Cold-pressed mats of lignocellulosic material having improved cold tack and a process for their production
View Patent ↗Cold-pressed mats of lignocellulosic material having a Push Off Test extension equal to at least 85% of that of a mat made with a urea-formaldehyde resin are produced from a lignocellulosic material and binder system. These mats are produced at ambient temperature by separately adding each component of the binder system to the lignocellulosic material, blending the lignocellulosic material and binder system to coat the lignocellulosic material with the binder system, forming the coated lignocellulosic material into the desired form and applying pressure to the formed lignocellulosic material to obtain the desired thickness. The binder system includes: (i) at least one polyfunctional isocyanate and (ii) at least one aqueous dispersion of an adhesive or tackifier.
1. A cold-pressed mat of a lignocellulosic material having a Push Off Test extension equal to at least 85% of that of a mat made with a urea-formaldehyde resin, which is produced at ambient temperature by a process comprising:
(a) separately adding each component of a binder system comprising:
(i) a polymeric derivative of diphenylmethane diisocyanate or a prepolymer of a polymeric derivative of diphenylmethane diisocyanate having an NCO functionality of from 2.2 to 3.3 and a viscosity of from 25 to 2,000 mPas
and
(ii) at least one aqueous dispersion of a material having adhesive or tackifying characteristics when contacted with lignocellulosic material to the lignocellulosic material;
(b) blending each of the components of the binder system and the lignocellulosic material until the lignocellulosic material is sufficiently coated with the binder system components that the lignocellulosic material can be formed into a mat;
(c) forming the coated lignocellulosic material into a mat;
and
(d) applying sufficient pressure to the mat at ambient temperature to form a mat having a desired thickness.
2. The mat of claim 1 in which the polyfunctional isocyanate is polymeric diphenylmethane diisocyanate.
3. The mat of claim 1 in which the aqueous dispersion comprises an aqueous dispersion of a polyurethane, a halogenated vinyl polymer, a vinyl alcohol polymer, a vinyl ester polymer, a polymer of acrylic acid, a polymeric ester of acrylic acid, a natural rubber, a terpene phenolic resin, a rosin ester, or a polymeric hydrocarbon resin.
4. The mat of claim 1 in which the amount of aqueous dispersion used is from 0.02 to 5% by weight, based on dry lignocellulose content.
5. The mat of claim 1 in which the pressure applied in (d) is sufficient to compress the mat formed in (c) by 30-40% of its initial thickness.
6. A binder system that imparts cold tack to a mat formed by cold pressing a lignocellulosic material having a Push Off Test extension that is at least 85% of that of a mat made with a urea formaldehyde resin comprising:
a) a polymeric derivative of diphenylmethane diisocyanate or a prepolymer of a polymeric derivative of diphenylmethane diisocyanate having an NCO functionality of from 2.2 to 3.3 and a viscosity of from 25 to 2,000 mPas
and
b) at least one aqueous dispersion of a polymeric material or non-polymeric compound having adhesive or tackifying characteristics when contacted with a lignocellulosic material, provided that the polymeric material is not a vinyl acetate polymer or a copolymer dispersion with a glass transition temperature less than about 5° C.