EP3010646A1

EP3010646A1 - Method for coating a surface of an electrically non-conductive substrate with powder coatings

Info

Publication number: EP3010646A1
Application number: EP14731286.2A
Authority: EP
Inventors: Thomas LENDL; René MATTERN
Original assignee: IGP Pulvertechnik AG
Current assignee: IGP Pulvertechnik AG
Priority date: 2013-06-19
Filing date: 2014-06-19
Publication date: 2016-04-27
Also published as: WO2014202724A1; US10010908B2; US20160121361A1

Abstract

The invention relates to a method for coating a surface of an electrically non-conductive substrate with powder coatings, comprising the following steps: providing a substrate to be coated, pre-heating the substrate to be coated to 40 to 140 °C in order to decrease the surface resistance of the substrate to less than 10¹² ohms, preferably to within the range of 10¹⁰ to less than 10¹² ohms, electrostatically coating the surface with powder coating in a single layer, which powder coating comprises a reactive system, which in particular cures into a thermoset, curing the powder coating layer at 170 °C or less.

Description

Process for coating a surface of an electrically non-conductive substrate with powder coatings

The present invention relates to a method for coating a surface of an electrically non-conductive substrate with powder coatings.

Methods known in the art for coating non-conductive substrates are known in the art.

For example, WO 02/04694 A1 shows a method for applying a coating to a plastic surface by means of a thermal spraying method, wherein the first layer

Adhesive is applied. However, the need for such a primer is considered disadvantageous at the present time.

WO 2007/054289 A2 discloses an aqueous powder dispersion and a method for applying such a dispersion to a plastic or a fiber composite.

WO 02/46321 A2 shows an aqueous effect

Coating material with a water-miscible organic

Solvent and a method for its use, inter alia, on a plastic or fiber composite. The

Use of solvents is not permitted in all areas and the drying of the aqueous dispersion is

energy intensive. WO 2010/028848 AI apparently a water-based composition of a two-component paint, which in the

Surface coating of fiber-plastic composites as

Filler is used. The curing temperature is below 40 ° C. Such two-component systems are complicated to use, a correct mixing ratio must be considered.

EP 1 321 197 A2 discloses a coating method with

Powder coatings, wherein the powder coating is applied by means of a transfer belt from a fluidized bed to a substrate. The substrate may be conductive or non-conductive. Not solved, however, are the problems of liability and the

Coating quality.

DE 197 48 927 A1 discloses a process for the production of functional glazes on the surface of non-metallic materials. Here, surfaces are preheated, irradiated with a powder and the coating cured by heat input. For preheating and curing high temperatures are required.

US 2010/266782 A1 discloses a coating method for conductive and non-conductive workpieces by means of two or more powder application. A first applied powder gels on a preheated surface, at least one further powder is applied and the coating is cured by heat input. It is an object of the invention to overcome the disadvantages of the prior art. In particular, a method for

Are made available, which allows a coating of non-conductive surfaces with dry powder coatings, which meets high demands on the coating quality and the adhesive strength and is as easy to implement. This object is achieved by the method defined in the independent claim. Further embodiments emerge from the dependent claims. Here and below, an electrically nonconducting substrate is understood as meaning a material or a material having a surface resistance of greater than 10 ¹² Ω (according to DIN EN 61340-2-3: 2000). It should be noted that the determination of the surface resistance is carried out on specimens which are cuboid-shaped and have a dimension in all directions of at least 1 mm x 110 mm x 120 mm (thickness x width x length). In the case of sheet-like or thin-walled substrates with a wall thickness of less than 1 mm, a test specimen is to be formed from a plurality of superimposed substrate sections, so that the resulting thickness is at least 1 mm. The determination of the surface resistance should in each case be carried out on at least 3 test specimens, the measured values obtained are too mittein. Measuring probes are to be used as specified in DIN EN 61340-2-3: 2000. The surface of the specimens should be cleaned with a soft cloth moistened with isopropanol. After this cleaning and before the

Determination of the surface resistance, the specimen is to be conditioned for at least one hour at 23 ° C +/- 2 ° C and a relative humidity of 30%. The measurement must be carried out with a test voltage of 100 V. It is the

Surface resistance or voltage read after the end of the measuring period determined in DIN EN 61340-2-3: 2000. Per

Specimens are at least three measurements to perform, the measurement results per sample are too mittein. All other data relevant for determining the surface resistance can be found in DIN EN 61340-2-3: 2000. In this way, a classification (conductive, dissipative, insulating) of a substrate before coating can be made. Here and in the following, electrostatic properties are discriminated. Here are substrates with a

Surface resistance of <10 ⁴ ohm conductive, from 10 ⁴ to <10 ¹² ohms conductive and> 10 ¹² ohms insulating. The transitions are flowing. Based on the aforementioned DIN EN preheated substrates are used to determine the influence of preheating on the conductivity / surface resistance.

In accordance with DIN EN 61340, the

Surface resistance measurements alternatively with a

Measuring device by Wolfgang Warmbier, for example. SRM-200 done. Thanks to the integrated electrodes, even smaller substrates with a size of at least 80 mm x 80 mm x 1 mm can be measured.

An inventive method for coating a

Surface of an electrically non-conductive substrate with

Powder coatings, comprises the steps: - Providing a substrate to be coated,

Preheating the substrate to be coated to 40 to 140 ° C to lower the surface resistance of the substrate to less than 10 ¹² ohms, preferably in the range of about 10 ¹⁰ to less than 10 ¹² ohms,

- Single-layer, electrostatic coating of the surface with powder coating, which, in particular to a

Thermosetting, reactive system comprises,

- Curing of the powder coating layer at a maximum of 170 ° C. By providing is meant in particular that the substrate, for example, brought from a warehouse and for the

Preheating is provided or delivered by a supplier on time for preheating. Of course, it is also possible to produce the substrate on site for immediate further processing.

By preheating the substrate, an at least

partial, in particular substantially complete degassing of the substrate can be effected. Depending on the temperature and duration of preheating the substrate is more or less degassed.

It should be noted that the substrate is not damaged by the preheating and / or deformed. Suitable conditions can easily be established by the person skilled in the art, depending on the substrate used.

Furthermore, the surface resistance of the substrate is lowered by the preheating to a temperature of 40 to 140 ° C of the substrate to be coated. Especially at

Plastics but also in wood or wood materials, the surface resistance can reduce when heated and the corresponding at room temperature electrically insulating substrate are conductive. The coating of the surface with powder coating takes place

single-layered and electrostatic. In this case, the powder coating comprises a reactive system, which is curable in particular to form a thermoset, which chemically crosslinks during curing.

Reactive systems crosslink during curing and become so

Thermosets. It thus forms a robust coating layer on the substrate. Such systems form a lacquer layer with high chemical and mechanical-technological properties, ie with a high resistance under load. An inventive coating with powder coating is particularly environmentally friendly, since no solvents are used and any generated overspray can be easily recycled. It can be produced in a single-coat order higher layer thicknesses compared to the liquid paint, whereby they are very resistant to the action of moisture. In addition, powder coatings have a high abrasion resistance and are

particularly robust.

The adhesion can be mediated only by electrostatic effects substantially without melting the powder coating on the substrate. In this case, the coating temperature with respect to the powder coating used may be selected such that the temperature below the gelation temperature of

Powder coating lies. The coating temperature corresponds to the temperature of the surface of the substrate immediately before the impact of the powder coating liquid on the substrate. The coating temperature can also be above the

Gelierungstemperatur be selected because when applying the

Powder coatings, in particular by spraying, the surface of the substrate is cooled by the air flow during spraying, for example by means of a spray gun. Therefore, the adhesion is mediated here only by electrostatic effects substantially without melting the powder coating on the substrate.

The coating of the surface may take place at an elevated temperature, which is the aforementioned preheating temperature

corresponds so that the surface conductivity of the substrate is constant during powder application.

The preheating can take place, in particular in the convection oven, in a temperature range as described above. Of Furthermore, the preheating can take place over a period of 5 seconds to 90 minutes.

The preheating can alternatively take place in the infrared and / or near-infrared oven (NIR). By the vote of

Radiant temperature, the wavelength spectrum of the radiator, the nature of the substrate, the use of filters and the IR or NIR absorption behavior of the substrate, this is heated to the desired temperature. The appropriate parameters for this are individually by simple field tests

determine .

Preheating from the combination of radiant energy, IR and / or NIR, and convection is also possible and even with complex three-dimensional part geometry

Shadows to prefer.

Preferably, the temperature of the preheating is in one

Range from 40 ° C to 140 ° C, depending on how much time is left between the preheat and the powder coating process

(Cooling rate). Depending on the used material of the substrate, the electrical surface resistance decreases with increasing temperature and the substrate becomes conductive and thus electrostatically powder-coatable. The necessary

Preheating temperature can be easily determined by practical tests. It should be noted that the shape of the workpiece is maintained by the thermal load.

Before coating, the surface to be coated can be cleaned. Such cleaning removes coarse dust and grease particles from the surface. The

Cleaning can be done mechanically by brushing or by wiping with a lint-free wipe. there For example, the brush or wipe may be moistened with, for example, an alcohol-water mixture, preferably an isopropanol-water mixture having a ratio of 50/50. Thus, traces of grease and salts can be removed as far as possible.

Before the coating can be carried out on the surface to be coated, in particular for increasing the

Surface tension to a value of> 40 mN / m, preferably of> 60 mN / m, more preferably of> 70 mN / m. The determination of the surface tension can be carried out with test inks based on DIN 53364 or also with the aid of the contact angle measurement according to DIN 55660-2. Pre-treatment is preferred before

Preheat carried out, but can also be carried out after preheating, depending on the type of pretreatment. An increased

Surface tension causes improved wettability of the substrate with that heated during cure

Powder paint.

The pretreatment may be a process selected from the group:

mechanically working, in particular by grinding and / or blasting, flaming,

- Plasma treatment.

Flaming is the simplest method in the field of plastics to activate a surface, to modify the microtopography and at the same time to remove impurities, in particular organic contaminants. Excess oxygen causes the flame to enter the oxidizing area added. This creates polar groups on the surface that activate them. For a short time, the substrate is at its

Surface heated to 150 ° C to 400 ° C, thereby becoming

Impurities burned while the surface melted and partially oxidized. This leads to a new formation of the surface with a changed topography and chemical composition. Any gas inclusions in the substrate can be partially expelled by this measure, which subsequently leads to an improved surface quality. The substrates may be treated with a gas burner and e.g. Propane gas, butane gas or propane-butane gas mixture are flamed. The distance of the flame is typically about 3 cm to 15 cm and the speed of the sweep of the surface of 1 cm / s to 20 cm / s. The surface is activated by the flaming and can with the subsequently applied

Powder coating layer to achieve improved intermediate adhesion. As a rule, the activation of the surface takes place

Repeated stroking, preferably between 1 and 15 times, the surface with the gas flame. Depending on the application, in addition to the fuel gases and an organic silane compound for

Haftungsoptimierung be introduced into the gas stream. Thus, for example, a Pyrosil® layer can be deposited, which increases the surface tension, hydrophilizes the surface and forms a defined chemical

Surface structure causes.

A plasma treatment of the substrate can be carried out, for example, with the OpenAir plasma method at atmospheric pressure. In this case, energy is supplied to a gas, so that it goes into the plasma state. This energy can be in the form of

Heating, applying an electrical voltage or feeding of electromagnetic waves are supplied. In which

Plasma jet is a mixture of mostly positive charged ions, electrons or neutrons. The resulting plasma jet flows onto the substrate and generates polar groups on the substrate surface, so that the surface tension and thus the adhesion of the subsequent lacquer layer are increased. In contrast to flaming, the substrate surface does not increase or only slightly increases. Also the

Surface temperature of the substrate increases only slightly compared to the flame treatment process and is usually less than 60 ° C. The plasma jet also cleans the surface and removes possible dirt, dust or grease residues,

in particular organic impurities. Also by means of a plasma treatment, any gas inclusions in the substrate can be expelled to some extent, which subsequently allows for improved surface quality. Similar to flaming, the surface is activated by the plasma treatment, so that with the subsequently applied powder coating an improved

Intermediate liability is achieved.

The increase of the surface tension of the substrate can be generated before and / or after preheating. By a

Prior increase of the surface tension simplifies the production process of the process, since, for example, the

Surface tension can be performed in a separate step in an independent workstation. It has been shown that depending on the type of production of the

Surface tension is quite stable over longer periods of time and can already be generated several days in advance. In particular, a generated by plasma treatment

Surface tension is quite stable over several days.

For example, a surface tension can already be generated by the manufacturer of the substrate or directly at the time of delivery or at the incoming inspection. The step of coating with powder coating can be carried out by a method or a combination of methods selected from the group: spraying, in particular with a corona or tribo process,

Swirl internally for powder application with or without parallel curing of the powder coating, electrostatic fluidization bed technique and / or with

Transfer application

- combinations of said methods.

A coating by spraying with powder coating has the

Advantage that conventional systems need only be slightly adapted and that there is already a lot of experience in this process step. The investment volume for adapting to the new method according to the invention is limited. By using the corona process, that of the

Spray gun emitted powder cloud homogeneous and "soft", so that a uniform coating is made possible

Application of the tribo process leads to a better coverage of the edge and edge regions of the substrate, which in turn results in a uniform coating up to the edge region of the substrate

Substrates leads. Both methods are well known to those skilled in the art.

A coating by means of vortex sintering allows a

procedurally simple coating, provided that

Residence time of the substrate in the fluidized bed and the

Temperature of the substrate are controlled with sufficient accuracy In addition, by means of vortex sintering a thicker lacquer layer can be applied than when spraying.

When the particles of the coating powder in the

Fluidizing be additionally charged electrostatically and simultaneously provided the substrate to be coated with an opposite charge, especially on its side facing away from the surface to be coated is provided with a Gegenpol, a thicker coating layer with the same or shorter residence time as in the vortex sintering arise.

A special form of the electrostatic Fluidisierbetttechnik is the transfer application, in which the powder on a first

Applied transfer tape and from there by means of a

high voltage leading electrode is transferred to the moving past the substrate. Such a transfer application is

For example, from EP 1 321 197 A2 known. Depending on the geometry of the substrate, a combination of methods, e.g. the electrostatic fluidization bed technique and the spray application an economical and efficient

Coating process. In each case, in a combination of the methods mentioned, the spray application can be carried out in parallel and / or downstream from the respective other method. With the aid of the electrostatic fluidising bed, the underside of the profiles can be easily and quickly coated. The coating of the top takes place in parallel or subsequently with one of the known spray applications with corona or

Tribo charging. The top and bottom of the substrate can be so in one step and / or in one

Workstation at the same time coat, which is an immense

Time saved. In the subsequent curing step Thus, the coating on the top and bottom can be cured simultaneously.

The step of curing the powder coating layer can be done by a method selected from the group:

- Baking in the convection oven at temperatures in one

Range from 80 ° C to 170 ° C, preferably from 100 ° C to 160 ° C, more preferably from 120 ° C to 140 ° C over a period of 1 min to 60 min, in particular from 3 min to 40 min, preferably from 5 minutes to 20 minutes,

- infrared radiation (IR), - irradiation by near infrared radiation (NIR),

Irradiation and curing by ultraviolet radiation (UV), in particular in combination with convection heat and / or IR radiation and / or NIR radiation for melting and / or curing the lacquer layer,

- combinations of said methods.

When curing is usually a melting and

at the same time crosslinking of the powder coating layer. In the

Crosslinking becomes a multiplicity of individual macromolecules of the

Powder coating linked to a three-dimensional network.

Through the process of networking they are changing

Properties of the crosslinked lacquer layer. There will be an increase in hardness, toughness, melting point and / or

Melting range and a lowering of the solubility observed. Overall, the chemical and physical resilience of the paint layer is improved. The changes mentioned are taking part increasing degree of crosslinking. Depending on the degree of crosslinking, crosslinking of the powder coating layer first results in a layer with properties similar to an elastomer and, with increasing crosslinking, a thermosetting coating layer.

The energy required for curing, in particular for melting and for crosslinking, can be entered thermally by convection and / or radiation energy. The energy can in the form of infrared radiation with a wavelength of 3 μιη to 50 μιτι, near infrared radiation with a

Wavelength of 0.7 μιη to 3 μιη or ultraviolet radiation having a wavelength of 1 nm to 380 nm are introduced.

Likewise are combinations of different radiations

with each other or in combination with convection conceivable. The optimum process for curing the powder coating layer depends on the powder coating system used and the substrate. Because not every color has any wavelength of the above

The same radiation is absorbed, the color of the color to be cured must be taken into account and adjusted either the wavelength of the radiation, the power density of the radiation and / or the duration of the irradiation. However, this corresponds to a professional routine measures. The use of chemical adhesion promoters can be dispensed with. This waiver of chemical adhesion promoters makes a significant contribution to environmental protection. In addition, it has been shown that when using a

Adhesive for some coated substrates the

Powder coating layer after curing is severely damaged by blistering. The primer may be in the substrate

diffuse and degas during curing, so that no closed or smooth surfaces can be achieved. In addition, the use of adhesion promoters can also lead to undesirable color changes of the powder coating.

100% solvent-free powder coatings can be used. Solvent free Powder coatings are generally preferable to those with solvents in terms of environmental aspects. Also the

Material utilization is significantly higher due to increased recoverability of the solvent-free powder coating and can be up to 97%, depending on the application.

The powder coatings may be selected from the group comprising:

- polyester powder coatings,

- epoxy powder coatings,

- polyester-epoxy powder coatings, - polyurethane powder coatings,

- acrylate powder coatings,

- fluoropolymer powder coatings,

- Polyamide powder coatings.

Polyester powder coatings meet the highest demands with regard to weathering stability. They are resistant to UV radiation and offer long-term protection, especially for outdoor use, for example for façade applications. In addition, with

Polyester powder coatings achieve excellent coating quality. The polyester powder coatings can be different Have networking mechanisms. Systems based on polyaddition do not release any cleavage products during crosslinking. Accordingly, no pinholes or rough will be

Surfaces formed. For systems based on

Polycondensation has many years of experience. They are characterized by low stoving temperatures and a smooth course. In their networking, however, water is usually formed, which is often the case with larger layer thicknesses

Pinholes and blistering can result. Systems based on a free-radical polymerization show the advantages of a polyaddition system and are accordingly ausgasungsarm.

Moreover, these systems are above the

Deblocking temperature of the starter molecule extremely reactive and crosslink very quickly. Until reaching the

Deblocking temperature of the starter molecule, the paint film can flow away and ensures a smooth flow on the

Surface. Below the deblocking temperature is the

Start temperature understood at which the starter molecule or initiator splits and the reaction can start.

Pure epoxy powder coatings are suitable for protection against

Corrosion and are characterized by a superb

Chemical resistance and good adhesion. Due to the lack of light resistance, however, these are only suitable for interior applications or as primers. For this reason, polyester-epoxy powder coatings, so-called hybrid powder coatings, are frequently used in which epoxy and

Polyester resins are crosslinked with each other. The properties of the two pure systems are combined so that one

wide range of applications arises. The

Weather resistance is better than pure epoxy systems, and resistance to chemicals is good to sufficient in many cases. There are different gloss and Texture settings easily realizable. The color variety is almost infinitely adjustable.

Polyurethane powder coatings offer a very good flow and excellent weathering and chemical resistance. So are polyurethane powder coatings because of their durability

used for example in the field of anti-graffiti coatings. Acrylate powder coatings have a good to excellent course and a very good weather resistance. The

Properties of acrylate powder coatings in particular meet the high requirements of the automotive industry. Thanks lower

Crosslinking temperatures can reduce energy costs during curing.

Fluoropolymer powder coatings have a particularly high UV resistance. They are always used when these outstanding UV resistances are required.

Polyamide powder coatings allow high layer thicknesses

realize. In addition, polyamide powder coatings have a high degree of flexibility, so that their application to moving or bending and / or torsion-loaded components is preferred.

The reactivities of powder coatings can be adjusted specifically. It is distinguished between

Low-temperature systems, also called NT systems, with a cross-linking temperature above 130 ° C and ultra-low-temperature powder coatings, also known as UNT systems, with stoving conditions of less than 130 ° C. However, this classification into NT and UNT systems is not sharply defined and can only be described as

Reference designation are used. NT systems, ie low-temperature powder coatings, can already be cured at temperatures from 130 ° C., usually from 140 ° C. By using such NT systems can

according to the energy requirement during curing essential

be reduced. In addition, the thermal load of the substrate is reduced.

A further development of the NT systems are the UNT systems, ie ultra-low temperature powder coatings. These can already be cured at temperatures below 130 ° C, for example at 120 ° C or even at 105 ° C. The development even goes in the direction of temperatures well below 100 ° C. With such UNT systems, it is also possible to coat substrates with powder, which must not be exposed to a higher temperature. The energy required for curing is further reduced.

The powder coating may include electrostatic additives that affect the electrostatic properties. Due to their conductivity, these ensure increased conductivity of the powder coating. In this way, poorly conductive substrates can be coated by means of electrostatic coating processes. Electrostatic additives change the electrical

Conductivity of the powder coating and can thus become one

lead to improved powder application. Electrostatic additives are known in the field of metal coatings, where they can in particular reduce Faraday cage effects.

The substrate may comprise a material selected from the group comprising:

- glass fiber reinforced plastic (GRP), - polyamides (PA),

- polyurethanes (PU), - polyesters,

- medium density fibreboard (MDF),

- High density fiberboard (HDF),

- natural woods,

- chipboard, - wood-plastic composite (WPC),

- carbon fiber reinforced plastic (CFRP),

- Glass,

- ceramics.

When using natural wood, chipboard, MDF, HDF or wood-plastic composites as a substrate conditioning can be done by the substrate at a

certain relative humidity and / or temperature is stored. Furthermore, when using natural wood, chipboard, MDF, HDF or wood-plastic composite materials as substrate this can be first ground to a smoothed and uniform surface for the electrostatic

To ensure coating process. By preheating, in particular to a temperature in the range of 40 to 140 ° C, as previously mentioned on wood-based substrate salts and / or volatile wood ingredients by Expelling moisture transported to the surface of the substrate and remain there for a long time

("Activation effect")

Surface conductivity of the wood-based substrate increases and thus an electrostatic coating possible. Irrespective of the type of wood used, however, the "activation effect" differs depending on the type of wood.The curing of the powder coating on a wood-based substrate can likewise take place in the temperature range from 80 to 170 ° C., preferably 100 to 160 ° C. particularly preferably 120 to 140 ° C. If the relative humidity is too high

Moisture of the substrate occurs paint defects in the form of bubbles and ejection. At a too low relative

Moisture of the substrate, the surface resistance is not shifted into the dissipative area. Accordingly, a conditioning substrate-specific and experimental to determine.

When using natural wood, chipboard, MDF, HDF or wood-plastic composite materials as a substrate, a pre-treatment by means of flame treatment has proven to be particularly advantageous. This will cause a flare off

erecting wood fibers, which can interfere with the surface quality reached. At the same time, the substrate is warmed up in this case ("activation effect").

The substrate may comprise a material having a content of glass fibers or of carbon fibers between 20% to 80%, in particular between 30% to 70%, preferably between 40% to 60%. Such substrates allow a considerably higher mechanical load. For example, such substrates as technical

Versatile use of plastics. Before coating the substrate, the substrate can be at least partially degassed by thermal action. Such degassing prevents or reduces the formation of bubbles during curing of the powder coating and thus favors a smooth surface of the coating.

Furthermore, the invention relates to a method for

Coating a surface of an electrically non-conductive substrate with powder coatings, in particular according to the preceding embodiments, comprising one or more electrostatic

Additives. This is an improved coating of

Surface of non-conductive substrates achieved.

The invention further relates to the use of a

Powder coating comprising one or more electrostatic additives for coating a surface of an electrically non-conductive substrate.

A substrate, in particular a non-conductive substrate, with a coated surface produced by a method as described above has the stated advantages.

The invention will be described in more detail below with reference to figures.

Figure 1 diagram with the temperature and the

Surface resistance of a substrate over time. Figure 2 substrate coatings with characteristic

Surface resistances. Figure 3 Comparison of substrate coatings with powder coating comprising electrostatic additives.

FIG. 1 shows a diagram which shows the

Temperature curve and the surface resistance of a substrate as a function of time maps. The substrate was placed in a heating oven for 10 seconds to heat and then removed from the oven. The temperature of the stove was constant at 130 ° C. Depending on the thickness of the substrate, this is heated to a temperature between the ambient temperature (outside the furnace) and the temperature of the heating furnace (see.

Figure 1, at about 44 ° C). The temperature and the

Surface resistance of the substrate was during the

Cooling process measured at room temperature. The measured values are plotted directly after removal from the heating furnace for 2 min. 30 sec.

By preheating the substrate was the

Surface resistance lowered to a value of approx. 5xl0 ¹⁰ ohms at a temperature of approx. 44 ° C. When stored at

Room temperature cools the substrate to 36 ° C within one minute. The surface resistance increases with decreasing temperature of about 5xl0 ¹⁰ ohms to about 7x1ο ¹¹ ohms within a minute. In this area can be complete and

high quality single-layer electrostatic

Achieve coatings as the substrate under these

Conditions has a sufficiently conductive surface.

FIG. 2 shows substrate coatings with characteristic surface resistances. The substrates were preheated and then by electrostatic powder application

coated. The applied powder coating was then cured. Figure 2A shows a coated substrate wherein the substrate was not preheated and had a surface resistance of> 10 ¹² ohms. After an electrostatic powder application, the substrate is insufficiently coated. The white areas have powder of the coating, while in the black areas the substrate can be seen without coating. A

Powder coating of the substrate with a surface resistance of> 10 ¹² ohms is incomplete and thus insufficient.

Figure 2B shows a coated substrate wherein the substrate was minimally preheated and thus had a surface resistance of δχΐθ ¹¹ ohms. After an electrostatic

Powder coating, the substrate is almost completely coated compared to Figure 2A, but still has black

(uncoated) areas.

FIG. 2C shows a coated substrate according to the invention, which after preheating had a surface resistance of 10 ¹¹ ohms. The electrostatic powder application under these conditions leads to a homogeneous, smooth and continuous coating of the substrate. The coating corresponds to a coating, as it is known for metals or conductive substrates.

FIG. 3 shows coated components, the coatings taking place under the same conditions. Component 1 has a

Powder coating on, wherein the powder coating

includes electrostatic additives. In comparison, the coating of component 2 does not comprise any electrostatic additives. Especially on the narrow front sides are the advantageous properties mediated by electrostatic additives

illustrated. Component 1 has in contrast to component 2 a advantageous coating on. By varnish modifications with electrostatic additives is additionally the

Improved coating result. Further aspects of the invention relate to:

A. A method of coating a surface of an electrically non-conductive substrate with powder coatings comprising

Steps :

Providing a substrate to be coated,

Preheating the substrate to be coated,

Coating the surface with powder coating,

- Curing the powder coating layer. B. Process according to A, characterized in that the preheating at a temperature between 100 ° C and 220 ° C, in particular between 110 ° C and 190 ° C, preferably between 120 ° C and 170 ° C and over a period of 5 min to 2 hours, in particular from 20 minutes to 90 minutes, preferably from 40 minutes to 75 minutes.

C. Method according to A or B, characterized in that on the surface to be coated before coating a

Pretreatment, in particular an increase in

Surface tension to a value of> 40 mN / m, preferably of> 60 mN / m, more preferably of> 70 mN / m occurs.

D. Method according to C, characterized in that the

Pretreatment is a procedure selected from the group:

mechanically roughening, in particular by grinding and / or blasting,

- Flaming,

- Plasma treatment. E. Method according to C or E, characterized in that the pretreatment of the surface takes place before and / or after preheating. F. Method according to one of the aspects A to E, characterized in that the step of coating with powder coating takes place by means of a method selected from the group:

Spraying, in particular with a corona or tribo process,

- Whirling,

electrostatic fluidising bed technology, in particular with transfer application,

- Combination of the mentioned methods. G. Method according to one of Aspects A to E, characterized

characterized in that the step of curing the

Powder coating layer by means of a method selected from the group: - Burning in the convection oven at temperatures in one

Range from 100 ° C to 230 ° C, preferably from 110 ° C to 190 ° C, more preferably from 130 ° C to 160 ° C over a period of 1 min to 60 min, in particular from 3 min to 40 min, preferably from 5 minutes to 20 minutes,

Infrared radiation (IR),

- irradiation by near infrared radiation (NIR),

- combinations of said methods. H. Method according to one of aspects A to G, characterized in that the use of chemical adhesion promoters is dispensed with. I. Method according to one of Aspects A to H, characterized

characterized in that solvent-free powder coatings are used.

J. Method according to one of aspects A to I, characterized

in that reactive systems are used as powder coatings.

K. Method according to one of the aspects A to J, characterized in that the powder coatings are selected from the

Group comprising:

- polyester powder coatings,

- epoxy powder coatings,

- polyester epoxy powder coatings,

- polyurethane powder coatings,

- acrylate powder coatings,

- fluoropolymer powder coatings,

- Polyamide powder coatings.

L. Method according to one of aspects A to K, characterized in that the powder coatings are low-temperature powder coatings or ultra-low-temperature powder coatings.

A method according to any one of aspects A to L, characterized in that the substrate comprises a material selected from the group comprising:

- glass fiber reinforced plastic (GRP),

- polyamides (PA),

Polyurethanes (PU), - polyester,

- medium density fibreboard (MDF),

- High density fiberboard (HDF),

- natural wood,

- Glass,

- ceramics.

N. Method according to one of the aspects A to M, characterized in that the substrate comprises a material with a content of glass fibers between 20% to 80%, in particular between 30% to 70%, preferably between 40% to 60%.

0. Method according to one of the aspects A to N, characterized in that before the coating of the substrate

Substrate by thermal action at least partially, in particular substantially completely degassed.

P. Substrate, in particular non-conductive substrate, with a coated surface produced by a method according to one of aspects A to O.

Claims

claims

A method of coating a surface of an electrically non-conductive substrate with powder coatings, comprising the steps of:

Providing a substrate to be coated,

Preheating the substrate to be coated to 40 to 140 ° C to lower the surface resistance of the substrate to less than 10 ¹² ohms, preferably in the range of 10 ¹⁰ to less than 10 ¹² ohms,

Single-layer, electrostatic coating of the

Surface with powder coating, which comprises a, in particular to a thermoset-curing, reactive system,

- Curing of the powder coating layer at a maximum of 170 ° C.

2. The method according to claim 1, characterized in that the preheating over a period of 5 seconds to 90 minutes

he follows . 3. The method according to any one of claims 1 and 2, characterized

in that the substrate is preheated by means of irradiation, in particular by means of infrared radiation, or in an oven. 4. The method according to any one of claims 1 to 3, characterized

characterized in that on the surface to be coated prior to coating, a pretreatment, in particular an increase in the surface tension to a value of> 40 mN / m, preferably of> 60 mN / m, more preferably of> 70 mN / m takes place.

A method according to claim 4, characterized in that the pretreatment is a method selected from the group:

mechanically working, in particular by grinding and / or blasting,

- Flaming,

- Plasma treatment.

A method according to claim 4 or 5, characterized in that the pretreatment of the surface takes place before and / or after preheating.

Method according to one of claims 1 to 6, characterized

characterized in that the step of coating with

Powder coating is carried out by a method selected from the group:

Spraying, in particular with a corona or tribo process,

- Whirling,

- Electrostatic Fluidisierbetttechnik and / or with

Transfer application

- Combination of the mentioned methods. Method according to one of claims 1 to 7, characterized in that the step of curing the

Powder coating layer by means of a method selected from the group:

- Baking in the convection oven at temperatures in a range of 80 ° C to 170 ° C, preferably from 100 ° C to 160 ° C, more preferably from 120 ° C to 140 ° C over a period of 1 min to 60 min, in particular of 3 minutes to 40 minutes, preferably from 5 minutes to 20 minutes,

Infrared radiation (IR),

- irradiation by near infrared radiation (NIR),

- Irradiation and curing by ultraviolet radiation (UV), in particular in combination with convection heat and / or IR radiation and / or NIR radiation for

Melting and / or hardening of the lacquer layer,

- combinations of said methods.

9. The method according to any one of claims 1 to 8, characterized

characterized in that the use of chemical

Adhesive agent is waived.

10. The method according to any one of claims 1 to 9, characterized

characterized in that solvent-free powder coatings are used.

11. The method according to any one of claims 1 to 10, characterized

in that the powder coatings are selected from the group comprising: - polyester powder coatings,

- epoxy powder coatings,

- polyester epoxy powder coatings,

- polyurethane powder coatings,

- acrylate powder coatings,

- fluoropolymer powder coatings,

- Polyamide powder coatings.

12. The method according to any one of claims 1 to 11, characterized

in that the powder coatings are low-temperature powder coatings or ultra-low-temperature powder coatings.

13. The method according to any one of claims 1 to 12, characterized

characterized in that the powder coating electrostatic

Includes additives.

14. The method according to any one of claims 1 to 13, characterized

characterized in that the substrate comprises a material selected from the group comprising:

- glass fiber reinforced plastic (GRP),

- polyamides (PA),

Polyurethanes (PU),

- polyester,

- medium density fibreboard (MDF),

- High density fiberboard (HDF),

- natural wood,

- chipboard,

- wood-plastic composite (WPC),

- Carbon fiber reinforced plastic (CFRP).

- Glass,

- ceramics.

15. The method according to any one of claims 1 to 14, characterized in that the substrate comprises a material having a content of glass fibers or carbon fibers between 20% to 80%, in particular between 30% to 70%, preferably between 40% to 60% ,

16. The method according to any one of claims 1 to 15, characterized

characterized in that the adhesion of the powder coating during coating only by electrostatic effects in

Essentially without melting the powder coating on the

Substrate is mediated.

17. A method for coating a surface of an electrically non-conductive substrate with powder coatings, in particular according to one of claims 1 to 16, comprising one or more electrostatic additives.

18. Substrate, in particular non-conductive substrate, with a coated surface produced by a method according to one of claims 1 to 16 or 17.

19. Use of a powder coating comprising one or more electrostatic additives for coating a surface of an electrically non-conductive substrate.