Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2000-04-26
2001-06-12
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S059000, C525S504000
Reexamination Certificate
active
06245877
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to moisture-cure urethane compositions that have ultra-high solids contents. In particular, the invention relates to moisture-cure urethane compositions derived from liquid alkoxylated phenolic resins.
BACKGROUND OF THE INVENTION
Urethane coatings are defined as coatings that contain urethane (—NHCOO—) or urea (—NHCONH—) groups. They are reaction products of isocyanates and hydroxyl functional resins. Depending on the hydroxyl components, urethane coatings can be divided into acrylic-urethanes, polyester-urethanes, polyether-urethanes, and many others. Properties and applications of urethane coatings depend largely on the hydroxyl components. For example, polyether-urethane coatings have excellent flexibility but poor weathering stability and chemical resistance, while acrylic-urethane coatings have excellent weathering stability and chemical resistance but low flexibility.
Urethane coating formulations can also be categorized into two-component (two-pack) and one-component (one-pack) systems. Two-component urethanes consist of a hydroxyl component and an isocyanate (NCO) component. These two components are packed separately and mixed in a desired ratio prior to application. One-component urethanes include urethane lacquers (solutions of thermoplastic urethanes), uralkyds, blocked urethanes, and moisture-cure urethanes. An advantage of one-component urethanes is their convenience of application. Moisture-cure urethane formulations contain in a single package an NCO-terminated resin, a solvent, and, optionally, a catalyst. When the coating is applied on a surface, the solvent evaporates, and the NCO groups react with moisture in the air and form urea linkages to crosslink the resin. Since they are cured by moisture in the air, their utility is limited to thin films. Another disadvantage of prior art moisture-cure urethane coatings is that the NCO-terminated resins have higher molecular weights, therefore higher viscosities than those of two-component urethane coating formulations. This limits the growth of moisture-cure urethane coatings because of the higher solvent demand and the resulting higher VOC (volatile organic compound) contents. Moisture-cure urethane coatings are usually polyether-urethanes. Because of the poor weathering stability and chemical resistance of polyether polyol systems, these moisture-cure urethane coatings are used primarily as primers and base-coats for surfaces of metal, wood, and concrete structures such as water tanks, pipes, bridges, and decks.
Phenolic resins, though widely used in other coatings, have found limited use in urethanes because phenolic hydroxyl groups are not sufficiently reactive with isocyanates. Modifying urethane coatings with phenolic resins has been attempted because they can potentially improve chemical resistance of urethanes, particularly moisture-cure urethanes. For example, U.S. Pat. No. 4,539,345 discloses moisture-cure urethanes based on blends of an NCO-terminated polymer, a terpene-phenolic resin, and a silane compound.
Alkoxylating phenolic resins changes phenolic hydroxyls into aliphatic hydroxyls and makes it possible to use phenolic resins in urethanes. For example, U.S. Pat. No. 4,167,538 teaches the preparation of a resinous (i.e., solid) alkoxylated phenolic resin. The resin has a softening point (for polymers, the softening point is usually about 50° C. below the melting point) within the range of 30° to 150° C., preferably from 40° to 80° C. However, the alkoxylated phenolic resin is not suitable for use in moisture-cure urethane coatings because it is too rigid and has a high solution viscosity.
Other alkoxylation techniques are known. For example, U.S. Pat. No. 5,679,871 teaches alkoxylating phenolic resins with alkylene carbonates rather than alkylene oxides. The advantage of using cyclic carbonates such as ethylene glycol carbonate or propylene glycol carbonate is that the alkoxylated phenolic resins do not contain long oxyalkylene chains; unlike alkylene oxides, alkylene carbonates do not polymerize during the alkoxylation. Alkoxylated phenolic resins with short oxyalkylene chains have high glass-transition temperatures or softening points.
Formulating urethane coatings from alkoxylated phenolic resins is also known. For example, WO 97/19972 teaches how to prepare a two-component urethane coating from a propoxylated phenolic resin. However, the coating has a low solids and high VOC contents.
It is unknown to formulate moisture-cure urethanes from alkoxylated phenolic resins, especially from liquid alkoxylated phenolic resins that have long oxyalkylene chains. We have surprisingly found that moisture-cure urethane coatings prepared from liquid alkoxylated phenolic resins have extremely low solvent demand and, therefore, very low VOC contents. In addition, the coatings have excellent chemical resistance compared to the conventional moisture-cure urethane coatings.
SUMMARY OF THE INVENTION
The invention is a moisture-cure urethane composition. The urethane composition comprises an isocyanate-terminated polymer. The polymer is the reaction product of from about 25 to about 95 wt % of a liquid alkoxylated phenolic resin and from about 5 to about 75 wt % of a multi-functional isocyanate. The liquid alkoxylated phenolic resin has an average oxyalkylene chain length from about 3 to about 25. The urethane composition has a solids content greater than about 70 wt %.
DETAILED DESCRIPTION OF THE INVENTION
Moisture-cure urethanes of the invention comprise an isocyanate (NCO) terminated polymer that contains from about 25 to about 95 wt % of a liquid alkoxylated phenolic resin. By “liquid,” we mean that the alkoxylated phenolic resin is pourable at room temperature (25° C.). It preferably has a viscosity at 25° C. less than 20,000 cps, more preferably less than 10,000 cps.
The alkoxylated phenolic resin used in making the NCO-terminated polymer has an average oxyalkylene chain length from about 3 to about 25, preferably about 5 to about 15 oxyalkylene units. The longer the oxyalkylene chain, the more flexible the alkoxylated phenolic resins. However, long oxyalkylene chains (i.e., more than about 25 oxyalkylene units) may result in final coating products with poorer weathering stability and less chemical resistance.
The alkoxylated phenolic resin preferably has an average hydroxyl functionality from about 2 to about 10, and more preferably from about 2 to about 5. Alkoxylated phenolic resins with high hydroxyl functionality can cause gel formation in the preparation of the NCO-terminated polymers.
The alkoxylated phenolic resins preferably have a number average molecular weight (Mn) from about 500 to about 10,000, more preferably from about 500 to about 5,000, and most preferably from about 1,000 to about 4,000.
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.
Alkoxylated phenolic resins can be prepared by alkoxylation of phenolic resins. Phenolic resins used in the alkoxylation include the reaction products of phenols with aldehydes and/or ketones. Methods for preparing phenolic resins from phenols with aldehydes and/or ketones 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. Aralkylated phenolic resins are more preferred because they give the alkoxylated phenolic resins low viscosity.
Isocyanate-terminated polymers for use in making the urethanes of the inventi
Goldstein Stephen L.
Rodriguez Carmen L.
Arco Chemical Technology L.P.
Gorr Rachel
Guo Shao
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