System and method for controlling curl in multi-layer webs

• US 8,647,556 B2
• Filed: 09/26/2007
• Issued: 02/11/2014
• Est. Priority Date: 09/28/2006
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Swanson, Ronald P., Henderson, Andrew J.
• Primary Examiner(s): WOLLSCHLAGER, JEFFREY MICHAEL
• Application Number:
  US11/861,769
• Publication Number:
  US 20080081164A1
• Time in Patent Office: 2,330 Days
• Field of Search: None
• US Class Current: 264/447
• CPC Class Codes: B05D 3/12 by mechanical means
• CPC Class Codes: B05D 7/04 to surfaces of films or sheets producing layered products by applying coatings of pasty or pulverulent plastics B29C41/00
• CPC Class Codes: B29C 55/023 using multilayered plates or sheets
• CPC Class Codes: B29C 55/026 of preformed plates or sheets coated with a solution, a dispersion or a melt of thermoplastic material
• CPC Class Codes: B65H 23/022 by tentering devices
• CPC Class Codes: B65H 23/025 by rollers
• CPC Class Codes: B65H 23/34 Apparatus for taking-out curl from webs
• CPC Class Codes: B65H 2301/5114 coating
• CPC Class Codes: B65H 2301/51212 perpendicularly to the direction of displacement of handled material, e.g. forming a loop
• CPC Class Codes: B65H 2301/5124 Stretching; Tentering
• CPC Class Codes: B65H 2301/51242 Stretching transversely; Tentering
• CPC Class Codes: B65H 26/00 Warning or safety devices, e.g. automatic fault detectors, stop-motions, for web-advancing mechanisms safety devices in general F16P; investigating chemical or physical properties of materials in general G01N; indicating devices in general G08B
• CPC Class Codes: B65H 2701/1864 Superposed webs
• CPC Class Codes: C08J 2433/00 Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
• CPC Class Codes: C08J 7/0427 with only one layer of a composition containing a polymer binder with more layers C08J7/042

Abstract

A system and method for controlling curl in multi-layer webs. The method can include providing a coated web, curing the coating to form a multi-layer web, and stretching the web during curing of the coating. Some coatings shrink at least partially when cured such that curing the coating induces a strain in the multi-layer web. Stretching the web occurs during curing to induce an opposing strain that at least partially counteracts the strain induced by curing to form a multi-layer web having a desired curvature. The system can include a curing section configured to cure the coating, and can further include a web stretching section, which can be located proximate the curing section and can be substantially coincident with the curing section, such that the web is stretched while the coating is cured.

Claims

1. A method for reducing strain-induced curl in a multi-layer web, the method comprising:

providing a coated web, the coated web including a coating applied to a web of indeterminate length, the coating being characterized by at least partially shrinking when cured;

curing the coating to form a multi-layer web, the multi-layer web including a strain induced by curing the coating during a coating stress development period; and

stretching the web during the coating stress development period, wherein stretching the web substantially cancels the strain induced by curing such that the resulting multi-layer web is substantially flat, wherein stretching the web increases a dimension of the web during the stretching step;

wherein curing at least includes applying radiation to the coating subsequent to stretching the web in a cross-machine direction.

2. The method of claim 1, wherein curing the coating induces a strain in the machine direction and the cross-machine direction, and wherein stretching the web includes stretching the web in the machine direction and the cross-machine direction.

3. The method of claim 2, wherein stretching the web in the machine direction and the cross-machine direction includes stretching the web in the machine direction and the cross-machine direction simultaneously.

4. The method of claim 2, wherein stretching the web in the machine direction and the cross-machine direction includes:

a first stretching step in which the web is stretched in one of the machine direction and the cross-machine direction, and

a second stretching step in which the web continues to be stretched in the one of the machine direction and the cross-machine direction and is additionally stretched in the other of the machine direction and the cross-machine direction,

wherein the coating is cured during the second stretching step.

5. The method of claim 1, wherein curing includes curing by at least one of actinic radiation, UV radiation, visible-light radiation, electron beam radiation, X-ray radiation, IR radiation, heat, and combinations thereof.

6. The method of claim 1, wherein the thickness of the resulting multi-layer web is less than about 500 μ

m.

7. The method of claim 1, wherein the coating comprises at least one of acrylate and epoxy.

8. The method of claim 1, wherein the multi-layer web comprises a multi-layer optical film.

9. The method of claim 1, wherein stretching includes applying a web line tension of at least about 525 N/m to the web.

10. The method of claim 1, wherein stretching the web includes passing the web through a web stretching assembly adapted to stretch the web in a cross-machine direction.

11. The method of claim 10, wherein the web includes lateral ends, and wherein the web stretching assembly includes:

a roller adapted to rotate about an axis of rotation;

an endplate positioned adjacent an end of the roller and adapted to rotate about the axis rotation, the endplate including an outer circumferential surface;

a groove formed in the outer circumferential surface, the groove extending circumferentially; and

a belt dimensioned to be received within a portion of the groove to grip a lateral end of the web between the groove and the belt,

wherein the endplate is oriented at an angle with respect to the axis of rotation such that the web is stretched in the cross-machine direction when it passes over the roller and endplate.

12. The method of claim 1, wherein stretching the web includes stretching the web within the elastic range of the web.

13. The method of claim 1, wherein applying radiation to the coating includes applying radiation selected from a group consisting of actinic radiation, ultraviolet radiation, visible light radiation, electron beam radiation, X-ray radiation, and infrared radiation.

14. The method of claim 13, wherein the radiation process occurs after a point of maximal stretch.

15. The method of claim 14, wherein the radiation process occurs after a point of maximal cross-machine stretch.

16. The method of claim 1, wherein at least some stretching occurs after a point of initial solidification of the coating.

17. The method of claim 1, wherein no stretching occurs between a start of the curing process and initial solidification of the coating.

18. The method of claim 1, wherein all of the stretching occurs after the point of initial solidification of the coating.

19. The method of claim 1, wherein all of the stretching occurs prior to the point wherein the coating is substantially cured.