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
  • C25D13/22—Servicing or operating apparatus or multistep processes

Definitions

• the invention relates to a method for deforming metallic substrates (objects) which have been coated by cathodic electrocoating and subsequent baking.
• Electrocoating is a known and often described process (EP-A 4090, US-A 392253, EP-B 66 859). It is used to evenly coat different metal surfaces and to protect them against corrosion. Additional successive layers can be applied to this primer.
• the general procedure is that the electrically conductive parts are immersed in an aqueous electrodeposition bath, switched as cathode or anode, and there the coating is coagulated by the flowing direct current on the substrate surface.
• An advantage of the method is that in the course of coating hollow bodies on the outside, the electrical resistance is increased and, increasingly, surfaces that are difficult to access, e.g. Internal parts or cavities can be coated with only small access openings. The material adhering to the surface is then melted physically by heating and optionally chemically crosslinked and gives a homogeneous, smooth, resistant surface.
• An advantage of the electrocoating process is that even areas of the surface that are difficult to reach are coated. Good corrosion protection can also be achieved at these points will.
• By varying different deposition parameters it is possible to promote the coating of cavities and edges. Usually no further major mechanical deformations are carried out on these metallic substrates after the electrocoating. If mechanical stresses are nevertheless applied to the substrate, it cannot be ruled out that cracks and flaking will occur on the coating agent. This significantly reduces corrosion protection.
• the mechanically stressed parts often form folds and cavities that are particularly susceptible to corrosion.
• Another method is to coat the metallic substrate with an anodic electrocoat. After crosslinking, these coatings can still be subjected to such mechanical loads that even this mechanical deformation does not damage the film surface.
• these anodic electrocoat coatings have the disadvantage that they are inferior to the cathodic electrocoat coatings in terms of corrosion protection.
• the wrap, i.e. coating cavities that are difficult to access is significantly worse than with cathodic electrocoating. That is why cathodic electrocoating has gained importance today.
• the disadvantages described above occur precisely when deforming cathodically electrocoated substrates.
• the object of the invention was therefore to provide a method for the mechanical deformation of cathodically electro-coated metal objects, in which the lacquer coatings are not damaged, cracks are avoided, and the cathodically deposited and baked electrodeposition paint achieved good corrosion protection is maintained.
• This object is surprisingly achieved by a method of the generic term mentioned at the outset, which is characterized in that the surface of the metallic substrate is heated to a temperature which is higher than 30 ° C. below the glass transition temperature and preferably higher than 20 ° C. below the glass transition temperature of the burned-in lacquers, after which the deformation takes place in the heated state.
• the upper limit of the heating temperature is not critical. Of course, it is below the decomposition temperature of the baked paint.
• cathodically deposited electrocoat coatings can also be deformed mechanically after baking or crosslinking if they are heated as described above. Therefore it is possible to use metallic substrates, e.g. Steel, aluminum or other metals to be provided with good corrosion protection and then to deform them mechanically without damaging the film surface.
• substrates For example, steel, aluminum, magnesium or alloys thereof are possible as substrates.
• the substrates can be present as objects of various shapes, for example as sheets.
• the deformation can take place in various ways, for example by slowly pressing in or pressing in, in particular small-area pressing in, for example of thorns or stamps.
• a particularly preferred example of mechanical deformation is the launching of metal parts. Two different sheets are put together and pressed against each other over a small area. As a result, the sheets are clamped together.
• the indentation area is generally about 0.1 to 1 cm2 and the indentation depth is 1 to 5 mm, depending on the substrate and its thickness. So far it has not been possible by cathodic electrodeposition to launch corrosion-protected substrates without regularly detecting cracks and flaking at and around the impression point. This is only made possible by the heating according to the invention.
• Another example of mechanical deformation is the compression of metal pipes, e.g. have a diameter of 0.5 cm and are pressed together at certain points. Damage to the paint surface usually occurs at the edges of these surfaces.
• the deformable substrates according to the invention can be coated with customary cathodically depositable lacquers or coating agents.
• the usual cathodically depositable electrodeposition coating compositions consist, for example, of customary basic base resins, optionally mixed with other resins or crosslinking agents, of inorganic and / or organic pigments or fillers, neutralizing agents and other additives which are necessary for the formulation of the coating.
• Organic acids such as e.g. Formic acid, acetic acid, lactic acid and / or alkyl phosphoric acid.
• Typical paint additives are, for example, anti-foaming agents, wetting agents, solvents for adjusting the viscosity, inhibitors or catalysts.
• the binders can consist of conventional self-crosslinking basic base resins and / or of conventional externally crosslinking base resins together with conventional crosslinkers.
• Typical base resins are, for example, amino epoxy resins, amino epoxy resins with terminal double bonds, aminopolyurethane resins, modified epoxy-carbon dioxide-amine reaction products or polymers of olefinically unsaturated monomers containing amino groups, such as, for example, acrylate resins. They are described for example in EP-A 12463, EP-A 82291, EP-A 209857, EP-A 234395 or EP-A 261385.
• the base resins can be self- or externally cross-linking.
• Triazine resins blocked isocyanates, transesterifiers capable of transesterification or transamidation, crosslinkers with terminal double bonds and crosslinkers capable of Michael addition activated double bonds with active hydrogen are customary as crosslinking agents. Examples of this are described in EP-A 245786, EP-A 4090 or in Park & Lack 89th volume, 12, 1983, page 928.
• the base resins have a sufficient amount of neutralizable or ionic groups.
• the deposition property of the electrocoating material can be influenced by the number of groups.
• the crosslinking density of the deposited and baked film can be influenced by the number of crosslinkable groups. All of this takes place in a manner which is familiar and customary to the person skilled in the art.
• the customary electrocoat materials used can contain customary pigments and fillers, such as e.g. Carbon black, titanium dioxide, finely dispersed silicon dioxide, aluminum silicate, lead and chromate-containing pigments, color pigments or even organic pigments.
• customary pigments and fillers such as e.g. Carbon black, titanium dioxide, finely dispersed silicon dioxide, aluminum silicate, lead and chromate-containing pigments, color pigments or even organic pigments.
• the properties and properties of the deposited lacquer can also be influenced via the amount and type of pigments, e.g. the elasticity.
• the pigments are usually dispersed in special grinding binders or in parts of the paint binder and then ground to the required particle size on a suitable grinder.
• Customary additives can also be added to influence the processing of the pigments.
• Cathodic electrodeposition coating compositions are produced in a manner known per se from the customary binders and pigments. Metallic substrates can be coated in these baths. To produce good corrosion protection, it is necessary that these substrates are well degreased before the electrocoating so that the subsequent coating layer has good adhesion.
• phosphate layer generally consists of iron or zinc phosphate crystals, which may contain further foreign ions, and covers the substrate surface homogeneously. Together with the following electrodeposition coating, it gives good adhesion to the substrate and promotes corrosion protection. These phosphate layers have a thickness of 1 to 10 ⁇ m. After coating in the cathodic electrodeposition bath, the coating film obtained is baked. So far, substrates coated in this way could no longer be mechanically deformed. This was only possible through the method according to the invention.
• the lacquer surfaces of the substrates are heated to a temperature above 30 ° C. below the glass transition temperature.
• the glass transition temperature is measured according to DSC (Differential Scanning Calorimetry). If upper and lower limits are determined, the mean value should be understood as the glass transition temperature.
• the parts can then be mechanically deformed, for example two sheets can be launched. This creates a firm mechanical connection between the two parts.
• the heating prevents damage to the homogeneous paint surface during mechanical deformation. There are no cracks or flaking. This also provides improved corrosion protection at these points.
• the optical appearance is not affected by cracks or flaking.
• a further example of working according to the invention is given when thin metal tubes are cathodically electrocoated. After the deposited film has been crosslinked, or also after temporary storage after the crosslinking, the latter is heated according to the invention. The tube can then be compressed or bent. There are no cracks or flaking, especially at the edges.
• the paint film can be heated to a temperature above 30 ° C below the glass transition temperature at various times. It is possible to heat up immediately after baking and then deform. Another possibility is that the lacquer film is only heated when it is used later and then mechanical deformation is carried out.
• Heating to an elevated temperature can be done in a number of ways.
• the metallic substrates as a whole can be heated in an oven. It is also sufficient if the paint surface is brought to an elevated temperature from the outside, for example by radiant heat. The mechanical deformation can then be carried out at this time. The substrate and the lacquer surface can then cool down again. Should have different deformations made, it is also possible to heat the coated substrate one or more times.
• the crosslinked cathodically deposited film is no longer negatively influenced by the heating. For example, the liability of subsequent layers is not affected. Likewise, the corrosion protection of a normal baked film is comparable to that of a film that was subsequently heated to a temperature above 30 ° C below the glass transition temperature.
• 2262 g of epoxy resin based on bisphenol A (epoxy equivalent weight approx. 260) are dissolved in 2023 g of diethylene glycol dimethyl ether at 60 ° to 70 ° and after adding 0.8 g of hydroquinone and 2453 g of a half ester of tetrahydrophthalic anhydride and hydroxyethyl methacrylate at 100 ° to 110 ° C heated. The temperature of 100 to 110 ° C is maintained until the acid number has dropped below 3 mg KOH / g.
• reaction product is reacted with 3262 g of a 70% solution of a monoisocyanate of tolylene diisocyanate and dimethylethanolamine (molar ratio 1: 1) in diethylene glycol dimethyl ether to an NCO value of zero.
• a mixture is prepared from 450 g of a resin according to C and 225 g according to A. This is largely freed from solvents by distillation, mixed with 18.5 g of formic acid (50%) and converted to a dispersion with a solids content of approx. 43% in the heat with demineralized water.
• acetic acid 100%) are added to 150 g of binder according to EP-A 0 183 025 Example 3 and mixed intimately with one another.
• 300 g of demineralized water are added, then 17.5 g of dibutyltin oxide, 22 g of lead oxide, 150 g of aluminum silicate and 28 g of carbon black are mixed with a high-speed stirrer. It is adjusted to a suitable viscosity (approx. 45% solids) with approx. 50 g of water and the pigment paste is ground to an adequate particle size in a corresponding mill.
• formic acid 50%
• 30 g of dibutyltin oxide, 30 g of lead oxide, 80 g of carbon black and 200 g of aluminum silicate are mixed on a high-speed stirrer.
• About 200 g of butylglycol are adjusted to a suitable viscosity and the pigment paste is ground to an adequate particle size in a corresponding mill.
• the sheets used had a thickness of about 3 mm. After baking, the mixture was cooled to room temperature. Then it was briefly warmed up and launched.

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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)

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• 1989
  • 1989-12-23 DE DE3942921A patent/DE3942921C1/de not_active Expired - Lifetime
• 1990
  • 1990-12-18 EP EP90124523A patent/EP0436880A1/de not_active Ceased
  • 1990-12-21 US US07/632,028 patent/US5140835A/en not_active Expired - Fee Related
  • 1990-12-25 JP JP2418270A patent/JPH04214897A/ja active Pending

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