WO2004069904A1

WO2004069904A1 - Water-spreading, scratch-resistant, and self-cleaning plastic body and method for the production thereof

Info

Publication number: WO2004069904A1
Application number: PCT/EP2003/013866
Authority: WO
Inventors: Thomas Hasskerl; Patrick Becker; Rolf Neeb; Ghirmay Seyoum; Egbert Schöla
Original assignee: Röhm GmbH & Co. KG
Priority date: 2003-02-06
Filing date: 2003-12-06
Publication date: 2004-08-19
Also published as: DE10304953A1; TW200422389A; AU2003289978A1

Abstract

The invention relates to water-spreading, scratch-resistant, and self-cleaning plastic bodies which are obtained by: a) applying and a siloxane coating (a) onto a plastic body and hardening said siloxane coating (a); b) increasing the polar ratio of the surface energy of the hardened siloxane coating to a minimum of 10 mN/m; c) applying a coating (b) containing photocatalytically active Ti02 particles onto the plastic body and hardening said coating (b); and d) applying a water-spreading, inorganic coating (c) onto the plastic body and hardening said coating (c).

Description

Water-spreading, scratch-resistant and self-cleaning plastic body and process for its production

The present invention relates to water-spreading, scratch-resistant and self-cleaning plastic bodies and processes for their production.

Self-cleaning bodies become superhydrophilic when exposed to UV light in the presence of water and are able to break down organic dirt down to carbon dioxide and water. This ability of the surface is generally achieved by the photocatalytic effect of titanium dioxide, which can be fixed on solid supports and, for example, can be firmly bonded to the substrate by baking at high temperatures. One example is silicate glasses for self-cleaning windows as described in EP 850 203 B1 by Rhodia Chemie.

Plastic substrates such as Acrylic glass or polycarbonate, which are used extensively as glazing material or for transparent noise barriers, should be as transparent and clean as possible for aesthetic reasons in order to give passengers on a train or motorists a clear view of the surrounding landscape. They are used primarily on bridges but also to loosen monotonous concrete noise barriers and are intended to help reduce driver fatigue.

Car exhaust fumes, tire abrasion, dust and organic dirt quickly make transparent noise barriers unsightly and unattractive. Numerous attempts have therefore been made to equip transparent plastics with self-cleaning coatings. The aim was to ensure the photocatalytic activity of titanium dioxide to make it accessible for the decomposition of the dirt adhering to the substrate surface, but on the other hand to protect the organic substrate itself from being destroyed by the titanium dioxide.

Plastic bodies provided with self-cleaning siloxane coatings are also known. Such substrates usually have a double layer of siloxane with different compositions, only the outer layer containing a photocatalytically active additive, for example Ti0 ₂ in anatase or brookite modification.

For example, the publication EP-A-1 022 318 describes coated plastic plates which have a photocatalytically active layer. In the examples, however, there are only plates or films which have a total coating of 1.2 μm thin. Such thin coatings, however, show only a very low scratch resistance.

The problem with these plastic bodies of the prior art is therefore their low scratch resistance or their low weather resistance. Due to environmental influences, the coating is worn away over time, so that they lose their ability to self-clean.

Furthermore, such plastic bodies only become hydrophilic when irradiated with sunlight. Accordingly, these coatings show no or only very low hydrophilic properties at night or in the case of very heavy cloud cover, so that rainwater containing dirt can lead to the known contaminants which are formed from the residues of the raindrops. It should be noted here that contamination leads to a shielding of the self-cleaning coating, so that the dirt can take off over time, since the UV light does not penetrate to the Ti0 ₂ particles.

In addition to the self-cleaning coatings that become hydrophilic when irradiated, water-spreading coatings with permanent hydrophilicity are also known. For example, documents EP-A-0 193 269 and EP-A-0 149 182 describe plastic bodies which are provided with a coating containing SiO ₂ .

A disadvantage of these coatings, however, is that such plastic bodies have no self-cleaning effect. So contamination of these plastic bodies over a longer period of time cannot be avoided if there are exhaust gases or similar components in the air from which the water is precipitated.

In view of the prior art specified and discussed herein, it was therefore an object of the present invention to provide scratch-resistant plastic bodies which have self-cleaning properties and are permanently hydrophilic.

Another object of the invention was that the plastic body have a high durability, in particular a high resistance to UV radiation or weathering.

Furthermore, the invention was based on the object of providing scratch-resistant, self-cleaning plastic bodies which can be produced particularly easily. For example, substrates which can be obtained by extrusion, injection molding and by casting processes should be able to be used for the production of the plastic bodies.

In addition, it was therefore an object of the present invention to provide plastic bodies which can be produced inexpensively.

In addition, it was therefore an object of the present invention to provide water-spreading and self-cleaning plastic bodies, the coatings of which have a particularly high adhesion to the plastic substrates. This property should not be affected by moisture. Furthermore, the plastic body should have a particularly high scratch resistance.

Another object of the present invention was to provide scratch-resistant, self-cleaning and water-spreading plastic bodies which have excellent mechanical properties. This property is particularly important for applications in which the plastic body is said to have high stability against impact.

In addition, the plastic body should have particularly good optical properties.

Another object of the present invention was to provide plastic bodies which can be easily adapted in size and shape to the requirements. These tasks are solved as well as others, which are not named literally, but which can be derived as a matter of course from the contexts discussed here, or which inevitably result from these, by the plastic bodies described in claim 1. Expedient modifications of the plastic body according to the invention are protected in the dependent claims referring back to claim 1.

With regard to manufacturing processes, claim 25 provides a solution to the underlying problem.

Characterized in that a) a siloxane coating (a) is applied and cured to a plastic substrate, b) the polar portion of the surface energy of the cured siloxane coating is increased to a value of at least 10 mN / m and c) a photocatalytically active Ti0 ₂ particle containing coating (b) applies and cures and d) a water-spreading, inorganic coating (c) applies and cures, it is possible to provide self-cleaning plastic bodies that have self-cleaning properties and are permanently hydrophilic.

The measures according to the invention include achieved the following advantages in particular:

The plastic bodies of the present invention are very insensitive to the formation of scratches on the surface. The plastic bodies according to the invention show a high resistance to UV radiation.

Furthermore, plastic bodies show a high level of self-cleaning when exposed to UV radiation.

In addition, the plastic bodies spread water without UV radiation. As a result, the formation of drop-shaped residues can be reliably avoided. Uniform, low soiling, which could be formed over time, is therefore reduced by UV light due to the self-cleaning effect of the photocatalytic layer. As a result, the contamination of the plastic bodies according to the invention is in many cases less than that of plastic bodies which have only a self-cleaning coating but no permanently effective water-spreading coating. This is especially true in seasons with little sunlight.

In addition, the plastic bodies of the present invention can be produced particularly inexpensively without the need to use expensive additives.

Furthermore, the present invention enables the production of self-cleaning, water-spreading coatings on plastic substrates already coated with siloxanes. This has the particular advantage that plates can be removed from the production of plastic bodies which are provided with scratch-resistant coatings and can later be provided with further coatings which have self-cleaning or water-spreading properties.

The scratch resistant plastic bodies of the present invention can be adapted to certain requirements. In particular, the size and shape of the plastic body can be varied over a wide range without impairing the excellent properties. Furthermore, the present invention also provides plastic bodies with excellent optical properties.

• The scratch-resistant plastic bodies of the present invention have good mechanical properties.

The plastic bodies according to the invention can be obtained by coating plastic substrates. Plastic substrates suitable for the purposes of the present invention are known per se. Such substrates include in particular polycarbonates, polystyrenes, polyesters, for example polyethylene terephthalate (PET), which can also be modified with glycol, and polybutylene terephthalate (PBT), cycloolefinic polymers (COC) and / or poly (meth) acrylates. Polycarbonates, cycloolefinic polymers and Poly (meth) acrylates, with poly (meth) acrylates being particularly preferred.

Polycarbonates are known in the art. Polycarbonates can be considered formally as polyesters from carbonic acid and aliphatic or aromatic dihydroxy compounds. They are easily accessible by reacting diglycols or bisphenols with phosgene or carbonic acid diesters in polycondensation or transesterification reactions.

Polycarbonates derived from bisphenols are preferred. These bisphenols include, in particular, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 2,2-bis (4-hydroxyphenyl) butane (bisphenol B), 1,1-bis (4-hydroxyphenyl ) cyclohexane (bisphenol C), 2,2'-methylene diphenol (bisphenol F), 2,2-bis (3,5-dibromo-4-hydroxyphenyl) propane (tetrabromobisphenol A) and 2,2-bis (3,5- dimethyl-4-hydroxyphenyl) propane (tetramethylbisphenol A).

Such aromatic polycarbonates are usually produced by interfacial polycondensation or transesterification, details of which are given in Encycl. Polym. Be. Engng. 11, 648-718.

In interfacial polycondensation, the bisphenols are emulsified as an aqueous, alkaline solution in inert organic solvents, such as, for example, methylene chloride, chlorobenzene or tetrahydrofuran, and reacted with phosgene in a step reaction. Amines are used as catalysts, and phase transfer catalysts are also used for sterically hindered bisphenols. The resulting polymers are soluble in the organic solvents used. The properties of the polymers can be varied widely by the choice of the bisphenols. If different bisphenols are used at the same time, block polymers can also be built up in multi-stage polycondensation.

Cycloolefinic polymers are polymers that can be obtained using cyclic olefins, in particular polycyclic olefins.

Cyclic olefins include, for example, monocyclic olefins, such as cyclopentene, cyclopentadiene, cyclohexene, cycloheptene, cyclooctene and alkyl derivatives of these monocyclic olefins having 1 to 3 carbon atoms, such as methyl, ethyl or propyl, such as methylcyclohexene or dimethylcyclohexene, and acrylate and / or methacrylate derivatives of these Links. In addition, cycloalkanes with olefinic side chains can also be used as cyclic olefins, such as, for example, cyclopentyl methacrylate.

Bridged polycyclic olefin compounds are preferred. These polycyclic olefin compounds can have the double bond both in the ring, these are bridged polycyclic cycloalkenes, and in side chains. These are vinyl derivatives, allyloxycarboxy derivatives and (meth) acryloxy derivatives of polycyclic cycloalkane compounds. These compounds may also have alkyl, aryl or aralkyl substituents. Exemplary polycyclic compounds are, without being restricted thereby, bicyclo [2.2.1] hept-2-ene (norbomene), bicyclo [2.2.1] hept-2,5-diene (2,5-norbornadiene), ethyl -bicyclo [2.2.1] hept-2-ene (ethyl norbomen), ethylidene bicyclo [2.2.1] hept-2-ene (ethylidene-2-norbomen), phenylbicyclo [2.2.1] hept-2-ene, bicyclo [4.3 .0] nona-3,8-diene, tricyclo [4.3.0.1 ² ' ⁵ ] -3-decene, tricyclo [4.3.0.1 ² ' ⁵ ] -3,8-decen- (3,8-dihydrodicyclopentadiene), tricyclo [4.4.0.1 ^2.5 ] -3-undecene, tetracyclo [4.4.0.1 ² ' ⁵ , 1 ⁷ ' ¹⁰ ] -3-dodecene, ethylidene tetracyclo [4.4.0.1 ^2.5 .1 ^7.10 ] - 3 -dodecen, methyloxycarbonyltetracyclo [4.4.0.1 ² ' ⁵ , 1 ⁷ ' ¹⁰ ] -3-dodecen, ethylidene-9-ethyltetracyclo [4.4.0.1 ² ' ⁵ , 1 ⁷ ' ¹⁰ ] -3-dodecen, pentacyclo [4.7.0.1 ² ' ⁵ , O, O ³ ' ¹³ , 1 ⁹ ^'12 ] -3-pentadecene, pentacyclo [6.1.1 ³ ' ⁶ .0 ^2.7 .0 ⁹ ^'13 ] -4-pentadecene, hexacyclo [6.6.1.1 ^3.6 .1 ¹⁰ ^'13 .0 ^2.7 .0 ^9.14 ] -4-heptadecene, dimethylhexacyclo [6.6.1.1 ^3.6 .1 ¹⁰ ' ¹³ .0 ² ' ⁷ .0 ⁹ ' ⁴ ] -4 -heptadecene, bis (allyloxycarboxy) t ricyclo [4.3.0.1 ^2,5 ] decane,

Bis (methacryloxy) tricyclo [4.3.0.1 ^2,5 ] decane, bis (acryloxy) tricyclo [4.3.0.1 ^2,5 ] decane.

The cycloolefinic polymers are produced using at least one of the cycloolefinic compounds described above, in particular the polycyclic hydrocarbon compounds. In addition, other olefins which can be copolymerized with the aforementioned cycloolefinic monomers can be used in the preparation of the cycloolefinic polymers. These include ethylene, propylene, isoprene, butadiene, methyl pentene, styrene and vinyl toluene. Most of the aforementioned olefins, especially the cycloolefins and polycycloolefins, can be obtained commercially. In addition, many cyclic and polycyclic olefins are available through Diels-Alder addition reactions.

The cycloolefinic polymers can be prepared in a known manner, as described in Japanese Patents 11818/1972, 43412/1983, 1442/1986 and 19761/1987 and Japanese Patent Laid-Open Nos. 75700/1975, 129434/1980, 127728/1983, 168708/1985, 271308/1986, 221118/1988 and 180976 / 1990 and in European patent applications EP-A-0 6 610 851, EP-A-0 6485 893, EP-A-0 640787Ö and EP-A-0 6 688 801.

The cycloolefinic polymers can be polymerized in a solvent, for example, using aluminum compounds, vanadium compounds, tungsten compounds or boron compounds as a catalyst.

It is believed that, depending on the conditions, in particular the catalyst used, the polymerization can take place with ring opening or with opening of the double bond.

In addition, it is possible to obtain cycloolefinic polymers by radical polymerization, using light or an initiator as a radical generator. This applies in particular to the acryloyl derivatives of the cycloolefins and / or cycloalkanes. This type of polymerization can take place both in solution and in bulk. Another preferred plastic substrate comprises poly (meth) acrylates. These polymers are generally obtained by free-radical polymerization of mixtures which contain (meth) acrylates. The term (meth) acrylates encompasses methacrylates and acrylates and mixtures of the two.

These monomers are well known. These include, among others

(Meth) acrylates derived from saturated alcohols, such as, for example, methyl (meth) acrylate, ethyl (meth) acrylate,

Propyl (meth) acrylate, n-butyl (meth) acrylicate, tert-butyl (meth) acrylicate,

Pentyl (meth) acrylate and 2-ethylhexyl (meth) acrylate;

(Meth) acrylates derived from unsaturated alcohols, such as. B.

Oleyl (meth) acrylate, 2-propynyl (meth) acrylate, allyl (meth) acrylate,

Vinyl (meth) acrylate;

Aryl (meth) acrylates, such as benzyl (meth) acrylate or

Phenyl (meth) acrylate, where the aryl radicals can in each case be unsubstituted or substituted up to four times;

Cycloalkyl (meth) acrylates, such as 3-vinylcyclohexyl (meth) acrylate,

Bornyl (meth) acrylate;

Hydroxylalkyl (meth) acrylates such as

3-hydroxypropyl (meth) acrylate,

3,4-dihydroxybutyl (meth) acrylate,

2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate;

Glycol di (meth) acrylates, such as 1,4-butanediol di (meth) acrylate,

(Meth) acrylates of ether alcohols, such as

Tetrahydrofurfuryl (meth) acrylate, vinyloxyethoxyethyl (meth) acrylate;

Amides and nitriles of (meth) acrylic acid, such as

N- (3-dimethylaminopropyl) (meth) acrylamide,

N- (diethylphosphono) (meth) acrylamide, 1-Methacryloylamido-2-methyl-2-propanol; sulfur-containing methacrylates, such as

Ethylsulfinylethyl (meth) acrylate,

4-Thiocyanatobutyl (meth) acrylate,

Ethylsulfonylethyl (meth) acrylate,

Thiocyanatomethyl (meth) acrylate,

Methylsulfinylmethyl (meth) acrylate,

Bis ((meth) acryloyIoxyethyI) sulfide; polyvalent (meth) acrylates, such as

Trimethyloylpropantri (meth) acrylate,

Pentaerythritol tetra (meth) acrylate and

Pentaerythritol tri (meth) acrylate.

According to a preferred aspect of the present invention, these mixtures contain at least 40% by weight, preferably at least 60% by weight and particularly preferably at least 80% by weight, based on the weight of the monomers, of methyl methacrylate.

In addition to the (meth) acrylates set out above, the compositions to be polymerized can also have further unsaturated monomers which are copolymerizable with methyl methacrylate and the aforementioned (meth) acrylates.

These include 1-alkenes such as 1-hexene, 1-heptene; branched alkenes such as vinylcyclohexane, 3,3-dimethyl-1-propene, 3-methyl-1-diisobutylene, 4-methylpentene-1;

acrylonitrile; Vinyl esters such as vinyl acetate;

Styrene, substituted styrenes with an alkyl substituent in the side chain, such as. B. α-methylstyrene and α-ethylstyrene, substituted styrenes with an alkyl substituent on the ring, such as vinyltoluene and p-methylstyrene, halogenated styrenes such as monochlorostyrenes, dichlorostyrenes, tribromostyrenes and tetrabromostyrenes;

Heterocyclic vinyl compounds, such as 2-vinylpyridine, 3-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2,3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole, 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone, 2-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiophene, vinylthiole hydrogenated vinyl thiazoles, vinyl oxazoles and hydrogenated vinyl oxazoles;

Vinyl and isoprenyl ether;

Maleic acid derivatives, such as maleic anhydride, methyl maleic anhydride, maleimide, methyl maleimide; and dienes such as divinylbenzene.

In general, these comonomers are used in an amount of 0 to 60% by weight, preferably 0 to 40% by weight and particularly preferably 0 to 20% by weight, based on the weight of the monomers, the compounds being used individually or can be used as a mixture.

The polymerization is generally started with known radical initiators. The preferred initiators include, among others, the azo initiators well known in the art, such as AIBN and 1, 1-azobiscyclohexane carbonitrile, and also peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, methyl isobutyl ketone peroxide, and cyclohexyl peroxide , tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, 2,5-bis (2-ethylhexanoyl-peroxy) -2,5- dimethylhexane, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy-3,5,5-trimethylhexanoate, dicumyl peroxide,

1, 1-bis (tert-butylperoxy) cyclohexane, 1, 1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide, bis (4-tert-butylcyclohexyl) peroxydicarbonate, Mixtures of two or more of the abovementioned compounds with one another and mixtures of the abovementioned compounds with compounds not mentioned which can likewise form free radicals.

These compounds are often used in an amount of 0.01 to 3% by weight, preferably 0.05 to 1% by weight, based on the weight of the monomers.

The aforementioned polymers can be used individually or as a mixture. Various polycarbonates, poly (meth) acrylates or cycloolefinic polymers can also be used here, which differ, for example, in molecular weight or in the monomer composition.

The plastic substrates according to the invention can be produced, for example, from molding compositions of the aforementioned polymers. Thermoplastic molding processes, such as extrusion or injection molding, are generally used here.

The weight average molecular weight M _{w of} the homopolymers and / or copolymers to be used according to the invention as a molding composition for the production of the plastic substrates can vary within wide limits, the molecular weight usually being matched to the intended use and processing mode of the molding composition. In general, however, it is in the range between 20,000 and 1,000,000 g / mol, preferably 50,000 to 500,000 g / mol and particularly preferably 80,000 to 300,000 g / mol, without any limitation. This size can be determined, for example, by means of gel permeation chromatography.

Furthermore, the plastic substrates can be produced by casting chamber processes. For example, suitable (meth) acrylic mixtures are given in a mold and polymerized. Such (meth) acrylic mixtures generally have the (meth) acrylates set out above, in particular methyl methacrylate. Furthermore, the (meth) acrylic mixtures can contain the copolymers set out above and, in particular for adjusting the viscosity, polymers, in particular poly (meth) acrylates.

The weight average molecular weight M _{w of} the polymers produced by casting chamber processes is generally higher than the molecular weight of polymers used in molding compositions. This results in a number of known advantages. In general, the weight average molecular weight of polymers which are produced by casting combs is in the range from 500,000 to 10,000,000 g / mol, without any intention that this should impose any restriction.

Preferred plastic substrates made by the casting chamber process can be obtained commercially from Cyro Inc. USA under the trade name © Acrylite.

In addition, the molding compositions to be used for the production of the plastic substrates and the acrylic resins can contain customary additives of all kinds. These include, among others, antistatic agents, antioxidants, mold release agents, flame retardants, lubricants, Dyes, flow improvers, fillers, light stabilizers and organic phosphorus compounds, such as phosphites, phosphorinanes, phospholanes or phosphonates, pigments, weathering protection agents and plasticizers. However, the amount of additives is limited to the application.

Particularly preferred molding compositions which comprise poly (meth) acrylates are commercially available under the trade name Acrylite® from Cyro Inc. USA. Preferred molding compositions comprising cycloolefinic polymers can be obtained under the trade names © Topas from Ticona and © Zeonex from Nippon Zeon. Polycarbonate molding compositions are available, for example, under the trade name ®Makrolon from Bayer or ®Lexan from General Electric.

The plastic substrate particularly preferably comprises at least 80% by weight, in particular at least 90% by weight, based on the total weight of the substrate, of poly (meth) acrylates, polycarbonates and / or cycloolefinic polymers. The plastic substrates particularly preferably consist of polymethyl methacrylate, it being possible for the polymethyl methacrylate to contain customary additives.

According to a preferred embodiment, plastic substrates can have an impact strength according to ISO 179/1 of at least 10 kJ / m ² , preferably at least 15 kJ / m ² .

The shape and size of the plastic substrate are not essential to the present invention. In general, plate-shaped or tabular substrates are often used, which have a thickness in the range from 1 mm to 200 mm, in particular 5 to 30 mm. Before the plastic substrates are provided with a coating, these can be activated by suitable methods in order to improve the adhesion. For this purpose, for example, the plastic substrate can be treated with a chemical and / or physical method, the respective method being dependent on the plastic substrate.

The plastic bodies of the present invention are first provided with a siloxane coating, which protects the plastic substrate against the photocatalytic degradation by the photocatalytically active coating containing TiO ₂ (b).

Scratch-resistant siloxane lacquers which can be used to produce the coating (a) are known per se and are used to finish polymeric glazing materials. Due to their inorganic character, they are characterized by good resistance to UV radiation and weather influences. The production of such paints is described, for example, in EP-A-0 073911. Among other things, varnishes that contain water and / or alcohol as a solvent in addition to the siloxane condensation products are common.

These siloxane lacquers can be produced, inter alia, by condensation or hydrolysis of organic silicon compounds of the general formula

(I)

R ¹ nSiX ₄ . _n (I), in which R ^{1 is} a group having 1 to 20 carbon atoms, X is an alkoxy radical with 1 to 20 carbon atoms or a halogen and n is an integer from 0 to 3, where different radicals X or R ^{1 are} each the same or different can be obtained. The expression "a group having 1 to 20 carbon" denotes residues of organic compounds with 1 to 20 carbon atoms. It includes alkyl, cycloalkyl, aromatic groups, alkenyl groups and alkynyl groups with 1 to 20 carbon atoms, as well as heteroalipatic and heteroaromatic groups which, in addition to carbon and hydrogen atoms, have in particular oxygen, nitrogen, sulfur and phosphorus atoms. The groups mentioned can be branched or non-branched, the radical R ^{1 being} substituted or unsubstituted. The substituents include in particular halogens, groups having 1 to 20 carbon, nitro, sulfonic acid, alkoxy, cycloalkoxy, alkanoyl, alkoxycarbonyl, sulfonic acid ester, sulfinic acid, sulfinic acid ester, thiol, cyanide, epoxy, (Meth) acryloyl, amino and hydroxy groups. In the context of the present invention, the term "halogen" denotes a fluorine, chlorine, bromine or iodine atom.

The preferred alkyl groups include the methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, 2-methylpropyl, tert-butyl, pentyl, 2-methylbutyl, 1, 1 -Dimethylpropyl, hexyl, heptyl, octyl, 1, 1, 3,3-tetramethylbutyl, nonyl, 1-decyl, 2-decyl, undecyl, dodecyl, pentadecyl and the eicosyl group ,

The preferred cycloalkyl groups include the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and the cyclooctyl group, which are optionally substituted by branched or unbranched alkyl groups.

The preferred alkenyl groups include the vinyl, allyl, 2-methyl-2-propene, 2-butenyl, 2-pentenyl, 2-decenyl and the 2-eicosenyl groups. The preferred alkynyl groups include the ethynyl, propargyl, 2-methyl-2-propyne, 2-butynyl, 2-pentynyl and the 2-decynyl group.

The preferred alkanoyl groups include the formyl, acetyl, propionyl, 2-methylpropionyl, butyryl, valeroyl, pivaloyl, hexanoyl, decanoyl and dodecanoyl groups.

The preferred alkoxycarbonyl groups include the methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, tert-butoxycarbonyl, hexyloxycarbonyl, 2-methylhexyloxycarbonyl, decyloxycarbonyl or dodecyloxycarbonyl group.

The preferred alkoxy groups include the methoxy, ethoxy, propoxy, butoxy, tert-butoxy, hexyloxy, 2-methylhexyloxy, decyloxy or dodecyloxy group.

The preferred cycloalkoxy groups include cycloalkoxy groups whose hydrocarbon radical is one of the preferred cycloalkyl groups mentioned above.

The preferred heteroaliphatic groups include the abovementioned preferred cycloalkyl radicals in which at least one carbon unit has been replaced by O, S or a group NR ⁸ and R ^{8 is} hydrogen, an alkyl having 1 to 6 carbon atoms and one having 1 to 6 carbon atoms Alkoxy or an aryl group means.

According to the invention, aromatic groups denote residues of mono- or polynuclear aromatic compounds with preferably 6 to 14, in particular 6 to 12, carbon atoms. Heteroaromatic groups characterize aryl radicals, in which at least one CH group is represented by N is replaced and / or at least two adjacent CH groups are replaced by S, NH or O. Aromatic or heteroaromatic groups preferred according to the invention are derived from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenylsulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole, 3,4-oxazole, pyrazole , 2,5-diphenyl-1, 3,4-oxadiazole, 1, 3,4-thiadiazole, 1, 3,4-triazole, 2,5-diphenyl-1, 3,4-triazole, 1, 2.5 Triphenyl-1, 3,4-triazole, 1, 2,4-oxadiazole, 1, 2,4-thiadiazole, 1, 2,4-triazole, 1, 2,3-triazole, 1, 2,3,4 -Tetrazole, benzo [b] thiophene, benzo [b] furan, indole, benzo [c] thiophene, benzo [c] furan, isoindole, benzoxazole, benzothiazole, benzimidazole, benzisoxazole, benzisothiazole, benzopyrazole, benzothiadiazole, benzotriazole, dibenzothuran , Carbazole, pyridine, pyrazine, pyrimidine, pyridazine, 1, 3,5-triazine, 1, 2,4-triazine, 1, 2,4,5-triazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, 1, 8 - naphthyridine, 1, 5-naphthyridine, 1, 6-naphthyridine, 1, 7-naphthyridine, phthalazine, pyride opyrimidine, purine, pteridine or 4H-quinolizine, diphenyl ether, anthracene and phenanthrene.

Preferred radicals R ¹ can be represented by the formulas (II),

- (CH ₂ ) _m NH - [(CH ₂ ) _n -NH] _p H (II), in which m and n are a number from 1 to 6 and p is zero or one, or the formula (III)

wherein q is a number from 1 to 6, or the formula (IV)

wherein R ^{2 is} methyl or hydrogen and r represents a number from 1 to 6.

The radical R ¹ very particularly preferably represents a methyl or ethyl group.

With regard to the definition of the group X in formula (I) with respect to the alkoxy group having 1 to 20 carbon atoms and the halogen, reference is made to the aforementioned definition, the alkyl radical of the alkoxy group preferably likewise being represented by the formulas (II), (III) or (IV) can be represented. Group X is preferably a methoxy or ethoxy radical or a bromine or chlorine atom.

These compounds can be used individually or as a mixture to produce siloxane paints.

Depending on the number of halogens or alkoxy groups bonded to the silicon via oxygen, chains or branched siloxanes are formed from the silane compounds of the formula (I) by hydrolysis or condensation. At least 60% by weight, in particular at least 80% by weight, of the silane compounds used preferably have at least three alkoxy groups or halogen atoms, based on the weight of the condensable silanes.

Tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-i-propoxysilane and tetra-n-butoxysilane; Trialkoxysilanes include methyl-trimethoxysilane, methyl-triethoxysilane, ethyl-trimethoxysilane, n-propyl-trimethoxysilane, n-propyl-triethoxysilane, i-propyl-triethoxysilane, i-propyl-trimethoxysilane, i-propyl-tripropoxysilane, n-butyl-triethoxysilane, n-pentyl-trimethoxysilane, n-hexyl-trimethoxysilane, n-heptyl-trimethoxysilane, n-octyl-trimethoxysilane, vinyl-trimethoxysilane, vinyl-triethoxysilane, cyclohexyl-trimethoxysilane, phenyloxililylylyl, cyclohexylilylylylylylilylilylylyliloxylilane, cyclohexylilylilyl, cyclohexylilylylilyl, cyclohexylilylilyl, cyclohexylilylylilyl, cyclohexylilylylilyl, cyclohexylilylilyl, cyclohexylilylilyl, cyclohexylilylilyl, cyclohexylilylyliloxylilyl, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 2-hydroxysilane 2-hydroxyethyl-triethoxysilane, 2-hydroxypropyl-trimethoxysilane, 2-hydroxypropyl-triethoxysilane, 3-hydroxypropyl-trimethoxysilane, 3-hydroxypropyl-triethoxysilane, 3-mercaptopropyl-trimethoxysilane, 3-mercaptopropyl-triethoxysiloxilane, 3-mercaptopropyl-triethoxysilane, lso cianatopropyl-triethoxysilane, 3-glycidoxypropyl-trimethoxysilane, 3-glycidoxypropyl-triethoxysilane, 2- (3,4-epoxycyclohexyl) ethyl-trimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyl-triethoxysilane, 3- (meth) acryloxysilane , 3- (meth) acryloxypropyl-triethoxysilane, 3-ureidopropyl-trimethoxysilane and 3-ureidopropyl-triethoxysilane;

Dialkoxysilanes include dimethyldimethoxysilane, dimethyl-diethoxysilane, diethyl-dimethoxysilane, diethyl-diethoxysilane, di-n-propyl-dimethoxysilane, di-n-propyldiethoxysilane, di-i-propyl-dimethoxysilane, di-n-propylane diet butyl-dimethoxysilane, di-n-butyldiethoxysilane, di-n-pentyl-dimethoxysilane, di-n-pentyl-diethoxysilane, di-n-hexyl-dimethoxysilane, di-n-hexyl-diethoxysilane, di-n-peptyl- dimethoxysilane, di-n-peptyl-diethoxysilane, di-n-octyl-dimethoxysilane, di-n-octyl-diethoxysilane, di-n-cyclohexyl-dimethoxysilane, Di-n-cyclohexyl-diethoxysilane, diphenyl-dimethoxysilane and diphenyl-diethoxysilane.

Methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane and ethyltriethoxysilane are particularly preferred. According to a particular aspect of the present invention, the proportion of these particularly preferred alkyl trialkoxysilanes is at least 80% by weight, in particular at least 90% by weight, based on the weight of the silane compounds used.

According to a further aspect of the present invention, it is also possible to use siloxane paints which contain colloidally dissolved SiO ₂ particles. Such solutions can be obtained by the sol-gel process, in particular tetraalkoxysilanes and / or tetrahalosilanes being condensed.

Water-containing coating compositions are usually prepared from the abovementioned silane compounds by hydrolysing organosilicon compounds with an amount of water sufficient for the hydrolysis, ie> 0.5 mol of water per mole of the groups intended for the hydrolysis, for example alkoxy groups, preferably with acid catalysis. Examples of acids which can be added are inorganic acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc., or organic acids, such as carboxylic acids, organic sulfonic acids, etc., or acidic ion exchangers, the pH of the hydrolysis reaction generally being between 2 and 4, 5, preferably 3. In general, an increase in temperature is evident after the reactants have been combined. In certain cases, it may be necessary to apply heat from the outside at the start of the reaction, for example by heating the batch to 40-50 ° C. In general, care is taken to ensure that the reaction temperature does not exceed 55 ° C. The reaction time is usually relatively short, it is usually less than one hour, for example 45 minutes.

The silane compounds can be condensed to give polymers which generally have a weight average molecular weight M _w in the range from 100 to 20,000, preferably 200 to 10,000 and particularly preferably 500 to 1500 g / mol. This molar mass can be determined, for example, by NMR spectroscopy.

The condensation reaction can be stopped, for example, by cooling to temperatures below 0 ° C. or by increasing the pH with suitable bases, for example alkali metal or alkaline earth metal hydroxides.

For further processing, part of the water-alcohol mixture and the volatile acids can be separated from the reaction mixture, for example by distillation.

Then with suitable organic solvents such as alcohols such as ethanol, methanol, isopropanol, butanol, ethers such as diethyl ether, dioxane, ethers and esters of polyols such as ethylene glycol, propylene glycol and ethers and esters of these compounds, hydrocarbons, for example aromatic hydrocarbons , Ketones such as acetone, methyl ethyl ketone, the Solids content to about 15-35 wt .-%, based on the total weight of the mixture. Ethanol and / or propanol-2 is particularly preferred as the solvent.

It has also proven to be advantageous to add to the coating compositions those solvents which normally dissolve the plastic provided as the substrate for the coating. In the case of polymethyl methacrylate (PMMA) as the substrate, it is advisable, for example, to add solvents such as toluene, acetone, tetrahydrofuran in amounts which make up 2 to 20% by weight, based on the total weight of the composition. The water content is generally adjusted to 5-20% by weight, preferably 11 to 15% by weight, based on the total weight of the compositions.

To improve the shelf life, the pH of the water-containing siloxane paints can be adjusted to a range from 3 to 6, preferably between 4.5 and 5.5. For this purpose, it is also possible, for example, to add additives, in particular propionamide, which are described in EP-A-0 073 911.

The siloxane lacquers which can be used according to the invention can contain curing catalysts, for example in the form of zinc compounds and / or other metal compounds, such as cobalt, copper or calcium compounds, in particular their octoates or naphthenates. The proportion of curing catalysts is generally 0.1-2.5% by weight, especially 0.2-2% by weight, based on the total siloxane lacquer, without any intention that this should impose a restriction. Zinc naphthenate, octoate, acetate, sulfate, etc. are particularly mentioned. The siloxane paints described above can be obtained commercially from Röhm GmbH & Co. KG under the trade names © Acriplex 100 and © Acriplex 180 SR.

The siloxane paints described above can be applied to the plastic substrates using any known method. These include immersion processes, spray processes, doctor blades, flood coatings and roller or roller application.

The siloxane lacquers applied in this way can generally be in a relatively short time, for example within 2 to 6 hours, generally within about 3 to 5 hours and at a comparatively low temperature, for example at 70-110 ° C., preferably at about 80 ° C cure to excellent scratch and adhesive coatings.

The layer thickness of the siloxane coating (a) is relatively uncritical. In general, however, this size after hardening is in a range from 1 to 50 μm, preferably 1.5 to 30 μm and particularly preferably 3 to 15 μm, without any intention that this should impose a restriction. The layer thicknesses of the coatings (a), (b) and / or (c) can be determined by taking a scanning electron microscope (SEM).

According to a particular aspect of the present invention, the polar fraction of the surface energy after curing of the first siloxane layer is preferably at most 8 mN / m, particularly preferably at most 6 mN / m. According to a preferred embodiment of the present invention, the proportion of silicon in the siloxane coating (a) after curing is at least 20% by weight, preferably at least 30% by weight, based on the total weight of the coating, without being restricted thereby should. The proportion of carbon is preferably at most 36% by weight, in particular at most 25% by weight, based on the total weight of the coating. These proportions can be determined by an elementary analysis according to J. Liebig or by atomic absorption spectroscopy (AAS).

After the first siloxane coating has hardened, the surface is activated by increasing the polar portion of the surface energy of the hardened siloxane coating to a value of at least 10 mN / m. The polar fraction of the surface energy is particularly preferably increased to at least 15 mN / m.

The surface energy is determined using the Ownes-Wendt-Rabel & Kaelble method. For this purpose, series of measurements are carried out using the standard Busscher series, in which the test liquids are water [SFT 72.1 mN / m], formamide [SFT 56.9 mN / m, diiodomethane [SFT 50.0 mN / m] and alpha- Bromonaphthalene [SFT 44.4 mN / m] can be used. The measurement is carried out at 20 ° C. The surface tension and the polar and disperse portion of these test liquids are known and are used to calculate the surface energy of the substrate.

The surface energy can be determined with a contact angle measuring system G40 from Krüss, Hamburg, the implementation being described in the user manual of the contact angle measuring system G40, 1993. Regarding the calculation methods, be on AW Neumann, About the Measurement Methodology for the Determination of Surface Energy Sizes, Part I, Zeitschrift für Phys. Chem., Vol. 41, pp. 339-352 (1964), and AW Neumann, About the Measurement Methodology for Determining Interfacial Energy Quantities, Part II, Zeitschrift für Phys. Chem., Vol. 43, pp. 71-83 (1964).

Various physical and chemical processes are suitable for activating the siloxane base coat. This includes, among other things, treating the surface with chemical processes, in particular with alkalis, corona treatment, flame treatment, plasma or atmospheric plasma treatment. Chemical processes and corona treatment are preferred.

The activation can take place chemically, the substrate coated with the siloxane base lacquer being subjected to a treatment with preferably liquid reagents. Here, only the uppermost atomic layers of the siloxane lacquer are preferably etched. According to a particular aspect, the surface is treated with an alkaline solution, the pH of which is at least 10, preferably at least 12.

For example, the substrate coated with the siloxane lacquer can be treated with an aqueous and / or alcoholic solution of alkali metal hydroxides. Preferred alcohols are methanol, ethanol, propanol and / or butanol. The concentration of the alkali metal hydroxides is preferably in the range from 1 to 20, in particular 2 to 10,% by weight, based on the weight of the etching solution. Alkali metals are in particular lithium, sodium, potassium, rubidium and / or cesium. Of these, sodium and / or potassium are preferred. The exposure time of the alkaline solution depends on the pH value and can therefore be in a wide range. In general, a few minutes are sufficient. The exposure time of the alkaline solution is particularly preferably in the range from 30 seconds to 60 minutes, in particular 1 minute to 10 minutes. This surface treatment can be interrupted, for example, by washing neutral or adding acids.

The alkaline solutions can be applied to the siloxane coating by any known method. These methods have been presented previously.

Furthermore, the polar portion of the surface energy can be increased by corona treatment. This method is described for example in EP-A-1 180 426. The treatment time depends on the energy used and is preferably in a range from 1 to 20 seconds, in particular from 2 to 5 seconds. A generator suitable for corona treatment can be obtained, for example, from Softal Electronic GmbH, Hamburg, which can be operated in the high-frequency range at 20 to 30 kHz (generator 3005).

After the activation of the first siloxane layer, which contains no photocatalytically active components, a second layer containing Ti0 ₂ particles is applied.

The lacquer for producing the second layer can essentially correspond to the first siloxane lacquer, although photocatalytically active TiO ₂ particles must be introduced. Such a lacquer can be produced, for example, by mixing a previously described siloxane lacquer with an aqueous and / or alcoholic composition containing TiO ₂ particles.

Coating agents which contain colloidally dissolved SiO ₂ particles are particularly suitable. These particles preferably have the same size as the Ti0 ₂ particles described below. Such dispersions can be prepared by the sol-gel process, in particular tetraalkoxysilanes and / or tetrahalosilanes being condensed.

Such compositions containing Ti0 ₂ particles are known, inter alia, from EP-A-0 826 663, EP-A-0 850 203 and EP-1 022 318. Furthermore, such compositions can be obtained commercially, for example, from Showa Denko Kabushiki Kaisha, Japan, under the trade name NTB 30A or Toto Ltd., Japan.

The TiO ₂ particles are photocatalytically active. Accordingly, at least some of the Ti0 ₂ particles are present in the brookite and / or anatase modification. The particle size is not critical, but the transparency depends on the particle size. The particles preferably have a size of at most 300 nm, they being in particular in a range from 1 to 200 nm, preferably 1 to 50 nm.

The second layer containing Ti0 ₂ particles can be applied and cured using the methods described above. According to a particular embodiment, the Ti0 ₂ particles in the second coating in an amount in the range of 0.01 to 90 wt .-%, preferably 0.1 to 75 wt .-%, based on the total weight of the second coating after Hardening, present.

The layer thickness of the coating (b) containing Ti0 ₂ particles is likewise not critical. In general, this size after curing is in the range from 0.05 to 2 μm, preferably 0.1 to 1 μm.

After the coating (b) containing TiO ₂ particles has dried, a water-spreading inorganic coating (c) is applied to it.

The term water-spreading means that a drop of water forms a contact angle of at most 20 °, preferably at most 10 °, on the surface. This size is determined at 20 ° C using a G40 contact angle measuring system from Krüss, Hamburg.

In the context of the present invention, the term inorganic means that the carbon content of the inorganic coating is at most 25% by weight, preferably at most 17% by weight and very particularly preferably at most 10% by weight, based on the weight of the inorganic coating (c ). This size can be determined using elementary analysis.

In particular, polysiloxanes, silane co-condensates and silica sols can be applied as the water-spreading inorganic coating (c), their carbon content being limited to the ranges set out above. The silane co-condensates and polysiloxanes have been presented in general form above, these preferably having at least 80% by weight, in particular at least 90% by weight, of the silane compounds used, four alkoxy groups or halogen atoms, based on the weight of the condensable silanes.

According to a further aspect of the present invention, silane condensates can also be used to produce the water-spreading coating (c) which contain colloidally dissolved SiO ₂ particles. Such solutions can be obtained by the sol-gel process, in particular tetraalkoxysilanes and / or tetrahalosilanes being condensed.

Furthermore, oxide layers, in particular semimetal and metal oxides, can also be used as the water-spreading coating (c). Suitable compounds include, in particular, oxides and hydroxides which are derived from silicon, aluminum, titanium, zirconium, zinc and / or chromium.

These oxides can be used individually or as mixtures, for example as mixed oxides, but the proportion of TiO ₂ is limited to amounts which do not greatly reduce the permanent water-spreading effect of the outer inorganic coating.

The solubility of these oxides and / or hydroxides in water should be as low as possible, for example the solubility in water at 20 ° should be below 1000 g / l, preferably below 200 μg / l. These oxides can be applied, for example, in the form of colloidal solutions which are obtained by hydrolysis of alkoxy compounds. Such colloidal solutions are known for example from EP-A-0 149 182, EP-A-0 826 663, EP-A-0 850 203 and EP-1 022 318.

The particle size of these oxide particles is not critical, but the transparency depends on the particle size. The particles preferably have a size of at most 300 nm, they being in particular in a range from 1 to 200 nm, preferably 1 to 50 nm.

According to a particular aspect of the present invention, the colloidal solution is preferably applied at a pH greater than or equal to 7.5, in particular greater than or equal to 8 and particularly preferably greater than or equal to 9.

Basic colloidal solutions are cheaper than acidic solutions. In addition, basic colloidal solutions of oxide particles are particularly simple and can be stored for a long time.

The previously described coating compositions can be obtained commercially under the trade name ®Ludox (from Grace, Worms); © Levasil (Bayer, Leverkusen); © Klebosol, (Clariant) can be obtained.

Furthermore, the coating compositions for producing the inorganic coating (a) can contain customary additives and processing aids. These include, in particular, leveling agents, which also include surfactants. The inorganic water-spreading coating (c) can be applied by any known method, examples of which have been set out above.

The applied coating compositions can generally be in a relatively short time, for example within 0.5 minute to 1 hour, generally within about 1 minute to 30 minutes, preferably within 3 minutes to 20 minutes and at a comparatively low temperature, for example at Cure 60 - 110 ° C, preferably at approx. 80 ° C to water-spreading coatings (c).

The layer thickness of the inorganic coating (c) is relatively uncritical, although the photocatalytic effect of the coating (b) below it must not be completely lost. In general, however, this size after hardening is in a range from 0.05 μm to 2 μm, preferably 0.05 μm to 1 μm and particularly preferably 0.05 μm to 0.5 μm, without any intention that this should impose a restriction.

According to a particular aspect of the present invention, the thickness of the inorganic water-spreading coating (c) is preferably in the range from 30 nm to 600 nm, preferably 50 nm to 400 nm and particularly preferably 100 nm to 250 nm.

According to a special embodiment of the plastic body, the total layer thickness of the coatings (a), (b) and (c) after curing is in a range from 2 to 30 μm, in particular from 3 to 15 m.

The plastic bodies of the present invention provided with a photocatalytic coating show a high abrasion resistance. The abrasion resistance according to DIN 53778 is preferred greater than or equal to 10,000 cycles, in particular greater than or equal to 15,000 cycles and particularly preferably greater than or equal to 20,000 cycles.

According to a special aspect of the present invention, the plastic body is transparent, the transparency XD _{65 .O} according to DIN 5033 being at least 70%, preferably at least 75%.

The plastic body preferably has an elastic modulus according to ISO 527-2 of at least 1000 MPa, in particular at least 1500 MPa, without this being intended to impose a restriction.

The plastic bodies according to the invention are generally very resistant to weathering. The weather resistance according to DIN 53387 (Xenotest) is at least 5000 hours.

Even after a long UV irradiation of more than 5000 hours, the yellow index according to DIN 6167 (D65 / 10) of preferred plastic bodies is less than or equal to 8, preferably less than or equal to 5, without this being intended to impose a restriction.

The plastic bodies of the present invention can be used, for example, in the construction sector, in particular for producing greenhouses or conservatories, or as a noise barrier.

The invention is explained in more detail below by means of examples and comparative examples, without the invention being restricted to these examples. example 1

PMMA sheets with a dimension of 150 * 350 * 3 mm were provided with a scratch-resistant lacquer (Acriplex 100 SR, Röhm GmbH & Co. KG), the layer thickness of the lacquer being 7.5 μm after curing.

After the paint had hardened, the polar portion of the surface energy was 5.5 mN / m. The surface was then treated for five minutes with a 5% KOH water / ethanol mixture (1: 3 parts by weight) and then washed neutral. The surface energy was determined using a G40 contact angle measuring system from Krüss, Hamburg, the test liquids being water [SFT 72.1 mN / m], formamide [SFT 56.9 mN / m, diiodomethane [SFT 50.0 mN / m] and alpha-bromonaphthalene [SFT 44.4 mN / m] were used. The polar portion of the surface energy was 15.3 mN / m.

After activation, a colloidal solution containing Ti0 ₂ particles and Si0 ₂ particles was applied by flood coating (3: 1 mixture of NTB 30A (Ti0 ₂ ) with NTB 30B (Si0 ₂ ) available from Showa-Denko). The course of the paint and the adhesion were good. The coating thus obtained was cured at 80 ° C for three hours.

An inorganic water-spreading layer was then applied using a wire knife. For this purpose, a 12 μm thick layer of an anionic silica sol modified on the surface with aluminum oxide (solids content 3%; © Ludox AM available from DuPont), which contains 0.01 part by weight of an eight-fold ethoxylated isotridecyl alcohol as a nonionic emulsifier, was coated. The still moist plate provided with the water-spreading layer was dried for 5 minutes at 80 ° C. in a forced-air drying cabinet.

The layer thickness of the extremely thin layers can be determined by means of a thin section in a transmission electron microscope, the water-spreading layer having a thickness of 0.15 μm.

The scratch resistance of the coating according to the wet abrasion test according to DIN 53778 was carried out using a wet abrasion tester from Gardner, model M 105 / A. A value of 20,000 cycles was determined.

A drop of water applied to the outer coating spread less than 10 °.

Furthermore, the plate was provided with a colored marking (© Edding Marker 400) and irradiated with several UV fluorescent tubes (type Ergoline Turbo Power from JK, Bad Honnef) for 7 days. As a result, the applied marking faded almost completely.

Comparative Example 1

Example 1 was essentially repeated, but no water-spreading coating was applied. The coating also showed a high scratch resistance of 20,000 cycles, with the marking also completely fading. However, the contact angle with water was approx. 37 ° after the plate was stored in the dark for 24 hours. Comparative Example 2

A PMMA plate was provided with a water-spreading coating in accordance with EP 149 182 (example 3 in accordance with EP 149 182). The contact angle with water was less than 10 °. However, the marking applied with the marker was clearly visible after irradiation with UV light.

Claims

claims

1. Water-spreading, scratch-resistant and self-cleaning plastic body, obtainable by a) applying and curing a siloxane coating (a) on a plastic substrate, b) increasing the polar proportion of the surface energy of the cured siloxane coating to a value of at least 10 mN / m and c) applying and curing a coating (b) containing photocatalytically active TiO ₂ particles, and d) applying and curing a water-spreading, inorganic coating (c).

2. Plastic body according to claim 1, characterized in that the plastic substrate comprises cycloolefin copolymers, polyethylene terephthalates, polycarbonates and / or poly (meth) acrylates.

3. Plastic body according to claim 2, characterized in that the plastic substrate consists of polymethyl methacrylate.

4. plastic body according to one or more of the preceding claims, characterized in that the plastic substrate has an impact strength of at least 10 kJ / m ² according to ISO 179/1.

5. plastic body according to one or more of the preceding claims, characterized in that the plastic substrate has a thickness in the range of 1 mm to 200 mm.

6. Plastic body according to one or more of the preceding claims, characterized in that the siloxane coating is obtainable by condensation of a composition which comprises at least 80% by weight of alkyltrialkoxysilanes, based on the content of condensable silanes.

7. Plastic body according to one or more of the preceding claims, characterized in that the siloxane coating comprises condensable polysiloxanes which have a molecular weight in the range from 500 to 1500 g / mol.

8. plastic body according to one or more of the preceding claims, characterized in that the proportion of silicon in the siloxane coating (a) is at least 30% by weight, based on the total weight of the coating.

9. Plastic body according to one or more of the preceding claims, characterized in that the polar portion of the surface energy of the siloxane coating (a) is reduced by hardening to a value less than or equal to 6 mN / m, before the polar portion of the surface energy increased at least 10 mN / m.

10. Plastic body according to one or more of the preceding claims, characterized in that one increases the polar portion of the surface energy of the siloxane coating (a) after curing by treatment with an alcoholic potassium hydroxide solution.

11. Plastic body according to one or more of the preceding claims, characterized in that the TiO ₂ particles have a size in the range from 1 nm to 300 nm.

12. Plastic body according to one or more of the preceding claims, characterized in that the TiO ₂ particles in the second coating (b) in an amount in the range of 0.01 to 90 wt .-%, based on the total weight of the second coating (b) after curing.

13. Plastic body according to one or more of the preceding claims, characterized in that the layer thickness of the siloxane coating (a) after curing is in the range from 1.5 to 30 μm.

14. Plastic body according to one or more of the preceding claims, characterized in that the layer thickness of the coating (b) after curing is in the range from 0.01 to 2 μm.

15. Plastic body according to one or more of the preceding claims, characterized in that the layer thickness of the coating (c) after curing is in the range from 0.01 to 1 μm.

16. Plastic body according to one or more of the preceding claims, characterized in that the layer thickness of the coatings (a), (b) and (c) after curing is in the range from 3 to 15 μm.

17. Plastic body according to one or more of the preceding claims, characterized in that the carbon content of the water-spreading, inorganic coating (c) is at most 17% by weight, based on the weight of the coating (c).

18. Plastic body according to one or more of the preceding claims, characterized in that the water-spreading, inorganic coating (c) is obtainable by curing colloidal solutions of inorganic and / or organometallic compounds.

19. Plastic body according to one or more of the preceding claims, characterized in that water forms a contact angle of at most 10 ° on the water-spreading, inorganic coating (c).

20. Plastic body according to one or more of the preceding claims, characterized in that the abrasion resistance of the plastic body according to DIN 53778 is at least 15,000.

21. Plastic body according to one or more of the preceding claims, characterized in that the plastic body has a modulus of elasticity according to ISO 527-2 of at least 1500 MPa.

22. Plastic body according to one or more of the preceding claims, characterized in that the plastic body has a weathering resistance according to DIN 53 387 of at least 5000 hours.

23. Plastic body according to one or more of the preceding claims, characterized in that the plastic body has a transparency according to DIN 5033 of at least 70%.

24. Plastic body according to one or more of the preceding claims, characterized in that the plastic body has a yellow index less than or equal to 5 after 5000 hours of UV radiation.

25. A process for the production of self-cleaning plastic bodies according to one or more of claims 1 to 24, characterized in that a) a siloxane coating (a) is applied and cured to a plastic substrate, b) the polar portion of the surface energy of the cured siloxane coating increases a value of at least 10 mN / m and c) applies and cures a coating (b) containing photocatalytically active TiO ₂ particles, and d) applies and cures a water-spreading, inorganic coating (c).