Method for forming high-impact transparent, distortion-free polymeric materials

• US 8,366,987 B2
• Filed: 04/13/2007
• Issued: 02/05/2013
• Est. Priority Date: 08/13/2001
• Status: Expired due to Term

• Current Assignee: Clear Armor, LLC, PH Realty, LLC
• Original Assignee: PH Realty, LLC
• Inventors: Oakey, Edwin J., Tinney, Rodney M.
• Primary Examiner(s): Gupta, Yogendra
• Assistant Examiner(s): ROBITAILLE, JOHN P
• Application Number:
  US11/787,266
• Publication Number:
  US 20070246865A1
• Time in Patent Office: 2,125 Days
• Field of Search: 264/322, 264/479, 264/544
• US Class Current: 264/544
• CPC Class Codes: B29C 2035/1658 using gas
• CPC Class Codes: B29C 2791/006 Using vacuum
• CPC Class Codes: B29C 2791/007 Using fluid under pressure
• CPC Class Codes: B29C 2793/00 Shaping techniques involving a cutting or machining operation
• CPC Class Codes: B29C 51/008 without using a mould, e.g. ballooning as prestretching step B29C51/06
• CPC Class Codes: B29C 51/04 Combined thermoforming and prestretching, e.g. biaxial stretching
• CPC Class Codes: B29C 51/082 by shaping between complementary mould parts
• CPC Class Codes: B29C 51/10 Forming by pressure difference, e.g. vacuum
• CPC Class Codes: B29C 51/262 Clamping means for the sheets, e.g. clamping frames
• CPC Class Codes: B29C 51/32 having cutting means
• CPC Class Codes: B29C 51/421 of preforms, specially adapted for thermoforming preheating sheets in general B29B13/023; B29C51/427 takes precedence
• CPC Class Codes: B29C 51/427 Cooling of the material with a fluid blast
• CPC Class Codes: B29C 51/428 of moulds or mould parts
• CPC Class Codes: B29C 51/46 Measuring, controlling or regulating
• CPC Class Codes: B29K 2033/08 Polymers of acrylic acid esters, e.g. PMA, i.e. polymethylacrylate
• CPC Class Codes: B29K 2069/00 Use of PC, i.e. polycarbonates or derivatives thereof, as moulding material
• CPC Class Codes: Y10T 428/31507 Of polycarbonate

Abstract

A method and apparatus are provided for forming a sheet of polymeric material, such as polycarbonate. A forming mold is provided having halves that engage for forming a heated sheet therebetween. Each of the halves defines an interior cavity having a peripheral edge. The sheet is retained between the peripheral edges of the halves and a vacuum is generated within one of the cavities for drawing the sheet therein, whereby a sensing mechanism detects a draw depth for initiating a cooling mechanism to cool the sheet to a temperature below a glass transition temperature of the material. A series of retention mechanisms are provided about the peripheral edge of one of the halves, for biasing the sheet into engagement with the peripheral edge of the opposing half. A trimming mechanism is further provided for trimming the perimeter of the sheet to a desired form.

Claims

1. A method for forming a sheet of polymeric material, comprising the steps of:

heating the sheet to a first temperature wherein the sheet is heated past a glass transition temperature and said sheet achieves a glass transition state;

terminating heating of said sheet prior to placing in a first mold half;

retaining the sheet between said first and a second mold half of a forming mold with the sheet supported along a peripheral edge of one of said first and second mold halves;

forming the peripheral edge of the sheet by the contacting of the first and second mold halves to form a desired non-planar contour or curve portion above or below a horizontal plane contour or curve on the peripheral edge;

generating a pressure on one side of the sheet thereby moving the sheet into a space of one of said first and second mold halves while a center portion of the sheet remains supported in space relationship to one of said first and second mold halves; and

cooling the sheet from said first temperature to a second temperature upon achieving a specified size depth of the sheet within one of said first and second mold halves; and

forming a sheet having a complementary non-planar contour or curve in an edge portion of the polymeric material contoured or curved peripheral edge.

2. The method for forming a sheet of polymeric material as set forth in claim 1, further comprising the step of detecting a size of the sheet within one of said first and second mold halves for initiating said cooling.

3. The method for forming a sheet of polymeric material as set forth in claim 2, wherein said detecting of said size is achieved using a laser and sensor.

4. The method for forming a sheet of polymeric material as set forth in claim 1, further comprising the steps of:

relieving said pressure from said one side of the sheet;

withdrawing one of said first and second mold halves from the other of said first and second mold halves; and

removing said sheet from said forming mold.

5. The method for forming a sheet of polymeric material as set forth in claim 1, wherein said first temperature is greater than or equal to a glass transition temperature of the sheet and less than a melting temperature of the sheet.

6. The method for forming a sheet of polymeric material as set forth in claim 1, wherein said second temperature is less than a glass transition temperature of the sheet.

7. The method for forming a sheet of polymeric material as set forth in claim 1, wherein said heating of the sheet occurs in stages.

8. The method for forming a sheet of polymeric material as set forth in claim 1, further comprising generating said pressure as a positive pressure.

9. The method for forming a sheet of polymeric material as set forth in claim 1, further comprising generating said pressure as a negative pressure.

10. The method for forming a sheet of polymeric material as set forth in claim 1, wherein said first mold half is closed.

11. The method for forming a sheet of polymeric material as set forth in claim 10, wherein said second mold half is closed.

12. A method for forming a sheet of polymeric material, comprising the steps of:

heating the sheet to a first temperature;

retaining the sheet between first and second mold halves of a forming mold with the sheet supported along a peripheral edge;

generating a positive pressure on one side of the sheet thereby moving the sheet into an interior space of one of said first and second mold halves while a center portion of the sheet remains supported in space relationship to one of said first and second mold halves; and

cooling the sheet from said first temperature to a second temperature upon achieving a specified size of the sheet within one of said first and second mold halves wherein said first temperature is greater than or equal to a glass transition temperature of the sheet and less than a melting temperature of the sheet.

13. The method for forming a sheet of polymeric material as set forth in claim 12, further comprising the step of detecting a size of the sheet within one of said first and second mold halves for initiating said cooling.

14. The method for forming a sheet of polymeric material as set forth in claim 12, further comprising the steps of:

relieving said pressure from said one side of the sheet;

withdrawing one of said first and second mold halves from the other of said first and second mold halves; and

removing said sheet from said forming mold.

15. The method for forming a sheet of polymeric material as set forth in claim 12, wherein said second temperature is less than a glass transition temperature of the sheet.

16. The method for forming a sheet of polymeric material as set forth in claim 12, wherein said heating of the sheet occurs in stages.

17. The method for forming a sheet of polymeric material as set forth in claim 12, wherein said first mold half is closed.

18. The method for forming a sheet of polymeric material as set forth in claim 16, wherein said second mold half is closed.

19. A method for forming a sheet of polymeric material, comprising the steps of:

heating the sheet to a first temperature wherein the sheet is heated past a glass transition temperature and said sheet achieves a glass transition state;

terminating heating of said sheet prior to placing in a first mold half;

retaining the sheet between said first and a second mold half of a forming mold;

supporting the sheet along a peripheral edge of one of said first and second mold halves;

forming the peripheral edge of the sheet by clamping of the first and second mold halves;

generating a pressure on one side of the sheet thereby moving the sheet into a space of one of said first and second mold halves while a center portion of the sheet remains supported in space relationship to one of said first and second mold halves;

coupling a device with one of said mold halves for actively generating an active circuit fluid flow directly into one of said mold halves;

actively generating an active circulating fluid flow directly within one of said mold halves for cooling the sheet from said first temperature to a second temperature upon achieving a specified size depth of the sheet within one of said first and second mold halves;

removing said sheet from said first and second mold halves; and

coating said sheet with a protective coating.

20. The method for forming a sheet of polymeric material as set forth in claim 19, further comprising said polymeric sheet being a polycarbonate sheet.

21. The method for forming a sheet of polymeric material as set forth in claim 19, further comprising said coating step including a primer coating and a hard coat top coating.

22. The method for forming a sheet of polymeric material as set forth in claim 21, further comprising coating both sides of said sheet.