CA2040521C

CA2040521C - Aqueous solutions or dispersions of oligoruethanes containing (meth)acryloyl groups, a process for their production and coated substrates prepared therefrom

Info

Publication number: CA2040521C
Application number: CA002040521A
Authority: CA
Inventors: Jurgen Meixner; Wolfgang Kremer; Manfred Muller; Holger Casselmann; Klaus Hoehne
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1990-04-18
Filing date: 1991-04-15
Publication date: 2003-04-08
Anticipated expiration: 2011-04-15
Also published as: EP0453838B1; DE59105757D1; EP0453838A3; EP0453838A2; ATE124063T1; CA2040521A1; JP2971171B2; DE4012339A1; JPH04227623A; ES2075246T3

Abstract

The present invention relates to aqueous solutions or dispersions of oligourethanes having a pH of 6.0 to 8.5 wherein the dissolved or dispersed oligourethanes contain carboxyl groups at least partially neutralized with ammonia and have i) a double bond content in the form of (meth)acryloyl groups (expressed as C=C, molecular weight 24) of 3 to 15% by weight and ii) a content of carboxyl groups, including the carboxyl groups neutralized with ammonia, which corresponds to an acid value of 20 to 100.

The present invention also relates to a process for the preparation of these aqueous solutions or dispersions of oligourethanes and to their use for the preparation of coated substrates.

Description

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Mo-35a2 LeA 27,624 AQUEOUS SOLUTIONS OR DISPERSIONS OF OLIGOURETHANES
CONTAINING (METH)ACRYl.OYL GROUPS, A PROCESS FOR
THEIR PRODUCTION AND COATED SUBSTRATES PREPARED THEREFROM
BACKGROUND OF THE INDENTION
Field of the Invention This invention relates to aqueous solutions or dispersions of certain ionically modi~Fied aligourethanes containing (meth)acryloyl groups, to a process far their production and to coated substrates prepared therefrom.
~.o Description of the Prior Art Polyurethanes containing (meth)acryloyl groups {so-called urethane (meth)acrylates) have long been known and are eminently suitable as binders, for example for paints {cf.
far example DE-OS 2,737,406). The relatively high viscosity of these products almost always necessitates the use of organic solvents.
Water-dilutable urethane (meth)acrylates are also known (cf. for example, DE-OS 2,936,039). The hydraphilicity of these known systems is based on the presence of ionic 2o centers, particularly sulfonate groups, which contain as counterions alkali cations or ammonium ions (from tertiary amines) which at least partly rema in in the coatings ultimately obtained from the systems and considerably impair their water resistance.
Accordingly, an object of the present invention is to provide new aqueous solutions or dispersions of urethane (meth)acrylates which are stable in storage without the addition of dispersants or external emulsifiers, without alkali can ons and without ammonium ions from tertiary amines, and which may be cured to form coatings combining resistance to water and chemicals with favorable mechanical properties.

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This object may be achieved in accordance with the solutions or dispersions of the present invention which are described in detail hereinafter and by the process for their production. The principal feature of the invention is that s carboxyl groups at least partly neutralized with ammonia are incorporated into the urethane (meth)aerylates using 2,2-bis-(hydroxymethyl)-alkane carboxylic acids.
DE-QS 3,641,494 relates to a process in which polyurethane elastomers dispersible in water are modified with to anions. Nevertheless, it can be said that the solution provided by the present invention to the stated object was not obvious from this prior publication. The solutions or dispersions of oligourethanes according to the present invention, which are described in detail hereinafter, differ 15 from the solutions or dispersions of polyurethanes according to the reference in several areas:
- The polyurethanes according to the prior publication are polyurethane elastomers wherein the molecules are based on structural units attributable to the incorporation of za relatively high molecular weight compounds containing at least two isocyanate-reactive groups, particularly hydroxyl groups. The oligourethanes according to 'the invention contain no such structural units.
The polyurethanes according to the prior publication 25 contain terminal or lateral polyether chains containing ethylene oxide units as further hydrophilic centers which are not present in the oligourethanes according to the invention.
- In addition to the ammonium carboxylate groups, the sa oligourethanes according to the present invention also have a high concentration of (me~th)acryloyl groups, which is net the case with the polyurethanes according to the prior publication. It could not have been expected that it would be possible to produce storable aqueous solutions s5 or dispersions of oligourethanes containing both high Mo-3552 ~'~ ' y :~' tr? ,"' tj .~'~.
concentrations of (meth)acryloyl groups and ammonia in the form of ammonium groups because it is known that ammonia, in the same way as primary or secondary amines, reacts spontaneously with activated double bonds by Michael addition. Accordingly, it could not have expected that the principle of ionic modification according to DE-OS

3,641,494 would be applicable to oligourethanes containing (meth)acryloyl groups of the type present in the solutions or dispersions according to the present invention.
to ,SUMMARY OF ThE 1NVENT10N
The present invention relates to aqueous solutions or dispersions of oligourethanes having a pH of 6.0 to 8.5 wherein the dissolved or dispersed oligourethanes contain carboxyl groups at least partially neutralized with ammonia and have l) a double bond content in the form of (meth)acryloyl groups (expressed as C=C, molecular weight 24) of 3 to 15% by i~eight and ii) a content of carboxyl groups, including the carboxyl groups neutralized with ammonia, which corresponds to an 2o acid value of 20 to 100.
The present invention also relates to a process for the preparation of aqueous solutions or dispersions of oligourethanes by reacting a) 20 to 80% by weight of an alcohol component containing at 2s least ane monohydric alcohol having one or more (meth)acryloyl groups and a molecular weight of 116 to 1,000, b) 4.5 to 20% by weight of at least one 2,2-bis-(hydroxy-methyl)-alkane carboxylic acid having at least 5 carbon ao atoms and c) 15 to 75% by weight of at least one polyisocyanate component containing at least one organic polyisocyanate having a molecular weight of 168 to 1,000, by initially introducing components a) and b), then reacting ~5 these components with component c) at a temperature of 50 to Mo-3552 l'.a ' ~ -' r J ;~',~ l ...'.'.
,.. ,, 100°C until the reaction mixture contains no more free isocyanate groups and subsequently dissolving or dispersing the reaction mixture in water, the carboxyl groups being at least partly neutralized by addition of ammonia during the dissolving or dispersing step so that the resulting solution or dispersion has a pH value of 6.0 to $.5, wherein A) the percentages of a), b) and c) add up to 100, based on the weight of a), b) and c), B) the amounts of a), b) and c) correspond to an NCO: OH
1o equivalent ratio of 0.5:1 to 1:1 and C) the amounts of a), b) and c) are otherwise selected within the stated limits so that the resulting oligourethanes have i) a double bond content in the form of (meth)acryloyl groups (expressed as C=C, molecular weight 24) of 3 to 15% by weight and ii) a content of carboxyl groups, including the carboxyl groups neutralized with ammonia, which corresponds to an acid value for the oligourethanes of ZO to 100.
2o Finally, the present invention is directed to coated substrates prepared from these solutions or dispersions of oligourethanes.
DETAILED DESCRIPTION OF THE INVENTION
Component a) contains at least one monohydric alcohol containing one or mare (meth)aeryloyl groups. Examples include esters which contain on average one free hydroxyl group and which are prepared from acrylic acid or methacrylic acid and polyhydric alcohols. The esters have a molecular weight of 116 to 1,000, preferably 116 to 750. Examples of such ethyl-Oo enically unsaturated esters are hydroxyethyl (meth)acrylate, 2-and 3-hydroxypropyl (meth)acrylate, 2-, 3- and 4-hydroxybutyl (meth)acrylate and reaction products of trimethylol propane or alkoxylated trimethylol propane with (meth)acrylic acid, such as the reaction product of 2 moles of acrylic acid with 1 mole Mo-X552 i 4~ fa , J .f ~ c;,~
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of an ethoxylated trimethylol propane (OH value 550, degree of ethoxylation approx. 4).
Component b) contains at least one 2,2-bis-(hydroxy methyl)-alkane carboxylic acid having at least 5 carbon atoms, s preferably 2,2-bis-(hydroxymethyl)-propionic acid.
Component c) contains at least one organic po7yiso-cyanate. Suitable polyisocyanates include any organic polyisocyanate known from polyurethane chemistry having aliphaticaliy, cycloaliphatically and/or aromatically bound to isocyanate groups and a molecular weight of 168 to 1,000, preferably 168 to 300. Examples of suitable polyisocyanates include 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyi cyclohexane (IPUI); 4,4'-diisocyanatodicyclahexyl methane;
4,4'-diisocyanatodiphenyl methane and mixtures thereof with 15 2,4'-diisocyanatodiphenyl methane and, optionally, the higher homologs of these diisocyanates; and 2,4-diisocyanatotoluene and mixtures thereof with 2,6-diisocyanatotoluene.
Biuret-, isocyanurate- or urethane-modified polyisocyanates based on these monomeric polyisocyanates are 2o also suitable. These derivatives generally have a molecular weight less than 1,000. The preparation of these derivatives is described, for example, in U.S. Patents 3,124,604, 3,183,112, 3,919,218 and 4,324,879.
The oligourethanes present in the solutions or a5 dispersions according to the invention have the above-mentioned content of olefinic double bonds. This content is preferably between 4 and 10% by weight. The oligourethanes have an ac id value of 20 to 100, preferably 25 to 80 mg K0H/g; the acid value encompasses both the free carboxyl groups and also the 30 carboxyl groups neutralized with ammonia. At least some, preferably 45 to 100% and more preferably 60 to 100%, of the carboxyl groups are neutralized with ammonia, i.e., are present as carboxylate groups. At the same time, it is impor'tan't during neutralization of the carboxyl groups to ensure that the 35 pH value of the aqueous solutions or dispersions is between 6.0 Mo-3552 F;a °~ ~..3 ~~ '°~ t ~ .~.
and 8.5, preferably between 6.5 and 8Ø The solutions or dispersions according to the invention generally have a solids content of 30 to 55% by weight, preferably 35 to 50% by weight.
The oligourethanes according to the invention are reaction products of comparatively low molecular weight starting materials in the presence of large quantities of chain-terminating synthesis components. Accordingly, there is every justification to refer to these reaction products not as °'polyurethanes," but instead as "oiigourethanes°' which have an average molecular weight calculated from the stoichiometry of to the starting materials of 700 to 5,000, preferably 700 to 2,000.
In the practical application of the process according t o the invention, component a) is preferably used in a quantity of 25 to 75% by weight, component b) is preferably used in a quantity of 5 to 19% by weight and component c) is preferably used in a quantity of 20 to 70% by weight, the percentages of a), b) and c) adding up to 100, based on 'the weight of a), b) and c). In addition, it is important in accordance with the present invention to ensure that the starting components are 2o used within the stated limits so that an NCO: OH equivalent ratio of 0.5:1 to 1:1, preferably 0.7:1 to 1:1 is maintained.
The polyisocyanate c) is generally used in slightly less than the stoichiometric quantity so that the end of the reaction is reached when no more isocyanate groups can be detected in the reaction mixture. Finally, the reactants and their amounts are suitable selected within the stated limits to ensure that 'the oligourethanes have the required double bond content and acid number.
The reaction according to the invention is preferably carried out in 'the presence of inert solvemts at solids contents of 60 to 95% by weight. Suitable solvents include dimethyl diglycol, N-methyl pyrrolidone, N-methyl caprolactane, ethyl glycol acetate, n-butyl acetate, acetone and mixtures of these solvents.
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To carry out the reaction, the alcohol component a) containing the (meth)acryloyi groups, the 2,2-bis-(hydroxy-methyl)-alkane carboxylic acid b) and the solvent preferably used are homogenized, the polyisocyanate c) is added over a s period of 1 minute to 2 hours at 50 to 100°C and the reaction mixture is then stirred at 60 to i00°C utilizing the exothermic reaction until a resin having the characteristics mentioned is obtained. The reaction is preferably carried out in the presence of oxygen, for example, by passing air through the ~o reaction mixture.
The reaction may be accelerated by the addition of suitable catalysts (such as dibutyl tin dioxide, dibutyl tin dilaurate and triethylamine) in quantities of 0.01 to 2.5% by weight, based on the weight of the reaction mixture as a whole.
i5 The reaction product may be protected against premature and unwanted polymerization by the addition of suitable inhibitors and antioxidants each in quantities of 0.001 t o 0.3°'° by weight, based on the mixture as a whole.
Where the residual organic solvent content has to zo meet particularly stringent requirements, the solvent may be partly removed by distillation before, during and/or after neutralization or dissolution or dispersion of the resin in water. Removal of solvents from the solution or dispersion by distllation is only appropriate far solvents which form an z5 azeotrope with water.
After the urethanization reaction, small quantities of other organic solvents (such as ethanol, n-propanol, isopropanol, n-butanol, tert.-butanol, pentanol, hexanol, octanol, butyl glycol, ethyl glycol, butyl diglycol, ethyl ao diglycol, methyl diglycol and methoxypropanol) may be added to obtain certain properties.
The reaction products, which preferably accumulate in the form of 60 to 95% by weight solutions in organic solvents, are dissolved or dispersed in 'the form of these solutions in a 05 mixture of water and ammonia, 'the ammonia preferably being used Mo-3552 _ 8..
in such a quantity that 45 to 100%, preferably 60 to 100% of the carboxyl groups are neutralized. At the same time, it is important to ensure that the pH value of the solution or dispersion formed is between 5.0 and 8.5, preferably between 6.5 and 8Ø The quantity of water used is gauged so that a solids content within the limits mentioned above is abstained.
The aqueous solutions or dispersions obtained in accordance with the present invention are valuable aqueous binders for coating compositions. They may be used as such or in combination with auxiliaries and additives known from paint to technology (such as fillers, pigments, solvents, flow control agents and the like) for the production of coatings on any substrate.
Suitable substrates include paper, paperboard, leather, wood, plastics, nonwovens, textiles, ceramic materials, mineral materials, glass, metal, artificial leather, photographic materials, for example, paper coated with a photographic layer.
The coating compositions may be applied in known manner by spray coating, knife coating, roll coating, spread 2o coating, dip coating or casting. After evaporation of the water and any inert solvents present, the coatings may be crosslinked either by high-energy radiation (such as UV light, electron beams or gamma rays) or by curing with metal salts of siccative acids and (hydro)peroxides or with metal salts of 25 siccative acids or with (hydro)peroxides alone at temperatures of 80 to 250°C. At temperatures above 150°C, it is generally not necessary to add (hydro)peroxides and/or metal salts.
When the coatings are crosslinked by UV 'irradiation, photoinitiators have to be added to 'the coating compositions.
so Suitable photoinitiators include known compounds such as those which are described, for example, in the book by J. Korsar, Light-Sensitive Systems, J. Wiley & Sons, New York-London-Sydney, 1965.
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Other suitable photoinitiators include benzoin ethers such as benzoin isopropyl ether, benzil ketals such as benzil dimethyl ketal, and hydroxyalkyl phenones such as 2-hydroxy-2-methyl-1-phenylpropan-1-one. The photoinitiators are used in quantities of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, depending upon the particular application for the compounds according to the invention. The photoinitiators may be used either individually or, by virtue of favorable syner-gistic effects, in combination with one another.
to The siccatives which are optionally used include cobalt, lead or manganese salts of acids such as linseed oil Fatty acid, tall oil fatty acids and soybean oil fatty acids;
resinic acids such as abietic acid and naphthenic acid; acetic acid; and isooctanoic acid. When they are used, they are used i5 in the form of organic solutions in such quantities that the metal content, based on the weight of the dispersed hydrophilic and hydrophobic polymers, corresponds to between 0.001 and 1%
by weight.
Examples of suitable (hydro)peroxides include dicumyl 2o peroxide, di-tart. butyl peroxide, benzoyl peroxide, cyclo-hexanone peroxide, methyl ethyl ketone peroxide, acetyl acetone peroxide, dinonyl peroxide, bis-(4-tart.-butyl-cyclohexyl)-peroxydicarbonate, tart. butyl hydroperoxide, 2,5-dimethyl-hexane-2,5-hydroperoxide, diisopropylbenzene monohydroperoxide 2s and hydrogen peroxide. These (hydro)peroxides are preferably used in quantities of 1 to 10% by weight, based on the weight of the dispersed or dissolved oligourethanes.
rn the following examples, all parts and percentages are by weight unless otherwise ind'ica'ted.
~a ~XAMIPI.ES
The quantities of components a) and b) set forth ~in Table 1 were dissolved in butyl acetate together with 0.2% tin diactoate and 0.1% 2,6-di-tart. butyl-p-cresol (see Table 1) and the resulting solution was heated to 60°C while air was 35 passed through. The quantity of component c) set forth in Mo-355 >!~ rv.:..~~
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-1~-Table 1 was then added dropwise. After 1 hour, the temperature was increased to 80"C and the mixture was kept at that temperature until the NCO content had fallen to below 0.1%
A solution of ammonia in water was 'then added to 'the solution of the oligourethane containing (meth)acryloyl groups obtained in a quantity sufficient to obtain a solids content of 50%. Ammonia was then added to provide a degree of neu~tral-ization of 80%n, based on dimethylal propionic acid. A solution of ammonia in water was then added in an amount which resulted to in an aqueous dispersion or solution having a pH value of approx. 7. The solids contents obtained and the pH values are set forth in Table 1.

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The aqueous dispersions were then applied to a glass plate in a wet film thickness of 60 ~cm. After evaporation of the water, the film was cured beneath two 1ST lamps (impulse lamps manufactured by Strahlentechnik Fiildebrancl, Warner and io Pfleiderer, output 80 watts/cm, arranged at a distance from the film of 20 cm) at a processing speed of 14 m/minute.
Clear, extremely hard (Konig pendulum hardness in accordance with DIN 53 157: approx. 200 sacs.) and scratch-resistant coatings which were resistant to water and chemicals were obtained.
Scratch resistance was determined by the finger nail test while resistance to water and chemicals was tested by the application of cotton wool plugs impregnated with - water (16 hours) - ethanol, 50% (I hour) - detergent (1 hour) - acetone (10 seconds).
b) Thermal curin--tc The aqueous dispersions of Examples 2, 3, 5 and 6 2s were applied to a glass plate in a wet film thickness of 60 ~Cm and cured for 30 minutes and 180°C. Clear, hard, scratch-resistant and water-resistant coatings were formed.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to Ibe understood that such detail is solely for that purpose and ~tha~t variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims

1. An aqueous solution or dispersion of oligourethanes having a pH of 6.0 to 8.5 wherein the dissolved or dispersed oligourethanes contain carboxyl groups at least partially neutralized with ammonia and have i) a double bond content in the form of (meth)acryloyl groups (expressed as C=C, molecular weight 24) of 3 to 15% by weight and ii) a content of carboxyl groups, including the carboxyl groups neutralized with ammonia, which corresponds to an acid value of 20 to 100, wherein said oligourethanes comprise the reaction product at an NCO:OH
equivalent ratio of 0.5:1 to 1:1 of a) 20 to 80% by weight of an acryloyl component comprising at least one monohydric alcohol having one or more (meth)acryloyl groups and a molecular weight of 116 to 1000, b) 4.5 to 20% by weight of at least one 2,2-bis-(hydroxymethyl)alkane carboxylic acid having at least 5 carbon atoms and c) 15 to 75% by weight of at least one polyisocyanate component comprising at least one organic polyisocyanate having a molecular weight of 168 to 1000, wherein the percentages of a), b) and c) add up to 100.

2. The solution or dispersion of Claim 1 wherein 45 to 100% of the carboxyl groups are neutralized with ammonia.

3. The solution or dispersion of Claim 1 wherein said 2,2-bis-(hydroxymethyl)-alkane carboxylic acid comprises 2,2-bis-(hydroxy-methyl)-propionic acid.

4. The solution or dispersion of Claim 2 wherein said 2,2-bis-(hydroxymethyl)-alkane carboxylic acid comprises 2,2-bis-(hydroxy-methyl)-propionic acid.

5. A process for the production of an aqueous solution or dispersion of oligourethanes which comprises reacting a) 20 to 80% by weight of an alcohol component comprising at least one monohydric alcohol having one or more (meth)acryloyl groups and a molecular weight of 116 to 1,000, b) 4.5 to 20% by weight of at least one 2,2-bis-(hydroxymethyl)-alkane carboxylic acid having at least 5 carbon atoms and c) 15 to 75% by weight of at least one polyisocyanate component comprising at least one organic polyisocyanate having a molecular weight of 168 to 1,000, by initially introducing components a) and b), then reacting these components with component c) at a temperature of 50 to 100°C until the reaction mixture contains no more free isocyanate groups and subsequently dissolving or dispersing the reaction mixture in water, the carboxyl groups being at least partly neutralized by addition of ammonia during the dissolving or dispersing step so that the resulting solution or dispersion has a pH value of 6.0 to 8.5, provided that A) the percentages of a), b) and c) add up to 100, B) the amounts of a), b) and c) correspond to an NCO:OH equivalent ratio of 0.5:1 to 1:1 and C) the amounts of a), b) and c) are otherwise selected within the stated limits so that the resulting oligourethanes have i) a double bond content in the form of (meth)acryloyl groups (expressed as C=C, molecular weight 24) of 3 to 15% by weight and ii) a content of carboxyl groups, including the carboxyl groups neutralized with ammonia, which corresponds to an acid value for the oligourethanes of 20 to 100.

6. A coated substrate wherein the coating is prepared from a coating composition comprising the aqueous solution or dispersion of oligourethanes of Claim 1.