1. Field of the Invention
The present invention relates to water-based adhesives, and more particularly to a water-based adhesive composition, comprising an admixture of an aqueous polyester polyurethane dispersion and an aliphatic polyurethane dispersion
2. Description of the Related Art
Polyurethanes are used in a variety of fields such as adhesives, impregnation agents, and coating agents. Polyurethanes have been particularly useful in the adhesive field due primarily to their desirable adhesive properties to a wide range of substrates including metals, woods, fabric, plastics, and the like. Polyurethane-based adhesives have been demonstrated to offer good chemical resistance, elasticity, and durability. Due to these advantages, polyurethane adhesives have found many applications, particularly in the automotive field and other fields where adhesion durability is desired.
Automobiles are exposed to a variety of environmental factors, such as wide temperature fluctuations, wind, water, salt, road dirt, insects and UV radiation. The adhesives used in bonding trim or other pieces must be resistant to these factors for many years in order to meet the quality standards that are demanded in the current marketplace. In addition, strict environmental regulations have limited the use of solvent-based adhesives. The solvents used in the manufacture of these adhesives result in several disadvantages. The organic solvents generally evaporate quickly and result in an adhesive mixture that may become too viscous for many applications. In addition, the costs associated with disposal of the organic solvents result in a higher cost of the product. Moreover, the vaporized solvents that are produced during manufacture or cure have an adverse effect on the environment and the workplace in that they are often toxic and/or odoriferous.
In addition to the above problems, manufacturers are using larger amounts of certain plastics, such as ABS plastic, which are resistant to certain adhesives. Forming metal-plastic laminates with these particular plastics has proven difficult due to unsuitable adhesives that are currently available.
Aqueous water-based adhesives have been utilized as a replacement for adhesives using organic solvents, and are the subject of existing patents. However, while environmentally responsible, current aqueous adhesives do not provide the level of adhesion and durability offered by adhesives using an organic solvent.
U.S. Pat. No. 4,507,430 to Shimeda discloses a water-based polyurethane emulsion useful for an adhesive or coating for a polyolefin resin, comprising a hydrogenated polyol component and a polyisocyanate component.
U.S. Pat. No. 4,740,536 to Chao discloses a water-based binder, coating, and adhesive composition comprising an aqueous dispersion of polymer latex and an amine curing agent. The polymer latex is alkali-curable and polymerized from a monomer mixture containing quaternary ammonium monomer and an epoxy resin.
U.S. Pat. No. 4,792,574 to Berkowitz discloses a stable polymer/polyisocyanate dispersion comprising a polyisocyanate, and a polymer that is the reaction product of an ethylenically unsaturated macromolecular monomer, a functional monomer, and at least one other ethylenically unsaturated monomer.
U.S. Pat. No. 5,523,344 to Maksymkiw et al. discloses an adhesive formulation comprising a hydrophobic elasticizer, and an aqueous plasticized dispersion consisting of sulfonated polyester urethane, a nonsulfonated polyester urethane, and a water-based polymer or copolymer.
U.S. Pat. No. 5,688,356 to Sagiv discloses a water-based adhesive composition made from two urethane resins, and methods of using the adhesive to adhere workpieces together.
What is needed in the art is an environmentally safe adhesive formulation that provides high adhesive strength over a wide variety of environmental conditions and with a wide variety of substrates, particularly resistant substrates like ABS plastics or laminates of metal and plastic. The present invention is believed to meet that need.
In one aspect, the present invention is directed to a water-based adhesive composition, comprising an admixture of: (A) about 5 to about 80 wt % of an aqueous polyester polyurethane dispersion; and (B) about 95 to about 20 wt % of an aqueous aliphatic polyurethane dispersion.
In another aspect, the present invention is directed to a water-based adhesive composition, comprising an admixture of: (A) about 17.5 to about 22.5 wt % of an aqueous polyester polyurethane dispersion; (B) about 82.5 to about 77.5 wt % of an aqueous aliphatic polyurethane dispersion; (C) about 0.005 to about 2 wt % of one or more additives selected from the group consisting of film-forming agents, adhesion promoters, tackifiers, surfactants, defoamers, and combinations thereof; and (D) about 0.5 to about 25 wt % of a solvent selected from the group consisting of water, N-methylpyrrolidone, butylcarbitol, 2-butoxyethanol, and combinations thereof.
In yet another aspect, the present invention is directed to a method of adhering a workpiece to a substrate, comprising the steps of: (A) applying a water-based adhesive composition to a substrate, said water-based adhesive composition comprising an admixture of: (1) about 17.5 to about 22.5 wt % of an aqueous polyester polyurethane dispersion; (2) about 82.5 to about 77.5 wt % of an aqueous aliphatic polyurethane dispersion; (3) about 0.005 to about 2 wt % of one or more additives selected from the group consisting of film-forming agents, adhesion promoters, tackifiers, surfactants, defoamers, and combinations thereof; and (4) about 0.5 to about 25 wt % of a solvent selected from the group consisting of water, N-methylpyrrolidone, butylcarbitol, 2-butoxyethanol, and combinations thereof; (B) curing said water-based adhesive onto said substrate; and (C) adhering said workpiece onto said substrate.
These and other aspects will be more fully understood from the following detailed description of the invention.