Liquid moisture curable polyurethane with improved adhesion to aluminum
Disclosed is a one component, liquid, moisture curable polyurethane adhesive composition comprising the reaction products of a mixture including at least one polyol with an excess of one or more polyisocyanates and an acid component. In one embodiment some or all of the acid component is applied separately from the adhesive composition. The adhesive composition has enhanced bond strength to metals such as aluminum compared to currently available adhesives. The composition finds special use in panel lamination applications.
1 . A method of making a composite structure, the method comprising:
applying an adhesive composition to a first bonding surface of a metal frame, a bonding surface of a first panel, or both, the adhesive composition being a one component, liquid, moisture curable polyurethane adhesive composition including the isocyanate functional reaction products of a mixture comprising at least one polyol and an excess of at least one organic polyisocyanate, and the adhesive composition not including an acid;
spraying an acid solution on the adhesive composition applied to the first bonding surface of the metal frame, the bonding surface of the first panel, or both;
contacting the first bonding surface of the metal frame and the bonding surface of the first panel to form the composite structure; and
curing the adhesive composition to bond the first panel to the metal frame.
2 . The method of claim 1 , wherein the acid solution comprises an acid and water.
3 . The method of claim 2 , wherein the acid is present in an amount of 1.5 wt. % or 5 wt. %, based on the total weight of the acid solution.
4 . The method of claim 3 , wherein the acid is present in an amount of 5 wt. %, based on the total weight of the acid solution.
5 . The method of claim 1 , wherein the metal frame is made of aluminum.
6 . The method of claim 1 , further comprising placing the composite structure in a press, wherein curing the adhesive composition is at least partially done while the composite structure is in the press.
7 . The method of claim 1 , wherein:
the metal frame has a second bonding surface opposite the first bonding surface, and the method further comprises:
applying the adhesive composition to the second bonding surface of the metal frame, a bonding surface of a second panel, or both;
spraying the acid solution on the adhesive composition applied to the second bonding surface of the metal frame, the bonding surface of the first panel, or both;
contacting the second bonding surface of the metal frame and the bonding surface of the second panel; and
curing the adhesive composition to bond the second panel to the metal frame.
8 . The method of claim 7 , wherein the second panel comprises a cured polymer or wood.
9 . The method of claim 1 , wherein the metal frame is made of mill grade aluminum that has not been cleaned.
10 . The method of claim 1 , wherein the metal frame is made of aluminum that has not been conversion coated or that has not been anodized.
11 . The method of claim 1 , wherein the first panel comprises a cured polymer or wood.
12 . The method of claim 1 , wherein the composite structure does not include any mechanical fasteners to secure the first panel to the metal frame.
13 . The method of claim 1 , wherein the at least one organic polyisocyanate has an average functionality of from 2.0 to 2.4.
14 . The method of claim 1 , wherein the acid solution comprises at least one inorganic acid.
15 . The method of claim 14 , wherein the at least one inorganic acid is selected from the group consisting of nitric acid, sulfuric acid, phosphoric acid, and any combination thereof.
16 . The method of claim 15 , wherein the at least one inorganic acid is phosphoric acid.
17 . The method of claim 1 , further comprising disposing insulation in a void area defined by the first bonding surface of the metal frame or the bonding surface of the first panel.
18 . The method of claim 1 , wherein:
the adhesive composition is applied to the first bonding surface of the metal frame; and
the acid solution is sprayed on the adhesive composition applied to the first bonding surface of the metal frame.
19 . A method of making a composite structure, the method comprising:
applying an adhesive composition to an aluminum surface, the adhesive composition being a one component, liquid, moisture curable polyurethane adhesive composition including the isocyanate functional reaction products of a mixture comprising at least one polyol and an excess of at least one organic polyisocyanate, and the adhesive composition not including an acid;
spraying an acid solution comprising phosphoric acid on the adhesive composition applied to the aluminum surface;
contacting the aluminum surface and another bonding surface; and
curing the adhesive composition to bond the aluminum surface to the another bonding surface.
20 . The method of claim 19 , wherein the another bonding surface comprises a cured polymer or wood.