Honeycomb Core Splice Adhesive with Improved Fire Retardancy

Abstract

The invention relates to a heat-activatable foamable honeycomb core splice adhesive having improved fire retardancy, particularly with respect to smoke toxicity and smoke opacity (smoke density).

Claims

1. A heat-activatable foamable adhesive comprising a) a curable polymer; b) a curing agent for the curable polymer; c) a blowing agent; and d) a fire retardant comprising a combination of (i) an ammonium polyphosphate and (ii) a metal hydroxide; and e) an anti-sagging agent comprising: (i) an elastomer, preferably a nitrile rubber; and/or (ii) fibers, preferably aramid fibers; and/or (iii) clay, preferably sepiolite, smectite, or a combination thereof.

2. The adhesive according to claim 1, wherein the ammonium polyphosphate has an average molecular weight within the range of from about 500 g/mol to about 5000 g/mol, more preferably about 1000 g/mol to about 3500 g/mol, still more preferably about 1500 g/mol to about 3000 g/mol.

3. The adhesive according to claim 1, wherein the ammonium polyphosphate (i) has a phosphorous content of at least about 15%, more preferably at least about 20%, still more preferably at least about 25%, or at least about 30%; and/or (ii) has a nitrogen content of at least about 4%, more preferably at least about 7%, still more preferably at least about 10%, or at least about 13%.

4-6. (canceled)

7. The adhesive according to claim 2, wherein the metal hydroxide is aluminum trihydroxide.

8-11. (canceled)

12. The adhesive according to claim 3, wherein the total content of fire retardants and smoke suppressors, preferably being independently from one another selected from ammonium polyphosphates, metal hydroxides, and expandable graphites, is not more than about 60 wt.-%, more preferably not more than about 50 wt.-%, still more preferably not more than about 45 wt.-%, yet more preferably not more than about 40 wt.-%, even more preferably not more than about 35 wt.-%, most preferably not more than about 30 wt.-%, and in particular not more than about 25 wt.-%, in each case relative to the total weight of the adhesive.

13. The adhesive according to claim 1, which provides a smoke density of not more than about 200, more preferably not more than about 180, still more preferably not more than about 160, and most preferably not more than about 140, in each case at a sample thickness of 6.35 mm and after a curing cycle under curing conditions comprising (i) an initial dynamic heating period from room temperature to a temperature of 125 C. at a heating rate of 3 C./min and (ii) a subsequent constant heating period of 55 minutes at a temperature of 125 C., in accordance with JAR/FAR 25.853 AITM 2.0007 A flaming modes.

14. The adhesive according to claim 13, which provides a smoke toxicity, with respect to (i) HF: of not more than about 60 ppm, more preferably not more than about 40 ppm, still more preferably not more than about 20 ppm, and most preferably about 0 ppm; and/or (ii) HCl: of not more than about 60 ppm, more preferably not more than about 40 ppm, still more preferably not more than about 20 ppm, and most preferably about 0 ppm; and/or (iii) NOx: of not more than about 100 ppm, more preferably not more than about 90 ppm, still more preferably not more than about 80 ppm, and most preferably not more than about 70 ppm; and/or (iv) SO2: of not more than about 70 ppm, more preferably not more than about 50 ppm, still more preferably not more than about 30 ppm, and most preferably not more than about 10 ppm; and/or (v) HCN: of not more than about 90 ppm, more preferably not more than about 70 ppm, still more preferably not more than about 50 ppm, and most preferably not more than about 30 ppm; in each case at a sample thickness of 6.35 mm and after a curing cycle under curing conditions comprising (i) an initial dynamic heating period from room temperature to a temperature of 125 C. at a heating rate of 3 C./min and (ii) a subsequent constant heating period of 55 minutes at a temperature of 125 C., in accordance with AITM 3.0005.

15. The adhesive according to claim 1, which (i) comprises a tackifier; and/or (ii) which prior to heat activation is tacky, wherein the maximum tack force measured in accordance with ASTM D 297 is at least about 2.5 Newton, more preferably at least about 5 Newton, still more preferably at least about 7.5 Newton, yet more preferably at least about 10 Newton, and even more preferably at least about 12.5 Newton.

16. The adhesive according to claim 15, which comprises a tackifier, wherein the tackifier comprises or essentially consists of an elastomer modified bisphenol-A-diglycidylether, wherein the elastomer is preferably selected from the group consisting of natural rubber, styrene-butadiene rubber, polyisoprene, polyisobutylene, polybutadiene, isoprene-butadiene copolymer, neoprene, nitrile rubber, butyl rubber, polysulfide elastomer, acrylic elastomer, acrylonitrile elastomers, silicone rubber, polysiloxanes, polyester rubber, diisocyanate-linked condensation elastomer, EPDM (ethylene-propylene diene rubbers), chlorosulphonated polyethylene, and fluorinated hydrocarbons.

17. The adhesive according to claim 15 or 16, which comprises a tackifier, wherein the tackifier comprises or essentially consists of a carboxyl terminated butadiene acrylonitrile elastomer modified bisphenol-A-diglycidylether, nitrile rubber modified bisphenol-A-diglycidylether, or a mixture thereof.

18-23. (canceled)

24. The adhesive according to claim 23, wherein the anti-sagging agent comprises an elastomer and fibers, wherein the relative weight ratio of the elastomer to the fibers is within the range of about (4.74.4):1, more preferably about (4.74.0):1, still more preferably about (4.73.6):1, yet more preferably about (4.73.2):1, even more preferably about (4.72.8):1, most preferably about (4.72.4):1, and in particular about (4.72.0):1.

25. (canceled)

26. The adhesive according to claim 1, wherein the total content of anti-sagging agent, relative to the total weight of the adhesive, is at least about 2.5 wt.-%, more preferably at least about 3.0 wt.-%, still more preferably at least about 3.5 wt.-%, yet more preferably at least about 4.0 wt.-%, even more preferably at least about 4.5 wt.-%, most preferably at least about 5.0 wt.-%, and in particular at least about 5.5 wt.-%.

27-28. (canceled)

29. The adhesive according to claim 16, wherein the total content of elastomers, relative to the total weight of the adhesive, is not more than about 20 wt.-%, more preferably not more than about 15 wt.-%, still more preferably not more than about 10 wt.-%, yet more preferably not more than about 9.0 wt.-%, even more preferably not more than about 8.0 wt.-%, most preferably not more than about 7.0 wt.-%, and in particular not more than about 6.0 wt.-%.

30. (canceled)

31. The adhesive according to claim 1, wherein the blowing agent comprises or essentially consists of a first physical blowing agent and a second physical blowing agent.

32. (canceled)

33. The adhesive according to claim 31, wherein the first physical blowing agent has an activation temperature within the range of from 105 C. to 155 C. and wherein the second physical blowing agent has an activation temperature within the range of from 120 C. to 200 C.

34-36. (canceled)

37. The adhesive according to claim 1, wherein the curable polymer comprises or essentially consists of an epoxy resin.

38. The adhesive according to claim 37, wherein the curable polymer comprises or essentially consists of a solid reaction product of epichlorohydrin and bisphenol A, an epoxy phenol novolac resin, or a mixture thereof.

39. The adhesive according to claim 1, wherein the total content of curable polymer, relative to the total weight of the adhesive, is at least about 7 wt.-%, more preferably at least about 9 wt.-%, still more preferably at least about 11 wt.-%, yet more preferably at least about 13 wt.-%, even more preferably at least about 15 wt.-%, most preferably at least about 17 wt.-%, and in particular at least about 19 wt.-%.

40-46. (canceled)

47. The adhesive according to claim 1 which demonstrates volume expansion upon cure of at least about 250%.

48-51. (canceled)

52. A method for assembling honeycomb structures, preferably for the bonding together of honeycomb structures and/or for edge finishing of honeycomb structures, comprising the steps of (a) applying a heat-activatable foamable honeycomb adhesive according to claim 1 to a honeycomb panel structure; and (b) heat-activating the adhesive.

53. (canceled)

Description

EXAMPLE 1

[0239] The following two core splice adhesives were prepared:

TABLE-US-00002 Comparative Inventive Example 1 Example 1 Function Ingredient wt.-% wt.-% Anti-sagging agent NIPOL DN 3335 5.70 5.70 Epoxy resin DER 671 19.96 19.96 Flame retardant/ Aflammit PMN 500 20.53 smoke suppressor Aflammit PCI 203 18.25 18.25 ATH SH30 20.53 Tackifier Hypox RA1340 29.65 29.65 Curing agent/ Dyhard 100S 1.14 1.14 curing accelerator Dyhard UR 400 2.17 2.17 Blowing agent Expancel 051 DU 40 2.57 2.57 Coloring pigment Bayferrox 600 0.03 0.03 Total 100.00 100.00

[0240] Compared to Comparative Example 1, the formulation of Inventive Example 1 gives half the smoke density and smoke toxicity.

EXAMPLE 2

[0241] The following two core splice adhesives were prepared:

TABLE-US-00003 Inventive Inventive Example 2 Example 3 Function Ingredient wt.-% wt.-% Anti-sagging agent Twaron fibers 1.12 Nipol DN 3335 5.62 5.62 Garamite 1958 1.69 Epoxy resin DER 671 19.66 19.66 Araldite EPN 9850 11.91 Flame retardant/ Aflammit PCI 203 18.56 18.56 smoke suppressor ATH SH30 19.36 19.36 Tackifier Struktol Polydis 3695 14.49 Hypox RA1340 29.21 Curing agent/ Dyhard 100S 3.15 3.15 curing accelerator Dyhard UR 400 2.10 2.10 Blowing agent Expancel 051 DU 40 2.30 2.30 Coloring pigment Bayferrox 600 0.03 0.03 Total 100.00 100.00

[0242] Compared to Inventive Example 2, the formulation of Inventive Example 3 had an even higher tack when uncured and a low flow during curing. The maximum tack force measured in accordance with ASTM D 2979 for inventive Example 3 was within the range of from 14-24 Newton, whereas that maximum tack force for inventive Example 2 was within the range of from 3-7 Newton.

[0243] As demonstrated by the above experimental data, the core splice adhesives according to the invention have excellent mechanical properties and improved flame retardancy, especially in terms of smoke density and smoke toxicity.