Biaxially oriented polyester film having more than one layer, process for its production, and its use as magnetic tape film
AssigneeMitsubishi Polyester Film GmbH
InventorsJoerg Hellmann, Gottfried Hilkert, Wolfram Goerlitz
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Abstract
The invention relates to a biaxially oriented polyester film which has three layers and which, together with very good electromagnetic properties compared with prior art films, has improved abrasion properties. The two sides of the film are built up from at least one base layer B and, applied to this base layer, outer layers A and C, where these outer layers have a defined number of elevations of defined height. The invention also relates to a process for producing the film and to its use as magnetic tape film.
Claims20
A biaxially oriented, coextruded polyester film comprising at least three layers and whose two surfaces are formed by outer layers A and C, where a base layer B is located between these outer layers, wherein layers A and C have different compositions, and wherein the outer layer A
- has an Ra value of ≦15 nm, and
- has an Rz value of ≦150 nm and
- has a number of elevations Na per 0.36 mm2 which is related as follows to their respective heights ha:
- A1·e−B1·ha≦Na≦A2·e−B2·ha (1)
- where
- A1=300, A2=7000
- B1=7.0, B2=8.0 and
- 0.01 μm≦ha≦1.0 μm
- and the outer layer C
- has an Ra value which is greater than that of the outer layer A and
- has a number of elevations Nc per 0.36 mm2 which is related as follows to their respective heights hc:
- Nc≦F·e−G·hc (2)
- where
- F=20,000, G=9.0
- and where the haze per unit thickness is ≦0.4%/μm.
Dependencies are inferred from the claim text.