Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-10-12
2003-09-16
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S055000, C528S295500, C528S302000, C528S306000
Reexamination Certificate
active
06620893
ABSTRACT:
This invention relates to a method of producing urethane-modified air-drying polyester dispersions, and to the use thereof in coating media.
BACKGROUND OF THE INVENTION
It is known that polyhydroxy compounds, such as polyester or alkyd resins for example, can be converted into water-thinnable binder vehicles, which comprise an incorporated carboxyl group which is stable to saponification, by reaction with diisocyanates and with a compound which contains at least 2 groups which react with isocyanates and at least one group which is capable of forming anions.
Thus U.S. Pat. No. 3,412,054, for example, describes the use of 2,2-bis(hydroxy-methyl)propionic acid, as a compound which comprises 2 groups which react with isocyanate and a group which is capable of forming anions, for the production of aqueous polyurethane dispersions which contain drying fatty acids. The 2,2-bis(hydroxy-methyl)propioniic acid is incorporated by esterification, via its hydroxyl groups, into an alkyd resin and the latter is then reacted with diisocyanates. As stated in EP-A-0 017 199, this method results in non-uniform products which dry relatively slowly and which do not possess superior lacquer technology properties.
EP-A-0 017 199 describes oil-modified polyurethane dispersions which contain carboxyl groups and which exhibit improved properties. These dispersions are produced, for example, from the transesterification product formed from a natural oil and a polyol, e.g. soya oil and pentaerythritol, and a prepolymer which contains isocyanate groups, such as the reaction product of toluene diisocyanate and 2,2-bis(hydroxymethyl)propionic acid. The reaction is conducted in dilute solution in acetone. The acetone then has to be separated by distillation and replaced by organic so-solvents such as butyl glycol, for example, in order to obtain satisfactory stability on storage and good lacquer technology properties. The removal by distillation and repeated work-up of the acetone constitutes an undesirable industrial processing cost.
Conducting the urethane-forming reaction in the melt (melt dispersion method), as is described in DE-A-3 901 190, EP-A-0 427 028 or EP-A-0 498 156 for example, is an alternative procedure. The distillation step can in fact be circumvented in this manner. However, as is stated many times in the aforementioned documents, a very highly viscous molten resin is obtained. This results, particularly towards the end of the urethane-forming reaction and during dispersion, to massive mixing problems due to a lack of stirring power. The consequences are inhomogeneities in the molten resin, which result in variations in product quality. Moreover, caked deposits can be formed on colder parts of the reactor (e.g. in the condenser region), which are associated with a loss of yield, additional cleaning costs and safety hazards due to the poor dissipation of heat during the strongly exothermic urethane-forming reaction.
The underlying object of the present invention was therefore to eliminate the disadvantages of the prior art and to develop a simple, economic method of producing aqueous urethane-modified air-drying polyester dispersions and which are suitable for the production of high-quality covering lacquers. The object was firstly to avoid the use of costly, time-consuming processes, such as distillation steps for example, and was secondly to prevent the viscosity of the molten resin becoming too high during or after the completion of the urethane formation stage.
It has been found that aqueous urethane-modified air-drying polyester resins and which dry at room temperature to form lacquer films with a good level of lacquer technology properties can be produced, with a low melt viscosity during and after completion of the urethane-forming reaction, by the use of 3-hydroxy-2,2-dimethylpropionic acid (hydroxypivalic acid) as an agent which imparts hydrophilic properties.
Since, as a monohydroxy-functional carboxylic acid, hydroxypivalic acid acts as a chain terminator during the urethane-forming reaction, it must be considered surprising that good lacquer properties can be achieved with the binder vehicles of relatively low molecular weight which are obtained in this manner.
DE-A-19 534 361 describes aqueous binder vehicles which dry by oxidation and which contain a polyurethane-alkyd resin component based on special fatty acid mixtures. The use of hydroxypivalic acid as an agent which imparts hydrophilic properties is in fact mentioned there. However, DE-A-19 534 361 does not disclose any teaching with regard to how the viscosity problem described above could be solved by the use of hydroxypivalic acid. Rather, the description and the examples disclose the production of polyurethane-alkyd resin components which are rendered hydrophilic by 2,2-dimethylolalkanoic acids and which are produced using auxiliary organic solvents such as methyl ethyl ketone for example. These auxiliary solvents are subsequently removed by distillation.
SUMMARY OF THE INVENTION
The present invention therefore relates to a method of producing urethane-modified, aqueous polyester resins which dry by oxidation and which have an acid number of 15-50 mg KOH/g, characterised in that (all data in percentages are given in % by weight)
a) 15-40% of a prepolymer which is produced in situ and which consists of
a1) a diisocyanate component consisting of at least one organic diisocyanate of molecular weight range 168-294, and
a2) hydroxypivalic acid.
wherein the ratio of a1:a2 is selected corresponding to an equivalent ratio of NCO:OH=1:1 to 5:1,
is reacted in 80-95% organic solution with
b) 60-90% of a polyester resin with an OH number of 30-100 mg KOH/g and an acid number≦5 mg KOH/g, produced by the reaction of
b1) 20-70% of a monocarboxylic acid component, at least 60% of which consists of at least one unsaturated fatty acid,
b2) 10-40% of a dicarboxylic acid, of a dicarboxylic anhydride or of a mixture of compounds such as these,
b3) 0-15% of one or more diols and
b4) 5-35% of one or more polyols with an OH-functionality>2, wherein b1, b2, b3 and b4 add up to 100%, and
c) 0-15% of one or more polyols with an OH-functionality≧2,
wherein a, b and c add up to 100%, and are subsequently dispersed in water, and wherein the carboxyl groups which are introduced into the reaction product are converted into carboxylate groups by 0.5-1.2 equivalents (with respect to the carboxyl groups present) of a base during the reaction of (a+b+c) or directly before, during or after dispersion.
DETAILED DESCRIPTION OF THE INVENTION
The present invention also relates to the use of the aqueous binder vehicles which are produced in this manner in or as lacquers or coating materials which dry by oxidation crosslinking at room temperature.
Starting component al is a diisocyanate component consisting of at least one organic diisocyanate of molecular weight range 140 to 294. Examples of suitable diisocyanates include hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), bis-(4-isocyanato-cyclohexyl)-methane (H
12
MDI), 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane (IMCI), toluene 2,4-diisocyanate, toluene 2,6-diusocyanate, 2,2,4-trimethyl-hexamethylene-1,6-diisocyanate, naphthalene diisocyanate and other isocyanates such as those described, for example, in Houben-Weyl, Methoden der organischen Chemie, Volume 14/2. 4th Edition, G. Thieme Verlag, Stuttgart 1963, pages 61-70.
Component al is converted to an NCO-functional prepolymer by using hydroxypivalic acid (component a2) in an equivalent ratio of NCO:OH ranging from 1:1 to 5:1, preferably from 1.8:1 to 3:1, most preferably from 2:1 to 2.5:1. The reaction can be carried out in the absence of solvent or in part of or in the complete amount of the organic solvent which is present during the urethane-forming reaction and which subsequently remains as a co-solvent in the aqueous binder vehicle dispersion. It is also possible to employ auxiliary solvents a this point: these auxiliary solvents have to be removed again, e.g. by d
Blum Harald
Melchiors Martin
Noble Karl-Ludwig
Bayer Aktiengesellschaft
Dawson Robert
Gil Joseph C.
Peng Kuo-Liang
Roy Thomas W.
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