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
1999-06-23
2003-10-21
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...
C524S507000, C524S590000, C524S591000, C524S839000, C524S840000, C525S123000, C525S455000, C525S920000
Reexamination Certificate
active
06635706
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polyurethane polymers, particularly urethane-acrylic hybrid polymer dispersions, and more particularly, crosslinked urethane-acrylic hybrid polymer dispersions, prepared from polyisocyanates.
It is known in the coating industry that polyurethane coatings exhibit excellent resistance to abrasion, chemicals and solvents, and are highly flexible and durable. Conventional solvent-borne urethanes often contain high levels of volatile organic compounds or VOC's. Water-borne urethanes or polyurethane dispersions (PUD) have been used as architectural VOC compliant alternatives to conventional solvent-borne urethane coatings for many years due to their environment advantages. In most architectural coating applications, acrylic latex is used to blend with these PUD's for economy. However, there is some compromise in performance by blending, particularly chemical resistance and the balance of film flexibility and hardness. The urethane-acrylic hybrids of this invention overcome these drawbacks due to their core-shell particle morphology.
Generally, most waterborne urethanes and urethane-acrylic hybrids are linear in structure. When applied as a coating, the water and cosolvent evaporate and a thermoplastic polymer film forms. This thermoplastic film is deficient in chemical resistance compared to a thermosetting polyurethane film due to the fact the linear thermoplastic film can be re-dissolved.
U.S. Pat. No. 4,408,008 to Markusch discloses that a stable aqueous dispersion of crosslinked urea-urethane polymers can be prepared by using polyfunctional amine chain extenders having an average functionality between 2.2 to 6.0 to extend the isocyanate-terminated urethane prepolymer.
U.S. Pat. Nos. 4,554,308 to Russiello and U.S. Pat. No. 4,745,151 to Noll et al propose methods to make stable pre-crosslinked polyurethane dispersions by dispersing a branch prepolymer solution made by reacting a mixture of polyfunctional hydrogen compounds with di- or polyfunctional isocyanate, and then dispersing and chain extending the prepolymer with di- or multi-functional amine.
U.S. Pat. No. 4,147,679 to Scriven suggests that the branched isocyanate-terminated prepolymer can also be prepared by using tris-(hydroxyethyl) isocyanurate as part of polyfunctional hydrogen compound. Russiello, Noll and Scriven are similar in that they all suggest a pre-crosslinked polyurethane dispersion can be prepared by chain extending a branched isocyanate-terminated prepolymer. A major problem with this approach is that branched prepolymers typically are much more viscous than linear prepolymers, therefore, they require significantly more solvent to achieve a manageable viscosity.
As mentioned above, water-borne polyurethane polymers are for the most part linear, producing films with poorer chemical resistance than the highly crosslinked films of two component solvent-borne urethane systems. Pre-crosslinking of the water-borne polyurethane polymers by incorporation of a significant amount of monomer(s) having functionalities greater than two in the prepolymer stage results in highly viscous prepolymers that typically cannot be dispersed. Sufficient pre-crosslinking of the prepolymer in the dispersion stage by means of chain extenders having functionalities greater than two can result in significant polymer gel.
The problem of highly viscous branched prepolymers or polymer gel due to highly functional chain extenders is addressed in U.S. Pat. No. 4,507,431 to Stutz. Therein it is proposed that crosslinked polyurethane ionomer dispersions be prepared by a method in which polyurethane prepolymers having an isocyanate group content of 0.1 to 2 percent by weight are mixed with polyisocyanates. After chain extension of the isocyanate-terminated prepolymer and polyisocyanate mixture by diamine, a pre-crosslinked polyurethane-urea is obtained. Since the polyisocyanates are mixed with the prepolymer just before or after dispersion, the problem of high viscosity prepolymer is overcome. These dispersions do not contain any acrylic polymer and are relatively expensive, for example, for architectural applications.
It is so proposed in U.S. Pat. No. 5,169,895 to Coogen et al. (1992) that a crosslinked aqueous polyurethane dispersion can be prepared in a low boiling point organic solvent by mixing a polyurethane prepolymer, having an isocyanate group content 2.1 to 10 percent by weight, with an organic polyisocyanate. This prepolymer-polyisocyanate is then dispersed and chain extended. The organic polyisocyanate has an average isocyanate functionality of 2.1 to 4.0. These dispersions do not contain any acrylic polymer and are relatively expensive for architectural applications.
Blending of acrylic emulsions with water-borne polyurethanes has been used as a means to reduce coating costs, however, as previously mentioned there is some compromise in performance such as, chemical resistance.
U.S. Pat. No. 4,644,030 to Loewrigkeit et al. proposes that non-crosslinked polyurethane-acrylic hybrid dispersions can be prepared by producing an NCO terminated carboxylic acid functional prepolymer in the presence of inert liquid vinyl monomer(s). The carboxylic acid group of the prepolymer is neutralized with a volatile amine and the blend dispersed into water. This neutralized, dispersed NCO terminated prepolymer is then chain extended with one or more active hydrogen containing compounds such as polyamines, hydrazine and hydrazides. This dispersion consisting of polyurethane polymer and vinyl monomer(s) is then subjected to free radical polymerization. While dispersions of this type may be essentially free of any cosolvent and emulsifier and lower in raw material costs compared to pure polyurethane dispersions, the polymer is essentially linear and, thus, does not provide sufficient chemical resistance in the absence of any second component crosslinking agents.
U.S. Pat. No. 5,571,857 to Gruber et al. proposes that solvent free urethane-acrylic hybrid polymers can be made by reaction of an excess of isophorone diisocyanate with polyol(s) and dihydroxy carboxylic acid. The resulting NCO terminated carboxylic acid functional prepolymer is blended with vinyl monomer(s) to reduce the viscosity. A tertiary amine is then added to neutralize the acid groups and the blend is dispersed into water. The NCO terminated urethane prepolymer is then chain extended with a blend of mono and diamines followed by free radical polymerization of the vinyl monomer(s). As with Loewrigkeit, these polymers are essentially linear. These dispersions are solvent and emulsifier free, however, in the absence of a second component, the film's chemical resistance is insufficient for coatings applications.
U.S. Pat. No. 5,104,928 to Craun et al. proposes that thermosetting urethane-acrylic hybrid dispersions can be prepared by using carbodiimide crosslinkers. The polymeric carbodiimide is added into the carboxyl-functional polyurethane dispersion after prepolymer chain extension. The polymeric carbodiimide reacts with carboxyl acid groups to form a crosslinking polyurethane.
It is proposed in U.S. Pat. No. 5,521,246 to Tien et al. that a room temperature self-crosslinkable polyurethane-acrylic hybrid dispersion can be prepared by first producing an NCO-terminated carboxyl functional polyurethane prepolymer. Vinyl monomers a portion of which is glycidyl methacrylate are added, the carboxyl groups neutralized with a tertiary amine, the mixture dispersed into water, an oil-soluble free radical initiator added, polymerizing the vinyl monomers and chain extending the urethane with water. Since the epoxy group is hydrophilic and reaction catalyzed by the presence of tertiary amines, the stability of these dispersions is questionable particularly, at elevated temperatures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a stable, pre-crosslinked, urethane-acrylic hybrid polymer dispersion.
It is another object of the present invention to provide a stable, pre-crosslinked urethane acrylic hybr
Petschke Glenn
Yang Shi
Myers Bigel & Sibley Sajovec, PA
Niland Patrick D.
Reichhold Inc.
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