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 to about 25 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.

2. A polyester film according to claim 1 wherein the polyester film is oriented, preferably a biaxially oriented film.

3. A polyester film according to claim 1 wherein the intrinsic viscosity of the film is at least about 0.70.

4. A polyester film according to claim 1 wherein the polyester film comprises said phosphonate flame retardant in an amount of at least about 5 wt %, preferably at least about 10 wt %, preferably at least about 12 wt %, preferably no more than about 20 wt %, preferably no more than about 18 wt %, by total weight of the film.

5. A polyester film according to claim 1 wherein said phosphonate flame retardant is a phosphonate flame retardant of formula I: ##STR00004## wherein: Ar is an aromatic group and —O—Ar—O— is derived from a compound having one or more, optionally substituted, aryl rings such as, but not limited to, resorcinols, hydroquinones, and bisphenols, such as bisphenol A, bisphenol F, and 4,4′-biphenol, phenolphthalein, 4,4′-thiodiphenol, 4,4′-sulfonyldiphenol, or combinations of these; X is a C.sub.1-20 alkyl, C.sub.2-20 alkene, C.sub.2-20 alkyne, C.sub.5-20 cycloalkyl or C.sub.6-20 aryl; and n is an integer from 1 to about 100, preferably from 1 to about 75, preferably from 2 to about 50, or any integer between these ranges.

6. A polyester film according to claim 5 wherein X is selected from C.sub.1-20 alkyl, preferably C.sub.1-10 alkyl, preferably C.sub.1-5 alkyl, preferably methyl.

7. A polyester film according to claim 5 wherein —O—Ar—O— is derived from bisphenol A, bisphenol F, and 4,4′-biphenol, preferably bisphenol A.

8. A polyester film according to claim 1 wherein the phosphonate flame retardant has formula II: ##STR00005##

9. A 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, preferably from about 50,000 to about 120,000, preferably from about 80,000 to about 120,000 g/mol.

10. A polyester film according to claim 1 wherein the phosphonate flame retardant is characterized by a phosphorus content of at least about 5 wt %, preferably at least about 8 wt %, preferably at least about 10 wt %, preferably no more than about 20 wt %, preferably no more than about 15 wt %, preferably no more than about 12 wt %, and is preferably about 11 wt %, by weight of the phosphonate flame retardant.

11. A 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., preferably in the range of from about 110° C. to about 110° C.

12. A polyester film according to claim 1 wherein the amount of said metal cations present in the film is at least 10 ppm and preferably not more than about 1000 ppm, relative to the amount of polyester, and/or wherein said metal cations are selected from sodium and potassium, and/or wherein said metal cations are present in the form of a salt with a counter-anion selected from hydroxide, polyacrylate, hydrogen carbonate, carboxylate, chloride, acetate, formate and nitrate.

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

14. A polyester film according to claim 1 which is a biaxially oriented film and/or wherein said polyester is polyethylene terephthalate.

15. A polyester film according to claim 1 wherein the intrinsic viscosity of the polyester from which the film is manufactured is at least 0.65, and not more than 0.85.

16. A polyester film according to claim 1, wherein the film thickness is from no more than about 250 μm, preferably no more than about 150 μm, preferably no more than about 100 μm, preferably no more than 75 μm, preferably no more than 50 μm, and preferably at least about 5 μm, preferably at least about 10 μm.

17. A polyester film according to claim 1 which is a clear film wherein the haze of the film is no more than about 8%, preferably no more than about 5%, preferably no more than about 4%, preferably no more than about 3%, preferably no more than about 2%, preferably no more than about 1%, and/or wherein the total light transmission of the film in the visible region is at least about 85%, preferably at least about 88%, preferably at least about 90%, preferably at least about 92%.

18. A 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.

19. A polyester film according to claim 1 which is a mono-layer polyester film.

20. A polyester film according to claim 1 wherein the film is coated with an adhesion-promoting layer, preferably an acrylic resin.

21. A polyester film according to claim 1, wherein the phosphonate flame retardant is at least partially copolymerised with the polyester, preferably in the form of a block copolymer.

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

23. A 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.

24. A 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%.

25. (canceled)

26. 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 to about 25.0 wt % by total weight of the film, and at least one metal cation selected from the group consisting of Group I and Group II metal cations.

27. A method according to claim 26 wherein said method to impart flame retardancy to or improve flame retardancy of said polyester film is a method to impart to the polyester film a VTM-0 rating in the UL 94 test method.

28. (canceled)

Description

EXAMPLES

[0114] 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.

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 particle 0.62 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

[0115] 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):

##STR00003##

[0116] 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.

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

[0117] 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

[0118] 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.

[0119] 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.

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

[0120] 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.

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

[0121] The results demonstrate that the flame retardant polyester films of the present invention retain commercially useful levels of crystallinity.