WO2001019932A2

WO2001019932A2 - Agents for producing self-cleaning thin surface coatings and methods suited therefor

Info

Publication number: WO2001019932A2
Application number: PCT/EP2000/008825
Authority: WO
Inventors: Georg Gros
Original assignee: Georg Gros
Priority date: 1999-09-15
Filing date: 2000-09-09
Publication date: 2001-03-22
Also published as: WO2001019932A3; AU7418300A; DE19944169B4; DE19944169A1

Abstract

The invention relates to a method for producing self-cleaning surface coatings, whereby an inventive coating agent dispersion or solution is applied with a thin coat to the surface and is dried thereon. Said coating agent dispersion or solution is comprised of: a) a film-forming plastic provided in the form of an aqueous dispersion or of a solution in an organic solvent; b) a hydrophobic polymer provided in the form of a powder with an average grain size ranging from 10-50 νm, which is insoluble in the above-mentioned solvent; c) a sufficient quantity of water and/or of an organic solvent for producing a coating agent that is capable of being spread or sprayed; d) whereby the applied layer is so thin that the grains of the hydrophobic polymeric powder are interspaced by a distance of 5 to 100 νm, and e) whereby the quantity of the film-forming plastic is measured so that it forms a layer after the solvent evaporates whose thickness is equal to 30-60 % of the average grain size of the hydrophobic powder.

Description

Means for the production of self-cleaning thin surface coatings and processes suitable therefor

The present invention relates to coating compositions for the production of thin self-cleaning surface coatings and processes suitable therefor, the self-cleaning preferably being carried out by exposing the surfaces to rain or moving water from time to time.

Self-cleaning surfaces of objects and methods for producing the same, the self-cleaning taking place by exposing the surface to rain or moving water from time to time, have already been described in EP 0 772 514 B1. According to this patent, the self-cleaning surfaces should have an artificial surface structure of elevations and depressions, the distance between the elevations in the range of 5-200 μm and the height of the elevations in the range of 5-100 μm and at least the elevations made of hydrophobic polymers or durable hydrophobic materials exist and are not removable by water or with water or detergents. To produce such surfaces, it is described either to spread an adhesive evenly and thinly on a smooth surface and then to coat it with a Teflon powder with an average particle size of 7 μm or to heat a Teflon coating until it is plastically deformable and then to use a high-mesh sieve from the offset printing on the Press on the surface and thereby plastically deform it to impress elevations and depressions.

According to the first method, appropriate surface coatings can be produced, from which water drips off and rinses off deposited particles. Due to the surface peaks of the Teflon against water, water A critical angle of over 135 ° drops, while water drops on glass have a critical angle of approximately 60 ° or on surfaces hydrophobicized with wax or grease of approximately 80-100 °. However, the method has the disadvantage that the coating can only be applied to horizontally lying surfaces and a uniform distribution of the Teflon particles on the adhesive base and their firm connection to the base is not guaranteed. The whole process is also relatively expensive. The second procedure mentioned in the patent is not economically feasible and already suffers from the problem of plasticizing Teflon.

From Yamauchi G. and others, Colloids and Surfaces 1996, Vol. 116 on pages 125-134 it is also known that the water-repellent properties of PTFE surfaces can be enhanced by applying the PTFE in the form of fine powders to the surface using a hot-melt adhesive is applied. The PTFE particles form a practically dense layer which, however, has an additional surface roughness compared to sintered PTFE, on which water rolls off with a larger contact angle than sintered layers. The materials are not suitable for dirt repellency or self-cleaning of these surfaces.

For further attempts to create technical surfaces that repel dirt and / or are self-cleaning, and the associated problems, reference is made to the literature mentioned in the above EP document, according to which such attempts have not been successful.

The task therefore was to find coating compositions and processes with which self-cleaning surfaces can be produced simply and economically. The solution to this problem is characterized by the features of the main claims and is promoted by the features of the subclaims.

Surprisingly, it is possible to combine the hydrophobic particles together with a film-forming plastic coating agent in a suitable solvent and to apply this agent in a thin layer to the surface to be protected, a self-cleaning effect then taking place if, after the solvents have evaporated, the solvents are juxtaposed on the surface Surface deposited hydrophobic plastic particles, which have a diameter of approximately 10-50 μm, preferably 10-30 μm and in particular 15-25 μm, are at a certain distance from one another of approximately 5-100 μm and the layer thickness of the dry film-forming plastic is approximately 30 -60% of the average diameter of the hydrophobic plastic particles. The film-forming plastic thus ensures firm adhesion between the hydrophobic plastic particles and the base and at the same time forms a waterproof covering. Because of the comparatively low cohesion between film former and hydrophobic plastic, only a very thin film of 0.5-2 μm, usually approx. 1 μm thick, remains on the top of the plastic particles. With freshly applied coatings, this thin film layer causes the entire surface to behave like the film-forming plastic itself. Aging due to atmospheric oxygen, fluctuations in temperature and humidity and, if necessary, exposure to water, however, surprisingly after a short time result in these thin film skins becoming detached and the parts of the plastic particles protruding from the film layer appearing as hydrophobic elevations and the water-repellent and self-cleaning effect trigger.

The plastics used for the production of paints and lacquers can be used as film-forming plastics, in particular in formulations such as those used for the production of glazes, ie particularly thin coatings. gene, are common. Examples include polyacrylates, polyolefins, in particular polyethylene, polyvinyl acetates and polyvinyl acetate copolymers, styrene acrylate copolymers, maleic acid copolymers, polyurethanes, alkyd resins, epoxy resins or mixtures of such substances.

The auxiliaries known for the production of paints and varnishes are usually added to the film formers in a customary amount. Examples include fillers and thickeners, matting agents, pigments, UV stabilizers and anti-microbial agents. Depending on the plastic, plasticizers, crosslinking agents, elasticizing agents, etc. must also be added. The addition of wax has proven to be particularly advantageous for the coating of wooden surfaces, since it not only promotes the bonding of the film material to the wood, but also reduces the film hardness and thus cracks in the film layer in wood working due to temperature and moisture fluctuations largely avoided. In addition, a certain amount of wax is advantageous for a rapid detachment of the thin film coatings on the polymer grains. Beeswax, Camara wax or recent resins such as montan wax are equally suitable as wax.

The hydrophobic particles usually consist of perfluoride hydrocarbons such as Teflon or PTFE, but particles of chlorofluorocarbons or silicone particles can also be used. It is crucial for the usability of such particles that their critical angle with respect to water is over 100, preferably over 135 °, so that water drops roll off such surfaces in the sense of self-cleaning.

The coating composition preferably consists of 20-60% of film-forming plastics, based on the solids content, 5-50% hydrophobic powder,

0-50% auxiliaries and on a volume part of the solids 2-10 volume parts solvent.

From an environmental point of view, water is preferably used as the solvent, to which water-miscible organic solvents such as lower alcohols, acetone etc. may have been added. The film-forming plastics are in the form of fine dispersions with particle sizes of 0.1-2 μm, wetting agents and emulsifiers bring about the necessary stabilization of the dispersion and also of the hydrophobic powders contained therein against segregation. Insofar as this is permissible from the processing location or the film-forming materials used require it, it is of course also possible to use organic solvents, for example an ester, ketone, ether, xylene or a hydrocarbon. Such solvents are known and used for the production of paints and varnishes.

A preferred glazing aqueous coating system based on acrylic resin has the following composition based on the solids content:

30-60 mass% polyacrylate dispersion (solids content of a 40-60% dispersion in water) 2.5-10 mass% elastic dispersions (e.g. polyurethanes) 20-50 mass% solid fluorine compounds (Teflon; particle size: 5-25 μm) 1-3 Mass% matting agent (silica; particle size: 5-100 μm)

0.5-20 mass% pigments and fillers 1-5 mass% paraffin waxes (particle size 0.2-10 μm)

0.5-5 mass% emulsifier, defoamer, preservatives,

Thickener, filming aid 0.2-3 mass% liquid organic fluorine compounds The above constituents are based on their volume fraction dispersed in 2-10 times the amount of water. Paraffin wax and liquid fluorine compounds, which are mixed into the film former, cause a certain hydrophobization, which causes the rainwater to roll off immediately after application of the mixture (surface critical angle approx. 100-120 °), but due to the lack of discrete hydrophobic surface structures, a self-cleaning effect in the desired Not yet enable the senses. This only occurs when the film skins covering the hydrophobic plastic particles are broken open.

The agents according to the invention are applied to the surfaces to be coated using the technique customary for the application of paints and paints, by brushing on, rolling on or spraying on, layer thicknesses of 30-200 .mu.m depending on the solids content. To achieve a safe covering, the application can be repeated 2 or 3 times. When the solvents dry, the film-forming component lies on the substrate as a uniform layer, from which the thicker plastic grains protrude as elevations. Because of the lower cohesion to the plastic, the residual layer of the film former above the plastic grains is thin (0.5-2 μm, usually approx. 1 μm).

In principle, the use of the coating compositions according to the invention is not restricted to certain surfaces. Wood surfaces exposed to the weather, corrugated bitumen panels or fiber cement panels can be coated directly with the agent in a particularly advantageous manner. On the other hand, it is also possible to provide an existing color primer of a customary known composition with a self-cleaning surface by subsequent glazing with the agent according to the invention. Since the applied layer is only 10-50 μm thick and in this case does not contain matting agents or pigments, the color of the substrate shines through completely, as is the case with wood glazes.

The method according to the invention is explained in more detail with reference to the attached FIGS. 1-3. It shows

1 shows the coating agent layer 2 applied to a substrate 1, in which the hydrophobic particles 3 are distributed.

FIG. 2 shows the substrate 1 with the dried coating agent 2 ', the hydrophobic grains 3 lying on the substrate 1 and projecting out of the surface of the film 2' due to their greater thickness, the projecting part being covered with a thin film layer 2 ".

3 shows the coated surface according to FIG. 2 after aging, as a result of which the thin film layers 2 "have been removed and the upper side 3 'of the hydrophobic grains 3 protrudes from the film layer 2'. On the one hand, the particles 3 protruding from the surface cause a very large increase in Hydrophobia, whereby water drops practically only rest on these elevations and therefore roll off easily, on the other hand that dirt particles lying between the elevations are taken away by the rolling water drops but not deposited on the surface again.

The binders according to the invention and the process for their use are described in the following examples. example 1

Aqueous acrylic dispersions according to the composition shown in the following table are applied with a brush in a thickness of 80-100 μm wet film thickness per coat to the surface of wooden panels. In order to achieve a safe coating of all parts of the wood structure, the application is repeated twice in the same way after each drying of the previous spread. After the film has dried, a dry film layer thickness of approx. 12 μm remains, from which the larger Teflon and matting agent particles protrude by the difference between particle size and film thickness. Each particle is coated with an approximately 1 μm thick film made of acrylic resin. Due to the proportion of paraffin wax and liquid fluorine compounds, the films produced in this way have a critical angle of 100-120 ° with respect to water. Water therefore rolls off, but there is no self-cleaning effect due to the lack of a surface structure. By weathering this coating for 1 to 2 weeks, the films covering the grains are destroyed and the Teflon particles are exposed. This creates a hydrophobic surface structure which, in addition to increasing the surface critical angle with respect to water to 125 to more than 135 °, now also achieves self-cleaning by means of water droplets.

The fact that the Teflon particles are firmly embedded in the glaze means that the outstanding Teflon and matting agent particles are only released from the underlying paint film over several years by prolonged weather conditions and mechanical stresses, so that the self-cleaning effect wears off. The original effect can be restored by re-coating once with the agent according to the invention.

Claims

claims

1. A process for producing self-cleaning surface coatings, wherein a coating agent dispersion or solution is applied to the surface

a) a film-forming plastic in the form of an aqueous dispersion or a solution in an organic solvent, b) a hydrophobic polymer in the form of a powder with an average particle size of 10-50 μm, which is insoluble in the above solvent, c) a sufficient amount Water and / or organic solvents to form a spreadable or sprayable coating agent,

apply in a thin layer and dry

d) the layer applied is so thin that the grains of the hydrophobic polymer powder are spaced from one another by 5-100 μm and e) the amount of the film-forming plastic is such that it forms a layer after the solvent has dried off, whose thickness is 30-60% of the average grain size of the hydrophobic powder.

2. The method according to claim 1, characterized in that the coating agent based on the solids content

20-60% film-forming plastic

5-50% hydrophobic powder

0-50% auxiliaries and 2-10 volumes of solvent for 1 volume of solids.

3. The method according to claim 1 or 2, characterized in that the film-forming plastic is a polyacrylate, polyolefin, polyvinyl acetate, styrene-acrylate copolymer, maleic acid copolymer, polyurethane, alkyd resin, epoxy resin or a mixture of such substances.

4. The method according to one or more of claims 1-3, characterized in that the hydrophobic particles consist of perfluorinated or fluorochlorohydrocarbons or silicone.

5. The method according to claim 4, characterized in that the particles consist of PTFE.

6. The method according to one or more of claims 1-5, characterized in that the auxiliaries contain fillers, thickeners, matting agents, pigments, crosslinking agents, UV stabilizers, plasticizers, emulsifiers, wetting agents, antimicrobial agents, elasticizing agents or waxes.

, Method according to one or more of claims 1-6, characterized in that the binder

30-60% polyacrylate dispersion

2.5-10% elastic dispersions (polyurethane)

20-50% solid fluorine compounds (Teflon; particle size: 10-25 μm)

1-3% matting agent (silica; particle size: 5-100 μm)

0.5-20% pigments and fillers

1-5% paraffin waxes (particle size 0.2-10 μm)

Contains 0.5-5% emulsifier, defoamer, preservatives, thickeners, film-forming aids, 0.2-3% liquid organic fluorine compounds and 2-10 parts water or water-miscible solvents.

8. Coating agent for the production of thin self-cleaning surface coatings containing a) a film-forming plastic in the form of an aqueous dispersion or a solution in an organic solvent, b) hydrophobic polymers in the form of a powder with an average grain size of 10-50 μm, which is in the above solvent are insoluble, c) a sufficient amount of water and / or organic solvent to form a spreadable or sprayable coating agent, d) the amount of film-forming plastic being such that it forms a layer after the solvent has dried off, the thickness of which is 30- 60% of the average grain size of the hydrophobic powder is.

, Coating composition according to claim 8, characterized in that it is based on the solids content

20-60% film-forming plastic

5-50% hydrophobic powder

0-50% auxiliaries and 2-10 volumes of solvent for 1 volume of solids.

10. Coating composition according to claim 8 or 9, characterized in that the film-forming plastic is a polyacrylate, polyelefin, polyvinyl acetate, styrene, acrylate copolymer, maleic acid copolymer, polyurethane, alkyd resins, epoxy resins or a mixture of such substances.

11. Coating composition according to one or more of claims 8-10, characterized in that the hydrophobic particles consist of perfluorinated fluorochlorohydrocarbons or silicone, preferably of PTFE.

12. Coating composition according to one or more of claims 8-11, characterized in that the auxiliaries contain fillers, thickeners, matting agents, pigments, crosslinking agents, UV stabilizers, plasticizers, emulsifiers, wetting agents, antimicrobial agents, elasticizing agents or waxes.

3. Coating agent according to one or more of claims 8-12, characterized in that the binder

30-60% acrylic dispersion

2.5-10% elasticized dispersions (polyurethane)

20-50% solid fluorine compounds (Teflon; particle size: 5-25 μm)

1-3% matting agent (silica; particle size: 5-100 μm)

0.5-20% pigments and fillers

1-5% paraffin waxes (particle size 0.2-10 μm)

Contains 0.5-5% emulsifier, defoamer, preservatives, thickeners, film-forming aids, 0.2-3% liquid fluorine compounds and 2-10 parts water or water-miscible solvents.

14. Coating agent according to one or more of claims 8-13, characterized in that 5-20% hydrophobic liquid fluoropolymers are added to the film-forming plastic.

15. Use of coating agents according to one of claims 8-14, for thin surface coating of wood, bituminous corrugated or fiber cement boards or color primers, the layer being 10-50 μm thick.