CS215101B2 - Method of making the binders for the water dilutable varnishes,hardenable by the acid - Google Patents

Abstract

Binders for water-thinnable, acid-curing coatings are prepared. These binders are obtained on mixing or partially cocondensing 45 - 90 % by weight of a low molecular weight, partially etherified, water-soluble urea-formaldehyde condensate, wherein the etherification alcohols are at least 50 % monoalcohols of 1 to 3 carbon atoms and 0 - 50 % monoalcohols of more than 3 carbon atoms and/or diols and/or diol monoalkyl ethers, with 10 - 55 % by weight of an oil-free saturated polyester having a hydroxyl number from 250 to 400 and containing from 10 to 25 % by weight of a polyethylene glycol having an average molecular weight between 300 and 1000, preferably 300 - 750. Conditions are atmospheric pressure and temperatures between 30 DEG C and reflux temperatures. The binders obtained can be used for any kind of coating for wood.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of acid-curable water-borne paint binders.

Acid-curable lacquers have been known for a long time. They are widely used for varnishing wood (varnishing furniture, parquet flooring); they are essentially a combination of a curable aminoformaldehyde resin with a plasticizing alkyd resin. Curing occurs after the addition of strong acids and can take place at normal or slightly elevated temperatures. A disadvantage of conventional acid-curable lacquers is their content of expensive and partially toxic solvents. In addition to aromatic hydrocarbons, butanol is used in particular, which has an unpleasant effect during the processing of the lacquers and often causes allergic reactions.

It was not missing. efforts to develop acid-curable water-borne lacquers. These efforts have so far largely failed because there were no suitable water-dilutable alkyd resins as plasticizers. All known aqueous solutions or emulsions of alkyd resins are alkaline stabilized and lose their stability when the acid is added as a catalyst.

In the German publication DOS

No. 11,537 discloses a process for the preparation of water-dilutable, acid-curable lacquers in which alkyd resins are used for plasticization which are water-soluble even without the addition of basic compounds. The solubility of these alkyd resins is achieved by a very high proportion, above 75%, of polyethylene glycol. Like curing. All types of amine resins are said to be suitable. These. paints are said to dry quickly and provide water-resistant films.

When verifying examples. German. however, it is conspicuous that only melamine resins are used as the curing component. In addition, extremely high catalyst additions are used: for example 7% p-toluenesulfonic acid or 21% concentrated hydrochloric acid based on the solid resin. Furthermore, the lacquers still contain considerable proportions of solvents, such as butanol and butyl glycol acetate.

The results obtained in the verification of the procedures described in the examples show that, indeed, only the use of melamine resins can achieve some acceptable results. the use of urea or benzoguanamine resins does not provide sufficient film formation. However, even with the use of melamine resins, they are only slowly obtained with only average properties of water resistance. In addition it induces a high proportion of acid number of problems: poor durability pressure, poor compatibility with pigments, corrosion upon contact with metal parts, delicate wood discoloration and embrittlement and finally re-softening of aging at ¹ films.

Insufficient properties of these lacquers can be derived from the composition of alkyd resins. These are either linear polyesters which are obtained by esterification of extremely high proportions of polyethylene glycol (over 75%) with maleic acid - optionally in a 'mixture with phthalic acid or other dicarboxylic acids - or with drying oils modified with polyethylene glycol'. Due to their low content of functional hydroxyl groups, such resins can only be crosslinked with aminoformaldehyde resins to a very limited extent. It can therefore be assumed that the formation of the lacquer film described in the German publication 20 11 537 is primarily due to the inherent condensation of melamine resins.

The alkyd resins remain substantially unbound and 'retain their' hydrophilic and thermoplastic character due to the high polyethylene glycol content.

It has now been found that water-borne, acid-curable lacquers having excellent film-forming properties are obtained. . when the low-polyethylene glycol and high hydroxyl-containing polyesters interspersed with polyesters are combined with an excess of a low molecular weight, water-soluble urea-formaldehyde resin which is etherified with monoalcohols of 1 to 3 atoms. carbon.

Accordingly, the present invention provides a process for the preparation of binders for water-borne, acid-curable lacquers based on combinations of alkyd resins with urea resins, characterized in that 45 to 90 why. % by weight of oligomeric, water-soluble and urea-formaldehyde condensate, optionally containing monomer fractions, containing on average 1,5 to 2,5 moles of bound formaldehyde per mole of urea, and whose methylol groups are etherified by 10 to 40 mole% of monoalcohols with 1 to 3 carbon atoms, wherein up to 50 mol% of these alcohols may be replaced by monoalcohols having 4 to 6 carbon atoms and / or diols having 2 to 4 carbon atoms and / or their monoethers with monoalcohols having 1 to 4 carbon atoms, contacted with 10 to 55% by weight of a saturated polyester-free oil having a hydroxyl number of from 250 to 400 and a content of 10 to 25. %. by weight of an average molecular weight of polyethylene glycol in the range of from 300 to 1000, preferably from 300 to 750, at temperatures in the range from 30 ° C to reflux temperature at atmospheric pressure until a viscosity limit value in the range of 5 to 10 ml is reached. g, measured in dimethylformamide at 20 degrees Celsius.

To prolong the pot life, i.e. the time that the feed with the catalyst already added remains workable, up to 10% by weight of urea-formaldehyde condensate may be replaced by partially or fully etherified, optionally in the presence of organic solvents, with a water-soluble condensate of aminotriazine with formaldehyde, or entirely methanol, ethanol, n- or isopropanol 'or mixtures thereof' of etherified melamine-formaldehyde condensates.

The water-soluble urea-formaldehyde condensates (so-called urea resins) used in the process of the present invention are produced in an alcoholic solution by forming a solution of formaldehyde in methanol, ethanol, n- or isopropanol, which may optionally be obtained by depolymerization of paraformaldehyde in this alcoholic medium. , condenses with urea at a pH in the range of 7.5 to 10 at reflux temperature. The etherification is carried out at reflux temperature and at a pH in the range of 2.5 to 6, using mineral acids or organic acids, preferably acetic acid, to adjust the pH. The resulting product can be used as is obtained for the binders of the invention or after distilling part of the alcohol-water mixture. The lower monoalcohol may be partially replaced by higher alcohols, such as butanols, pentanols, hexanols, etc., and / or diols, such as ethylene glycol, propylene glycol and homologues thereof, and / or their monoethers with lower monoalcohols. However, care should be taken that at least 50% of the etherified methylol groups are bound by residues of lower monoalcohols having 1 to 3 carbon atoms. In most cases, a relatively small proportion of said other hydroxyl compounds is sufficient to achieve a specific adjustment of the lacquer properties.

For urea resins useful in the process of the invention, about 1.5 to 2.5 moles of formaldehyde per mole of urea; at least 10% of the methylol groups are etherified.

The polyester-free oils useful in the process of the invention are obtained by esterification. from dicarboxylic acids, polyols and polyethylene glycol.

All of the products customary in the art can be used as dicarboxylic acids. Adipic acid and phthalic anhydride are preferred. The polyols or polyol blends must be selected so that the desired hydroxyl value is in the range of 250-400 mg KOH / g. Thus, a sufficient proportion of trivalent, optionally quaternary or polyvalent alcohols must be used. Suitable are, among others, glycerol, trimethylolpropane, pentaerythritol, sorbitol, optionally in an admixture with diols ja215101 ко ethylene glycol, diethylene glycol, propylene glycol ⁵ pro- and neopentyl glycol.

Suitable polyethylene glycols are products having a molecular weight in the range of 300 to 1000, preferably in the range of 300 to 750. To a lesser extent, monomethoxypolyethylene glycols may also be used. In contrast to the known basically stabilized alkyd resin emulsions, in which polyethylene glycols having a molecular weight in the range of 1000 to 3000 are preferably used for better emulsifying effect, the oil-free alkyl resin used for the binders of the invention need no, due to their high hydroxyl group content long chain polyethylene glycols. By using short-chain polyethylene glycols, more resistant films are obtained by uniformly distributing the crosslinkable functional groups. The acid number of the polyesters used is in the range of 10 to 45 mg KOH / g, preferably in the range of 30 to 45 mg KOH / g. The viscosity limit value, measured in dimethylformamide at 20 ° C, is within the range. 5 to 9 ml / g.

The azcotropic carrier (xylene or toluene) used in the estrification is preferably removed by vacuum distillation so that no aromatic solvents are introduced into the resulting product. The resins are combined with urea resin, usually undiluted. Only when the intrinsic viscosity is too high, is it diluted with ethanol to a dry matter content of 80 or 90% by weight.

The alkyd-free oils used for the binders of the invention are in themselves only partially compatible with water. Combination with the urea resin, optionally with slight condensation, results in a water-dilutable binder.

The combination with the urea resin is carried out either by simple mixing at a temperature in the range of 30-40 ° C or by mild mixed condensation, at most at reflux under atmospheric pressure, the molecular weight increase can be controlled by measuring the limit viscosity number in dimethylformamide.

The preferred value is in the range of 5 to 10 ml / g. As the viscosity limit increases, in some cases the water dilutability first increases and then decreases again.

The binders according to the invention can be processed in unpigmented as well as in pigmented form in a glossy or matt state. All pigments which are also used in conventional ⁴ lacquers dissolved in organic solvents and acid-curable can be used as pigments.

Corrosion inhibitors may be added to prevent corrosive attack on packaging or equipment. In addition, up to a maximum of 5% of polyvinyl alcohol, methylcellulose or cellulose acetopropionate can be used as the thickening agent to adjust the viscosity. The catalysis is carried out with inorganic or organic acids, such as dilute hydrochloric, orthophosphoric acid or preferably p-toluenesulfonic acid, optionally in the form of their ethanolic solutions.

Due to their composition, the binders produced by the process of the invention require relatively low amounts of catalysts, for example about 1% p-toluenesulfonic acid or orthophosphoric acid. They can be used for all types of wood painting, for which solvent-solubilized products have been used exclusively, such as parquet flooring, furniture coatings with unclosed or filled pores, etc. The coatings are characterized by excellent scratch, abrasion and solvent resistance, excellent cold-check stability, high gloss as well as good hiding and yellowing resistance.

Particular emphasis should be placed on rapid drying and drying, which ensure rapid stacking strength, which is important for practice. Varnishes are applied by brushing, pouring, rolling or spraying. Curing may take place at room temperature or forced at elevated temperature.

The following examples illustrate the invention in greater detail without limiting its scope. In Tables I, II, III and IV, all parts are by weight and all percentages are by weight.

A) Preparation of urea-formaldehyde condensates (urea resins)

In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, paraformaldehyde is depolymerized in the first step at 90 ° C in an alcohol or in a mixture of alcohols having a pH in the range of 7.5 to 10 (adjusted with triethylamine). After complete dissolution, urea is added and after adjusting the pH to 2.5-6 with acetic acid, etherification is allowed to proceed at reflux for 2-10 hours.

Table I

Product AI A2 A3 A 4 A5 urea 60 60 60 60 60 paraformaldehyde (91%) 66 59.5 76 76 76 ethanol, techn. (96%) 76.5 62 96 76.5 83 monoethylene glycol 18.5 - - - 9 monoethylene glycol - - __ 27 Mar: monoethylether 52 62 57 54 57 solids content (%) 1,8 1.6 2.3 2.3 2.2 the number of methylol groups, of them etherified 0.45 0.4 0.5 0.46 0.4

В) Manufacture of polyesters (alkyd resins)

The composition and other parameters of the alkyd resins are summarized in Table II below. The esterification of the components takes place at a temperature in the range of 170 to 180 ° C, with toluene added as an azeotropic carrier to accelerate the reaction. Toluene is distilled off under reduced pressure until the acid number 45-50 is reached. The reaction mixture was then heated at 170 ° C until the desired parameters were reached. The resins produced are cooled to approximately 50 ° C and further processing takes place without the need for dilution.

Table II

В 1 В 2 В 3 В 4 В 5 adipic acid 90 - 100 ALIGN! 100 ALIGN! 90 phthalic anhydride - 112 - - - trimethylolpropane 100 ALIGN! 80 - 111 1.00 glycerine - - 67 - - pentaerythrit - 20 May - - - ethylene glycol 5 - - - —- diethylene glycol - - 20 May - 9 polyethylene glycol 300 - - - 40 - polyethylene glycol 600 30 45 33 - - polyethylene glycol 1000 - - -. - 30 Solids content (° / o) 99.8 99.7 99.2 99.6 99.0 acid number (mg / KOH / g) 38.5 37 32 34 27 Mar: limit viscosity number in dimethyl- formamide at 20 ° C (ml / g) 5.5 5.2 5.8 5.5 6.5 hydroxyl value (mg / KOH / g) 365 277 391 368 354

Examples 1 to 11

Example 12 (comparative example)

The urea-formaldehyde condensates (urea resins) are mixed with the polyester resins mentioned, optionally (x) in the examples, mixed condensate for about 3 hours at reflux temperature, then water-dilute melamine resins and / or thickeners and catalyst acid solution are added. -toluenesulfonic acid or orthophosphoric acid in ethanol, after which the reaction mixture is diluted with water or a mixture of water and lower alcohols or water-compatible solvents until a viscosity suitable for processing in the range of about 18 to 20 s is reached (DIN 53 211). The lacquers obtained are tested in the batches listed in the table.

According to Example 1 of German Offenlegungsschrift DOS 20 11 537, a lacquer is prepared; tests were carried out in the same manner as the lacquers of Examples 1 to 11 of the present invention. The results are shown in the results table.

Explanatory notes to the example table:

Melamine formaldehyde condensates (Melamine resins):

(1) hexamethoxymethylmelamine (2) partly methanol-etherified melamine-formaldehyde condensate (average CH ₂ OH 5,2, of which —CH ₂ OCH ₃

4.3 per 1 mol of melamine, 50% solution in diethylene glycol diethyl ether J.

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1) Workability time: Time in hours, indicating the time the paint can be worked, from the addition of the catalyst to the gelling of the paint. The test is carried out at room temperature and in an open vessel.

2) Drying: The coating film of a given thickness is wetted with a metal bar. The evaluation is carried out according to the drying trace. Test equipment: BK-DRYING RE7 CORDER, with pull-out cube for wet coating film thickness 152 μΐη; measurements on glass plates at 23 ° C and 55% relative humidity. Evaluation: time in minutes required for drying (film formation).

3) Pendulum hardness: according to Konig, in accordance with DIN 53 157 after different time intervals at a wet film thickness of 300 / / 120 μΐη. Storage of test plates in an air-conditioned room at 23 ° C and 55% relative humidity.

4) Teapot test: A wet cloth is placed on a layer of lacquer stored for 5 weeks at room temperature after application and a teapot of boiling water is placed on it. After the water has cooled down, the formation of a white veil in the paint, the creation of a pot or cloth impression and the softening of the paint are considered.

5) Resistance: a wad of cotton wool impregnated is placed on a layer of lacquer deposited 5 weeks after application at room temperature. 5 ml of the test liquid, and cover with a glass dish (diameter 40 mm, height 25 mm, with ground edge), assessing the effect of the test liquid (alcohol, acetone, water) on the lacquer layer (eg dyeing, softening, lifting the lacquer layer) a certain period of exposure.

Explanation of abbreviations in Table VI:

Solvent Teapot test Water resistance

1 OK OK OK 2 weak stretch slight edge weak stretch 3 softening formation of white veil softening 4 scrape scrape scrape

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Table VI Resistance example acetone Resistant against ethanol water stability during the test with a teapot 30 min 60 min 60 min 24 h 60 min 24 h 1 1 1 1 2 (+) 1 2 2 2 1 1 1 2 1 1 2 3 1 1 1 2 (+} 1 2 3 4 1 1 1 2 (+ -) 1 2 (+] 3 5 1—2 1—2 1—2 3—4 1 1 2 6 1 1 1—2 3—4 1 3 2 7 1—2 1—2 1—2 3 1 2 (+] 2 8 1 1 1 2 (+) 1 2 3 9 1 1 1 2 (+) 1 2 2 10 1 1 1 2 (+) 1 2 3 11 1 1 1 2 1 1 2 (+) 12 1—2 2 4 4 (+) 3 4 4

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Claims (2)

Process for the production of acid-curable water-borne varnishes based on combinations of alkyd resins with urea resins, characterized in that: 45 to 90% by weight of an oligomeric, water-soluble urea-formaldehyde condensate, optionally containing monomer fractions, containing on average 1.5 to 2.5 moles of bound formaldehyde per mole of urea and whose methylol groups are etherified from 10 to 40 mole% And optionally up to 50 mol% of these alcohols is replaced by monoalcohols having 4 to 6 carbon atoms and / or diols having 2 to 4 carbon atoms and / or their monoalcohols having monoalcohols having 1 to 4 carbon atoms, contacted with 10 to 55% by weight of an oil-free saturated polyester having a hydroxyl number of from 250 to 400 and a content of 10 to 25% by weight of polyethylene glycol of an average molecular weight of from 300 to 1000, preferably 300 to 750, at temperatures ranging from 30 ° C to a reflux temperature at atmospheric pressure until a viscosity limit of 5 to 1 is reached 0 ml / g, measured in dimethylformamide at 20 ° C. 2. Process according to claim 1, characterized in that up to 10% by weight of the urea-formaldehyde condensate is replaced in part or wholly by etherification, optionally in the presence of organic co-solvents, with a water-soluble condensate of aminotriazine with formaldehyde.