Aqueous binder mixture

Details Aqueous binder mixture Aqueous binder mixture

2001-10-11

2003-09-09

Yoon, Tae H. (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...

C524S524000, C524S839000, C524S840000, C524S845000, C525S123000

Reexamination Certificate

active

06617393

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to aqueous binder mixtures, to a process for preparing them and to their use for formulating baking varnishes, especially water-dilutable primer-surfacers for automobile finishing.
BACKGROUND OF THE INVENTION
There is a general desire to maximize the mass fraction of binders (resins) and pigments in paints in order to shorten the drying times and to minimize the amount of energy required for drying. This is particularly significant with waterborne paints, owing to the high vaporization enthalpy of water. At the same time, however, there should not be a disproportionate increase in the viscosity of the paint in the application form, in order not to impair application and impede the flow of the paint on the substrate.
Aqueous primer-surfacer materials whose binders comprise water-dilutable polyurethane resins and/or polyester resins are customary. Primer-surfacer materials of this kind are described, for example, in EP-A 0 517 707, where the mass fraction of water is approximately 45%.
SUMMARY OF THE INVENTION
Surprisingly it has now been found that by means of binder combinations comprising water-miscible hydroxy urethanes as one constituent it is possible to raise significantly both the mass fraction of solids of the respective binder combinations in the supply form and also the mass fraction of solids in the formulated paint.
The invention therefore provides aqueous binder mixtures comprising a water-dilutable resin and a water-miscible hydroxy urethane, the water-dilutable resin being selected from polyesters which have been anionically modified by incorporation of bishydroxyalkylcarboxylic acids or polycarboxylic acids whose carboxyl groups differ in their reactivity with respect to polycondensation; polyesters obtainable by cocondensing polyfunctional alcohols and acids with a functionality of more than 2, the acids being used in excess; and condensation products AB of hydroxyl group-containing resins B, which on their own are not water-soluble, and water-soluble or water-dispersible resins A containing acid groups, the resins A and B being selected independently of one another from the groups of the polyester resins mentioned supra, alkyd resins, polyurethane resins, polyacrylate resins and epoxy resins.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Water-miscible in the context of the present invention means that the substance in question as a binary mixture with water forms single-phase mixtures over the entire concentration range.
Water-dilutable binders are the known synthetic resins, especially polyester resins, alkyd resins, polyurethane resins, polyacrylate resins, ketone resins and aldehyde resins, polyamide resins and epoxy resins which have been rendered hydrophilic by addition of emulsifiers or by chemical modification, i.e., are dispersible in water or at least partly soluble in water and form stable single-phase or multiphase mixtures with water.
As emulsifiers it is possible to use the known anionic, cationic, amphoteric and nonionic substances whose lipophilic radicals are selected from linear and branched (saturated or unsaturated) alkyl groups, aryl groups and alkylaryl groups. Preferred anionic hydrophilic groups include carboxylate, sulfonate, sulfate, phosphate and phosphonate groups; preferred cationic hydrophilic groups include quaternary ammonium groups or amino groups which are able to form ammonium compounds on addition of acid; preferred amphoteric structural elements include ammonium groups and carboxylate groups present in the same molecule; and preferred nonionic hydrophilic groups include polyoxyethylene, polyoxypropylene, polyol, especially sugar alcohol, and poly- or oligo-saccharide groups.
The synthetic resins become hydrophilic by chemical modification by virtue of the fact that substances containing the abovementioned hydrophilic groups are incorporated into the synthetic resins chemically by means of appropriate reaction (during the synthesis) or are grafted onto the finished resins. The type and amount of the hydrophilicizing substance must be chosen according to the nature of the resin. Preference is given to those synthetic resins whose hydrophilicity has been generated by incorporating anionic groups or groups which are convertible into anionic groups upon addition of bases. One preferred example of anionic modification is the incorporation of bis(hydroxyalkyl) carboxylic acids such as dimethylolpropionic acid or of polycarboxylic acids whose carboxyl groups differ in reactivity with respect to polycondensation, such as citric acid or trimellitic acid. Where monomers with acid functionality are used in the synthesis of the resins, it is likewise possible to build branched or dendritic molecule structures by using reactants having a funtionality of more than 2, in which case there should be acid groups at the ends of the branches in each case. In the case of polyesters this is particularly easy to do, for example, by cocondensing polyfunctional alcohols or acids (i.e., those with a functionality of more than 2), where acids should be used in excess. In this way it is possible to synthesize those resins having a sufficient number of acid groups for hydrophilicization. Preferentially, these anionically modified hydrophilic resins contain no cationic groups or groups which form cations in water upon addition of acids.
Particularly suitable binders are condensation products AB of hydroxyl group-containing resins B which on their own are not water-soluble, and water-soluble or water-dispersible resins A containing acid groups, the resins A and B being selected independently from one another from the stated groups of polyester resins, alkyd resins, polyurethane resins, polyacrylate resins and epoxy resins.
Resins which are referred to as not being water-soluble are those where, following mixing and attainment of an equilibrium with 10 times the mass of water at room temperature, the aqueous phase contains a mass fraction of less than 5% of the resin in question. Otherwise, the resins are referred to as (partially) water-soluble or as water-dispersible.
The resin A, containing acid groups, preferably has an acid number of from 100 to 230 mg/g, in particular from 70 to 160 mg/g, and the resin B, containing hydroxyl groups, preferably has a hydroxyl number of from 50 to 500 mg/g, in particular from 60 to 350 mg/g.
The acid number is defined in accordance with DIN 53 402 as the ratio of the mass M
KOH
of potassium hydroxide required to neutralize a sample under analysis to the mass m
B
of this sample (mass of the solids in the sample in the case of solutions or dispersions); its customary unit is “mg/g”. The hydroxyl number is defined in accordance with DIN 53 240 as the ratio of that mass m
KOH
of potassium hydroxide which has exactly the same number of hydroxyl groups as a sample under analysis to the mass m
B
of this sample (mass of the solids in the sample in the case of solutions or dispersions); its customary unit is “mg/g”.
The formerly so-called “limiting viscosity number” called “Staudinger index” J
g
in accordance with DIN 1342, part 2.4, is the limiting value of the Staudinger function J
v
at decreasing concentration and shear stress, J
v
being the relative change in viscosity based on the mass concentration &bgr;
B
=m
B
/V of the dissolved substance B (with the mass m
B
of the substance in the volume V of the solution); i.e., J
v
=(&eegr;
r
−1)/&bgr;
B
. Here, &eegr;
r
−1 is the relative change in viscosity, in accordance with the equation &eegr;
r
−1=(&eegr;−&eegr;
s
)/&eegr;
s
. The relative viscosity &eegr;
r
is the ratio of the viscosity &eegr; of the solution under analysis to the viscosity &eegr;
s
of the pure solvent. (The physical meaning of the Staudinger index is that of a specific hydrodynamic volume of the solvated polymer coil at infinite dilution and in the state of rest.) The unit commonly used for J is “cm
3
/g”; formerly often “dl/g”.
The condensation products AB preferred for the invention preferably have an a

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