Polyurethane hot melt adhesive for low temperature application
Disclosed is a moisture reactive polyurethane hot melt adhesive composition that can be applied to substrates at a low coating weight even at application temperatures as low as 60 to 95° C. while retaining the advantageous high tack, green strength, cured bond strength and toughness of conventional high melting point polyurethane hot melt adhesives.
1. A moisture curable, polyurethane, hot melt adhesive comprising an isocyanate functional prepolymer that is the reaction product of a mixture comprising:
3 to 30 wt. %, based on the total weight of the hot melt adhesive, of an amorphous polyester polyol having a Tg greater than 0° C.;
10 to 40 wt. %, based on the total weight of the hot melt adhesive, of at least one crystalline polyester polyol, wherein the at least one crystalline polyester polyol has a melting point in the range of from 20° C. to 100° C.;
wherein the weight ratio of crystalline polyester polyol: amorphous polyester polyol is in the range of 2:1 to 1:2;
10 to 30 wt. %, based on the total weight of the hot melt adhesive, of a diisocyanate;
5 to 50 wt. %, based on the total weight of the hot melt adhesive, of at least one polyether polyol;
a catalyst; and
either:
(i) 0.1 to 3 wt. %, based on the total weight of the hot melt adhesive, of a polyisocyanate having a functionality greater than 2, or
(ii) 0.1 to 10 wt. %, based on the total weight of the hot melt adhesive, of a thermoplastic polyurethane having hydroxyl functionality,
wherein:
the weight ratio of the total amount of the at least one crystalline polyester polyol to the total amount of the amorphous polyester polyol is of from 2:1 to 1:2, and
the hot melt adhesive has a green strength of at least 0.4 psi or more 5 minutes after application of the hot melt adhesive to a substrate at a temperature of from 60 to 95° C. and a coating weight of 10 gsf or less.
2. The moisture curable, polyurethane, hot melt adhesive of claim 1 , further comprising another amorphous polyester polyol having a Tg of from −60° C. to 0° C.
3. The moisture curable, polyurethane, hot melt adhesive of claim 1 , further comprising another crystalline polyester polyol different from the at least one crystalline polyester polyol and having a melting point of from 20° C. to 100° C.
4. The moisture curable, polyurethane, hot melt adhesive of claim 1 , further comprising another polyether polyol different from the at least one polyether polyol.
5. The moisture curable, polyurethane, hot melt adhesive of claim 1 , further comprising 10 to 30 wt. %, based on the total weight of the hot melt adhesive, of one or more additives.
6. The moisture curable, polyurethane, hot melt adhesive of claim 1 , wherein the hot melt adhesive is free of organometallic catalysts.
7. The moisture curable, polyurethane, hot melt adhesive of claim 1 , wherein the weight ratio of the total amount of the at least one crystalline polyester polyol to the total amount of the amorphous polyester polyol is 1:1.
8. The moisture curable, polyurethane, hot melt adhesive of claim 1 , wherein the hot melt adhesive has a Lauan board to vinyl foil green strength of 1.0 psi or more.
9. The moisture curable, polyurethane, hot melt adhesive of claim 1 , wherein the hot melt adhesive has an Azdel board to vinyl foil green strength of 0.4 psi or more.
10. The moisture curable, polyurethane, hot melt adhesive of claim 9 , wherein the hot melt adhesive has an Azdel board to vinyl foil green strength of 0.8 psi or more.
11. A moisture curable, polyurethane, hot melt adhesive comprising an isocyanate functional prepolymer that is the reaction product of a mixture comprising:
3 to 30 wt. %, based on the total weight of the hot melt adhesive, of an amorphous polyester polyol having a Tg greater than 0° C.;
10 to 40 wt. %, based on the total weight of the hot melt adhesive, of at least one crystalline polyester polyol, wherein the at least one crystalline polyester polyol has a melting point of from 20° C. to 100° C.;
either:
10 to 30 wt. %, based on the total weight of the hot melt adhesive, of a diisocyanate, or
5 to 50 wt. %, based on the total weight of the hot melt adhesive, of at least one polyether polyol;
a catalyst;
0.1 to 3 wt. %, based on the total weight of the hot melt adhesive, of a polyisocyanate having a functionality greater than 2; and
0.1 to 10 wt. %, based on the total weight of the hot melt adhesive, of a thermoplastic polyurethane having hydroxyl functionality,
wherein:
the weight ratio of the total amount of the at least one crystalline polyester polyol to the total amount of the amorphous polyester polyol is of from 2:1 to 1:2, and
the hot melt adhesive has a green strength of at least 0.4 psi or more 5 minutes after application of the hot melt adhesive to a substrate at a temperature of from 60 to 95° C. and a coating weight of 10 gsf or less.
12. A cured reaction product comprising the moisture curable, polyurethane, hot melt adhesive of claim 1 .
13. An article comprising the moisture curable, polyurethane, hot melt adhesive of claim 1 .
14. An article comprising the cured reaction product of claim 12 .
15. The moisture curable, polyurethane, hot melt adhesive of claim 1 , wherein the hot melt adhesive has a maximum viscosity of 12,000 cps at 95° C.
16. The moisture curable, polyurethane, hot melt adhesive of claim 15 , wherein the hot melt adhesive has a maximum viscosity of 5,000 cps at 95° C.
17. A method of coating a substrate, the method comprising:
heating the moisture curable, polyurethane, hot melt adhesive of claim 1 to a temperature of from 60 to 95° C.; and
coating the heated moisture curable, polyurethane, hot melt adhesive onto a coating surface of a first substrate at a coating weight of 10 grams per square foot (gsf) or less.
18. The moisture curable, polyurethane, hot melt adhesive of claim 11 , wherein the weight ratio of the total amount of the at least one crystalline polyester polyol to the total amount of the amorphous polyester polyol is 1:1.
19. The moisture curable, polyurethane, hot melt adhesive of claim 11 , further comprising one or more additives.
20. A moisture curable, polyurethane, hot melt adhesive comprising an isocyanate functional prepolymer that is the reaction product of a mixture comprising:
about 13.5 wt. %, based on the total weight of the hot melt adhesive, of an amorphous polyester polyol having a Tg greater than 0° C.;
about 25 wt. %, based on the total weight of the hot melt adhesive, of at least one crystalline polyester polyol, wherein the at least one crystalline polyester polyol has a melting point of from 20° C. to 100° C.;
about 18 wt. %, based on the total weight of the hot melt adhesive, of a diisocyanate;
about 15.5 wt. %, based on the total weight of the hot melt adhesive, of at least one polyether polyol;
a catalyst;
either:
(i) about 0.8 wt. %, based on the total weight of the hot melt adhesive, of a polyisocyanate having a functionality greater than 2, or
(ii) about 1.5 wt. %, based on the total weight of the hot melt adhesive, of a thermoplastic polyurethane having hydroxyl functionality; and
one or more additives, wherein:
the hot melt adhesive has a green strength of at least 0.4 psi or more 5 minutes after application of the hot melt adhesive to a substrate at a temperature of from 60 to 95° C. and a coating weight of 10 gsf or less.