Water Dispersible Polyisocyanate Adhesive

The polyurethane latex adhesive of the present invention contemplates wide usage as a universal water-based adhesive. While other uses, including that of construction adhesive are contemplated, in the detailed description of the specification, is directed to using the material to adhere any type of floor covering material/floor combination. Optional cross-linking agents impart greater solvent resistance and environmental stability to accommodate more severe application conditions. Types of carpet materials typically include Actionback (a trademark of Patchoque-Plymouth Division of Amoco Fabrics), jute-backed; latex or urethane unitary structure; carpet tiles (polyvinyl chloride, urethane or polyurethane or polypropylene) hot-melt secondaries, e.g., Unibond (a trademark of Burlington Industries Lees Carpets), carpets with attached cushion backings or urethane or rubber polymer backings and in direct or double glued systems (pad to floor and carpet to pad) also adhere well. All types of sheet vinyl materials may be fixed including those that are mineral, paper or felt-backed; cushion vinyls (full spread or perimeter installations); pure vinyl (full spread); linoleums; and pure vinyl or vinyl composition tiles. Other floor coverings contemplated include rubber radial tiles, ceramic tiles, vinyl planks, laminated wood parquet and laminated wood plank. Installation may be indoors or, with cross-linking, outdoors or under more stressful environments.

Not only are the adhesive qualities of the formulations in accordance with the present invention superior to conventional adhesives such as those made with styrene-butadiene latex (SBR) and/or acrylic latex with respect to adhesion and environmental stability, the water-based materials are extremely stable in storage, much more convenient to work with, and contain no volatile solvents or other chemical ingredients which emit undesirable vapors. The adhesives are one-step bonders and so require no separate activation step to fully cure. Bonding time is reduced (8-10 hours) so that carpet can be installed "overnight" and used the next morning. Furthermore, in addition to exhibiting excellent bonding characteristics, the adhesives of the invention are also excellent sealant for moisture emitting surfaces.

The general formulation of the adhesive of the invention includes an amount of a polyester-polyisocyanate (polyurethane) in aqueous dispersion combined with an amount of rosin acid ester hardening agent in the form of an aqueous dispersion of synthetic resin, an amount of a thickening agent, typically polyacrylate, and sufficient water to yield the desired percent solids. The material normally includes an amount of a polymer latex modifier, inert filler additive and a plasticizer/extender modifier. In addition, the formulation typically includes an amount of polyisocyanate cross-linking material to cross-link the polyester/polyisocyanate resin material.

The cross-linking agent is also a water-dispersible polyisocyanate preferably in the form of an aliphatic polyisocyanate. One successfully used in the formula of the invention was based on a 1,6-Hexamethylene Diisocyanate (HDI), also known as polymeric hexamethylene diisocyanate, such products are available from the Polystar Rubber Division of Miles Inc. in Pittsburgh, Pa., identified as "Desmodur DA" or "R 255".

The formula also contains significant amounts of rosin acid ester hardening agents in the form of an aqueous dispersion of rosin ester, also known as a synthetic resin dispersion. An example of this is known as Tacolyn 1085 or Hercules Res A-2340A (trademarks of Hercules Incorporated). In addition, the preferred adhesive formulation of the invention further contains varying amounts of polymer latex modifiers, inert filler additives and plasticizer/extender modifier compounds. The polymer latex modifiers include acrylics, styrene-butadiene, carboxylated styrene-butadiene, nitriles, neoprenes, ethylene vinyl acetates, and the like.

Inert filler additives are also utilized, such as calcium carbonate in the form of whiting material, one of which is known as Marble White 199 available from Filler Products, Inc., Chatsworth, Ga. That material is typically a minimum of 95% carbonates, including calcium (Ca) and magnesium (Mg), of which the magnesium carbonate is typically 20%-30%. The balance of the materials includes silica (SiO.sub.2), 1-1.5% and iron and aluminum oxides (Fe.sub.2 O.sub.3 and Al.sub.2 O.sub.3), 1-1.5%. The material is typically fine enough to pass -325 mesh. Other inert filler additives include Kaolin (hydrated aluminum silicate or china clay). This material is also typically -325 mesh and is available as spray-dried beads or in slurry form. Other useful inert filler additives include barium sulfates, silicate spheres, ground reprocessed rubber, cellulose, synthetic fiber (reclaimed) and any other materials having the chemical compatibility and physical properties desired.

The material also typically contains some plasticizer/extender modifying material such as paraffinic, naphthenics, and phthalates. These generally affect the spreadability of the material.

According to the present invention, the following represents an approximate weight percentage composition range of the preferred combination.

Based on dry weight, a particularly useful formula included:

This material, made up in a smooth aqueous blend exhibits a pH of 8-9, viscosity at 20.degree. C. #7 of 15-20 and weighs 9.5-10.5 pounds per gallon. For water resistance, approximately 7% aliphatic polyisocyanate (1,6-hexamethylene diisocyanate based polyisocyanate) cross-linking agent or a poly-functional water dispersible isocyanate may be added for modified curing properties and to provide additional water and solvent resistance.

Once mixed, the pot-life of the material with the cross-linking agent is up to 12 hours; however, wet adhesion and tack diminish with the length of open time of mixtures with cross-linking agent added. The best results are obtained if the material is spread within a two-hour period. The set time is approximately 3-4 hours and maximum bonding strength can be reached as early as 8-10 hours (4-6 hours with cross-linker) after application.

The thickener material adds body and spreadability to the material and is typically an acrylic polymer in the form of a polyacrylate copolymer, ammonium salt, such as "Alcogum Arm" available from Alco Chemical Division of National Starch and Chemical Company, Chattanooga, Tenn.

The polyester-polyisocyanate (polyurethane) aqueous dispersion is of a class of dispersible materials exemplified by products such as Dispercoll UE-1409 available from Miles Inc., Polysar Rubber Division, Pittsburgh, Pa., available in liquid form. This is the principal resin material.

This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope of the invention itself.

Variations of the composition within the parameters of the General Formula adjust physical properties to meet specific installation specifications and requirements where advantageous, e.g., installation of rubber radial tiles, hardwood (laminated) plank or parquet and ceramic tiles.

While the aqueous dispersion formulae are freeze/thaw sensitive, compatible freeze point depressive materials may be incorporated where below freezing temperatures are likely to be encountered. One material that has been used successfully to prevent freezing and to extend and lower the curing temperature is urea, also a chemically compatible, water soluble and environmentally benign material.

The adhesive material of the invention has been found to provide complete resistance to alkali or caustic materials through at least pH 11.0. A further attribute is the moisture resistance of the material. This applies both to subsurface moisture and moisture associated with flooding, cleaning processes or spillage. Present subsurface moisture resistant materials are limited to resisting a maximum of about 3.0 pounds per 1000 square feet per 24 hours (as determined by the Rubber Manufacturers Association Calcium Chloride Test Method). The adhesive preparation of the present invention used as a flooring primer or sealcoating layer on concrete, wood or other porous or semi-porous material has been observed to prevent subsurface moisture penetration or emission where the emission potential is as high as 5.5-6.0 pounds water per 1000 square feet per 24 hours.

When the material is used as a sealcoating, one layer is applied to the bare floor and allowed to cure. Thereafter, a second application is used as the bonding material to bond the floor covering to the subfloor.