Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-04-27
2003-06-17
Maki, Steven D. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C525S131000
Reexamination Certificate
active
06579406
ABSTRACT:
This invention relates to a hot melt adhesive composition, particularly a moisture reactive hot melt adhesive composition, a method for forming the adhesive composition, a method for bonding substrates, such as structural components, using the adhesive composition. More particularly this invention relates to a hot melt adhesive composition formed by admixing a polyisocyanate, an amorphous polyol, and 0.1 to 10%, by weight based on the weight of the adhesive composition, of certain styrene/allyl alcohol copolymers.
Hot melt adhesives are known to be desirable for their quick setting and for the absence of aqueous or solvent media which provide fluidity to other types of adhesives. Moisture reactive hot melt adhesives which are based on an isocyanate group-containing urethane prepolymer can be designed to yield a relatively low melt viscosity for facile handling and application; reaction with moisture augments the final properties of the adhesive. However, adhesive strength prior to completion of the reaction with moisture which is known in the art as “green strength” may be inadequate for necessary early handling of formed laminates. In such cases it has been disclosed to use low viscosity hot melt adhesives which via incorporation of crystalline polyesters or polyethers such as, for example, hexanediol adipates, polycaprolactones, and polytetramethyl ethylene glycol in the urethane prepolymers can crystallize during cooling after application to a substrate, thereby augmenting green strength. But many of the crystalline polyesters and polyethers are expensive and/or prone to hydrolytic attack over time.
U.S. Pat. No. 4,999,407 discloses a quick-setting hot melt polyurethane composition which is a mixture of at least two amorphous polyurethane prepolymers, preferably a first polyurethane prepolymer having a Tg above room temperature and a second polyurethane prepolymer a Tg below room temperature
The problem faced by the inventor is the provision of an alternative moisture reactive hot melt adhesive composition containing a polyurethane prepolymer free from the reacted residues of crystalline polyester or polyether precursors and which provides effective bonding of substrates. Surprisingly, the inventor found that the incorporation of 0.1 to 10%, by weight based on the weight of the adhesive composition, of certain styrene/allyl alcohol addition copolymers into a polyurethane prepolymer-forming reaction mixture containing amorphous polyesters or polyethers and free from crystalline polyesters and polyethers provided the desired balance of properties.
According to a first aspect of the present invention there is provided a moisture reactive hot melt adhesive composition formed by admixing components including a polyisocyanate, an amorphous polyol, and 0.1 to 10%, by weight based on the weight of the adhesive composition, styrene/allyl alcohol copolymer having a hydroxyl number of 100-300 and Mn of 1,000-4,000, wherein the ratio of isocaynate groups/hydroxyl groups (“NCO/OH groups”) of the components on an equivalents basis is from 1.05 to 2.5, the components being free from crystalline polyesters and polyethers and the components containing less than 1%, by weight based on the total weight of the components, water.
According to a second aspect of the present invention there is provided a method for forming a moisture reactive hot melt adhesive by admixing components including a polyisocyanate, an amorphous polyol, and 0.1 to 10%, by weight based on the weight of the adhesive composition, styrene/allyl alcohol copolymer having a hydroxyl number of 100-300 and Mn of 1,000-4,000, wherein the ratio of NCO/OH groups of the components on an equivalents basis is from 1.05 to 2.5, the components being free from crystalline polyesters and polyethers and the components containing less than 1%, by weight based on the total weight of the components, water.
According to a third aspect of the present invention there is provided a method for bonding substrates by forming a moisture reactive hot melt adhesive including admixing components including a polyisocyanate, an amorphous polyol, and 0.1 to 10%, by weight based on the weight of the adhesive composition, styrene/allyl alcohol copolymer having a hydroxyl number of 100-300 and Mn of 1,000-4,000, wherein the ratio of NCO/OH groups of the components on an equivalents basis is from 1.05 to 2.5, the components being free from crystalline polyesters and polyethers and the components containing less than 1%, by weight based on the total weight of the components, water; heating the adhesive to a temperature of 50° C. to 160° C.; applying the heated hot melt adhesive to a first substrate in the presence of moisture; contacting the applied heated hot melt adhesive with a second substrate; and cooling, or allowing to cool, the adhesive.
The composition of this invention is a moisture reactive hot melt adhesive composition. By “moisture reactive” is meant herein that the composition contains isocyanate groups which are capable of reacting with water desirably to effect an increase in the molecular weight of the adhesive composition and/or effect crosslinking of the adhesive composition so as to increase the strength properties of the adhesive subsequent to being contacted with water. By “hot melt” is meant herein that the adhesive which may be a solid, semi-solid or viscous mass can be advantageously heated to provide a fluid adhesive of a viscosity suitable for application to and adhesion to substrates.
The moisture reactive hot melt adhesive composition of the present invention is formed by admixing components which include a polyisocyanate, i.e., an isocyanate bearing at least two isocyanate groups. Polyisocyanates which may be used include aromatic, aliphatic, cycloaliphatic polyisocyanates and combinations thereof, such as, for example, m-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 1,4-cyclohexane diisocyanate, hexahydrotoluene diisocyanate, 1,5-naphthalene diisocyanate, 1-methoxy-2,4-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 4,4′-biphenylene diisocyanate, 3, 3′-dimethoxy-4,4′-biphenyl diisocyanate, 3,3′-dimethyl-4,4′-biphenyl diisocyanate, 3,3′-dimethyl-4,4′-diphenylmethane diisocyanate, isophorone diisocyanate, 4,4′,4″-triphenylmethane triisocyanate, polymethylene polyphenylene polyisocyanate, 2,4,6-toluene trilsocyanate, and 4,4′-dimethyl-diphenylmethane tetraisocyanate, or prepolymers having Mn less than 2000 and bearing at least two isocyanate groups. Preferred is a mixture of 4,4′-diphenylmethane diisocyanate and 2,4-diphenylmethane diisocyanate.
The moisture reactive hot melt adhesive composition of the present invention is formed by admixing components which include an amorphous polyol, by which is meant a polyol bearing two or more hydroxyl groups, which polyol does not crystallize under ambient conditions. Amorphous polyols such as amorphous polyesters and amorphous polyethers, polyester/polyethers having both ester and ether linkages, and mixtures thereof may be used. The amorphous polyols preferably have a weight average molecular weight (“Mw”) as measured by gel permeation chromatograph, from 250 to 8,000, more preferably from 250 to 3,000 and preferably have an acid number less than 5, more preferably less than 2. Amorphous polyester polyols are preferably aromatic such as those formed from phthalic anhydride and diethylene glycol. Amorphous polyether polyols may be prepared by the reaction of an alkylene oxide with a polyhydric alcohol.
The moisture reactive hot melt adhesive composition of the present invention is formed by admixing components which include 0.1 to 10%, by weight based on the weight of the polyol, of a styrene/allyl alcohol addition copolymer having a hydroxyl number of 100-300 and Mn of 1,000-4,000. Such copolymers are commercially available from Lyondell Chemical, Houston, Tex. such as SAA-100, disclosed
Bakule Ronald D.
Maki Steven D.
Rohm and Haas Company
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