AU2431500A - Coating compositions containing cerium dioxide - Google Patents

Description

WO 00/37577 PCT/EP99/09913 Coating compositions containing cerium dioxide The present invention relates to coating compositions that contain cerium dioxide and are based on hydrolysable silanes containing epoxy groups, to articles coated 5 therewith, and to the use thereof. By means of the sol-gel process it is possible to produce materials that are suitable as coatings from alkoxides, for example aluminium propanolate or butanolate, using modified alkoxysilanes. Such sol-gel processes are substantially characterised in that 10 a mixture of the starting components reacts to form a viscous liquid phase by means of a hydrolysis and condensation process. By means of that synthesis method there forms an organically modified inorganic basic structure that has an increased surface hardness as compared with conventional organic polymers. A deciding disadvantage, however, is that a high degree of storage stability (pot life) cannot be achieved 15 owing to the high reactivity of the aluminium-containing component. In comparison with inorganic materials, the resulting layers are still relatively soft. The reason therefor is that, although the inorganic components in the system have a pronounced crosslinking action, the mechanical properties, such as, for example, hardness and abrasion resistance, do not come to bear owing to their very small size. The 20 favourable mechanical properties of the inorganic components can be made full use of by means of so-called filled polymers, because particle sizes of several micrometres are present therein. However, the transparency of the materials is lost thereby, and applications in the field of optics are no longer possible. Although it is possible to use small particles of SiO 2 (e.g. Aerosils*) to produce transparent layers 25 having increased abrasion resistance, the levels of abrasion resistance that can be achieved at the small concentrations that can be used are similar to those of the above-mentioned system. The upper limit of the amount of filler is determined by the high surface reactivity of the small particles, which results in agglomerations or intolerable increases in viscosity. 30 WO 00/37577 PCT/EP99/09913 -2 WO 95/13326 describes a process for the preparation of an organically modified inorganic system that has a markedly increased hardness as compared with the systems described above and exhibits a high degree of optical transparency. That publication also describes organically modified inorganic systems that are suitable 5 for protecting metal surfaces from corrosion, as well as corresponding systems for hydrophilic coatings. The compositions are obtained by a process that consists in adding a particulate material that is selected from oxides, hydroxides, nitrides and carbides of Si, Al and B or transition metals and that has a particle size in the range from 1 to 100 nm, preferably boehmite, and/or a preferably non-ionic surfactant 10 and/or an aromatic polyol to at least one pre-hydrolysed silicon compound containing a radical that has an epoxy group and is bonded directly to Si. By combining the pre-hydrolysed silicon compound with the particulate material, high scratch resistance is achieved. On the other hand, combining the pre-hydrolysed silicon compound with a surfactant yields hydrophilic coatings, while it is possible 15 by combining the pre-hydrolysed silicon compound with an aromatic polyol to obtain corrosion-inhibiting coatings. If desired, it is possible in the process to add fluorinated silanes in order to produce hydrophobic or oil-repellent coatings, Lewis bases or alcoholates as crosslinking catalysts, or further hydrolysable compounds. 20 DE-OS 40 20 316 describes a coating ased on hydrolysable silanes which, after hardening, yields abrasion-resistant and flexible coatings. It is obtainable by reacting one or more epoxy-group-containing silicon compounds with water, the molar ratio of water to hydrolysable groups that are present being from 1:1 to 0.4:1. In addition to the silicon compound, further hydrolysable compounds, for example of 25 aluminium, titanium, zirconium, vanadium, tin, lead and boron, may also be used. Suitable catalysts for the hardening of the composition are especially tertiary amines, which bring about crosslinking of the epoxy groups at temperatures above 60*C. DE-OS 30 21 018 discloses a coating composition containing a partially hydrolysed 30 condensation product of alkyltrialkoxysilanes, an organic carboxylic acid and an WO 00/37577 PCT/EP99/09913 -3 anionic surface-active fluorocarbon agent. The silanes used do not contain epoxy groups. The composition yields surface coatings having an abrasion-resistant surface as well as good transparency, heat resistance and adhesion to the base material, as well as water resistance. 5 US-5 134 191 discloses a hard coating composition which contains an organic epoxy-group-containing silicon compound and inorganic sub-micron particles such as silica sol, and which is hardenable with a minimal amount of an antimony compound as hardening catalyst. It can be used as a coating film for optical articles 10 of plastics. The composition may optionally also contain an aluminium compound. DE-OS 43 38 361 discloses coating compositions that contain epoxy-group containing silicon compounds, nano-scale oxides or hydroxides of Si, Al, B or transition metals, with boehmite being especially preferred, surfactants and aromatic 15 polyols. The compositions may additionally contain Lewis bases, alcoholates of titanium, zirconium or aluminium. The object of the present invention was to provide compositions having still further improved hydrolytic stability, scratch resistance and UV stability. 20 That object is achieved by a coating composition containing (a) at least one silicon compound (A) containing at least one radical that is bonded directly to Si and cannot be cleaved by hydrolysis and that contains 25 an epoxy group, (b) from 0.5 to 15 wt.% of particulate boehmite (B) having a particle size in the range from 1 to 100 nm, (c) from 5 to 30 wt.% of particulate cerium oxide (C) having a particle size in the range from 1 to 100 nm, 30 (d) at least one hydrolysable silicon compound (D), and WO 00/37577 PCT/EP99/09913 -4 (e) at least one hydrolysable aluminium compound (E). In order to achieve a hydrophilic nature of the composition according to the invention, a Lewis base (F) may additionally be used as catalyst. 5 It is also possible additionally to use a hydrolysable silicon compound (G) having at least one non-hydrolysable radical, for example dialkyldialkoxysilanes, preferably dimethyldimethoxysilane. Replacing a portion of the silicon compound (D) by silicon compounds (G) brings about a reduction in the hardness of the resulting 10 coatings. There may additionally be used a preferably non-ionic surfactant (G) in order to achieve long-term hydrophilic properties and/or an aromatic polyol (H) in order to achieve corrosion-inhibiting properties (increased resistance to condensation water). 15 If the coating composition according to the invention contains at least 20 wt.% cerium oxide (C), then the amount of boehmite (B) should not exceed 5 wt.% in order that the coatings do not become too brittle. 20 Compounds (A) to (H) are described in greater detail below: Silicon compound (A) The silicon compound (A) is a silicon compound that has two or three, preferably 25 three, hydrolysable radicals and one or two, preferably one, non-hydrolysable radical(s). The single radical, or at least one of the two non-hydrolysable radicals, has an epoxy group. Examples of hydrolysable radicals are halogen (F, Cl, Br and I, especially Cl and 30 Br), alkoxy (especially C 1 -alkoxy, such as, for example, methoxy, ethoxy, n- WO 00/37577 PCT/EP99/09913 -5 propoxy, isopropoxy and n-butoxy, isobutoxy, sec-butoxy and tert-butoxy), aryloxy (especially C....-aryloxy, for example phenoxy), acyloxy (especially Cl-,acyloxy, such as, for example, acetoxy and propionyloxy) and alkylcarbonyl (for example acetyl). Especially preferred hydrolysable radicals are alkoxy groups, especially 5 methoxy and ethoxy. Examples of non-hydrolysable radicals without an epoxy group are hydrogen, alkyl, especially C,-alkyl (such as, for example, methyl, ethyl, propyl and butyl), alkenyl (especially C 2 -alkenyl, such as, for example, vinyl, 1-propenyl, 2-propenyl and 10 butenyl), alkynyl (especially C 2 g-alkynyl, such as, for example, acetylenyl and propargyl) and aryl, especially C,- 1 o-aryl (such as, for example, phenyl and naphthyl), it being possible for the above-mentioned groups to contain optionally one or more substituents, such as, for example, halogen and alkoxy. Methacryl- and methacryloxy-propyl radicals may also be mentioned in this context. 15 Examples of non-hydrolysable radicals having an epoxy group are especially those that have a glycidyl or glycidyloxy group. Concrete examples of silicon compounds (A) that may be used according to the 20 invention will be found, for example, on pages 8 and 9 of EP-A-195 493, the disclosure of which is incorporated by reference in the present Application. Especially preferred silicon compounds (A) according to the invention are those of the general formula 25

R

3 SiR' in which the radicals R are the same or different (preferably identical) and represent a hydrolysable group (preferably C,-4alkoxy and especially methoxy and ethoxy), 30 and R' represents a glycidyl- or glycidyloxy-(C, 20 )-alkylene radical, especially @- WO 00/37577 PCT/EP99/09913 -6 glycidyloxyethyl-, y-glycidyloxypropyl-, S-glycidyloxybutyl-, 6-glycidyloxypentyl-, o)-glycidyloxyhexyl-, o-glycidyloxyoctyl-, co-glycidyloxynonyl-, o-glycidyloxy decyl-, co-glycidyloxydodecyl- and 2-(3,4-epoxycyclohexyl)-ethyl-. 5 On account of its ready accessibility, special preference is given according to the invention to the use of y-glycidyloxy-propyltrimethoxysilane (hereinafter abbreviated to GPTS). Particulate boehmite (B) 10 Particulate boehmite (B) is preferably used in a particle size in the range from 1 to 100 nm, preferably from 2 to 50 nm and especially from 5 to 20 nm. That material may be employed in the form of a powder but is preferably used in the form of a sol (especially an acid-stabilised sol). Special preference is given to the use of nano 15 scale boehmite particles. Particulate boehmite is commercially available in the form of powders, and the preparation of (acid-stabilised) sols therefrom is also known in the prior art. Moreover, reference may be made in this connection to the Preparation Examples given below. Special preference is given to the use of boehmite sol having a pH in the range from 2.5 to 3.5, preferably from 2.8 to 3.2, which can be obtained, 20 for example, by suspending boehmite powder in dilute HCl. Particulate cerium oxide (C) Particulate cerium oxide (C) is preferably used in a particle size in the range from 1 25 to 100 nm, preferably from 2 to 50 nm and especially from 5 to 20 nm. That material may be employed in the form of a powder but is preferably used in the form of a sol (especially an acid-stabilised sol). Particulate cerium oxide is commercially available in the form of sols and powders, and the preparation of (acid-stabilised) sols therefrom is also known in the prior art. Moreover, reference may be made in 30 this connection to the Preparation Examples given below.

WO 00/37577 PCT/EP99/09913 -7 Hydrolysable silicon compounds (D) In addition to the silicon compounds (A), hydrolysable silicon compounds are also 5 used for the preparation of the compositions according to the invention and are preferably hydrolysed with the silicon compound(s) (A). The hydrolysable silicon compound (D) is a compound of the general formula 10 RXSiR' 4 X wherein R represents a hydrolysable radical, R' represents a non-hydrolysable radical, and x may be from 1 to 4. If more than one radical R and/or R' is present in a compound (D), then those radicals may be the same or different. x is preferably 15 greater than 1. That is to say, the compound (D) has at least one, preferably more than one, hydrolysable radical. Examples of hydrolysable radicals are halogen (F, Cl, Br and I, especially Cl and Br), alkoxy (especially C 4 -alkoxy, such as, for example, methoxy, ethoxy, n 20 propoxy, isopropoxy and n-butoxy, isobutoxy, sec-butoxy or tert-butoxy), aryloxy (especially C,-,o-aryloxy, for example phenoxy), acyloxy (especially C, 1 -acyloxy, such as, for example, acetoxy and propionyloxy) and alkylcarbonyl (for example acetyl). Especially preferred hydrolysable radicals are alkoxy groups, especially methoxy and ethoxy. 25 Examples of non-hydrolysable radicals are hydrogen, alkyl, especially C, 1 -alkyl (such as, for example, methyl, ethyl, propyl and n-butyl, isobutyl, sec-butyl and tert butyl), alkenyl (especially C 2 4 -alkenyl, such as, for example, vinyl, 1-propenyl, 2 propenyl and butenyl), alkynyl (especially C 24 -alkynyl, such as, for example, 30 acetylenyl and propargyl) and aryl, especially C, 61 -aryl (such as, for example, WO 00/37577 PCT/EP99/09913 -8 phenyl and naphthyl), it being possible for the above-mentioned groups to contain optionally one or more substituents, such as, for example, halogen and alkoxy. Methacryl- and methacryloxy-propyl radicals may also be mentioned in this context. 5 Concrete examples of silicon compounds (D) that may be used are given below. Si(OCH 3

)

4 , Si(OC 2

H)

4 , Si(O-n- or iso-C 3

H

7

)

4 , Si(OC 4

H)

4 , SiCl 4 , HSiCl 3 , Si(OOCCH 3

)

4 ,

CH

3 -SiCl 3 , CH 3 -Si(OC 2

H)

3 , C 2

H

5 -SiCl 3 , C 2

H

5 -Si(OC 2

H)

3 , 10 C 3

H

7 -Si(OCH 3

)

3 , C 6

H

5 -Si(OCH 3

)

3 , C 6

H

5 -Si(OC 2

H)

3 ,

(CH

3 0) 3 -Si-C 3

H

6 -C1,

(CH

3

)

2 SiCl 2 , (CH 3

)

2 Si(OCH 3

)

2 , (CH 3

)

2 Si(OC 2

HS)

2 ,

(CH

3

)

2 Si(OH) 2 , (C 6

H

5

)

2 SiCl 2 , (C 6

H

5

)

2 Si(OCH 3

)

2 ,

(C

6

H

5

)

2 Si(OC 2

HS)

2 , (iso-C 3

H

7

)

3 SiOH, 15 CH 2 =CH-Si(OOCCH 3

)

3 ,

CH

2 =CH-SiCl 3 , CH 2 =CH-Si(OCH 3

)

3 , CH 2 =CH-Si(OC 2

H)

3 ,

CH

2 =CH-Si(OC 2

H

4

OCH

3

)

3 , CH 2

=CH-CH

2 -Si(OCH 3

)

3 ,

CH

2

=CH-CH

2 -Si(OC 2

H)

3 ,

CH

2

=CH-CH

2 -Si(OOCCH 3

)

3 , 20 CH 2

=C(CH

3

)-COO-C

3

H

7 -Si(OCH 3

)

3 ,

CH

2

=C(CH

3

)-COO-C

3

H

7 -Si(OC 2

H)

3 . Special preference is given to the use of SiR 4 compounds, wherein the radicals R may be the same or different and represent a hydrolysable group, preferably an 25 alkoxy group having from 1 to 4 carbon atoms, especially methoxy, ethoxy, n propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy or tert-butoxy. Hydrolysable aluminium compound (E) 30 Compound (E) is preferably a compound of Al having the following general formula WO 00/37577 PCT/EP99/09913 -9 Al(R'")3 wherein the radicals R"' may be the same or different and represent a hydrolysable 5 group. Examples of hydrolysable groups are halogen (F, Cl, Br and I, especially Cl and Br), alkoxy (especially C 16 -alkoxy, such as, for example, methoxy, ethoxy, n-propoxy, isopropoxy and n-butoxy, isobutoxy, sec-butoxy or tert-butoxy, n-pentyloxy, n 10 hexyloxy), aryloxy (especially C 6

.

10 -aryloxy, for example phenoxy), acyloxy (especially C 1

.

4 -acyloxy, such as, for example, acetoxy and propionyloxy) and alkylcarbonyl (for example acetyl), or a C.

6 -alkoxy-C 23 -alkyl group, that is to say a group derived from C..-alkyl-ethylene glycol or -propylene glycol, alkoxy having the meaning given above. R'" is especially preferably ethanolate, sec-butanolate, n 15 propanolate or n-butoxy ethanolate. Examples of hydrolysable aluminium compounds (E) that may be used according to the invention are Al(OCH 3 ), Al(OC 2

H,)

3 , Al(O-n-C 3

H

7

)

3 , Al(O-iso-C 3

H

7

)

3 , Al(OC 4

H)

3 , Al(O-iso-C 4

H,)

3 , Al(O-sec-C 4

H)

3 , AiCl 3 , AlCl(OH) 2 , 20 Al(OC 2

H

4 0C 4

H)

3 . Lewis base (F) The Lewis base (F) is preferably a nitrogen compound. Such nitrogen compounds 25 may be selected, for example, from N-heterocycles, amino-group-containing phenols, polycyclic amines and ammonia (preferably in the form of an aqueous solution). Concrete examples thereof are 1-methylimidazole, 2-(N,N-dimethyl aminomethyl)phenol, 2,4,6-tris(N,N-dimethylaminomethyl)phenol and 1,8 diazabicyclo[5.4.0]-7-undecene. Of those compounds, special preference is given to 30 1-methylimidazole.

WO 00/37577 PCT/EP99/09913 -10 A further class of nitrogen-containing Lewis bases that may be used according to the invention are hydrolysable silanes having at least one non-hydrolysable radical that contains at least one primary, secondary or tertiary amino group. Such silanes may 5 be hydrolysed together with the silicon compound (A) and then represent a Lewis base incorporated into the organically modified inorganic network. Preferred nitrogen-containing silicon compounds are those of the general formula

R

3 SiR" 10 wherein the radicals R are the same or different (preferably identical) and represent a hydrolysable group (preferably C 1 4 -alkoxy and especially methoxy and ethoxy), and R" represents a non-hydrolysable radical that is bonded to Si and contains at least one primary, secondary or tertiary amino group. Concrete examples of such silanes 15 are 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2 aminoethyl)-3-aminopropyltrimethoxysilane, N-[N'-(2'-aminoethyl)-2-aminoethyl] 3-aminopropyltrimethoxysilane and N-[3-(triethoxysilyl)propyl]-4,5-dihydro imidazole. 20 The Lewis base is used in the corresponding compositions generally in an amount of from 0.01 to 0.5 mol per mol of epoxy group in the silicon compound (A). Amounts in the range from 0.02 to 0.3 and especially from 0.05 to 0.1 mol of Lewis base per mol of epoxy group are preferred. 25 Surfactant (G) The surfactant (G), which can be used in order to achieve a long-term anti-mist effect and for the purposes of increased hydrophilicity of the coatings, is preferably a non-ionic surfactant. Special preference is given to non-ionic surfactants that are in 30 liquid form at room temperature. Not only is it possible to use such surfactants WO 00/37577 PCT/EP99/09913 - 11 during the preparation of the compositions by the process according to the invention, they may also be introduced subsequently (preferably in aqueous solution) by thermal diffusion at approximately from 50 to 60*C. Preferred surfactants are polyoxyethylene oleyl ethers of various chain lengths (e.g. Brij* 92, 96 or 98 from 5 ICI), polyoxyethylene cetyl ethers of various chain lengths (e.g. Malipal* 24/30 to 24/100 from Hils, and Disponil* 05 from Henkel), sodium lauryl sulfate (e.g. Sulfopon* 101 Spezial from Henkel), lauryl-pyridinium chloride (e.g. Dehydquad C Christ* from Henkel) and polyoxyethylene-sorbitan monooleate (e.g. Tween* from Riedel de Haen). 10 The surfactant is generally employed in amounts of from 0.1 to 35 wt.%, based on the coating composition. 15 Aromatic polyol (H) The aromatic polyol used according to the invention has an average molecular weight of not more than 1000. Examples of such polyols are polyphenylene ethers that carry hydroxy groups on at least two of the phenyl rings, as well as oligomers in 20 which aromatic rings are bonded to one another by a single bond, -0-, -CO-, -S02 or the like and which have at least (and preferably) two hydroxy groups bonded to aromatic groups. Especially preferred aromatic polyols are aromatic diols. Of those, special preference 25 is given to compounds having the following general formulae: H OH OH OH 30 WO 00/37577 PCT/EP99/09913 -12 wherein X represents a (C,-C,)-alkylene or -alkylidene radical, a (C,-C,,)-arylene radical, -0-, -S-, -CO- or -SO2-, and n is 0 or 1. X is preferably C 1

-C

4 -alkylene or -alkylidene, especially -C(CH 3

)

2 -, and -SO 2 -. The aromatic rings of the compounds may carry, in addition to the OH groups, up to three or four further substituents such 5 as, for example, halogen, alkyl and alkoxy. Concrete examples of aromatic polyols (H) that can be used according to the invention are bisphenol A, bisphenol S and 1,5-dihydroxynaphthalene, with bisphenol A being preferred. 10 The polyol (H) is generally used in amounts such that from 0.2 to 1.5 mol, preferably from 0.3 to 1.2 mol and especially from 0.6 to 1.0 mol of hydroxy groups of the aromatic polyol (H) are present per mol of epoxy ring of the silicon compound (A). 15 The use in the compositions according to the invention of silicon compounds (A) having at least two epoxy groups results in coatings and moulded bodies having improved stability towards condensation water. 20 The compositions according to the invention are preferably obtained by means of a process described in greater detail below, in which a sol of material (B) having a pH in the range from 2.5 to 3.5, preferably from 2.8 to 3.2, is reacted with a mixture of the other components. 25 More preferably, they are obtained by a process, likewise defined hereinbelow, in which the sol as defined above is added in two portions to the mixture of (A) and (D), particular temperatures preferably being maintained, and the addition of (E) taking place between the two portions of (B), also preferably at a particular temperature. 30 WO 00/37577 PCT/EP99/09913 - 13 The hydrolysable silicon compound (A) may optionally be pre-hydrolysed together with compound (D) in aqueous solution using an acid catalyst (preferably at room temperature), there being used preferably approximately 1/2 mol of water per mol of hydrolysable group. Hydrochloric acid is preferably used as the catalyst for the pre 5 hydrolysis. The particulate boehmite (B) is preferably suspended in water and the pH adjusted to from 2.5 to 3, preferably from 2.8 to 3.2. Hydrochloric acid is preferably used for acidification. A clear sol forms under those conditions. 10 Compound (D) is mixed with compound (A). The first portion of the particulate boehmite (B) suspended as described above is then added. The amount is preferably so chosen that the water contained therein is sufficient for the semi-stoichiometric hydrolysis of compounds (A) and (D). 15 A few minutes after the addition, the sol warms to approximately from 28 to 35*C and is clear after approximately 20 minutes. The mixture is then stirred for from 0.5 to 3 hours, preferably from 1 to 2 hours. The batch is cooled to approximately 0*C. Compound (E) is then added, during which a temperature of approximately 3*C is 20 not to be exceeded. When the addition of compound (E) is complete, the sol is stirred further for from 0.5 to 3 hours, preferably from 1 to 2 hours, at 0*C. The remainder of the particulate material (B) is then added, during which the temperature is not to exceed 5*C. The reactor temperature is then adjusted to 20*C in order to bring the composition to room temperature. Room temperature is to be understood 25 as being a temperature of from 20 to 23*C. Compound (C) is preferably added at that point in order to stabilise the scratch-resistant coating system to UV. Compound (C) is preferably in the form of a sol. The composition is stored in a refrigerator at 4*C. Compound (E) and, optionally, the Lewis base (F) are preferably added slowly after 30 the addition of the first portion of material (B), likewise at 0*C.

WO 00/37577 PCT/EP99/09913 - 14 In order to adjust the theological properties of the compositions, inert solvents may optionally be added at any desired stage of the preparation. Such solvents are preferably alcohols that are liquid at room temperature and that, moreover, are also 5 formed in the hydrolysis of the alkoxides that are preferably used. Especially preferred alcohols are C 1 , alcohols, especially methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, n-hexanol, n-octanol and n-butoxyethanol. Also preferred are C,_,-glycol ethers, especially n butoxyethanol. 10 The compositions according to the invention may also contain conventional additives, such as, for example, colouring agents, flow agents, UV stabilisers, photoinitiators, photosensitisers (if photochemical hardening of the composition is intended) and thermal polymerisation catalysts. 15 Application to the substrate is carried out by standard coating processes such as, for example, dipping, painting, brush application, doctor application, roll coating, spraying, falling-film application, spin-coating and whirl-coating. 20 Hardening of the coated substrate is optionally carried out after previous partial drying at room temperature. Hardening is preferably carried out thermally at temperatures in the range from 50 to 300*C, especially from 70 to 200*C and more especially from 90 to 180*C, optionally under reduced pressure. The time required for full hardening under such conditions is to be less than 200 minutes, preferably 25 less than 100 minutes and more preferably less than 60 minutes. The layer thickness of the hardened layer is to be from 0.5 to 100 Rm, preferably from 1 to 20 pm and especially from 2 to 10 pm. Where unsaturated compounds and photoinitiators are present, hardening may also 30 be effected by radiation, optionally followed by thermal after-hardening.

WO 00/37577 PCT/EP99/09913 - 15 The choice of substrate materials for coating is not limited. The coating compositions according to the invention are suitable preferably for the coating of wood, textiles, paper, stoneware, metals, glass, ceramics and plastics, and especially 5 for the coating of thermoplastics, such as are described in Becker/Braun, Kunststofftaschenbuch, Carl Hanser Verlag, Munich, Vienna 1992. The compositions are suitable very especially for the coating of transparent thermoplastics and preferably of polycarbonates, or for the coating of metals or metallised surfaces. Spectacle lenses, optical lenses, vehicle windscreens and 10 thermal heads in particular can be coated with the compositions obtained according to the invention.

WO 00/37577 PCT/EP99/09913 -16 Examples Preparation of the boehmite dispersion 5 In order to prepare the boehmite dispersion, 0.1 N hydrochloric acid is placed in a vessel. Boehmite is then slowly added thereto, with stirring. The dispersion is then treated with ultrasound for approximately 20 minutes. Preparation of the scratch-resistant coating system 10 GPTS and TEOS are placed in a vessel and mixed. With stirring, the amount of boehmite dispersion necessary for semi-stoichiometric pre-hydrolysis of the silanes is added slowly. The reaction mixture is then stirred for 2 hours at room temperature. The solution is then cooled to 0*C with the aid of a thermostat. Aluminium 15 tributoxyethanolate is then added dropwise by means of a dropping funnel. After the addition of the aluminate, stirring is carried out for a further one hour at 0*C. The remainder of the boehmite dispersion is then added, while cooling by means of a thermostat. After stirring for 15 minutes at room temperature, the cerium dioxide dispersion and the flow agent are added. 20 WO 00/37577 PCT/EP99/09913 - 17 Starting amounts: Example 21 Example 23 Example 25 TEOS - 62.50 g (0.3 mol) 62.50 g (0.3 mol) DMDMS 36.09 g (0.3 mol) - 36.09 g (0.3 mol) GPTS 236.34 g (1 mol) 236.34 g (1 mol) 236.34 g (1 mol) Boehmite 5.47 g (2 wt.%, 5.53 g (2 wt.%, 6.14 g (2 wt.%, based on total based on total based on total solids) solids) solids) 0.1 N hydrochloric 48.97 g 59.18 g 74.21 g acid Cerium dioxide 222.60 g 257.14 g (20 wt.%, 285.66 g (20 wt.%, dispersion (20 (17.5 wt.%, based based on total based on total wt.% in 2.5 wt.% on total solids) solids) solids) acetic acid) Boehmite 36.06 g 41.38 g 46.83 g dispersion for semi stoichiometric pre hydrolysis Aluminium 113.57 g (0.3 mol) 113.57 g (0.3 mol) 113.57 g (0.3 mol) tributoxyethanolate Flow agent 2.00 g (0.3 wt.%, 2.21 g (0.3 wt.%, 2.45 g (0.3 wt.%, based on the total based on the total based on the total amount of coating) amount of coating) amount of coating) Further examples and comparison examples were carried out according to that 5 process, the amounts of the components being changed according to the values given in Table 1.

WO 00/37577 PCT/EP99/09913 - 18 Using the resulting coatings, test pieces were obtained as follows: Sheets of polycarbonate based on bisphenol A (Tg = 147*C, M,, 27,500) having the dimensions 105 x 150 x 4 mm were cleaned with isopropanol and primed by 5 immersion in a mixture of 3 wt.% aminopropyltrimethoxysilane and 97 wt.% butanol, with subsequent heat treatment for 0.5 hour at 130*C. Each of the sheets was then coated with a coating layer having a thickness of from 10 to 20 pm at a dip rate V = from 60 to 100 cm/min. After cooling for 10 minutes at room temperature, the coated sheets were dried for one hour at 130*C. The layer thickness of the 10 coatings after drying was approximately from 2 to 4 pm. Once the coated sheets had hardened fully, they were stored for 2 days at room temperature and then subjected to the following defined tests. The properties of the coatings obtained using those coating compositions were 15 determined as follows: Cross-cut adhesion test: EN ISO 2409:1994 Cross-cut adhesion test after storage in water: 65*C, tt = 0/1. The coated 20 sheets are provided with a cross-cut according to EN ISO 2409:1994 and stored in water having a temperature of 65*C. The storage time (days) at which the first loss of adhesion occurs in the tape test from 0 to 1 is recorded. Taber Abraser test: wear test DIN 52 347 (1000 cycles, CS1OF, 500 g) 25 Sun test: To that end, the coated samples (with Makrolon 2808 as substrate) are placed in a sun test (type: Heraeus CPS) with a quartz glass filter at maximum power for 3 weeks. After one, two and three weeks, the yellowness index is determined by WO 00/37577 PCT/EP99/09913 - 19 means of UV-VIS spectroscopy (parameters: standard light C, 20 standard observer). A visual assessment of the samples is additionally carried out (crack formation, etc.). Storage in water: 5 A glass desiccator filled with deionised water is placed in a drying cabinet having a temperature of approximately 65*C. After tempering, the coated polycarbonate samples, with which a cross-cut/tape test has previously been carried out, are placed in the desiccator. After 2, 4, 6, 8, 10, 12 and 14 days, the samples are tested in respect of their adhesion by means of a cross-cut/tape test. To that end, the original 10 cross-cut is tested in each case and a completely new cross-cut/tape test is carried out. In addition, the samples are evaluated visually (crack formation, separation, etc.). Boiling test: 15 In this test, a Schott flask filled with deionised water is used. The vessel is insulated by means of a polystyrene jacket and the water is brought to boiling (temperature approximately 97*C) with the aid of a magnetic heating stirrer. The samples (coated polycarbonate), which have previously been tested by means of a cross-cut/tape test, are introduced. After 1, 2, 3, 4, 5, 6, 7 and 8 hours, the sheets are removed and 20 evaluated visually (cracks, separation, etc.). Furthermore, the adhesion is tested both at the original cross-cut and at a freshly prepared one. Determination of layer thickness: Determination of the layer thickness is carried out by means of the profile method 25 using a fine diamond needle which is guided over the surface. In order to carry out the determination, it is necessary to unstick a portion of the sheet during the coating operation in order to verify the difference in height between the uncoated and the coated areas.

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Claims (8)

1. Coating composition containing 5 a) at least one silicon compound (A) containing at least one radical that is bonded directly to Si and cannot be cleaved by hydrolysis and that contains an epoxy group, b) from 0.5 to 15 wt.% of particulate boehmite (B) having a particle size 10 in the range from I to 100 nm, c) from 5 to 30 wt.% of particulate cerium oxide (C) having a particle size in the range from I to 100 nm, 15 d) at least one hydrolysable silicon compound (D), and e) at least one hydrolysable aluminium compound (E).

2. Composition according to claim 1, characterised in that (A) is a compound of 20 the general formula R 3 SiR' in which the radicals R are the same or different and represent a hydrolysable 25 group, preferably C 1 -alkoxy, and R' represents a glycidyl- or a glycidyloxy (C 1 20 )-alkylene radical, (D) is a compound of the general formula 30 SiR 4 WO 00/37577 PCT/EP99/09913 - 22 wherein the radicals R are the same or different and represent a hydrolysable group, preferably C, 4 -alkoxy, and 5 (E) is a compound of the formula AlR 3 wherein the radicals R are the same or different and represent a hydrolysable 10 group, preferably a C, 6 -alkoxy group, a C,_,-alkoxy propanolate group or a C,_,-alkoxy ethanolate group.

3. Composition according to claim 1 or 2, wherein (A) is y-glycidyl oxypropylsilane, (D) is tetraethoxysilane and (E) is Al(butoxy ethanolate) 3 . 15

4. Process for the preparation of compositions according to any one of claims 1 to 3, in which the silicon compound (A) and compound (D) are pre-mixed and then 20 a) a first portion of from 10 to 70 wt.% of the total amount of the sol of material (B) having a pH of from 2.5 to 3.5 is added, and then there are added b) compound (E), then 25 c) the second portion of the sol of material (B) and, finally, d) cerium oxide (C) and 30 e) optionally flow agent and inert solvents. WO 00/37577 PCT/EP99/09913 -23

5. Process for the preparation of compositions according to any one of claims 1 to 3, in which the addition in step a) is carried out at a temperature > 25*C 5 and the addition in step b) and in step c) is carried out at 0 ± 2*C.

6. Use of the composition according to any one of claims 1 to 5 in the coating of substrate materials of any kind, preferably of thermoplastics, especially of polycarbonates. 10

7. Use according to claim 6, characterised in that the composition, which optionally contains an inert solvent, preferably a C,-C, alcohol and/or a monoalkyl glycol ether, especially n-butoxyethanol, for the purposes of adjusting the rheological properties, is applied to the substrate surface and (a) 15 is hardened thermally preferably at temperatures of from 90 to 180*C or (b) after the previous addition of a photoinitiator is hardened photochemically and optionally after-hardened thermally.

8. Articles coated with a composition obtained according to any one of claims 1 20 to 5.