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
  • C25D13/14—Tubes; Rings; Hollow bodies

Definitions

• the invention relates to a method for coating hollow bodies which are open on one side, such as a metal box provided with a bottom, with lacquer or the like, in which the individual hollow bodies are washed, coated on the inside and outside and dried and then, if appropriate, printed and dried again and also flared at the open end.
• ETL electro dip painting process
• Hollow bodies closed on one side such as cans provided with a bottom, cannot simply be coated electrophoretically, because it is necessary for a uniform coating that the air in the hollow body escapes completely.
• the mechanical engineering industry has developed special methods that are carried out step by step, ie painting is carried out in individual successive steps, for example first on the inside.
• the constructions known for this have some things in common.
• the cans for the interior painting are kept on the floor and at the same time the necessary electrical contacts are made.
• a counter electrode is inserted into the can from the open end, which must be at a short distance of 0.25 to 5 mm from the inner wall of the can, so that the shape of the electrode must be adapted very precisely to that of the can.
• the cans have to be coated one after the other, so that only very short coating times of 10 to 500 msec are available if one wants to achieve a high can throughput.
• closed systems for example in a vertical arrangement (EP 50 045, EP 19 669, GB-PS1 117 831, US-PS 3 922 213 and DE-OS 29 29 570), liquid must be pumped at high speeds in order to alternate ETL liquid and a water flush in a short time to be able to carry out clamping and to discharge the gases (oxygen or hydrogen, depending on the polarity) generated during the ETL coating.
• the approximately horizontally arranged cans must be rotated in order to achieve a uniform coating (DE-OS 26 33 179 and US Pat. No. 4,107,016). When blowing out the cans, there is a great risk of contamination.
• the object of the invention is to simplify the coating of hollow bodies which are only open on one side, such as metal cans provided with a bottom, in such a way that coating can be carried out both externally and internally in one continuous operation.
• the invention makes it possible to coat hollow bodies which are open on one side, such as metal cans provided with a base, on the outside and inside at the same time in one operation and to dry them immediately afterwards and, if necessary, to print or label them.
• the mechanical effort and space requirements are relatively low, so that an economical mode of operation is possible. For example, up to 16 cans can be passed through an electro-dip bath at the same time, ie side by side, and coated with lacquer.
• the trimmed or untrimmed cans are vertical, i.e. pressed with the bottom down into the ETL basin or - more advantageously, faster - filled with bath liquid through a filler neck.
• the cans When transporting through the ETL basin, the cans are either immersed under the bath surface or, particularly with untrimmed cans, advantageously guided so that the can opening is above the bath liquid surface.
• they To lift the cans out of the immersion bath, they are tilted again so that their opening lies downwards so that the liquid in the cans can drain off completely.
• the transport element can be an endless conveyor belt or an endless chain on which the cans hang practically vertically or stand on it, ie the conveyor belt can run above the surface of the bath or can also be guided through the ETL immersion bath. Since the hollow bodies for coating are passed through an immersion bath and it is also possible to pass several hollow bodies next to one another at the same time. Even with mass production with high throughput, sufficiently long coating times can be achieved in order to also apply higher-quality lacquer coatings properly can. For example, with a coating time of 1 to 120 seconds, a pigmented or unpigmented lacquer is applied electrophoretically using direct current, the wet film deposited on the hollow body having a sheet resistance of at least 0.6 x 10 8 ohm. cm.
• the hollow bodies to be coated are switched via the holding device when using an anionic ETL lacquer as an anode and when using a cationic ETL lacquer as a cathode.
• the counter electrode is located at a distance from the hollow bodies in the immersion bath.
• the inner coating is carried out using a so-called wrap, which achieves the varnish because of its highly insulating effect in the deposited film, or with the help of an inner electrode inserted into the can.
• the electrophoretic coating runs in such a way that first the wall opposite the counterelectrode, ie the outer wall of the hollow body is coated. The wet wall that builds up initially isolates the outer wall. The electric field lines then migrate into the interior of the hollow body, where the deposition continues.
• the deposition time and the insulating effect of the material, characterized by the sheet resistance, must be coordinated in order to achieve a good grip. The longer the coating time, the higher the layer resistance due to the increase in the layer thickness and through electro-osmotic processes which are used to reduce the content of neutralizing agent or for electrochemical dewatering.
• the lower limit of the coating time should therefore be over 3 seconds, in particular over 5 seconds and particularly suitably over 10 seconds.
• the upper limit is determined by the length of the immersion bath, the transport speed and the amount of hollow bodies to be coated to be managed. In order to achieve an economically acceptable level, the upper limit should expediently be less than 60 seconds and preferably less than 30 seconds of coating time.
• the amount of film applied depends on the deposition voltage, which is between 50 and 400 volts. With increasing tension, the wrap is improved. In order to avoid electrical breakdowns, either the voltage is continuously increased or a short bias is used, ie before the actual coating, voltages of less than 100 volts are used for 0.1 to 0.5 seconds.
• the wet film resistance necessary for good insulation should be as high as possible.
• its lower limit is limited by the desired short coating time. So the lower limit should be at least 1 x 10 8 0hm. cm, suitably over 1.5 x 10 8 0hm and preferably over 2 x 10 8 0hm. cm. The higher the layer resistance, the thinner the achievable layer on the can wall.
• the upper limit is therefore below 10 x 10 8 , suitably below 7 x 10 8 and preferably below 4x10 8 0hm. cm.
• the bath conductivity which is determined by the degree of neutralization of the binder, is above 800 ⁇ Scm -1 , suitably above 1200 and preferably above 1600 ⁇ Scm -1 .
• anionic and cationic resins can be used as binders, the anionic for acidic fillings and the cationic for basic fillings being preferred.
• the anionic resins such as maleinized or acrylated butadiene oils, maleinized natural oils, epoxy esters and acrylate resins containing carboxyl groups, acrylic epoxy resins, unmodified or polyesters modified with fatty acids have an acid number of 30 to 180, in particular between 40 and 80, and are at least partially neutralized with ammonia, amines or amino alcohols .
• Highly volatile amines are preferred so that they can achieve the desired short burn-in times of 30 sck. up to 300 seconds as completely as possible from the film. Ammonia is particularly preferred.
• crosslinking takes place either oxidatively via unsaturated double bonds or by thermal reaction with corresponding crosslinking agents such as phenolic resins or amine-formaldehyde resins.
• corresponding crosslinking agents such as phenolic resins or amine-formaldehyde resins.
• External or self-crosslinking acrylate resins are preferred for the production of white lacquer coatings.
• Acrylated or maleinized epoxy esters or epoxy acrylates are preferred for coating with clear lacquers.
• the cationic resins such as butadiene oil aminoalkylimides, Mannich bases of phenolic resins, Michael addition products of primary and / or secondary amines and / or alkanolamines on resins with unsaturated double bonds or amino epoxy resins have an amine number of 30 to 120 mg KOH / g / solid resin, preferably from 50 to 90, and are at least partially neutralized with organic monocarboxylic acids such as carbonic acid, formic acid, acetic acid, lactic acid etc.
• Blocked isocyanates or resins which contain ester groups capable of transesterification are preferably used as crosslinking agents.
• the binders are neutralized with the neutralizing agents and, if appropriate, diluted with deionized or distilled water in the presence of solvents.
• Suitable solvents are alcohols, ethylene or propylene glycol mono- or diethers, diacetone alcohol or even small amounts of non-water-dilutable solvents such as petroleum hydrocarbon.
• the aim is to have as low a solvent content as possible, expediently less than 15% by weight and preferably less than 5% by weight, because with increasing solvent content the wrap worsens.
• the bath solid is generally between 5 and 30% by weight, in particular over 10 and under 20% by weight. With increasing solids, the bath conductivity is increased and the deposition equivalent (amperes x sec / g) is reduced, whereby the wrap can be increased. Due to the high concentration of layer-forming ions, the layer resistance goes through a maximum.
• the bath temperature is between 20 and 35 ° C. As the temperature falls, the wrap increases. Temperatures below 20 ° C are uneconomical because the heat generated by the ETL coating has to be dissipated again by plenty of cooling water. Temperatures above 35 ° C make it difficult to run the bath because too much solvent evaporates and hydrolysis on the binder system produces fluctuations in the electrical data.
• the coating agent can additionally contain customary lacquer aids such as catalysts, leveling agents, anti-foaming agents, lubricants, etc.
• customary lacquer aids such as catalysts, leveling agents, anti-foaming agents, lubricants, etc.
• such additives should be selected that do not cause any disturbing reactions with water at the pH of the bath, do not bring in any disturbing foreign ions, and do not precipitate out in a form that cannot be stirred when they are left standing for a long time.
• the binders can be used pigmented or unpigmented. Such materials can be used as pigments and fillers which, owing to their small particle size below 10 ⁇ m, in particular below 5 ⁇ m, can and are dispersed stably in the lacquer let stir again when standing. They must not contain any interfering foreign ions and must not react chemically with water or the neutralizing agent.
• the pigmentation can be both white and colored; white is preferred. With the additional incorporation of interference pigments, it is possible to apply metal effect paints such as B. aluminum, gold, etc. to achieve.
• the pigments such as Titanium dioxide is ground in a concentrated regrind and then adjusted with a further binder to a pigment-binder ratio of approximately 0.1: 1 to 0.7: 1.
• the incorporation of pigments increases the wrap.
• finely powdered, insoluble resins such as powdered polycarbonates, epoxy resins or blocked polyisocyanates, the amounts added being chosen so that they do not exceed the maximum sheet resistance.
• the binder, pigment content, bath solids content, solvent content, choice of neutralizing agent and degree of neutralization are coordinated with the coating conditions such as bath temperature, deposition voltage and deposition rate, so that a complete full coating takes place in the electrocoating bath (ETL bath), which after baking inside the can Layer thicknesses of at least 3 ⁇ m, preferably at least 4 ⁇ m, very preferably at least 5 ⁇ m and at most 10 ⁇ m, particularly at most 7 ⁇ m, is pore-free.
• the electrodeposition is done in an immersion bath.
• the hollow bodies closed on one side e.g. cans
• the hollow bodies closed on one side can be practically vertical, i.e. with a magnetic, electromagnetic or mechanical holding device, which also means holding with a vacuum. with the opening facing upwards, under the bath surface of the ETL basin.
• the filling of the can is supported by pumping in additional bath material via a filler neck, which can also be designed as a hollow electrode. Direct current is used as the current source.
• the hollow body is electrically connected via the holding device as an anode or as a cathode.
• the counter electrode is basically outside the hollow body in the electro-immersion bath.
• the can Due to the encapsulation of the varnish and the necessary separation and coating time for the respective can shape, the can is completely coated on the inside and outside.
• This process has the advantage that the entire coating is carried out in a single process step and, due to the low mechanical expenditure on the hanger, many cans can be coated side by side at the same time.
• An auxiliary electrode can also be inserted into the box to provide support, especially when high throughput speeds are required.
• the immersion electrode has a shape not determined by the can and is less than half the diameter of the can. It is preferably arranged so that it goes into the interior of the can holder at the same time Cans is introduced.
• the auxiliary electrode can be made hollow. Filtered varnish is pumped into the can through this feed line.
• the inner coating is carried out after filling the vertical cans with an inner electrode and the outer coating is carried out in the usual way with a second counter electrode in the ETL bath.
• the untrimmed cans are only so far immersed that they are completely coated after trimming. On the other hand, it must be ensured that the edges of the can do not dip under the surface of the bath. This makes it possible to coat the outside with a different paint first on the inside and then in a further step in a second ETL basin.
• the coating can also be done simultaneously on the inside and outside with two different paint qualities.
• the cans are emptied by rotating the cans, with the can bottom being raised.
• the hanger When the hanger is extended, it is rinsed off together with the cans first with ultrafiltrate and then with water, to which an emulsifier can optionally be added in order to avoid malfunction.
• the paint is burned in at times from 1 to 300 seconds at temperatures from 180 to 250 ° C.
• the conveyor belt with buckets and cans is fed through the furnace.
• the can base can be predried and provided with a protective auxiliary layer. Afterwards, the transfer can take place on a conveyor belt leading through the drying oven.
• the opening of the can can be directed downwards or preferably upwards.
• Continuous coating in the ETL tank enriches the amine with an anionic binder and carboxylic acid with a cationic one.
• the refill materials are either neutralized correspondingly lower or the excess neutralizing agents are removed by electrodialysis.
• the rinsing water is enriched by ultrafiltration and returned to the paint basin, which increases the degree of utilization of the paint and removes unwanted foreign ions.
• An anionic, self-crosslinking acrylate resin according to DE-AS 1 669 107 was neutralized with ammonia and diluted to a solids content of 15% by weight with deionized water.
• a flanged can (diameter 56 mm, length 116 mm) was held at the flanged edge with an electrically conductive clamp and carefully immersed completely in a conductive container insulated against earth and filled with diluted lacquer with a diameter of 19 cm.
• the direct current from a voltage source was connected to the socket and the other pole to the outer vessel.
• the coating was carried out with an auxiliary electrode with a diameter of 1 cm, which was immersed in the can 8 cm deep.
• the can was baked in a convection oven at 215 ° C. for 3 minutes. The can was completely covered on the inside and outside with a thin and pore-tight clear lacquer. For measured values, see Table 1.
• the binder from Example 1 was pigmented with 0.4 part by weight of titanium dioxide to 1 part by weight of binder and, after neutralization with ammonia, diluted to a solids content of 9% by weight.
• the coating was carried out without an auxiliary electrode.
• the can was completely covered with a white varnish.
• the porosity, measured in an electrolyte solution at 4 volts, is 5 mA after 30 seconds.Measured values see Table 1.
• a cationic amino epoxy resin according to DE-OS 31 22 641 was pigmented with 0.4 part by weight of a mixture of 99 parts by weight of titanium dioxide and 1 part by weight of carbon black and after neutralization with formic acid to a solids content of 15% by weight deionized water.
• the coating was carried out without an auxiliary electrode.
• the can was completely covered with a gray varnish. For measured values, see Table 1.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Paints Or Removers (AREA)
• Materials For Medical Uses (AREA)
• Orthopedics, Nursing, And Contraception (AREA)
• Details Of Rigid Or Semi-Rigid Containers (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Pens And Brushes (AREA)

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• 1983
  • 1983-07-12 DE DE19833325068 patent/DE3325068A1/de not_active Withdrawn
• 1984
  • 1984-07-06 DE DE8484107925T patent/DE3479747D1/de not_active Expired
  • 1984-07-06 EP EP84107925A patent/EP0131282B1/fr not_active Expired
  • 1984-07-06 AT AT84107925T patent/ATE46370T1/de not_active IP Right Cessation
  • 1984-07-10 CA CA000458519A patent/CA1227161A/fr not_active Expired
  • 1984-07-10 ES ES534164A patent/ES534164A0/es active Granted
  • 1984-07-10 US US06/629,566 patent/US4529492A/en not_active Expired - Fee Related
  • 1984-07-10 ZA ZA845310A patent/ZA845310B/xx unknown
  • 1984-07-11 JP JP59142470A patent/JPS6039199A/ja active Granted

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