Emulsifiers for high-solids alkyd resin emulsions

Details Emulsifiers for high-solids alkyd resin emulsions Emulsifiers for high-solids alkyd resin emulsions

2000-09-26

2002-10-22

Lovering, Richard D. (Department: 1712)

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...

C427S388400, C516S074000, C516S077000, C526S911000, C528S295500

Reexamination Certificate

active

06469096

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to water-soluble (or water-dispersible polyesters suitable as emulsifiers for alkyd resins, to the high-solids alkyd resin emulsions prepared therewith, and to their use.
2. Description of the Prior Art
In recent years, water-dilutable binders have been developed for paints and other coating compositions in various forms, essentially for environmental reasons. For reasons of preparation, stabilization or their further processing, the aqueous alkyd resin emulsions used for high-quality coating compositions have a low mass fraction of solids of not more than 45%, and they also usually comprise organic solvents and/or volatile neutralizing agents, such as amines and ammonia.
It is true that the amount of organic solvents may be reduced, as described in U.S. Pat. No. 3,269,967 and 3,440,193, using emulsifiers such as alkylphenol ethoxylates and fatty alcohol ethoxylates. These low molar mass substances remain unchanged in the cured film, however, and influence the service properties of the films adversely, such as the rate and extent of drying, hardness, water resistance, and weathering stability.
In the Austrian patents AT-B 325 742, 333 035 and 336 277, polyethylene-glycol-modified emulsifier resins are used to emulsify alkyd resins, as a result of which the aforementioned disadvantages are said to be substantially avoided. However, it is necessary to add a large amount of neutralizing agents and organic cosolvents to these binders in order to obtain stable emulsions. Owing to the high amount of emulsifier resin which is necessary in this case, the films obtained from such binder emulsions likewise exhibit deficiencies in water resistance and weathering stability.
Using both alkoxypolyethylene glycol (polyethylene glycol monoalkyl ethers) and cocondensed units derived from polyhydroxycarboxylic acids to hydrophilicise the alkyd resin does lead, according to U.S. Pat. No. 3,457,206, in conjunction with the neutralization of free carboxyl groups of the resin using alkanolamines and alkali metal hydroxides, to aqueous alkyd resins, but these resins are unsuitable for high-solids coating compositions and exhibit poor weathering stability.
According to WO 94/18260, the use of alkoxypolyethylene glycol makes it possible, even without the neutralization of acidic groups, to obtain water-soluble resins which find application as dispersants or wood preservatives. These resins, however, are readily hydrolysable in aqueous solution and cannot be diluted with water until shortly before use, and they are unsuitable for weather-resistant coatings.
Surprisingly it has now been found that high-solids aqueous emulsions of alkyd resins are obtained if the emulsions are prepared using selected polyesters as emulsifier resins and under certain process conditions. The term “high-solids” here refers to aqueous alkyd resin emulsions having a mass fraction of solids of 55% or more, preferably at least 60%.
SUMMARY OF THE INVENTION
The present invention accordingly provides a water-soluble or water-dispersible polyester B as emulsifier for aqueous emulsions of alkyd resins A, wherein the polyester B is obtained by reacting, under polycondensation conditions, polyhydroxyl components Ba from the class of the sugar alcohols having more than 4 carbon atoms and at least three, preferably at least four, and with particular preference at least five hydroxyl groups per molecule, alkoxypolyethylene glycols Bb having 1 to 4 carbon atoms in the alkyl radical and a number-average molar mass M
n
of from 500 to 2000 g/mol, cycloaliphatic dicarboxylic acids Bc and unsaturated or saturated fatty acids Bd having 10 to 22 carbon atoms.
Monocarboxylic acids Be which are different from the fatty acids Bd may also be used as further components in the mixture of starting materials.
To prepare the polyesters B it is preferred to use the following mass fractions in the mixture of starting materials:
from 10 to 40%, preferably from 15 to 35%, of the polyhydroxyl component Ba,
from 35 to 70%, preferably from 40 to 60%, of the alkoxypolyethylene glycol Bb,
from 10 to 30%, preferably from 15 to 25%, of the cycloaliphatic dicarboxylic acid Bc,
from 15 to 40%, preferably from 20 to 35%, of the fatty acid Bd, and
from 0 to 15%, preferably from 3 to 10%, of another monocarboxylic acid Be which is different from Bd.
The polycondensation is conducted preferably up to an acid number of the polycondensate B of less than 10 mg/g, the solution of B in water having a mass fraction of solids of from 30 to 60% and a dynamic viscosity of from 5000 to 50,000 mPa·s.
The invention further provides aqueous alkyd resin emulsions having a mass fraction of solids of preferably from 60 to 80%, comprising mass fractions, based on the solids of the emulsion, of from 70 to 97%, preferably from 80 to 95%, of a water-insoluble alkyd resin A having an oil content of from 40 to 85%, preferably from 45 to 75%, and an acid number of less than 15 mg/g, preferably less than 10 mg/g, and from 3 to 30%, preferably from 5 to 20%, of the polyester B used as emulsifying resin. The mass fractions of A and B are chosen so that their sum is 100%.
The present invention still further provides a process for preparing the aqueous alkyd resin emulsion of the invention, comprising the synthesis of the emulsifier resin component B by reacting the stated components Ba to Be at a temperature of from 160 to 250° C. under esterification conditions, it being possible also to add the conventional amounts of the known catalysts which accelerate the esterification reaction.
The water formed by the esterification reaction is preferably stripped off by means of an inert gas stream which is passed through the reaction mixture or by means of an organic solvent which forms an azeotrope with water. In the latter case, following separation of the water, the solvent is recycled to the reaction mixture and distilled off after the end of the reaction. After this come the following steps: diluting the resultant emulsifier resin with water to a mass fraction of solids of from about 30 to about 60%, the viscosity of the aqueous solution being preferably between 5000 and 50,000 mPa·s; mixing the water-insoluble alkyd resin A with the aqueous solution of the emulsifier resin at a temperature below 100° C.; and, finally, diluting the resultant mixture with water to a mass fraction of solids of the resultant emulsion of preferably from about 60 to 80% and a dynamic viscosity of preferably from 500 to 3000 mPa·s.
The mixing of alkyd resin A and emulsifier B may take place such that the alkyd resin in liquid or, if desired, melted form is stirred into the aqueous solution of the polyester. It is also possible to stir the aqueous solution of the polyester B into the liquid or melted alkyd resin, in which case its temperature should then preferably not be more than 120° C. One advantageous embodiment is the preparation of the emulsion in a mixing tube which preferably contains static mixers. A further favorable mode of preparation is that of mixing in a rotor/stator dispersing unit. In each case, however, it is necessary to prepare an aqueous solution or dispersion of the polyester B beforehand.
The invention still further provides for the use of the alkyd resin emulsions of the invention as binders in coating compositions, especially in paints and other coating materials.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It was surprising and unforeseeable that by virtue of the specific structure of the water-soluble polyester B used as emulsifying resin a sufficiently high hydrolysis stability of the aqueous solution and a broad compatibility with the alkyd resins to be emulsified are achieved which make it possible to emulsify solvent-free alkyd resins in the form of their melt at a temperature of up to 100° C.
During the mixing of the components, an oil-in-water emulsion is formed, so that the emulsion obtained may be diluted to the desired solids content after just short homogenization. As a result, there is no incidence of the very

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