Graft-modified ultrahigh-molecular-weight polyethylene and process for producing same

Claim 2

A graft-modified ultrahigh-molecular-weight polyethylene obtained by grafting (A) an ultrahigh-molecular-weight polyethylene having an inherent viscosity [11], determined at 135°C in decalin, of at least 5 dl/ g with (C) an unsaturated carboxylic acid graft-copolymerizable therewith or a graft-copolymerizable derivative thereof, under melt-kneading condition in the presence of (B) an aliphatic compound having a melting point, determined by the DSC method, of at least 10°C and a boiling point of at least 130°C, the amount of component (C) grafted in said graft-modified ultrahigh-molecular-weight polyethylene being 0.01 to 10% by weight, and said graft-modified ultrahigh-molecular-weight polyethylene being substantially free of insoluble gel product and having a tensile strength of at least 1.0 GPa.

Claim 3

A graft-modified polyethylene according to claim 1 having a tensile modulus of elasticity of at least 10 GPa.

Claim 4

A graft-modified polyethylene according to claim 1 or 2 wherein the amount of component (C) grafted is 0.05 to 10% by weight.

Claim 5

A graft-modified polyethylene according to claim 1, 2 or 3 wherein component (C) is a C 3 -C 15 unsaturated dicarboxylic acid or an acid anhydride thereof.

Claim 6

A graft-modified polyethylene according to any one of claims 1 to 4 wherein component (B) is a paraffinic wax having a melting point, determined by the DSC method, of 40 to 120°C and a weight average molecular weight (Mw), determined by the GPC method, of 230 to less than 2,000.

Claim 7

A graft-modified polyethylene according to claim 5 wherein the weight average molecular weight (Mw) of the paraffinic wax is from 230 to less than 1,000.

Claim 8

A graft-modified polyethylene according to claim 5 or 6 wherein the melting point of the paraffinic wax is 45 to 110°C.

Claim 9

A graft-modified polyethylene according to any one of the preceding claims wherein component (B) is an aliphatic compound having 12 to 50 carbon atoms and a molecular weight of 130 to 2,000, selected from aliphatic carboxylic acids, aliphatic alcohols, aliphatic acid amides, aliphatic carboxylic acid esters, aliphatic mercaptans, aliphatic aldehydes and aliphatic ketones.

Claim 10

A graft-modified polyethylene according to any one of the preceding claims wherein inhereent viscosity sη] of component (A) is 5 to 30 dl/g.

Claim 11

Stretched shaped articles of a graft-modified polyethylene as claimed in any one of the preceding claims.

Claim 12

A process for producing a graft-modified ultrahigh-molecular-weight polyethylene as defined in claim 1, which process comprises (1) melt-kneading a mixture composed of 15 to 80 parts by weight of component (A), per 100 parts by weight of the components (A) and (B) combined, 85 to 20 parts by weight of component (B), per 100 parts by weight of the components (A) and (B) combined, and at least 0.1 part by weight of component (C), per 100 parts by weight of component (A), in a screw extruder while maintaining the temperature of the mixture at a temperature from the melting point of the mixture to 280°C, and (2) melt-extruding the molten mixture through a die kept at a temperature from the melting point of the mixture to 300°C. 12. A process according to claim 11 which further comprises (3) cooling the resulting unstretched extrudate to solidify it, and (4) subjecting the unstretched solidified extrudate to a stretching treatment at a temperature from the melting point, determined by the DSC method, of component (B) to a point 20°C above the melting point of the mixture at a stretch ratio of at least 3:1 when step (2) is carried out while a draft is applied to the unstretched extrudate or at a stretch ratio of at least 10:1 when step (2) is carried out in the absence of a draft.