Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/04—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain a surface receptive to ink or other liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
  • B05D7/16—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies using synthetic lacquers or varnishes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2202/00—Metallic substrate
  • B05D2202/20—Metallic substrate based on light metals
  • B05D2202/25—Metallic substrate based on light metals based on Al
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/20—Chromatation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/60—Adding a layer before coating
  • B05D2350/63—Adding a layer before coating ceramic layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2401/00—Form of the coating product, e.g. solution, water dispersion, powders or the like
  • B05D2401/20—Aqueous dispersion or solution

Definitions

• the invention relates to a method for forming hydrophilic coatings on aluminum surfaces using aqueous polymer solutions or dispersions.
• the effectiveness of the heat radiation / cooling should be as high as possible.
• the radiation and cooling components are therefore designed with the largest possible surface area and the distance between them is kept extremely short. If a heat exchanger is used for cooling, this leads to condensation of air humidity on the heat exchanger surface, especially in the spaces between. Water condensed in this way forms droplets, and the more hydrophobic the surface of the ribs, the more so is. The water droplets accumulate in the interstices and prevent air from passing through to an increased extent, which ultimately leads to reduced heat exchanger performance.
• heat exchanger fans cause the droplets to splash around in the interstices of the fins, so that the drip catchers fitted under the heat exchangers cannot prevent the droplets from falling onto adjacent areas and contaminating them.
• Japanese Patent Laid-Open Sho 60-101156 (1985) relates to a chemical for forming a hydrophilic layer on aluminum containing alkali silicate and carbonyl compounds (aldehydes, esters, amides, etc.).
• Japanese Patent Laid-Open Sho 59-205596 describes a method in which organic compounds are applied using an organic solvent.
• the organic compounds are, in particular, acrylic resins, resins based on epoxy or urethane, vinyl resins, such as, for example, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, resins based on styrene, phenolic resins, fluorine resins, silicone resins, diaryl phthalate resins, polycarbonate resins, polyamide resins, alkyd resins, polyester resins , Urea resins, melamine resins, polyacetal resins and cellulose resins.
• acrylic resins resins based on epoxy or urethane
• vinyl resins such as, for example, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, resins based on styrene, phenolic resins, fluorine resins, silicone resins, diaryl phthalate resins, poly
• polyacrylamide as a chemical for the hydrophilic treatment is known from the Japanese patents Sho-60-101156 and Sho 61-8598.
• This compound can be mixed uniformly with water as long as the polyacrylamide content is low. With increasing concentration, which is caused by the drying process etc., the alkali silicate and polymer split into two phases, which often leads to non-reproducible results.
• polyacrylamide is applied to the hydrophilic inorganic film to form a hydrophilic organic layer.
• the degree of polymerization of the polyacrylamide is adjusted so that removal of the lubricating oil used for processing by means of a solvent is possible without problems and that the organic polymer layer remaining on the hydrophilic inorganic layer after degreasing fills any specks in said inorganic layer.
• a crosslinking agent composed of Zr, Ti compounds etc. can bring about a crosslinking between the polyacrylamide and the hydrophilic group, but in such a way that there is no total crosslinking of said group.
• the last layer remaining after solvent cleaning of the heat exchanger fins is an inorganic hydrophilic layer, which is achieved by applying a silicate or boehmite layer as the base layer.
• the object of the invention is to provide a process for producing hydrophilic coatings on aluminum surfaces which does not have the disadvantages of the known, in particular the aforementioned processes, leads to coatings of high hydrophilicity which, even over a long period of time, are adherent and corrosion-protecting.
• the coatings should be processable in a simple manner with coating agents, which are in particular free of organic solvents, and be able to withstand any subsequent treatments (the effects of forces and heat).
• a preferred embodiment of the invention consists in subsequently applying and drying a water glass solution on the polymer coating.
• the water-soluble crosslinking agent B can be inorganic, organic or also combined inorganic / organic in nature.
• Suitable inorganic crosslinking agents are, in particular, metal compounds which can form a complex compound with the water-soluble polymer or copolymer. Such compounds, of which those with a coordination number of more than 4 are particularly effective, can be found in Table 1.
• Cr, Ti, Al and Zr compounds those with a very high water solubility are particularly effective, for example chromic acid, Bichromic acid and its salts, di-isopropoxy-titanium-bis-acetylazetone, the reaction product of lactic acid and alkoxy-titanium compound, zirconyl nitrate, zirconyl acetate, zirconylammonium carbonate, fluorozirconic acid and its salts, aluminum sulfate etc.
• chromic acid Bichromic acid and its salts
• di-isopropoxy-titanium-bis-acetylazetone the reaction product of lactic acid and alkoxy-titanium compound
• zirconyl nitrate zirconyl acetate
• zirconylammonium carbonate zirconylammonium carbonate
• fluorozirconic acid and its salts aluminum sulfate etc.
• Suitable water-soluble organic crosslinking agents are water-soluble, neutralized polyisocyanate and / or water-soluble polymethylol, polyglycidyl, polyaziridyl compound, for example polyisocyanate neutralized with NaHSO3 (for example ELASTRON: product from DAI-ICHI KOGYO SEIYAKU Co., Ltd.), methylolmelamine, Methylol urea, methylol polyacrylamide, diglycidyl ether of polyethylene oxide, diaziridyl polyethylene oxide etc.
• NaHSO3 for example ELASTRON: product from DAI-ICHI KOGYO SEIYAKU Co., Ltd.
• Suitable combined inorganic / organic crosslinking agents are, for example, compounds of Cr, Ti, Al and Zr as inorganic water-soluble compounds and neutralized polyisocyanates, polymethylol / polyglycidyl / polyaziridyl compounds as organic water-soluble compounds.
• the amount of crosslinking agent (B) used depends on its type. It also plays a role whether the (co) polymer layer (A) serves as a base layer and mainly for corrosion protection or is provided as a single layer. In general, the amount used per 100 parts by weight of polymer or copolymer will be 1 to 400 parts by weight, preferably 5 to 200 parts by weight.
• Drying is generally carried out at 90-300 ° C, preferably 100-250 ° C.
• the polymer used should have a molecular weight of more than 5,000. If the weight is less than 5,000, and especially if the polymer has a high hydrophilicity, an increased crosslinking agent ratio is required for the purpose of water insolubility.
• (III) is represented by the general formula where M stands for one of the following formulas a) to e).
• Examples of the Mannich and Hofmann reaction for (iii) include:
• the application can be by dipping, spraying, brushing, rolling or flow
• the molecular weight should be set to less than 2,000,000, preferably 1,000,000, to avoid that the coating agent pulls strings .
• suitable values have to be determined according to the coating method used and the desired layer thickness.
• a further advantageous embodiment of the invention provides for a boehmite layer or a chemical conversion coating, such as a chromate coating, to be applied beforehand.
• a boehmite layer or a chemical conversion coating such as a chromate coating
• the addition of chromic acid, bichromic acid or their salts to the polymer solution is particularly effective.
• the aforementioned (co) polymer (A), which is crosslinked with a water-soluble crosslinking agent (B), has sufficient mixing stability so that two processes by which the aluminum surface is corroded with the aid of chromate made permanent and a (co) polymer layer is formed - can be carried out in one operation.
• these forms of treatment may have a synergistic effect by producing a particularly excellent surface quality.
• An improvement in the hydrophilic properties of the rib can also be achieved if such an organic polymer layer is applied to a silicate film. If necessary, an organic layer of high hydrophilicity can also be applied to a double layer consisting of a base layer with high corrosion resistance and a sufficiently hydrophilic, even top layer. In this way it is avoided that the formers are exposed to hydrophilic layers such as silica gel and water glass, so that associated problems of tool wear during subsequent processing are eliminated.
• Corrosion inhibitors such as Corrosion inhibitors, fillers, pigments, surfactants, foam inhibitors, leveling agents, antibacterial / antifungal agents, etc. can be added as long as they do not interfere with the results intended by this invention.
• water-soluble solvents such as alcohol, ketone and cellosolve in small amounts.
• the stability of the coating solution varies depending on the composition. In general, it is advisable to design the solution or dispersion so that when a cationic polymer is used, it is used in the neutral to acidic range and when an anionic polymer is used, it is used in the neutral to alkaline range.
• crosslinking agents are used under the conditions e.g. applied in terms of pH, which are common for them.
• water glass with an SiO2 / M2O ratio (M stands for Na, K or Li) of 2: 5 is generally used, although there are no special limits here.
• concentration of the aqueous silicate solution can be set as long as long as an effective hydrophilic surface, i.e. a simple coating is guaranteed.
• a 0.1 - 5 ⁇ silicate layer is obtained after heating / drying.
• a thickness of less than 0.1 ⁇ does not result in sufficient long-term hydrophilicity, while more than 5 ⁇ often leads to insufficient hardening (water insolubility) or cracking on the layer, which affects the performance of the heat exchanger.
• polymer i.e. a water-soluble acrylate to water glass effectively prevents cracking.
• the heating / drying conditions for silicate should be in the range of 100 - 250 ° C and 20 s - 10 min, with shorter times for higher temperatures and longer times for lower temperatures.
• the present invention makes it possible to use polymer crosslinked with water-soluble crosslinking agent for coating aluminum because the film formed in the process becomes water-insoluble.
• excellent corrosion resistance is achieved.
• a coating with the aforementioned excellent properties is particularly suitable for the treatment of heat exchanger surfaces which are made from aluminum.
• Water droplets of 1 to 2 mm in diameter were placed on a coated surface and the contact angle using a device for measuring the surface contact angle, model CA-P, manufactured by Kyowa Kaimenkagaku Co., Ltd. certainly. Both fresh layers shortly after application and those that had been immersed in sea water for a week were tested.
• test specimen was immersed in flowing water at room temperature for 8 hours and then dried at 80 ° C. for 16 hours. After repeating this cycle five times, the water contact angle was measured.
• the layer thus obtained was dried in an electric oven at 180 ° C. for 3 minutes.
• the film thickness averaged 0.5 ⁇ .
• An aqueous solution of sodium silicate No. 3 was applied to achieve an average thickness of 0.5 ⁇ in the dry state, and then dried.
• Example 3 According to the process conditions of Example 1, but with pretreatments and coating agents according to Table 2, further coatings were applied. The results are summarized in Table 3.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
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Citations (5)

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• 1986
  • 1986-12-29 JP JP61315816A patent/JP2512452B2/ja not_active Expired - Fee Related
• 1987
  • 1987-12-17 AU AU82643/87A patent/AU587671B2/en not_active Expired - Fee Related
  • 1987-12-24 DE DE19873744032 patent/DE3744032A1/de not_active Withdrawn
  • 1987-12-24 EP EP87119189A patent/EP0276476A1/fr not_active Withdrawn

Patent Citations (5)

Non-Patent Citations (1)

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