Polyester film comprising a polymeric phosphonate flame retardant

Abstract

A polyester film comprising a polymeric phosphonate flame retardant in an amount of from about 1.0 to about 25.0 wt % by total weight of the film and further comprising at least one metal cation selected from the group consisting of Group I and Group II metal cations.

Claims

1. A polyester film comprising a polymeric phosphonate flame retardant in an amount of from about 1 wt % to about 25 wt %, by total weight of the film, and further comprising at least one metal cation, wherein said at least one metal cation comprises sodium cation, wherein said at least one metal cation is present in the form of a salt with a counter-anion, wherein said counter-anion comprises polyacrylate, wherein the polyester is polyethylene terephthalate, wherein the polyester makes up at least 70% by weight of the total weight of a given layer in the polyester film, wherein the amount of said at least one metal cation is greater than 0 ppm and not more than about 150 ppm relative to the amount of polyester, and wherein the phosphonate flame retardant comprises the formula: ##STR00004## wherein n is an integer from 1 to about 100, or any integer between this range.

2. The polyester film according to claim 1 wherein the polyester film is an oriented film, or a biaxially oriented film.

3. The polyester film according to claim 1 or 2 wherein the intrinsic viscosity of the film is at least about 0.70 dL/g.

4. The polyester film according to claim 1 wherein the polyester film comprises said phosphonate flame retardant in an amount of at least about 5 wt % and/or no more than about 20 wt % by total weight of the film.

5. The polyester film according to claim 1 wherein the weight average molecular weight (Mw) of the phosphonate flame retardant is in the range from about 10,000 to about 120,000 g/mol.

6. The polyester film according to claim 1 wherein the glass transition temperature (Tg) of the phosphonate flame retardant is in the range of from about 95° C. to about 120° C.

7. The polyester film according to claim 1 wherein the amount of said at least one metal cation present in the film is at least 10 ppm relative to the amount of polyester.

8. The polyester film according to claim 1 which exhibits a VTM-0 rating in the UL 94 test method.

9. The polyester film according to claim 1 wherein the intrinsic viscosity of the polyester from which the film is manufactured is at least 0.65 dL/g, and not more than 0.85 dL/g.

10. The polyester film according to claim 1 wherein the film thickness is from no more than about 250 μm and/or at least about 5 μm.

11. The polyester film according to claim 1 which is a clear film wherein the haze of the film is no more than about 8% and/or wherein the total light transmission of the film in the visible region is at least about 85%.

12. The polyester film according to claim 1 wherein the whiteness index is at least 85 and/or the L* value of the film is at least 90 and/or the transmission optical density of the film is at least about 0.5.

13. The polyester film according to claim 1 which is a mono-layer polyester film.

14. The polyester film according to claim 1 wherein the film is coated with an adhesion-promoting layer.

15. The polyester film according to claim 1 wherein the phosphonate flame retardant is at least partially copolymerised with the polyester.

16. The polyester film according to claim 1 which is a semi-crystalline film exhibiting a crystallinity in the range of 20% to 50%.

17. The polyester film according to claim 1 which exhibits a shrinkage of less than 5% at 150° C. over 30 minutes in both the longitudinal and transverse dimensions of the film.

18. The polyester film according to claim 1 which exhibits an Ultimate Tensile Strength (UTS) in each of the longitudinal and transverse directions of the film of at least 15 kg/mm.sup.2 and/or an Elongation To Break (ETB) in each of the longitudinal and transverse directions of the film of at least 130%.

19. A method for imparting flame retardancy to or improving the flame retardancy of a polyester film, the method comprising the step of providing in the film a combination of a polymeric phosphonate flame retardant, in an amount of from about 1.0 wt % to about 25.0 wt % by total weight of the film, and at least one metal cation, wherein said at least one metal cation comprises sodium cation, wherein said at least one metal cation is present in the form of a salt with a counter-anion, wherein said counter-anion comprises polyacrylate, wherein the polyester is polyethylene terephthalate, wherein the polyester makes up at least 70% by weight of the total weight of a given layer in the polyester film, wherein the amount of said at least one metal cation is greater than 0 ppm and not more than about 150 ppm relative to the amount of polyester, and wherein the phosphonate flame retardant comprises the formula: ##STR00005## wherein n is an integer from 1 to about 100, or any integer between this range.

20. The polyester film according to claim 14, wherein the adhesion-promoting layer is an acrylic resin.

21. The polyester film according to claim 15, wherein the phosphonate flame retardant is at least partially copolymerised with the polyester in the form of a block copolymer.

22. The polyester film according to claim 1, wherein the salt of the metal cation is present in an amount of at least 10 ppm and less than or equal to 275 ppm, relative to the amount of polyester.

23. The polyester film according to claim 1, wherein the salt of the metal cation is present in an amount of at least 50 ppm and less than or equal to 200 ppm, relative to the amount of polyester.

24. The polyester film according to claim 1, wherein the amount of said at least one metal cation is not more than about 100 ppm relative to the amount of polyester.

25. The polyester film according to claim 1, wherein the amount of said at least one metal cation is not more than about 40 ppm relative to the amount of polyester.

Description

EXAMPLES

(1) A series of PET polyesters (P1 to P7) were prepared using a conventional synthetic procedure and comprising various additives, as shown in Table 1. The amounts in Table 1 are provided by weight relative to the final weight of the polymer produced, unless otherwise indicated. Polyesters P1, P2 and P7 were subjected to solid state polymerisation to increase their IV.

(2) TABLE-US-00002 TABLE 1 Polyester Additives IV P1 China clay: 0.21 wt %; 0.80 Sodium salt of an acrylic copolymer (500 ppm of a 40% solids aq. dispersion) P2 Irganox ® 1010 (Ciba-Geigy; tetrakis- 0.80 (methylene 3-(4′-hydoxry-3′, 5′-di-t- butylphenyl propionate) methane): 500 ppm; Sodium salt of an acrylic copolymer (40% solids aq. dispersion): 500 ppm P3 Silicone resin particles (average 0.62 particle size 2 μm): 1800 ppm Amorphous silica particles (average particle size 0.25-0.35 μm): 2600 ppm P4 Micronized synthetic amorphous silica-gel 0.61 particles Sylysia 340: 1.10 wt % P5 China clay: 1.05 wt % 0.63 P6 — 0.62 P7 — 0.65

Comparative Examples 1-4 and Examples 1-3

(3) A first series of polyester films based on polyesters P1, P6 and P7 was made. Forwards draw ratios were from about 3.0 to 3.3; sideways draw ratios were from about 3.3 to 3.5; and heat-setting was conducted at a temperatures of from about 190 to about 225° C., preferably with an initial zone having a temperature of about 225° C. and a final zone having a temperature of about 190° C. A phosphonate flame retardant of formula I was added to the polyester at the start of the barrel of the extruder during film manufacture. In all cases, the phosphonate flame retardant was FRX Nofia® HM1100 (available from FRX Polymers, Inc.) which has the structure shown below as formula (1):

(4) ##STR00003##

(5) The amount of phosphonate flame retardant present in the film is shown in Table 2, which also shows the haze and TLT (measured as described herein) of the final film.

(6) TABLE-US-00003 TABLE 2 Flame Extrusion retardant temperature Haze TLT Example Polymer (wt %) (° C.) (%) (%) Comp. Example 1 P6 5 275 17.2 82.9 Comp. Example 2 P6 10 275 25.2 78.8 Comp. Example 3 P7 5 275 9.98 85.9 Comp. Example 4 P7 10 275 19.8 81.7 Example 1 P1 5 275 4.72 88.9 Example 2 P1 5 295 4.6 89.6 Example 3 P1 10 295 2.95 89.8

(7) The results in Table 2 demonstrate that the addition of the sodium ions significantly improves the optical properties of the polyester films comprising FRX Nofia® HM1100. Comparative Examples 2 and 4 and Example 3 were tested for flame retardancy. Surprisingly, only Example 3 achieved an VTM-0 rating despite having similar amounts of flame retardant to Comparative Examples 2 and 4, indicating that the sodium salt was important for both the optical properties as well as the flame retardancy.

Examples 4 to 16

(8) A second series of polyester films based on PET polyesters P1-P7 were made, which in all cases contained 15 wt % of FRX Nofia® HM1100 and having a final film thickness of 50 μm. Examples 5-16 were coated on one side with an acrylic resin adhesion-promoting layer (thickness <0.5 μm). The composition of the films is described in Table 3, along with its properties, measured as described herein.

(9) The results demonstrate that the polyester films of the present invention unexpectedly exhibit excellent flame retardancy, with a VTM-0 rating in the UL94 test method, as well as excellent optical properties of low haze and high total luminous transmission in the visible region.

(10) TABLE-US-00004 TABLE 3 TLT Haze Fire test Ex. Polyester (%) (%) L* A (s) B (s) C (s) D E F Class 4 P1 90.1 4.18 92.25 0.00 <0.90 <0.90 No No No VTM-0 5 P1 91.8 4.07 92.19 0.00 <0.90 <0.90 No No No VTM-0 6 50% P2 + 50% P1 90.6 2.54 92.34 0.00 <1.10 <1.10 No No No VTM-0 7 70% P2 + 30% P1 92.3 2.22 92.29 0.00 <0.90 <0.90 No No No VTM-0 8 80% P2 + 20% P1 92.4 1.30 92.33 0.00 ≤1.20 ≤1.20 No No No VTM-0 9 90% P2 + 10% P1 92.6 0.80 92.37 <0.40 <1.20 <1.25 No No No VTM-0 10 85% P2 + 15% P4 91.9 7.07 92.23 <1.40 <1.75 <1.75 No No No VTM-0 11 90% P2 + 10% P4 92.2 4.23 92.28 <1.00 <1.00 <1.45 No No No VTM-0 12 95% P2 + 5% P4 92.3 2.34 92.32 0.00 <1.05 <1.05 No No No VTM-0 13 80% P2 + 20% P5 91.9 5.19 92.24 <1.60 <0.95 ≤1.40 No No No VTM-0 14 85% P2 + 15% P5 91.9 3.88 92.27 ≤0.85 <1.65 <2.10 No No No VTM-0 15 90% P2 + 10% P5 92.2 2.50 92.32 <1.50 <1.40 <2.85 No No No VTM-0 16 90% P2 + 10% P3 92.2 3.68 92.28 0.00 <1.10 <1.10 No No No VTM-0

Comparative Example 5 and Examples 17-19

(11) A third series of sodium salt-containing films based on polyester P2 was made, containing varying amounts of FRX Nofia® HM1100 flame retardant, as shown in Table 4.

(12) TABLE-US-00005 TABLE 4 Flame retardant T.sub.g T.sub.m ΔH.sub.m Crystallinity Example (wt %) (° C.) (° C.) (J/g) (%) Comp. Ex. 5 0 — 248.80 36.41 26.01 Example 17 10 90.82 248.00 40.78 29.13 Example 18 15 90.77 242.97 28.49 20.35 Example 19 20 90.64 243.79 28.78 20.56

(13) The results demonstrate that the flame retardant polyester films of the present invention retain commercially useful levels of crystallinity.