(Meth)acrylic esters containing urethane groups, their...

Details (Meth)acrylic esters containing urethane groups, their... (Meth)acrylic esters containing urethane groups, their...

2000-03-30

2001-11-20

Short, Patricia A. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Ethylenically unsaturated reactant admixed with either...

C525S031000, C525S438000, C525S440030, C525S445000, C525S528000, C525S532000, C528S075000

Reexamination Certificate

active

06319983

ABSTRACT:

The present invention relates to nondispersing (meth)acrylic esters containing urethane groups, to their preparation and to radiation-curable coating compositions comprising said esters, and a process for preparing these coating compositions.
Radiation-curable binders based on polyesters containing acrylic groups are known. Thermoforming resins of this kind are of great interest owing in particular to their ability to be processed rapidly and with little or even no solvent. The low solvent content of these systems removes the need for laborious, evaporative removal and reprocessing of the solvents. The emissions risks through solvents is substantially reduced. Generally, also important for economic processability, on the part of the binders, besides low raw materials costs and high reactivity, is, in particular, the small amount of very costly reactive diluents that is required in order to establish appropriate processing viscosities.
One possibility to reduce the amount of reactive diluents added, or to do without them entirely, is to use aqueous, radiation-curable binder dispersions.
DE-A-195 25 489, for instance, describes polyester acrylate urethane dispersions based on hydroxyl-containing polyester acrylate prepolymers. These dispersions are prepared by the addition reaction of
A) from 40 to 90% by weight of one or more hydroxyl-containing polyester acrylate prepolymers having an OH content of from 40 to 120 mg KOH/g and
B) from 0.1 to 20% by weight of one or more mono- and/or difunctional, isocyanate-reactive compounds containing cationic groups, anionic groups and/or groups which have a dispersing action as a result of ether units, together with
C) from 10 to 50% by weight of one of more polyisocyanates, followed by reaction with
D) from 0.1 to 10% by weight of one or more diamines and/or polyamines.
The cured films obtained from such dispersions are capable of improvement in terms of their mechanical properties, especially as regards a combination of good surface hardness with film flexibility. Furthermore, it is necessary when using these dispersions as coating compositions to take into account the disadvantages associated with the use of water, so that in many cases the use of low-solvent or solvent-free systems is preferred.
Radiation-curable urethane preparations are described in DE 29 15 846. EP-A-0 126 341 and EP-A-0 127 766 describe processes for preparing radiation-curable (meth)acrylic esters by esterifying OH-containing polyesters with excess acrylic or methacrylic acid and then addition-reacting the remaining acrylic or methacrylic acid with diglycidyl or polyglycidyl ethers so as to form nonvolatile 2-hydroxyacrylate esters.
Finally, building on this art, EP-B-0 279 303 describes radiation-curable acrylates obtainable by reacting simultaneously
A) 1 equivalent of a dihydric to hexahydric alkoxylated C
2
-C
10
-alcohol with
B) from 0.05 to 1 equivalent of a dibasic to tetrabasic C
3
-C
36
-carboxylic acid or anhydride thereof, and
C) from 0.1 to 1.5 equivalents of acrylic acid and/or methacrylic acid
and further reacting the excess carboxyl groups with the equivalent amount of an epoxy compound. Crosslinking of these coating compositions by electron beams or, following the addition of photinitiators, by UV rays gives films which in general conform to the requirements of practice. Nevertheless, in certain cases it can be desirable to improve the hardness, flexibility and/or chemical resistance of the resultant films.
It is an object of the present invention to provide coating compositions based on (meth)acrylic esters which can be used to obtain radiation-cured films of high hardness, good flexibility and sufficient chemical resistance.
We have found that this object is achieved by nondispersing (meth)acrylic esters which contain urethane groups and are obtainable by
a) reacting at least one hydroxyl-containing compound with (meth)acrylic acid in a solvent, to form an ester;
b) removing the solvent and optionally a part of unreacted (meth)acrylic acid;
c) reacting the mixture resulting from stage a) or b) with at least one epoxy-functional compound in an amount corresponding to the acid number of the mixture; and
d) reacting the mixture resulting from stage c) with at least one compound containing isocyanate groups.
The (meth)acrylic esters containing urethane groups, according to the invention, are nondispersing; that is, in the absence of further auxiliaries they do not form stable dispersions and/or emulsions. The (meth)acrylic esters containing urethane groups of the invention do not possess dispersing-active groups to a sufficient extent to form stable dispersions and/or emulsions. Dispersing-active groups are, generally, polar functional groups, such as ionogenic and/or ionic groups, especially carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, phosphoric acid groups, alkali metal salts and ammonium salts thereof, quaternary ammonium groups, and ether groups. Hydroxycarboxylic acids, amino acids, aminosulfonic acids, and also polyetherols or &agr;,&ohgr;-diaminopolyethers having molecular weights from about 500 to 2000, are commonly used to synthesize dispersing-active polyurethanes, which are then processed in the form of dispersions. The (meth)acrylic esters of the invention, containing urethane groups, are preferably prepared without the abovementioned dispersing-active components; in particular, no dispersing-active groups are incorporated into the (meth)acrylic esters containing urethane groups via the reaction with compounds containing isocyanate groups.
Examples of suitable hydroxyl-containing compounds having two or more hydroxyl groups per molecule are dihydric to hexahydric C
2
-C
20
-polyols, preferably C
2
-C
10
-polyols, examples being diols, such as ethylene glycol, 1,2-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-methylpentane-1,5-diol, 2-ethylbutane-1,4-diol, 1,10-decanediol, diethylene glycol, 2,2,4-trimethylpentane-1,5-diol, 2,2-dimethylpropane-1,3-diol, 1,4-dimethylolcyclohexane, 1,6-dimethylolcyclohexane, 1,1′-isopropylenebis(p-phenyleneoxy)di-&bgr;-ethanol, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); triols, such as glycerol, trimethylolethane, trimethylolpropane, trimethylolbutane; tetraols, such as pentaerythritol, ditrimethylolpropane and hexols, such as erythritol, sorbitol and dipentaerythritol.
Preference is given to trihydric to hexahydric C
3
-C
6
-alcohols, such as trimethylolpropane, glycerol, pentaerythritol and sorbitol.
Also suitable are alkoxylation products. For the purposes of the invention, alkoxylation products are the polymerization products obtainable in accordance with conventional techniques by reacting hydroxyl-containing compounds with alkylene oxides or alkylene oxide mixtures, such as ethylene oxide, propylene oxide, tetrahydrofuran and/or butylene oxide. Preference is given to ethoxylation and propoxylation products of the abovementioned polyols. The degree of alkoxylation of these polyetherpolyols is generally between 1 and 30, preferably between 1 and 10.
Preference is given to alkoxylated trimethylolpropane, especially ethoxylated trimethylolpropane.
The abovementioned hydroxyl-containing compounds having two or more hydroxyl groups per molecule have (average) molecular weights in the range from preferably 62 to 4000, in particular from 80 to 800 and, especially, from 90 to 500.
Suitable hydroxyl-containing compounds having one hydroxyl group per molecule are C
5
-C
30
-monoalcohols, preferably C
8
-C
20
-monoalcohols, examples being 2-ethylhexanol, lauryl alcohol, stearyl alcohol, 4-t-butylcyclohexanol, 3,3,5-trimethylcyclohexanol, 2-methyl-3-phenylpropan-1-ol and phenylglycol.
Also suitable are corresponding alkoxylation products, preferably ethoxylation and propoxylation products, of C
2
-C
12
-monoalcohols. The degree of alkoxylation is generally from 1 to 10, preferably from 1 to 5.
The abovementioned hydroxyl-containing compounds having one hydroxyl group per molecule preferably have molecular weights of bet

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