Apparatus for producing low birefringence plastic film and sheet

• US 20020114922A1
• Filed: 02/16/2001
• Published: 08/22/2002
• Est. Priority Date: 02/16/2001
• Status: Active Grant

• Current Assignee: Sabic Innovative Plastics IP BV (Government of Saudi Arabia)
• Original Assignee: General Electric Company
• Inventors: Lilly, Kenneth L., Morrow, Robert, Wildeman, Russell Wayne, Bourne, Robert Allan, Schenk, Brian Scott, Coyle, Dennis Joseph
• Granted Patent: US 6,773,649 B2
• Time in Patent Office: Days
• US Class Current: 428/141
• CPC Class Codes: B29C 43/222 characterised by the shape of the surface
• CPC Class Codes: B29C 43/24 Calendering
• CPC Class Codes: B29C 48/00 Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor extrusion blow-moulding B29C49/04
• CPC Class Codes: B29C 48/08 flexible, e.g. films
• CPC Class Codes: B29K 2995/0032 Birefringent
• CPC Class Codes: B32B 15/013 one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
• CPC Class Codes: Y10T 428/24355 Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]

Abstract

An apparatus for producing a thermoplastic film having low-birefringent, low stress and at least one polished surface for optical media applications as well as low stress film for non-optical applications using a continuous extrusion process. The apparatus consists of a novel calendering roll in a calendering roll stack wherein, at least one roll consists of an inner steel shell, a resilient covering over the inner steel roll and a multi-layer metal sleeve outer covering of at least two layers. The metal sleeve preferably consists of three layers. The inner layer of the multi-layer outer sleeve is preferably nickel, the intermediate layer is preferably copper and the outer layer is preferably chrome with a highly polished surface.

The film produced by the process has a retardation value (birefringence times thickness) of less than about 100 nanometers and a surface roughness of less than about 4 microinches. The process is a continuous extrusion process for producing such film or sheet and does not require any further finishing operations.

Claims

1. A low birefringence and low stress transparent or translucent thermoplastic film which is highly polished on at least one surface which film is suitable for optical media applications and which film has a retardation value of less than about 100 nanometers and wherein the highly polished surface has a roughness of less than about 4 microinches.

2. The thermoplastic film of claim 1, wherein the thermoplastic film has a thickness of about 0.001 to about 0.060 inches.

3. The thermoplastic film of claim 1 wherein both surfaces of the thermoplastic film are highly polished.

4. The thermoplastic film of claim 1, wherein the thermoplastic film is an aromatic polycarbonate film prepared from Bisphenol-A

5. The thermoplastic film of claim 1, wherein the retardation value is less than about 20 nm.

6. The thermoplastic film of claim 1, wherein at least one highly polished surface has a roughness of about 0.5 to about 2.0 microinches.

7. A low stress opaque thermoplastic film for non optical applications wherein the thermoplastic film has at least one highly polished surface having a roughness of less than 4 microinches.

8. The thermoplastic film of claim 7 wherein the film has a thickness of about 0.001 to about 0.060 inches.

9. The thermoplastic film of claim 7 wherein at least one highly polished surface has a roughness of about 0.5 to about 2.0 microinches.

10. The thermoplastic film of claim 7 wherein both surfaces of the thermoplastic film are highly polished.

11. A continuous film extrusion process for producing a transparent or translucent thermoplastic film for optical media applications having a low birefringence, low stress and wherein at least one surface of the film has a roughness of less than about 4 microinches and a retardation value of less than about 100 nanometers, which process comprises the steps of extruding a molten thermoplastic film, passing the molten thermoplastic film through an opening between two opposing calendering rolls wherein at least one calendering roll is a finishing roll and subsequently cooling the hot thermoplastic film to a temperature below its solidification temperature of the thermoplastic film, said finishing roll is a multi component structure comprised of an inner steel shell, an intermediate resilient covering over the inner steel and a metal layer metal sleeve outer covering comprised of at least two layers.

12. The process of claim 11, wherein the cooled thermoplastic film has a thickness of about 0.001 to about 0.060 inches.

13. The process of claim 11 wherein at least one surface of the thermoplastic film has a roughness of about 0.5 to about 2.0 microinches.

14. The process of claim 11 wherein the thermoplastic film produced thereby is an opaque thermoplastic film for non optical media applications.

15. The process of claim 11 wherein the 2 opposing calendering rolls are finishing rolls used to produce a thermoplastic film of low birefringence, low stress and wherein both surfaces of the thermoplastic film have a roughness of less than about 4 microinches.

16. The process of claim 15 wherein both surfaces of the thermoplastic film have a roughness of about 0.5 to about 2.0 microinches.

17. The finishing roll of claim 11 wherein the structure comprises an inner metal shell and an outer multi layer metal sleeve of at least two layers and having interdisposed there between an intermediate resilient cover over said inner metal shell.

18. The finishing roll of claim 17, wherein the intermediate resilient cover has sufficient resiliency to allow for deformation of the surface of the outer multi-layer metal sleeve in order to reduce flow induced stress in the thermoplastic film, said resilient cover having a hardness of about 50 to about 150 durometers.

19. The finishing roll of claim 17 wherein the outer multi-layer metal sleeve is capable of flexing to match the intermediate resilient cover.

20. The finishing roll of claim 17, wherein the outer layer of the multi-layer metal sleeve is capable of being polished to a surface roughness of less than about 4 microinches and is capable of flexing without failing.

21. The finishing roll of claim 17, wherein the inner layer of the multi-layer outer metal sleeve is comprised of nickel.

22. The finishing roll of claim 17, wherein the outer metal layer of the multi-layer outer metal sleeve is comprised of chrome.

23. The finishing roll of claim 17 wherein the multi-layer outer metal sleeve is comprised of 3 layers.

24. The finishing roll of claim 23 wherein the 3 layer outer metal sleeve is comprised of an inner layer comprised of nickel, an intermediate layer comprised of copper and an outer layer comprised of chrome.