Patent ID: 11945201
Assignee: TOYOBO CO., LTD.
Field: Other special machines (Mechanical engineering)
Classification: CPC B | IPC B

Claim 16:
17. A method for producing the cavity-containing polyester film according to claim 1, the method comprising:
producing a cavity-containing polyester film having an apparent density ranging from 0.8 to 1.2 g/cm3, comprising the step of: melt-extruding a laminate into a sheet form, this laminate being a laminate comprising a layer (layer A) which comprises a composition comprising a polyester resin and a polypropylene resin satisfying all of the following requirements (4) to (6), and layers (layers B) which each comprise a polyester resin containing inorganic particles and which are laminated, respectively, over both surfaces of the layer A:
(4) the polypropylene resin having a melt flow rate (MFR) ranging from 1.0 to 10 g/10-minutes (at a temperature of 230° C. under a load of 2.16 kg),
(5) the polypropylene resin showing a deflection temperature of 85° C. or higher under load (at a bending stress of 0.45 MPa), and
(6) the polypropylene resin having a weight-average molecular weight Mw ranging from 200000 to 450000, this weight-average molecular weight being measured by gel permeation chromatography (GPC), and having a molecular weight distribution ranging from 2 to 6, this molecular weight distribution being represented as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the polypropylene resin (Mw/Mn);
and next drawing the sheet into at least one axial direction of the sheet to incorporate cavities into the layer A.