METHOD FOR FORMING HIGH-IMPACT TRANSPARENT, DISTORTION-FREE POLYMERIC MATERIALS

• US 20070246865A1
• Filed: 04/13/2007
• Published: 10/25/2007
• Est. Priority Date: 08/13/2001
• Status: Active Grant

• Current Assignee: Clear Armor, LLC, PH Realty, LLC
• Original Assignee: PH Realty, LLC
• Inventors: Oakey, Edwin, Tinney, Rodney
• Granted Patent: US 8,366,987 B2
• Time in Patent Office: Days
• US Class Current: 264/409
• 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

1-38. -38. (canceled)

39. 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, said peripheral edge having a desired contour or curve;

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 contoured or curved peripheral edge.

40. The method for forming a sheet of polymeric material as set forth in claim 39, further comprising the step of detecting a size of the sheet within one of said first and second mold halves for initiating said cooling.

41. The method for forming a sheet of polymeric material as set forth in claim 40, wherein said detecting of said size is achieved using a laser and sensor.

42. The method for forming a sheet of polymeric material as set forth in claim 39, 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.

43. The method for forming a sheet of polymeric material as set forth in claim 39, 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.

44. The method for forming a sheet of polymeric material as set forth in claim 39, wherein said second temperature is less than a glass transition temperature of the sheet.

45. The method for forming a sheet of polymeric material as set forth in claim 39, wherein said heating of the sheet occurs in stages.

46. The method for forming a sheet of polymeric material as set forth in claim 39, further comprising generating said pressure as a positive pressure.

47. The method for forming a sheet of polymeric material as set forth in claim 39, further comprising generating said pressure as a negative pressure.

48. The method for forming a sheet of polymeric material as set forth in claim 39, wherein said first mold half is closed.

49. The method for forming a sheet of polymeric material as set forth in claim 48, wherein said second mold half is closed.

50. 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

activating a fluid flow in one of said first and second mold halves;

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.

51. The method for forming a sheet of polymeric material as set forth in claim 50, further comprising the step of detecting a size of the sheet within one of said first and second mold halves for initiating said cooling.

52. The method for forming a sheet of polymeric material as set forth in claim 50, 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.

53. The method for forming a sheet of polymeric material as set forth in claim 50, 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.

54. The method for forming a sheet of polymeric material as set forth in claim 50, wherein said second temperature is less than a glass transition temperature of the sheet.

55. The method for forming a sheet of polymeric material as set forth in claim 50, wherein said heating of the sheet occurs in stages.

56. The method for forming a sheet of polymeric material as set forth in claim 50, wherein said first mold half is closed.

57. The method for forming a sheet of polymeric material as set forth in claim 55, wherein said second mold half is closed.

58. 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;

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;

actively 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.

59. The method for forming a sheet of polymeric material as set forth in claim 58, further comprising said polymeric sheet being a polycarbonate sheet.

60. The method for forming a sheet of polymeric material as set forth in claim 58, further comprising said coating step including a primer coating and a hard coat top coating.

61. The method for forming a sheet of polymeric material as set forth in claim 60, further comprising coating both sides of said sheet.