Sprayable water-based adhesive
Water-based adhesive compositions are improved by the incorporation of hollow polymeric microspheres having outer surfaces coated with one or more barrier materials such as calcium carbonate particles. The adhesive compositions exhibit enhanced rheology, sprayability, drying time, tack and storage stability as compared to analogous adhesives that are not modified with coated hollow polymeric microspheres. Such compositions are useful as both contact adhesives as well as wet bonding one-way adhesives.
1. A process for bonding a first substrate to a second substrate comprising:
a) applying a water-based adhesive composition on a surface of the first substrate, wherein the water-based adhesive composition comprises a) at least about 30 weight percent of water; b) an adhesive polymer which is a homopolymer or copolymer of chloroprene having a glass transition temperature that is less than about 0° C.; and c) about 1 weight percent to about 3 weight percent of hollow, polymeric microspheres, based on the weight of the water-based adhesive composition, wherein the microspheres are coated with at least one barrier material which provides an outer coating;
b) drying, at least partially, the water-based adhesive composition to form an adhesive film layer on the surface of the first substrate; and
c) bonding the first substrate to the second substrate.
2. The process of claim 1 , wherein bonding step c) comprises contacting the second substrate with the adhesive film layer on the surface of the first substrate.
3. The process of claim 2 , wherein bonding step c) further comprises pressing the first and second substrates together.
4. The process of claim 2 , wherein the adhesive film layer is heated above ambient temperature prior to contacting the second substrate with the adhesive film layer on the surface of the first substrate.
5. The process of claim 1 , further comprising:
prior to bonding step c), applying the water-based adhesive composition on a surface of the second substrate; and
drying, at least partially, the water-based adhesive composition to form an adhesive film layer on the surface of the second substrate;
wherein the bonding comprises contacting the adhesive film layer on the surface of the second substrate with the adhesive film layer on the surface of the first substrate.
6. The process of claim 1 , wherein in step a) the water-based adhesive composition is applied by spraying.
7. The process of claim 6 , wherein the water-based adhesive composition is sprayed on the surface of the first substrate from a pressurized canister.
8. The process of claim 1 , wherein the first and second substrates are selected from the group consisting of plastic, wood, metal, rubber, glass, ceramic, paper, fabric, plasterboard, fiber, leather, concrete, rock, and sheet rock.
9. The process of claim 1 , wherein one or both of the first and second substrates are porous substrates.
10. The process of claim 1 , wherein the microspheres are coated with finely divided calcium carbonate particles.
11. The process of claim 1 , wherein the microspheres have a composite density of not greater than about 0.15 g/cm 3 , as measured including the outer coating.
12. The process of claim 1 , wherein the outer coating is an adherent outer coating.
13. The process of claim 1 , wherein the microspheres have shells comprising at least one thermoplastic polymer.
14. The process of claim 1 , wherein the microspheres have shells comprising a polymer that is a methyl methacrylate-acrylonitrile copolymer, a vinylidene chloride-acrylonitrile copolymer, or a vinylidene chloride-acrylonitrile-methyl methacrylate copolymer.
15. The process of claim 1 , wherein the microspheres are pre-expanded.
16. The process of claim 1 , wherein the adhesive polymer has a glass transition temperature that is less than about −20° C.
17. The process of claim 1 , wherein the water-based adhesive composition further comprises at least one additive selected from the group consisting of an antioxidant, a defoamer, a wetting agent, a fungicide, a preservative, a biocide, a stabilizer, a tackifying resin, a filler, a processing oil, a corrosion inhibitor, a pigment, a plasticizer, an adhesion promoter, a viscosity modifier, an internal coagulant, a pH adjustment agent, a flame retardant, a rheology improver, and a mixture thereof.
18. The process of claim 1 , wherein the microspheres have an average diameter of about 20 microns to about 60 microns.
19. The process of claim 1 , wherein the water-based adhesive composition has a viscosity of less than about 300 Pas at a shear stress of 10 Pa.
20. The process of claim 1 , wherein the adhesive film layer formed on the surface of the first substrate exhibits a homogeneous dispersion of the microspheres throughout the film, wherein each individual microsphere is uniformly coated or surrounded by a matrix containing the adhesive polymer.