Void-free molded polyurethane articles with surface attachment strips

In a method for making a molded polyurethane article having a nonwoven material secured to the article's surface which comprises placing the nonwoven material on the internal surface of a mold, adding and foaming a polyurethane composition in the mold and recovering the molded polyurethane article with the nonwoven material attached to the surface of the article, the improvement which comprises coating the nonwoven material with a composition consisting essentially of a fully hydrolyzed polyvinyl alcohol, an organic polyisocyanate and a catalyst for the urethane reaction, and curing the coating on the nonwoven material prior to adding and foaming the polyurethane composition in the mold.

TECHNICAL FIELD 
The invention relates to polyurethane foam articles containing as an 
integral part thereof, molded-in-place nonwoven attachment strips on the 
surface. 
BACKGROUND OF THE INVENTION 
Velcro strips are a cost reduction method of attaching seat coverings to 
polyurethane pads principally used by the automotive companies. These 
strips are attached to the polyurethane foam during the molding step 
simultaneously causing the cost reduction and a problem. The problem 
arises from the molded-in-place Velcro strips releasing air into the 
rising polyurethane foam during the molding step. This release of air 
produces large voids at the Velcro strip/foam interface adversely 
affecting the foam's quality, load bearing and adhesion to the Velcro 
strips. As an aid to understanding the problem, a brief description of the 
construction of a Velcro strip/polyurethane foam article composite 
follows: 
The Velcro strip consists essentially of a network of molded plastic teeth 
and usually a nonwoven or knitted backing material. Only the backing 
material is important to the problem. For cost reasons, polyolefin fibers 
are predominantly used to make the backing fabric. Polyolefins, by their 
chemical nature, are non-polar materials characterized by low free energy 
surfaces. The nonwoven construction technique comprises piling fibers in a 
random manner to form a web. The fibers where they intersect are bonded 
together with a polymeric binder resulting in a vast number of air 
pockets, or voids, in the fabric. Knitted fabrics are constructed by 
looping the yarn together to form the fabric. The knitted fabric like the 
nonwoven fabric is characterized by a large number of voids. The problem 
would also be present with woven backing material. 
In a process that takes place in approximately 40-50 seconds, the Velcro 
strips at ambient temperature are placed plastic mating teeth side down in 
the mold cavity. The mating teeth are covered by a thin plastic film to 
prevent coverage by the developing foam. The surface temperature of the 
mold is about 135.degree.-155.degree. F. depending upon the manufacturer's 
preference. Within 20 seconds after the strip is placed in the mold 
cavity, mixed liquid foam chemicals are poured into the mold. The pour 
pattern may or may not cover the Velcro strip with the liquid. The mold is 
closed and, within 5-6 seconds after pouring, the chemical reaction begins 
to convert the liquid into solid polyurethane foam. The rapidly expanding 
mass will fill the entire mold within 15-20 seconds after it is closed. 
During the filling process, the foam's viscosity and integrity is 
dramatically changing. It's viscosity changes from a liquid of a few 
hundred centipoise to a solid with a tensile strength of 10-15 
lbs/in.sup.2 within 2-6 minutes depending upon the mold temperature and 
foam chemicals. 
As a chemical entity, polyurethane is highly polar being characterized by a 
high free energy surface. This disparity in surface free energy with that 
of the nonwoven backing material prevents the wetting of the polyolefin 
fibers by the polyurethane foam, i.e. prevents the displacement of the air 
entrapped in the voids of the nonwoven material. To compound the problem, 
the entrapped air is absorbing heat energy from the mold surface and the 
exothermic reaction that forms the foam. This heat energy adsorption 
causes the air pressure in the voids to rapidly rise and blow out at the 
time the foam strength is beginning to develop. The result is large voids 
at the Velcro strip/foam interface. To describe the problem 
semi-quantitatively, instead of having 6400-10,000 attachment 
points/in.sup.2, the Velcro strip may have less than 100 attachment 
points/in.sup.2, based on good quality foam having 80-100 cells/inch while 
the voids are 1/8 to 3/4 inch in diameter. 
One of the first approaches to solve this problem was to pretreat the 
nonwoven backing with various components of the liquid polyurethane foam 
composition. The idea was to displace the air by the liquid. It did not 
work because the highly polar liquid components were not able to wet the 
fibers. 
A variety of surfactants were used to pretreat the nonwoven backing. Both 
anionic and nonionic surfactants were tested with partial success at 
levels from 0.1 to 1 wt.%. Nonylphenoxy poly(ethoxy)ethanol with an 
ethylene oxide content of 60 wt% significantly reduced the void size when 
tested at 0.2%, but the voids were not eliminated. 
Solvent (acetone, ethyl alcohol, hexane, toluene and methylene chloride) 
extraction of the nonwoven backing fabric was also tried without success. 
Both faster and slower, blowing and gelling catalyst changes were tried 
without success. Mechanical changes in the molds and altered pour patterns 
also were attempted without success. Even a vent directly above the Velcro 
strip to permit fast air release could not eliminate void formation. 
SUMMARY OF THE INVENTION 
The present invention relates to a method for making a molded polyurethane 
article having a nonwoven material, or fabric, especially a Velcro 
attachment strip, secured to the surface of the polyurethane article by 
positioning the nonwoven material on the internal surface of a mold, 
adding and curing a polyurethane composition in the mold, and recovering 
the molded polyurethane article with the nonwoven material secured to and 
as an integral part of the surface of the article. The present invention 
provides for polyurethane articles which are void free at the region of 
attachment of the nonwoven material by coating the nonwoven material with 
a composition consisting essentially of a polyvinyl alcohol, an organic 
polyisocyanate, a catalyst for the urethane reaction, optionally, a 
plasticizer for the polyvinyl alcohol and curing the coating on the 
nonwoven fabric prior to adding and curing the polyurethane composition in 
the mold. 
For purpose of the description of the invention and the pending claims, 
whenever the term "nonwoven" is used it is to be understood that "knitted" 
and "woven" is also encompassed. 
The invention provides a solution to the problem that can be carried out by 
the nonwoven material (Velcro strip) manufacturer prior to final assembly. 
Alternatively, the coating can be used as the nonwoven binder to bond the 
fibers of the nonwoven material, i.e. the fibers composing the backing of 
a Velcro strip. 
During the application/curing steps, sufficient time exists to outgas the 
nonwoven material and fill or cover over the small voids. 
The invention is particularly suitable for nonwoven, woven and knitted 
materials of synthetic fibers having a low surface free energy, i.e., less 
than about 30 dynes/cm for example, polyolefins, such as polypropylene, 
polyethylene and copolymers thereof. 
In addition, the coating contains enough hydroxyl groups on its surface to 
react with the components of the polyurethane composition and develop a 
strong chemical bond. 
As yet another advantage, the coated backing now has a surface free energy 
similar to that of the polyurethane which will further enhance adhesion of 
the nonwoven material to the surface of the polyurethane article. 
DETAILED DESCRIPTION OF THE INVENTION 
The nonwoven backing of a Velcro strip is coated with a composition 
consisting essentially of (in parts by weight) 
(a) 0.5 to 10 parts polyvinyl alcohol, 
(b) 15 to 60 parts organic polyisocyanate, 
(c) 1 to 15 parts plasticizer for polyvinyl alcohol, and 
(d) 0.05 to 0.5 parts tertiary amine catalyst. 
Components (a)-(d) are preferably present as a mixture in 9.5 to 39.5 parts 
water. 
The coated strip is heated for a sufficient time at a suitable elevated 
temperature to cure the coating composition. A suitable time and 
temperature would be 45 minutes at 120.degree. F. although other times and 
temperatures can be used, for example, shorter periods at higher 
temperatures or longer periods at lower temperatures, such as 80.degree. 
to 200.degree. C. for 5 to 75 minutes. 
While any polyvinyl alcohol is suitable for use in the coating composition 
according to the invention, the polyvinyl alcohols that are preferred are 
the fully hydrolyzed polyvinyl alcohols, i.e. those which are at least 
about 96 mole% hydrolyzed, preferably about 98-99.5+mole% hydrolyzed and 
have a degree of polymerization ranging from 300 to 2000, especially 
about 600 to 1200. The composition should preferably contain 0.5 to 7.5 
parts of the fully hydrolyzed polyvinyl alcohol. 
Contemplated as the functional, or operative, equivalent of the polyvinyl 
alcohol for purposes of this invention is any material which is 
water-soluble and film-forming and has a plurality of active hydrogens, 
preferably a high degree of hydroxyl groups such as cellulose and its 
derivatives like hydroxyethyl cellulose, methyl cellulose and the like. 
Examples of suitable organic polyisocyanates are hexamethylene 
diisocyanate, phenylene diisocyanate, toluene diisocyanate and 
4,4'-diphenylmethane diisocyanate. Especially suitable are 
4,4'-diphenylmethane diisocyanate and the 2,4- and 2,6-toluene 
diisocyanates, individually or together as their commercially available 
mixtures. Other especially suitable mixtures of diisocyanates are those 
known commercially as "crude MDI", also known as PAPI, which contain about 
60% of 4,4'-diphenylmethane diisocyanate along with other isomeric and 
analogous higher polyisocyanates. Also suitable are "prepolymers" of these 
polyisocyanates comprising a partially prereacted mixture of a 
polyisocyanate and a polyether or polyester polyol. Especially desirable 
for the production of automotive foam cushions are the isocyanates 
normally used in high resilient polyurethane foam systems such as toluene 
diisocyanate 80/20 or 65/35; 4,4'-diphenylmethane diisocyanate and blends 
of toluene diisocyanates and 4,4'-diphenylmethane such as 75/25 or 80/20. 
The polyisocyanate is present preferably at 30 to 50 parts. 
A catalytically effective amount of the catalyst is used in the coating 
composition. Any tertiary amine typically used to promote the urethane 
reaction between a hydroxyl group and an isocyanate group may be used in 
the coating composition preferably at 0.075 to 0.3 parts. Illustrative of 
suitable tertiary amines are triethylenediamine, trimethylamine, 
dimethylethylamine, dimethylethanolamine, triethanolamine, N-methyl 
morpholine, bis(dimethylaminoethyl)ether, tris(dimethylaminopropyl)amine, 
dimethylaminoethyl-N-methylethanolamine and the like. 
Any material known to be a plasticizer for polyvinyl alcohol, such as 
dioctylphthalate, dibutylphthalate, dioctylsebecate, dibutylsebecate and 
the like may be used in amounts ranging from 1 to 15 parts, desirably 2 to 
10 parts. 
After the Velcro strip has been coated on the backside with the 
above-described coating composition and subjected to a suitable 
time/temperature curing cycle, the coated Velcro strip is appropriately 
positioned inside a preheated mold previously sprayed with a mold release 
composition as is well known in the art. The liquid polyurethane foam 
composition poured into the mold would comprise components typically used 
in the art to yield a foam product suitable for its intended use. Such 
compositions would contain suitable polyisocyanates as hereinbefore 
described, especially those used in high resilient foam compositions, 
suitable polyols, and suitable catalyst systems comprising tertiary amines 
and mixtures thereof, organotin compounds and mixtures thereof or mixtures 
of tertiary amines and organotin compounds. The compositions would also 
contain water or other suitable blowing agents and cell stabilizers such 
as silicone surfactants. 
Illustrative of suitable polyols as a component of the polyurethane foam 
formulation are the polyalkylene ether and polyester polyols. The 
polyalkylene ether polyols include the poly(alkylene oxide) polymers such 
as poly(ethylene oxide) and poly(propylene oxide) polymers and copolymers 
with terminal hydroxyl groups derived from polyhydric compounds including 
diols and triols for example, among others, ethylene glycol, propylene 
glycol, 1,3-butane diol, 1,4-butane diol, 1,6-hexane diol, neopentyl 
glycol, diethylene glycol, dipropylene glycol, pentaerythritol, glycerol, 
diglycerol, trimethylol propane, cyclohexane diol and low molecular weight 
polyols. 
Useful polyester polyols include those produced by reacting a dicarboxylic 
acid with an excess of a diol for example, adipic acid with ethylene 
glycol or butane diol, or reacting a lactone with an excess of a diol such 
as caprolactone and propylene glycol. 
Other typical agents found in the polyurethane formulations include blowing 
agents such as water, methylene chloride, trichlorofluoromethane and the 
like, and cell stabilizers such as silicones. 
The mold temperature and mold reaction time would be those typically used 
for the particular mold and polyurethane foam composition.

EXAMPLE 1 
In Runs 1-3 the nonwoven (polyolefin) backside of a 4.times.1.75 inch 
Velcro strip manufactured by Velcro Corp. was coated with a coating 
composition using a wire wound rod (6-10 turns/inch to yield a coating of 
about 0.5 g/cm.sup.2). The coating composition comprised 1.5 parts 
hydroxy-containing polymer as set forth in Table 1, 45 parts 
4,4'-diphenylmethane diisocyanate, 3 parts dioctylphthalate, 0.1 parts 
triethylenediamine and 28.5 parts water. The coated strip was oven cured 
for 45 minutes at 250.degree. F. 
After coating the Velcro strip was allowed to return to ambient temperature 
and then placed in a preheated (150.degree. F.) mold previously sprayed 
with mold release. A polyurethane foam composition comprising the 
following ingredients (parts by wt.) was poured into the mold: 
______________________________________ 
Parts 
______________________________________ 
6000 mol. wt. Polypropyleneoxide ethyleneoxide 
60 
tipped triol 
6000 mol. wt. Polyurea filled polyol 
40 
Polyalkylene oxide methylsiloxane copolymer 
1.3 
Water 4 
Diethanolamine 1.5 
Triethylenediamine in dipropylene glycol (1:2) 
0.6 
Bis(dimethylamino ethyl) ether in dipropylene 
0.2 
glycol (7:3) 
Dibutyl tin dilaurate 0.007 
Toluene diisocyanate 80/20 of 2,4/2,6 
102 Index 
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The rising foam flowed over the treated strip as it filled the closed mold. 
After 4 minutes the foam was removed from the mold and evaluated. The foam 
product produced in Run 1 showed the Velcro strip to have been firmly 
adhered to the foam product. The foam was cut around and under the strip 
disclosing a fine, uniform cell structure free of large coarse voids. 
TABLE I 
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HYDROXY- 
CONTAINING CHARACTER OF FOAM 
RUN POLYMER UNDER VELCRO STRIP 
______________________________________ 
1 PVOH (98-99 mole % 
fine, uniform cell structure; no 
hydrolyzed) large coarse voids 
2 PVOH (98-99 mole % 
fine, uniform in cell structure, 
hydrolyzed) small void at corner of strip 
3 PVOH (98-99 mole % 
fine, uniform in cell structure, 
hydrolyzed) small void at corner of strip 
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STATEMENT OF INDUSTRIAL APPLICATION 
The invention provides a method for attaching Velcro strips to automotive 
polyurethane foam pads without adversely affecting the foam's quality, 
load bearing and adhesion to the Velcro strips.