NO750747L - - Google Patents

Description

Procedure for the production of self-crosslinking varnishes.

The present invention relates to a method for producing optionally pigmented self-crosslinking varnishes based on an aqueous dispersion.

The currently common coatings on metals, based on a tory-dried oil, a quick-drying lacquer base with natural resins, a combination of natural and synthetic resins and an alkyd resin modified with urea, melamine or phenol formaldehyde resin, contain volatile organic solvents - are agents which are often flammable and which during the application process develop harmful fumes. For these reasons, nddve&c&Lg urgently needs special precautions for recycling the solvents.

Other suggested binders for coatings contain unsaturated polymer systems such as e.g. butadiene-styrene latexes. However, this type of polymer has the well-known disadvantage that it becomes brittle and discolored with further oxidation.

There has therefore for a long time been a need for coating compositions which can be applied from aqueous media and consequently do not develop any unwanted, flammable or toxic vapors and which are self-crosslinking when exposed to heat alone.

Known aqueous systems are described in US patents 2,760,886, 2,918,391 and 3,033,811. These coating mixtures are not satisfactory as, when applied, they tend to dry too quickly and, due to blistering during the heat treatment, fail to form any smooth film surfaces. There are also known heat-sealable coating compositions in the form of "breathable latexes" (German specification 2.211.169), which are produced according to a common emulsion polymerization method and whose binder is made up of two components, first of all an addition copolymer , consisting of an aromatic monbvinyl monomer, an ester of acrylic or rue tacrylic acid, at least one olefinically unsaturated monomer with an amide or hydroxyl group and an olefinically unsaturated monomer with a carboxyl group and secondly of a

water-soluble urea-formaldehyde resin.

The disadvantage of these coating compositions is that they are not self-crosslinking and thus the considerable addition of another crosslinking component affects a number of important properties, such as pigment tolerance and pigment distribution, adhesiveness, gloss, water and solvent resistance, thermal and weather stability.

It is an aim of the present invention to produce self-crosslinking varnishes based on an aqueous dispersion, with good thermo- and weather stability, with high chemical resistance and which provide coatings with a high gloss which are both hard and tough.

The distinctive feature of the method according to the invention is that a binder is used which essentially consists of

a) 30 70 parts by weight of a monomer or a monomer mixture, the theoretical glass transition temperatures for the homopolymer being below 10°C. b) 30 - 70 parts by weight of a monomer or a monomer mixture, the theoretical glass transition temperatures for the homopolymer being above 30°C. c) 0.5 - 5 parts by weight of a polymerizable acid or salt thereof.

d) 2^35 parts by weight of a reactive monomer and

d) 0.5 - 5 parts by weight of an alkali or ammonium salt of a polymerizable sulfonic acid compound.

As the polymerization is carried out at temperatures of 15 - 30°C using a redox system, consisting of 0.005 - 0.5%, calculated on the total amount of all monomers present, an alkali or ammonium persulfate, 0.001 - 0.5% calculated on the total amount of all monomers present aV ascorbic acid and 10 - 30 ppm of an iron (II) salt, calculated on the total amount of all monomers present, at an initial pH of 3 - 4. whereby a maximum of 30% of the total amount of all monomers present together with the main amount of the persulphate is added and the remaining amount of the monomer is added in parallel with the iron (C£3) salt and the ascorbic acid so that a preselected constant polymerization temperature (+ 1°C) results .

The temperature that is appropriately used is 20 - 23°C. The temperature regulation is expediently automatic, as the dosage of the iron (I3) salt and the ascorbic acid as well as the monomers and the external cooling are matched to each other in order to maintain a pre-selected polymerization temperature, which during the polymerization should only deviate by 1°C.

r

Potassium persulphate is preferably used as persulphate, although sodium and ammonium persulphate can also be used. The preferred amounts are 0.05 - 0.2%. Of this, at least 50% is added and the rest is dosed during or at the end of the reaction.

Ascorbic acid is preferably supplied in amounts of 0.01-0.2% together with emulsifiers and the iron (II> salt. As iron-0:i)-salt, iron-II-sulphate is preferably used in amounts of 10 - 20 ppm . In addition, other iron compounds and complexes can be used which, under the given conditions, can release iron-(EI>-ions. These are iron-(CII)-sulfate, iron-(E3>-chloride, iron salt of ethylenediamine-tetraacetic acid<p>g second.

The starting pH, which lies between 3 and 4, preferably at 3;,<!>.5, is adjusted if necessary by means of organic acids, preferably with polymerizable acids, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, etc. During the polymerization, can. The pH value changes without affecting the polymerization.

For special purposes, e.g. in order to reduce the firing temperature, 1 - 15 percent by weight, calculated on the dispersion, of water-soluble melamine or urea resins can be added to the dispersion after polymerization.

As monomers, whose homopolymers have a theoretical glass transition temperature of below 10°C, e.g. acrylic acid esters with 1-8 C atoms in the ester residue, such as methyl acrylate, ethyl acrylate, ethylhexyl acrylate, meacrylic acid esters with 6-18 C atoms in the ester residue, such as hexyl methyl acrylate, octylmethyl acrylate, n-decyl methacrylate, n-tetradecyl methacrylate, vinyl esters with 3 - 20.C atoms in the acid residue, preferably those with a branched C chain such as e.g. vinyl propionate, vinyl butyrate, vinyl valerate, vinyl capronate, vinyl stearate, and vinyl isobutyrate, ____ olefins such as ethylene, butylene, propylene, butadiene, maleic and fumaric acid esters with up to 4-18 C atoms in the ester residue in consideration. Preferably, 40 - 60 parts by weight of these monomers are used.

As monomers, whose homopolymers exhibit a theoretical glass transition temperature of over 30°C, suitably 30 - 150°C, e.g. Methacrylic acid esters with 1-4 C atoms in the ester residue in consideration, such as methyl methacrylate, ethyl methyl acrylate propyl methacrylate, butyl methacrylate, further acrylonitrile, vinyl chloride, vinyl acetate, chloroacetic acid vinyl ester, trifluoroacetic acid vinyl ester, benzoic acid vinyl ester, styrene, α-methylstyrene, vinyl toluene. Appropriately, 40-60 parts by weight of these monomers are used. -

Glass-omdanriel is seen the temperatures form a common criterion and

is described by Flory in "Principles of Polymer Chemistry", pages 56 to 57, (1953), Cornell University Press. Although the actual measurement of the glass transition temperature is preferred, it can also be calculated, as described by Pox in Bull. Am. Physics Soc. 1, 3, page 123 (1956).

As polymerizable acids or salts thereof come e.g. acrylic, methacrylic, itaconic and crotonic acids as well as unsaturated dicarboxylic acids, such as maleic and fumaric acids, their half-esters with 1-18 carbon atoms in the ester residue or their anhydrides in consideration. The preferred amount of these acids is 2-4 parts by weight.

The reactive monomers, which are used in preferred amounts of 10-25 parts by weight, are e.g. monomers with functional byhydroxyl groups, such as glycol monoacrylate and -monomethacrylate, hydroxymaleic acid ester, butanediol-1,3-monoacrylate and -monomethacrylate, butanediol-1,4-monoacrylate and -monomethacrylate, monopropylene glycol acrylate and -methacrylate, ^-chlorohydroxy esters of unsaturated acids, such as 3-(1-chloro-2-hydroxy)-propyl acrylate, 3-(1-chloro-2-hydroxypropyl)-isopropyl maleate, monomers with functional amide groups, such as acrylamide, maleic monoureide, with methylated amide groups, such as N-methylol methacrylamide or their camouflaged methylol derivatives , such as n-butoxymethyleneacrylamide, monomers with allyl functional groups, such as methacrylic acid allyl ester, maleic acid diallyl ester, monomers with aziridinyl functional groups, such as 2(1-aziridinyl)-ethyl methacrylate.

Alkali or ammonium salts of polymerisable sulphonic acid compounds are understood to mean e.g. such compounds of metallyl sulfonic acids, vinyl sulfonic acid, sulfonated allyl esters, e.g. sulfonated maleic acid and fumaric acid esters as well as sulfobetaines.

. Preferably, 1-3 parts by weight are used.

As emulsifiers, the anionic wetting agents known per se can be used, suitably in amounts of 0.05 - 5%, calculated on the monomers. Suitable anionic emulsifiers are alkyl sulphates, sulphates of alkyl and alkylaryl polyethoxyalkanols, alkyl sulphates, alkylaryl sulphonates, as well as esters of sulphoraic acid with alkane groups.

The viscosity of these latexes that can be used as a binder for coatings can be adjusted afterwards with different thickeners. Colloids can be used for this, such as e.g. polyvinyl alcohol and water-soluble modifications thereof, insoluble cellulose derivatives, such as hydroxyethyl, hydroxypropyl, methyl, ethyl, carboxymethyl cellulose, water-soluble polysaccharides and derivatives thereof, polyacrylic acid and insoluble derivatives of this...

The dispersions obtained after the polymerization are adjusted with a water-insoluble tertiary amine, such as e.g. triethylamine, dimethylaminoethanol, triethanolamine at a pH of between 5 and 9, preferably pH 6, and to improve the pigment wearability and storage stability aged at approx. 10 minutes of heating at 50 - 60°C.

The products that can be produced by the method according to the invention can be pigmented without the necessary addition of dispersing aids. When pigments are used, the ratio between pigments and solids in the coating can be varied within a wide range, depending on the pigment used and the particular type of application. Thus lean the ratio between pigment and solids in the coating from 1-20 to 20-1. The clear covers are particularly valuable as tire covers such as

. used to protect decorative under-overcovers without detrimentally affecting the decorative effect. As the coatings are completely clear and transparent and are both hard and tough, have a high gloss, a pronounced resistance to solvents and water and good adhesion to a large number of surfaces, they are excellently suited as topcoats. The self-crosslinking varnishes which can be produced by the method according to the invention can

is applied to a large number of substrates, with the only limitation that the substrate can withstand the curing process which is essential for the production of the coatings. Metals are particularly suitable and thus iron, steel, chrome-plated steel, tin-plated steel, aluminium, copper, bronze or brass in sheet or wound form are excellent substrates for the coating compositions. Ceramic surfaces and in some cases wooden surfaces

are also suitable as substrates.

A number of pigments can be used for the lacquers. Typical suitable pigments are titanium dioxide, iron oxide, chromium oxide, kadraium&syd, calcium silicate, quartz flour, talc, carbon black, calcium carbonate,

toaryt and organic pigments.

The coating compositions can be applied with suitable devices, e.g. with spray guns, brushes or rollers or by immersion and surprisingly also by direct rolling, i.e.

a single roller brings the coating onto the substrate as it rotates in a bath of the coating composition. The applied layer can in any case be hardened by direct heat to a glossy film.

The resulting varnishes are characterized by high gloss, good chemical resistance, special toughness and hardness as well as by excellent pigment tolerance and pigment distribution. These good properties are achieved by very finely divided dispersions, so-called hydrosols. is achieved by the method according to the invention.

General pollmerization method.

In a stirred autoclave with heating and cooling devices as well as dosing devices, a part of the aqueous phase, in which emulsifiers and persulphate are dissolved, is first introduced.

After flushing with nitrogen, a certain amount of the monomer mixture is emulsified, the desired temperature (20-23°C) is set and the polymerization is started by dosing an aqueous solution of ascorbic acid and iron (t^-salt). temperature increase of 1 2?C, after which the dosing rate of the reducing agent is throttled. At the same time, the supply of the rest of the monomers can be adjusted using the cooling capacity of the reaction vessel to the dosing rate of the reducing agent, in such a way that the preselected constant polymerization temperature (+ 1°C) is maintained therein .

Polymerizable components that are not monomer soluble, e.g. certain acids, reactive monomers or emulsifiers, are added in aqueous solution, parallel to the rest of the monomer mixture. Polymerizable acids can be partially neutralized for the addition with a water-insoluble tertiary an in.

If the reactive methylol grouping is introduced in situ, the necessary amount of formaldehyde is introduced, together with the aqueous phase, and the montameric amide used is dosed in the usual way.

EXAMPLE 1.

By this general procedure, the following portion was polymerized in a 2-liter tube

1. Insert mixture

2.. Dosage 2.1. aqueous phase. 2.2. monomer phase 2.3 activator release

» £H. adjusted to 6 with triethylamine.

Corresponding to example 1), a number of further experiments were carried out, with the composition and reaction conditions varying according to Table IA.

In table 13, the properties of the obtained dispersion are listed. The turnover amounted in each case to over 99.5%. The solids content is between 35 and 40%.

Table 2 shows the coating technical properties of the pigmented oven-sized films.

EXAMPLE 2.

The amount of initiator used could be reduced to approximately half.

EXAMPLE 3.

In relation to example IA), the ratio between styrene and ethyl acrylate was increased and in the introduced mixture a further emulsifier was co-used.

EXAMPLE 4.

The incorporated formaldehyde was incorporated in situ into acrylamide and maleic acid monoureide. The proportion of methallyl sulphonate dosed was increased.

EXAMPLE. 5.

The emulsifier mixture corresponded to example 3). In relation to example 1A), polypropylene glycol monoacrylate was used as an additional cross-linking component and the formaldehyde addition was made to acrylamide as in example 4). The dosed proportion of methallyl sulphonate corresponded to the proportion in example 4).

The dispersions prepared according to examples 1a-5 were ground in a ball mill with titanium dioxide (rutile) in the ratio lsl calculated on the solids content in the dispersion.

The one with an 80^a, spindle on chromated aluminium. (0.5 mm thick^ applied film of the produced pigmented burnish lacquer was oven dried for 2 minutes at 180 - 260°C. Blister-free white lacquer coatings with a high gloss were obtained with very good flow* properties and very good lacquer technical properties.

Claims (4)

1. Method for the production of self-crosslinking varnishes, possibly pigmented by heat treatment, on the basis of an aqueous dispersion, characterized by the use of a binder which essentially consists of a) 30 - 70 parts by weight of a monomer or a monomer mixture, with the theoretical glass transition temperature for the homopolymer being below 10°C. bl}) 30 70 parts by weight of a monomer or monomer mixture, the theoretical glass transition temperature for the homopolymer being above 30°C. c) 0.5 - 5 parts by weight of a polymer in serbar,; acid or salt thereof d) 2 - 35 parts by weight of a reactive monomer e) 0.5 - 5 parts by weight of an alkali or ammonium salt of a polymerizable sulfonic acid compound ■ > as the polymerization is carried out at temperatures of 15 - 30°C with the help of a redox system, consisting of 0.005 - 0.5%, calculated. on the total amount of monomers, of an alkali or ammonium persulfate, 0.001-0.5%, calculated on the total amount of monomers, ascorbic acid and 10 - 30 ppm of an iron (II) salt calculated on the total amount of monomers, at an initial pH of 3 - 4, with a maximum of 30% of the monomers together with the main amount of the persulfate being introduced into the starting mixture and the remaining amount of the monomers being added in parallel with the iron (II) salt and ascorbic acid Mik that a preselected constant polymerization temperature (+ 1°C) results . 2. Method as stated in claim 1, characterized in that the polymerization rate is controlled in such a way by means of the supply of the reducing initiator components that a constant polymerization temperature of (+ 1°C) is maintained. 3. Method as stated in claim 1 or 2, characterized in that the self-crosslinking varnishes are set with a tertiary amine to a pl"-^erd± in the Otmrådet 5 - 9 and then made storage stable by a short aging treatment at a higher temperature, especially between 50 and 60°C and in any case below the firing temperature. 4. Method as set forth in claims 1-3, characterized by J in that after polymerization 1-15 percent by weight, calculated on the dispersion, of a water-soluble melamine or urea resin is added.