Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-04-30
2001-12-04
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C524S591000, C528S060000
Reexamination Certificate
active
06325887
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to stable colloidal aqueous dispersions of partially and homogeneously crosslinked polyurethane/polyurea adhesives that are heat activatable at 70° C., and have high bond strengths and good heat resistance at 70° C. It relates more particularly to dispersions wherein the average size of the adhesive particles is about 0.12 micron and in which the particle size distribution is very narrow.
Chemical resistance, toughness, elasticity, and durability are desirable properties of polyurethane/polyurea resins (sometimes referred to hereinafter as PUR resins) used as adhesives and coatings for fabrics, plastics, wood, glass fibers, and metals. Good initial green strength, a low heat activation temperature, and high heat resistance are necessary properties of such resins when they are being considered for use as adhesives in the manufacture of such dissimilar products as automobiles and shoes. Prior to this invention, two-component systems (e.g., a PUR resin+an ethylene vinyl acetate polymer) have been used generally to provide the combination of high heat resistance, good contactability, good green strength, and low activation temperature required by auto manufacturers for their assembly of dashboards and door panels, and installation of carpets and headliners. External crosslinking agents usually have been required for the PUR resin adhesives of the prior art. One U.S. auto manufacturer's specifications require an aqueous dispersion of an adhesive that achieves good bond strength when activated on the substrate at 70° C. without the need for an external crosslinking agent and retains that strength upon prolonged exposure to such heat.
The shoe industry requires its adhesives to have very high initial tack and green strength, quick bonding of PVC, rubber, fabric, and leather substrates, and excellent heat- and water resistance. It has been very slow to adapt to aqueous adhesives because of such requirements.
Aqueous dispersions of anionic polyurethane compositions which can be one component or two component adhesives are taught in U.S. Pat. No. 5,608,000, which is incorporated herein by reference. The polyurethane backbone of the adhesive of said patent comprises the reaction product of an isocyanate terminated prepolymer, a chain extending diamine, and a chain stopping aminoalcohol. A sulfonated polyester polyol group is incorporated into the polyurethane as an internal emulsifier. Conventional crosslinkers for isocyanate-terminated polyurethanes are taught to be less than optimal because their use requires a high level of chain extending diamine which makes it more difficult to maintain a stable dispersion. The preferred method of crosslinking, according to this patent, is by reaction at room temperature of carboxylic acid groups incorporated in the polyurethane with a crosslinker such as a polyfunctional aziridine compound.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a polyurethane/polyurea which is partially and homogeneously crosslinked with a triamine to give a stable aqueous dispersion which is useful as a low-temperature heat activatable adhesive.
It is another object of the invention to provide a stable, colloidal aqueous dispersion of a polyurethane/polyurea adhesive which can be activated when heated to about 60-70° C.
It is another object of the invention to provide a partially crosslinked polyurethane/polyurea adhesive that provides good initial green strength and is heat resistant at 70° C.
These and other objects which will become apparent from the following description of the invention are achieved by a stable aqueous dispersion of a heat-activatable adhesive comprising a partially and homogeneously cross-linked polyurethane/polyurea wherein the polyurethane segment contains an integral ionic emulsifier and the polyurea segment, which contains an integral emulsion stabilizer, is a product of a chain extension of an isocyanate-terminated polyurethane with mixture of amines comprising an aliphatic diamine and an aliphatic triamine having three primary amino groups, said mixture having a functionality of from 2.05 to 2.18, and, optionally, reacting a portion of the isocyanate-terminated polyurethane with a monoaminoalkanol, an aminoacid, a vinyl-substituted amine, or amixture of two or more of said amines.
Said objects are achieved also by a process for the preparation of a stable aqueous dispersion of a partially cross-linked polyester-based polyurethane/polyurea which comprises:
a) forming a solution in a high boiling, water-soluble organic solvent that is inert toward the isocyanate group of at least about 36% by weight of a dihydroxycarboxlic acid having up to 12 carbon atoms at from about 40 to about 80° C.;
b) forming an isocyanate-terminated polyurethane by reacting a stoichiometric excess of an aliphatic diisocyanate with a polyesterdiol or polycaprolactone diol or mixture thereof with from about 0.02 to about 0.05 of said dihydroxycarboxlic acid per hundred grams of final dry polyurethane/polyurea;
c) adding a water-soluble ketone before or after the reaction occurs to form a solution of the isocyanate-terminated polyurethane;
d) adding a monoamine containing a hydrophilic oxyalkylene moiety with a second portion of the diisocyanate, and neutralizing the carboxylic acid moiety with a tertiary amine;
e) dispersing the isocyanate-terminated polyurethane in water by adding water to the ketone solution thereof at a rate of from about 600 to about 900 mls/sec;
f) forming a mixture of ketimines by dissolving an aliphatic diamine and an aliphatic amine having three primary amino groups in a water-soluble ketone, the amine mixture having a functionality of from 2.05 to 2.18;
g) optionally, adding a monoaminoalkanol, an aminoacid, a vinyl substituted amine, or a mixture of said amines to the amine mixture, and
h) adding the mixture of ketimines to the aqueous dispersion, whereby the ketimines hydrolyze to the original amines and ketone, and reacting the amines with the isocyanate-terminated polyurethane to form the polyurethane/polyurea, and removing the water-soluble ketone by distillation.
FIG. 1
is a graph of the particle size of the adhesive.
DETAILED DESCRIPTION OF THE INVENTION
The polyesterdiols used in the preparation of a polyurethane are preferably linear and have a weight average molecular weight of from about 750 to about 5600, preferably greater than about 1600 and more preferably from about 2800 to about 3200. The hydroxyl number may be from about 20 to about 150 but is preferably from about 20 to about 70 and more preferably from about 30 to about 40. They may be produced by a conventional procedure in which one or more dicarboxylic acids and one or more glycols are heated in the presence of an acid catalyst until the acid number is reduced to about 30 or less, preferably less than 1, more preferably less than 0.8. Transesterification of a dicarboxylic acid ester by reaction with one or more of such glycols is also suitable. The glycol to acid mole ratio is preferably greater than one so as to obtain linear chains having a preponderance of terminal hydroxyl groups.
The ester-forming glycols may be aliphatic, cycloaliphatic, aromatic or mixtures thereof. Examples of the glycol component include alkylene glycols having from 2 to 10 carbon atoms as exemplified by ethylene glycol, 1,2-propanediol, 1,4-butanediol, 2,6-hexamethylenediol, and mixtures thereof. ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2-methyl-1,3-propane diol; 2-butyl-2-ethyl-1,3-propane diol; 2,2,4-trimethyl-1,3-pentanediol; cyclohexanedimethanol, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like.
The dicarboxylic acid component of the polyesterdiol is predominantly aliphatic and includes cycloaliphatic acids, aromatic acids which ha
Falk Stephen T.
Gallagher John J.
Morton International Inc.
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