EP0306801B1 - Use of an aquous suspension in air jet blasting - Google Patents

Abstract

The addition of aqueous dispersions based on certain organic binders to the carrier air stream in air jet blasting leads to good binding of the resulting dusts, permits good disposal and provides simultaneously highly effective provisional corrosion protection.

Description

The invention relates to the use of aqueous dispersions based on a carboxyl group-containing binder, the carboxyl groups of which are at least partially neutralized, for compressed air blasting.

In building protection, it is regularly necessary to remove rust or the remains of an old coating from the substrate - usually steel - before applying a coating. A proven method for this is the compressed air blasting known as "sandblasting". Because of the dust development that occurs, which is not always physiologically harmless, particularly due to the composition of the old coatings (think, for example, red lead or zinc chromate), it was considered early on to introduce a liquid into the air stream containing the blasting agent, which together with this is blown against the surface to be treated and thus binds the dusts at least temporarily (US Pat. No. 2,405,854, 2,440,643).

This process, referred to as "wet blasting", has been improved by introducing the liquid in the form of a mist into the air flow so that the necessary amount of liquid could be reduced ("wet blasting", DE-OS 2 724 318).

A further development of this method is that the liquid is introduced as foam into the air flow and thus the effective surface of the liquid to be introduced is greatly increased (DE-OS 3 415 174).

In the processes described, some have already considered corrosion protection agents such as Zinc or lead in the form of metal dust or chemical compounds to be introduced into the air flow. So far, however, there has been a lack of a method that could take all of the wishes into account.

The object of the invention was therefore to find additives for compressed air jets which should combine a good binding of the resulting dusts with good disposal options with a simultaneously highly effective provisional corrosion protection.

Surprisingly, it has been found that organic binders containing carboxyl groups, the carboxyl groups of which have been at least partially neutralized with certain amines, solve the problem described.

The invention relates to the use of an aqueous dispersion based on organic binder, the carboxyl groups (before neutralization) correspond to an acid number of 40 to 70 and at least 60, preferably at least 70%, in particular at least 80% by a tertiary amine formula



NR¹R²R³,



wherein
R¹, R², R³ independently of one another C₁-C₆-alkyl, C₆-C₁₂-aryl, hydroxy-C₂-C₃-alkyl
mean,
are neutralized
for compressed air blasting.

The aqueous dispersions to be used according to the invention, in addition to the primarily desired binding of the dust by the permanent dust binding, permit unproblematic disposal, offer surprisingly good temporary corrosion protection and are compatible with subsequent corrosion protection coatings.

Suitable organic binders for the dispersions to be used according to the invention are preferably (1) oil-free polyesters, (2) alkyd resins, (3) acrylate resins and (4) polyurethanes.

Oil-free polyesters (1) and alkyd resins (2) are understood to be polycondensates of the type produced from alcohols and carboxylic acids by polycondensation by known processes, of the type described, for example, in Römpp's Chemielexikon, Vol. 1, p. 202, Frankh'sche Verlagbuchhandlung, Stuttgart, 1966 or described in DH Solomon, The Chemistry of Organic Filmformers, pp. 75-101, John Wiley & Sons Inc., New York, 1967.

In this application, “alkyd resins” are understood to mean fatty acid- or oil-modified polyesters.

Preferred acid components for the synthesis of the polyesters (1) or alkyd resins (2) are aliphatic, cycloaliphatic saturated or unsaturated and / or aromatic polybasic carboxylic acids, preferably di-, tri- and tetracarboxylic acids, with 2 to 14, preferably 4 to 12 C- Atoms per molecule or their esterifiable derivatives (for example anhydrides or esters), for example phthalic anhydride, isophthalic acid, tetrahydro- and hexahydrophthalic anhydride, endomethylene tetrahydrophthalic acid, succinic acid, glutaric acid, trimellitic acid, trimellitic acid, trimellitic acid Phthalic anhydride is the most common acid component.

Preferred alcohols for the synthesis of the polyesters (1) or alkyd resins (2) are aliphatic, cycloaliphatic and / or araliphatic alcohols with 1-15, preferably 2-6 C atoms, and 1-6, preferably 1-4, of non-aromatic C-bonded OH groups per molecule, e.g. Glycols such as ethylene glycol, 1,2-propanediol and -1,3, 1,2-butanediol, 1,3 and -1,4, 1,3-2-ethylpropane, 1,3-2-ethylhexane, neopentyl glycol, 2,2-trimethylpentanediol-1,3, hexanediol-1,6, cyclohexanediol-1,2 and -1,4, 1,2- and 1,4-bis (hydroxymethyl) cyclohexane, adipic acid bis (ethylene glycol ester) ); Ether alcohols such as di- and triethylene glycol, dipropylene glycol; Dimethylolpropionic acid, oxalkylated bisphenols with 2 C₂-C₃-oxalkyl groups per molecule, perhydrogenated bisphenols; 1,2-butanetriol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, trimethylolhexane, glycerol, pentaerythritol, dipentaerythritol, mannitol and sorbitol. The most common alcohols are glycerin, trimethylolpropane, neopentyl glycol and pentaerythritol.

Monocarboxylic acids preferred for the preparation of the polyesters (1) or alkyd resins (2) are aliphatic, cycloaliphatic saturated and unsaturated and / or aromatic monocarboxylic acids with 3-24 carbon atoms per molecule, such as benzoic acid, p-tert-butylbenzoic acid, tolylic acid, hexahydrobenzoic acid , Abietic acid and lactic acid.

The alkyd resins (2) or polyester (1) can also monohydric alcohols with 1 to 8 carbon atoms such as methanol, propanol, cyclohexanol, 2-ethylhexanol, benzyl alcohol in amounts up to 15 wt .-%, based on alkyd resin (2) or polyester (1), condensed in. It is also possible to replace up to 25% of the ester bonds with urethane bonds.

Polyisocyanates, preferably diisocyanates, are suitable for introducing these urethane bonds. Preferred diisocyanates for this purpose are aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic diisocyanates, as described, for example, by W. Siefken in Justus Liebigs Annalen der Chemie 562 , pages 75-136, for example ethylene diisocyanate, 1,4-tetramethylene diisocyanate , 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate and any mixtures of these isomers, 1-isocyanato-3,3,5- trimethyl-5-isocyanatomethyl-cyclohexane (DE-AS 1 202 785), 2,4- and 2,6-hexahydrotoluylene diisocyanate and any mixtures of these isomers, hexahydro-1,3- and / or -1,4-phenylene diisocyanate, Perhydro-1,3'- and / or -4,4'-diphenylmethane diisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate and any mixture of these isomers, diphenylmethane-2 , 4'- and / or -4,4'-diisocyanate, naphthylene-1,5-diisocyanate.

The length of the oil in the alkyd resins (2), calculated as triglyceride and based on the alkyd resin (2), is generally 5 to 50, preferably 20 to 40,% by weight. The drying or non-drying fatty acids, which generally contain 6 to 24 carbon atoms, can be used either as such or in the form of their glycerol esters (triglycerides).

Vegetable and animal oils, fats or fatty acids, such as e.g. Coconut, peanut, castor, wood, olive, soybean, linseed, cottonseed oil, safflower oil or oil fatty acids, dehydrated castor oil or fatty acid, monounsaturated fatty acids, lard, tallow and tears, tall oil fatty acid and synthetic fatty acids, which can be made from natural unsaturated oils or fatty acids by conjugation or isomerization. Preferred saturated fatty acids are e.g. Coconut oil fatty acids, 2-ethylhexanoic acid, isononanoic acid (3,4,4-trimethylhexanoic acid) as well as palmitic and stearic acid.

The number average molecular weight of the polyester (1) or alkyd resin (2) is 2000 - 10,000 (up to molecular weights of 5000 determined by vapor pressure osmometry in dioxane and acetone, whereby the lower value is considered correct if the values differ; for molecular weights over 5000 membrane osmometric determined in acetone).

worin

R¹

für Wasserstoff oder Methyl,

R²

für Wasserstoff, Alkyl,

R³

für Alkyl oder Cycloalkyl, wie Methyl, Ethyl, n-Propyl, Isopropyl, n-Butyl, Isobutyl, Cyclohexyl stehen;

N,N-dialkylsubstiutierte Acryl- und Methacrylsäureamide;
primäre, sekundäre und tertiäre Aminoalkylester der Acrylsäure und Methacrylsäure.Preferred acrylate resins (3) are copolymers with number-average molecular weights M _n from 600 to 5000, where at least 2 of the following monomers can be selected as starting products:
Acrylic acid and methacrylic acid;
Acrylic acid and methacrylic acid alkyl esters with 1-18, preferably 1-8 C atoms in the alcohol component, such as, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate and the corresponding methacrylic acid esters;
Acrylic and methacrylic acid cyclohexyl esters; Esters of acrylic acid and methacrylic acid with dihydric, saturated, aliphatic alcohols with 2-4 C atoms, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate and the corresponding methacrylic acid esters;
cross-linking acrylic and methacrylic compounds, such as, for example, acrylic and / or methacrylic acid allyl esters, methylenebisacrylamide, methylenebismethacrylamide, triacryloyl-perhydro-s-triazine, bisacrylates or bismethacrylates of glycols or polyglycols with 2-20 C atoms, such as ethylene glycol (meth -) acrylate, propylene glycol di (meth) acrylate, butylene glycol 1,4-di (meth) acrylate, tetraethylene glycol di (meth) acrylate, tris (meth) acrylates of triethanolamine and trimethylolethane, propane, hexane and glycerol;
Acrylic and methacrylic acid vinyl esters;
Acrylonitrile and methacrylonitrile;
Acrylamide and methacrylamide;
N-methylol ether of acyl acid and methacrylic acid amide of the formula

wherein

R¹

for hydrogen or methyl,

R²

for hydrogen, alkyl,

R³

represent alkyl or cycloalkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, cyclohexyl;

N, N-dialkyl-substituted acrylic and methacrylic acid amides;
primary, secondary and tertiary aminoalkyl esters of acrylic acid and methacrylic acid.

• I) Polyisocyanaten mit durchschnittlich mindestens 1,8, vorzugsweise mindestens zwei Isocyanatgruppen pro Molekül und
• II) zur Reaktion mit Isocyanatgruppen befähigte H-Atome enthaltenden Polymeren.

Preferred polyurethanes (4) are reaction products

• I) polyisocyanates with an average of at least 1.8, preferably at least two isocyanate groups per molecule and
• II) polymers capable of reacting with isocyanate groups containing H atoms.

• (i) beliebige organische Polyisocyanate, vorzugsweise Diisocyanate der Formel
  
  
  
          Q(NCO)₂
  
  
  
  wobei Q einen aliphatischen Kohlenwasserstoffrest mit 4 bis 12 Kohlenstoffatomen, einen cycloaliphatischen Kohlenwasserstoffrest mit 6 bis 15 Kohlenstoffatomen, einen aromatischen Kohlenwasserstoffrest mit 6 bis 15 Kohlenstoffatomen oder einen araliphatischen Kohlenwasserstoffrest mit 7 bis 15 Kohlenstoffatomen bedeutet.

Starting materials for the production of component I are:

• (i) any organic polyisocyanates, preferably diisocyanates of the formula
  
  
  
  Q (NCO) ₂
  
  
  
  wherein Q represents an aliphatic hydrocarbon group having 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon group having 6 to 15 carbon atoms, an aromatic hydrocarbon group having 6 to 15 carbon atoms or an araliphatic hydrocarbon group having 7 to 15 carbon atoms.

Examples of such preferred diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate ("isophorone diisocyanate"), 4,4'-diisocyanato-dicyclohexylmethane, 4,4'-diisocyanate dicyclohexylpropane- (2,2), 1,4-diisocyanatobenzene, 2,4- and 2,6-diisocyanatotoluene or mixtures of these isomers, 4,4'- or 2,4'-diisocyanatodiphenylmethane, 4,4'-diisocyanato-diphenylpropane - (2,2), p-xylylene diisocyanate and α, α, α ', α'-tetramethyl-m- or -p-xylylene diisocyanate and mixtures containing these compounds.

It is, of course, also possible to use the polyfunctional polyisocyanates known per se in polyurethane chemistry or else modified polyisocyanates containing, for example, carbodiimide groups, allophanate groups, isocyanurate groups, urethane groups and / or biuret groups. Examples of such higher-functionality polyisocyanates are tris (6-isocyanatohexyl) biuret, optionally in a mixture with its higher homologues, tris (6-isocyanatohexyl) isocyanurate, optionally in a mixture with its higher homologues, as described, for example, in DE-OS 28 39 133 is accessible by trimerizing hexamethylene diisocyanate, and further by trimerizing aliphatic and / or aromatic diisocyanates, such as. B. "Isophorone diisocyanate", diisocyanatotoluene and hexamethylene diisocyanate available, isocyanurate group-containing polyisocyanates as they belong to the known prior art. Also very useful polyisocyanates are the polyisocyanates known per se, such as those obtained by reacting excess amounts of 2,4-diisocyanatotoluene or "isophorone diisocyanate" with simple polyhydric alcohols in the molecular weight range 62 to 300, in particular with trimethylolpropane, and subsequent distillatives Removal of the unreacted excess diisocyanate can be obtained.

• (ii) Polyether- und/oder Polyesterpolyole der in der Polyurethanchemie an sich bekannten Art, vorzugsweise Polyether- und Polyesterdiole mit Molekulargewichten von 300 bis 2.000. Die in Frage kommenden Hydroxylgruppen aufweisenden Polyether werden z. B. durch Polyaddition von cyclischen Ethern wie vorzugsweise Propylenoxid oder auch Butylenoxid, Tetrahydrofuran, Styroloxid und/oder Epichlorhydrin mit sich selbst, z. B. in Gegenwart von Bortrifluorid, oder durch Anlagerung dieser Verbindungen, gegebenenfalls im Gemisch oder nacheinander, an Startkomponenten mit reaktionsfähigen Wasserstoffatomen wie Alkohole und Amine, z. B. Wasser, Ethylenglykol, Propylenglykol-(1,3) oder -(1,2), Bisphenol-A oder Anilin, hergestellt.

If monofunctional polyisocyanates are used, their amount should preferably be such that the resulting minimum blocked functionality of the resulting blocked polyurethane prepolymers is not undercut.

• (ii) polyether and / or polyester polyols of the type known per se in polyurethane chemistry, preferably polyether and polyester diols with molecular weights of 300 to 2,000. The hydroxyl-containing polyethers are z. B. by polyaddition of cyclic ethers such as preferably propylene oxide or butylene oxide, tetrahydrofuran, styrene oxide and / or epichlorohydrin with itself, for. B. in the presence of boron trifluoride, or by the addition of these compounds, optionally in a mixture or in succession, to starting components with reactive hydrogen atoms such as alcohols and amines, for. B. water, ethylene glycol, propylene glycol (1,3) or - (1,2), bisphenol-A or aniline.

The hydroxyl-containing polyesters are z. B. Reaction products of preferably polyhydric, particularly preferably dihydric and optionally additionally trihydric alcohols with preferably polybasic, particularly preferably dibasic carboxylic acids. Instead of the free carboxylic acids, the corresponding carboxylic acid anhydrides or corresponding carboxylic acid esters of lower alcohols can also be used to prepare the polyesters.

The alcohols to be used as the polyester construction component are e.g. B. ethylene glycol, propylene glycol (1,2) and - (1,3), butanediol (1,4), hexanediol (1,6), neopentyl glycol, octanediol (1,8), 2-ethyl-hexanediol - (1,3), 1,4-bishydroxymethylcyclohexane, diethylene glycol, dipropylene glycol, trimethylolpropane, glycerin and pentaerythritol.

• (iii) Gegebenenfalls niedermolekulare Polyole mit Molekulargewichten von 62 bis 300. Beispiele für solche erfindungsgemäß geeigneten Polyole sind Ethandiol, Propandiol-(1,2) und -(1,3), Butandiol-(1,4) und -(1,3), Pentandiole, Hexandiole, Octandiole wie z. B. 2-Ethylhexandiol-(1,3), Trimethylolpropan, Glycerin und Pentaerythrit.

Carboxylic acids to be used as polyester components are e.g. B. adipic acid, succinic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid, fumaric acid, saturated and unsaturated fatty acids such as. B. stearic acid, oleic acid, ricinoleic acid, linoleic acid, ricinic acid, linolenic acid, elaostearic acid and from natural oils, such as. B. linseed oil, soybean oil, peanut oil, safflower oil, castor oil or wood oil, obtained fatty acid mixtures.

• (iii) If appropriate, low molecular weight polyols with molecular weights from 62 to 300. Examples of such polyols suitable according to the invention are ethanediol, propanediol- (1,2) and - (1,3), butanediol- (1,4) and - (1,3 ), Pentanediols, hexanediols, octanediols such as B. 2-ethylhexanediol- (1,3), trimethylolpropane, glycerol and pentaerythritol.

• (iv) Gegenüber Isocyanaten monofunktionelle Verbindungen, die sich zur reversiblen Blockierung von Isocyanatgruppen eignen und wie sie z. B. bei Z. W. Wicks, Progress in Organic Coatings 9, 3-28 (1981) beschrieben sind. Beispiele solcher zur Herstellung der Komponente (I) der Polyurethane (4) geeigneten Blockierungsmittel sind Lactame wie z. B. Caprolactam, Oxime wie Acetonoxim, Methylethylketonoxim und Cyclohexanonoxim, C-H-acide Verbindungen wie Malonsäureester, Acetessigsäureester und Acetylaceton, Alkohole wie die einfachen Monoalkohole mit 1 bis 4 C-Atomen, 2-Ethylhexanol, Ethylenglykolmonoethylether und Diethylenglykolmonomethylether, Phenole wie Phenol, Kresol und Xylenol sowie heterocyclische Verbindungen wie Triazole, Imidazoline, Imidazole und Tetrahydropyridine.

Representatives of the polyisocyanate and hydroxyl compounds to be used for the preparation of the binders (4) are, for. B. High Polymers, Vol. XVI, "Polyurethane Chemistry and Technology" by Saunders-Frisch, Interscience Publishers, New York, London, Volume I, 1962, pp. 32-42 and pp. 44-54 and Band II, 1964, pp. 5-6 and 198-199, as well as in the Kunststoff-Handbuch , Volume VII, edited by Vieweg-Höchtlen, Carl Hanser Verlag, Munich, 1966, z. B. on pp. 54-71.

• (iv) Compared to isocyanates monofunctional compounds which are suitable for the reversible blocking of isocyanate groups and how they z. B. at ZW Wicks, Progress in Organic Coatings 9 , 3-28 (1981). Examples of such blocking agents suitable for the production of component (I) of the polyurethanes (4) are lactams such as, for. B. caprolactam, oximes such as acetone oxime, methyl ethyl ketone oxime and cyclohexanone oxime, CH-acidic compounds such as malonic esters, acetoacetic acid esters and acetylacetone, alcohols such as the simple monoalcohols with 1 to 4 carbon atoms, 2-ethylhexanol, ethylene glycol monoethyl ether and diethylene glycol and phenol monomethyl ether, phenols Xylenol and heterocyclic compounds such as triazoles, imidazolines, imidazoles and tetrahydropyridines.

The blocking agents can be used alone or as mixtures. Preferred blocking agents are ε-caprolactam, butanone oxime and diethyl malonate.

The polyurethane prepolymers (component I) suitable as polyisocyanates I can be prepared by customary methods be prepared in accordance with the prior art, for example by reacting polyisocyanates (i) with higher molecular weight polyols (ii) and low molecular weight polyols (iii), the molar ratio of the isocyanate groups of the polyisocyanate (i) to the hydroxyl groups of the polyols (ii) and ( iii) can be from 1.5 to 3.0. The resulting polyurethane prepolymers with free isocyanate groups are then reversibly blocked with suitable monofunctional compounds (iv) to block the isocyanate groups. The structure of polyurethane prepolymers (I) is described, for example, in German Pat. No. 1,644,813.

Component I comprises both reaction products of the polyisocyanates (I) and blocking agents (iv) and blocked polyisocyanate prepolymers based on the above-mentioned compounds (i) and (ii) and / or (iii).

The polymers (component II) containing H atoms which are reactive with isocyanate groups are polyester or polyether polyols, polyhydric low molecular weight alcohols, polyamines, polyepoxypolyols, polyhydroxy acrylates or any mixtures of the products mentioned.

The polyester polyols and polyether polyols are compounds of the type known per se in polyurethane chemistry with number average molecular weights M _n from 300 to 10,000, preferably 300 to 5,000. they are preferably formed from the structural components (ii) of the polyurethane prepolymers (I) described above. The low molecular weight alcohols are polyalcohols of the known type with at least 2 hydroxyl groups per molecule and molecular weights between 62 and 300.

The polyamines in question are preferably di- or polyfunctional aliphatic or cycloaliphatic amines such as 1,2-diaminoethane, tetramethylene diamine, hexamethylene diamine, dodecamethylene diamine, 1,4-diaminocyclohexane, 1,4-bis-aminomethyl-cyclohexane, "isophorone" diamine, 4,4'-diamino-dicyclohexylmethane, 2,2-bis (4-amino-cyclohexyl) propane or m- or p-xylylenediamine. 4,4'-Diamino-3,3'-dimethyl-dicyclohexylmethane is particularly preferred.

Components (I) and (II) are preferably used in amounts such that the molar ratio of blocked isocyanate groups to hydroxyl and / or amino groups is 0.5 to 2, preferably 0.8 to 1.5.

In order to obtain the desired carboxyl groups, dimethylolpropionic acid is preferably used in the preparation of the polyurethanes (4).

The organic binders suitable for the aqueous dispersions to be used according to the invention are preferably selected so that they are at least temporarily sticky. In other words, you should Have the property of binding them to their surface under practical conditions when they collide with the abrasive used as "sand" and the particle blasted off the substrate.

Ideally, a droplet of binder would be completely surrounded by dust particles.

In principle, it is then irrelevant whether the binder remains sticky or dries while still holding the dust particles. It is of course to be taken into account that the dispersion droplets in the jet lose at least part of the water during the flight to the substrate, but under certain circumstances also completely lose the water, and the desired stickiness is not only present when it is introduced into the jet, but rather when it hits the substrate should. Good results are usually obtained when a layer of a wet film thickness of 100 μm applied from the aqueous dispersion to a glass plate when stored at 25 ° C. after a maximum of 2 hours to unlimited, preferably after 2 hours to 1 week, sand dry in the sense of DIN 53 150, T1 (= part 1).

Tertiary aines preferred for neutralizing the carboxyl groups of the organic binders include, for example, triethyl, tripropyl and tributylamine, methyldiethanolamine, dimethylethanolamine, triethanolamine, methyldipropanolamine, dimethylpropanolamine, tripropanolamine, N, N-dimethylaniline. Tripropylamine and dimethylethanolamine are particularly preferred amines.

The water content of the aqueous dispersions to be used according to the invention is 60 to 95, preferably 85 to 93,% by weight, based on the aqueous dispersion.

The dispersions to be used according to the invention are preferably introduced in countercurrent to the blasting material, so that an optimal distribution is ensured and they reach the surface to be blasted with the blasting material in the finest distribution.

Application example 1. Preparation of the test plates

1. Sandstrahlen =

Strahlen mit trockener Hochofenschlacke

2. Feuchtstrahlen =

Strahlen mit wasserbefeuchteter Hochofenschlacke

3. Dispersionsstrahlen =

Strahlen mit Hochofenschlacke, die mit einer 7 gew.-%-igen wäßrigen Dispersion befeuchtet ist.

Steel plates used in steel construction, with the dimensions 1000x1000x4 mm, were cleaned under practical conditions in a vertical position using a variety of processes using a metallic blank - degree of purity Sa 2 1/2 according to DIN 55 928.

1. Sandblasting =

Blasting with dry blast furnace slag

2. Wet blasting =

Blasting with blast furnace slag moistened with water

3. Dispersion blasting

Blasting with blast furnace slag, which is moistened with a 7 wt .-% aqueous dispersion.

The steel plates were then cut to the size required for the respective corrosion protection tests.
Salt spray test}
Condensation test} 190 x 106 mm
Salt dissolving station 330 x 165 mm.

2. Aqueous dispersion for dispersion blasting

256 g of precondensate from 0.077 mol of soybean oil fatty acid, 0.43 mol of trimethylolpropane, 0.87 mol of 1,6-hexanediol, 0.5 mol of adipic acid and 0.5 mol of isophthalic acid are mixed with 21.7 g of dimethylolpropionic acid, 72 g of isophorone diisocyanate, 52.5 g N-methylpyrrolidone, 10.3 g dimethylethanolamine and water processed to an aqueous dispersion with a solids content of 7 wt .-%.

During the blasting process, the resulting dust, consisting of rust and old coating, was irreversibly bound together with the blasting slag. The material could be swept up and removed with the broom without raising dust.

3. Coating the test panels with paint

The test panels were coated according to the following criteria:

The subsequent coatings were applied every 24 hours. The paints were applied in such a way that the behavior of the coatings on one, two and three layers can be assessed. The paints were processed by spray application.

4. Painting system

A tried and tested 3-layer structure based on polyurethane resin was used Painting structure Paint system Layer thickness (µm) Primer 1K-PUR / zinc (RR 2742/1) about 80 1. Top coating 1K-PUR / iron mica (RR 2760/28) approx. 100 2. Top coating 2K-PUR / unipigmented (RR 2383 / A) about 70

5. Corrosion protection test

• Salzsprühnebeltest, DIN 53 167
• Kondenswassertest, DIN 50 017/KK
• Lagerung an der Salzlösestation

festgelegt. Die Salzlösestation ist Betriebsteil der Produktionsanlage zur Chlor-Alkali-Elektrolyse mit, auf die Korrosion von Stahl bezogener, sehr aggressiver Atmosphäre. Die Exposition der Platten in salzhaltiger, feuchter Luft ermöglicht, das Verhalten von Anstrichen unter verschärften Bedingungen in der Praxis zu prüfen. Sandstrahlen Feuchtstrahlen Dispersionsstrahlen Dispersionsstrahlen + abwaschen Salzsprühnebeltest nach 42 Tagen Primer B5/1-2 B5/1-2 B5/1-2 B5/1-2 Primer/1. Deckbesch. B3/1-2 B1/1-2 B1/1-2 B3/1-2 Primer/1. Deckbesch./2. Deckbesch. Wd 3 Wd 4, B1/1-2 Wd 0 Wd 7 Flächenrost in Grundierung 5 4 1 5 Kondenswassertest nach 42 Tagen o.B. Rostdurchbrüche in Grundierung o.B. Rostdurchbrüche in Grundierung Primer o.B. o.B. o.B. B1/1 Primer/1. Deckbesch. o.B. o.B. o.B. Ri 0,5 Primer/1. Deckbesch./2. Deckbesch. o.B. o.B. o.B. B2/1 Salzlösestation nach 6 Monaten (mit Schnitt nach DIN 53 167) Primer Wd 4 Wd 3 Wd 1 Wd 4 Primer/1. Deckbesch. Wd 3 o.B. o.B. Wd 2 Primer/1. Deckbesch./2. Deckbesch. Wd 5 Wd 3 Wd 2 Wd 5 o.B. = ohne Befund As test criteria were

• Salt spray test, DIN 53 167
• Condensed water test, DIN 50 017 / KK
• Storage at the salt dissolving station

fixed. The salt dissolving station is part of the production plant for chlor-alkali electrolysis with a very aggressive atmosphere related to the corrosion of steel. The exposure of the plates in salty, humid air makes it possible to test the behavior of paints under harsher conditions in practice. Sandblasting Wet blasting Dispersion rays Dispersion rays + wash off Salt spray test after 42 days Primer B5 / 1-2 B5 / 1-2 B5 / 1-2 B5 / 1-2 Primer / 1. Cover coat B3 / 1-2 B1 / 1-2 B1 / 1-2 B3 / 1-2 Primer / 1. Deck coat. Cover coat Wd 3 Wd 4, B1 / 1-2 Wd 0 Wd 7 Surface rust in primer 5 4th 1 5 Condensation test after 42 days if Rust breakthroughs in the primer if Rust breakthroughs in the primer Primer if if if B1 / 1 Primer / 1. Cover coat if if if Ri 0.5 Primer / 1. Deck coat. Cover coat if if if B2 / 1 Salt dissolving station after 6 months (with cut according to DIN 53 167) Primer Wd 4 Wd 3 Wd 1 Wd 4 Primer / 1. Cover coat Wd 3 if if Wd 2 Primer / 1. Deck coat. Cover coat Wd 5 Wd 3 Wd 2 Wd 5 oB = without finding

The designation for the formation of bubbles is composed of "B" for "bubbles", a number as a measure for the area fraction of the bubbles (5 = 100%, 3 = 60%) and the average bubble diameter in millimeters.

"Wd" indicates the infiltration by rust in millimeters.

The table above shows that the invention leads to at least the same coating quality as the prior art (the advantage being the problem-free removal of rust, old coating and blasting agent). A comparison of the last two columns in the table shows the corrosion protection surprisingly obtained by the binder used.

Claims (4)

1. The use of an aqueous dispersion based on organic binder of which at least 60% of the carboxyl groups are neutralized by a tertiary amine corresponding to the formula
   
   
   
           NR¹R²R³,
   
   
   
   wherein
   R¹, R² and R³ independently of one another represent c₁₋₆ alkyl, C₆₋₁₂aryl, hydroxy-C₂₋₃-alkyl,
   the carboxyl groups having an acid value (before neutralization) of 40 to 70,
   for air jet blasting.
2. The use claimed in claim 1, characterized in that at least 70% of the carboxyl groups are neutralized.
3. The use claimed in claim 1, characterized in that at least 80% of the carboxyl groups are neutralized.
4. The use claimed in claims 1 to 3, characterized in that the tertiary amine is selected from the group consisting of tripropylamine and dimethyl ethanolamine.