JPH0236136B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a crosslinked molded article made of a fluorine-containing elastomer, particularly a copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms. Tetrafluoroethylene and α- having 2 to 4 carbon atoms
Copolymers with olefins, especially tetrafluoroethylene-propylene copolymers, have excellent heat resistance, oil resistance, chemical resistance, electrical insulation properties, etc., so they can be used for hoses, tubes, heat-shrinkable tubes, gaskets, etc. It is a material that is highly expected to be applied to packings, diaphragms, sheets, wire coatings, etc. Crosslinking of such a copolymer is usually carried out by adding a chemical crosslinking agent, molding it into a predetermined shape, and then heating it at high temperature, but this poses a problem in terms of manufacturing efficiency because the crosslinking time is relatively long. For this reason, crosslinking by irradiation with ionizing radioactivity such as electron beams has been considered, but in this case, the resulting molded product does not have sufficient mechanical strength such as tensile strength, and Experiments conducted by the present inventors have revealed that there are limits to its use in this field. As a result of various studies aimed at improving the strength of such copolymers, the present inventors discovered that mixing polyvinylidene fluoride is extremely effective, leading to the present invention. In particular, the present invention was found to be highly effective in producing long extruded products such as electric wires and tubes. Thus, an object of the present invention is to provide a manufacturing method that can prevent a decrease in mechanical strength of a fluorine-containing elastomer molded article due to ionizing radiation irradiation. In the present invention, carbon atoms having 2 to 4 carbon atoms are copolymerized with tetrafluoroethylene to exhibit elastomer properties.
The α-olefins include propylene and budene-1 alone, as well as ethylene, propylene,
Examples include combinations of two or more selected from budene-1 and isobutene, but propylene can be preferably used to achieve the purpose of the present invention. The tetrafluoroethylene-propylene copolymer suitable for the present invention includes, in addition to the main components tetrafluoroethylene and propylene, components copolymerizable with these, such as ethylene, butene-1, isobutene, acrylic acid, and alkyl esters, methacrylic acid and its alkyl esters, vinyl fluoride, vinylidene fluoride, hexafluoropropene, chloroethyl vinyl ether,
It may contain glycidyl vinyl ether, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, etc. as appropriate. In such a copolymer, the molar ratio of tetrafluoroethylene/propylene is 95/5 to 95/5.
It is preferable to select from the range of 30/70, especially from 90/10 to 45/55, from the viewpoint of heat resistance, moldability, etc., and the content of components other than the main component, which may be added as appropriate, is usually 50 mol%. Below, it is particularly preferable to select from a range of 30 mol% or less. The number average molecular weight of such a copolymer is preferably 20,000 to 150,000 from the viewpoint of extrudability and mechanical strength. If the number average molecular weight is too large, cracks will easily occur in the molded product, while if it is too small, cracks will easily occur in the molded product. Mechanical strength tends to be insufficient. In the present invention, polyvinylidene fluoride is not particularly specified, but it is preferably one having a molecular weight in the range of tens of thousands to hundreds of thousands from the viewpoint of the balance between strength and processability. Tetrafluoroethylene and α- having 2 to 4 carbon atoms
The weight ratio of copolymer with olefin/vinylidene polyfluoride is preferably selected from the range of 95/5 to 40/60, considering the mechanical strength and flexibility of the molded product obtained. If the content of vinylidene is too low, there will be no improvement in mechanical strength, and if the content is too high, the copolymer will lose its original characteristic of flexibility. Melt blending of the copolymer and polyvinylidene fluoride is performed by kneading the copolymer with polyvinylidene fluoride powder at a temperature below its melting point, for example, 50°C to 150°C, using a roll or a Banbury mixer. The above may be used for molding, or the two may be kneaded in advance using a roll, Banbury, or extruder at a temperature higher than the melting point of the pinylidene polyfluoride. In the present invention, it is also possible to incorporate a crosslinking aid in order to enhance the radiation crosslinking reactivity. Examples of crosslinking aids include allyl compounds, sulfur, organic amines, maleimides, divinyl compounds, methacrylates, polybutadiene, and allyl compounds represented by triallyl isocyanurate and triallyl cyanurate are particularly preferred. Compounding agents other than the above include 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, and to improve processability. carbon black, aluminum silicate, magnesium silicate,
Examples include inorganic fillers such as silicic anhydride, other stabilizers, antioxidants, and plasticizers. Examples of the present invention will be described below along with comparative examples. Add various ingredients according to the amounts shown in each example in Table 1.
The mixture was mixed uniformly by kneading at 200°C for 10 minutes using a roll. Press this at 200℃ and gauge pressure 150.
Formed into 1mm thick sheets under Kg/cm ² conditions, these
A crosslinked sheet was obtained by irradiation with an electron beam of 3 Mrad. Table 1 shows the results of measuring the tensile strength of the crosslinked sheet thus obtained. In addition, various ingredients were added according to the amounts shown in each example in Table 1, head: 200°C, cylinder 1: 195°C,
Cylinder 2: The mixture was introduced into a 40 m/m extruder (L/D=22) set at 180°C, and extrusion coated on the outer periphery of a tin plated copper wire with an outer diameter of 1.6 mmφ to a thickness of 0.6 mm.
This was irradiated with a 5 Mrad electron beam to obtain a crosslinked insulated wire. Table 1 shows the results of measuring the tensile strength and deflection of the crosslinked insulated wire thus obtained. The amount of deflection is determined by cutting the wire into a length of 50 mm.
Measurements were made by fixing one end and applying a load of 100 g to the other end.

[Table] As is clear from Table 1, by mixing polyvinylidene fluoride with the tetrafluoroethylene/α-olefin copolymer, it has excellent mechanical strength (tensile strength) and flexibility (deflection amount). )
In this case, a crosslinked molded article having practically sufficient properties can be obtained. The method of the present invention is suitable for obtaining various crosslinked molded products, especially long crosslinked molded products, and is suitable for obtaining insulating and protective coatings for electric wires, protective coatings for optical fibers, tubes (especially heat-shrinkable tubes, tapes, etc.). Applicable.

Claims (1)

[Claims] 1. Tetrafluoroethylene and α having 2 to 4 carbon atoms
- A method for producing a crosslinked fluorine-containing elastomer molded article, which comprises molding a mixture containing a copolymer with olefin and vinylidene polyfluoride into a predetermined shape, and then crosslinking it by irradiating it with ionizing radiation. 2 Tetrafluoroethylene and α having 2 to 4 carbon atoms
The method for producing a crosslinked fluorine-containing elastomer molded article according to claim 1, wherein the weight ratio of copolymer with olefin/vinylidene polyfluoride is from 95/5 to 40/60. 3. The method for producing a crosslinked fluorine-containing elastomer molded article according to claim 1 or 2, wherein the α-olefin is propylene. 4. The method for producing a crosslinked fluorine-containing elastomer molded article according to claim 3, wherein the molar ratio of tetrafluoroethylene/propylene is from 95/5 to 30/70.