DE102012208653B4 - Process for the preparation of a surface coating with ice-repellent properties, surface coating and their use - Google Patents

Abstract

Method for producing an ice-repellent coating from a pyroelectric film by the method steps:
a) coating a surface with a coating liquid, of PVDF (polyvinylidene fluoride) in pure form, as a solution or mixture or dispersion,
b) drying the coated surface
c) phase transformation of the PVDF by means of a heat treatment of the coated surface at temperatures between 135 ° C and 150 ° C.
d) acting on the coated surface of an electric field.

Description

The invention relates to a method for producing a surface coating with ice-repellent properties, the surface coating and their use.

Ice-repelling is understood to mean that not so much ice is deposited on the coated surface under the same conditions as on an uncoated surface and / or that ice formation starts later and / or that the ice is easier to remove mechanically. The adhesion of ice is a major problem for a number of industrial plants. It affects primarily sectors of the energy industry, the telecommunications industry, electrical supply units, transport, in particular the aviation industry, etc. Ice and hoarfrost lead to the reduction of efficiency up to the inability of technical equipment. Great icing problems also occur in the cooling technology. Fans, piping systems, heat exchangers, etc. must be taken out of operation at regular intervals and lavishly de-iced.

The known methods of avoiding ice start at various points.

On the one hand, it is attempted to achieve a reduction of the ice adhesion force and the weakening of intermolecular forces at the interface of components to the adherent ice by means of different coating systems. This approach is essentially based on measures for ultrahydrophobization of the surfaces, which consist of a minimization of the surface energy and a targeted surface structuring ( JP2000044863A ). Overall, coating systems with hydrophobizing properties can reduce the adhesion of adhering ice and thus facilitate mechanical processes of ice removal. They can have a freeze-delay effect, but they can not prevent it.

On the other hand, attempts were made to minimize the adhesion of ice over its share of electrostatic forces of attraction. About a constant electrical DC voltage, these forces can be influenced. Between electrically insulating coating and ice, a fine-meshed network is applied, which realizes the electrical contact ( US20030024726A1 . VF Petrenko, Ryzhkin, IA; Surface states of Charge Carriers and Electrical Properties of the Surface Layer of Ice, J. Phys. Chem. B 1997, 101, pp. 6285-6289 ). As this mechanism presupposes a conductivity of the ice, it can only be used for aqueous solutions (eg NaCl dissolved) and is not applicable to distilled water.

Heterogeneous surface clustering, as known from the hydrophilic / hydrophobic membrane surface of ice-nucleating bacteria, was simulated in two runs with sol-gel chemistry. The aim in both cases was to establish a hydrophobic, anti-adhesive and ice-opaque character of the coating. First, a modification of the hydrophilic-hydrophobic behavior was carried out by a particle reinforcement of sol-gel layers, primarily with silicone particles, but also other organic and inorganic admixtures not mentioned by name. US 006153304A ). Second, an attempt was made to biomimetically adapt the heterogeneously designed membrane surface of ice nucleating bacteria. Some tiny hydrophilic molecules in the layer allow localized ice formation at these sites. In this way, the energy balance is intervened to form stable ice crystal nuclei. Spontaneous freezing of the surfaces should be avoided and the freezing process should be controlled in order to support the ice-repellent layer properties ( WO 2005/075112 A1 or. WO 02/09 04 59 A1 ). In the WO 2008/071752 A1 It was reported how it is possible by means of a polymeric hydrophilic / hydrophobic layer structure, to obtain an air or liquid film between the surface and ice freezing. In this way, ice adhesion is reduced.

Application examples of the inventions described demonstrate an ice adhesion reducing effect such that once formed hoarfrost can be more easily removed mechanically on the coated surfaces than on uncoated surfaces. If one analyzes the interaction of the mechanisms of ice-defying bacteria, one finds besides the frequently discussed effects such as hydrophobing or hydrophilic / hydrophobic clustering another indispensable component, namely an ability of the outer membrane to shed already formed ice nuclei. For the adaptation of this mechanism for technical surfaces, this means that although the mechanism of hydrophilic / hydrophobic clustering allows controlled ice nucleation, it requires a circulating medium, for example of air masses or liquids, to direct the ice nuclei due to the shear forces from the surface solve and transport away.

As the causes of ice adhesion, electrostatic attractions, covalent bonds, hydrogen bonds and fluctuating van der Waals bonds are discussed. Ice consists of polar water molecules that preferentially interact with polar surfaces. In fact, of honor et. al. ( Honor, D., Etay Lavert, M. Lahav, I. Lubomirski; Water freezes differently on positively and negatively charged surfaces of pyroelectric materials, Science, Vol. 327, Feb. 2010, 672-675 ) confirms that water molecules close to polar surfaces form clusters other than water volume.

In the US 2010/0135937 A1 A method is presented how a coating of nanoparticles can be applied to a surface and given a polar character. Nanoparticles with a narrow size distribution of an organometallic precursor, which is associated with an alcohol at temperatures below 350 ° C, are generated. A polymerization of the precursor can be used to produce a film which serves as a surface coating.

Surface coatings of piezoelectric or pyroelectric substances are already used in various fields. So that beats GB 2 145 106A a method of producing a piezoelectric film for ultrasonic transducers. In the US 10 2011 085 790 A1 a pyroelectric film is used for the disinfection of air conditioning units. The US 2009/0022899 A1 describes the production of an anti-fouling coating for submarines.

The EP 1769544 B1 describes methods for producing piezoelectric or pyroelectric thin films. In this case, a ceramic powder suspension is mixed with a polymer solution and the resulting so-called Kompositschlicker applied to a substrate and dried at about 100 ° C. The process is described in more detail for PMMA solutions. Also described is the so-called polarity, in which the resulting layer is exposed to an electric field until it has cured. The method provides to apply the poling only to the finished polymer layer. This is disadvantageous since ceramic particles can only move in the polymer layer to a limited extent.

It has as its object to provide a method with which it is possible to coat a surface in such a way that it tends less to ice formation, allows for easier removal of ice and active during operation with given or induced temperature changes again ice repellent effect.

According to the invention the object is achieved by the method according to claims 1 and 2. Subject matter of claims 13 and 14 is the use of a surface coating, which is produced by the method according to the invention. Advantageous embodiments are shown in the dependent claims.

Pyroelectric crystals have a polar structure. They react to a change in temperature with the formation of a polarization charge on the surfaces of the crystallites, which can be dissipated in time dependence. Each temperature change leads to a renewed polarization and thus to the rebuilding of an electrical potential.

With layers of pyroelectric crystals or with layers containing pyroelectric crystals, three mechanisms are simultaneously used, which interfere with the process of ice formation on surfaces.

On the one hand, the heat of transformation released during states of aggregation is utilized. During the crystallization process of initially liquid or gaseous atmospheric water at the surface, energy of transformation is released and causes a stimulation of the pyroelectrics due to its noticeable temperature change in the near environment. Overall, the electrical surface charges on the pyroelectric particles influence the balance of the surface energy in a targeted manner. They actively control the interaction with surrounding water molecules or ice particles and do not allow ice adhesion or only locally. In addition, the resulting charge changes of the pyroelectrics lead to dipole displacements and thus to significant mechanical instabilities in the already adherent, hexagonal crystallized ice crystallites, as a result, the bond between the surface coating and adhering ice is solved due to resulting incoherencies of the interface and modified volumes. The incoming spatial deflection of the pyroelectric crystals supports the detachment of already adhering ice nuclei. One way to enhance this effect is the optional additional use of piezoelectric layer components (nano- or microparticles) that are included in the surface coating. The piezoelectric nanoparticles or microparticles significantly enhance the mechanical effect of the pyroelectrics. They are stimulated in a chain process. The electrical charge built up during the crystallization process of the surrounding water due to the described thermal stimulation of the pyroelectric components induces the piezoelectrics to a local spatial deflection, which also causes a rejection of already adhering ice crystallites.

These mechanisms cause the ice to form only at discrete, nanoscopically distributed crystallization points, to adhere only loosely to the coating, and by means of the optional embedded switchable piezoelectric nano-or Microparticles can be easily removed again.

An ice-repellent surface coating may thus consist entirely of a pyroelectric material or of pyroelectric nanocomponents embedded in an elastic, wear-minimizing or otherwise protective matrix.

In recent years, however, the reservation against the mass use of nanoparticles has increased, as there are assumptions about possible health risks. In particular for surfaces which are exposed to environmental influences and on which a constant abrasion must be expected, these should be avoided or at least reduced. Thus, in addition to surfaces in which pyroelectric nanoparticles are incorporated, those surfaces which have pyroelectric properties in their entirety are also of interest.

Taking these restrictions into account, a method is used according to the invention in which a film is formed and during the preparation one or more conditioning steps are carried out to form corresponding pyroelectric properties. The conditioning steps provide for the action of an electric field and a heat treatment. The film itself has either pyroelectric properties and / or pyroelectric particles are embedded in the film. Both variants are referred to below as a pyroelectric coating, surface coating or coating of pyroelectric material.

The coating of pyroelectric material is prepared by providing the surface with a single or multiple coating of this coating. By a subsequent heat treatment and preferably simultaneously acting on an electric field conditioning takes place. The electric field is preferably directed so that after completion of the heat treatment, the surface preferably negatively charged by the pyroelectric effect at temperature decrease. The action of the field is preferably completed only after extensive cooling and can be terminated in a further preferred embodiment, but also before cooling the sample.

A further preferred embodiment provides that the heat treatment takes place separately from the action of an electric field. This procedure is preferably used for thick films (thicker than 1 micron).

The coating of the surface is preferably carried out by dipping once or several times in the coating liquid. However, other methods known from the prior art for coating are possible, such as, for example, spraying, spin coating, wave coating, etc. After coating, the applied layer is solidified. This is preferably done by air drying and possibly accompanied by a polymerization (if the coating liquid is polymerizable and was only partially polymerized). Further preferred embodiments provide supportive measures such as infrared radiation, hot air shower or the like.

The coating is preferably applied to a metallic surface, glasses, glass-ceramic or composite materials. However, it is conceivable in principle any solid surface as a carrier of the coating. In a preferred method step, the surface coating is detached from the surface before or after the conditioning step and further processed as a film. This further processing preferably also includes the application of further layers and subsequent conditioning steps. In this case, the film itself serves as a surface to be coated.

The coating with subsequent, at least partial curing is preferably carried out several times. Thus, a greater layer thickness is advantageously achieved. The layer thickness is preferably 40 nm to 100 μm, particularly preferably 60 nm to 80 μm and very particularly preferably 80 nm to 50 μm. The individual coating operations are preferably carried out with the same coating liquid. An advantageous development, however, provides that different coating liquids are used, which differ in particular in their content of other pyroelectric and / or piezoelectric components.

When the necessary thickness of surface coating is achieved, the conditioning step follows. In particular, it is achieved by the conditioning that the surface preferably negatively charges due to the pyroelectric effect when the temperature decreases. The constantly occurring change in the charge conditions due to the pyroelectric properties of the surface coating leads to an influence on the clustering of the water molecules and thus to the desired delay of ice nucleation. Finally, if condensation of the water molecules takes place, the heat of condensation released in turn can be used to activate the pyroelectric surface coating, as a result of which the charge ratios at the water / coating interface undergo a further change. Especially important for the ice-repellent property The surface coating is thus that there is a constant or frequent charge change on the surface.

The conditioning includes a temperature treatment. Preferably already during the temperature treatment, the surface coating is exposed to an electric field. This is preferably done in a capacitor arrangement. The coated surface is placed between the electrodes of a capacitor, which is preferably directed parallel to the negatively charged electrode of the capacitor. As a result, the negatively charged electrode faces the side of the surface on which later icing is to be expected.

Experiments have shown that an ice-repellent effect is also achieved when the positive electrode faces the side of the surface, which is to be reckoned with later icing. In this case, however, the observed ice-repelling effect is less. The described procedures are correspondingly applicable with reverse electric charges.

Preferably, the cooling process is initiated only after the action of the electric field on the surface. The exposure time depends on the surface layer thickness. An effective time of the electric field of about 60 minutes has proved to be advantageous.

The field strength used influences the success of the polarization treatment. It also depends on the thickness of the surface coating and is preferably in the range of 1 * 10 ⁶ V / m at 50 nm surface layer thickness to 80 * 10 ⁶ V / m at 50 microns film or film thickness.

embodiment

The coating is preferably produced by means of a sol-gel process. In this case, a material layer is applied, which itself has no or only very low pyroelectric properties. Nano and / or microparticles are embedded in this material layer. These nanoparticles and / or microparticles preferably have a size of 10 to 5000 nm. The nano- and / or microparticles are preferably made of lithium niobate, lithium tantalate, barium titanate or other perovskite ceramics having pyroelectric properties. Most preferably, the nano- and / or microparticles consist of strontium barium niobate. The crosslinking carrier liquid (material layer) for the nano- and / or microparticles is preferably TEOS (tetraethyl orthosilicate), TMOS (tetramethyl orthosilicate), TEOT (tetratorthotitantate) or TPOT (tetratisopropyl orthotitanate) or aluminum propylate or mixtures of the precursors mentioned. The processing takes place in a sol-gel process according to the prior art. Steady carrier layers of silicon, aluminum or titanium oxides are produced by acidic or alkaline hydrolysis of the sols. Preferred coating solutions have 1 to 25% by weight silane content. The proportion of pyroelectric nanoparticles and / or microparticles therein is preferably 1-50% by mass, particularly preferably 10-20% by mass.

The conditioning step for TEOS with nano- and / or microparticles provides that after the coating one or more thermal treatments are performed under the influence of an electric field. The thermal treatment is preferably carried out at a temperature of 50 ° C to 100 ° C, more preferably between 55 ° C and 60 ° C.

In the case of using the most preferred strontium barium niobate, ceramics are used whose ratio of strontium to barium ranges from 2.5: 7.5 (Sr _0.25 Ba _0.75 Nb ₂ O ₆ ) to 8.5: 1 , 5 (Sr _0.85 Ba _0.15 Nb ₂ O ₆ ); particularly preferably in the range from 3: 7 (Sr _0.3 Ba _0.7 Nb ₂ O ₆ ) to 8: 2 (Sr _0.8 Ba _0.2 Nb ₂ O ₆ ,) and very particularly preferably in the range from 6: 4 (Sr _0.6 Ba _0.4 Nb ₂ O ₆ ) to 8: 2 (Sr _0.8 Ba _0.2 Nb ₂ O ₆ ).

The production of the particularly preferred strontium barium niobate is preferably carried out via the so-called oxalate route:

Ammonium nioboxalate NH4 [NbO (C2O4) 2 (H2O) 2] · (H2O) + strontium acetate (C4H6SrO4) + (barium acetate C4H6BaO4); spray-dry at 110-115 ° C, then anneal at 700 ° C / 1h. This preparation can be found in the prior art z. In: RG Mendes, EB Araújo, JA Eiras, Structural Characterization and Ferroelectric Properties of Strontium Barium Niobates (Srx Ba1-x Nb2 O6) Thin Films, Materials Research, Vol. 2, 113-116, 2001 ,

Preferably, during the temperature treatment, the surface coating is exposed to an electric field. The field strength is preferably between 1 * 10 ⁶ V / m and 2 * 10 ⁶ V / m, more preferably between 1.3 * 10 ⁶ V / m and 1.7 * 10 ⁶ V / m. Larger field strengths lead to a shortening of the necessary exposure time. The action of the electric field aligns the pyroelectric nanoparticles and / or microparticles. Alignment is fixed by cooling after the temperature treatment.

embodiment

The surface coating is preferably formed from PVDF (polyvinylidene fluoride). The material of the surface coating is preferably pure in liquid form (coating liquid) or as a solution or mixture or dispersion. In particular, the PVDF is preferably present as a mixture with the copolymer trifluoroethylene. In the commercially available liquid used by Solvay Solexis, preferably used as a coating liquid, the PVDF is present in particular at least partially polymerized.

The surface coating preferably has at least 50% of the pyroelectric polymer in each layer. However, the content may vary in each layer.

The surface coating exhibits a phase transition when heated at a limiting temperature, converting the trans-gauche chain conformation of the non-polar α phase into the all-trans chain conformation of the polar β phase. Above this phase transition, the polymer chains can be aligned by an electric field. When the surface coating is cooled below the threshold temperature, this alignment is maintained and the alignment state is virtually frozen. Such phase transformation is also achievable with PVDF-containing coatings with mechanical stretching. This is preferably done by stretching the film on the surface or by blowing on the surface under pressure.

In the conditioning step, the surface coating is heated at least once to a temperature above this phase transition.

For PVDF, this phase transition temperature is about 135 ° C. Since the PVDF coating would evaporate at about 150 ° C (boiling point of the solvent), the coating is preferably at a temperature between 135 ° C and 150 ° C, more preferably at a temperature between 138 ° C and 145 ° C, and more particularly preferably heated to about 140 ° C. The temperature treatment is preferably carried out under the influence of an electric field. The field strength is preferably between 1 * 10 ⁶ V / m and 2 * 10 ⁶ V / m, more preferably between 1.3 * 10 ⁶ V / m and 1.7 * 10 ⁶ V / m. Larger field strengths lead to a shortening of the necessary exposure time. Thus, for a film with a thickness of 50 microns, a field strength of up to 80 * 10 ⁶ V / m has proved to be advantageous.

In a preferred development, pyroelectric nanoparticles and / or microparticles are additionally dispersed in the coating liquid. The proportion of pyroelectric nanoparticles and / or microparticles therein is preferably 1-50% by mass, particularly preferably 10-20% by mass.

As pyroelectric nanoparticles and / or microparticles, particles of strontium barium niobate are also preferably used here. This strontium barium niobate has a ratio of strontium to barium ranging from 2.5: 7.5 (Sr _0.25 Ba _0.75 Nb ₂ O ₆ ) to 8.5: 1.5 (Sr _0.85 Ba _0.15 Nb ₂ O ₆ ); more preferably in the range of 3: 7 (Sr _0.3 Ba _0.7 Nb ₂ O ₆ ) to 8: 2 (Sr _0.8 Ba _0.2 Nb ₂ O ₆ ) and most preferably in the range of 6: 4 (Sr _0.6 Ba _0.4 Nb ₂ O ₆ ) to 8: 2 (Sr _0.8 Ba _0.2 Nb ₂ O ₆ ).

The preparation of the preferred strontium barium niobate is preferably carried out via the above-described oxalate route of ammonium niobium oxalate, barium acetate and strontium acetate.

In a further particularly preferred development of both embodiments, particles, preferably nano- or microparticles, having piezoelectric properties are dispersed in the coating solutions. These piezoelectric particles are oriented during the conditioning step by the action of the electric field so that they react with the formation of charges in the pyroelectric surface coating with significant changes in length mainly perpendicular to the surface of the surface coating and thus hinder the adhesion of the ice layer on the surface. These piezoelectric particles are preferably made of lithium niobate, lithium tantalate, barium titanate or other related ceramics having piezoelectric properties. The particle size of the embedded particles is preferably 10 nm to 5000 nm, particularly preferably 40 nm to 3500 nm and furthermore particularly preferably 50 nm to 500 nm. The proportion of the particles is preferably 1% by mass to 30% by mass. The piezoelectric nanoparticles and / or microparticles are oriented so that they undergo a change in length when charge is introduced. In a preferred procedure, one or more conditioning steps are carried out and subsequently further coating and conditioning steps are carried out.

The surface coating according to the invention has at least one layer. In a preferred embodiment, the surface coating according to the invention consists of three to seven and particularly preferably five layers.

Embodiment 1

A glass carrier (Crystec) of dimensions 30 × 20 mm, thickness 0.2 mm is immersed in a PVDF solution. The PVDF solution is a PVDF copolymer from Solvay Solexis, with a content of 95% vinylidene fluoride and 5% trifluoroethylene.

This is followed by a drying time of 20 minutes at ambient temperature (20 ° C.) and atmospheric pressure without additional air movement. Thereafter, the dipping and drying operations are repeated four more times. Subsequently, the coated glass is placed in a preheated to a temperature of 140 ° C drying oven and annealed for a period of 60 min. The sample is then removed from the oven and cooled at standard conditions. The resulting surface layer has a thickness of 80-120 nm.

Here, the first measurement of the freezing temperature of an applied defined volume of water takes place.

Now, the sample is placed between the electrodes of a plate capacitor and heated again in the preheated oven to a temperature of 140 ° C. At the same time, an electric field of 1.55 * 10 ⁶ V / m is applied across the capacitor. The sample is held at the temperature of 140 ° C for a period of 60 minutes and, upon removal from the drying cabinet, cools under standard conditions. The limit temperature of 135 ° C is undercut after about 2 minutes.

This is followed by a new measurement of the freeze delay to be achieved with this coating.

Results

With a simple unpolarized PVDF coating, a freezing delay of about 1 Kelvin is achieved compared to the measurement result on an uncoated glass slide. A subsequent polarization of the applied coating during annealing causes in any case an increase in the desired supercooling. By choosing the polarity of the electric field during the heat treatment, the icing temperature is affected and varies by 3 - 7 Kelvin. It may also be reversibly switched repeatedly, with negative orientation of the coating surface (i.e., the coating surface to be conditioned facing the negative electrode thereof) causing more supercooling of adherent liquids.

Embodiment 2

An aluminum substrate, (chip, diameter 16 mm, thickness 2 mm) is coated with a sol. The sol consists of commercially available TEOS, 0.1 molar HCl, the solvent ethanol and a volume fraction of nanoparticulate LiNbO ₃ . The size fraction of the nanoparticles is in the range of 50 nm to 5 μm. The coated sample is then tempered at 60 ° C. Meanwhile, it undergoes an electric field in a capacitor array and can be oriented both positively and negatively with respect to the incoming polarization during temperature change. The electric field in the capacitor is 1.55 * 10 ⁶ V / m. The sample is held at the temperature of 60 ° C for a period of 60 minutes and, after removal from the drying cabinet, cools under standard conditions.

Results

With an uncoated aluminum substrate, an icing temperature of about -14 ° C is achieved under given conditions. The icing temperature decreases when the sample is coated with a sol-gel coating of TEOS and embedded LiNbO3. If the sample is exposed to an electric field during its gelling at elevated temperatures, the achievable temperatures change. With a corresponding negative polarization (the surface faces the negative electrode) of the coating surface as the temperature decreases, a further supercooling of 4-5 Kelvin is achieved. Positive polarizations can promote ice formation.

Embodiment 3

An aluminum chip, diameter 16 mm, thickness 2 mm, is coated with a sol. The sol consists of commercially available TEOS and a nanoparticulate (Sr _0.62 Ba _0.38 Nb ₂ O ₆ ) (ratio Sr: Ba is 6.2: 3.8) in a molar ratio of 16: 1. Due to the addition of the nanoparticles, the pH shifts into the basic range during the sol-gel process. This is counteracted by targeted addition of acid. The size fraction of the nanoparticles is in the range of 50 nm to 5 μm. The coated sample is then tempered at 60 ° C. Meanwhile, it undergoes an electric field in a capacitor array and can be oriented both positively and negatively with respect to the incoming polarization during temperature change. The electric field in the capacitor is 1.55 * 10 ⁶ V / m. The sample is held at the temperature of 60 ° C for a period of 60 minutes and, after removal from the drying cabinet, cools under standard conditions.

Results

With an uncoated aluminum substrate, an icing temperature of about -14 ° C is achieved under given conditions. The icing temperature decreases when the sample is coated with a sol-gel coating of TEOS and embedded therein Sr _0.62 Ba _0.38 Nb ₂ O ₆ . If the sample is exposed to an electric field during its gelling at elevated temperatures, the achievable temperatures change. With a corresponding negative polarization (the surface faces the negative electrode) of the coating surface while the temperature is falling, an undercooling of at least 5 Kelvin is achieved. Positive polarizations can promote ice formation.

list of figures

• 1 shows how the icing temperature changes due to the treatment according to the method of the invention. While the icing temperature of the uncoated glass surface is about -11 ° C, it drops due to the coating, without conditioning to about -13 ° C. The following columns of the diagram show how the icing temperature changes due to conditioning treatments. In particular, the difference between opposing field orientations is recognizable. The lowest icing temperatures (approx. -18.5 ° C) are achieved when working with the - field, ie when the negatively charged electrode is facing the coated surface during field treatment.
• 2 shows how the icing temperature changes due to a further treatment according to the inventive method. The icing temperature of an uncoated aluminum substrate is approx. -14 ° C. It sinks to approx. -15 ° C due to the pyroelectrically active coating. If the sample is exposed to an electric field during its gelling at elevated temperatures, the achievable temperatures change. If a pyroelectrically negative polarizing reaction at temperature drop is set, a lowering of the icing temperature by up to 4 K is achieved (in the example -18 ° C).
• 3 shows how the icing temperature can be lowered on a coated with a polyvinylidene fluoride foil metallic substrate after treatment according to the inventive method of polyvinylidene fluoride film. Achievable subcooling temperatures are compared to annealed and not further conditioned foils and to tempered and conditioned condenser samples. By completing both technological treatment steps, the icing temperature can be reduced by a further 2 Kelvin.

Claims (19)

Method for producing an ice-repellent coating from a pyroelectric film by the method steps: a) coating a surface with a coating liquid, of PVDF (polyvinylidene fluoride) in pure form, as a solution or mixture or dispersion, b) drying the coated surface c) phase transformation of the PVDF by means of a heat treatment of the coated surface at temperatures between 135 ° C and 150 ° C. d) acting on the coated surface of an electric field. A process for producing an ice-repellent coating from a pyroelectric film by the process steps: a) coating a surface with a coating liquid, TEOS, containing pyroelectric nanoparticles and / or microparticles of strontiumbarium niobate or LiNbO ₃ , b) drying the coated surface c) heat treatment the coated surface at temperatures between 50 ° C and 100 ° C d) acting on the coated surface by an electric field. Method according to Claim 1 or 2 , characterized in that the steps a) and b) are repeated several times alternately, wherein in step a) the same or different coating liquids are used. Method according to Claim 1 or 2 , characterized in that steps c) and d) are carried out simultaneously. Method according to one of the preceding claims, characterized in that the steps a) to d) are repeated several times. Method according to one of the preceding claims, characterized in that the electric field is directed so that upon cooling the surface is negatively charged by the pyroelectric effect. Method according to one of Claims 1 to 5 , characterized in that the electric field is directed so that upon cooling the surface positively charged by the pyroelectric effect. Method according to Claim 2 , characterized in that the coating takes place by means of the sol / gel process. Method according to one of the preceding claims, characterized in that the drying of the coating is supported by irradiation with electromagnetic radiation or by a hot air shower. Method according to Claim 1 or 2 , characterized in that piezoelectric nanoparticles or microparticles are added in one or more coating steps of the coating liquid. Method according to Claim 10 , characterized in that the piezoelectric nano- or microparticles of lithium niobate, lithium tantalate, barium titanate or other perowskitverwandten ceramics are made with piezoelectric properties. Method according to one of the preceding claims, characterized in that the ice-repellent coating at the earliest after a single execution of steps a) and b) after Claim 1 or 2 as a film is subtracted from the surface and further processed. Use of a surface coating produced by a method of Claims 1 to 12 , of at least one layer of a pyroelectric film, the surface of which preferably negatively charges on temperature decrease as an ice-repellent surface coating. Use of a surface coating produced by a method of Claims 1 to 12 , from at least one layer of a pyroelectric film, the surface of which preferably positively charges when the temperature decreases as an ice-repellent surface coating. Ice-repellent surface coating after Claim 13 or 14 , characterized in that the surface coating contains PVDF. Ice-repellent surface coating after Claim 15 , characterized in that the surface coating contains pyroelectric nanoparticles and / or microparticles. Ice-repellent surface coating after Claim 16 , characterized in that the pyroelectric nanoparticles and / or microparticles consist of strontium barium niobate or LiNbO ₃ . Ice-repellent surface coating after Claim 13 or 14 , characterized in that the surface coating contains dispersed pyroelectric nanoparticles and / or microparticles of strontium barium niobate or LiNbO ₃ . Ice-repellent surface coating according to one of Claims 13 to 18 , characterized in that in at least one layer piezoelectric nanoparticles or microparticles are embedded.

Images