Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-12-04
2004-05-04
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C156S331400
Reexamination Certificate
active
06730738
ABSTRACT:
This invention relates to a hot-melt adhesive, particularly a moisture-reactive hot-melt adhesive composition, a method for forming the adhesive composition, and 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 polyether polyol, a polyester polyol, a styrene/allyl alcohol copolymer, and a polyisocyanate, with the ingredients adjusted in specified ways to give the desired balance of properties.
BACKGROUND
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 that 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, moisture-reactive hot-melt adhesives may not be adequate at resistance to slow deformation when subjected to sustained stress over time (such resistance is known in the art as “creep resistance”).
U.S. patent application Ser. No. 09/84,3706 discloses moisture-reactive hot-melt adhesives that incorporate styrene/allyl alcohol addition copolymers into a polyurethane prepolymer-forming reaction mixture containing amorphous polyesters or polyethers. These adhesives achieve good “green strength” (ie, adhesive strength prior to completion of the reaction with moisture), but they may not give sufficient creep resistance for some uses.
The problem faced by the inventor is the provision of an alternative moisture-reactive hot-melt adhesive composition with improved creep resistance that also has good adhesion to substrates. Surprisingly, it has been found that incorporation of styrene/allyl alcohol copolymer in certain compositions with sufficiently high levels of free NCO groups provided the desired balance of properties.
STATEMENT OF THE INVENTION
In a first aspect of the present invention, there is provided a moisture-reactive hot-melt adhesive composition formed by admixing components comprising a polyether polyol, a polyester polyol, a styrene/allyl alcohol copolymer, and a polyisocyanate; wherein the ratio of NCO/OH groups of said components on an equivalents basis is from 1.8/1 to 3.0/1; wherein said components contain less than 1%, by weight based on the total weight of said components, water; and wherein the free NCO content of said components is at least 4%, based on the total weight of said components.
In a second aspect of the present invention, there is provided a method for forming a moisture-reactive hot-melt adhesive comprising admixing components comprising a polyether polyol, a polyester polyol, a styrene/allyl alcohol copolymer, and a polyisocyanate; wherein the ratio of NCO/OH groups of said components on an equivalents basis is from 1.8/1 to 3.0/1; wherein said components contain less than 1%, by weight based on the total weight of said components, water; and wherein the free NCO content of said components is at least 4%, based on the total weight of said components.
In a third aspect of the present invention, there is provided a method for bonding substrates comprising
(a) forming a moisture-reactive hot-melt adhesive by admixing components comprising a polyether polyol, a polyester polyol, a styrene/allyl alcohol copolymer, and a polyisocyanate; wherein the ratio of NCO/OH groups of said components on an equivalents basis is from 1.8/1 to 3.0/1; wherein said components contain less than 1%, by weight based on the total weight of said components, water; and wherein the free NCO content of said components is at least 4%, based on the total weight of said components;
(b) heating said hot-melt adhesive;
(c) applying said heated hot-melt adhesive to a first substrate in the presence of moisture;
(d) contacting said applied heated hot-melt adhesive with a second substrate; and
(e) cooling, or allowing to cool, said hot-melt adhesive.
DETAILED DESCRIPTION
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 is 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, ie., 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 triisocyanate, 4,4′-dimethyl-diphenylmethane tetraisocyanate, prepolymers having Mn less than 2000 and bearing at least two isocyanate groups, and mixtures thereof. Preferred are 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, and mixtures thereof; more preferred is 4,4′-diphenylmethane diisocyanate.
The moisture-reactive hot-melt adhesive composition of the present invention is formed by admixing components which include a polyester polyol. Polyester polyols suitable for use in the present invention include those formed from diacids, or their monoester, diester, or anhydride counterparts, and diols. The diacids may be saturated C
4
-C
12
aliphatic acids, including branched, unbranched, or cyclic materials, and/or C
8
-C
15
aromatic acids. Examples of suitable aliphatic acids include, for example, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, 1,12-dodecanedioic, 1,4-cyclohexanedicarboxylic, and 2-methylpentanedioic acids. Examples of suitable aromatic acids include, for example, terephthalic, isophthalic, phthalic, 4,4′-benzophenone dicarboxylic, 4,4′-diphenylamine dicarboxylic acids, and mixtures thereof The diols may be C
2
-C
12
branched, unbranched, or cyclic aliphatic diols. Examples of suitable diols include, for example, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butandediol, neopentyl glycol, 1,3-butandediol, hexanediols, 2-methyl-2,4-pentanediol, cyclohexane-1,4-dimethanol, 1,12-dodecanediol, and mixtures thereof. Mixtures of the various suitable polyester polyols are also suitable for use in the present invention.
In the practice of the present invention, the preferred polyester polyols are amorphous, which means that they do not crystallize under ambient conditions. The amorphous polyols preferably have a weight-average molecular weight (“Mw”) as measured by gel permeation chromatography, 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. Mixt
Gorr Rachel
Hemenway Carl P.
Rohm and Haas Company
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