Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/66—Electroplating: Baths therefor from melts
  • C25D3/665—Electroplating: Baths therefor from melts from ionic liquids
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/16—Apparatus for electrolytic coating of small objects in bulk
  • C25D17/28—Apparatus for electrolytic coating of small objects in bulk with means for moving the objects individually through the apparatus during treatment
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/08—Electroplating with moving electrolyte e.g. jet electroplating
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces

Definitions

• the invention relates to a coating method for a workpiece, and to an apparatus for coating a workpiece.
• coating methods are known for this purpose where a liquid coating agent is used based on a binder, it is also known to cover a workpiece with a metal coat that directly chemically or physically adheres to the substrate.
• a widely used approach for this is the electrochemical deposition of metal from a coating liquid in which a salt of this metal is dissolved.
• the workpiece to be coated is dipped into a bath of the coating liquid.
• the workpiece in most cases acts as a cathode on which the metal ions are reduced.
• a voltage is applied to the workpiece resulting in a predetermined, usually negative, potential on the workpiece with respect to a reference electrode.
• This method allows excellently adhering, closed, anti-corrosive metal coatings to be produced, as the case may be after suitable pre-treatment.
• semi-metals and semiconductors such as silicon, can be deposited as well as metals. It is also possible to electrochemically coat non-metallic workpieces, as long as their surfaces have been made conductive by a pre-treatment.
• a potential range of about 2V is defined by the deposition processes of oxygen on the one hand and hydrogen on the other, within which the elements must be present that are to be used for coating in aqueous solution. It is known from research that this drawback can also be overcome by the use of a different solvent.
• Ionic liquids are of growing importance in this context. They are salts having a melting temperature of below 100° C. The corresponding salt melt can also serve as a solvent for a salt of the desired coating metal. By using ionic liquids, according to the state of the art, the accessible potential range with respect to water is extended from about 2V to up to 6V.
• the anions of the ionic liquid can be identical to those of the dissolved salt.
• US 2004/0238352 thus discloses a method wherein aluminum chloride is dissolved in a melt of 1-butyl-3-methylimidazolium chloride and aluminum is deposited from this solution.
• the object is achieved by a coating method for a workpiece, by an apparatus and by a workpiece as disclosed herein.
• the method comprises the following method steps:
• the temperature of the workpiece is adjusted in such a way that the temperature of the coating liquid only deviates from a predetermined set temperature by no more than 10° C. during the coating process.
• the essential idea underlying the present invention is that the useful life of an ionic liquid used as a coating liquid is particularly stable and durable, and thus industrially useful, if it is maintained within a range of a predetermined temperature, the set temperature, that is within tight limits, i.e. deviating by no more than 10° C. from the set temperature.
• the term set temperature refers to a precisely defined temperature that is deemed optimal.
• the temperature of the coating liquid—and thus the quality of the coating— is determined in the industrial method in particular by the fact that usually a great number of workpieces, or a large workpiece, is coated in the individual coating process. This is how the great mass of the workpiece(s) absorbs a lot of heat from the coating liquid (or introduces it, as the case may be). This applies all the more since metallic workpieces usually have excellent heat conductivity and high specific heat capacity.
• industrial facilities usually work in a continuous operation, i.e. coating processes of the individual batches follow each other without major pauses. Keeping the temperature of the coating liquid as constant as possible has thus been shown to considerably extend the useful life of the ionic liquid for coating, and is advantageous for the quality of the coating when used in industrial coating methods.
• the workpiece to be coated is heated and/or cooled, either as a sole process or in combination with heating or temperature controlling the coating liquid.
• Heating or temperature controlling the workpiece has the advantage that there is no undesired cooling or heating effect on the coating liquid by the workpiece at precisely the point where the deposition takes place. By these means, an excellent quality of the deposited layer is ensured.
• the terms “heating” and “warming” will be used as synonyms in the following, i.e. they are not to be construed as identifying different strengths of heat flows or different temperature ranges.
• one and the same coating bath can be used over long periods of time, i.e. there is less ionic liquid that has become unusable, which must be disposed of. This means on the one hand that costs can be saved and on the other hand that there is less impact on the environment.
• the coating liquid preferably all components of the coating liquid are explicitly included, i.e. also excess components, still adhering to the workpiece until they are removed, or even beyond that, as the case may be, if removal is incomplete, and which are preferably recycled to be used for renewed coating of workpieces.
• workpieces with a metallic surface are preferably coated, i.e. those that are either completely of metal, or an alloy, as the case may be, or are provided with a metallic coating.
• This metallic coating can also include non-metallic components.
• workpieces with a non-metallic surface can also be used, such as plastic parts that are prepared for electrochemical coating by means of activation, i.e. having a surface that has already been made conductive by means of pre-treatment, for example, with a suitable varnish, or that is already conductive due to the presence of additives in the plastic material.
• the ions of the at least one element to be deposited are metal ions.
• metal ions particularly preferred are ions of at least one of the elements aluminum, zinc, magnesium, nickel, chromium, tantalum, titanium, copper, silver and/or gold.
• ions of at least one of the elements aluminum, zinc, magnesium, nickel, chromium, tantalum, titanium, copper, silver and/or gold.
• Ions of semimetals or semiconductors, in particular silicon and/or germanium ions are also preferred, however.
• the coating liquid according to method step a) is usually applied by dipping the workpiece into the coating liquid. It is also conceivable to apply the coating liquid by different means, e.g. by means of casting devices.
• the temperature of the workpiece is adjusted in such a manner that the temperature of the coating liquid deviates during the coating process by no more than 5° C. from the predetermined set temperature.
• the temperature of the coating liquid is critically influenced by its contact with the workpiece.
• One way of preventing any deleterious effects by the workpiece is to maintain its surface temperature within the range of the set temperature to a sufficient degree. This is why in a preferred embodiment of the invention, care is taken that the surface temperature of the workpiece does not deviate from the set temperature by more than 10° C. during the method steps a) to d). If this temperature range is adhered to, a substantial interfering factor in the deposition of metal layers from ionic liquids is eliminated.
• surface means all surfaces of the workpiece with which the coating liquid can come into contact.
• the workpiece is heated for this purpose prior to and/or during the method steps a)-d) at least on its surface by means of hot air, infrared irradiation, by blasting the surface, by contact with a heat bath or in an inductive manner.
• advance heating can depend, for example, on the size or geometry of the workpiece. A large workpiece with a relatively small surface area loses its initial temperature more slowly than a small workpiece with a relatively large surface area.
• Heating with hot air has the advantage that all exposed surfaces of a plurality of workpieces, as the case may be, can be treated. Infrared irradiation is advantageous due to the more efficient heat transfer. Inductive heating has the advantage that the workpiece is not only heated on the surface but also in its interior. This method is also particularly efficient. Heating by means of blasting (e.g. sand blasting) the surface has the advantage that heating is accompanied by a pre-treatment of the surface. Heating in a heat bath in which the workpiece is dipped, can also be combined, as the case may be, with degreasing or the like of the workpiece in the same bath. Furthermore, heating in a bath can be realized with relatively little technical overhead, and good heat transfer to the workpiece is ensured.
• blasting e.g. sand blasting
• a workpiece heated too much due to pre-treatment it is preferable to cool the workpiece prior to and/or during the method steps a)-d) at least on its surface by means of cold air, by contact with a cold bath, or by means of evaporation.
• the cold air can either be stagnant or flow around the workpiece as an air flow.
• a cold bath can either be a solid body or a liquid, which are cooler than the workpiece.
• a holding or receiving device can serve as a cold bath.
• a gripping arm, guiding the workpiece, or a basket in which the workpiece resides can be cooled in turn, in order to cool the workpiece.
• a particularly effective method of cooling is by means of evaporation.
• a liquid is evaporated on the surface of the workpiece, whereby a particularly large amount of heat is removed from the workpiece. If the temperature of the workpiece is below the boiling temperature of the liquid, evaporation can be forced by an air flow or a reduction of the air pressure.
• a plurality of different temporal sequences are suitable for heating.
• Which temporal sequence is chosen in each individual case depends, for example, on the duration of the individual method steps and the nature of the workpiece (size, surface area, material etc.).
• a suitable guideline for estimating the required heat amount is the mass to be coated. If the mass of the workpieces to be coated is known, the required heat amount can still vary, e.g. depending on the heat conductance of the workpieces and on the surface area of the workpieces. If the coating liquid is temperature controlled, the amount of heat introduced by temperature controlling must also be considered in the estimation. Taking all these factors into account, the amount of heat necessary for heating or temperature controlling the workpieces can usually be estimated or calculated with sufficient precision.
• the above-mentioned method steps are carried out in an inert gas atmosphere.
• This precaution is necessary for a number of ionic liquids to ensure durable quality, typically with those ionic liquids that are strongly hygroscopic. It must be taken care of, in particular, that in the method steps c) and d), liquid is exposed to the atmosphere in film or drop form, which means with a relatively large surface area. If the components of the liquid in question are to be recuperated, protection by inert gas is particularly important.
• the coating liquid is mixed prior to and/or during the method steps a)-d). This can be done by means of a mechanical stirrer that is driven by a motor and a shaft. Magnetic stirrers are also advantageous, however, since they do not need an additional opening in a container wall for mechanical coupling. Mixing by means of ultrasonic waves is particularly advantageous since no additional parts are needed inside of the respective container at all.
• the respective means for mixing can be periodically or continuously operated. In addition to homogenizing the coating liquid, mixing also contributes to the uniform temperature control of the coating liquid.
• the excess coating liquid removed from the workpiece is at least partially recycled into the bath. Recycling can be passive, by draining back, or active, by means of pumping or the like. By these means, the losses due to removal of liquid together with the workpiece can be substantially reduced, which leads to high cost-savings in particular when a great number of coating processes are involved.
• the workpiece is thus preferably cleaned and/or dried for introduction into the coating bath.
• Various methods are suitable for cleaning. This can be done mechanically, such as by sand blasting, metal blasting, glass bead blasting or soda blasting of the workpiece.
• Chemical cleaning steps are also of particular importance, such as etching, pickling or degreasing of the workpiece.
• Degreasing substances in addition to organic solvents, are, in particular, aqueous solutions, in particular alkaline solutions or those to which additives, such as tensides, have been added.
• Degreasing can be done by spraying under pressure or in a dip bath, wherein, in the latter case, the degreasing process is substantially improved by the use of ultrasonic waves.
• the efficiency can also be increased by higher temperatures, such as with hot alkaline degreasing.
• Drying the workpiece can be carried out by means of cold or hot air, by irradiation with infrared or microwaves and/or by means of negative pressure. According to a preferred embodiment of the invention, drying of the cleaned workpieces can be used for heating or cooling the workpiece.
• the above described measures for preparing the workpiece are of particular importance for working with ionic liquids, since they are often sensitive with respect to contamination of any kind, and in particular with respect to introduced moisture.
• the workpiece is electrolytically polished prior to the deposition process.
• This is also referred to as “in situ” electrochemical etching.
• ions are detached from the surface of the workpiece by applying a suitable voltage (usually over a short period of time), i.e. the workpiece functions as an anode.
• a suitable voltage usually over a short period of time
• microscopic bumps are thus removed, and on the other hand microscopic contamination is removed from or out of the surface.
• This method is also suitable, for example, to remove oxide layers from steel, which would interfere with the adhesion of any coating to be deposited.
• This cleaning step can be carried out in the ionic liquid that is also used for coating, wherein the voltage is reversed with respect to the coating process. It is also conceivable, however, to provide a separate bath for this purpose. While the first variant needs simpler apparatuses and saves time, the latter variant helps to avoid that the coating liquid is contaminated by substances removed from the workpiece.
• rinsing liquid also includes liquids in which the ionic liquid can be emulsified, in addition to those in which it is dissolvable. Rinsing on the one hand is for cleaning the workpiece.
• the workpiece can also be prepared for any other coating processes by means of the rinsing process.
• rinsing liquid residue often still adheres to the workpiece.
• a top coat is applied after coating. Suitable top coats are known from the state of the art.
• the usability of an ionic liquid in the context of an industrial coating process is ensured over long periods of time by the method according to the present invention. Degredation of the conductivity of the coating liquid due to temperature changes is prevented.
• the method thus enables the deposition of high quality metal layers, in particular of aluminum, from a coating bath, which remains useful over a long period.
• the coating bath thus only rarely needs to be refilled or exchanged, which results in substantial cost savings.
• the disposal of ionic liquid that has become useless is far less frequent, which is advantageous both from an economic and an ecological point of view.
• the method according to the present invention can be carried out by means of an apparatus for coating a workpiece. Since coating is achieved by means of deposition from a coating liquid, which comprises an ionic liquid containing ions of at least one element, the apparatus must comprise at least two electrodes according to the state of the art (one electrode for contacting the workpiece, and a counter electrode). Usually a coating container for receiving the coating liquid during the coating process is also necessary. It may be advantageous to carry out the coating process with a so-called “three-electrode arrangement” to apply a precise potential to the workpiece.
• such an apparatus comprises means for temperature measurement, by means of which a deviation of the temperature of the workpiece by 10° C., preferably by 5° C., from a predetermined set temperature can be determined, and means for heating and/or cooling the workpiece.
• the means for temperature measurement can either work in a contact-free manner (by measuring the infrared radiation) or by contacting the workpiece or the coating liquid respectively (for example as a bimetal thermometer or a resistance thermometer).
• Such temperature sensors are known from the state of the art and usually work with a sufficiently high (usually substantially better) measuring accuracy to be able to determine temperature differences of 5° C. or 10° C.
• such an apparatus can optionally comprise further components, for example, for spinning off coating liquid from the workpiece or for mixing the coating liquid.
• the bolts are prepared for coating first by sand blasting and then by degreasing in a basket in a cleaning solution consisting of water in which 9 g of potassium phosphate and 27 g of potassium hydroxide have been dissolved per one liter of water, at 85° C.
• a thermostat connected to the bath is used to ensure that its temperature is within a range of between 80° C. and 90° C. After a soaking time of 5 minutes, the basket is lifted out of the bath. The basket with the bolts is rinsed with tap water at a temperature of about 80° C. and subsequently spun dry. Thereafter, the bolts are further dried by means of an airflow preheated to about 90° C.
• the basket is introduced through a first lock door into a lock chamber, the first lock door is closed, and the lock chamber is partially evacuated to 0.05 bar.
• the lock chamber is flooded with nitrogen.
• Induction coils are integrated in the walls of the chamber, by means of which the bolts can be inductively heated, if necessary.
• it is checked by means of an infrared camera, whether the temperature of the bolts is within the predetermined range of between 70° C. and 90° C.
• the lock chamber communicates with a coating chamber filled with a nitrogen atmosphere via a second lock door.
• the bottom of the coating chamber is configured as a basin filled with a coating bath.
• the coating bath consists of a melt of 1-ethyl-3-methyl-1H-imidazolium chloride (EMIC), in which aluminum chloride is dissolved.
• EMIC 1-ethyl-3-methyl-1H-imidazolium chloride
• the mass ratio of EMIC:AlCl 3 is 1.7:1.
• Temperature sensors are used to continuously check whether the temperature of the walls of the coating chamber deviates from the set temperature. In the case of a deviation, additional heating is carried out by means of heating elements integrated into the walls, wherein the heating power is adjusted in dependence on the magnitude of the deviation. In this way it is ensured that the temperature never deviates from the set temperature by more than 10° C.
• a plurality of temperature sensors is also spatially distributed in the basin, which check the temperature of the coating liquid itself.
• a vertically traversable coating drum with perforated walls is arranged in the coating chamber.
• the drum can be rotated about its longitudinal axis by means of a motor.
• the drum itself is also heatable and is maintained within the predetermined temperature range by means of a thermostat.
• the basket is introduced into the coating chamber through the second lock door, then the second lock door is closed.
• the coating drum is located outside of the coating bath.
• the bolts are introduced into the coating drum through an opening, subsequently the drum is traversed downwards into the coating bath.
• the coating liquid flows around an aluminum electrode, which is connected to the outer wall of the drum via a voltage supply.
• the drum is slowly rotated at 20 rpm while a voltage of 20V is applied between the aluminum electrode and the outer wall of the drum so that the aluminum electrode functions as an anode.
• the bolts in contact with the walls of the drum are coated by the deposition of aluminum from the coating liquid, while aluminum ions are continuously detached from the anode by oxidation, so that the aluminum concentration remains constant in the coating liquid.
• the voltage is switched off, the drum is stopped and lifted up out of the bath, wherein most of the liquid drains off. Subsequently, the drum is caused to rotate in a fast rotation at 300 rpm, to spin off liquid residue. After spinning, the basket is traversed to a position below the drum to receive the bolts, the drum is opened and emptied into the basket through the opening rotated into a bottom position.
• the basket is introduced into a rinsing chamber filled with nitrogen through a third lock door, and the third lock door is closed.
• final residues of the coating liquid are removed, which are carried off together with the rinsing substance for separation and recycling into the coating bath.
• the basket is spun again and traversed out of the rinsing chamber through a fourth lock door.
• Rinsing in this case, is carried out with tap water at a temperature of about 20° C. This is followed, again, by a spin drying process.
• the bolts are further dried by means of an airflow heated to about 40° C.
• the temperature of the airflow which is increased with respect to the set temperature, is for compensating heat losses due to the evaporation of liquid.
• the basket is, again, introduced through a first lock door into a lock chamber, where last liquid residues are evaporated by means of partial evacuation. Subsequently, the lock chamber is flooded with nitrogen having a temperature of 20° C. Induction coils are integrated in the chamber walls, by means of which the bolts can be inductively heated as needed. There is an additional possibility of directing a flow of nitrogen at a temperature of 0° C. onto the bolts by means of a nozzle integrated in the chamber wall to cool them if necessary. An infrared camera is used to check whether the temperature of the bolts is within the predetermined range of between 10° C. and 30° C.
• the lock chamber communicates via a second lock door with a coating chamber filled with a nitrogen atmosphere.
• the structure of the coating chamber is similar to the one in example 1.
• the bottom of the coating chamber is configured as a basin filled with a coating bath.
• This basin is made of a ceramic material that is chemically particularly insensitive.
• the coating bath consists of a melt of 1-ethyl-3-methylimidazolium chloride, in which aluminum chloride is dissolved.
• the molar ratio of 1-ethyl-3-methylimidazolium chloride to ALCl 3 is 2:3.
• Temperature sensors are used to continuously check whether the temperature of the walls of the coating chamber deviates from the set temperature.
• heating or cooling can be carried out by passing water at a suitable temperature through the heating/cooling pipes integrated into the walls.
• the above mentioned pipes have water flowing in them at a temperature of 20° C.
• a plurality of temperature sensors is also spatially distributed in the basin for checking the temperature of the coating liquid itself.
• the coating chamber comprises a snake-like heat exchanger system arranged within the basin and extending through the coating liquid.
• the arrangement is chosen in such a manner that any contact between the drum and the heat exchanger system is prevented. Cool water can be caused to flow through this heat exchanger system while, in the normal state, water at a temperature of 20° C. is used.
• a continuously operated magnetic stirrer which, on the one hand, homogenizes the coating liquid and, on the other hand, ensures uniform temperature control and, by moving the coating liquid, also promotes the heat exchange between the liquid and the heat exchanger system.
• a coating drum with an aluminum electrode is used as in example 1.
• the drum is coated with a ceramic material, a series of electrodes for contacting the bolts are, however, provided on the inner wall.
• the introduction of the workpieces and the traversal of the coating drum is carried out as in example 1.
• the bolts are treated with in situ electrochemical etching.
• a voltage of 0.8V is applied between the electrodes in the wall of the drum and the aluminum electrode.
• the drum is caused to rotate at a slow 20 rpm, wherein the bolts function as an anode due to their contact with the electrodes in the drum wall.
• the last residue of oxide is removed.
• the etching process is finished, and an opposite voltage of ⁇ 0.2V is applied, whereby the aluminum electrode now functions as an anode, while the bolts are coated by the deposition of aluminum from the coating liquid.
• the rotation of the drum is continued during the coating process lasting 10 min.

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• 2009
  • 2009-02-20 AT AT09715063T patent/ATE531835T1/de active
  • 2009-02-20 EP EP09715063A patent/EP2250301B1/fr not_active Not-in-force
  • 2009-02-20 US US12/919,697 patent/US20110000793A1/en not_active Abandoned
  • 2009-02-20 WO PCT/EP2009/001243 patent/WO2009106269A1/fr not_active Ceased

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