NO171279B - ETSGRUNNMALING - Google Patents

Description

The invention relates to etching primers which give the thus treated metal surfaces excellent corrosion resistance, which do not penetrate the topcoat, and which are produced and used without the concomitant use of chromate pigments.

Etching primers must primarily provide metal parts, especially those used in shipbuilding or in the manufacture of other steel structures, with temporary corrosion protection and which can later be coated. As Wash-Primer in layer thicknesses of 8-12 pm or Shop-Primer in layer thicknesses of 8-40 pm, they must withstand thermal stress that occurs during welding, so that they remain pore-free so that the weld seam does not later form corrosion sites. Oxidatively drying alkyd resins are usually used as topcoats.

In addition, it is desirable to equip metal objects whose cover or intermediate varnishes are cross-linked thermally with a similarly effective etch primer, even if this does not depend on temporary protection, but the individual varnishes are carried out in sequence. In addition to improving the adhesion of the paintwork, these etching primers also provide excellent corrosion protection. Against these, however, is the fact that the known etching primers, which must usually contain phenolic resins to achieve a good effect, penetrate the topcoat, and there give rise to discolouration. For construction parts that are to be temporarily protected, long-oiled petrol-soluble alkyl resins have been used as topcoats as binders, because these reduce the tendency to penetration. Other topcoats, e.g. based on short-oiled alkyl resins, which are soluble in aromatic hydrocarbons and/or alcohols, or nitro-cellulose varnishes, mixed polymers based on a) vinyl chloride and b) vinyl isobutyl ether or vinyl acetate, are not suitable for this purpose in the same way as the other common varnish systems . The priming of metal parts whose paintwork is later to be thermally cross-linked was, due to the penetration of the etching primer, hitherto impossible or associated with a reduction in corrosion protection, as with a combination of alkyl and urea resins.

The reason for the breakthrough is undoubtedly to be found in the phenolic resin components. If you leave out the phenolic resin in an etching primer, there will be no penetration, but then the etching primer provides little or only insufficient corrosion protection, and the adhesive properties become poor. The phenolic resin components affect the cross-linking speed and the degree of cross-linking of the oxidatively drying topcoat that is exclusively applicable in the state of the art.

The most effective etching primers are solvent varnishes which usually contain polyvinyl butyral, phosphoric acid, pigments and phenolic resins. When choosing the pigments (this also includes fillers and extenders), until now reference was made to the combined use of chromate pigments, especially zinc chromates. The zinc chromates not only provided significantly improved corrosion protection, but also improved the adhesion of the metallic surfaces, especially on aluminum and zinc. In the case of these surfaces, improvement of the adhesion is in the foreground, in the case of iron surfaces, corrosion protection. However, Krompig-ment has the disadvantage that it is carcinogenic.

It is desirable to produce etching primers which do not have the above-mentioned disadvantages and are usable without causing discolouration of the topcoat, enable the use of thermally hardening lacquer structures, and are also usable without the concomitant use of the carcinogenic chromate pigments.

According to the invention, this is achieved by etching primers based on polyvinyl acetals dissolved in organic solvents, as well as pigments, acidic phosphorous compounds, artificial resin and possibly further common additives, the weight ratio between polyvinyl acetal and artificial resin being between 4:1 and 1:4, characterized by the fact that the artificial resin contains ethers of epoxy resins and/or esters of epoxy resins with mono- or dicarboxylic acids, where at least 80$ of the epoxy groups have been converted.

Organic solvents such as e.g. lower alcohols with up to 4 C atoms such as methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, the ester of these alcohols with monocarboxylic acid, especially with acetic acid, glycol ethers, such as ethylene glycol, monomethyl ether, or —monoethyl ether, propylene glycol monomethyl ether, or —monoethyl ether or their esters with monocarboxylic acid, especially with acetic acid ketones such as acetone, methyl ethyl ketone, diethyl ketone, or aromatic hydrocarbons, such as toluene, xylene, ethylbenzene or mixtures of these solvents.

As polyvinyl acetals, it is suitable, e.g. formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde and higher aldehydes with up to 10 C atoms, especially however polyvinyl butyrals resp. — isobutyrals of different molecular sizes, and different degrees of acetalisation. The ratio between the polyvinyl acetal and synthetic resin is between 4:1 and 1:4.

Compounds that are chromate-free, e.g. iron oxide red, titanium dioxide of the rutile or anatlas type, carbon black, zinc phosphate, zinc oxide, aluminum zinc phosphate and several others. As common additives, there are e.g. applicable with fillers, resp. extenders such as talc, barium sulphate, fumed silica.

Chromate-containing pigments can be disregarded without affecting adhesive and corrosion protection properties. Nevertheless, it is also possible to add these pigments.

As phosphorus compounds, it is suitable, e.g. the acid esters of the various phosphoric acids, acid phosphates, preferably, however, the orthophosphoric acid itself. These are usually added in amounts of 1-30, preferably 1.5-20%, referred to binder part, or to resin + polyvinyl acetal. When used as a two-component etching primer as defined below with basic pigments, it is advisable not to increase the phosphorus-acid part above 15%.

Suitable epoxy resin esters and/or esters of epoxy resins with mono- or dicarboxylic acids are those in which at least 80% of the epoxy groups have been converted.

Epoxy resins based on diphenylolalkanes, especially diphenylolpropane and/or -methane and epihalohydrin, preferably epichlorohydrin, preferably epichlorohydrin with molecular weights of 200 to 4000, preferably 300 to 2000, are used above all for the production of ethers. phenol ethers of epoxy resin in the usual way so that the epoxy resin is reacted in melt or by solution with an amount of phenol at least equivalent to the epoxy group in the presence of a basic catalyst, e.g. alkali hydroxide, tertiary amines or triphenylphosphane at temperatures from room temperature to 200°C, preferably 120-180°C. If you work with tertiary amines as catalyst, these can also have primary and/or secondary amino functions, so that the catalyst is incorporated into the resin. it is also possible, using the above reaction conditions, to react low molecular weight epoxy resins, e.g. diglycidyl ethers of diphenylolalkanes with diphenylolalkanes and/or phenols in a one-step process, as the molar ratios between the components can control the molecular size of the final product. from finished epoxy resins, and otherwise works under the same conditions as with phenols.

The production of epoxy resin ester takes place in the usual way, usually at 60-200°C, preferably 100-170°C by esterification of the above-mentioned epoxy resins with monocarboxylic acid and/or dicarboxylic acids which can also be olefinically unsaturated in solution or melt. Thereby, it is appropriate not to increase the amount of carboxylic acid above the amount necessary for complete esterification of the epoxy group. For carrying out this reaction, the above-mentioned catalyst may be present, but it does not have to be. These epoxy resin esters can be produced a) from relatively high molecular weight or, as mentioned, by reaction with the phenols, low molecular weight epoxy resins, e.g. diglycidyl ethers of diphenylolalkanes and possibly additional diphenylolalkanes, and b) carboxylic acid and/or carboxylic acid glycidyl esters. If you start from low molecular weight epoxy resins, then the above-mentioned catalysts must be present.

As phenols, mono- and/or polyhydroxybenzenes can be used, especially mononuclear and above all monovalent phenols, such as the isomeric cresols or ethylphenols, or the isomeric alkylphenols with 3-18 C atoms or resorcin, hydroquinone, pyrocatechin, or the isomeric trihydrobenzenes. Particularly preferred is the use of phenol (hydroxybenzene). When producing the epoxy resin phenol ethers with the co-use of monovalent phenols, the weight ratios can be chosen so that the desired content of free phenol is established by itself. However, free phenols can also be added to the resin after completion of the derivative formation or to the varnish. It is particularly surprising that with free phenol no discoloration of the paint occurs.

The production of the etching primer itself takes place suitably by dissolving the polymers, the synthetic resins, possibly the phenols in solvents and then incorporating pigments and possibly common additives. Preferably, the incorporation of the pigments takes place in the synthetic resin solution. The phosphorus compound is added after these work processes, possibly in a mixture with part of the lacquer components, preferably with the solvents used for dilution, or also immediately before use. In this case, one speaks of a two-component primer.

The metal surfaces to be protected, especially surfaces of iron, chrome, zinc, tin or aluminium, are usually degreased before painting without this being absolutely necessary. The primer is excellently corrosion-resistant, hard, adheres very well to the substrate, and can be heated with it without damage to it. Furthermore, the primer is pore-free weldable. These properties already occur shortly after application at ambient temperature.

All common paint systems can be used for overcoating. The etching primer does not penetrate the topcoat. Topcoats include, in particular, varnishes based on the following binders: oxidatively hardening alkyl resins, nitrocellulose (NC) and NC combinations with isocyanate cross-linked acrylic and polyester resins, with polyamines or polyamido-amines cross-linked epoxy resins and vinyl chloride blend polymers, e.g. the above, further as heat-setting binder, polyester, alkyd and acrylic resins in combination with urea and/or melamine resins, and self-crosslinking acrylic resins. However, for the development of the etching primer's protective properties, thermal finishing is not necessary. However, it is possible when the nature of the topcoat requires it. In this case too, there is no breakthrough.

In the above and in the following examples, parts, parts by weight and percentages are given in percentages by weight.

Examples

1. In a reaction vessel equipped with piping and a thermometer, 507 parts of the technical diglycidyl ether of 4,4'-diphenylpropane (epoxy equivalent weight 190, average molecular weight 380, viscosity 22 Pa.s/25°C), 152 parts 4,4'-diphenylolpropane and 125 parts of phenol added 0.24 parts of dimethylaminopropylamine and heated to 140°C. At this temperature it was stirred for 8 hours. The mixture was then dissolved in 389 parts of n-butanol, 195 parts of isopropanol and 100 parts of toluene. The yield was quantitative. The Earpik solution had a solids content of 60.5% and a viscosity of 1200 mPa.s/20°C. Free phenol content 0.59%, epoxy number 0.13. 2. In an apparatus equipped with stirrer, thermometer and reflux condenser, 264 parts of glycidyl esters of isononanoic acid, 304 parts of 4,4'-diphenylolpropane and 253 parts of diglycidyl ethers of 4,4'-diphenylolpropane and 0.25 parts of dimethylaminopropylamine to 140°C and this temperature was maintained for 8 hours. 350 parts of n-butanol were then added while cooling. The yield was quantitative. The viscosity of the 70% solution 6200 mPa.s/20°C, epoxy number 0.19.

Lacquer technical tests

With the resins from examples 1 and 2 and three comparison lacquer systems according to the state of the art, lacquer technical tests were carried out. Polyvinylbutyral had a softening range according to the ring and ball method (DIN ISO 4625) of 150-170°C, a density of approx. 1.1, a content of butyral groups of 83-86 equivalent % of the acetate group of approx. 3 equivalent-% and of the alcohol group of 11-14 equivalent-%. The viscosity according to Eoppler DIN 53 015 was in a 10% butanol solution at 20° C between 90 and 150 mPa.s. The following resins were used for the comparison tests: 1. By acid catalysis curable phenolic resin, viscosity according to DIN 53 177/20°C 500 - 650 mPa.s, residue according to DIN 53216, approx. 70%. II. A curable, non-plasticized phenolic resin, viscosity according to DIN 53 177/20°C 190 - 300 mPa.s, residue according to DIN 53 216, approx. 70%. III. Medium oil, non-drying alkyd resin with phthalic anhydride part of 32%, viscosity according to DIN 53 177/2CPC 90-130 mPa.s, acid number according to DIN 53 402 below 10, and residue according to DIN 53 216 of approx. 80%. IV. Unplasticized urea resin, viscosity according to DIN 53 177/20°C, 100-1200, residue according to DIN 53 216, approx. 65%.

For comparison III, a mixture of 6.3 parts of resin III and 7.7 parts of resin IV was used.

Production of etching primer

The pigments and extender were crushed with the synthetic resin solution in a high-speed pipe mill to a fineness of approx. 10 p.m. Then polyvinyl butyral solution, phosphoric acid/butanol mixture and the diluent were added.

Application

The etching primer was sprayed at an outlet viscosity of approx.

20 DIN/s (DI cup 4 mm, DIN 53 211) with a spray gun with air atomization on the test surfaces. The dry film thickness amounts to 30 to 35 pm. The films were immediately examined for their drying speed, the other tests took place after 7 days of storage and room temperature. Assessment of the films took place according to a subjective scale according to DIN 53 230, with the designation 0 meaning no change, the designation 5 the worst possible value. The resistance to the impact of water, salt spray test and drying speed were examined on an iron substrate.

To determine penetration of the topcoat, after three days of storage, the iron test cans were spray-painted with a room-temperature cross-linking and a thermally cross-linking topcoat of the following composition, the heat-setting topcoat after a deaeration time of 10 minutes being baked in for 30 minutes at 120°C in a circulation drying cabinet .

The topcoats were applied to a dry layer thickness of 30 to 35 µm on the etching primer as a comparison on a neutral glass plate. The drying speed was tested immediately. After 10 days of storage at 23°C, the assessment of the relative yellowing took place, compared to the lacquer film on the glass surface. Assessment of the yellowing took place two hours after burning.

Claims (1)

Etching primer on the basis of polyvinyl acetals dissolved in organic solvents, as well as of pigments, acidic phosphorus compounds, synthetic resin and possibly additional common additives, the weight ratio between polyvinyl acetal and synthetic resin being between 4:1 and 1:4, characterized by the synthetic resin containing ethers of epoxy resins and/or esters of epoxy resins with mono- or dicarboxylic acids, where at least 80% of the epoxy groups have been reacted.