Polyurethane resins

Details Polyurethane resins Polyurethane resins

1998-12-09

2001-04-24

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...

C427S372200, C427S385500, C427S388100, C428S423100, C428S425800, C524S589000, C524S590000, C524S539000, C524S839000, C524S840000, C528S044000, C528S072000

Reexamination Certificate

active

06221955

ABSTRACT:

This invention relates to polyurethane resins. In particular, it relates to polyurethane dispersions and to surface coatings such as metal primers containing the polyurethane dispersions.
According to the invention, there is provided a polyurethane resin which comprises a reaction product of:
a first component comprising at least one phosphated polyol; and
a second component comprising at least one polyisocyanate.
By a “phosphated polyol” is meant a polyol containing at least one phosphorus-containing reactive group, for example, a phosphonate anion. The polyurethane resin of the invention is thus a phosphated polyurethane resin.
Typically, the phosphated polyol is a polymeric or oligomeric polyol. The polyol may be selected from the group consisting of a polyester polyol, a polyether polyol, a polycarbonate-polyesterpolyol, a polyhydroxylated polybutadiene, and the like, and mixtures thereof. Generally, the molecular mass of the phosphated polyol may be In the range 500-3000, however, the molecular mass of the phosphated polyhydroxiated polybutadiene is generally in the range 20,000-50,000.
More particularly, the phosphated polyol is a hydroxyl-terminated, phosphated polyester polyol which is the reaction product of at least one carboxylic acid, at least one polyol and at least one organophosphorus monomer. By an organophosphorus monomer is meant a monomer containing at least one carbon-phosphorus covalent bond.
The carboxylic acid may be an aromatic, aliphatic, or cycloaliphatic polycarboxylic acid, for example, a C
6
-C
10
polycarboxylic acid having two reactive COOH groups per molecule. The polycarboxylic acid may be selected from the group consisting of 1,4-cyclohexanedicarboxylic acid, hexanedioic acid, isophthalic acid, sebacic acid, azelaic acid, and mixtures thereof.
The particular carboxylic acid(s) used is selected according to the physical properties required in the ultimate phosphated, polyurethane resin, such as chain flexibility (e.g. hexanedioic acid) and hydrolytic resistance and hardness/flexibility balance (e.g. 1,4-cyclohexanedicarboxylic acid).
The polyol may be a polyhydric alcohol. Typically, the polyhydric alcohol is a C
4
-C
8
polyhydric alcohol having at least two reactive primary OH groups per molecule. The polyhydric alcohol may be selected from the group consisting of 2,2-dimethyl-1,3-propane diol, 2-methyl-1,3-propane diol, 1,6-hexanediol, 1,1,1-tris(hydroxymethyl) propane, and mixtures thereof.
The particular polyol(s) used is selected according to the physical properties required in the ultimate phosphated polyurethane resin, such as branching and hence hardness (e.g. 2,2-dimethyl-1,3-propane diol).
The phosphate monomer may be a polycarboxylic acid, for example, 2-phosphonobutane-1,2,4tricarboxylic acid.
The phosphate monomer is selected to provide phosphate reactive groups in the main chain of the ultimate phosphated polyurethane resin to improve adhesion of the polyurethane resin to a metal by the formation of P—O
−
/M
2+
ionic bonds.
The hydroxyl-terminated, phosphated polyester polyol may be the reaction product of 25-45% by mass of the carboxylic acid(s), preferably 37%; 40-53% by mass of the polyol(s), preferably 47%; and 5-20% by mass of the phosphate monomer, preferably 15%; the mass percentages being based on total solids of the reactants. When the carboxylic acid is a mixture of 1,4-cyclohexanedicarboxylic acid and hexanedioic acid, the respective amounts of these carboxylic acids may be 10-20%, preferably 15% and 15-25%, preferably 22%.
The hydroxyl-terminated, phosphated polyester polyol may have an acid number in the range 5-20 KOH/g, for example, 12 mg KOH/g, and a hydroxyl number in the range 130-180 KOH/g.
The phosphated polyurethane resin may be water-dispersible. To provide for water-dispersibility, the reaction mixture used to produce the phosphated polyurethane resin typically includes a stabilising monomer having at least one salt-forming group. Most conveniently, the phosphated polyurethane resin is made anionic, whereby the salt-forming groups are carboxylic acid groups which can subsequently be neutralized to salt form. In that case, the monomer can be a polyol having a carboxylic acid group, A preferred carboxyl group-containing diol is dimethylol propionic acid. The phosphate monomer 2-phosphonobutane-1,2,4tricarboxylic acid also contributes to the stability of the dispersion. In another embodiment of the Invention, said salt forming groups are not neutralised and said phosphated polyurethane resins can be applied as surface coatings in solution by dissolving them in an organic solvent. Suitable organic solvents include propylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate.
The concentration of salt-forming groups is chosen so as to provide stability to an aqueous dispersion of the phosphated polyurethane resin in water. This will vary in accordance with the hydrophilicity of the particular resin. The concentration of the stabilising monomer may be in the range 3-8% by mass, for example, 3.6%.
When the stabilising monomer is dimethylol propionic acid, the reaction mixture for preparing the phosphated polyurethane resin typically includes a solvent such as N-methyl pyrrolidone.
The polyisocyanate may be, for example, toluene diisocyanate. Hexamethylene diisocyanate or isophorone diisocyanate, or any derivatives thereof, are also suitable polyisocyanates. Mixtures of said polyisocyanates may also be used.
The water-dispersible, hydroxyl-terminated, phosphated polyurethane resin may be the reaction product of 60-80% by mass of the phosphated polyol, preferably 75%; 15-25% by mass of the polyisocyanate, preferably 22%; and 3-8% by mass of the stabilising monomer, preferably 3.6%; the mass percentages being based on total solids of the reactants. Typically, the molecular mass of the polyurethane resin is in the range 8000-10,000.
The invention extends to a method of preparing a polyurethane resin which comprises reacting together a first component comprising at least one phosphated polyol and a second component comprising at least one polyisocyanate.
The method may comprise reacting together the first and second components and a third component comprising at least one stabilising monomer having at least one salt-forming group.
The phosphated polyol, the polyisocyanate, and the stabilising monomer, and the relative proportions thereof, etc. may be as described above.
The anionic, water-dispersible, phosphated polyurethane resin may be prepared by reacting the polyisocyanate with the hydroxyl-terminated, phosphated polyester polyol at an elevated temperature until all the polyisocyanate is reacted. The polyisocyanate and the polyol component are suitably reacted in such proportions that the ratio of equivalents of isocyanate groups to equivalents of hydroxyl groups is in the range 0.8:1 to 0.95:1, preferably 0.85:1, and such that the polyurethane resin has terminal hydroxyl groups.
The invention further extends to a composition comprising a resin as described above, and a liquid carrier for the resin. The liquid carrier may be water or an organic solvent. The resin can be applied as a coating in solution form.
Typically, the liquid carrier is water, the composition being in the form of an aqueous dispersion comprising the resin dispersed in the water.
Optionally, the composition contains additives such as surfactants, flow-promoters, plasticizers, anti-foams, etc.
Thus, the invention provides a polyurethane dispersion comprising the water-dispersable, hydroxyl-terminated, phosphated polyurethane resin as described above, dispersed in water.
Before the polyurethane resin is dispersed in water, an amine, preferably a tertiary amine such as triethylamine or triethanolamine, is added to the mixture in an amount sufficient to substantially neutralize the pendant carboxylic acid groups. The amine is added at about 0.8-1 % amine equivalent per equivalent of carboxyl functionality, preferably about 1:1 (in other words, between 80% and 100% neutralisation). Amines that may be used for neu

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