Method of making a uniaxially stretched polymeric film having structured surface

• US 20060138686A1
• Filed: 12/23/2004
• Published: 06/29/2006
• Est. Priority Date: 12/23/2004
• Status: Abandoned Application

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Ouderkirk, Andrew J., Biernath, Rolf W., Merrill, William Ward, Benson, Olester Jr., Kowitz, David A.
• Application Number:
  US11/184,026
• Publication Number:
  US 20060138686A1
• Time in Patent Office: Days
• US Class Current: 264/2.700
• CPC Class Codes: B29C 55/04 uniaxial, e.g. oblique

Abstract

A process for uniaxially stretching films having a structured surface comprising a geometric feature is described. The process provides a film in which the cross sectional shape of the feature after stretching is substantially identical to the cross sectional shape of the feature prior to stretching.

Claims

1. A method of making a structured surface polymeric film comprising the steps of:

(a) providing a polymeric film having (i) a first structured and a second surface, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axis in a thickness direction of the polymeric film, wherein the first structured surface comprises at least one geometric feature thereon; and

subsequently

(b) stretching the structured surface polymeric film in a direction substantially parallel to the first in-plane axis of the polymeric film;

wherein the cross sectional shape of the geometric feature before step (b) is substantially retained after step (b).

2. A method according to claim 1 wherein the polymeric film is substantially unstretched prior to step (b).

3. A method according to claim 1 wherein the polymeric film is substantially unoriented prior to step (b).

4. A method according to claim 1 wherein the polymeric film is stretched in step (b) to a stretch ratio of at least 1.1.

5. A method according to claim 4 wherein the polymeric film is stretched in step (b) to a stretch ratio of at least 1.5 and wherein the ratio of the larger to smaller of the stretch ratios along the second in-plane axis and the third axis is 1.4 or less.

6. A method according to claim 1 wherein the polymeric film is uniaxially stretched in step (b).

7. A method according to claim 6 wherein the film is stretched only in step (b).

8. A method according to claim 1 wherein the polymeric film is birefringent after step (b).

9. A method according to claim 8 wherein the polymeric film has a relative birefringence of 0.3 or less.

10. A method according to claim 1 wherein the polymeric film is derived from a polymer selected the group consisting of amorphous polymers, semicrystalline polymers, crystalline polymers, and liquid crystalline polymers.

11. A method according to claim 1 wherein the polymeric film is derived from a thermoplastic polymer, a thermosettable polymer, a radiation curable polymer and combinations thereof.

12. A method according to claim 1 wherein the structured surface polymeric film comprises a plurality of layers.

13. A method according to claim 1 wherein the geometric feature is elongate and is disposed on the first structured surface in a direction substantially parallel to the first in-plane axis.

14. A method according to claim 1, wherein the polymeric film after step (b) is a continuous roll having the structured surface.

15. A method according to claim 1, wherein step (a) further comprises extruding or coextruding the polymeric film and simultaneously forming the structured surface thereon.

16. A method according to claim 1 wherein the structured surface comprises a plurality of geometric features.

17. A method according to claim 16 wherein the geometric features are continuous in the direction of the first in-plane axis.

18. A method according to claim 16 wherein the geometric features are discontinuous in the direction of the first in-plane axis.

19. A method according to claim 1 wherein the structured surface comprises at least one micro-feature.

20. A method according to claim 1 wherein the polymeric film has a first orientation state prior to stretching and a second orientation state, different than the first orientation state, after stretching.