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
2000-01-21
2002-02-26
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...
C524S590000, C524S591000, C524S839000, C524S840000, C528S044000, C528S076000, C528S085000
Reexamination Certificate
active
06350811
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to water-dispersible polyurethane resins and aqueous polyurethane dispersions. In particular, the invention relates to water-dispersible polyurethane resins derived from alkoxylated phenolic resins, and aqueous polyurethane dispersions made from the water-dispersible resins.
BACKGROUND OF THE INVENTION
Water-borne polyurethanes have been commercially available since the 1960's. Their use has grown steadily through the years. Initially, the acceptance of water-borne polyurethanes was spurred by the need to reduce VOCs (volatile organic compounds) in coatings. However, in the last decade the properties of water-borne polyurethanes have started to approach the properties of solvent-based polyurethanes.
In general, there are two types of water-borne polyurethane coatings: aqueous polyurethane dispersions and two-component water-borne polyurethanes. Two-component water-borne polyurethanes are prepared by combining a hydroxyl functional resin component and an isocyanate component. These two components are packed separately, dispersed in water, and mixed in a desired ratio prior to application.
Aqueous polyurethane dispersions are high molecular weight, essentially linear polyurethanes or ureas dispersed in water. They are more convenient to use than two-component water-borne polyurethanes. Water dispersibility of the polyurethane is generally achieved by introducing ionic groups along the polymer backbone. The ionic source is usually carboxylate, sulfonate, or amine groups (e.g., see U.S. Pat. No. 5,354,808). Most commercial polyurethane dispersions use the carboxylate-containing compound, dimethylolpropionic acid (DMPA), as the ionic source because it has a structure well suited for this technology. DMPA is a primary diol that can be easily incorporated into the polyurethane backbone. Its carboxyl group is located on a sterically hindered tertiary carbon that minimizes its reactivity with isocyanate.
Preparation of polyurethane dispersions involves several steps: preparing an isocyanate (NCO)-terminated prepolymer; neutralizing the carboxyl groups; extending the polyurethane chain; and dispersing the resin in water. Chain extension can be performed before or after dispersion. When chain extension is performed before forming the dispersion, the NCO-terminated prepolymer is generally reacted with a chain extender in the presence of a volatile organic solvent such as acetone. The solvent usually is evaporated after the polyurethane is dispersed in water. When the chain extension is performed after the dispersion, a chain extender is added into water in which the polyurethane is dispersed. The latter process usually has a lower production cost.
Due to a lack of crosslinking, polyurethane dispersions usually give coatings that have less resistance to moisture, chemicals, and corrosion.
Phenolic resins have been widely used in coatings, adhesives, and molded articles. Most commonly used phenolic resins are prepared by reacting phenols with aldehydes. The reaction usually produces a phenolic resin with a functionality of greater than 3. Because phenolic hydroxyl groups react very slowly with isocyanates, phenolic resins have found very limited use in polyurethanes.
Aralkylated phenolic resins are also known. They are prepared by reacting phenols with styrene or substituted styrene. Compared with phenolic resins prepared from phenols and aldehydes, aralkylated phenolic resins have a better-controlled functionality. It is feasible to make a di- or tri-functional aralkylated phenolic resin.
Methods for alkoxylating phenolic resins are also known in the art. For example, U.S. Pat. No. 4,167,538 teaches the preparation of alkoxylated aralkylated phenolic resins. The alkoxylated aralkylated phenolic resins can be emulsified and used, for example, for surface-treating fibers.
However, water-dispersible polyurethane resins containing phenolic resin moieties and their dispersions are unknown. We have surprisingly found that incorporating phenolic resins into polyurethane dispersions significantly enhances the resistance of coatings to moisture, acids, chemicals, and corrosion.
SUMMARY OF THE INVENTION
The invention is a water-dispersible polyurethane resin. The resin comprises from about 5% to about 75% by weight of recurring units of an alkoxylated phenolic resin, from about 5% to about 25% by weight of recurring units of a carboxylate-containing diol, and about 15% to about 75% by weight of recurring units of a multi-functional isocyanate. The resin has a number average molecular weight within the range of about 2,500 to about 500,000, an acid number within the range of about 10 to about 100 mg KOH/g, and a free NCO content within the range of about 2.5% to 15% by weight.
The invention includes a neutralized resin, which is a reaction product of the water-dispersible resin with a neutralizing agent, and a chain-extended resin, which is a reaction product of the water-dispersible resin with a chain extender. The invention also includes a chain-extended and neutralized resin that is prepared by neutralizing the chain-extended resin or chain-extending the neutralized resin.
The invention also includes aqueous dispersions of the water-dispersible resin, the neutralized resin, the chain-extended resin, and the chain-extended and neutralized resin.
DETAILED DESCRIPTION OF THE INVENTION
The water-dispersible polyurethane resins of the invention comprise from about 5% to about 75% by weight of recurring units of an alkoxylated phenolic resin. Preferably, the polyurethane resins contain from about 25% to about 50% by weight of recurring units of an alkoxylated phenolic resin.
Alkoxylated phenolic resins used in the invention preferably have an average hydroxyl functionality from about 2 to about 10, more preferably about 2 to about 5, and most preferably about 2 to about 3. Alkoxylated phenolic resins with high hydroxyl functionality can cause gel formation in the preparation of water-dispersible polyurethane resins. The alkoxylated phenolic resins preferably have a number average molecular weight (Mn) from about 500 to about 10,000, more preferably about 500 to about 5,000, and most preferably from about 500 to about 2,000. They also preferably have an average oxyalkylene chain length from about 1 to about 15, more preferably about 1 to about 10, and most preferably about 1 to about 5. The longer the oxyalkylene chain, the more flexible the alkoxylated phenolic resins. However, long oxyalkylene chains may result in final coating products with poorer weathering stability and less chemical resistance.
Alkoxylated phenolic resins used in the invention include propoxylated, ethoxylated, and butoxylated phenolic resins, and the like, and mixtures thereof. They also include alkoxylated phenolic resins that have mixtures of oxyalkylene units.
The alkoxylated phenolic resins can be prepared by alkoxylation of phenolic resins. Phenolic resins used in the alkoxylation include the reaction products of phenols and aldehydes. Methods for preparing phenolic resins from phenols and aldehydes are known. For example, U.S. Pat. No. 4,241,201, the teachings of which are incorporated herein by reference, discloses the preparation of phenolic resins from 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and an aldehyde.
Phenolic resins used in the alkoxylation also include aralkylated phenolic resins. Aralkylated phenolic resins are made, for example, by reacting a phenolic monomer or resin with styrene or a substituted styrene. U.S. Pat. No. 5,889,137, the teachings of which are incorporated herein by reference, discloses the preparation of aralkylated phenolic resins.
There are many ways to alkoxylate phenolic resins. They can be alkoxylated by either alkylene oxides or alkylene carbonates. For example, U.S. Pat. No. 4,167,538, the teachings of which are incorporated herein by reference, discloses the preparation of alkoxylated phenolic resins with alkylene carbonates.
Water-dispersible polyurethane resins of the invention contain from about 5% to about 25% by weight of recur
Goldstein Stephen L.
Rodriguez Carmen L.
Arco Chemical Technology, l.p.
Guo Shao
Niland Patrick D.
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