Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D13/00—Electrophoretic coating characterised by the process
  • C25D13/12—Electrophoretic coating characterised by the process characterised by the article coated
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D13/00—Electrophoretic coating characterised by the process
  • C25D13/22—Servicing or operating apparatus or multistep processes

Definitions

• the invention relates to a method for painting radiators and radiators that have been painted by this method.
• Rib radiators and plate radiators with and without convector sheets are known, for example.
• Electro-dip painting processes are often used to paint radiators.
• the radiators are passed through an aqueous electrodeposition bath, switched as an anode or cathode, and with the help of direct current, a lacquer film is then deposited electrochemically, which is then together with a e.g. is burned on by spraying or conventional dipping or without such a further layer of lacquer.
• the known methods for painting radiators are in need of improvement in many ways.
• the radiators painted according to the known processes should be resistant to yellowing, Surface quality, corrosion resistance and condensation resistance as well as alkali and chemical resistance can be further improved.
• the amount of paint required for painting radiators should be further reduced and the elaborate use of auxiliary electrodes should be restricted as much as possible.
• the problem underlying the present invention is to provide a method for painting radiators with which the disadvantages of the prior art can be overcome or reduced.
• the radiators painted with the process according to the invention have surfaces free of surface defects (e.g. runners) with a high degree of resistance to yellowing, corrosion, condensation and alkali and chemicals. Further advantages of the method according to the invention lie in the fact that only small amounts of electrodeposition paint are required to achieve the good surface properties and that the complex use of auxiliary electrodes can largely be dispensed with.
• GB-A-970 506 describes electrodeposition coating processes for coating substrates which have both "electrophoretically easily accessible” surfaces and “electrophoretically less easily accessible surfaces”.
• the substrate is subjected to an electrocoating process in a first stage and, after the deposited electrocoating film has been stoved, is subjected to a further electrocoating process in a second stage.
• Automotive body parts, such as doors, are mentioned as examples of suitable substrates. There are no references to the painting of radiators.
• the generally pretreated radiators are immersed in a first aqueous electrodeposition bath in stage A-1.
• the pretreatment of the radiators usually consists of an alkaline degreasing and subsequent iron or zinc phosphating.
• This first aqueous electrocoating bath contains at least one cationic amine-modified epoxy resin which has active hydrogen atoms and at least one aliphatic or cycloaliphatic blocked polyisocyanate which is part of the amine-modified epoxy resin and / or is present as a separate component.
• Cationic amine-modified epoxy resins containing active hydrogen atoms are known to the person skilled in the art as cathodically depositable synthetic resins (cf. for example DE-PS-27 01 002, EP-B-4090, DE-OS-35 18 770 and DE-OS-35 18 732). They can be prepared by reacting optionally modified polyepoxides (component (a)) with primary and / or secondary amines or their salts and / or salts of tertiary amines (component (b)).
• Polyepoxides are understood to mean compounds which contain two or more epoxy groups in the molecule.
• Suitable components (a) for the preparation of the cationic amine-modified epoxy resins which have active hydrogen atoms are all compounds which contain two or more epoxy groups in the molecule.
• Preferred compounds are those which contain two epoxy groups in the molecule and have a relatively low molecular weight of at most 750, preferably 400 to 500.
• compositions which can be prepared by a monofunctional starter which is carried out at 100 to 195 ° C., optionally in the presence of a catalyst, and which either has an alcoholic OH group, a phenolic OH group or carries an SH group, initiated polyaddition of a diepoxide compound and / or a mixture of diepoxide compounds, optionally together with at least one monoepoxide compound, to form an epoxy resin in which the diepoxide compound and starter are incorporated in a molar ratio of greater than 2: 1 to 10: 1 (cf. DE-OS-35 18 732).
• Polyepoxides which can be used to produce the particularly preferred (a) components and also themselves from (a) components are polyglycidyl ethers of polyphenols produced from polyphenols and epihalohydrins.
• Bisphenol A and bisphenol F can, for example, very particularly preferably be used as polyphenols.
• 4,4'-Dihydroxybenzophenone bis- (4-hydroxyphenyl) -1,1-ethane, bis- (4-hydroxyphenyl) -1,1-isobutane, bis- (4-hydroxy-tertiary-butylphenyl) - are also 2,2-propane, bis (2-hydroxynaphthyl) methane, 1,5-dihydroxynaphthalene and phenolic novolak resins are suitable.
• polyepoxides are polyglycidyl ethers of polyhydric alcohols, such as, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and bis- (4- hydroxycyclohexyl-) 2,2-propane.
• polyhydric alcohols such as, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and bis- (4- hydroxycyclohexyl-) 2,2-propane.
• Polyglycidyl esters of polycarboxylic acids e.g. Oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, dimerized linoleic acid can be used as component (a).
• Typical examples are glycidyl adipate and glycidyl phthalate.
• component (a) are hydantoin epoxides, epoxidized polybutadiene and polyepoxide compounds which are obtained by epoxidizing an olefinically unsaturated aliphatic compound.
• Modified polyepoxides are understood to mean polyepoxides in which some of the reactive groups have been reacted with a modifying compound.
• Primary and / or secondary amines or their salts and / or salts of tertiary amines can be used as component (b), the secondary amines being particularly preferred (b) components.
• the amine should preferably be a water-soluble compound.
• examples of such amines are mono- and dialkylamines, such as methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, methylbutylamine and the like.
• the like are also suitable alkanolamines, e.g. Methylethanolamine, diethanolamine u.
• Dialkylaminoalkylamines e.g. Dimethylaminoethylamine, diethylaminopropylamine, dimethylaminopropylamine and the like. suitable.
• Low molecular weight amines are used in most cases, but it is also possible to use high molecular weight monoamines.
• Polyamines with primary and secondary amino groups can be reacted with the epoxy groups in the form of their ketimines.
• the ketimines are prepared from the polyamines and ketones in a known manner.
• the amines can also contain other groups, but these should not interfere with the reaction of the amine with the epoxy group and should not lead to gelation of the reaction mixture.
• Necessary negative charges can be generated by protonization with water-soluble acids (for example boric acid, formic acid, lactic acid, preferably acetic acid) or by reacting the oxirane groups with salts of an amine.
• water-soluble acids for example boric acid, formic acid, lactic acid, preferably acetic acid
• the salt of a tertiary amine can be used as the salt of an amine.
• the amine portion of the amine acid salt is an amine which can be unsubstituted or substituted as in the case of the hydroxylamine, these substituents should not interfere with the reaction of the amine acid salt with the polyepoxide and the reaction mixture should not gel.
• Preferred amines are tertiary amines such as dimethylethanolamine, triethylamine, trimethylamine, triisopropylamine and the like. The like. Examples of other suitable amines are given in US Pat. No. 3,839,252 in column 5, line 3 to column 7, line 42.
• the electrocoating bath used in stage A-1 also contains at least one aliphatic or cycloaliphatic blocked polyisocyanate which is part of the amine-modified epoxy resin and / or is present as a separate component. If the blocked polyisocyanate is part of the amine-modified epoxy resin, then there is a self-crosslinking resin. If the blocked polyisocyanate is present as a separate component, then an externally crosslinking resin is present. It is preferred to use an electrocoating bath in stage A-1 in which the blocked polyisocyanate is used as separate component is present.
• aliphatic and / or cycloaliphatic polyisocyanates As blocked aliphatic and / or cycloaliphatic polyisocyanates, aliphatic and / or cycloaliphatic polyisocyanates are used, the isocyanate groups of which have been blocked by reaction with a blocking agent in such a way that they are not reactive towards hydroxyl and amino groups at lower temperatures, but unblock at elevated temperatures and with react the hydroxyl and / or amino groups of the amine-modified epoxy resin.
• aliphatic and / or cycloaliphatic polyisocyanates which can be used are: hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1,3- and 1,4-diisocyanate and dicyclohexylmethane-2,4 'and 4,4'diisocyanate.
• Carbodiimide groups and / or isocyanurate groups and / or biuret groups and / or urethane groups and / or urea groups containing aliphatic or cycloaliphatic polyisocyanates can also be used.
• Aliphatic or cycloaliphatic polyisocyanates containing urethane groups can be obtained, for example, by reacting some of the isocyanate groups with polyols, e.g. Trimethylolpropane, glycerol, polyester polyols and polyether polyols can be obtained. Trimerized hexamethylene diisocyanate is used as the preferred polyisocyanate. Mixtures of aliphatic or cycloaliphatic polyisocyanates can also be used.
• Blocking agents are used which, on the one hand, prevent the isocyanate groups from undergoing chemical reactions with other paint components before the baking process begins and, on the other hand, release the isocyanate groups so quickly and completely during the baking process that, if possible, all blocked isocyanate groups can react with NCO-reactive groups of the amine-modified epoxy resin .
• blocking agents are: aliphatic alcohols, such as methyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl, 3,3,5-trimethylhexyl , Decyl and lauryl alcohol; cycloaliphatic alcohols such as cyclopentanol and cyclohexanol; aromatic alkyl alcohols such as phenylcarbinol and methylphenylcarbinol; Hydroxylamines such as ethanolamine; Oximes such as methyl ethyl ketoxime, acetone oxime and cyclohexanone oxime and amines such as dibutylamine and diisopropylamine. Amines such as dibutylamine and diisopropylamine are used as preferred blocking agents.
• aliphatic alcohols such as methyl, ethyl, chloroethyl, prop
• Self-crosslinking amine-modified epoxy resins in which the blocked polyisocyanate is part of the amine-modified epoxy resin, can be produced, for example, by reacting a partially blocked polyisocyanate, which on average has one free isocyanate group per molecule, with the amine-modified epoxy resin.
• the first aqueous electrocoating bath used in stage A-1 preferably contains at least one white pigment, in particular titanium dioxide and optionally extenders, such as barium sulfate, zinc oxide, basic lead carbonate, basic lead sulfate, aluminum silicate, kaolin, silicon dioxide, magnesium silicate etc.
• the pigment content of the first aqueous electrocoating bath used in stage A-1 should preferably be between 20 to 40% by weight. The process according to the invention gives coatings with a high degree of whiteness.
• the temperature of the first electrocoat bath used in stage A-1 of the process according to the invention must be 22 to 35 ° C., preferably 24 to 28 ° C.
• the conductivity of the first electrocoat bath used in stage A-1 of the process according to the invention must be at least 1000 ⁇ S cm ⁇ 1. It should preferably be at least 1300 ⁇ S cm ⁇ 1, particularly preferably at least 1500 ⁇ S cm ⁇ 1.
• the guide values are to be measured at 20 ° C.
• the pH of the electrocoating bath used in stage A-1 of the process according to the invention must be below 7.0. It should preferably be below 6.5, particularly preferably below 6.0.
• stage A-2 of the method according to the invention the radiators are switched as cathode and in stage A-3 a voltage of 20 to 450 V is then applied. Then, in step A-4, a lacquer film is deposited on the radiators by means of direct current within 5 to 120 seconds.
• the at this stage of the Lacquer film deposited according to the method of the invention should have a dry film thickness of 1 to 20, preferably 5 to 12 ⁇ m after baking.
• the radiators in stage A-5 are removed from the first electrodeposition bath and in stage B the non-electrochemically deposited electrodeposition coating is rinsed off. It is of great importance for the quality of the coating that the electro-dip coating which is not electrochemically deposited is rinsed off as completely as possible. Deionized water is preferably used for rinsing. For economic reasons, it is advisable to rinse in stage B with ultrafiltrate and to return the rinsed, not electrochemically deposited paint residues to the electrocoating bath. In order to ensure that the radiators are rinsed as thoroughly as possible, it is preferred to carry out both a spray rinse and an immersion rinse.
• the deposited electrocoating film which has been cleaned of non-electrochemically deposited electrocoating material, is dried until it has a specific electrical resistance of at least 5 ⁇ 1010 ⁇ cm .
• the paint film can be dried at room temperature. To save time, however, it is advantageously carried out at higher temperatures, preferably at 100 to 180 ° C. Before immersing in the second electrocoating bath, the radiators should be cooled to a maximum temperature of 40 ° C.
• the radiators in stage D-1 of the process according to the invention are again placed in the electrocoating bath used in stage A-1 or in a second aqueous electrocoating bath which contains at least one active hydrogen atom-containing, cationic amine-modified epoxy resin and at least one aliphatic or cycloaliphatic blocked polyisocyanate , which is part of the amine-modified epoxy resin and / or is present as a separate component, is immersed.
• the cationic amine-modified epoxy resins described above for the first electrocoating bath and the aliphatic or cycloaliphatic blocked polyisocyanates described above for the first electrocoating bath are used in the second electrocoating bath.
• the cationic amine-modified epoxy resins and aliphatic or cycloaliphatic blocked polyisocyanates used in the first and second electrocoating baths can have the same chemical structure; but they can also have a different chemical structure.
• the second aqueous electrocoating bath preferably contains, in addition to the amine-modified epoxy resin and the blocked polyisocyanate, preferably at least one white pigment, in particular titanium dioxide and, if appropriate, extenders, such as barium sulfate, zinc oxide, basic lead carbonate, basic lead sulfate , Aluminum silicate, kaolin, silicon dioxide, magnesium silicate etc.
• the pigment content of the electrodeposition bath used in stage D-1 should preferably be between 20 to 40% by weight. The process according to the invention gives coatings with a high degree of whiteness.
• the temperature of the electrocoating bath used in stage D-1 of the process according to the invention must be 22 to 35 ° C., preferably 28 to 32 ° C.
• the conductivity of the electrodeposition bath used in stage D-1 of the process according to the invention must be at least 1000 ⁇ S cm ⁇ 1. It should preferably be at least 1300 ⁇ S cm ⁇ 1, particularly preferably at least 1500 ⁇ S cm ⁇ 1.
• the guide values are to be measured at 20 ° C.
• the pH of the electrocoating bath used in stage D-1 of the process according to the invention must be below 7.0. It should preferably be below 6.5, particularly preferably below 6.0.
• the radiators are switched as cathodes, the anode being selected such that the quotient of the active area of the anode and the area of the radiators still to be painted is greater than 0.05, preferably greater than 0, 1, particularly preferably greater than 0.25.
• stage D-3 of the method according to the invention a voltage of 50 to 500 V is applied.
• step D-4 another paint film is deposited on the radiators by means of direct current within 60 to 240 seconds. This paint film is particularly or exclusively on the areas not yet painted the radiator is deposited.
• the lacquer film deposited at this stage of the process according to the invention should have a dry film thickness of 1 to 20 ⁇ m, preferably 5 to 12 ⁇ m, after baking.
• the radiators are removed from the electrocoating bath in stage D-5 and in stage E the electrocoating material which has not been electrochemically deposited is rinsed off. It is of great importance for the quality of the coating that the electro-dip coating which is not electrochemically deposited is rinsed off as completely as possible. Deionized water is preferably used for rinsing. For economic reasons, it is advisable to rinse in stage E with ultrafiltrate and to feed the rinsed, not electrochemically deposited paint residues back into the electrocoating bath.
• the electrocoat films applied in the aforementioned steps are baked. It is also possible to overcoat the electrocoat films which have not yet been baked with a second lacquer layer which has not been applied by electrochemical deposition and then to bake the overcoated lacquer layer together with the applied electrocoat films.
• the second layer of paint can be made using a Powder coating, an aqueous coating or a coating based on organic solvents, for example by spraying, brushing, flooding or dipping. It is also possible to burn in the electrocoat films applied by the process according to the invention and only then to apply the second coat of paint and burn it in in a separate step.
• the second layer of lacquer can also be dispensed with.
• the resin has a solids content of 70.2% and a base content of 0.97 milliequivalents / gram.
• 1120 g of the resin solution prepared according to item 1. are mixed with 420 g of the solution of the blocked polyisocyanate prepared according to item 2. at room temperature with stirring.
• 2.2 g of a 50 percent by weight solution of a commercially available defoaming agent (Surfynol; commercial product from Air Chemicals) are stirred into ethylene glycol monobutyl ether and 18 g of glacial acetic acid.
• 678 g of deionized water are added in 4 portions. It is then diluted in small portions with a further 1154 g of deionized water.
• the resulting aqueous dispersion is freed from low-boiling solvents in a vacuum distillation and then diluted with deionized water to a solids content of 33% by weight.
• 2200 parts by weight of the dispersion prepared according to item 3 are mixed with 810 parts by weight of the pigment paste prepared according to item 5 and made up to 5000 parts by weight with deionized water.
• the radiator is degreased and subjected to the usual phosphating.
• the heater pretreated in this way is then immersed in an electrocoating bath which contains the electrocoating material prepared according to item 6, a temperature of 26 ° C, a conductivity of 1300 ⁇ S cm ⁇ 1 (measured at 20 ° C) and a pH of 6 , 0 has.
• the radiator is switched as a cathode.
• a DC voltage of 200 V is applied and maintained for 30 seconds.
• the radiator is removed from the electrocoating bath and rinsed thoroughly with deionized water.
• the radiator is then dried for 30 minutes at an object temperature of 110 ° C.
• the deposited lacquer film has a specific electrical resistance which is greater than 10 12 ⁇ cm.
• Electrodeposition paint produced contains a temperature of 30 ° C, a conductivity of 1300 ⁇ S cm ⁇ 1 (measured at 20 ° C) and a pH of 6.0.
• the radiator is switched as a cathode.
• the quotient of the active area of the anode sheets used and the area to be painted is 0.17.
• a DC voltage of 380 V is applied and maintained for 180 seconds.
• the radiator is removed from the electrocoating bath and rinsed thoroughly with deionized water.
• the deposited paint films are then baked for 20 minutes at an object temperature of 170 ° C.
• the paint film formed on the radiator in the manner described above is free from surface defects, is resistant to acids and alkalis, has a Berger whiteness of 75%, a resistance to salt spray test according to DIN 50021 of 480 hours and a resistance to condensation water test DIN 50017 from 1000 hours.
• the radiator painted by the process according to the invention is further characterized in that the minimum dry film thickness on the entire radiator surface is 5 ⁇ m.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Paints Or Removers (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Resistance Heating (AREA)
• Forging (AREA)

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Citations (2)

• 1991
  • 1991-11-02 DE DE4136237A patent/DE4136237A1/de not_active Withdrawn
• 1992
  • 1992-10-28 AT AT92118393T patent/ATE127170T1/de not_active IP Right Cessation
  • 1992-10-28 ES ES92118393T patent/ES2079766T3/es not_active Expired - Lifetime
  • 1992-10-28 DK DK92118393.5T patent/DK0540996T3/da active
  • 1992-10-28 EP EP92118393A patent/EP0540996B1/fr not_active Expired - Lifetime
  • 1992-10-28 DE DE59203462T patent/DE59203462D1/de not_active Expired - Fee Related

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