EP0963795B1 - Process for powder coating components - Google Patents

Abstract

Process for powder lacquering electrically non-conducting components comprises applying an apparatus to the electrically non-conducting surface and adhering a charged powder lacquer to the surface.

Description

The invention relates to a method according to the preamble of patent claim 1.

Known methods for powder coating are used on components electrically conductive materials, mainly made of metal. On the components, for example, positive, charge applied before the one with an opposite one Cargo, e.g. negatively charged, powder paint sprayed on becomes. Because of the opposite charges, the powder coating adheres to the component. The adhesive powder coating is then baked at an elevated temperature. With the known The process is the powder coating of components made of electrically non-conductive Materials not possible because no load can be applied to such components.

According to FR-A-24 29 620, p. 5, the material for components is known per se electrically non-conductive materials (polyester) before shaping (extrusion) to mix with electrically conductive substances or particles and the components after the shape as with electrically conductive materials. This has the Disadvantage that the properties of the base material and / or the component changes and time-consuming and costly tests, e.g. for firmness or others Properties that become necessary.

In a process example according to the preamble of claim 1 the master solution is dipped and dipped onto the plastic molded component a predetermined draining time electrostatically applied a resin powder thereon, that melted during a subsequent heat treatment and finally is cured. A notable layer thickness and a regular layer To achieve the powder coating, the workpiece is before electrostatic adhesion of the powder at 100 ° C or slightly more, so that the workpiece for the powder still has a predetermined residual heat. The key solution can be one contain quaternary ammonium compound.

From GB 10 997 13 it is known objects made of PE, nylon or the like with an organic liquid composition to be wetted, containing, for example, a quaternary alkyl ammonium chloride is. The objects can be dried after wetting.

From FR-A-27 13 518 it is known to paint plastic objects with a Pre-treat the conductive liquid, for example an aqueous solution with alkyl ammonium is. After wetting can be dried. After painting is cooled.

From WO92 / 22912 it is known to add plastic objects with a conductive liquid treat a quaternary ammonium salt dissolved in water and / or alcohol contains. After wetting can be dried.

From DE-A-15 71 125 it is known as a guiding liquid for objects to be coated with insulating surfaces using a water and / or alcohol based gel to use a polar liquid, including quaternary ammonium halide or ammonium chloride with alkyl groups can be used. After wetting can be dried up to 55 ° C. For wooden objects for furniture or uses in which the wood is roughly sanded, sawn, turned, planed etc. is to be processed, and that after spraying the lead solution with sprayed on The wood is coated in terms of its later use predried to a reduced moisture content.

From DE-A-44 17 172 it is known to use a conductive solvent for pretreatment to apply for powder coating and to paint on a wet surface.

From EP-A-0 114 252 it is known as a pretreatment for electrostatic painting of plastic parts to apply a conductive liquid, which is a solution polar Leading substances in rapidly volatile alcohols.

From GB-A-11 98 462 it is known to use glass or ceramic articles to apply an aqueous solution of an electrolyte, the ammonium nitrate or sodium chloride can be. Can be used in conjunction with the final surface coating be dried.

From an IBM Bulletin, Volume 15, No. 9, Feb. 1973, pp. 2726 to 2727, New York, US, Author T.L. Elis et al is known to pretreat non-conductors before Powder coating to apply a solution of a surfactant, for example Contains alcohol and tergitol. The surface to be treated is, for example processed by sandblasting. The surface agent applied is dried in an oven before cooling before electrostatic coating.

It is an object of the invention to provide a method which is relatively simple when powder coating components made of materials that are not electrically conductive enables high quality powder coating.

According to the invention, this object is achieved with the features of claim 1.

By placing only an electrically or electrostatically chargeable on the surface of each component Equipment is applied that allows the oppositely charged Adhesion of powder coating before baking remains in the component its predetermined Get properties. Subsequent, complex and costly Checks whether the original properties or the desired properties of the non-conductive material or within a tolerance range, omitted, since only the surface is made conductive or chargeable with the aid of the equipment has been. After applying the equipment, the component can be like a Powder-coated component made of conductive material. The components are pre-wetted pre-dried to drive off volatile components that adversely affect the adhesion of the powder coating could be detrimental. This allows the quality of the later ones Improve painting.

According to claim 2, the predrying is individually tailored to the material and / or the formation of the components. So little time is wasted as possible.

According to claim 3, the components in a forced air oven, a dry air oven, pre-dried in a vacuum dryer, an infrared dryer or a microwave dryer.

According to claim 4 are favorable conditions for the cooling subsequent wetting created. In addition, a procedural under Possibly unfavorable time pressure for the sequence of the process steps between pre-drying and wetting avoided.

Alternatively, according to claim 5, energy is saved by pre-drying in the Component introduced thermal energy after wetting to dry the component surfaces is used.

According to claim 6 is already in the manufacture of the components as injection molded plastic parts a pretreatment process step is carried out, the later paint quality benefits. By evacuating the injection mold, a Favorably low proportion of volatile components in the components achieved.

Fig. 1

schematisch ein grundsätzliches Verfahren zum Pulverlackieren von Bauteilen aus elektrisch nichtleitenden Werkstoffen, und

Fig. 2

einen optimierten Gesamtverfahrensablauf in schematischer Darstellung.

The subject matter of the invention is explained with the aid of the drawing. Show it:

Fig. 1

schematically a basic method for powder coating components made of electrically non-conductive materials, and

Fig. 2

an optimized overall process flow in a schematic representation.

In Fig. 1 is at least one made of electrically non-conductive material Component 1 in a first method step A in a basin 2 into a master solution 3, z. B. immersed in a salt bath. alternatively, it is possible to spray the components 1, Vaporization or similar application processes with the lead solution 3. As Salt of the lead solution 3, a quaternary alkyl ammonium salt can be used, that is dissolved in a liquid.

In a further method step B, e.g. then the one with the lead solution 3 wetted component placed on a paint holder 4. At the paint holder 4 is the component 1 or the conductive solution 3 adhering to its surface electrically or electrostatically charged, e.g. positively charged. After that, e.g. negative, more charged Powder coating 5, e.g. with spray guns or spray nozzles 6, onto the surface of component 1 are applied. Due to the opposite charges from Conductive solution 3 or component 1 and powder coating 5, the powder coating 5 adheres to the surface of component 1. Subsequently, the powder coating 5 is covered with suitable means Treated to preferably 150 to 180 ° C for a predetermined period of time, to uniformly coat the surface of component 1 and subsequently cure. This can be for about 10 to 20 minutes and continuously or intermittently respectively.

2 shows an optimized process course. In a pretreatment step A1 is a component 11 made of at least one electrically non-conductive material freed from volatile components that would otherwise occur during the paint hardening process could volatilize what the paint adhesion and / or surface quality would adversely affect. Pretreatment step A1 includes predrying, for example with a continuous or discontinuous process, e.g. in one Convection oven. Other devices can also be used for predrying, e.g. on Dry air oven, a vacuum dryer, an infrared dryer or a microwave dryer.

Parameters to be taken into account during predrying are e.g. the salary more volatile Proportions or the wall thickness of the respective component. Predrying can take up to last for several hours at 180 ° C. The higher the temperature during predrying is, the faster the predrying takes place. The greater the wall thickness of the component is, the slower the predrying is. The less volatile parts in the material are available, the shorter the necessary pre-drying time. Little volatile For example, parts can already be injected in molded plastic components Obtain evacuation of the injection mold during the injection molding process become. Such a step in the injection molding process can be part of the pretreatment on.

In a further pretreatment step A2, the predried component 11 is cooled, preferably to room temperature. Such cooling will later optimal quality properties of the paint achieved.

In the subsequent first process step A3, the non-conductive material-related or non-conductive components 11, e.g. for a few seconds, in one with one Lead solution 13 filled basin 12 submerged. The control solution 13 contains the already mentioned salt dissolved in a liquid substance. The liquid substance can be water his. It is cheaper to use alcohol as a liquid substance because alcohol is evaporates more quickly during subsequent drying.

The components 11 are then left to drain in method step A4 and, e.g. at room temperature, completely dried. To speed up the drying, it may be beneficial to use elevated temperatures. Preferably is dried for 2 to 15 minutes at approx. 25 to 70 ° C.

Alternatively, drying can be simplified in process step A4 if the from the predrying components 11 that are still warm into the lead solution 13 (process step A3) are dipped. This is how the drying process in process step A4 the energy of the warm components is used for drying, and is only used after cooled down after wetting.

In process step B1, powder coating 15 is applied as in Fig. 1, e.g. with spray devices 16, and cured in process step B2. Each component 11 is previously on the paint holder 4 with the desired charge, so that oppositely charged powder coating 15 adheres uniformly.

Basically, the process can be used for all types of electrically non-conductive materials. This can e.g. reinforced and unreinforced polyamides, polyesters, polyurethanes, but also glass, ceramics, thermosets and wood. Restrictions on The types of materials for which the method can be used can result from the temperature resistance of the respective material in the case of the lacquer hardening required Temperatures of approx. 150 to 180 ° C result. However, since the development of powder coating systems with lower curing temperatures than the previous ones in progress With such new coating systems, the process can offer an even greater choice on paintable non-conductive materials such as plastic with lower melting or Include glass transition area.

In principle, it is possible that, according to the process, the lead solution or the conductive particles in the electrically non-conductive materials used or from these components not only stick to the surface, but at least slightly penetrate or diffuse into the surface. This has for the desired properties of the components have no significant negative impact.

In the description of the method according to the invention, it was previously assumed that that the powder coating is negatively charged while the component surface is positively charged. The signs of the respective charges can, however also be exchanged.

Claims (6)

1. A process for powder-coating components (1, 11) of electrically non-conductive materials, wherein an electrically conductive finish in the form of a wetting conductive solution (3, 13) is applied in intimate contact to the in itself electrically non-conductive surface of the component and charged electrically or electrostatically to adhere an oppositely charged powder coating to the surface and the component with the adherent powder coating is subjected to heat treatment to coat the component surface and harden the powder coating, characterised in that, prior to wetting with the conductive solution (3, 13), highly volatile material constituents which have a negative influence on powder coating adhesion and/or powder coating surface quality are removed from the components (1, 11) by predrying with thermal energy.
2. A process according to claim 1, characterised in that the predrying is performed during a pretreatment stage (A1), taking account of component-specific and/or material-specific parameters, preferably as a function of component wall thickness and/or the content of highly volatile material constituents.
3. A process according to claim 1, characterised in that the components (1, 11) are predried in a circulating air oven, a dry air oven, a vacuum dryer, an infrared dryer or a microwave dryer.
4. A process according to claim 1, characterised in that the components (1, 11) are cooled after predrying approximately to room temperature.
5. A process according to claim 1, characterised in that the predried components (1, 11) are wetted with the conductive solution (3, 13) when still hot and then dried and/or cooled.
6. A process according to one of claims 1 to 3, characterised in that, in the case of injection-moulded plastics components (1, 11) produced for powder coating, evacuation is carried out during the injection moulding process to reduce the volatile material constituents of the injection mould.

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