Process for making opaque polyester film

Patent metadata

Field	Value
Publication number	US-9556540-B2
Application number	US-98873709-A
Country	US
Kind code	B2
Filing date	Apr 20, 2009
Priority date	Apr 24, 2008
Publication date	Jan 31, 2017
Grant date	Jan 31, 2017

Abstract

The invention relates to a process for making an opaque and glossy film from a thermoplastic polyester composition, comprising the steps of a) extruding the polyester composition through a slot die, and quenching to form a substantially amorphous film having a crystallinity of at most 5%; b) rapidly heating the amorphous film to a drawing temperature in the range from T g to (T g +50)° C. while applying a draw ratio in the range of from λ initiation to λ max. in longitudinal direction, and a drawing rate of at least 1 m/min to form an oriented film showing stress-whitening, wherein λ initiation is the draw ratio at which a transfer from a transparent product to a stress-whitened product occurs and λ max. is the draw ratio at which failure of the stress whitened film occurs; and c) heat-setting the oriented stress-whitened film; the thermoplastic polyester composition substantially consisting of at least one crystallizable polyester derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid.
With this process it is possible to make a unitary, glossy, opaque film from a polyester composition that does not contain void-forming additives like high amounts of fine pigment particles or dispersed non-miscible polymer particles. The film obtained also has very good mechanical properties. It is a further advantage that the process can be performed continuously on conventional extrusion and stretching equipment used for making transparent film from polyesters.
The invention also relates to an opaque polyester film obtainable by said process.

First claim

The invention claimed is:

1. A process for making an opaque and glossy film from a thermoplastic polyester composition, comprising the steps of
a) extruding the polyester composition through a slot die, and quenching to form a substantially amorphous film having a crystallinity of at most 5%;
b) heating the amorphous film to a drawing temperature in the range of from 80 to 95° C. by immersing the film in a liquid heating bath, while applying a draw ratio in the range of 5.1 to 5.7 in longitudinal direction using sets of feed and draw rollers the speed of which can be controlled in such a way that speed fluctuations of at most about 1% occur, and a drawing rate of from about 5 to about 20 m/min to form an oriented film showing stress-whitening; and
c) heat-setting the oriented stress-whitened film in the range of about 150 to 250° C.;
wherein the composition is free of barium sulfate;
wherein the composition is free of pigments, mineral particles, and dispersed incompatible polymers, which act as initiators for voiding,
wherein the thermoplastic polyester composition comprises 95 mass % or more of at least one crystallisable polyester derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid, and
wherein the film has a density of 500-1300 kg/m 3 .

2. The process according to claim 1 , wherein the polyester is selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and their copolymers.

3. The process according to claim 1 , wherein the amorphous film has less than 3% crystallinity.

4. The process according to claim 1 , further comprising subsequent to longitudinal drawing a step of applying a draw ratio in transverse direction at a temperature in the range of from T g to (T g +50° C. to form a bi-axially oriented film, before the heat setting step.

5. The process according to claim 1 , further comprising using the opaque oriented polyester film to make finished and semi-finished articles.

6. The process according to claim 5 , comprising using the opaque oriented polyester film to make a woven fabric, a rope or a bag.

7. The process according to claim 1 , wherein the composition is free of void-inducing additives.

8. The process according to claim 1 , wherein the film has a tensile strength of at least 250 MPa.

9. The process according to claim 8 , wherein the film has a density of 800-1200 kg/m 3 and a tensile strength of at least 300 MPa.

10. The process according to claim 1 , wherein the film has a surface gloss at 60° of at least 50 GU and showing a haze value of at least 80%.

Assignees

• Bashir Zahir
• Ward Ian Macmillan
• Thompson Glen Peter
• Unwin Anthony Paul
• Saudi Basic Ind Corp

Inventors

• Bashir Zahir
• Ward Ian Macmillan
• Thompson Glen Peter
• Unwin Anthony Paul

Classifications

• B29C48/9135

  of flat articles, e.g. using specially adapted supporting means · CPC title

• B29C48/92

  Measuring, controlling or regulating · CPC title

• B29C55/12

  biaxial · CPC title

• D01D5/426

  by cutting films · CPC title

• B65D88/16

  flexible (B65D88/34 - B65D88/78 take precedence) · CPC title