Oriented polyglycolic acid film and production process thereof

A process for producing an oriented polyglycolic acid film, comprising the steps of melt-extruding a thermoplastic resin material which comprises polyglycolic acid having a repeating unit represented by the following formula (1):

• ##STR11## and the following physical properties:
• (a) the melt viscosity, .eta.*, as measured at a temperature of the melting point, Tm, of the polymer+20.degree. C. and a shear rate of 100/sec, being 500-100,000 Pa.s;
• (b) the melting point, Tm, being at least 150.degree. C.;
• (c) the melt enthalpy, .DELTA.Hm, being at least 20 J/g;
• and
• (d) the density being at least 1.50 g/cm.sup.3 as measured in an unoriented, crystallized form, the melt extruding being performed through a T-die and in a temperature range of from the melting point, Tm, to 255.degree. C., to form the thermoplastic resin material into a sheet;
• immediately quenching the sheet to the crystallization temperature, Tc.sub.1, of the polymer or lower;
• causing the quenched sheet to pass through stretching rolls in a temperature range of from the glass transition temperature, Tg, of the polymer to the crystallization temperature, Tc.sub.1, to stretch the sheet in a uniaxial direction at a draw ratio higher than one time but not higher than 20 times;
• and optionally heat-setting the stretched sheet for 1 second to 3 hours in a temperature range of from Tc.sub.1 to Tm+10.degree. C. while maintaining its length constant or under tension.

A process for producing an oriented polyglycolic acid film, comprising the steps of melt-extruding a thermoplastic resin material which comprises polyglycolic acid having a repeating unit represented by the following formula (1):

• ##STR12## and the following physical properties:
• (a) the melt viscosity, .eta.*, as measured at a temperature of the melting point, Tm, of the polymer+20.degree. C. and a shear rate of 100/sec, being 500-100,000 Pa.s;
• (b) the melting point, Tm, being at least 150.degree. C.;
• (c) the melt enthalpy, .DELTA.Hm, being at least 20 J/g;
• and
• (d) the density being at least 1.50 g/cm.sup.3 as measured in an unoriented, crystallized form, the melt extruding being performed through a T-die in a temperature range of from the melting point, Tm, to 255.degree. C., to form the thermoplastic resin material into a sheet;
• immediately quenching the sheet to the crystallization temperature, Tc.sub.1, of the polymer or lower;
• causing the quenched sheet to pass through stretching rolls in a temperature range of from the glass transition temperature, Tg, of the polymer to the crystallization temperature, Tc.sub.1, to stretch the sheet in a machine direction at a draw ratio higher than one time but not higher than 10 times;
• stretching the uniaxially stretched sheet at a temperature ranging from Tg to Tc.sub.1 in a transverse direction at a draw ratio higher than one time but not higher than 10 times;
• and optionally heat-setting the biaxially stretched sheet for 1 second to 3 hours in a temperature range of from Tc.sub.1 to Tm+10.degree. C. while maintaining its length constant or under tension.

A process for producing an oriented polyglycolic acid film, comprising the steps of melt-extruding a thermoplastic resin material which comprises polyglycolic acid having a repeating unit represented by the following formula (1):

• ##STR13## and the following physical properties:
• (a) the melt viscosity, .eta.*, as measured at a temperature of the melting point, Tm, of the polymer+20.degree. C. and a shear rate of 100/sec, being 500-100,000 Pa.s;
• (b) the melting point, Tm, being at least 150.degree. C.;
• (c) the melt enthalpy, .DELTA.Hm, being at least 20 J/g;
• and
• (d) the density being at least 1.50 g/cm.sup.3 as measured in an unoriented, crystallized form, the melt extruding being performed through a ring die for blown-film extrusion and in a temperature range of from the melting point, Tm, to 255.degree. C., to form the thermoplastic resin material into a tube;
• immediately quenching the tube to the crystallization temperature, Tc.sub.1, of the polymer or lower;
• inflating the quenched tube at a temperature ranging from the glass transition temperature, Tg, of the polymer to the crystallization temperature, Tc, to a blow-up ratio higher than one time but not higher than 10 times;
• taking up the blown tube at a take-up rate of 0.5-100 m/min in a machine direction through nip rolls at a draw ratio higher than one time but not higher than 10 times;
• and optionally heat-setting the biaxially stretched tube for 1 second to 3 hours in a temperature range of from Tc.sub.1 to Tm+10.degree. C. while maintaining its length constant or under tension.