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Clear choice silica crystals cat litter are well known in the art. The crystalline molecular structure of choice crystalline silica provides good litter absorption, good odor control, and low dusting characteristics. Crystalline silica is a naturally occurring non-toxic, non-corrosive, and water-insoluble siliceous material which has been widely used for several decades as a filler and reinforcing agent in cement, concrete, plastics, rubbers, and the like. During that time, methods of making crystalline silica are continuously being developed and refined to provide the best use and properties of the material in the many applications of silica in a variety of products.
A major drawback in the use of silica as a filler in concrete is that the silica is very expensive. To reduce the cost of the concrete, less silica must be used. However, due to the lack of compatibility between the crystalline silica and the binder of the concrete, a large percentage of silica must be incorporated into the concrete to ensure adequate durability. This increase in silica content generally means an increase in the use of plasticizers in the concrete, thus causing the cost of the concrete to increase. This is a substantial drawback in the use of crystalline silica.
On the other hand, in order to make the cement useful, more silica must be added to the cement. The addition of additional silica in the cement is not commercially feasible because of the increased costs associated with the additional silica. The conventional method of compensating for the increased cost of cement due to the increased amount of silica is to reduce the strength of the cement. This is detrimental for numerous reasons including, but not limited to, the need to strengthen or retrn concrete structures, etc.
Various methods have been attempted in an effort to address the problems associated with the use of crystalline silica. One method of solving the problems associated with the use of crystalline silica as a filler or reinforcing agent for various materials is to manufacture a synthetic polymer having a polymeric backbone with silicon atoms which is chemically similar to crystalline silica and chemically compatible with the filler or reinforcing agent. These siloxanes, which are referred to as xe2x80x9corganosiloxanesxe2x80x9d, have been well-documented in the art and are generally described in a publication by H. M. Walling (Walling, H. M., Chemistry and Applications of Silanes, Interscience Publishers, N.Y., 1957). One important use of organosiloxanes is to produce the high strength, high modulus concrete formulations previously mentioned. These organosiloxanes are incorporated into the mixture of cement, silica, and water. The organosiloxanes reduce the cost of the concrete and, due to their chemical similarity to crystalline silica, increase the durability of the concrete.
While many studies of the chemistry and uses of organosiloxanes have been done, little work has been done with respect to the use of organosiloxanes to improve the physical properties of aqueous and non-aqueous adhesive compositions. Because adhesives have been used for decades, much of the basic work in this field has been done in the chemical industry. For example, silicone emulsions have been widely used in many commercial applications as lubricants for metals, particularly for internal combustion engines, to prevent wear, as mold release agents for rubber products, etc. In the past, only a few of the many uses of organosiloxanes have been in the field of adhesives.
U.S. Pat. No. 3,810,853 to Farkas et al. describes the use of organosiloxanes as plasticizers for non-aqueous adhesives. Farkas et al. discloses using the organosiloxane for rubber products, rubber molds, gaskets and other elastomeric goods. The disclosed organosiloxanes are non-polar solvents and include linear polydiorganosiloxanes of the formula R1SiO1/2xe2x88x92b(RSiO1/2)b wherein R is an organic radical which is essentially free of carbon-halogen bonds, R1 is the same or different and is an alkyl, cycloalkyl, aromatic or substituted aromatic radical, and b is 0 to 1. Farkas et al. teaches that the organosiloxane is applied to the composition in amounts of from 0.1 to 10 percent by weight and that the organosiloxane can function as a plasticizer and a binder or both. Farkas et al. requires that the organosiloxane not function as a solvent for the composition. Therefore, it does not teach any aqueous adhesive compositions having low levels of organic solvents.
European Patent Publication No. EP 0 577 024 A1 discloses liquid aqueous acrylic adhesive compositions having from about 25 to 50 percent by weight acrylic polymer and from 0 to 40 percent by weight solvent, the solvent being an organic solvent other than water. The acrylic adhesive compositions of the EP '024 A1 do not include the preferred silicone-based plasticizers.
While many current silicone based aqueous adhesives work well for their intended purposes, improvements are continuously sought.
It has now been found that silicone-based aqueous adhesives having high elongation and good bonding can be prepared having low levels of organic solvent.
In particular, it has now been discovered that silicone-based aqueous adhesives with high elongation and good bonding are prepared using silicone-based plasticizers. The silicone-based plasticizers can be any of a wide range of silicone-based plasticizers. Preferably, the plasticizers can be polyorganosiloxanes and dimethylsilicones. It is now also preferred that the silicone-based plasticizers be non-polar. A non-polar silicone-based plasticizer tends to have high viscosity (high molecular weight), whereas a polar silicone-based plasticizer has low viscosity (low molecular weight). Therefore, a low molecular weight silicone-based plasticizer is a preferred silicone-based plasticizer.
It is now preferred that the silicone-based plasticizer be a monomeric silicone-based plasticizer, such as polydiorganosiloxane, polyorganohydrogensiloxane, and dimethylpolysiloxane.
It is now preferred that the silicone-based plasticizers have a viscosity less than about 1,000,000 centipoise at 25xc2x0 C. When the silicone-based plasticizer has a viscosity less than about 500,000 centipoise, the adhesive has excellent shear properties and bonding properties. When the silicone-based plasticizer has a viscosity greater than about 500,000 centipoise