Methods and apparatus for embossing a precision optical pattern in a resinous sheet or laminate

• US 4,601,861 A
• Filed: 08/10/1984
• Issued: 07/22/1986
• Est. Priority Date: 09/30/1982
• Status: Expired due to Term

• Current Assignee: Avery Dennison Corporation
• Original Assignee: Amerace Corporation (ABB Limited)
• Inventors: Pricone, Robert M., Roberts, William N.
• Primary Examiner(s): Lowe, James
• Application Number:
  US06/640,011
• Time in Patent Office: 711 Days
• Field of Search: 264/1.3, 264/1.4, 264/1.6, 264/1.9, 264/2.7, 264/106, 264/107, 264/284, 264/235, 264/346, 425/174.4, 425/373, 425/384, 425/385, 425/404, 425/446, 425/71
• US Class Current: 264/1.6
• CPC Class Codes: B29C 59/022 characterised by the disposition or the configuration, e.g. dimensions, of the embossments or the shaping tools therefor
• CPC Class Codes: B29C 59/046 for layered or coated substantially flat surfaces
• CPC Class Codes: B29D 11/00 Producing optical elements, e.g. lenses or prisms grinding or polishing of optical elements B24B; constructional form of optical elements G02B; optical parts of spectacles G02C7/00
• CPC Class Codes: B29D 11/00009 Production of simple or compound lenses
• CPC Class Codes: B29D 11/00278 Lenticular sheets B29D11/00269 takes precedence
• CPC Class Codes: B29D 11/00605 Production of reflex reflectors
• CPC Class Codes: B29L 2011/0083 Reflectors
• CPC Class Codes: B32B 2307/416 Reflective
• CPC Class Codes: B32B 38/06 Embossing
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet

Abstract

Disclosed herein are an improved method and apparatus for continuously embossing a repeating pattern of precise detail, in particular, cube-corner type reflector elements, on one surface of a single sheet or on one surface of a laminate of transparent thermoplastic materials, to form retroreflective sheeting. A continuous embossing tool in the form of a flexible thin metal belt or cylinder has on its outer surface an embossing pattern which is the reverse of the precision optical pattern to be formed. The embossing tool is continously moved at a predetermined speed along a closed course through a heating station where the temperature of a portion of the embossing tool is raised to be above the glass transition temperature of the sheeting or laminate and a cooling station where the heated portion of the embossing tool is cooled while in a relatively planar condition to be below that glass transition temperature. The sheeting is continuously moved at the predetermined speed from a supply thereof into engagement with the embossing pattern on the tool and is pressed thereagainst continuously at a plurality of pressure points sequentially spaced along the heating station, with the one surface of the sheeting confronting and engaging the embossing pattern until the sheeting is raised above its glass transition temperature and conforms to the embossing pattern on the one face. The sheeting is maintained in engagement with the tool until the tool passes through the cooling station and the sheeting is lowered below its glass transition temperature and the pattern solidifies. The sheeting thereafter is stripped from the tool and next passed through a reheating station where the embossed sheeting is heated to an annealing temperature where the stresses formed in the thermoplastic material during cooling are relieved, while preserving and enhancing the precision optical pattern previously formed.

Claims

1. An improved method for continuously embossing a precision optical pattern requiring sharp angles and flatness of faces in certain detail on one surface of a continuous resinous sheeting material, the method being performed with the aid of a generally cylindrical endless metal embossing element having an inner surface and an outer surface, the outer surface having a precision optical embossing pattern which is the reverse of the precision optical pattern to be formed on one surface of said sheeting, and wherein the method includes the steps of:

(a) continuously moving the endless embossing element along a closed course through a heating station, where said embossing element is heated through its inner surface to a predetermined temperature and then to a cooling station where said embossing element is cooled below said predetermined temperature;

(b) continuously feeding onto said embossing element as it passes through a part of said heating station superimposed resinous film and sheeting materials, said resinous materials of said film and said sheeting each having different glass transition temperatures, said sheeting being in direct contact with the outer precision patterned surface of said embossing tool;

(c) continuously heating said embossing element to said predetermined temperature at said heating station, said temperature being greater than the glass transition temperature of said sheeting and less than the glass transition temperature of said resinous film;

(d) pressing said superimposed film and sheeting against said embossing element at a plurality of pressure points sequentially spaced along said heating station with one surface of said sheeting confronting and engaging said precision optical pattern on said embossing element until said one surface of said sheeting conforms to said precision optical embossing pattern;

(e) continuously passing said embossing element and said superimposed film and sheeting through said cooling station where the temperature of said embossing element and said sheeting is lowered below said sheeting glass transition temperature, with said film serving to substantially continuously maintain said sheeting in engagement with said embossing element through the heating station and through said cooling station; and

(f) continuously stripping said superimposed layer of film and embossed sheeting from said embossing element, said film being later strippable from the other face of said sheeting without destroying said optical pattern formed on said one face of said sheeting, the improvement comprising;

(g) said cooling step being substantially effected while said superimposed film and sheeting and embossing tool are disposed in a generally planar condition, thereby to achieve an increase in the optical efficiency of the embossed sheeting.

2. The method of claim 1, wherein said course is cylindrical through the heating station and said pressure points are provided by at least three spaced pressure rollers, and said course is generally planar through said cooling station.

3. The method of claim 1, wherein said cooling is achieved by directing a chilled fluid against said sheeting and said film, thereby to effect an abrupt and substantial drop in temperature thereof and thereby to quickly rigidify the precision optical elements while the embossing element and formed sheeting are in a generally undistorted condition.

4. The method of claim 1, wherein said embossing tool is a thin flexible seamless metal belt, the heating station is a heated roller, and said cooling station is in juxtaposition with said film as said element leaves said heating roller and passes through said planar area, and includes means for directing a chilled fluid against said film as it passes thereover.

5. The method of claim 4 wherein said means for directing a chill fluid against said film as it passes thereover includes a cooling manifold.

6. The method of claim 1, wherein the temperature of said sheeting is lowered to about 120°

F. at said cooling station.

7. The method of claim 1, wherein said sheeting is acrylic, said film is polyester, the temperature of said embossing pattern at said heating station is sufficiently high to raise the temperature of said sheeting to a range between 425°

F. and 475°

F., and the temperature at said cooling station is sufficiently low to lower the temperature of said sheeting to 180°

F. or below as said sheeting passes through said cooling station.

8. The method of claim 1, wherein said precision optical pattern is in the form of an array of female cube-corner type elements whereby the sheeting formed thereby has male cube-corner elements on the one face thereof in contrast with said tool, and the finished sheeting thereby is provided with an array of retroreflective cube-corner elements thereon.

9. The method set forth in claim 1, and further including the step of reheating said embossed sheeting and film to a temperature in the range of about 180°

F. to 200°

F. thereby to improve the optical efficiency of said embossed sheeting.

10. The method set forth in claim 9, wherein the temperature achieved in said sheeting at reheating is about 195°

F.

11. The method set forth in claim 9, wherein said reheating is accomplished on a continuous basis by causing said superimposed layer of embossed sheeting and film to be continuously directed through a reheating station after said film and sheeting are stripped from said embossing element.

12. The method set forth in claim 9, wherein said stripped film and sheeting are reheated long enough to assure that all of the film and embossed sheeting reaches a temperature in the range between 180°

F. and 200°

F.

13. An improved method for continuously embossing a precision optical pattern requiring sharp angles and flatness of faces in certain detail on one surface of a continuous resinous sheeting material, the method being performed with the aid of a generally cylindrical endless metal embossing element having an inner surface and an outer surface, the outer surface having a precision optical embossing pattern which is the reverse of the precision optical pattern to be formed on one surface of said sheeting, and wherein the method includes the steps of:

(a) continuously moving the endless embossing element along a closed course through a heating station, where said embossing element is heated through its inner surface to a predetermined temperature and then to a cooling station where said embossing element is cooled below said predetermined temperature;

(b) continuously feeding onto said embossing element as it passes through a part of said heating station superimposed resinous film and sheeting materials, said resinous materials of said film and said sheeting each having different glass transition temperatures, said sheeting being in direct contact with the outer precision patterned surface of said embossing tool;

(c) continuously heating said embossing element to said predetermined temperature at said heating station, said temperature being greater than the glass transition temperature of said sheeting and less than the glass transition temperature of said resinous film;

(d) pressing said superimposed film and sheeting against said embossing element at a plurality of pressure points sequentially spaced along said heating station with one surface of said sheeting confronting and engaging said precision optical pattern on said embossing element until said one surface of said sheeting conforms to said precision optical embossing pattern;

(e) continuously passing said embossing element and said superimposed film and sheeting through said cooling station where the temperature of said embossing element and said sheeting is lowered below said sheeting glass transition temperature, with said film serving to substantially continuously maintain said sheeting in engagement with said embossing element through the heating station and through said cooling station; and

(f) continuously stripping said superimposed layer of film and embossed sheeting from said embossing element, said film being later strippable from the other face of said sheeting without destroying said optical pattern formed on said one face of said sheeting, the improvement comprising the step of;

(g) reheating said embossed sheeting and film to a temperature in the range of about 180°

F. to 200°

F., thereby to relieve any strain in said film caused by cooling thereof at said cooling station.

14. The method set forth in claim 13, wherein the temperature achieved in said reheating is about 195°

F.

15. The method set forth in claim 13, wherein said reheating is accomplished on a continuous basis by causing said superimposed layer of embossed sheeting and film to be continuously directed through a reheating station after said film and sheeting are stripped from said embossing element.

16. The method set forth in claim 13, wherein said stripped film and sheeting are heated long enough to assure that all of the film and embossed sheeting reaches a temperature in the range between 180°

F. and 200°

F.

17. Apparatus for continuously embossing a precision optical pattern on one surface of transparent resinous material or materials, said apparatus comprising:

embossing means including a continuous seamless embossing tool in the form of a thin metal element having an inner surface and an outer surface, said outer surface having a precision optical embossing pattern thereon which is the reverse of the precision optical pattern to be formed in the resinous material;

means for continuously moving said embossing element along a closed course;

means for introducing superimposed film and sheeting of resinous materials onto said embossing element with one face of said sheeting in direct contact with said optical pattern on said embossing element;

heating means for raising the temperature of said embossing pattern to be above the glass transition temperature of said sheeting and below the glass transition temperature of said film while said embossing element is in a first portion of its course;

cooling means for lowering the temperature of said sheeting to be below said glass transition temperature while said element and said sheeting are in a generally planar condition in their course, thereby to rigidify said precision pattern while in an undistorted condition;

a plurality of pressure means sequentially spaced along said first portion of said course for pressing said superimposed film and sheeting against said embossing element with said one surface of said sheeting confronting and engaging said embossing pattern until said one surface conforms to said embossing pattern, with said film serving to substantially continuously maintain said sheeting in engagement with said embossing element until the latter passes said second portion of said course; and

means for thereafter stripping said superimposed film and sheeting from said embossing element.

18. The apparatus of claim 17, wherein said embossing element is a thin seamless flexible metal belt.

19. The apparatus of claim 17, wherein said heating means is provided by an internally heated heating roller and said cooling means includes a manifold adopted to direct a chilled fluid against said film and said sheeting and said tool as said film passes thereover.

20. The apparatus of claim 17, wherein said precision optical pattern comprises an array of cube-corner type reflective elements.

21. The apparatus set forth in claim 17, and further including means for reheating said superimposed sheeting and film to a temperature in the range of 180°

F. to 200°

F. after stripping thereof from said embossing element.

22. The apparatus set forth in claim 21, wherein said reheating means is arranged to continuously reheat said superimposed film and sheeting as the same are continously stripped from said embossing element.

23. Apparatus for continuousy embossing a precision optical pattern on one surface of transparent resinous material or materials, said apparatus comprising;

embossing means including a continuous seamless embossing tool in the form of a thin metal element having an inner surface and an outer surface, said outer surface having a precision optical embossing pattern thereon which is the reverse of the precision optical pattern to be formed in the resinous material;

means for continuously moving said embossing element along a closed course;

means for introducing superimposed film and sheeting of resinous materials onto said embossing element with one face of said sheeting in direct contact with said optical pattern on said embossing element;

heating means for raising the temperature of said embossing pattern to be above the glass transition temperature of said sheeting and below the glass transition temperature of said film while said embossing element is in a first portion of its course;

cooling means for lowering the temperature of said sheeting to be below said glass transition temperature while said element and said sheeting are in a generally planar condition in their course, thereby to rigidify said precision pattern while in an undistorted condition;

a plurality of pressure means sequentially spaced along said first portion of said course for pressing said superimposed film and sheeting against said embossing element with said one surface of said sheeting confronting and engaging said embossing pattern until said one surface conforms to said embossing pattern, with said film serving to substantially continuously maintain said sheeting in engagement with said embossing element until the latter passes said second portion of said course;

means for thereafter stripping said superimposed film and sheeting from said embossing element; and

means for reheating said superimposed sheeting and film to a temperature in the range of 180°

F. to 200°

F. after stripping thereof from said embossing element.