Resin treatment of fibrous sheets
View Patent ↗A method of forming an impregnated fibrous sheet comprising impregnating a fibrous material with a tin catalyst to form a catalyst-impregnated material, treating the catalyst-impregnated material with a polyisocyanate composition to form a polyisocyanate-impregnated fibrous material, and curing the polyisocyanate-impregnated fibrous material to provide a resin-impregnated fibrous sheet. Laminated materials and a method of producing the same are also provided.
1. A method of forming an impregnated fibrous sheet comprising:
impregnating a fibrous material with a tin catalyst to form a catalyst-impregnated material;
removing sufficient volatiles from the fibrous material to provide a catalyst-impregnated material having a volatile content of about 2 to 4 wt. %; then
treating the catalyst-impregnated material with a polyisocyanate resin composition to form a polyisocyanate-impregnated fibrous material; and
curing the polyisocyanate-impregnated fibrous material to provide a resin-impregnated fibrous sheet.
2. The method of claim 1 wherein the curing step comprises heating the polyisocyanate-impregnated fibrous material.
3. The method of claim 2 wherein the curing operation comprises heating the polyisocyanate-impregnated fibrous material at about 250 to 350 degrees F.
4. The method of claim 2 wherein the curing operation comprises heating the polyisocyanate-impregnated fibrous material under pressure of no more than about 50 psig.
5. The method of claim 2 wherein the curing step comprises heating the polyisocyanate-impregnated fibrous material sufficiently to convert the polyisocyanate composition to at least a C-stage resin.
6. The method of claim 1 wherein the tin catalyst comprises tin(II) carboxylate.
7. The method of claim 1 wherein the impregnating operation comprises treating the fibrous material with a catalyst solution which includes catalyst solvent and the tin catalyst.
8. The method of claim 7 wherein the catalyst solvent includes one or more alkanols having 1-6 carbon atoms.
9. The method of claim 7 wherein the catalyst solution comprises a colorant.
10. The method of claim 1 wherein the polyisocyanate composition comprises a second solvent and polyisocyanate resin.
11. The method of claim 10 wherein the second solvent comprises triethyl citrate, triacetin or a mixture thereof.
12. The method of claim 10 wherein the second solvent comprises propylene carbonate.
13. The method of claim 10 wherein the second solvent comprises phthalate diester.
14. The method of claim 1 wherein the polyisocyanate composition has a Brookfield viscosity of no more than about 250 cps at 77 degrees F.
15. The method of claim 1 further comprising applying a phenolic glueline to at least one side of the resin-impregnated fibrous sheet.
16. A method of producing a laminated material comprising:
providing a resin-impregnated fibrous sheet having a phenolic glueline on a side; wherein the resin-impregnated fibrous material is impregnated with a tin catalyst and a polyisocyanate resin, and the resin has been cured to at least a C-stage resin; and
bonding the phenolic side of the resin-impregnated fibrous sheet to a substrate.
17. The method of producing a laminated material according to claim 16 , wherein the resin-impregnated fibrous material is formed in a step of impregnating a fibrous material with a tin catalyst and a polyisocyanate resin.
18. The method of producing a laminated material according to claim 17 , wherein the impregnating step comprises
impregnating the fibrous material with a tin catalyst and a solvent,
removing at least a portion or all of the solvent,
then impregnating the fibrous material containing the tin catalyst with a polyisocyanate resin.