this crosslinked sheet are shown in the lower column of Table 1.

In addition, the above mixture was added to the head: 200°C, cylinder 1
: 195°C 1 cylinder 2 : Introduced into a 40m/m extruder (L/D=22) set at 180°C, with an outer diameter of 1
．． 6mm copper conductor (tin plated copper wire) with insulation thickness of 0.6m
After coating with M, the wire was irradiated with an electron beam of 5 M r a d to produce a crosslinked insulated wire.

The results of measuring the tensile strength and deflection of the crosslinked insulated wire are shown in the lower column of Table 1. To measure the amount of deflection, cut the wire into a length of 50 mm, fix one end, and attach 100 mm to the other end.
This was done by applying a load of g.

Examples 1 to 5 within the scope of the present invention all have excellent mechanical strength (tensile strength) and sufficient flexibility for practical use (
A crosslinked molded body having a deflection amount) is obtained.

Comparative Example 1 is a case where the crystallinity of the vinylidene fluoride-fluoromonomer copolymer is outside the specified value of the present invention, and Comparative Example 2 is a case where the vinylidene fluoride-fluoromonomer copolymer is not contained. Poor mechanical strength and flexibility.

[Effects of the Invention] As explained above, the present invention provides a method for producing a mixture containing a copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms and a copolymer of vinylidene butyrate and a fluoromonomer. The present invention provides a method for producing a crosslinked molded body, which makes it possible to realize a fluorine-containing elastomer crosslinked molded body with excellent mechanical strength and flexibility.

Claims (3)

[Claims] (1) A mixture containing a copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms and a copolymer of vinylidene fluoride and a fluoromonomer with a crystallinity of 5% or more is specified. 1. A method for producing a crosslinked fluorine-containing elastomer molded article, which comprises molding it into a shape and then crosslinking it by irradiating it with ionizing radiation. (2) The method for producing a crosslinked fluorine-containing elastomer molded article according to claim 1, wherein the α-olefin is propylene. (3) The method for producing a crosslinked fluorine-containing elastomer molded article according to claim 1, wherein the fluoromonomer is at least one selected from fluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and hexafluoroisobutylene. .