Binder for high wet-strength substrates
View Patent ↗The present invention is directed to a fibrous substrate made of chemically bonded fibers, where the fibers are bound with a polymeric binder in an amount which is sufficient to bind the fibers together to form a self-sustaining web, and where the binder is characterized as having a wet tensile strength of greater than 4500 grams per inch (g/in) when measured at a 20 percent add-on on Whatman #4 CHR chromatography paper which is drum dried for 90 seconds at 210 to 215° F. and cured for 2 minutes at 300 to 325° F. Preferably the level of free formaldehyde in the fibrous substrate is less than 15 ppm. The emulsion binders of the invention may be used to bind fibers together in a substrate; may be used to bind pigment, colors or other substances to a substrate; may be used as a backing material; or may be used to finish or surface-treat a substrate. Because of the high level of crosslinking, substrates bound, or treated with the emulsion polymer have excellent wet strength and good durability/weatherability and water/solvent resistance.
1. A fibrous substrate comprising fibers bonded with an emulsion polymer binder, said polymer comprising:
a) at least 50 percent by weight percent of vinyl acetate monomer units;
b) 0 to 40 percent by weight of ethylene monomer units;
c) 5 to 20 percent by weight of cross-linking monomer composition; and
d) 0 to 40 percent by weight of other co-monomers,
wherein said polymer binder provides a characteristic wet strength value of greater than 4,500 g/in.
2. The fibrous substrate of claim 1 wherein said substrate is a non-woven material.
3. The fibrous substrate of claim 2 wherein said non-woven material comprises a chemically-bonded dry-formed non-woven web.
4. The fibrous substrate of claim 1 wherein said fibers are natural fibers, synthetic fibers, or a mixture thereof.
5. The fibrous substrate of claim 1 wherein said cross-linking monomer comprises a blend of n-methylol acrylamide and acrylamide.
6. The fibrous substrate of claim 2 wherein said non-woven material is formed by an air-laid process.
7. The fibrous substrate of claim 1 wherein said substrate is a double recreped paper, fiberglass, an abrasive pad, a carpet or a floor covering, a wall covering, a fiberfill, or a paper.
8. The fibrous substrate of claim 1 comprising at least 7 percent by weight of cross-linking monomer composition.
9. The non-woven product of claim 1 , comprising 7 to 12 percent by weight of cross-linking monomer composition.
10. The fibrous substrate of claim 1 , wherein the cross-linking monomer composition comprises compounds with N-methylol(meth)acrylamide and/or N-alkoxy methyl(meth)acrylamide.
11. The fibrous substrate of claim 1 , wherein the cross-linking monomer composition is selected from the group consisting of: N-methylol acrylamide; N-methylol methacrylamide; a blend of N-methylol acrylamide and acrylamide; N-methylol allyl carbamate, iso-butoxy methyl acrylamide, n-butoxy methyl acrylamide, and mixtures thereof.
12. The fibrous substrate of claim 1 , wherein the cross-linking monomer composition comprises N-methylol acrylamide.
13. The fibrous substrate of claim 1 , wherein the cross-linking monomer composition consists essentially of a blend of N-methylol acrylamide and acrylamide.
14. The fibrous substrate of claim 1 , wherein the polymer comprises from 6 to 20 wt. percent cross-linking monomer composition.
15. The fibrous substrate of claim 1 , wherein the polymer comprises about 7 wt. percent cross-linking monomer composition.
16. The fibrous substrate of claim 1 , wherein the polymer comprises about 8 wt. percent cross-linking monomer composition.
17. The fibrous substrate of claim 1 , wherein said polymer binder provides a characteristic wet strength value of greater than 4750 grams per inch (g/in).
18. The fibrous substrate of claim 1 , wherein said polymer binder provides a characteristic wet strength value of greater than 5000 grams per inch (g/in).
19. The fibrous substrate of claim 1 , wherein said fibrous substrate is characterized as having a free formaldehyde level of less than 15 ppm.
20. The fibrous substrate of claim 1 , wherein the emulsion polymer is an ethylene-vinyl acetate copolymer.
21. A fibrous nonwoven web which includes a polymer binder that is derived from an aqueous emulsion, wherein said binder comprises an ethylene-vinyl acetate copolymer with from 6 to 20 wt. percent of cross-linking monomer composition,
wherein the aqueous emulsion exhibits a viscosity of less than 1350 cps when measured at a solids content of about 50 wt. percent, and
wherein said polymer binder provides a characteristic wet strength value of greater than 4,500 g/in.
22. The fibrous substrate of claim 21 , wherein the aqueous emulsion exhibits a viscosity of less than 750 cps when measured at a solids content of about 50 weight percent.
23. The fibrous substrate of claim 21 , wherein the aqueous emulsion exhibits a viscosity of less than 500 cps when measured at a solids content of about 50 weight percent.
24. The fibrous substrate of claim 21 , wherein the aqueous emulsion exhibits a viscosity of less than 350 cps when measured at a solids content of about 50 weight percent.
25. The fibrous substrate of claim 21 , wherein the polymer binder is emulsion polymerized at a reaction temperature in the range of from 25° C. to 60° C. for a controlled conversion rate with a redox initiator system that is slow-added during polymerization such that the rate of addition is adjusted to maintain conversion rate.
26. The fibrous substrate of claim 21 , wherein the polymer binder is emulsion polymerized in the presence of a transition metal or salt thereof, and a chelating agent.