Process for producing modified ultrahigh-molecular-weight polyolefins

Claim 2

A process for producing a modified ultrahigh-molecular-weight polyolefin composition, which comprises mixing a powder of an ultrahigh-molecular-weight polyolefin (A) having an intrinsic viscosity [η] of at least 5 dl/g, a flowability improver (B) having a melting point lower than the melting point of the ultrahigh-molecular-weight polyolefin (A), a monomer (C) having an olefinically unsaturated bond and a radical initiator (D) with stirring at the melting point of the flowability improver (B) or a higher temperature but below the melting point of the ultrahigh-molecular-weight polyolefin (A), and then melt-kneading the mixture at the melting point of the ultrahigh-molecular-weight polyolefin (A) or a higher temperature to react the monomer (C) with the ultrahigh-molecular-weight polyolefin (A).

Claim 3

A process according to claim 1 in which the ultrahigh-molecular-weight polyolefin powder has a particle diameter of 1 to 500 µm.

Claim 4

A process according to claim 1 or 2 in which the polyolefin (A) is a homopolymer of ethylene or a highly crystalline copolymer of ethylene with another α-olefin.

Claim 5

A process according to any one of claims 1 to 3 in which the polyolefin (A) has an intrinsic viscosity [η] of 7 to 30 dl/g.

Claim 6

A process according to any one of claims 1 to 4 in which the flowability improver (B) is a waxy substance compatible with the ultrahigh-molecular-weight polyolefin.

Claim 7

A process according to claim 5 in which the flowability improver (B) is an aliphatic hydrocarbon compound or a derivative thereof; an n-alkane having at least 22 carbon atoms; an alkane mixture composed mainly of said n-alkane; a paraffin wax; a polyethylene wax; a C₁₂-C₅₀ fatty acid, aliphatic alcohol, fatty acid amide, fatty acid ester, aliphatic mercaptan, aliphatic aldehyde, or aliphatic ketone; or a solvent for the polyolefin (A).

Claim 8

A process according to any one of claims 1 to 6 in which the monomer (C) is an ethylenically unsaturated carboxylic acid or a derivative thereof; an ethylenically unsaturated epoxy monomer; an ethylenically unsaturated silane monomer; maleic or Nadic acid or an anhydride thereof; glycidyl acrylate or glycidyl methacrylate; vinyltrimethoxysilane, vinyltriethoxysilane or vinyltris(methoxyethoxy)silane.

Claim 9

A process according to any one of claims 1 to 7 in which the radical initiator (D) is an organic peroxide, an organic perester or an azo compound having a half-life temperature in the range of 100 to 200°C.

Claim 10

A process according to any one of claims 1 to 8 in which the amount of the powdery ultrahigh-molecular-weight polyolefin (A) is 5 to 80% by weight and the amount of the flowability improver (B) is 20 to 95 % by weight and, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), the amount of the monomer (C) is 0.1 to 20 parts by weight and the amount of the radical initiator (D) is 0.01 to 5 parts by weight.

Claim 11

A process according to clam 9 in which the amount of the powdery ultrahigh-molecular-weight polyolefin (A) is 20 to 60 % by weight and the amount of the flowability improver (B) is 40 to 80 % by weight and, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), the amount of the monomer (C) is 0.5 to 10 parts by weight and the amount of the radical initiator (D) is 0.02 to 0.5 part by weight.

Claim 12

A process according to clam 9 in which the amount of the powdery ultrahigh-molecular-weight polyolefin (A) is 20 to 60 % by weight and the amount of the flowability improver (B) is 40 to 80 % by weight and, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), the amount of the monomer (C) is 0.5 to 10 parts by weight and the amount of the radical initiator (D) is 0.02 to 0.5 part by weight.

Claim 13

A process according to any one of claims 1 to 10 in which the mixing of the components (A), (B), (C) and (D) with stirring is carried out at a temperature ranging from a temperature 10°C higher than the melting point of the flowability improver (B) to a temperature 20°C lower than the melting point of the ultrahigh-molecular-weight polyolefin (A).

Claim 14

A process according to any one of claims 1 to 11 in which at a temperature ranging from a temperature 10°C higher than the melting point of the flowablity improver (B) to a temperature 20°C lower than the melting point of the ultrahigh-molecular-weight polyolefin (A), particles of the ultrahigh-molecular-weight polyolefin (A) are dispersed in a melt of the flowability improver (B), then the monomer (C) and the radical initiator are added to the resulting dispersion, and the mixing with stirring is continued.

Claim 15

A process for producing a stretched molded article of a graft-modified ultrahigh-molecular-weight polyolefin composition, which comprises mixing 5 to 80 % by weight of a powder having a particle diameter of 1 to 500 µm of an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity [η] of 5 to 30 dl/g, 20 to 95 % by weight of a normally solid flowability improver (B) having a melting point 20-70°C lower than the melting point of the ultrahigh-molecular-weight polyolefin (A), 0.1 to 20 parts by weight, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), of a monomer (C) selected from the group consisting of ethylenically unsaturated carboxylic acids, derivatives of the carboxylic acids, ethylenically unsaturated epoxy monomer and ethylenically unsaturated silane monomer, and 0.01 to 5 parts by weight, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), of a radical initiator (D) at the melting point of the flowablity improver (B) or a higher temperature but below the melting point of the ultrahigh-molecular-weight polyolefin (A) to form a dispersion in which the flowability improver (B) forms the dispersion medium and the ultrahigh-molecular-weight polyolefin (A) forms the disperse phase, the monomer (C) and the radical initiator (D) are dissolved or uniformly dispersed in the dispersion medium, and the ultrahigh-molecular-weight polyolefin (A) is swollen with the flowablity improver (B); melt-kneading the dispersion at the melting point of the ultrahigh-molecular-weight polyolefin (A) or a higher temperature; extruding the melt-kneaded mixture through a die to form an extruded article; stretching the extruded article; and removing the flowablity improver (B) from the molded article before, during or after the stretching.

Claim 16

A process for producing a stretched molded article of a graft-modified ultrahigh-molecular-weight polyolefin composition, which comprises mixing 5 to 80 % by weight of a powder having a particle diameter of 1 to 500 µm of an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity [η] of 5 to 30 dl/g, 20 to 95 % by weight of a normally solid flowability improver (B) having a melting point 20-70°C lower than the melting point of the ultrahigh-molecular-weight polyolefin (A), 0.1 to 20 parts by weight, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), of a monomer (C) selected from the group consisting of ethylenically unsaturated carboxylic acids, derivatives of the carboxylic acids, ethylenically unsaturated epoxy monomer and ethylenically unsaturated silane monomer, and 0.01 to 5 parts by weight, per 100 parts by weight of the ultrahigh-molecular-weight polyolefin (A), of a radical initiator (D) at the melting point of the flowablity improver (B) or a higher temperature but below the melting point of the ultrahigh-molecular-weight polyolefin (A) to form a dispersion in which the flowability improver (B) forms the dispersion medium and the ultrahigh-molecular-weight polyolefin (A) forms the disperse phase, the monomer (C) and the radical initiator (D) are dissolved or uniformly dispersed in the dispersion medium, and the ultrahigh-molecular-weight polyolefin (A) is swollen with the flowablity improver (B); melt-kneading the dispersion at the melting point of the ultrahigh-molecular-weight polyolefin (A) or a higher temperature; extruding the melt-kneaded mixture through a die to form an extruded article; stretching the extruded article; and removing the flowablity improver (B) from the molded article before, during or after the stretching.

Claim 17

A process according to claim 13 in which the monomer (C) is an ethylenically unsaturated silane monomer; and the silane monomer is crosslinked by impregnating the stretched molded article with a silane crosslinking catalyst and then contacting the molded article with moisture.