Minute-cellular polyester film

• US 4,871,784 A
• Filed: 09/15/1988
• Issued: 10/03/1989
• Est. Priority Date: 02/05/1987
• Status: Expired due to Term

• Current Assignee: Diafoil Co., Ltd. (Mitsubishi Chemical Group Corp.)
• Original Assignee: Diafoil Co., Ltd. (Mitsubishi Chemical Group Corp.)
• Inventors: Sato, Yoshinori, Masuda, Narihiro, Kotani, Tomoyuki, Otonari, Satoshi
• Primary Examiner(s): Foelak, Morton
• Application Number:
  US07/245,318
• Time in Patent Office: 383 Days
• Field of Search: 521/97, 521/138, 264/154, 264/210.7, 264/288.8, 264/290.2
• US Class Current: 521/138
• CPC Class Codes: C08J 2367/02 Polyesters derived from dicarboxylic acids and dihydroxy compounds; C08J2367/06 takes precedence
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: C08L 23/00 Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 23/12 Polypropene
• CPC Class Codes: C08L 67/02 Polyesters derived from dicarboxylic acids and dihydroxy compounds C08L67/06 takes precedence

Abstract

The polyester film according to the present invention is produced by molding a composition comprising an aromatic polyester, 3 to 40 wt %, based on the amount of said polyester, of a crystalline polypropylene having a melt flow index of 0.2 to 120, and 0.001 to 3 wt %, based of the total amount of said polyester and said polypropylene, of a surface-active agent into a sheet; and stretching the thus obtained sheet at least one direction. The polyester film according to the present invention, which is obtained by the above process is low in the apparent specific gravity because of a large number of minute closed cells contained therein. Further, the polyester film according to the present invention shows a high opacifying power by adding a small amount of titanium oxide or without adding the titanium oxide, which have been added in a large amount. The polyester film can be used as the materials for printing plates and substrates in data devices.

Claims

1. A polyester film containing minute closed cells having a diameter of 1 to 300 μ

m in the surface and inner parts thereof, which comprises an aromatic polyester, 3 to 40 wt %, based on the amount of said polyester, of a crystalline polypropylene having a melt flow index of 0.2 to 120, and 0.001 to 3 wt %, based of the total amount of said polyester and said polypropylene, of a surface-active agent, wherein the film is stretched at least one direction of the machine and transverse directions.

2. The polyester film according to claim 1, wherein said crystalline polypropylene comprises not less than 95 mol % of propylene unit as the constitutional repeating unit.

3. The polyester film according to claim 1 or 2, wherein said surface-active agent is one selected from the group consisting of anionic surface-active agents, cationic surface-active agents, amphoteric surface-active agents and nonionic surface-active agents.

4. The polyester film according to any one of claims 1 to 3, wherein said polyester film is produced by molding a composition comprising said polyester, 3 to 40 wt %, based on the amount of said polyester of said crystalline polypropylene having a melt flow index of 0.2 to 120, and 0.001 to 3 wt %, based on the total amount of said polyester and said polypropylene, of said surface-active agent, into a sheet.

5. The polyester film according to any one of claims 1 to 4, wherein the apparent specific gravity of said polyester film is 0.4 to 1.3 g/cm³.

6. The polyester film according to any one of claims 1 to 5, wherein the opacifying power obtained by measuring the density of transmitted light under Filter G is 0.2 to 5.

7. The polyester film according to any one of claims 1 to 6, wherein the strength at break of said polyester film is 1 to 50 kg/mm³.