Nonwoven binders with high wet/dry tensile strength ratio
This invention is directed to an improvement in a crosslinkable vinyl acetate/vinyl versatate based polymeric binder for use in nonwoven applications. The improvement in the binder for nonwoven and, particularly premoistened wipes, resides in a polymer comprised of vinyl acetate and vinyl versatate produced by either of the methods: batch polymerization where polymerized units of an in situ or internal crosslinking (polyolefinically unsaturated) monomer are incorporated into the polymer; or, delayed addition of vinyl versatate where the vinyl versatate is polymerized into the polymer by delayed addition such that vinyl versatate rich polymer segments are formed; and, preferably, polymerized units of a polyolefinically unsaturated monomer are incorporated into the polymer.
1 . In a nonwoven product comprising a nonwoven web of fibers bonded together with a polymer comprised of polymerized units of vinyl acetate and vinyl versatate, and polymerized units of a crosslinking monomer, the improvement which comprises incorporating polymerized units of a polyolefinically unsaturated monomer as an internal crosslinking agent into said polymer.
2 . The nonwoven product of claim 1 wherein the polymer is comprised of from 30 to 90% by weight of polymerized units of vinyl acetate, from about 5 to 70% by weight of polymerized units of vinyl versatate, from 0 to 25% by weight ethylene and from 1 to 10% by weight of a crosslinking monomer, and 0.005 to 1.5% by weight of the polyolefinically unsaturated monomer, based upon the total weight of the polymer.
3 . The nonwoven product of claim 2 wherein the crosslinking monomer is N-methylol acrylamide.
4 . The nonwoven product of claim 3 wherein said polymer has a T g from 35 to −20° C.
5 . The nonwoven product of claim 4 wherein said polymer has from about 15 to 45% by weight vinyl versatate based upon the total weight of the polymer.
6 . The nonwoven product of claim 5 wherein the polymer has from 3 to 8% crosslinking monomer by weight based upon the total weight of the polymer.
7 . The nonwoven product of claim 6 wherein the insoluble fraction of said polymer in tetrahydrofuran is at least 55% by weight.
8 . The nonwoven product of claim 6 wherein said polyolefinically unsaturated monomer is triallylcyanurate.
9 . The nonwoven product of claim 6 wherein the polyolefinically unsaturated monomer is 1,6-hexanediol diacrylate.
10 . The nonwoven product of claim 6 wherein wet tensile strength of the nonwoven web is at least 1650 g/5 cm as measured at a 20% add-on weight using TAPPI T-456 (Wet Tensile Strength Determination Using Finch Cup Apparatus).
11 . The nonwoven product of claim 10 wherein the wet tensile strength is at least 2000 g/5 cm.
12 . In a nonwoven product comprising a nonwoven web of fibers bonded together with a polymer comprised of polymerized units of vinyl acetate and vinyl versatate and polymerized units of a crosslinking monomer the improvement which comprises forming said polymer by delaying the addition of vinyl versatate to the polymerization medium such that vinyl versatate rich polymer segments are formed.
13 . The nonwoven product of claim 12 wherein the vinyl versatate is added to the polymerization medium such that a major amount of vinyl versatate is polymerized after a majority of the vinyl acetate has been polymerized.
14 . The nonwoven product of claim 13 wherein the polymer is comprised of from 30% to 90% by weight of polymerized units of vinyl acetate, from about 5 to 70% by weight of polymerized vinyl versatate, from about 0 to 25% by weight of polymerized units of ethylene, from 1 to 10% of a crosslinking monomer, and from 0 to 1.5% by weight of polymerized polyolefinically unsaturated monomer as an internal crosslinking agent, based upon the total weight of the polymer.
15 . The nonwoven product of claim 14 wherein the crosslinking monomer is N-methylol acrylamide.
16 . The nonwoven product of claim 15 wherein said polymer has a T g from 35 to −20° C.
17 . The nonwoven product of claim 15 wherein said polymer has from about 15 to 45% vinyl versatate based upon total weight of the polymer.
18 . The nonwoven product of claim 17 wherein the polymer has from 3 to 8% by weight crosslinking monomer, based upon the total weight of the polymer.
19 . The nonwoven product of claim 18 wherein the insoluble fraction of said polymer in tetrahydrofuran is at least 55% by weight.
20 . The nonwoven product of claim 18 wherein said polyolefinically unsaturated monomer is triallylcyanurate.