To provide a method for producing modified polytetrafluoroethylene, in which formation of a fluorinated oligomer as a by-product is little. A method for producing modified polytetrafluoroethylene which contains substantially no C.sub.6-34 fluorinated oligomer containing hydrophilic functional groups and which contains substantially no fluorinated surfactant, the method comprising conducting copolymerization of tetrafluoroethylene and a monomer having a polar group, in a liquid dispersion 1 comprising a polymer containing units derived from a non-fluorinated monomer and an aqueous medium, or in a solution 2 obtainable by mixing at least one member selected from the group consisting of a polyalkylene oxide compound and a hydrocarbon-containing surfactant, with an oxidizing agent, in an aqueous medium, under such a condition that the amount of the monomer having a polar group to be used, is at most 0.150 mass % to the whole amount of tetrafluoroethylene, to obtain modified polytetrafluoroethylene.

To provide a copolymer capable of producing a molded article excellent in strength at a high temperature. A copolymer comprising ethylene units, tetrafluoroethylene units and other monomer units, wherein to the sum of ethylene units and tetrafluoroethylene units, the ethylene units are from 49 to 40 mol % and the tetrafluoroethylene units are from 51 to 60 mol %; to all units in the copolymer, other monomer units are from 2.6 to 6.0 mol %; the melting point is at least 230 C.; and the melt flow rate is from 1 to 15 g/10 min.

To provide a dielectric film which is excellent in dielectric properties and stability in the electric corrosion test and which is suitable for producing a high-precision printed board.

A roll film comprising a melt-processable fluororesin as the main component and having a thickness of from 1 to 100 m, the dimensional change rate of which is less than 1.0%, in terms of an absolute value, in each of MD and TD, when heated at 150 C. for 30 minutes and then cooled to 25 C., based on the dimension at 25 C.

To provide a dielectric film which is excellent in dielectric properties and stability in the electric corrosion test and which is suitable for producing a high-precision printed board.

A roll film comprising a melt-processable fluororesin as the main component and having a thickness of from 1 to 100 m, the dimensional change rate of which is less than 1.0%, in terms of an absolute value, in each of MD and TD, when heated at 150 C. for 30 minutes and then cooled to 25 C., based on the dimension at 25 C.

A material having a fluorinated resin layer is subjected to heat treatment. The fluorinated resin layer is composed of a composition containing a fluorinated copolymer (a) having at least one type of functional group selected from a carbonyl group-containing group, a hydroxy group, an epoxy group and an isocyanate group, having a melting point of from 280 to 320 C. and a melt flow rate of at least 2 g/10 min measured at 372 C. under a load of 49 N. The heat treatment is carried out at a temperature of at least 250 C. and lower by at least 5 C. than the melting point of the fluorinated copolymer (a) so that the ratio of the melt flow rate of the fluorinated resin layer after the heat treatment to that before the heat treatment, and the melt flow rate of the fluorinated resin layer after the heat treatment, are respectively within specific ranges.

To provide a method for producing a laminate, capable of forming a coating film excellent in abrasion resistance by using a fluororesin powder, and capable of suppressing foaming when the coating film is formed by using the fluororesin powder.

A method for producing a laminate 10 comprising a substrate 12 and a coating film 14 formed on a surface of the substrate 12, which comprises applying the following powder composition to the surface of the substrate 12 to form the coating film 14.

Powder composition: A powder composition comprising a fluororesin powder formed of a resin material containing as the main component a melt-moldable fluororesin which has a carbonyl group-containing group or the like, and having D50 of from 0.01 to 100 m, and a non-fluororesin powder formed of a resin material containing as the main component a non-fluororesin such as a polyarylketone, and having D50 of from 0.01 to 100 m, in a specific volume proportion.

Poly(ethylene tetrafluoroethylene) (ETFE) polymers having an average molecular weight of at least 300,000 g/mol and a melt enthalpy of at least 57 J/g are provided. The ETFE polymer may include at least one additional comonomer. The ETFE polymer is used to form a porous tape or membrane that has a node and fibril structure. A porous ETFE tape may be formed by lubricating the ETFE polymer and subjecting the lubricated polymer to pressure at a temperature below the melting point of the ETFE polymer. Optionally, the ETFE tape may be expanded at a temperature below the melting temperature of the ETFE polymer to form an expanded ETFE membrane. Alternatively, the ETFE polymer may subjected to heat and pressure without the addition of a lubricant to form a dense preform. The dense preform may be subsequently slit in a length direction and stretched to form a dense ETFE fiber.

To provide a resin film which comprises an ethylene/tetrafluoroethylene copolymer and which is to be used as, for example, a rubber plug lamination film to prevent breakage at the time of producing a laminated rubber plug. The resin film comprises an ethylene/tetrafluoroethylene copolymer and is characterized in that the product of the value of the endothermic peak height H (mW/mg) obtained by its DSC-analysis and the haze (%) measured at a thickness of 100 m, is from 0.1 to 0.2 (mW/mg.Math.%).

To provide a fluorinated elastic copolymer capable of obtaining a crosslinked rubber which is excellent in tensile strength and has a low compression set under high temperature conditions; a method for producing such a fluorinated elastic copolymer; a crosslinked rubber; and a method for producing such a crosslinked rubber. A fluorinated elastic copolymer having structural units based, respectively, on monomers (a), (b) and (c), and further having iodine atoms. Monomer (a): at least one member selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, chlorotrifluoroethylene and perfluoro(alkyl vinyl ether). Monomer (b): at least one member selected from the group consisting of compounds represented by formula (I): CR.sup.1R.sup.2CR.sup.3R.sup.4CR.sup.5CR.sup.6R.sup.7 (I) (wherein R.sup.1, R.sup.2, R.sup.3, R.sup.5, R.sup.6 and R.sup.7 are each independently a hydrogen atom, a fluorine atom or a methyl group; and R.sup.4 is a C.sub.1-10 perfluoroalkylene group which may have an etheric oxygen atom inserted between carbon atoms). Monomer (c): at least one member selected from the group consisting of ethylene and propylene.

A method of producing a heat-resistant crosslinked fluororubber formed body, including a step (1) of melt-mixing, with respect to 100 mass parts of base rubber containing 40 to 98 mass % of fluororubber and 2 to 40 mass % of ethylene/tetrafluoroethylene copolymer resin, 0.003 to 0.5 mass parts of organic peroxide, 0.5 to 400 mass parts of inorganic filler, 2 to 15 mass parts of a specific silane coupling agent, and silanol condensation catalyst, and including a step (a) of melt-mixing a part of the base rubber, the organic peroxide, the inorganic filler and the silane coupling agent at a temperature equal to or higher than a decomposition temperature of said organic peroxide, and a step (b) of melt-mixing a remainder of the base rubber, and the silanol condensation catalyst, and the fluororubber and the ethylene/tetrafluoroethylene copolymer resin are melt-mixed in any of the steps (a) and (b).