DE102010022265A1 - Hydrophobic coating and application - Google Patents

Abstract

The invention relates to coatings for all types of surfaces, in particular for insulating plastics in outdoor use, in particular for transformer blocks made of polyamide to improve weather resistance, corrosion protection and tracking resistance. The invention also relates to a method for coating such transformer blocks. According to the invention, hydrophobic particles are installed primarily in the surface area of the coating.

Description

The invention relates to coatings for epoxy resin components in outdoor use, in particular for transformer blocks of epoxy resin to improve the weather resistance, corrosion protection and tracking resistance. Moreover, the invention relates to a method for coating such transformer blocks.

Hydrophobic surfaces are now widely used. Thus, car windows, baths or films can be coated to achieve a water-repellent and self-cleaning effect. Also, for example, housing of water-sensitive components, such. As electrical assemblies are provided with a water-repellent layer to ensure a faster flow of water. In this way, for. As corrosion processes avoided or slowed down or electrical flashovers or short circuits can be prevented. Here, the higher the contact angle (measure of hydrophobicity) of the coating system, the better the protection against water sticking and thus also against electrical short circuits or flashovers.

Many components of electrical systems are encapsulated with epoxy resin for insulation purposes. Other plastics such as polyamide are used, for example, to store the transformers for medium voltage on special blocks and thus electrically decouple them (transformer blocks). However, the insulation effect of these components can be greatly influenced by weather conditions. Moisture or moisture can form conductive paths on their surface, which in the worst case result in electrical flashover. The reason for this is that the durability against environmental influences and water-repellent effect of epoxy resin components is not sufficient. For example, anhydrous or amine-hardened bisphenol A or F-diglycidyl ether resins are not suitable or only conditionally suitable for outdoor use as electrical insulation materials because of their hydrophilic character, since atmospheric moisture or polluted condensation water wets well or even completely on the surface.

• a) Einerseits können die verwendeten Materialien als Bulk-Material chemisch modifiziert werden. Chemisch modifizierte Epoxidharze weisen zwar eine gesteigerte Hydrophobizität auf, können aber einen Kontaktwinkel von 100° nicht mehr übertreffen. Oftmals sind aber deutlich höhere Wasserkontaktwinkel erforderlich um ein leichtes Ablaufen von Regen oder kondensiertem Wasser zu ermöglichen. Daher können aktuell verfügbare Lösungen zwar eine leichte Verringerung des Problems bewirken, sie beseitigen es aber in keinem Falle.
• b) Die zweite Möglichkeit der Verringerung der Benetzbarkeit der Bauteile ist die Aufbringung einer hydrophoben Beschichtung. In diesem Fall können Oberflächen zum Einsatz kommen die zu großen Teilen aus Siloxanen mit fluorierten Alkylketten bestehen. Die Dauer-Haftung dieser Schichten ist aber auf vielen Kunststoffen, insbesondere wenn diese Umwelteinflüssen ausgesetzt sind, unzureichend. Des Weiteren sind oftmals Härtungstemperaturen nach der Aufbringung der Beschichtung erforderlich, die dem Kunststoff schaden oder diesen sogar zerstören können.

To reduce this wetting with water, two basic options are available.

• a) On the one hand, the materials used can be chemically modified as a bulk material. Although chemically modified epoxy resins have increased hydrophobicity, but can no longer exceed a contact angle of 100 °. Often, however, significantly higher water contact angles are required to allow easy drainage of rain or condensed water. Therefore, although currently available solutions may cause a slight reduction in the problem, they will never eliminate it.
• b) The second possibility of reducing the wettability of the components is the application of a hydrophobic coating. In this case surfaces can be used which consist to a large extent of siloxanes with fluorinated alkyl chains. However, the permanent adhesion of these layers is inadequate on many plastics, especially when exposed to environmental influences. Furthermore, curing temperatures after application of the coating are often required, which can damage the plastic or even destroy it.

Commercial coating systems achieve contact angles of approx. 105 °. This achieves a maximum value (theoretically 117 °) for a superficially smooth coating.

Higher values can not be achieved by a purely chemical modification of the surface. According to Wenzel ( RN Wenzel, Ind. Eng. Chem., 1936, 28, 988 ) in addition to the surface chemistry a certain micro or nanorail required. If the substrate can be patterned (eg by sand blasting of metal), it is no problem to achieve contact angles of over 150 ° by applying a structure-retaining surface chemistry. If the substrate is the structural support, such superhydrophobic coatings are generally very mechanically stable, comparable to the mechanical properties of the substrate material.

Unfortunately, substrate structuring is only a reasonable way to produce superhydrophobic surfaces in exceptional cases. Often, the substrate is too hard or crack-sensitive (see Steels or glass), as a structuring would be economically or industrially feasible.

It is therefore an object of the present invention to provide a coating and a method for producing the coating in which values of the contact angle greater than 105 ° are achieved without substrate structuring.

The solution of the object and the subject of the invention are disclosed in the description, the claims and the figures.

Accordingly, it is a general recognition of the invention that a superhydrophobic coating can be produced by incorporating hydrophobic particles into a bovine layer which, for example, may also be hydrophobic.

Accordingly, the subject matter of the invention is a hydrophobic coating having a contact angle greater than 105 °, which comprises two components, a bovine component as coating material 1 and a particle component as coating material 2. In addition, the invention relates to a process for coating a substrate, wherein first a binder component is applied to the substrate to be coated and then brought to the preferably not yet cross-linked binder layer, the particles, which then partially sink into this, but basically remain on the surface ,

The hydrophobicity of the coating is correspondingly determined by the hydrophobicity of the surface of the particles, whereas the mechanical properties of the coating are essentially based on the bovine layer.

According to a preferred embodiment of the invention, the particles are distributed inhomogeneously within the layer by being present at or directly below the surface of the binder in higher concentration than otherwise in the layer.

As bovine component or casting compound of the coating, it is possible to use any polymer or compounds which crosslink via a sol-gel process.

• – hydrophober Grundcharakter aufgrund der Materialchemie, bevorzugt WKW > 70°, gegebenenfalls durch Additive einstellbar,
• – verdünn- und/oder sprühbar, beispielsweise mit gängigen Lösungsmitteln wie z. B. Iso-butylacetat,
• – besondere Trocknungseigenschaften, insbesondere schnelles Antrocknen an Luft sowie Ausbildung einer klebrigen Oberfläche vor der späteren Durchhärtung,
• – gute mechanische Eigenschaften im Bezug auf Kratzfestigkeit, Elastizität sowie Hydrolysebeständigkeit,
• – auftragbar bevorzugt über übliche Beschichtungsmethoden, beispielsweise durch Lackieren, Tauchverfahren, Streichprozessen oder Sprühen.

The binder preferably has the following properties:

• Hydrophobic basic character due to the material chemistry, preferably HPC> 70 °, optionally adjustable by additives,
• - Dilutable and / or sprayable, for example, with common solvents such. For example iso-butyl acetate,
• Special drying properties, in particular rapid drying in air and formation of a sticky surface before the subsequent hardening,
• Good mechanical properties with regard to scratch resistance, elasticity and hydrolysis resistance,
• - Applicable preferably via conventional coating methods, for example by painting, dipping, brushing or spraying.

Due to the properties mentioned, a two-component PU lacquer system (if appropriate using additives) is preferably used as the coating component 1.

The following compounds may be mentioned by way of example as coating material 1:
A mixture of epoxycyclohexyl-terminated, polyhedral oligomeric silsesquioxane (liquid Picopartikel, Hybrid Plastics ^™, a hydrophobic, or Trisilanol- triaminisooctyl-POSS ^® d ₅₀ = 0.5-0.8 nm) and methylhexahydrophthalic anhydride (anhydride, preferably fully hydrogenated Alkylphthalsäureanhydrid, Hexion ^TM , ^EPC® 868).

A mixture of epoxycyclohexyl POSS (A) + anhydride curing agent (preferably fully hydrogenated alkylphthalic anhydride) (B) + reaction accelerator (E) + crosslinking, hydrophobic trisilanol or triamine isooctyl-POSS (F) is, for example, in a ratio of the components A, B, E, F with the following preferred proportions by weight: A: 40-60%, B: 35-55%, E: 0.1-5%, F = 0.1-10%, total 100%.

This mixture may contain a small addition of trisilanol isooctyl substituted, polyhedral silsesquioxane (liquid picoparticle, Sigma Aldrich ^™ ) to the precursor mixture to further increase the contact angle of the cured resin layer. Furthermore, the mixture may contain a small addition of a tertiary amine (such as dimethylbenzylamine) as an accelerator substance.

The mixture is preferably soluble in organic solvents (eg tetrahydrofuran) and thus stable over a period of weeks or months. The application can be carried out by various industrially established methods; this includes u. a. Spraying, dipping, spinning, squeegeeing, jetting, dispensing. After being applied to the respective substrates, the applied mixture prepared according to the invention is freed from the solvent by means of heating and then cured (for example thermally).

For example, the mixture used (1 no.) Is an epoxycyclohexyl-terminated POSS ^®, which is a liquid at room temperature component that has proved to be particularly scratch stable in the cured state. Due to the radially arranged Oxiranendeinheiten it behaves like a conventional epoxy resin, the z. B. anhydridisch (No.2) or aminic can be cured. The use of particle mixtures of the size ranges micrometer and nanometer (Nos. 3, 4) results in a self-organizing surface roughness, as nanoparticles occupy the surface of the microparticles. By curing the resin and hardener components contained in the reaction mixture (Nos. 1, 2), the micro / nanoparticles are permanently fixed by covalent bonding between the epoxide units on the surface of the microparticles and the hardener matrix. The reaction resin used (Nos. 1, 2) shows considerable scratch resistance due to the high density of (SiO) units and imparts high stability to the potting layer.

By slight admixture of an additional kratzresistiven and water-repellent additive - ideally a POSS ^® derivative of the type no. 5 - can be up to contact angles of 150 ° or more to achieve a more hydrophobization, since due to the good miscibility with the liquid phase (# 1. , 2) a kind of doping of the embedding matrix as well as a saturation of remaining, uncoated Si-OH groups of the filler surfaces (Nos. 3, 4) can take place. To initiate a thermal curing reaction in areas around 80 ° C, the use of e.g. B. aminic accelerators (No. 6) appropriate.

According to a preferred embodiment of the invention, a two-component PU lacquer system, optionally with the use of additives, is used as the binder or casting component.

According to a further preferred embodiment, the coating material 1, the binder or the potting compound, cold-curing.

According to a preferred embodiment of the method, the binder or casting component, ie the coating component 1, is adjusted, for example, with the addition of suitable solvents, so that about 4 minutes after the application, the work-hardening has already begun.

Preferably, a coating component 1 is chosen so that initially forms a sticky surface before curing.

Preferably, the method is carried out so that the particles (that is, the coating material 2) is applied to the hardened and sticky surface.

The coating material 2, that is, the particles can include all types of hydrophobic materials which may be mentioned metal oxides, epoxy-silane treated micro and nanoparticles (z. B. Quarzwerke Frechen, Silbond ^® W12 EST, d ₅₀ = 20 microns and alkylsilanmodifiziertes, produced by flame pyrolysis fused silica Aerosil ^TM, Aeroxide ^® LE1, d ₅₀ = 20 nm u. more other inorganic fillers.

For example, the coating material 2 is a material system of microparticles (preferably epoxy silated quartz powder / material) (C) and / or nanoparticles (fused silica or diamond, alkylated or perfluoroalkylated coated) (D).

It is provided in particular that the components C and D are present in the following amounts: C: 50-99%; D: 0.1% by weight to 50%, particularly preferably C: 80 to 99% and D: 1.10%, all in percent by weight and in each case based on the dry weight of the total coating.

The amount of coating material 2 in the coating material 1 is (ie particles in the binder), for example: 10 to 90% by weight, in particular 50 to 80% by weight. In this case, for example, a multimodal distribution of the particles is provided.

The coating material 2 is a powdery material having hydrophobic groups on the surface, for example alkyl and / or fluorinated alkyl groups. Depending on the application, the surface can be chemically and / or physically functionalized as desired, and optical effects or filters can also be incorporated into the coating.

The particle size of the powder is to be selected as a function of the desired hydrophobic properties, with a mean particle size of the powder of 5-500 nm, preferably 70-250 nm being selected for low hysteresis of the coating and substantial independence of the wetting from the drop size. Of the average agglomerate diameter is for example in the range of 100 nm to 2000 nm, preferably 500 nm-1500 nm.

Particularly suitable are different surface-modified silicon oxides have been found.

The order of the coating material 2 takes place from the powder form. It has been found to be insignificant for the hydrophobic effectiveness of the coating, whether the order is done by dusting by sieve, by means of a commercially available powder coating gun or via a solvent-free spraying process.

The layer thickness may be in the range from 0.1 .mu.m to 100 .mu.m, preferably 1 .mu.m to 10 .mu.m, and more preferably in the range from 10 .mu.m to 20 .mu.m. In particular, layer thicknesses in the range of less than 20 microns, for example, with the coating material 1 POSS ^® , realized.

The inventive combination and incorporation of micro, nano and sub-nano (= Pico) particles can prepare a solvent-compatible precursor reagent based on epoxy resin, which can be applied to any substrate by a spray process. Subsequent curing (eg, heat curing) then forms the particular final topology according to the invention, which on the one hand sets the desired hydrophobicity and, on the other hand, has a remarkable scratch and abrasion stability.

The combination of the described materials in the embodiment presented as preferred, in which the distribution of the particles within the layer is inhomogeneous, causes the hydrophobic particles, on the one hand, to mechanically bond firmly to the binder system, and, on the other hand, be concentrated where they are to act the surface.

Part of the particles sinks into the coating system and ensures the survival of the superhydrophobic properties even after the layer has been damaged. A large part of the applied particles lead to the binder surface, forming the desired surface structure but is anchored mechanically in the binder.

The mechanical properties of the coating essentially correspond to those of the binder. If, for example, a PU coating system is used, excellent wiping, scratching and abrasion resistance can be achieved.

Verwendetes Basisharz und Härter

Verwendete Mikro- und Nanopartikel aus Ausführungsbeispiel 1

Verwendetes Hydrophobisierungsreagenz und Beschleuniger Exemplary mixtures are composed as follows: Tab. 1: Exemplary embodiment 1 No. component substance Weighing [g] 1 Reactive resin / Picofüllstoff Epoxycyclohexyl POSS ^® 60,50 2 reaction hardener methylhexahydrophtalic 54,50 3 microfiller Silbond ^® W12 EST 276.00 4 nanofiller Aeroxide ^® LE1 6.90 5 reaction accelerators dimethylbenzylamine 1.00 6 Kontaktwinkelmodifikant Trisilanol isooctyl-POSS ^® 4.60 Tab. 2: Exemplary embodiment 2 No. component substance Weighing [g] 1 Reactive resin / Picofüllstoff Epoxycyclohexyl POSS ^® 60,50 2 reaction hardener methylhexahydrophtalic 54,50 3 microfiller Micro Diamond SYNDIA RBM 6-12 276.0 4 nanofiller SYNDIA SYP 0-0.1 6.90 5 reaction accelerators dimethylbenzylamine 1.0 6 Kontaktwinkelmodifikant Trisilanol isooctyl-POSS ^® 4.60

Used base resin and hardener

Used micro- and nanoparticles of embodiment 1

Used hydrophobization reagent and accelerator

In the exemplary embodiment, an epoxy resin component was coated with the composition described above. An advantage in the coating of epoxy-based substrates is the equality of both Base materials. Thus, an epoxy resin substrate can additionally crosslink during the thermal curing of the epoxy resin coating according to the invention with the coating and provide for a very good adhesion of the coating. This can prevent delamination under heavy mechanical load.

Surfaces of electrical insulator components of conventional aromatic bisphenol A / F resins can be easily and inexpensively hydrophobized with the formulation according to the invention. This makes it possible to use the established aromatic resins for the outdoor area, which at the same time, however, have hydrophobic properties.

Due to the scratch-resistant single-use resin based on POSS ^® , this layer can be kept very thin with high resistance and good flexibility (typically layer thicknesses less than 20 μm). The additional hydrophobization by means of water-repellent POSS ^® derivatives (No. 5) leads to a further increase in stability of the particle surfaces with simultaneous increase in contact angle. Substrates coated in this way can have long lifetimes, for example in the case of creep resistance tests due to the rapid dripping and the low tendency to wetting. Embodiment 3 No. component substance Weighing [g] 1 diol FreiLacke EFDEDUR UR1040GRA999 16 2 cyanate FreiLacke EFDEDUR HU0001 4 3 solvent butyl 20 4 nanoparticles Aeroxide LE 1 about 1 g

In Embodiment 3, an ABS plastic component having the above-described composition was coated. After exactly 240 s of drying, 1 g of Aeroxide LE 1 (Degussa Evonik) was sprinkled through a sieve onto the dried coating. The layer was dried in air overnight and cured. Subsequently, the water contact angle was measured. He was 155 °.

In the case according to the invention, the binder material is a polyurethane consisting of a diol, a cyanate as hardener and butyl acetate as dilution in a mixing ratio of 4: 1: 5. As a solid component was alkylsilanmodifiziertes, fused silica produced by flame pyrolysis Aerosil ^TM, Aeroxide ^® LE1, d50 = 20 nm used. The application of the PU lacquer can be carried out by various industrially established methods; These include spraying, dipping, spinning, doctoring, jetting, dispensing.

After application to the respective substrates, the applied mixture prepared according to the invention is freed from air or air for exactly 240 s and then sprinkled with the solid component until the substrate is completely covered with the solid component.

Subsequently, the substrate is dried for 30 minutes in air. Supernatant solid is blown off and the substrate is dried for a further 12 hours in air.

The layer system described was successfully tested in a project for the hydrophobization of polyamide transformer blocks. An application, especially in existing systems as a retrofit solution is considered promising.

Coated components thus promise, in addition to a self-cleaning effect, high resistances against weather-related damage. Furthermore, the electrical breakdown strengths of Epoxidharzmatrices known from the literature are high (> 30 kV / mm). Due to the low required layer thicknesses, this represents an enormous cost-saving potential in contrast to the conventional rubber coating.

1 shows the result of Salzkammerbesprühung.

To investigate the resistance of such a coated surface of a commercially available epoxy resin based on bisphenol A diglycidyl ether / acid anhydride base to weather-like external conditions, a cyclic salt spray test of Schärfestufe 2 after DIN EN 60068-2-52 [2] completed. In addition were five Epoxidharzprobekörper according to the invention as described in point 5 and then spray three phases (sodium chloride solution, 5 wt .-%) of 2 h each with intervening 20-hour climatic storage at 40 ° C / 93% r. H. subjected. 1 shows the course of the water contact angle over the number of cycles.

As 1 can be seen, the layer coated according to the invention undergoes on average a decrease of 7% over the entire Besprühungsperiode. The uncoated blank sample suffers surface damage due to treatment with the saline solution and subsequent climatic storage, whereby the average roughness increases. This manifests itself in an increase in the wetting angle. The coating of the invention thus shows superior resistance to weather-related surface stress.

To test the resistance of a coated epoxy resin component for outdoor use against strong sunlight, a UV stress test was performed. For this purpose, five Epoxidharzprüfbekörper were coated and then exposed for 100 hours in a Suntest tester strong sunlight. A comparison of the contact angles before and after the load should provide information about the UV resistance.

As a result, it was found that on average the contact angle decreased by 2. However, these minimal losses have no effect on the effectiveness of the coating according to the invention and thus it can be regarded as UV resistant.

Both exams were with regard to the examination standard ASTM G154 which combines a salt spray test and a UV stress test.

2 shows the embodiment in which the particles are no longer enclosed by the matrix material; they are partly free on the surface. The surface modification of the particles is fully retained for the hydrophobicity of the coating.

The sinking of the particles can also be excluded by material selection and process control. A sinking in the layer to the substrate is not possible by the drying of the layer material. The particles sink only slightly into the layer material. This preserves the functionality of the surface modification. The controlled embedding of the particles on or in the layer material forms a high mechanical stability with respect to the maintenance of the superhydrophobic properties of the particle surface.

The combination according to the invention and the application of nanoparticles hydrophobically modified by surface coating make it possible to prepare a solvent-compatible precursor reagent based on PU lacquer, which can be applied to any desired substrate by a spraying process. The subsequent incorporation of the particles then forms the particular topology, which on the one hand sets the desired hydrophobicity and on the other hand has a remarkable scratch and abrasion stability.

The invention relates to coatings for all types of surfaces, in particular of insulating plastics in outdoor use, in particular for transformer blocks made of polyamide for improving the weather resistance, corrosion protection and tracking resistance. Moreover, the invention relates to a method for coating such transformer blocks. According to the invention, hydrophobic particles are mainly incorporated in the surface area of the coating.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• RN Wenzel, Ind. Eng. Chem., 1936, 28, 988 [0006]
• DIN EN 60068-2-52 [2] [0052]
• ASTM G154 [0056]

Claims (9)

Hydrophobic coating with a contact angle greater than 105 °, comprising two components, a binder component as coating material 1 and a particle component as coating material 2. A hydrophobic coating according to claim 1, wherein the distribution of the particle component, ie of the coating material 2 in the binder component, that is to say the coating material 1, is inhomogeneous. A hydrophobic coating according to any one of the preceding claims, wherein the coating material 1 comprises 60% -90% diol, 10% -40% cyanate and 0% -70% solvent. A hydrophobic coating according to claim 3, wherein in the coating material 1 the components are present in the ratio 4: 1: 5 (diol: cyanate: LM). Hydrophobic coating according to one of the preceding claims, which is present in a layer thickness of 0.1 μm to 100 μm. A hydrophobic coating according to any one of the preceding claims, wherein the coating material 2, the particles, is present in an agglomerate size of on the average 100 nm to 2000 nm. A hydrophobic coating according to any one of the preceding claims, wherein the average particle size is in the range of 5-500 nm. A hydrophobic coating according to any one of the preceding claims, wherein the coating material 2 is a silicon oxide. Application of a coating according to one of the preceding claims to electrical and electronic components and components such as HV / MV / MV insulators, cable bushings, switch housings, transformer sheathing, supports, covers.

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