Biaxially oriented, white flame-retardant polyester film
View Patent ↗The biaxially oriented, white polyester film of the present invention having improved flame-retardancy, covering ability, flexibility and heat-resistance comprises a polyester resin having an intrinsic viscosity of 0.4 to 0.9 dl/g, a flame-retardant which is alkylene bistetrabromophthalimide or decabromodiphenylalkane, and a fluorescent whitening agent, said polyester film being biaxially drawn at a total draw ratio of 9 or more.
1. A biaxially oriented, white flame-retardant polyester film which comprises:
(A) a polyester resin having an intrinsic viscosity of 0.4 to 0.9 dl/g which is composed of 60% by weight or more of ethylene terephthalate repeating units;
(B) a flame-retardant which is alkylene bistetrabromophthalimide or decabromodiphenylalkane in an amount ranging from 5 to 18% by weight based on the weight of the resin; and
(C) a fluorescent whitening agent in an amount ranging from 0.04 to 0.2% by weight based on the weight of the resin,
said film being drawn at a total draw ratio (the sum of the longitudinal draw ratio and transverse draw ratio) of 9 or more.
2. The polyester film of claim 1 , wherein the fluorescent whitening agent is a bisbenzoazole compound.
3. The polyester film of claim 1 , which further comprises a flame-retardancy enhancing agent in an amount ranging from 1 to 9% by weight based on the weight of the resin.
4. The polyester film of claim 3 , wherein the flame-retardancy enhancing agent is antimony trioxide or zinc sulfide.
5. The polyester film of claim 1 , which is drawn in the longitudinal direction at a draw ratio of 2.5 or more and in the transverse direction at a draw ratio of 2.5 or more, at a temperature ranging from 90 to 140° C.
6. The polyester film of claim 1 , which is heat-set at a temperature ranging from 200 to 240° C.
7. The polyester film of claim 1 , which has a density of 1.00 to 1.25 g/cm 3 and a surface tension of at least 43 dyne/cm.