Process for blowing film from linear thermoplastic material

Claim 1

A method for the continuous blowing of film from linear polyethylene materials which, after exit of a melt of the thermoplastic material from an annular die accompanied by introduction of air to an interior of the tubular melt thus formed, forms a neck portion having an essentially constant diameter followed at its upper part by rapidly diverging main bubble before solidification at a frost line, the upper part of the neck being defined as the most narrow part or the part where the outward bending has its smallest radius, the improvement comprising, ejecting the melt from an annular die of a diameter greater than 200 mm and manipulating the melt temperature, the cooling rate and the take-up speed to (a) give a linear film velocity (V 1 ) at the upper part of the neck exceeding 15 m/min., and (b) give a linear velocity ratio (V 1 /V o ), between the velocity of the material at the upper part of the neck portion (V 1 ) and the velocity of the material when leaving the annular die (V o ), at least as great as the velocity ratio (V 2 /V 1 ), between the final velocity of the material at the frost line (V 2 ) and the velocity (V 1 ) at the upper part of the neck portion.

Claim 2

A method for the continuous blowing of film from linear polyethylene materials which, after exit of a melt of the thermoplastic material from an annular die accompanied by introduction of air to an interior of the tubular melt thus formed, forms a neck portion having an essentially constant diameter followed at its upper part by rapidly diverging main bubble before solidification at a frost line, the upper part of the neck being defined as the most narrow part or the part where the outward bending has its smallest radius, the improvement comprising, ejecting the melt from an annular die of a diameter greater than 200 mm and manipulating the melt temperature, the cooling rate and the take-up speed to (a) give a linear film velocity (V 1 ) at the upper part of the neck exceeding 15 m/min., and (b) give a linear velocity ratio (V 1 /V o ), between the velocity of the material at the upper part of the neck portion (V 1 ) and the velocity of the material when leaving the annular die (V o ), at least as great as the velocity ratio (V 2 /V 1 ), between the final velocity of the material at the frost line (V 2 ) and the velocity (V 1 ) at the upper part of the neck portion.

Claim 11

A method for continuous blowing of film from linear polyethylene materials which, after exit of a melt of the thermoplastic material from an annular die accompanied by introduction of air to an interior of the tubular melt thus formed, forms a neck portion having an essentially constant diameter followed at its upper part by a rapidly diverging main bubble before solidification at a frost line, the upper part of the neck being defined as the most narrow part or the part where the outward bending has its smallest radius, the improvement comprising ejecting at least 100 kg melt per hour from an annular die of a diameter greater than 200 mm and having a slit width exceeding 1.2 mm and manipulating the melt temperature, the cooling rate and the take-up speed to (a) give a linear film velocity (V 1 ) at the upper part of the neck exceeding 15 m/min, and (b) give a linear velocity ratio (V 1 /V o ), between the velocity of the material at the upper part of the neck portion (V 1 ) and the velocity of the material when leaving the annular die (V o ), at least as great as the velocity ratio (V 2 /V 1 ), between the final velocity of the material at the frost line (V 2 ) and the velocity (V 1 ) at the upper part of the neck portion, and (c) give a neck length measured from the die opening to the upper part of the neck portion, exceeding 3 times the diameter, while maintaining a take-up velocity above 75 m/min. and restricting the blow-up ratio to less than 3.5.

Claim 12

A method for continuous blowing of film from linear polyethylene materials which, after exit of a melt of the thermoplastic material from an annular die accompanied by introduction of air to an interior of the tubular melt thus formed, forms a neck portion having an essentially constant diameter followed at its upper part by a rapidly diverging main bubble before solidification at a frost line, the upper part of the neck being defined as the most narrow part or the part where the outward bending has its smallest radius, the improvement comprising ejecting at least 100 kg melt per hour from an annular die of a diameter greater than 200 mm and having a slit width exceeding 1.2 mm and manipulating the melt temperature, the cooling rate and the take-up speed to (a) give a linear film velocity (V 1 ) at the upper part of the neck exceeding 15 m/min, and (b) give a linear velocity ratio (V 1 /V o ), between the velocity of the material at the upper part of the neck portion (V 1 ) and the velocity of the material when leaving the annular die (V o ), at least as great as the velocity ratio (V 2 /V 1 ), between the final velocity of the material at the frost line (V 2 ) and the velocity (V 1 ) at the upper part of the neck portion, and (c) give a neck length measured from the die opening to the upper part of the neck portion, exceeding 3 times the diameter, while maintaining a take-up velocity above 75 m/min. and restricting the blow-up ratio to less than 3.5.