Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-12-01
2002-05-14
Short, Patricia A. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C525S054420, C525S054440, C525S125000, C525S131000, C525S438000, C525S440030
Reexamination Certificate
active
06387449
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to reactive hot melt urethane adhesives. More particularly, the invention relates to a hot melt urethane adhesive including: an isocyanate compound; a polyester-polyol compound; a reactive tackifying resin including non-polar polyols; and a thermoplastic polymer.
BACKGROUND OF THE INVENTION
Both hot melt adhesives and moisture cure, hot melt urethane adhesives are well known generic adhesive classes. Hot melt adhesives can be conveniently applied by extruding the adhesive composition at elevated temperatures directly onto a work piece for the purpose of forming a structural bond with another work piece as the temperature of the adhesive compositional mass cools. While hot melt adhesives have many adhesive preparation and workpiece production benefits, they have an effective temperature use range which is lower than its application temperature. In other words, the bonding mass can lose bond strength as the temperature of the work piece and the bond line increase.
In sharp contrast, moisture curable, hot melt urethane adhesives have little green strength in the their open state, limited peel and shear strength after set and require curing before these properties improve. After application of a urethane adhesive, the joined workpieces can require external mechanical support until the urethane adhesive can cure to a strong resilient, crosslinked bondline. Cured polyurethane bonds have high tensile strength and maintain their strength above their application temperature, 100-130° C. Such adhesives have value where initial green strength is not important since substantial bond formation requires a period of curing time, which can range from hours to a number of days.
Clearly an adhesive displaying the high initial peel and shear strength of a hot melt which builds in strength over time is desirable. Early attempts to formulate such an adhesive have been made, notably attempts disclosed in U.S. Pat. Nos. 4,775,719 and 4,808,255, but none have been entirely successful. These early formulas set as a hot melt, but produced only modest increases in heat resistance when fully cured. This stems from the fact that only prepolymers made of non:polar polyols are compatible with APAO's, EVA and other commonly used hot melt polymers. Likewise the ingredients, which are used to modify and formulate hot polymers, are too non-polar to mix with most polyester or polyether based urethanes. The most polar hot melt ingredients contain carboxylic acids or high level of hydroxyl groups, which are unstable with NCO groups at elevated temperatures.
Some of these early adhesives result in adhesive formulations having good green strength, but short open times, low heat resistance as cured, (i.e., low peel adhesion failure temperature (PAFT)), and limited adhesion to plastics. Accordingly, a substantial need exists in finding better hot melt adhesive formulations.
SUMMARY OF THE INVENTION
The inventors have developed compatible blends of components that form hot melt curing urethane adhesives with heat stability, green bond strength and fully cured bond strength that are surprisingly compatible in production and use. The reactive hot melt adhesive composition of this invention includes an isocyanate compound; a polyester-polyol compound; a reactive tackifying resin including non-polar polyols; and a thermoplastic polymer. The components of the adhesive composition cooperate in at least some embodiments to form a hot melt compatible adhesive composition that has substantial initial green strength, substantial cured bond strength, chemical and heat resistance when cured, extended pot life, long open times, high heat resistance, (i.e., high PAFT), and good adhesion to plastics.
In at least one embodiment, the invention includes a hot melt adhesive composition including: an isocyanate compound; a polyester-polyol; a reactive tackifying resin which includes a terpene-phenolic copolymer resin having a hydroxyl number of about 50 or less; and a thermoplastic polymer.
In at least one embodiment, the invention includes a method of increasing temperative resistance and open time in a hot melt adhesive composition, the method including incorporating into the adhesive an isocyanate compound; a polyester-polyol, and a reactive tackifying resin including a non-polar polyol having a hydroxyl number of about 50 or less.
DETAILED DESCRIPTION OF THE INVENTION
The inventors have found useful hot melt adhesive compositions that include: an isocyanate compound; a polyester-polyol compound; a reactive tackifying resin including non-polar polyols; and a thermoplastic polymer.
Isocyanate Compounds
The term “isocyanate compound” in the context of this invention indicates a typically monomeric small molecule having 2 or more NCO groups. Isocyanate compounds useful for forming the compositions of the invention include organic, aliphatic and aromatic isocyanate compounds having an isocyanate functionality of about 2 or more. The isocyanate compounds can also contain other substituents which do not substantially adversely affect the viscosity of the isocyanate terminated compositions, the adhesive properties of the bond line or the reactivity of the NCO groups during the formation of the composition. The isocyanate compound can also include mixtures of both aromatic and aliphatic isocyanates and isocyanate compounds having both aliphatic and aromatic character.
Typical aromatic isocyanate compounds include diphenylmethane diisocyanate compounds (MDI) including its isomers, carbodiimide modified MDI, diphenylmethane-4,4′-diisocyanate, diphenylmethane-2,2′-diisocyanate, diphenyl-methane-2,4′-diisocyanate, oligomeric phenyl methylene isocyanates; toluene diisocyanate compounds (TDI) including isomers thereof, tetramethylxylene diisocyanate (TMXD), isomers of naphthylene diisocyanate, isomers of triphenylmethane triisocyanate, and mixtures thereof. Aliphatic di, tri, and polyisocyanates are also useful including for example isophorone diisocyanate, hydrogenated aromatic diisocyanates, aliphatic polyisocyanates, cycloaliphatic polyisocyanates, and others.
Polyester-Polyol Compounds
The polyester-polyol compounds can be produced by reacting polyols with a polyfunctional carboxylic acid compound.
Suitable polyols that can be used as reactants to form the polyester-polyols have a molecular weight in excess of 250, more typically in excess of 500, most preferably in the molecular weight range of about 500-10,000. Typical polyols include monomeric diols, triols, etc. and polymeric diols, triols comprising a chain of repeating methylene units providing a major contribution to the molecular weight of the material. A typical polymeric polyol includes either a linear or branched chain of the repeating units which is terminated with hydroxyl groups and for the sake of simplicity these hydroxyl groups will normally be the active hydrogen containing substituents in the polyol structure reacting with the capping isocyanate compounds.
Preferred polyols include monomeric polyols having 2 or 3, hydroxyl groups per molecule. Representative, but exclusive examples include ethylene glycol, propylene glycol, glycerine, trimethylol propane, 1,2,6-hexane triol, butene diol, 1,4-butanediol, 1,3-propanediol, neopentyl glycols.
Some preferred polyols include hexane diol, higher polyalkylene diols, cyclic polyols containing 1 to 3 -hydroxyl groups and a cycloaliphatic structure. Examples of such preferred diols include 1,4-dihydroxymethyl cyclohexane, hydrogenated bisphenol-A, hexane diol, dodecane diol, or other higher molecular weight diols. Especially preferred polyols include neopentyl glycols.
Under certain conditions release of vaporized isocyanate compositions can occur during manufacture or application of the adhesive of the invention. In order to reduce isocyanate volatility, a small amount of a low moleoular weight polyol can be added, with the polyester-polyol, that can react with free isocyanate compounds.
The polyester-polyols can be produced by reacting the above discussed po
Haider Gary J.
Reid Kevin J.
Zimmel John M.
Bin Su
H. B. Fuller Licensing & Financing Inc.
Johnson Allison A.
Short Patricia A.
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