Honeycomb from paper having flame retardant thermoplastic binder
View Patent ↗This invention relates to an improved flame retardant honeycomb comprising high modulus fiber and a flame retardant thermoplastic binder having a melt point of from 120° C. to 350° C. and a limiting oxygen index of 26 or greater, methods for making the honeycomb, and articles comprising the honeycomb. In a preferred embodiment the paper in the honeycomb has a flame classification of UL-94 V-0.
1. A honeycomb having cells comprising a flame resistant non-woven paper,
the cells being expanded paper sheets bonded to each other along a number of node lines of applied adhesive;
the non-woven paper comprising:
a) 5 to 50 parts by weight thermoplastic material having a melting point of from 180° to 300° C., and
b) 50 to 95 parts by weight of a high modulus fiber having a modulus of 600 grams per denier (550 grams per dtex) or greater, based on the total amount of thermoplastic material and high modulus fiber in the paper,
wherein the thermoplastic has a limiting oxygen index of at least 26; and
wherein the thermoplastic material is required to flow in a manner of a viscous liquid when heated and solidify when cooled and do so reversibly time and time again on subsequent heating and cooling steps.
2. The honeycomb of claim 1 wherein the paper has a flammability classification of UL-94 V-0 or better.
3. The honeycomb of claim 1 wherein the thermoplastic is selected from the group consisting of anisotropic melt polyesters, poly(butylene terephthalate), poly(acrylonitrile butadiene styrene), polyvinylchloride, polysulfone, poly(ether-ether-ketone), poly(ether-ketone-ketone), polyethersulfone, polyarylate, polyphenylsulfone, polyetherimide, polyamide-imide, and mixtures thereof.
4. The honeycomb of claim 1 wherein the thermoplastic is selected from the group consisting of flame retardant nylon, flame retardant polyester, flame retardant polyolefins and mixtures thereof.
5. The honeycomb of claim 1 wherein the high modulus fiber comprises para-aramid fiber.
6. The honeycomb of claim 5 wherein the para-aramid fiber is poly (paraphenylene terephthalamide) fiber.
7. The honeycomb of claim 1 wherein the high modulus fiber is selected from the group consisting of carbon fiber, polybenzazole fiber, polypyridazole fiber, and mixtures thereof.
8. The honeycomb of claim 1 wherein the thermoplastic material is present in an amount of from 20 to 40 parts by weight.
9. The honeycomb of claim 1 wherein the high modulus fiber is present in an amount of from about 60 to 80 parts by weight.
10. The honeycomb of claim 1 further comprising a thermoset matrix resin.
11. The honeycomb of claim 1 further comprising inorganic particles.
12. An article comprising the honeycomb of claim 1 .
13. An aerodynamic structure comprising the honeycomb of claim 1 .
14. A panel comprising the honeycomb of claim 1 and a facesheet attached to a face of the honeycomb.
15. The honeycomb of claim 1 wherein the melting point of the thermoplastic is 220° to 250° C.