COATED POLYESTER FILMS

Abstract

Polyester films with abrasion resistant coatings and methods for making the same are provided. The coated polyester films include a polyester film substrate having a coating on at least one side thereof, wherein the coating is derived from a coating composition that includes (i) a melamine crosslinker component and (ii) a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol.

Claims

1. A coated polyester film comprising a polyester film substrate and a coating on at least one side of the polyester film substrate, wherein the coating is derived from a coating composition comprising: (i) a melamine crosslinker component; and (ii) a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol.

2. A coated polyester film according to claim 1, wherein the melamine crosslinker component (i) and the polyurethane component (ii) taken together constitute at least 80% by weight of the solids in the coating composition, preferably at least 90% by weight of the solids in the coating composition.

3. A coated polyester film according to claim 1 or claim 2, wherein the weight ratio of the polyurethane component (ii) relative to the melamine crosslinker component (i) is in the range of from 1% to 300%, more preferably from 5% to 200%, more preferably from 10% to 100%, more preferably from 15% to 75% and most preferably from 20% to 50%.

4. A coated polyester film according to any one of the preceding claims, wherein the weight ratio of the polyurethane component (ii) relative to the melamine crosslinker component (i) is in the range of 1% to 160%, more preferably 1% to 150%, more preferably 1% to 140%, more preferably 1% to 130%, more preferably 1% to 120%, more preferably 1% to 110%, more preferably 1% to 100%, more preferably 5% to 100%, more preferably 10% to 90%, more preferably 15% to 75% or most preferably 20% to 50%.

5. A coated polyester film according to any one of the preceding claims, wherein the polyester film substrate is a polyethylene terephthalate film or a polyethylene-2,6-naphthalate film, preferably a polyethylene terephthalate film.

6. A coated polyester film according to any one of the preceding claims, wherein the polyester film substrate is optically clear or translucent.

7. A coated polyester film according to any one of the preceding claims, wherein the polyester film substrate is biaxially oriented.

8. A coated polyester film according to any one of the preceding claims, wherein the polyester film substrate has a thickness in the range of from about 5 m to about 500 m.

9. A coated polyester film according to any one of the preceding claims, wherein the melamine crosslinker component (i) comprises one or more monomeric derivatives of melamine in which some or all of the amino groups are functionalised with alkoxymethyl or hydroxymethyl groups and/or oligomers derived from said monomeric melamine derivatives.

10. A coated polyester film according to claim 9, wherein the melamine crosslinker component (i) has a formaldehyde stoichiometry of at least 3.

11. A coated polyester film according to claim 9 or claim 10, wherein the melamine crosslinker component (i) has an alkylation stoichiometry of at least 1.

12. A coated polyester film according to any one of claims 9 to 11, wherein the alkoxymethyl groups are methoxymethyl groups.

13. A coated polyester film according to claim 12, wherein the melamine crosslinker component (i) comprises hexamethoxymethylmelamine.

14. A coated polyester film according to any one of the preceding claims, wherein the at least one diisocyanate is an aliphatic diisocyanate.

15. A coated polyester film according to claim 14, wherein the aliphatic diisocyanate is selected from hexamethylenediisocyanate and isophoronediisocyanate.

16. A coated polyester film according to any one of claims 1 to 13, wherein the at least one diisocyanate is an aromatic diisocyanate.

17. A coated polyester film according to claim 16, wherein the aromatic diisocyanate is selected from methylenediphenyl-4,4-diisocyanate, methylenediphenyl-2,4-diisocyanate, methylenediphenyl-2,2-diisocyanate, or a mixture thereof.

18. A coated polyester film according to any one of the preceding claims, wherein the at least one polymeric polyol has from 2 to 8 reactive hydroxyl groups, more preferably 2 to 4 reactive hydroxyl groups and most preferably 2 reactive hydroxyl groups.

19. A coated polyester film according to any one of the preceding claims, wherein the at least one polymeric polyol has a weight average molecular weight of from 200 to 8,000, for example from 500 to 5,000, or from 1,000 to 3,000.

20. A coated polyester film according to any one of the preceding claims, wherein the at least one polymeric polyol is selected from polyester polyols, polyether polyols, polyacrylate polyols and polycarbonate polyols.

21. A coated polyester film according to claim 20, wherein the at least one polymeric polyol is selected from polycarbonate polyols.

22. A coated polyester film according to any one of the preceding claims, wherein the polyurethane is a polyurethane elastomer.

23. A coated polyester film according to any one of the preceding claims, wherein the coating has a dry thickness of no more than 5.0 m, preferably no more than 2.0 m, more preferably no more than 1.5 m, for example no more than 1.0 m, no more than 0.8 m or no more than 0.5 m.

24. A coated polyester film according to any one of the preceding claims, wherein the coating has a dry thickness (i.e. the thickness of the coating in the finished film) of at least 200 nm, more preferably at least 250 nm, more preferably at least 300 nm, more preferably at least 350 nm, more preferably at least 400 nm, more preferably at least 500 nm, more preferably at least 600 nm, more preferably at least 800 nm, or most preferably at least 1000 nm.

25. A coated polyester film according to any one of the preceding claims, wherein the coating has a dry thickness (i.e. the thickness of the coating in the finished film) of between 200 nm and 5 m, more preferably between 250 nm and 5 m, more preferably between 300 nm and 5 m, more preferably between 350 nm and 5 m, more preferably between 400 nm and 5 m, more preferably between 500 nm and 5 m, more preferably between 500 nm and 2 m, more preferably between 600 nm and 2 m, more preferably between 800 nm and 2 m, or most preferably between 1 m and 2 m.

26. A coated polyester film according to any one of the preceding claims, wherein the coated polyester film is optically clear or translucent.

27. A coated polyester film according to any one of the preceding claims, which exhibits an increase in Taber haze of no more than 10%, preferably no more than 8% and most preferably no more than 5% when the coating is tested according to ASTM D-1044 wherein a loading of 500 g is used over 100 cycles.

28. A coated polyester film according to any one of the preceding claims, wherein the crack onset strain of the coated polyester film is about 5% or more, preferably about 10% or more, preferably about 15% or more, preferably about 20% or more, preferably about 25% preferably about 30% or more of the original dimension of the coated polyester film.

29. A coated polyester film according to any one of the preceding claims, wherein the number of cracks in the coating at 25% elongation is 25 or less, preferably 20 or less, preferably 15 or less, preferably 10 or less, preferably 5 or less, preferably 2 or less, and most preferably 0.

30. A coated polyester film according to any one of the preceding claims, wherein the coating is disposed directly on the polyester substrate.

31. A method of manufacturing a coated polyester film comprising: (a) disposing a coating composition comprising a solution or dispersion of (i) a melamine crosslinker component; and (ii) a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol in a liquid vehicle (preferably an aqueous liquid vehicle) on at least one surface of a polyester film substrate; (b) drying the coating composition; and (c) curing the dried coating composition by heating.

32. A method according to claim 31, wherein the melamine crosslinker component (i) and the polyurethane component (ii) taken together constitute at least 80% by weight of the dried coating composition, for example at least 90% by weight of the dried coating composition, at least 95% by weight of the dried coating composition, at least 98% by weight of the dried coating composition, or at least 99% by weight of the dried coating composition.

33. A method according to claim 31 or claim 32, wherein the weight ratio of the melamine crosslinker component (i) to the polyurethane component (ii) is from 30:70 to 99:1, preferably from 40:60 to 95:5, for example from 50:50 to 90:10, or from 55:45 to 85:15, or from 60:40 to 80:20.

34. A method according to any one of claims 31 to 33, wherein, the weight ratio of the polyurethane component (ii) relative to the melamine crosslinker component (i) is in the range of 1% to 160%, more preferably 1% to 150%, more preferably 1% to 140%, more preferably 1% to 130%, more preferably 1% to 120%, more preferably 1% to 110%, more preferably 1% to 100%, more preferably 5% to 100%, more preferably 10% to 90%, more preferably 15% to 75% or most preferably 20% to 50%.

35. A method according to any one of claims 31 to 34, wherein the polyester film substrate is as defined in any one of claims 5 to 8 and/or wherein the melamine crosslinker component (i) is as defined in any one of claims 9 to 13 and/or wherein the polyurethane component (ii) is as defined in any one of claims 14 to 22.

36. A method according to any one of claims 31 to 35, wherein the coating composition is applied at a dry thickness of no more than 5.0 m, preferably no more than 2.0 m and more preferably no more than 1.5 m, for example no more than 1.0 m, no more than 0.8 m or no more than 0.5 m.

37. A method according to any one of claims 31 to 36, wherein the coating preferably is applied at a dry thickness of at least 200 nm, more preferably at least 250 nm, more preferably at least 300 nm, more preferably at least 350 nm, more preferably at least 400 nm, more preferably at least 500 nm, more preferably at least 600 nm, more preferably at least 800 nm, or most preferably at least 1000 nm.

38. A method according to any one of claims 31 to 37, wherein the coating preferably is applied at a dry thickness of between 200 nm and 5 m, more preferably between 250 nm and 5 m, more preferably between 300 nm and 5 m, more preferably between 350 nm and 5 m, more preferably between 400 nm and 5 m, more preferably between 500 nm and 5 m, more preferably between 500 nm and 2 m, more preferably between 600 nm and 2 m, more preferably between 800 nm and 2 m, or most preferably between 1 m and 2 m.

39. A method according to any one of claims 31 to 38, wherein the coating composition is dried in an oven at a temperature of from about 100 C. to about 150 C., preferably from about 120 C. to about 140 C.

40. A method according to any one of claims 31 to 39, wherein the dried coating composition is cured in an oven at a temperature of from about 150 C. to about 250 C., preferably about 190 C. to about 250 C., more preferably about 200 C. to about 230 C., and most preferably about 215 C. to about 230 C.

41. A method according to any one of claims 31 to 40, wherein step (a) is conducted in-line.

42. A method according to claim 41, wherein the polyester film substrate is biaxially oriented.

43. A method according to claim 42, wherein the coating composition is disposed on the at least one surface of the polyester film between first and second stretching steps during manufacture of the biaxially oriented polyester film substrate.

44. A method according to claim 43, wherein transverse stretching of the polyester film substrate takes place simultaneously with drying of the aqueous coating composition, and preferably at a temperature of from about 100 C. to about 150 C., preferably from about 120 C. to about 140 C.

45. A method according to claim 43 or claim 44, wherein heat-setting of the film takes place simultaneously with curing of the coating, preferably at a temperature in the range of from 150 C. to 250 C., preferably 190 C. to 250 C., more preferably 200 C. to 230 C., and most preferably 215 C. to 230 C., and preferably for a heating duration in the range of from 10 to 40 seconds, and more preferably 20 to 30 seconds.

46. A method according to any one of claims 31 to 45, wherein the coating composition has a solids content of at least 20% by weight, for example at least 30% by weight, at least 40% by weight, or at least 50% by weight.

47. A method according to any one of claims 31 to 46, wherein the coating composition is applied to provide a dry thickness of no more than 1.5 m, preferably no more than 1.0 m, more preferably no more than 0.8 m, for example no more than 0.5 m of the coating.

48. A method of improving the flexibility of a crosslinked melamine resin coating disposed on a polyester film substrate, the method comprising incorporating a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol into the crosslinked melamine resin coating.

49. A method of improving the abrasion resistance of a polyester film substrate, the method comprising: (a) disposing a coating composition comprising a solution or dispersion of (i) a melamine crosslinker component; and (ii) a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol in a liquid vehicle (preferably an aqueous liquid vehicle) on at least one surface of a polyester film substrate; (b) drying the coating composition; and (c) curing the dried coating composition by heating.

50. Use of a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol to improve the flexibility of a crosslinked melamine coating for a polyester film substrate.

51. Use of a coating composition comprising a melamine crosslinker component and a polyurethane component derivable from at least one diisocyanate and at least one polymeric polyol to improve the abrasion resistance of a polyester film substrate.

52. An electronic or opto-electronic device comprising a coated polyester film as defined in any one of claims 1 to 30 or a coated polyester film manufactured according to the method of any one of claims 31 to 49.

53. A device according to claim 52 which is a graphic display device, preferably wherein the coated polyester film is disposed on a viewing surface of the graphic display device.

Description

EXAMPLES

Comparative Example 1 and Examples 2 to 6

[0135] In Comparative Example 1 and Examples 2 to 6, CYMEL 385 from Cytec Industries was used as the melamine crosslinker component (i), and ALBERDINGK UC84 was used as the polyurethane component (ii). CYMEL 385 is an aqueous solution having a solids content of 80 wt % and ALBERDINGK UC84 is an aqueous dispersion having a solids content of 35 wt %. CYMEL 385 was diluted to a solids content of 50 wt % before use. TWEEN 20 was used as a surfactant and ammonium nitrate was used as a catalyst.

[0136] Coated films were prepared as follows:

[0137] Polyethylene terephthalate was melt extruded, cast onto a cooled rotating drum and stretched in the direction of extrusion to approximately 3 times its original dimensions at a temperature of 150 C. The film was coated on its upper surface with a coating composition as defined in Table 1 below in an amount sufficient to provide a final dry thickness of 1.0 m. The coated film was passed into a stenter oven at a temperature of 120 C. where the film was dried and stretched in the transverse direction to approximately 3 times its original dimensions. The biaxially stretched film was heat set at a temperature of about 200 C. with simultaneous curing of the coating. The heat-set biaxially stretched film was then unwound and then further heat-stabilised in a roll-to-roll process by passing the film through an additional set of ovens, of which the maximum temperature was above 150 C., for a duration of no more than 2 seconds. The film was transported through the ovens under a low line tension, allowing it to relax and stabilize further. The final coated polyester film thickness was 100 m, in which the final dry thickness of the coating was 1.0 m on one side.

TABLE-US-00001 TABLE 1 CYMEL TWEEN Ammonium 385 UC 84 20 Nitrate Solids (50 wt %) (35 wt %) Water (10 wt %) (10 wt %) %.sup.b PU %.sup.c Comparative 2549.8.sup.a 0 337.4 12.9 106.3 42.8 0 Example 1 Example 2 1821.3 260.0 194.0 10.1 75.91 42.8 10 Example 3 1821.3 521.0 146.0 11.0 75.91 42.8 20 Example 4 1821.3 781.0 97.0 12.0 75.91 42.8 30 Example 5 1821.3 1040.0 49.0 12.8 75.91 42.8 40 Example 6 1821.3 1302.0 0 13.7 75.91 42.8 50 .sup.aAll values (except %) are in grams. .sup.bSolids % defines the weight of solids in the aqueous coating composition relative to the total weight of the composition .sup.cPU % defines the weight of the polyurethane component (UC 84) in the aqueous coating composition relative to the weight of the melamine crosslinker component (CYMEL 385)

[0138] The films of Comparative Example 1 and Examples 2 to 6 were tested for the number of cracks at 25% elongation, the crack onset strain and Taber Haze according to the protocols described above. The results are provided in Table 2 and in FIG. 1.

TABLE-US-00002 TABLE 2 Number of Taber cracks at 25% Crack onset Optical Haze % elongation strain % Haze % Comparative 5.5 26.7 5 0.85 Example 1 Example 2 5.6 22.2 10 0.74 Example 3 6.3 13.6 15 0.81 Example 4 4.8 2 15 0.87 Example 5 5.8 0 25 0.80 Example 6 6.2 0 30 0.85

[0139] The foregoing examples demonstrate that a significant improvement in the flexibility of the coated films is obtained by the inclusion of a polyurethane component (ii) with only a negligible increase in Taber Haze and little or no change in the clarity of the film as measured by the optical haze.