Process for forming articles from extruded polymer sheet
Method for forming a transparent article comprising: heating a polymer sheet 40 to form a heated sheet; creating a pressure differential across the heated sheet; pushing the heated sheet onto the contoured surface 20 to form a shaped article; and releasing the shaped article from the mold 12 . Also included herein are articles made therefrom.
1. A method for forming a transparent article, comprising:
non-contact heating a polymer sheet to form a heated sheet, wherein the polymer sheet has a thickness of greater than 2.5 mm;
creating a pressure differential across the heated sheet to push the heated sheet onto a contoured surface of a mold to form a shaped article; and
releasing the shaped article from the mold;
wherein the shaped article has a difference in thinning across the shaped article of less than or equal to 35%;
wherein, without pre-drying the polymer sheet, a total cycle time for heating and forming the shaped article from the polymer sheet is less than or equal to 10 minutes.
2. A method for forming a transparent article, comprising:
non-contact heating a polymer sheet to form a heated sheet, wherein the polymer sheet has a thickness of greater than 2.5 mm;
creating a pressure differential across the heated sheet;
isostatically forming the heated sheet onto a contoured surface to form a shaped article; and
releasing the shaped article from the mold;
wherein the shaped article has a difference in thinning across the shaped article of less than or equal to 35%;
wherein, without pre-drying the polymer sheet, a total cycle time for heating and forming the shaped article from the polymer sheet is less than or equal to 10 minutes.
3. A method for forming a polycarbonate article, comprising:
heating a transparent polycarbonate sheet to form a heated sheet, having a transparency of greater than or equal to 1% measured according to ASTM D-1003-00 Procedure B, Spectrophotometer, using illuminant C with diffuse illumination and unidirectional viewing, wherein the polycarbonate sheet has a thickness of greater than 2.5 mm;
creating a pressure differential across the heated sheet to push the heated sheet onto a contoured surface of a mold to form a shaped article; and
releasing the shaped article from the mold;
wherein the polycarbonate sheet comprises greater than or equal to 50 wt % polycarbonate based upon a total weight of the polycarbonate sheet;
wherein the polycarbonate sheet has at least one of a UV protective coating and an abrasion-resistant coating; and
wherein the shaped article has a difference in thinning across the shaped article of less than or equal to 35%;
wherein, without pre-drying the polymer sheet, a total cycle time for heating and forming the shaped article from the polymer sheet is less than or equal to 10 minutes.
4. The method of claim 1 , wherein the thickness is greater than or equal to 3.0 mm.
5. The method of claim 1 , wherein the thickness is 3 mm to 18 mm.
6. The method of claim 1 , wherein the heating is to a temperature of the heated sheet of greater than HDT to (HDT+40° C.) as determined by ISO75-2.
7. The method of claim 6 , wherein the temperature is (HDT+5° C.) to (HDT+30° C.) as determined by ISO75-2.
8. The method of claim 1 , wherein the heating is to a temperature of the sheet of material of 10 to 65° C. above the Vicat softening temperature B/50, wherein the Vicat softening temperature B/50 is determined according to ISO 306 (50 N; 50° C./h).
9. The method of claim 1 , wherein the pressure differential is less than 300 bar.
10. The method of claim 9 , wherein the pressure differential is less than 200 bars.
11. The method of claim 1 , wherein a time for forming the shaped article from the polymer sheet is less than or equal to 5 minutes.
12. The method of claim 11 , wherein a time for forming the shaped article from the polymer sheet is less than or equal to 3 minutes.
13. The method of claim 1 , wherein the shaped article has no cracks visible to the unaided eye having normal vision.
14. The method of claim 1 , wherein the heating is achieved by way of radiant heating with the aid of infrared radiation.
15. The method of claim 1 , wherein the polymer sheet comprises polycarbonate.
16. The method of claim 1 , wherein the polymer sheet further comprises a drape formable coating, wherein the drape formable coating comprises at least one of a UV protective coating and an abrasion-resistant coating.
17. The method of claim 1 , comprising no heating for greater than or equal to 15 minutes to dry the heated sheet before forming the shaped article.
18. The method of claim 1 , wherein the heating is to a temperature of the heated sheet of (HDT+5° C.) to (HDT+30° C.) as determined by ISO75-2.