Polyurethane adhesives containing alkyl-substituted 4,4′-di(aminocyclohexyl)alkanes, 2,4′-di(aminocyclohexyl)alkanes and/or 2,2′-di(aminocyclohexyl)amines
Two component polyurethane adhesives contain (a) at least one alkyl-substituted 4,4′-di(aminocyclohexyl)alkane wherein each cyclohexyl group is alkyl-substituted in at least one position ortho to the amino group, (b) at least one 2,4′-di(aminocyclohexyl)alkane or 2,2′-di(aminocyclohexyl)alkane, (c) a mixture of (ii) at least one alkyl-substituted 4,4′-di(aminocyclohexyl)alkane wherein each cyclohexyl group is alkyl-substituted and (ii) at least one 2,4′-di(aminocyclohexyl)alkane and/or 2,2′-di(aminocyclohexyl)alkane, or (d) a mixture of 40 to 99.9% by weight (a), (b) or (c) with 0.1 to 60% by weight of at least one unsubstituted 4,4′-di(aminocyclohexyl)alkane, The adhesives also contain one or more polyols, in which at least 50% of the hydroxyl groups are secondary hydroxyls. These adhesive provide a useful combination of long open time and excellent sag resistance.
1. A two-component polyurethane adhesive composition comprising an isocyanate component and a curative component, wherein the isocyanate component is an aromatic polyisocyanate or mixture of aromatic polyisocyanates and the curative component is a mixture containing (1) polyols wherein at least 90% of the hydroxyl groups provided by said polyols are secondary hydroxyl groups wherein the polyols include castor oil and a polyether polyol having a hydroxyl equivalent weight of 100 to 250 and a hydroxyl functionality of 2 to 6 and said castor oil and the polyether polyol having a hydroxyl equivalent weight of 100 to 250 together constitute at least 90% of the weight of the polyols and (2) at least one polyamine compound having at least two primary or secondary amine groups, wherein the polyamine compound constitutes 0.75 to 5% of the combined weight of the polyamine compound(s) and the polyol(s) and further wherein the polyamine compound is
(a) at least one alkyl-substituted 4,4′-di(aminocyclohexyl)alkane wherein each cyclohexyl group is alkyl-substituted in at least one position ortho to the amino group;
(b) at least one 2,4′-di(aminocyclohexyl)alkane or 2,2′-di(aminocyclohexyl)alkane;
(c) a mixture of (i) at least one alkyl-substituted 4,4′-di(aminocyclohexyl)alkane wherein each cyclohexyl group is alkyl-substituted in at least one position ortho to the amino group and (ii) at least one 2,4′-di(aminocyclohexyl)alkane and or 2,2′-di(aminocyclohexyl)alkane; or
(d) a mixture of 40 to 99.9% by weight (a), (b) or (c) with 0.1 to 60% by weight of at least one unsubstituted 4,4′-di(aminocyclohexyl)alkane,
and further wherein the polyol component contains no more than 0.25 weight percent of other primary or secondary amine-containing compounds.
2. The two-component polyurethane adhesive of claim 1 , wherein the alkyl-substituted 4,4′-di(aminocyclohexyl)alkane has the structure:
in which A is alkyl, each X is independently alkyl and each Y is independently hydrogen or alkyl.
3. The two-component polyurethane adhesive of claim 2 , wherein the A group is gem-substituted with the two aminocyclohexyl groups, each X is independently alkyl having up to 4 carbon atoms, and each Y is independently hydrogen or alkyl having up to 4 carbon atoms.
4. The two-component polyurethane adhesive of claim 1 , wherein the polyamine compound is 3,3′-dimethyl-4,4′-diaminocyclohexyl methane; 3,3′-diethyl-4,4′-diaminocyclohexyl methane, 3,5,3′,5′-tetramethyl-4,4′-diaminocyclohexyl methane, 3,5,3′,5′-tetramethyl-4,4-diaminocyclohexyl methane, 3,3′-di-t-butyl-4,4′-diaminocyclohexyl methane, 3,5,3′,5′-tetra-t-butyldiaminecyclohexyl methane or a mixture of any two or more thereof.
5. The two-component polyurethane adhesive of claim 1 , wherein the polyamine compound is a mixture of 40-99.9% by weight of the alkyl-substituted 4,4′-di(aminocyclohexyl)alkane and 0.1 to 60% by weight of an unsubstituted 4,4′-di(aminocyclohexyl)alkane.
6. The two-component polyurethane adhesive of claim 5 , wherein the unsubstituted 4,4′-di(aminocyclohexyl)alkane is 4,4′diaminocyclohexyl methane.
7. The two-component polyurethane adhesive of claim 1 , wherein the polyamine compound(s) are the only primary or secondary amine-containing compounds present in the curative component.
8. The two-component polyurethane adhesive of claim 1 , wherein the polyamine compound(s) constitute from 1 to 4% of the combined weight of the polyols and the polyamine compound(s) in the curative component.
9. The two-component polyurethane adhesive of claim 1 , wherein the polyols are devoid of tertiary amine groups.
10. The two-component polyurethane adhesive of claim 1 , wherein the polyisocyanate is a polymeric MDI.
11. The two-component polyurethane adhesive of claim 1 , wherein the polyisocyanate is a urethane group-containing prepolymer.
12. The two-component polyurethane adhesive of claim 1 which is devoid of tertiary amine and tin-containing catalysts.
13. The two-component polyurethane adhesive of claim 1 , which is devoid of tertiary amine and phosphine compounds, metal chelates, acidic metal salts of strong acids; strong bases, metal alcoholates, metal phenolates, metal salts of organic acids, organometallic derivatives of tetravalent tin, trivalent and pentavalent As, Sb and Bi, and metal carbonyls of iron and cobalt.
14. The two-component polyurethane adhesive of claim 1 , which further contains fumed silica and filler particles.