Reactive hot melt adhesives

The reactive hot melt adhesive of the present invention comprises 40 to 60 percent by weight of a polytetramethylene ether glycol or derivative thereof, 1 to 10 percent by weight of a polyether polyol, 0 to 15 percent by weight of a hydrolytically stable polyester polyol, 0.5 to 3.0 percent by weight of a silane, and 10 to 30 percent by weight of an organic polyisocyanate.

BACKGROUND AND FIELD OF THE INVENTION 
The present invention relates to a hot melt adhesive, and particularly a 
reactive hot melt adhesive having improved hydrolytic stability. 
Hot melt adhesives are a well known class of adhesives. Typically these 
adhesives are applied in a molten form, cooled to solidify and cured using 
a crosslinking reaction. Of particular interest are the reactive urethane 
hot melt adhesives. Such reactive urethane hot melt adhesives, however, 
have little green strength, and, the substrate or workpiece often must be 
supported until the adhesive can cure to a crosslinked bond. Such 
adhesives also tend to be unstable in the presence of water and solvents. 
Thus, there is a need for a reactive polyurethane hot melt adhesive that 
has a high initial green strength, and is stable, particularly is 
hydrolytically stable. 
With respect to the reactive urethane hot melt adhesives and such adhesives 
having high initial green strength, a number of urethane compositions have 
been proposed. For example, U.S. Pat. No. 3,931,077 to Uchigaki et al. 
proposes a high viscosity hot melt adhesive composition comprising a 
reactive urethane prepolymer, a specific ethylene-vinyl acetate 
theremoplastic polymer and a phenolic or abietic acid type tackifying 
resin. 
U.S. Pat. No. 4,585,819 to Reischle et al. proposes a hot melt adhesive 
composition comprising an isocyanate prepolymer, a thermoplastic 
polyurethane or polyester and a low molecular weight synthetic resin such 
as ketone resins or hydrogenation products of acetophone condensation 
products. 
U.S. Pat. No. 4,808,255 to Markevka et al. proposes a urethane prepolymer 
which is a reaction product of a polyester polyol and isocyanate 
composition, a tackifier resin and an ethylene-vinyl monomer thermoplastic 
copolymer resin. 
U.S. Pat. No. 5,558,941 to Stobbie, IV et al. proposes a blend of 
isocyanate-terminated polyurethane prepolymers consisting of a first 
crystalline prepolymer based on polyhexamethylene adipate and a second 
prepolymer based on polytetramethylene ether glycol. 
There, however, remains a need for reactive hot melt adhesive having both a 
high initial green strength and excellent hydrolytic stability. 
SUMMARY OF THE INVENTION 
To this end, the present invention provides a reactive hot melt adhesive 
which is a low viscosity product that has good initial strength. This 
facilitates avoiding tunneling and delamination when lamination equipment 
is stopped. 
The reactive hot melt adhesive of the present invention comprises 40 to 60 
percent by weight of a polytetramethylene ether glycol or derivative 
thereof, 1 to 10 percent by weight of a polyether polyol, 0 to 25 percent 
preferably 1 to 25 percent by weight of a hydrolytically stable polyester 
polyol, 0.5 to 3.0 percent by weight of a silane, and 10 to 30 percent by 
weight of an organic polyisocyanate. Optionally, defoamers, fillers and 
conventional additives such as plasticizers, tackifiers, anti-oxidants, 
pigments, stabilizers, etc. may be included. 
DETAILED DESCRIPTION OF THE INVENTION 
As discussed above, it has been discovered that a reactive hot melt 
adhesive having improved initial green strength and hydrolytic stability 
can be obtained via a composition comprising 40 to 60 percent by weight of 
a polytetramethylene ether glycol or derivative thereof, 1 to 10 percent 
by weight of a polyether polyol, 0 to 25 preferably 1 to 25 percent by 
weight of a hydrolytically stable polyester polyol, 0.5 to 3.0 percent by 
weight of a silane, and 10 to 30 percent by weight of an organic 
polyisocyanate. Optionally, defoamers, fillers and conventional additives 
such as plasticizers, tackifiers, anti-oxidants, pigments, stabilizers, 
etc. may be included. 
The adhesive of the invention retains excellent hydrolytic stability when 
cured. The reactive hot melt adhesive is particularly useful to bond 
dissimilar and similar materials together. Exemplary materials include 
textiles (e.g., cloth, fabric, etc.), films, wood, metal, etc. 
Particularly commercially significant products are fabric laminates having 
two or more layers bonded together such as those used by the medical 
industry as garments. Such garments must be able to withstand at least 100 
autoclave cycles. The term "garment" is intended to mean any type of 
apparel including diapers, incontinence apparel, surgical gowns, head 
coverings, face masks, booties, gloves, socks, pants, shirts, jackets, 
robes, underwear and the like. These garments are typically formed from 
so-called "barrier fabrics." Such fabrics are relatively impermeable to 
the transmission of fluids particularly body fluids, but are also 
breathable. An exemplary fabric is a layered construction of an 
elastomeric meltblown thermoplastic, a liquid impermeable film and a 
liquid permeable material such as described in U.S. Pat. No. 5,520,980 to 
Morgan et al. the disclosure of which is incorporated herein by reference 
in its entirety. Layered constructions can be held together by the 
reactive hot melt adhesive of the invention. 
Polytetramethylene ethylene glycol is sometimes referred to as poly THF. 
Poly THF typically is produced by the cationic polymerization of 
tetrahydrofuran. Derivatives can be prepared by incorporating other 
monomer materials in the polymerization mixture. An example of another 
monomer is ethylene oxide. An example of a commercially available THF is 
Terathane 2000 available from DuPont, Wilmington, Del. 
Suitable polyether polyols include those prepared by polymerizing an 
alkylene oxide in the presence of a difinctional or trifunctional 
initiator compound. Examples of such polyols include polyethyleneoxy 
polyols, polypropyleneoxy polyols, polybutyleneoxy polyols, and block 
copolymers of ethylene oxide and propylene oxide. Preferably, the 
polyether polyol is a polypropyleneoxy polyol, or a block copolymer of 
ethylene oxide and propylene oxide , and is most preferably a 
polypropyleneoxy polyol or a block copolymer of ethylene oxide and 
propylene oxide. A particularly suitable polyether polyol is Voranol 
230-238 available from The Dow Chemical Company, Midland, Michigan. 
Suitable hydrolytically stable polyester polyols include polyesters formed 
from a glycol and a saturated polyfunctional dicarboxylic acid such as 
prepared by reacting hexanediol with dodecanedioic acid. A particularly 
preferred polyester polyol is Dynacoll 7380 available from HULS America, 
Piscataway, N.J. 
Suitable silanes are ethylenically unsaturated silanes which will 
participate directly in the reaction by free-radical polymerization and 
which do not contain active hydrogen. Representative commercially 
available silanes of this type include vinyltrichlorosilane, 
vinyltriethoxysilane, vinyltrimethoxysilane, 
vinyltris(2-methoxyethoxy)silane, 3-methacryloxypropyltrimethoxysilane, 
3-methacryloxypropyltris(2-methoxyethoxy)silane, vinyltriacetoxysilane, 
4-(3-trimethethoxysllylpropyl-benxylstyrene sulfonate, 
3-acryloxypropyltrimethoxy-silane, allyltriethoxysilane, 
allyltrimethoxysilane, vinylmethyldiethoxysilane, 
vinyldi-methylethoxysilane, vinylmethyldiacetoxysilane, 
3-methyacryloxypropylmethyl-diethoxysilane, 
3-acryloxypropyldimethylmethoxysilane, and 
phenylaminopropyl-trimethoxysilane, etc. A particularly suitable silane is 
Silquest Y-9669 available from OSI Specialties, Inc., Danbury, Conn. 
Suitable organic polyisocyanates include ethylene diisocyanate, ethylidene 
diisocyanate, propylene diisocyanate, butylene diisocyanate, hexamethylene 
diisocyanate, toluene diisocyanate, cyclopentylene-1,3,-diisocyanate, 
cyclohexylene-1,4diisocyanate, cyclohexylene-1,2-diisocyanate, 
4,4'-diphenylnethane diisocyanate ("MDI"), 
2,2-diphenylpropane-4,4'-diisocyanate, p-phenylene diisocyanate, 
m-phenylene diisocyanate, xylylene diisocyanate, 1,4-naphthylene 
diisocyanate, 1,5-naphthylene diisocyanate, diphenyl-4,4'-diisocyanate, 
azobenzene-4,4'-diisocyanate,diphenylsulphone-4,4'-diisocyanate, 
dichlorohexamethylene diisocyanate, furfurylidene diisocyanate, 1 
-chlorobenzene-2,4-diisocyanate, 4,4',4"-triisocyanatotriphenylmethane, 
1,3,5-triisocyanato-benzene, 2,4,6-triisocyanato-toluene, 
4,4'-dimethyldiphenylmethane-2,2',5,5-tetraisocyanate, and the like. A 
particularly preferred polyisocyanate is Isonate 2125M MDI available from 
Dow Chemical, Midland, Mich. 
The adhesive may be used to bond substrates by heating the adhesive prior 
to application and then applying it by an suitable method. For example, 
the adhesive may be placed in an extrusion apparatus which can dispense 
the adhesive in a molten state. The adhesive may be extruded in any 
suitable size or shaper at any suitable speed, depending of course, on the 
bonding application for which it is employed. After the adhesive is 
applied, it quickly cools to ambient temperature and provides sufficient 
bonding to provide an initial "green strength" before the adhesive cures 
completely in the presence of moisture (e.g., steam). 
A catalyst may be included in the reaction mixture to prepare the 
compositions of this invention. Any of the catalysts known in the art to 
catalyze the reaction of an isocyanate with a reactive hydrogen may be 
employed. Representative catalysts include organoetallic catalysts such as 
stannous octoate, stannous oleate, bismuth octoate, dibutyline dioctoate, 
dibutyline dilaurate, and the like. Catalysts are typically used in 
amounts ranging from 0.01 to 2 percent by weight. 
The reactive hot melt adhesive compositions of the invention optionally may 
contain filler to modify the rheological properties such as viscosity sag 
resistance and flow rate of the adhesive. Such materials include for 
example carbon black, surface-treated fumed silicas, titanium dioxide, 
silicas, calcium carbonate, talc, mica, aluminum oxide, clays, ultraviolet 
stabilizers antioxidants and glass phenolic or aluminum oxide bubbles. 
When talc, mica, or a mixtures thereof are used it is preferably used in 
an amount based on the weight of the adhesive, of from about 1 percent to 
about 30 percent. 
The following examples illustrate specific embodiments of the present 
invention. In the examples and throughout the specification, all parts and 
percentages are by weight, unless otherwise indicated

EXAMPLES 
Example 1 
The following are charged to a vessel under nitrogen and heated with mixing 
to 190.degree.-200.degree. F.; 238.4g Terathane 2000, 20.Og Voranol 
230-238, 48.Og Dynacoll 7380, and 0.4 BYK070 defoamer (available from BYK 
Chenie, Wallingford, Conn. Once at temperature, 86.0 g MDI is added to the 
can and allowed to be held at 220.degree. to 240.degree. F. for one hour. 
The product is then cooled to 210 to 220.degree. F, Silquest Y9669 is 
added, and mixed 10-15 minutes. Stirring is stopped, the can is held at 
250.degree. F. for 60 minutes, and properties are checked. Typical 
properties are: 1900 cps@250.degree. F., 2.25 minutes open time, and 
50+psi initial strength in two minutes. At this time a 5-10 mil film is 
drawn down and allowed to cure one week. After a week or greater, 0, 12, 
and 18 hours at 262.degree. F./21 psi tensile strengths are determined and 
% tensile strength retained is calculated as 100 after 0 hours; 92 after 
12 hours and 69 after 18 hours. 
The resulting reactive hot melt adhesive has the following properties: 
Viscosity 1800 cps at 250.degree. F. 
Tensile Strength 3200 psi 
Elongation 600% 
2% Secant Modulus 10,000 psi 
Open Time 2.0 to 2.5 minutes 
Green Strength (sec) 30 psi at 30s 
35 psi at 60s 
50+psi at 180s 
Examples 2-5 
In order to demonstrate the improvement due to the addition of the silane 
with respect to hydrolytic stability, four hot melt adhesive compositions 
were formulated with varying amounts of silane. 
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Examples (% By Weight) 
Component 2 3 4 5 
______________________________________ 
Terathane 2000 
61.90 60.90 59.60 
57.90 
Voranol 230-238 
5.00 5.00 5.00 5.00 
Dynacoll 738D 12.00 12.00 12.00 
12.00 
BYK 070 0.10 0.10 0.10 0.10 
Silquest Y-9689 
0.00 1.00 1.80 3.00 
MDI 21.00 21.00 21.50 
22.50 
______________________________________ 
Tensile strengths at break were measured using a Model 4207 Instron 
equipped with a 100 pound load cell. The dogbone samples which were about 
0.010 inches thick and 1.5 inches in length were pulled at 5 inches per 
minute. The data obtained was an average of four to five samples. 
______________________________________ 
Examples 
2 3 4 5 
______________________________________ 
12 Hours 18 13 8 6 
18 Hours 42 42 31 27 
______________________________________ 
The results illustrate that substantial improvement in hydrolytic stability 
can be obtained by using from up to 3.0 percent silane. 
The present invention has been described in detail above. This invention 
may, however, be embodied in many different forms and should not be 
construed as limited to the embodiments set forth herein above; rather, 
these embodiments are provided so that this disclosure will be thorough 
and complete, and will fully convey the scope of the invention to those 
skilled in the art.