Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-04-30
2004-04-13
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S807000, C524S839000, C524S840000
Reexamination Certificate
active
06720385
ABSTRACT:
This invention relates to polyurethane latexes, processes for preparing them and polymers prepared therewith. This invention particularly relates to stable polyurethane polymer latexes.
Latex polymers are known to be useful in many applications such as paints, sealants, and films. Polyurethane latexes are less widely used due to inherent difficulties in preparing stable aqueous polyurethane latexes. For example, polyurethane formulation components, such as polyisocyanates can be reactive with water. Polyurethane prepolymers useful for forming latexes are often not low viscosity liquids at ambient conditions. These and other properties can cause polyurethane latexes to be unstable, that is to form a dispersion which separates from the continuous aqueous phase of the latex, which is often not desirable in an industrial venue.
One solution to at least some of the problems of preparing polyurethane latexes is to use a solvent/water based process wherein the solvent is optionally removed prior to use in the final application. For example, a polyurethane can be prepared by processes such as: 1) dissolving a polyurethane in an organic solvent, 2) emulsifying the solution in water, and 3) removing the solvent. Such processes are disclosed in U.S. Pat. Nos. 3,360,599; 3,503,917; 4,123,403; and 5,037,864. Unfortunately, processes to remove solvent are often not completely efficient and leave behind traces of solvents in the latex to be later released in latex applications, also solvent removal is an added cost.
In other situations unstable latexes are tolerated. A polyurethane latex which is described as being useful for preparing films is disclosed in GB 1 432 112. Therein, a latex is prepared which is allowed to separate into a thixotropic layer and a “serum” wherein the thixotropic layer has a solids concentration of about 30 to 50 percent.
It would be desirable in the art to prepare polyurethane latexes which are stable. It would also be desirable in the art to prepare polyurethane latexes which are stable without resort to the use of organic solvents, such as toluene, acetone, and the like.
SUMMARY OF THE INVENTION
In one aspect, the present invention is a process for preparing a stable polyurethane latex comprising admixing a polyurethane prepolymer with water, a surfactant, and a chain extender under conditions sufficient to disperse the prepolymer and chain extender reaction product to form a latex wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and polyol component, (ii) from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap onto a propylene oxide or higher oxyalkylene polyoxyalkylene polyol, and (iii) no more than 45 percent of the weight of polyol component is ethylene oxide.
In another aspect, the present invention is a stable polyurethane latex prepared by a process for preparing a stable polyurethane latex comprising admixing a polyurethane prepolymer with water, a surfactant, and a chain extender under conditions sufficient to disperse the prepolymer and chain extender reaction product to form a latex wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and polyol component, (ii) from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap onto a propylene oxide or higher oxyalkylene polyoxyalkylene polyol, and (iii) no more than 45 percent of the weight of polyol component is ethylene oxide.
In yet another aspect, the present invention is a polyurethane polymer coated substrate prepared by a process comprising the steps of (1) admixing a polyurethane prepolymer with water, a surfactant, and a chain extender under conditions sufficient to disperse the prepolymer and chain extender reaction product to form a latex wherein: (i) the prepolymer is prepared from a prepolymer formulation including a polyisocyanate component and polyol component, (ii) from 5 to 40 percent of the weight of the polyol component is ethylene oxide in the form of ethylene oxide applied as an end cap onto a propylene oxide or higher oxyalkylene polyoxyalkylene polyol, and (iii) no more than 45 percent of the weight of polyol component is ethylene oxide, (2) applying the latex to a substrate, and (3) dehydrating the latex to form a coating.
Another aspect of the present invention is a stable polyurethane latex containing no organic solvents comprising:(1) a continuous aqueous phase; and dispersed therein: (2) from about 0.1 to about 10.0 percent by weight of an anionic surfactant; and (3) a polymer comprising the reaction product of:(i) an ethylene oxide capped poly(propylene oxide) polyol component having a molecular weight of from about 1500 to about 6000 wherein from 5 to 40 percent by weight of the polyol component is ethylene oxide, (ii) a polyether monol having an ethylene oxide content of greater than 40% by weight, (iii) a diol having a molecular weight of from about 30 to 500, (iv) an aromatic polyisocyanate, and (v) a diamine, water, or combination thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In one embodiment of the present invention, a polyurethane latex is formed. For the purposes of the present invention, the term “polyurethane” is defined to include the compounds known in the art as “polyureas” The terms polyurea and polyurethane are well known in the art of preparing polymers, but for clarity, these terms are defined as follows. A “polyurethane” is a polymer having a structure similar to that of a polymer prepared by reacting a polyisocyanate and a poly-alcohol. A “polyurea” is a polymer having a structure similar to that of a polymer prepared by reacting a polyisocyanate with a polyamine. It is further recognized in the art of preparing polyurethanes that either material can have some linkages other than the named primary linkage. For example, a polyurethane prepared using a base polyol but also an amine chain extender would have some urea linkages but would still be a polyurethane. Likewise a polyurea prepared using a base polyamine but also using a glycol chain extender would have some urethane linkages but would still be a polyurea, but may be referred to herein also as a polyurethane.
The polymers of the present invention are prepared by applying a latex to a substrate. The latex can be applied by means of painting or spraying. For purposes of the present invention, painting is defined as applying a material, such as a polyurethane latex, to a brush or other applicator, and then depositing the polyurethane latex on a substrate, or, in alternative, the material can be puddled or pooled on a substrate and then spread over the substrate using a brush or other spreading means. Also for the purposes of the present invention, spraying is defined as applying a material, such as a polyurethane latex, by atomizing the material and ejecting the atomized material onto the substrate.
Another process useful with the present invention for applying a polyurethane latex to a substrate is dipping. In a dipping process, a substrate is lowered into a pool of latex and then removed. The latex which is retained on the substrate can be allowed to dry as is or can be further spread to make a more even application. Parts of the substrate can be masked to avoid getting polyurethane latex on the entire surface of the dipped substrate.
Still another process for applying a latex to substrate useful with the present invention is application by means of a transfer process. In a transfer process, a polyurethane latex is applied to a material which has very little ability to adhere to the polymer which forms upon dehydration. This “transfer” material is brought into contact with another substrate which has a higher adhesive affinity for the polymer. The transfer material is removed and the polymer is retained on the substrate. While the above processes for applying a latex to a substrate are preferred, any process known to be useful to one of ordinary skill
Jakubowski James J.
Moore Douglas R.
Solis Ruben
Tabor Rick L.
Willkomm Wayne R.
Niland Patrick D.
The Dow Chemical Company
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