Method of producing biaxially stretched polyester bottles
In effecting the stretching by using a stretch rod in a method of producing a biaxially stretched polyester bottle, the air is blown into the preform at such a flow rate that the preform does not come in contact with the stretch rod but the end thereof and does not come in contact with the surfaces of the mold, either. There can be produced a biaxially stretched polyester bottle having an average thickness of about 0.05 to about 0.2 mm or having a further decreased thickness using a resin in decreased amounts and having a decreased weight without developing burst or whitening caused by over-stretching, without forming ring-like thick portion yet maintaining a good yield and efficiency.
1. A method of producing a biaxially stretched polyester bottle by stretching a polyester preform heated at a stretching temperature by using a stretch rod and by blowing the air, wherein, the temperature for stretching said preform is in a range of 100 to 130° C. on the outer surface of the preform, and a temperature difference between the outer surface of the preform and the inner surface thereof is not larger than 2° C., and in effecting the stretching by using said stretch rod, the air is blown as a pre-blow into the preform at such a flow rate that the preform does not at least come in contact with stretch rod but the end thereof and does not come in contact with the surfaces of the mold, either, the pre-blow air is discontinued simultaneously with the end of the stretching that uses the stretch rod and, thereafter, the stretching is effected by a main blow, said pre-blow for blowing 25 to 40% of the volume of the biaxially stretched bottle blowing the air that has been adjusted to a pressure of 0.05 to 0.1 MPa and a temperature of 200 to 300° C.
2. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein the stretching by said main blow works to stretch, in substantially the circumferential direction, the preform that has been stretched in the longitudinal direction by the stretching by using the stretch rod.
3. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein said pre-blow is for blowing 10 to 50% of the volume of the biaxially stretched bottle.
4. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein said main blow uses the air of a pressure adjusted to 0.5 to 4.0 MPa.
5. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein said main blow uses the air of a temperature adjusted to 70 to 250° C.
6. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein said stretch rod stretches the preform in the vertical direction to not less than 70% of the final size of the bottle.
7. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein in effecting the stretching by using said stretch rod, a maximum speed of the stretch rod is not greater than 500 mm/sec.
8. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein in effecting the stretching by using said stretch rod, the speed of the end of the stretch rod when it comes in contact with the inner surface of the bottom of the preform is not greater than 200 mm/sec.
9. A method of producing a biaxially stretched polyester bottle according to claim 1 , wherein the stretching ratios are such that the longitudinal stretching ratio is not smaller than 2.7 times and the area ratio is 12 to 25 times.