WO2010054975A1 - Process for the distribution of silicates in coating materials - Google Patents

Abstract

Process for the preparation of silicate-containing polyolic binders suitable for two-component polyurethane coating materials, comprising an isocyanate component (A) and a polyolic binder component (B), comprising the steps - addition of from 0 to 10 times the amount of water (based on the SiO₂ content used) and from 0.1 to 20 times the amount (based on the SiO₂ content used), at a temperature of from 10 to 60°C, of at least one organic solvent (L) - at least one alkoxysilane (C) in an amount of from 0.1 to 20 μmol per m² of surface area of (K), and - if appropriate, further solvent (L), to an aqueous silica sol (K) having a mean particle diameter of from 5 to 150 nm and a silicic acid content, calculated as SiO₂, of from 10 to 60% by weight, with a pH of from 2 to 4, - addition of the polyolic binder component (B) to the mixture thus obtained and - at least partial distillation of the organic solvent (L).

Description

Process for the distribution of silicates in coating materials

Description

The present invention describes a process for the homogeneous dispersion of inorganic nanoparticles in two-component polyurethane coating materials with the aim of improving the scratch resistance of coatings obtained therefrom.

In order to incorporate inorganic particles into organic coating materials, these particles are frequently prepared as milled or precipitated solids or a slurry or paste and then suspended in the organic coating material.

A disadvantage of this is that the particles cannot be transferred into an organic matrix without agglomerates by known methods, such as dry milling, wet milling, ultrasonic treatment or extrusion. In addition, for example, particles dispersed by wet milling tend to agglomerate after removal of the solvent, so that the particles are nonuniformly distributed on introduction into a medium, such as, for example, a coating material. As a rule, this results in a loss of transparency of the coating material and, owing to the phase separation of the coating material, leads to abrasion-labile coatings having little hardness.

Since a particular embodiment of the present invention is to use aqueous inorganic nanoparticle sols as inorganic filler for organic coating materials, a suitable pretreatment of the particles is required in order to transfer them into the organic resin without agglomeration.

Direct suspension of the particles in the aqueous solvent in the organic coating materials is not possible, generally owing to the incompatibility of the solvents. However, it is necessary substantially to dispense with solvents since solvents constitute an additional component in the finish system, and this would mean removal of the solvent by the end user. Ready-to-use, low-solvent coating materials which already comprises inorganic particles are therefore sought.

US 3699049 describes the removal of water by distillation at from 50 to 100⁰C from acidic or basic, colloidal silica sols with polyfunctional alcohols, such as, for example, glycerol.

A disadvantage is that the solvent cannot be removed in this method since the glycerol used in the explicitly disclosed examples has a boiling point of about 290⁰C at atmospheric pressure. This prevents removal of the solvent under gentle conditions. EP 75545 A1 describes the preparation of silicate-containing unsaturated polyester resins by distilling off water from acidic silica sols in the presence of building blocks of the polyesters and subsequently adding monomers capable of free radical polymerization.

In this case, a Siθ2-filled polyester solid which is no longer flowable and hence also cannot be used as coating material is prepared.

EP 1236765 A describes a process in which an alkali metal silicate solution is acidified with an acidic ion exchanger and converted into a silica sol and surface-modified with a silane, an isopropanol is then added thereto and water is distilled off. The silicates thus obtained and having a particle size of from 3 to 50 nm can then be taken up in organic coating materials. The silica sols prepared are rendered alkaline after their preparation by acidic polycondensation for protection from agglomeration (paragraph [0042], cf. in this context also example 1 of EP 1366112 B1 ). Thereafter, i.e. in the alkaline pH range, the surface of the silica sol is optionally modified by reaction with functional silanes.

A disadvantage of this preparation process is that the products thus obtained have a relatively high viscosity. Another disadvantage is that commercially available silica sols which are modified in the alkaline pH range have a substantial tendency to agglomeration and gelling.

WO 2006/044376 describes the preparation of inorganic oxides, in particular silicates, in an aqueous medium and subsequent distribution in organic coating materials. The process disclosed there (example 3) comprises, starting from a silica sol, ion exchange with liberation of the acid, mixing with an organic solubilizer, addition of base and addition of a silane for surface modification. The complete surface modification with the silane takes place in the alkaline pH range. Thereafter, the solvent is removed to dryness and the residue is taken up in an organic solvent.

A disadvantage of this process is that the resulting solutions of silica sols with the use of commercial silica sols have a high viscosity and in addition the surface on the particles must be completely reacted with silane in order to give a free-flowing powder. Although it is pointed out that the surface treatment with silanes can take place under acidic or basic conditions, only alkaline reaction conditions are explicitly disclosed.

In another process (example 1 ), a solubilizer, which can simultaneously act as a reactive diluent, and the organic coating material are added directly to the aqueous nanosilicate sol, and the water is separated off by distillation and the residue then taken up with an organic solvent. Here too, the surface modification with a silane takes place in the alkaline range. A disadvantage is that the solubilizer remains in the coating material and this process can be used only for those solubilizers which can simultaneously act as reactive diluents.

In a further process (example 2), a further silica sol is functionalized with a functionalized silane using a catalyst in the alkaline range. The product is taken up in a large amount of solvent and the catalyst is removed by washing. The functionalized silicate is then further used as an organic solution in coating materials.

A disadvantage of this process is that the catalyst has to be removed from the product in a complicated manner by washing, in order to stop the reaction. In addition, the powders obtained can no longer be completely redispersed, which leads to relatively large agglomerates in the product and hence to reduced transparency of the coating.

The unpublished International Patent Application with the file number PCT/EP2008/056270 and the filing date May 21 , 2008, discloses a process for the preparation of silicate-containing organic coating materials, especially for radiation curable coatings.

It was an object of the present invention to provide two-component polyurethane coating materials having a low viscosity which comprise finely divided silicates prepared starting from economical commercially available products, being intended to distribute the silicates uniformly in the coating material. The surface modification should be effected with as little agent as possible.

The object was achieved by a process for the preparation of silicate-containing polyolic binders suitable for two-component polyurethane coating materials, comprising an iso- cyanate component (A) and a polyolic binder component (B), comprising the steps

- addition of from 0 to 10 times the amount of water (based on the Siθ2 content used) and from 0.1 to 20 times the amount (based on the Siθ2 content used), at a tempera- ture of from 10 to 60⁰C, of at least one organic solvent (L)

- at least one alkoxysilane (C), selected from the group consisting of compounds of formula (C1 ),

R²

R O — Si -(CH₂),,

R³ formula (C2), R²

R³ and formula (C3), R²

R¹O — Si R⁶

R³ wherein n is an integer from 1 to 6,

R¹ can be H or d-Cε alkyl (straight, branched or cyclic, preferably straight), R² and R³ independently are -OH, OR¹, or d-Cε alkyl (straight, branched or cyclic, preferably straight),

R⁴ and R⁵ independently are H, d-Cε alkyl (straight, branched or cyclic, preferably straight), d-Cε hydroxyalkyl (straight, branched or cyclic, preferably straight), or d-Cβ aminoalkyl (straight, branched or cyclic, preferably straight);

R⁶ is Cr to C2o-alkyl (straight or branched), Cs- to Ci2-cycloalkyl, Cβ- to Ci2-aryl, or Cj- to C2o-aralkyl (straight or branched).

in an amount of from 0.1 to 20 μmol per m² of surface area of (K), and

- if appropriate, further solvent (L), to an aqueous silica sol (K) having a mean particle diameter of from 5 to 150 nm and a silicic acid content, calculated as Siθ2, of from 10 to 60% by weight, with a pH of from 2 to 4,

- addition of the polyolic binder component (B) to the mixture thus obtained and - at least partial distillation of the organic solvent (L), wherein the solvent (L)

- exhibits a water solubility of at least 200 g/l at 25 ⁰C,

- has a boiling point of less than 80⁰C at 50 hPa, and

- is capable of dissolving at least 200 g/l of the polyolic binder component (B) at 25 ⁰C, and wherein a solution of 200 g polyolic binder component (B) in 1000 g solvent (L) exhibits a viscosity at 25°C of not more than 500 mPa-s (according to DIN EN ISO 3219 in cone-and-plate rotational viscometer at a sheer gradient of 100 S^"1).

The aqueous colloidal solution (K) of polysilicic acid particles which is used (silica sol) comprises particles having a mean particle diameter of from 1 to 150 nm, preferably from 2 to 120 nm, particularly preferably from 3 to 100 nm, very particularly preferably from 4 to 80 nm, in particular from 5 to 50 nm and especially from 8 to 40 nm. The content of silicic acid, calculated as Siθ2, is from 10 to 60% by weight, preferably from 20 to 55% by weight, particularly preferably from 25 to 40% by weight. It is also possible to use silica sols having a lower content, but the additional content of water must then be separated off by distillation in a subsequent step.

The aqueous solutions (K) are colloidal solutions of partly condensed polysilicic acid which, if appropriate, can be stabilized to a slight extent with alkali metal, alkaline earth metal, ammonium, aluminum, iron(ll), iron(lll) and/or zirconium ions, preferably alkali metal, alkaline earth metal, ammonium and/or iron(lll) ions, particularly preferably alkali metal, alkaline earth metal and/or ammonium ions, very particularly preferably alkali metal and/or alkaline earth metal ions and in particular alkali metal ions.

Among the alkali metal ions, sodium and/or potassium ions are preferred and sodium ions are particularly preferred.

Among the alkaline earth metal ions, magnesium, calcium and/or beryllium ions are preferred, magnesium and/or calcium ions are particularly preferred and magnesium ions are very particularly preferred.

The molar ratio of metal ions to silicon atoms in (K) is from 0:1 to 0.1 :1 , preferably from 0.002 to 0.04:1.

After adjustment of the pH, the silica sols (K) used have a pH of the aqueous phase of from 2 to 4, preferably from 2 to 3.

In this document, an aqueous colloidal solution is understood as meaning a solution of optionally stabilized silicic acid particles having a mean particle diameter of from 1 to 150 nm, which did not settle out even on storage over a period of one month at 20⁰C.

In this document, a sol is understood as meaning a colloidal, incoherent (i.e. each particle is freely mobile) solution of a solid substance in water, in this case a colloidal solution of silica in water as a silica sol.

The acidic aqueous silica sols (K) used according to the invention can be obtained, for example, by three different methods:

- by acidification of the corresponding alkaline silica sols,

- by preparation from low molecular weight silicic acids, preferably waterglass, i.e. salt-like particles having a diameter of less than 1 nm, or - by condensation of esters of low molecular weight silicic acids. The aqueous solutions of alkaline silica sols have as a rule a pH of from 7 to 10, preferably from 8 to 9. These alkaline silica sols are commercially available and are therefore a readily available and preferred starting material for the process according to the invention.

The particles in these alkaline silica sols generally have a mean particle diameter of from 1 to 150 nm, preferably from 2 to 120 nm, particularly preferably from 3 to 100 nm, very particularly preferably from 4 to 80 nm, in particular from 5 to 50 nm and especially from 8 to 30 nm.

The content of silicic acid, calculated as Siθ2, is from 15 to 60% by weight, preferably from 20 to 55% by weight, particularly preferably from 25 to 40% by weight. Alkaline silica sols having a lower solids content can also be used, but the additional content of water must then be separated off by distillation in a subsequent step.

The alkaline silica sols can be stabilized with the abovementioned metal ions.

The molar ratio of metal ions to silicon atoms in (K) is from 0:1 to 0.1 :1 , preferably from 0.002 to 0.04:1.

The pH of these alkaline silica sols is as a rule at least 8, preferably from 8 to 12, particularly preferably from 8 to 11 and very particularly preferably from 8 to 10.

The preparation of the silica sols (K) to be used according to the invention from these alkaline silica sols is effected by establishing the desired pH in these silica sols, for example by addition of mineral acids or by addition of an ion exchanger to the alkaline silica sols.

The acidification can be effected with any desired acids, preferably with hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, methanesulfonic acid, or para-toluenesulfonic acid, or by addition of an acidic ion exchanger, preferably by acidification with hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid or acetic acid, particularly preferably with hydrochloric acid, nitric acid or sulfuric acid and very particularly preferably by acidification with sulfuric acid.

A preferred embodiment is to prepare the silica sols (K) by addition of an ion exchanger to alkaline silica sols. As a result of this, the electrolyte content in the silica sols (K) is low, for example is less than 0.2% by weight, preferably less than 0.1 % by weight.

Here, electrolytes are understood as meaning inorganic ionic constituents other than silicates, hydroxides and protons. These electrolytes originating predominantly from the stabilization of the alkaline silica sols are added to the suspension for stabilizing the particles after the preparation thereof.

The preparation of the silica sols (K) from water glass by acidification, for example with an ion exchanger, or by addition of a mineral acid is also conceivable. A water glass preferably used for this purpose is potassium and/or sodium silicate, which particularly preferably has a ratio of 1-10 mol of Siθ2 to 1 mol of alkali metal oxide, very particularly preferably 1.5-6 and in particular 2-4 mol of Siθ2 to 1 mol of alkali metal oxide.

In this case, the reaction mixture is allowed to react until a silica sol (K) of the desired size has formed, and the process according to the invention is then continued.

The low molecular weight silicic acids (ortho- and oligosilicic acid) are usually stable only in highly dilute aqueous solutions having a content of a few % by weight and are as a rule concentrated before further use.

Futhermore, the preparation of the silica sols (K) can be affected by condensation of esters with low molecular weight silicic acids. These are generally d- to C4-alkyl esters, in particular ethyl esters of oligosilicic acids and in particular orthosilicic acids, which form silica sols (K) in the acidic or basic range.

Functionalizing the surface of the Siθ2 nanoparticles, from 0 to 10 times, preferably from 0.2 to 5 times, particularly preferably from 0.4 to 3 times and very particularly preferably from 0.5 to 2 times the amount of water (based on the amount of the silica sol used) and from 0.1 to 20 times, preferably from 0.3 to 10 times, particularly preferably from 0.5 to 5 times and very particularly preferably from 1 to 2 times the amount (based on the amount of the silica sol used) of at least one organic solvent (L) are added to the acidified solution obtained.

The solvent (L) can be added to the reaction mixture before or during the reaction with the silane (C), preferably before or during and particularly preferably before the reaction with the silane.

The organic solvent (L) is selected according to the following criteria: under the mixing conditions, it should have both sufficient miscibility with water and miscibility with the organic coating material.

The miscibility with water under the reaction conditions should be at least 20% by weight (based on the prepared water/solvent mixture), preferably at least 50% by weight and particularly preferably at least 80% by weight. If the miscibility is too low, there is the danger that the gel will form from the modified silica sol and relatively large nanoparticle aggregates will separate out by flocculation. The coating material should be completely soluble in the solvent (L) or the water/solvent mixture.

In addition, it is preferable if the solvent (L) is capable of suspending at least 2 g/l of the resulting silicates without sedimentation.

According to the invention the solvent (L)

- exhibits a water solubility of at least 200 g/l at 25 ⁰C, this means that 1 litre of water is miscible with at least 200 g solvent (L) at 25 ⁰C without separation of phases,

- has a boiling point of less than 80⁰C at 50 hPa, and

- is capable of dissolving at least 200 g/l of the polyolic binder component (B) at 25 ⁰C, this means that 1 litre of solvent (L) is capable of dissolving with at least 200 g binder component at 25 ⁰C.

Further according to the invention a solution of 200 g polyolic binder component (B) in 1000 g solvent (L) exhibits a viscosity at 25°C of not more than 500 mPa-s (according to DIN EN ISO 3219 in cone-and-plate rotational viscometer at a sheer gradient of 100

In a preferred embodiment, the solvent (L) forms an azeotrope or heteroazeotrope with water under the distillation conditions, so that the distillate forms an aqueous and an organic phase after the distillation.

The solvents (L) are preferably selected from the group consisting of halogenated hydrocarbons, ketones, esters, alcohols, and ethers. Particular preference is given to esters and, among them, to alkyl alkanoates and alkoxylated alkyl alkanoates.

Halogenated hydrocarbons are, for example, chlorobenzene and dichlorobenzene or its isomer mixtures.

Ethers are, for example, THF, dioxane, and also the dimethyl, diethyl or di-n-butyl ethers of ethylene glycol, diethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol or tripropylene glycol.

Ketones are, for example, acetone, ethyl methyl ketone, diethyl ketone, isobutyl methyl ketone, cyclohexanone or cyclopentanone.

Alcohols are, for example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-chloro-2-propanol, mixtures of pentanol isomers, 1-hexanol, mixtures of hexanol isomers, cyclopentanol, and cyclo- hexanol. Esters are, for example, n-butyl acetate, ethyl acetate, 1 -methoxy-2-propyl acetate, and 2-methoxyethyl acetate.

Preferred examples of suitable solvents (L) are ethanol, 1-propanol, 2-propanol, 1- butanol, 2-butanol, 2-methyl-2-propanol, 1-chloro-2-propanol, cyclopentanol, cyclohexanol, 1 ,4-dioxane, tetrahydrofuran, 1-methoxy-2-propanol, 1-ethoxy-2- propanol, 2-ethoxyethanol, 2-methyl-2-propanol, 2-methoxyethanol, dimethylformamide, acetonitrile and acetone.

In a possible preferred embodiment, water and solvent (L) are added simultaneously to the solution of the silicate, and it may also be expedient to add water and solvent (L) in a form premixed with one another.

The addition of water and solvent (L) or of the mixture thereof can be effected in one portion, in portions or continuously.

By means of this measure, agglomeration of the silicate particles can be reduced or preferably even prevented, depending on the pretreatment of the sols.

In case the polyolic compound (B) and solvent (L) are not sufficiently miscible it is possible to further add a co-solvent (Lc) in order to increase the compatibility between compound (B) and solvent (L).

Examples of co-solvents (Lc) are aromatic hydrocarbons, aliphatic hydrocarbons, and halogenated hydrocarbons, ketones, esters, alcohols, and ethers which do not fulfill the requirements of the solvent (L).

Preferred examples of co-solvents (Lc) are aliphatic and aromatic hydrocarbon mixtures, and also mixtures thereof. The latter are sold for example under the trade names Solvesso® from ExxonMobil, Hydrosol® from Kemetyl or Shellsol® from Shell, or under the designations solvent naphtha, Kristalloel, white spirit, heavy benzine, etc., in different and varying compositions.

According to the invention, at least one compound (C) which has at least one, preferably exactly one, at least monoalkoxylated, for example, mono- to trialkoxylated, preferably exactly trialkoxylated, silyl group and at least one, preferably exactly one, group which is either reactive toward the isocyanate component (A) (compound (C1 )) or reactive towards the polyolic binder component (B) (compound (C2) or compatible with the coating material (compound (C3) is also added to the reaction mixture.

Alkoxysilane (C) According to the invention the alkoxysilane (C) is selected from the group consisting of compounds of formula (C1)

R'

FT

formula (C2)

R²

R^ό

and formula (C3)

R²

R O — Si R^c

R^J

wherein n is an integer from 1 to 6, preferably from 2 to 4, more preferably 2 or 3,

R¹ can be H or d-Cε alkyl (straight, branched or cyclic, preferably straight),

R² and R³ independently are -OH, OR¹, or d-Cε alkyl (straight, branched or cyclic, preferably straight), preferably -OR¹ or d- to Cβ-alkyl, more preferably -OR¹,

R⁴ and R⁵ independently are H, d-Cε alkyl (straight, branched or cyclic, preferably straight), d-Cε hydroxyalkyl (straight, branched or cyclic, preferably straight), and d-

Cβ aminoalkyl (straight, branched or cyclic, preferably straight);

R⁶ is Cr to C2o-alkyl (straight or branched), Cs- to Ci2-cycloalkyl, Cβ- to Ci2-aryl, or d- to C2o-aralkyl (straight or branched). Examples of d- to C2o-alkyl are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec- butyl, tert-butyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl and n-eicosyl.

Examples of d- to Cβ-alkyl are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec- butyl, tert-butyl, and n-hexyl.

Examples of Cs- to Ci2-cycloalkyl are cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, and a saturated or unsaturated bicyclic system such as norbornyl or norbornenyl, for example.

Examples of Cβ- to Ci2-aryl are phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl, 4-biphenylyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, iso-propyl- phenyl, tert-butylphenyl, dodecylphenyl, methylnaphthyl, isopropylnaphthyl, and 2,6- dimethylphenyl, 2,4,6-trimethylphenyl.

Examples of C7- to C2o-aralkyl (straight or branched, preferably straight) are d- to Cs- alkyl-groups substituted by Ce- to Ci2-groups, such as benzyl, 2-phenylethyl, 2- phenylpropyl, or naphthylmethyl.

Preferred groups R¹ are methyl and ethyl.

Preferred groups R² and R³ are methyl and ethyl and OR¹, particularly preferred OR¹.

Preferred groups R⁴ and R⁵ are methyl, ethyl, isopropyl, n-butyl and H, particularly preferred are hydrogen and methyl, very particularly preferred is hydrogen.

Preferred groups R⁶ are methyl, ethyl, n-butyl, sec-butyl, tert-butyl, n-hexyl, and n-octyl, particularly preferably methyl, ethyl, and n-butyl and very particularly preferably n-butyl.

In one preferred embodiment the alkoxysilane (C1) has at least one, more preferably

two of a -CH2CH2-OH- and /or a - CH₂CH₂-NH₂ group as R⁴ and R⁵.

Compound (C) is preferably (C1 ) or (C3) and more preferably (C1 ).

Preferred compounds (C) are 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4- epoxycyclohexyl)ethyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-butyltrimethoxysilane, isooctyltrimethoxysilane, N-(3-

(trimethoxysilyl)propyl)ethylenediamine, 1-(3-(trimethoxysilyl)propyl)diethylenetriamine, bis(3-(methylamino)propyl)trimethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyl- trimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl-dimethoxysilane, gamma aminopropyltrimethoxysilane, 3-(N-styrylmethyl-2-aminoethylamino) propyl trimethoxysilane, N-phenyl aminomethyl triethoxy silane and bis-(gammatrimethoxysilyl propylamine, 3-[Bis(2-hydroxyethyl)amino] propyl triethoxysilane] or 3-(2- aminoethylamino)propyl) trimethoxysilane, 3-aminopropyltrimethoxysilane, 3- aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-amino- propylmethyldimethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropyl- dimethylethoxysilane, N-(2'-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2'-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-(2'-aminoethyl)-3-amino- propylmethoxysilane, N-(2'-aminoethyl)-3-aminopropylethoxysilane, 3-mercaptopropyl- trimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxy- silane, 3-mercaptopropylmethyldiethoxysilane, 3-glycidyloxypropyltriethoxysilane or 3-glycidyloxypropyltrimethoxysilane.

The compounds (C) are particularly preferably N-(3- (trimethoxysilyl)propyl)ethylenediamine, 1-(3-(trimethoxysilyl)propyl)diethylenetriamine, bis(3-(methylamino)propyl)trimethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyl- trimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl-dimethoxysilane, gamma aminopropyltrimethoxysilane, 3-(N-styrylmethyl-2-aminoethylamino) propyl trimethoxysilane, N-phenyl aminomethyl triethoxy silane and bis-(gammatrimethoxysilyl propylamine and combinations of the foregoing.

In one preferred embodiment the alkoxysilane compound (C) is 3-[Bis(2- hydroxyethyl)amino] propyl triethoxysilane] or 3-(2-aminoethylamino)propyl) trimethoxysilane.

What is decisive according to the invention is that the reaction of the silica sol (K) with at least one compound (C) be effected in a pH range which corresponds to the isoelectric point of the silica sol used ± one pH unit. In general, the pH is from 2 to 4.

The acidification can be effected with any desired acids, preferably with hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, methanesulfonic acid, or para-toluenesulfonic acid, or by passing over acidic ion exchangers, preferably by acidification with hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, acetic acid or ion exchangers, particularly preferably with hydrochloric acid, nitric acid, sulfuric acid or ion exchangers and very particularly preferably by acidification with sulfuric acid or ion exchangers. As a result of the reaction with the compound (C), the surface of the silica sol (K) used is modified so that the compatibility between the originally polar silica sol and the generally nonpolar coating material is improved. At the same time, complete modification of the surface as described in WO 2006/044376 has no further advantages.

According to the invention, it is therefore sufficient if (C) is used in an amount of from 0.1 to 20 μmol per m² surface area of (K).

This corresponds as a rule to an amount of from 0.01 to 5 mmol of (C) per gram of (K), preferably from 0.05 to 4 mmol of (C) per gram of (K) and particularly preferably from 0.1 to 3 mmol of (C) per gram of (K).

The reaction may for example be effected in such a way that not more than 20 mol% of the silane (C) used remain unconverted in the reaction mixture, preferably not more than 15 mol%, particularly preferably not more than 10 mol% and very particularly preferably not more than 5 mol%.

Usually the reaction with (C) is carried out with stirring at a temperature of from 10 to 60⁰C, preferably from 20 to 50⁰C, particularly preferably from 20 to 40°C.

Under these reaction conditions, the reaction is allowed to continue for from 2 to 48 hours, preferably from 3 to 36 hours, particularly preferably from 4 to 24 hours.

The compound (C) is added in amounts of from 0.1 to 30 mol%, preferably from 0.3 to 25 and particularly preferably from 0.5 to 20 mol%, based on the SiC"2 content.

After addition of water and solvent (L) and the subsequent reaction with the silane, the silica sol (K) is as a rule present as a 3 to 30% strength by weight colloidal solution, the ratio of water to solvent (L) being as a rule from 10:90 to 90:10 (v/v), preferably from 30:70 to 70:30 and particularly preferably from 40:60 to 60:40.

The polyolic binder component (B) is introduced into the solution.

The polyolic binder components (B) are in principle not limited. They advantageously have a viscosity at 25°C of not more than 4000 mPa-s (according to DIN EN ISO 3219 in cone-and-plate rotational viscometer at a sheer gradient of 100 S^"1), preferably not more than 3000 mPa-s, particularly preferably not more than 2000 mPa-s, very particularly preferably not more than 1500 and in particular not more than 1000 mPa-s.

In case the binder component has a higher viscosity it is possible to dilute the binder component with a suitable solvent, for example with one of the above-mentioned solvents (L), preferably with a solvent selected from the group consisting of halogenated hydrocarbons, ketones, esters, alcohols, and ethers, and particularly preferably butyl acetate in order to reduce the viscosity to accordingly.

A condition is that the polyolic binder component (B) should have a boiling point above the boiling point of the solvent under the conditions of the distillation, preferably at least 10⁰C higher, particularly preferably at least 25°C and very particularly preferably at least 40⁰C higher.

Water and the organic solvent (L) are distilled off under atmospheric or reduced pressure, preferably at from 10 hPa to atmospheric pressure, particularly preferably at from 20 hPa to atmospheric pressure, very particularly preferably at from 50 hPa to atmospheric pressure and in particular at from 100 hPa to atmospheric pressure.

The temperature at which the distillation is effected depends on the boiling point of water and/or organic solvent (L) at the respective pressure.

The distillation conditions are preferably chosen so that water and the organic solvent form an azeotrope under the conditions.

Preferably, the temperature is not more than 80⁰C, particularly preferably not more than 70°C.

The distillation can be effected batchwise, semicontinuously or continuously.

For example, it can be effected batchwise from a stirred tank to which, if appropriate, a short rectification column can be attached.

In the case of the stirred tank, the heat is supplied via internal and/or external heat exchangers of conventional design and/or double-walled heating, preferably external circulation evaporators with natural or forced circulation. The reaction mixture is thoroughly mixed in a known manner, for example by stirring, circulation by means of pumping or natural circulation.

The distillation is effected continuously, preferably by passing the distillate via a falling film evaporator or heat exchanger.

All distillation apparatuses known to the person skilled in the art, for example, circulation evaporators, thin-film evaporators, falling-film evaporators, wiped surface evaporators, if appropriate in each case with attached rectification columns, and stripping columns, are suitable as a distillation apparatus for this purpose. For example Robert evaporators or tubular or plate-type heat exchangers are suitable as heat exchangers.

Water and solvent (L) are as a rule distilled off until the content of silicates in the coating material is from 5 to 80% by weight, preferably from 20 to 60 and particularly preferably from 20 to 50% by weight.

The residual water content in the finished product should be less than 5% by weight, preferably less than 3, particularly preferably less than 2, very particularly preferably less than 1 , in particular less than 0.5 and especially less than 0.3% by weight.

In case the solvent (L) bears a group which is reactive towards isocyanate groups, the residual content of this solvent in the finished product should be less than 5% by weight, preferably less than 3, particularly preferably less than 2, very particularly preferably less than 1 , in particular less than 0.5 and especially less than 0.3% by weight.

In other cases, the residual content of solvent (L) in the finished product should be less than 15% by weight, preferably less than 10, particularly preferably less than 5, very particularly preferably less than 3, in particular less than 2 and especially less than 1 % by weight.

Instead of distillation, the water can also be removed by absorption, pervaporation or diffusion via membranes.

The two-component polyurethane comprises at least one, preferably one isocyanate component (A) and at least one, preferably one polyolic binder component (B).

Isocyanate component (A)

lsocyanates suitable for the present invention are known to the person skilled in the art or can be synthesized according to methods known to the person skilled in the art.

An isocyanate for the purpose of the present invention is an organic molecule contain- ing at least one -NCO group per molecule. If the isocyanate molecule contains two -NCO groups, it is a diisocyanate. An isocyanate containing two or more isocyanate groups or an isocyanate representing a mixture of different isocyanates, where the number average of isocyanate groups per molecule is at least 2, is referred to as poly- isocyanate throughout this invention. It is preferred if isocyanate component (A) is a polyisocyanate. Preferably isocyanate component (A) has an average number of at least 2 NCO groups per molecule (number-weighted average).

Component (A) may contain at least one oligomer of at least one diisocyanate. As parent diisocyanates preferably diisocyanates having from 4 to 20 carbon atoms are used. In principle, the parent diisocyanates can be used as such or as mixture with oligomers. Preferably, however, diisocyanates are used in oligomeric form.

Examples of conventional diisocyanates are aliphatic diisocyanates, such as tetrame- thylene diisocyanate, 1 ,5-pentamethylene diisocyanate, hexamethylene diisocyanate (1 ,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysine diisocyanate, trimethylhexane diisocyanate or tetramethylhexane diisocyanate, cycloaliphatic diisocyanates, such as 1 ,4-, 1 ,3- or 1 ,2-diisocyanatocyclohexane, 4,4'- or 2,4'-di(isocyanatocyclohexyl)methane, 1-isocyanato-3,3,5-trimethyl-5-(isocyanato- methyl)cyclohexane (isophoronediisocyanate), 1 ,3- or 1 ,4-bis(isocyanato- methyl)cyclohexane or 2,4- or 2,6-diisocyanato-1-methylcyclohexane, and 3(or 4),8(or 9)-bis(isocyanatomethyl)tricyclo[5.2.1.0²'⁶]decane isomer mixtures, and aromatic diiso- cyanates, such as toluene 2,4- or 2,6-diisocyanate and the isomer mixtures thereof, m- or p-xylylene diisocyanate, 2,4'- or 4,4'-diisocyanatodiphenylmethane and the isomer mixtures thereof, phenylene 1 ,3- or 1 ,4-diisocyanate, 1-chlorophenylene 2,4- diisocyanate, naphthylene 1 ,5-diisocyanate, biphenylene 4,4'-diisocyanate, 4,4' diiso- cyanato-3,3'-dimethylbiphenyl, 3-methyldiphenylmethane 4,4'-diisocyanate, tetrame- thylxylylene diisocyanate, 1 ,4-diisocyanatobenzene or 4,4'-diisocyanatodiphenyl ether.

Also suitable in principle are higher isocyanates, having on average more than 2 isocyanate groups. Examples that are suitable include triisocyanates such as triisocyana- tononane, 2,4,6-triisocyanatotoluene, triphenylmethane triisocyanate or 2,4,4'- triisocyanato-diphenyl ether, or the mixtures of diisocyanates, triisocyanates and higher polyisocyanates that are obtained by phosgenating corresponding aniline/formaldehyde condensates and represent polyphenyl polyisocyanates containing methylene bridges.

Cycloaliphatic and aliphatic diisocyanates are preferred. Particularly preferred are 1- isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)-cyclohexane (isophorone diisocyanate), 1 ,6 diisocyanatohexane, 4,4'-di(isocyanatocyclohexyl)methane, and 3(or 4),8(or 9)-bis(isocyanatomethyl)tricyclo[5.2.1.0²'⁶]decane isomer mixtures.

Component (A) may comprise polyisocyanates and polyisocyanate-containing mixtures which contain biuret, urethane, allophanate and/or isocyanurate groups, preferably polyisocyanates containing isocyanurate groups and/or polyisocyanates containing allophanate groups. Particular preference is given to polyisocyanates comprising pre- dominantly isocyanurate groups. With very particular preference the fraction of the iso- cyanurate groups corresponds to an NCO value of at least 5%, preferably at least 10%, more preferably at least 15% by weight (calculated as C3N3O3 with a molar mass of 126 g/mol).

Examples of preferred polyisocyanates as component (A) include:

1 ) Polyisocyanates having isocyanurate groups and obtained from aromatic, aliphatic and/or cycloaliphatic diisocyanates. Particularly preferred here are the cor- responding aliphatic and/or cycloaliphatic isocyanatoisocyanurates and in particular those based on hexamethylene diisocyanate and isophorone diisocy- anate. The isocyanurates present are in particular trisisocyanatoalkyl or trisiso- cyanatocycloalkyl isocyanurates, which are cyclic trimers of the diisocyanates, or are mixtures with their higher homologs having more than one isocyanurate ring. The isocyanatoisocyanurates generally have an NCO content of from 10 to 30% by weight, in particular from 15 to 25% by weight, and an average NCO functionality of from 2.6 to 8.

2) Uretdione diisocyanates having aromatically, aliphatically and/or cycloaliphati- cally bonded isocyanate groups, preferably having aliphatically and/or cycloaliphatically bonded groups and in particular those derived from hexamethylene diisocyanate or isophorone diisocyanate. Uretdione diisocyanates are cyclic dimerization products of diisocyanates. The uretdione diisocyanates can be used as a sole component or as a mixture with other polyisocyanates, in par- ticular those mentioned under 1 ).

3) Polyisocyanates having biuret groups and having aromatically, cycloaliphatically or aliphatically bonded, preferably cycloaliphatically or aliphatically bonded, isocyanate groups, in particular tris(6-isocyanatohexyl)biuret or mixtures thereof with its higher homologs. These polyisocyanates having biuret groups generally have an NCO content of from 18 to 22% by weight and an average NCO functionality of from 2.8 to 6.

4) Polyisocyanates having urethane and/or allophanate groups and having aromati- cally, aliphatically or cycloaliphatically bonded, preferably aliphatically or cycloaliphatically bonded, isocyanate groups, as can be obtained, for example, by reaction of excess amounts of hexamethylene diisocyanate or of isophorone diisocyanate with mono- or polyhydric alcohols, such as, for example, methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-hexanol, n-heptanol, n-octanol, n-decanol, n-dodecanol (lauryl alcohol), 2 ethylhexanol, n-pentanol, stearyl alcohol, cetyl alcohol, lauryl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 1 ,3-propanediol monomethyl ether, cyclopentanol, cyclohexanol, cyclooctanol, cyclododecanol, trimethylolpropane, neopentyl glycol, pentaerythritol, 1 ,4-butanediol, 1 ,6 hex- anediol, 1 ,3 propanediol, 2-ethyl-1 ,3-propanediol, 2-methyl-1 ,3-propanediol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pen- taethylene glycol, glycerol, 1 ,2-dihydroxypropane, 2,2-dimethyl-1 ,2-ethanediol,

1 ,2-butane-diol, 1 ,4-butanediol, 3-methylpentane-1 ,5-diol, 2-ethylhexane-1 ,3-diol, 2,4-diethyl-octane-1 ,3-diol, neopentyl glycol hydroxypivalate, ditrimethylolpro- pane, dipentaerythritol, 2,2-bis(4-hydroxycyclohexyl)propane, 1 ,1-, 1 ,2-, 1 ,3-, and 1 ,4 cyclohexanedimethanol, 1 ,2-, 1 ,3-, or 1 ,4-cyclohexanediol or mixtures thereof. These polyisocyanates having urethane and/or allophanate groups generally have an NCO content of from 12 to 24% by weight, in particular 18-24% by weight for those based on HDI, and an average NCO functionality of from 2.5 to 4.5.

5) Polyisocyanates comprising oxadiazinetrione groups, preferably derived from hexamethylene diisocyanate or isophorone diisocyanate. Such polyisocyanates comprising oxadiazinetrione groups can be prepared from diisocyanate and carbon dioxide.

6) Polyisocyanates comprising iminooxadiazinedione groups, preferably derived from hexamethylene diisocyanate or isophorone diisocyanate. Such polyisocyanates comprising iminooxadiazinedione groups can be prepared from diisocy- anates by means of specific catalysts.

7) Uretonimine-modified polyisocyanates.

8) Carbodiimide-modified polyisocyanates.

9) Hyperbranched polyisocyanates, of the kind known for example from DE-A1 10013186 Or DE-AI I OOISIe/.

10) Polyurethane polyisocyanate prepolymers, from di- and/or polyisocyanates with alcohols.

1 1 ) Polyurea-polyisocyanate prepolymers.

The polyisocyanates 1) to 11 ) can be used as a mixture, if appropriate also as a mixture with diisocyanates.

Preference is given to polyisocyanates containing isocyanurate and/or biuret groups. In addition, these mixtures may also contain minor amounts of uretdione, biuret, urethane, allophanate, oxadiazinetrione, iminooxadiazinedione and/or uretonimine groups, preferably at less than 25% by weight in each case, more preferably less than 20% by weight in each case, very preferably less than 15% by weight in each case, in particular below 10% by weight in each case and especially below 5% by weight in each case, and very specially below 2% by weight in each case, based on the respective func- tional group.

Particularly preferred as isocyanates in component (A) are isocyanurates of isophorone diisocyanate having an NCO content according to DIN EN ISO 11909 of 16.7% - 17.6%, and/or an average NCO functionality of from 3.0 to 4.0, preferably from 3.0 to 3.7, more preferably from 3.1 to 3.5. Compounds of this kind containing isocyanurate groups preferably have a HAZEN/APHA color number according to DIN EN 1557 of not more than 150.

Also particularly preferred as isocyanate in component (A) is the isocyanurate of 1 ,6- hexamethylene diisocyanate, having an NCO content to DIN EN ISO 11909 of 21.5 - 23.5%, and/or an average NCO functionality of 3.0 to 8, preferably 3.0 to 3.7, more preferably 3.1 to 3.5. Compounds of this kind containing isocyanurate groups preferably have a color number to DIN ISO 6271 of not more than 60. Compounds of this kind containing isocyanurate groups preferably have a viscosity at 23°C to DIN EN ISO 3219 of 1000 to 20 000 mPas, preferably 1000 to 4000 mPas, at a shear rate of 1000 s-¹.

In one preferred embodiment the isocyanate component (A) has a total chlorine content of less than 400 mg/kg, more preferably a total chlorine content of less than 80 mg/kg, very preferably less than 60, in particular less than 40, especially less than 20, and less than 10 mg/kg even.

Binder component (B)

Binders suitable for the present invention are known to the person skilled in the art or can be synthesized according to methods known to the person skilled in the art.

A binder for the purpose of the present invention is a compound containing at least two hydrogen atoms reactive to isocyanates. Preferably, the binder contains hydroxyl groups (OH groups) and/or primary and/or secondary amino groups.

In one embodiment of the present invention, a polyol is an organic molecule comprising an average number of at least 2 OH groups per molecule (number-weighted). Furthermore, a polyamine is an organic molecule comprising an average number of at least 2 primary or secondary (i.e., reactive) amino groups per molecule (number-weighted). Preferably, the binder component (B) contains at least one polyol or at least one poly- amine or both, at least one polyol and at least one polyamine. Particular preference is given to binder components (B) containing at least one polyol.

Component (B) preferably exhibits an OH number according to DIN 53240-2 of at least 15, preferably at least 40, more preferably at least 60, and very preferably at least 80 mg KOH/g resin solids. The OH number can be up to 350, preferably up to 240, more preferably up to 180, and very preferably up to 140 mg KOH/g resin solids.

The preferred OH numbers are also dependent on the application. According to Manfred Bock, "Polyurethane fur Lacke und Beschichtungen", p. 80, Vincentz-Verlag, 1999, lower OH numbers are advantageous for effective adhesion and corrosion control. For topcoat materials, for example, use is made of polyacrylates having OH numbers of about 40 to 100; for weather-resistant coating materials, OH numbers of around 135; and for high chemical resistance, those with OH numbers of around 170 mg KOH/g resin solids are used. Polyesters for aircraft coatings have in some cases much higher OH numbers.

Examples of such preferred binders are polyacrylate polyols, polyester polyols, poly- ether polyols, polyurethane polyols; polyurea polyols; polyester polyacrylate polyols; polyester polyurethane polyols; polyurethane polyacrylate polyols, polyurethane- modified alkyd resins; fatty acid modified polyester polyurethane polyols, copolymers with allyl ethers, graft polymers of the stated groups of compound with, for example, different glass transition temperatures, and also mixtures of the binders stated. Particu- lar preference is given to polyacrylate polyols, polyester polyols and polyether polyols, in particular to at least one polyacrylate polyol that contains per molecule on average at least two, preferably two to ten, more preferably three to ten, and very preferably three to eight hydroxyl groups.

Preferred OH numbers, measured in accordance with DIN 53240-2, are from 40 to 350 mg KOH/g resin solids for polyesters, preferably from 80 to 180 mg KOH/g resin solids, and from 15 to 250 mg KOH/g resin solids for polyacrylate-ols, preferably from 80 to 160 mg KOH/g.

The polyols may further comprise acid groups, preferably carboxylic acid groups.

Hence, the binders may additionally have an acid number according to DIN EN ISO 3682 of up to 200 mg KOH/g, preferably up to 150 and more preferably up to 100 mg KOH/g.

The acid number ought preferably to be at least 10, more preferably at least 80 mg KOH/g. Alternatively, it may be less than 10, so that the binder is virtually acid-free. Polyacrylate polyols of this kind preferably have a molecular weight Mn of at least 1000, more preferably at least 2000 and very preferably at least 5000 g/mol. The molecular weight Mn may for example be up to 200 000, preferably up to 100 000, more preferably up to 80 000 and very preferably up to 50 000 g/mol.

The polyacrylate polyols are copolymers of at least one (meth)acrylic ester with at least one compound having at least one, preferably precisely one hydroxy group and at least one, preferably precisely one (meth)acrylate group.

The latter may be, for example monoesters of α,β-unsaturated carboxylic acids, such as acrylic acid, methacrylic acid (referred to in this specification for short as "(meth)acrylic acid"), with diols or polyols, which have preferably 2 to 20 C atoms and at least two hydroxy groups, such as ethylene glycol, diethylene glycol, triethylene gly- col, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,1-dimethyl-1 ,2-ethanediol, dipropyl- ene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, tripropylene glycol, 1 ,4-butanediol, 1 ,5-pentanediol, neopentyl glycol, neopentyl glycol hy- droxypivalate, 2-ethyl-1 ,3-propanediol, 2-methyl-1 ,3-propanediol, 2-butyl-2-ethyl-1 ,3- propanediol, 1 ,6-hexanediol, 2-methyl-1 ,5-pentanediol, 2-ethyl-1 ,4-butanediol, 2-ethyl- 1 ,3-hexanediol, 2,4-diethyl-octane-1 ,3-diol, 2,2-bis(4-hydroxycyclohexyl)propane, 1 ,1-, 1 ,2-, 1 ,3- and 1 ,4-bis(hydroxymethyl)cyclohexane, 1 ,2-, 1 ,3- or 1 ,4-cyclohexanediol, glycerol, trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, sorbitol, mannitol, diglycerol, threitol, erythritol, adonitol (ribitol), arabitol (lyxitol), xylitol, dulcitol (galactitol), maltitol, isomalt, poly-THF with a molar weight between 162 and 4500, preferably 250 to 2000, poly-1 ,3- propanediol or polypropylene glycol with a molar weight between 134 and 2000 or polyethylene glycol with a molar weight between 238 and 2000.

Preference is given to 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2- or 3- hydroxypropyl acrylate, 1 ,4-butanediol monoacrylate or 3-(acryloyloxy)-2-hydroxypropyl acrylate and particular preference to 2-hydroxyethyl acrylate and/or 2-hydroxyethyl methacrylate.

The hydroxyl-bearing monomers are used in the copolymerization in a mixture with other polymerizable monomers, preferably free-radically polymerizable monomers, preferably those composed of more than 50% by weight of C1-C20, preferably C1-C4, alkyl (meth)acrylate, (meth)acrylic acid, vinylaromatics having up to 20 C atoms, vinyl esters of carboxylic acids comprising up to 20 C atoms, vinyl halides, nonaromatic hydrocarbons having 4 to 8 C atoms and 1 or 2 double bonds, unsaturated nitriles and mixtures thereof. Particular preference is given to those polymers composed of more than 60% by weight of C1-C10 alkyl (meth)acrylates, styrene, vinylimidazole or mixtures thereof. Above these the polymers may comprise hydroxy-functional monomers in accordance with the above hydroxy group content and, if appropriate, further monomers, examples being (meth)acrylic acid glycidyl epoxy esters, ethylenically unsaturated acids, especially carboxylic acids, acid anhydrides or acid amides.

Further polymers are, for example, polyesterols, as are obtainable by condensing poly- carboxylic acids, especially dicarboxylic acids, with polyols, especially diols. In order to ensure a polyester polyol functionality that is appropriate for the polymerization, use is also made in part of triols, tetrols, etc, and also triacids etc.

Polyester polyols are known for example from Ullmanns Enzyklopadie der technischen Chemie, 4th edition, volume 19, pp. 62 to 65. It is preferred to use polyester polyols which are obtained by reacting dihydric alcohols with dibasic carboxylic acids. In lieu of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof to prepare the polyester polyols. The polycarboxylic acids may be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and may if appropriate be substituted, by halogen atoms for example, and/or unsaturated. Examples thereof that may be mentioned include the following:

Oxalic acid, maleic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedioic acid, o-phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, azelaic acid, 1 ,4-cyclohexanedicarboxylic acid or tetrahydrophthalic acid, suberic acid, azelaic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic anhydride, dimeric fatty acids, their isomers and hydrogena- tion products, and also esterifiable derivatives, such as anhydrides or dialkyl esters, Ci CA alkyl esters for example, preferably methyl, ethyl or n-butyl esters, of the stated acids are employed. Preference is given to dicarboxylic acids of the general formula HOOC-(CH2)y-COOH, where y is a number from 1 to 20, preferably an even number from 2 to 20, and preferably succinic acid, adipic acid, sebacic acid, and dodecanedi- carboxylic acid.

Suitable polyhydric alcohols for preparing the polyesterols include 1 ,2-propanediol, ethylene glycol, 2,2-dimethyl-1 ,2-ethanediol, 1 ,3-propanediol, 1 ,2-butanediol, 1 ,3- butanediol, 1 ,4-butanediol, 3-methylpentane-1 ,5-diol, 2-ethylhexane-1 ,3-diol, 2,4- diethyloctane-1 ,3-diol, 1 ,6-hexanediol, PoIy-THF having a molar mass of between 162 and 4500, preferably 250 to 2000, poly-1 ,3-propanediol having a molar mass between 134 and 1 178, poly-1 ,2-propanediol having a molar mass between 134 and 898, polyethylene glycol having a molar mass between 106 and 458, neopentyl glycol, neopentyl glycol hydroxypivalate, 2-ethyl-1 ,3-propanediol, 2-methyl-1 ,3-propanediol, 2,2-bis(4- hydroxycyclohexyl)propane, 1 ,1-, 1 ,2-, 1 ,3- and 1 ,4-cyclohexanedimethanol, 1 ,2-, 1 ,3- or 1 ,4-cyclohexanediol, trimethylolbutane, trimethylolpropane, trimethylolethane, neopentyl glycol, pentaerythritol, glycerol, ditrimethylolpropane, dipentaerythritol, sorbitol, mannitol, diglycerol, threitol, erythritol, adonitol (ribitol), arabitol (lyxitol), xylitol, dul- citol (galactitol), maltitol or isomalt, which if appropriate may have been alkoxylated as described above.

Preferred alcohols are those of the general formula HO-(CH2)x-OH, where x is a number from 1 to 20, preferably an even number from 2 to 20. Preferred are ethylene glycol, butane-1 ,4-diol, hexane-1 ,6-diol, octane-1 ,8-diol and dodecane-1 ,12-diol. Additionally preferred is neopentyl glycol.

Also suitable, furthermore, are polycarbonate diols of the kind obtainable, for example, by reacting phosgene with an excess of the low molecular mass alcohols specified as synthesis components for the polyester polyols.

Also suitable are lactone-based polyester diols, which are homopolymers or copolymers of lactones, preferably hydroxy-terminated adducts of lactones with suitable di- functional starter molecules. Suitable lactones are preferably those which derive from compounds of the general formula HO-(CHb)Z-COOH, where z is a number from 1 to 20 and where one H atom of a methylene unit may also have been substituted by a Ci to a CA alkyl radical. Examples are ε-caprolactone, β-propiolactone, gamma- butyrolactone and/or methyl-ε-caprolactone, 4-hydroxybenzoic acid, 6-hydroxy-2- naphthoic acid or pivalolactone, and mixtures thereof. Examples of suitable starter components include the low molecular mass dihydric alcohols specified above as a synthesis component for the polyester polyols. The corresponding polymers of ε- caprolactone are particularly preferred. Lower polyester diols or polyether diols as well can be used as starters for preparing the lactone polymers. In lieu of the polymers of lactones it is also possible to use the corresponding, chemically equivalent polycon- densates of the hydroxycarboxylic acids corresponding to the lactones.

Also suitable as polymers, furthermore, are polyetherols, which are prepared by addition reaction of ethylene oxide, propylene oxide or butylene oxide with H-active components. Polycondensates of butanediol are also suitable, for example poly-THF with a molar weight between 162 and 4500, preferably 250 to 2000, poly-1 ,3-propanediol or polypropylene glycol with a molar weight between 134 and 2000 or polyethylene glycol with a molar weight between 238 and 2000.

The polymers can of course also be compounds containing primary or secondary amino groups.

In one preferred embodiment component (B) is a polyacrylate polyol or polyester polyol, more preferably a polyacrylate polyol. For polyurethane finishes, in principle a component (A) containing isocyanate groups, frequently referred to as crosslinking agent is reacted with a component (B) which has groups reactive toward isocyanate, generally hydroxyl groups. The latter compound is also referred to as a binder.

In two-component polyurethane finishes crosslinking agent (A) and binder (B) are mixed with one another only shortly before application and then reacted with one another in the curing.

In the latter case, it is expedient according to the invention to incorporate the silicates into the binder component since the isocyanate component usually reacts at least with water but often also with the organic solvent (L).

In addition further additives typical for finishes may furthermore be added, for example antioxidants, oxidation inhibitors, stabilizers, activators (accelerators), fillers, pigments, dyes, degassing agents, brighteners, antistatic agents, flameproofing agents, thickeners, thixotropic agents, leveling agents, binders, antifoams, fragrances, surface- active agents, viscosity modifiers, plasticizers, plastifiers, tackifiers, chelate formers or compatibilizers, may furthermore be added.

For example, tin octanoate, zinc octanoate, dibutyltin laurate or diaza[2.2.2]bicyclo- octane may be used as accelerators for the thermal curing.

Further examples are aromatic, aliphatic, secondary or tertiary amines, organometallic compounds of a metal selected from the group consiting of Ti, Zn, Sn, Mn, Bi, Sb, Pb, and Ca, preferably a metal octoate, naphenate, acetyl acetone or hydroxide.

For example, ethylenediamineacetic acid and salts thereof and β-diketones may be used as chelate formers.

Suitable fillers comprise silicates, for example silicates obtainable by hydrolysis of silicon tetrachloride, such as Aerosil^® from Degussa, silica, talc, aluminum silicates, magnesium silicates, calcium carbonates, etc. Since silicates are introduced uniformly into a coating material by the process according to the invention, a preferred embodiment is to add no further fillers.

Suitable stabilizers comprise typical UV absorbers, such as oxanilides, triazines and benzotriazole (the latter obtainable as Tinuvin^® brands from Ciba-Spezialitatenchemie) and benzophenones. These can be used alone or together with suitable free radical scavengers, for example sterically hindered amines, such as 2,2,6,6-tetramethyl- piperidine, 2,6-di-tert-butylpiperidine or derivatives thereof, e.g. bis(2,2,6,6-tetramethyl- 4-piperidyl) sebacate. Stabilizers are usually used in amounts of from 0.1 to 5.0% by weight, based on the solid components present in the formulation.

With the process according to the invention, it is possible to distribute silicate particles finely in organic coating materials and to use only a small proportion of organic solvent for this purpose. By means of the process according to the invention, silicate particles can be introduced by simple means uniformly and without significant aggregation of the particles into coating materials. In the prepared coating materials, this leads to virtually complete transparency in the visible range and even to increased scratch resistance. By means of the process according to the invention, the viscosity increase of the coating materials obtained is less pronounced than that according to comparable processes of the prior art.

For the preparation of a coating composition, polyisocyanate (A) and binders are mixed with one another in a molar ratio of isocyanate groups to isocyanate-reactive groups of 0.1 :1 to 10:1 , preferably 0.2:1 to 5:1 , more preferably 0.3:1 to 3:1 , and very preferably 0.5:1 to 2.5:1 , it also being possible, if appropriate, for further, typical coatings constituents to be mixed in, and the final composition is applied to the substrate.

Curing typically takes place until the cured materials can be handled further. The properties associated with this are, for example, dust drying, through-drying, blocking resistance or packability.

In one preferred embodiment the curing takes place at room temperature within not more than 12 hours, preferably up to 8 hours, more preferably up to 6 hours, very preferably up to 4 hours, and more particularly up to 3 hours.

In another preferred version the curing takes place, for example, for half an hour at temperatures up to 80⁰C. After cooling, a room-temperature postcure may be necessary in addition.

The coating of the substrates takes place in accordance with typical methods known to the skilled worker, which involve applying at least one coating composition in the desired thickness to the substrate that is to be coated, and removing any volatile constituents that may be present in the coating composition, if appropriate with heating. This operation can if desired be repeated one or more times. Application to the substrate may take place in a known way, as for example by spraying, troweling, knifecoating, brushing, rolling, roller coating, pouring, laminating, injection backmolding or coextruding.

The thickness of a film of this kind to be cured can be from 0.1 μm up to several mm, preferably from 1 to 2000 μm, more preferably 5 to 200 μm, very preferably from 10 to 60 μm (based on the coating material in the state in which the solvent has been removed from the coating material).

Also provided by the present invention are substrates coated with a multicoat paint system of the invention.

Polyurethane coating materials of this kind are especially suitable for applications requiring a particularly high level of application reliability, external weathering resistance, optical qualities, solvent resistance, chemical resistance, and water resistance.

The resulting coating compositions and coating formulations are suitable for coating substrates such as wood, wood veneer, paper, paperboard, cardboard, textile, film, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials, such as cement moldings, fiber-cement slabs or metals, each of which may optionally have been precoated and/or pretreated, more particularly for plastics surfaces.

Coating compositions of this kind are suitable as or in interior or exterior coatings, i.e., applications of this kind involving exposure to daylight, preferably of parts of buildings, coatings on (large) vehicles and aircraft, and industrial applications, decorative coatings, bridges, buildings, power masts, tanks, containers, pipelines, power stations, chemical plants, ships, cranes, posts, sheet piling, valves, pipes, fittings, flanges, couplings, halls, roofs, and structural steel, furniture, windows, doors, woodblock flooring, can coating and coil coating, for floor coverings, as in the case of parking levels, or in hospitals, and in automobile finishes as OEM and refinish application.

Coating compositions of this kind are preferably used at temperatures between ambient temperature to 80⁰C, preferably to 60⁰C, more preferably to 40⁰C. The articles in question here are preferably those which cannot be cured at high temperatures, such as large machines, aircraft, large-volume vehicles, and refinish applications.

The coating compositions of the invention are employed more particularly as clearcoat, basecoat, and topcoat materials, primers, and surfacers.

Figures in ppm or percent that are used in this specification relate, unless otherwise indicated, to weight percentages and ppm by weight.

The examples which follow are intended to illustrate the invention but not to confine it to these examples.

Examples Example 1

5.0 g of Amberjet^® 1200H (strongly acidic cationic ion exchanger, Sigma Aldrich Che- mie GmbH, Taufkirchen, Germany) was mixed with 100 g of Levasil^® 200 (30 wt % SiO₂, mean particle size 15 nm, HCStark GmbH, Leverkusen, Germany) and stirred strongly at room temperature for 30 minutes. Subsequently the ion exchange resin was removed by filtration to obtain an acidic, ion-exchanged silica nanoparticle dispersion with pH=2~3. Then 100.0 g of isopropanol was added drop by drop into the ion- exchanged silica nanoparticle dispersion under vigorous stirring. Finally 7.08 g of iso- butyltriethoxysilane was added and stirred at room temperature to get a transparent modified silica sol and it was used in the subsequent process without any treatment.

Example 2

5.O g of Amberjet^® 1200H was mixed with 100 g of Levasil^® 200 (30 wt % SiO₂) and stirred strongly at room temperature for 30 minutes. Subsequently the ion exchange resin was removed by filtration to obtain an acidic, ion-exchanged silica nanoparticle dispersion with pH=2~3. Then 100.0 g of isopropanol was added drop by drop into the ion-exchanged silica nanoparticle dispersion under vigorous stirring. Finally 8.87 g of octyltriethoxysilane was added and stirred at room temperature to get a modified silica sol and it was used in the subsequent process without further treatment.

Example 3

Dispersion of modified silica sol into polyol: 50 g of Polytetrahydrofuran was weighed in a round bottomed flask and mixed very well with 235 g of isopropanol. Then 120 g of modified silica sol from example 1 or example 2 was taken and mixed thoroughly. Water and isopropanol was removed from the mixture using rotary evaporator operated at 40⁰C and 50mbar vacuum. Finally, flowable transparent polytetrahydrofuran containing SiO₂ solid content of 25 % which has only 0.2 % water content and stable for at least 6 months was obtained.

Example 4

Polyurethane/silica hybrid coating: About 2 g of polyetherol containing 25 wt % modified silica prepared as described in example 3 was taken and mixed with 0.25 g of pure polyetherol and 2 ml of butyl acetate. Then 2.374 g of Basonat^® HI 100 (BASF SE, Ludwigshafen, Germany, isocyanurate group containing polyisocyanate based on 1 ,6- hexamethylene diisocyanate) and 1 ml. of butyl acetate was added and the resulting mixture was vigorously stirred at room temperature for about 30 minutes. An amount of 1.5 μl_ of dibutyltin dilaurate was added as a catalyst into the above mixture and the reaction was stirred for another 5 minutes before curing. Finally the resulting solution was coated on a polyvinylchloride sheet using a coil bar coater with a thickness of 24 μm. The coating can be cured either at room temperature or at 60 ⁰C.

Claims

Claims

1. Process for the preparation of silicate-containing polyolic binders suitable for two- component polyurethane coating materials, comprising an isocyanate component (A) and a polyolic binder component (B), comprising the steps

- addition of from 0 to 10 times the amount of water (based on the Siθ2 content used) and from 0.1 to 20 times the amount (based on the Siθ2 content used), at a temperature of from 10 to 60⁰C, of at least one organic solvent (L)

- at least one alkoxysilane (C), selected from the group consisting of compounds of formula (C1),

R²

R O — Si -(CH₂),,

R³ formula (C2), R²

R³ and formula (C3), R²

R¹O — Si R⁶

R³ κ wherein n is an integer from 1 to 6,

R¹ can be H or C-i-Cβ alkyl (straight, branched or cyclic, preferably straight),

R² and R³ independently are -OH, OR¹, or C-i-Cβ alkyl (straight, branched or cyclic, preferably straight),

R⁴ and R⁵ independently are H, C-i-Cβ alkyl (straight, branched or cyclic, preferably straight), C-i-Cβ hydroxyalkyl (straight, branched or cyclic, preferably straight), or C-i-Cβ aminoalkyl (straight, branched or cyclic, preferably straight); R⁶ is Cr to C2o-alkyl (straight or branched), Cs- to Ci2-cycloalkyl, Cβ- to Ci2-aryl, or C7- to C2o-aralkyl (straight or branched).

in an amount of from 0.1 to 20 μmol per m² of surface area of (K), and - if appropriate, further solvent (L), to an aqueous silica sol (K) having a mean particle diameter of from 5 to 150 nm and a silicic acid content, calculated as SiO₂, of from 10 to 60% by weight, with a pH of from 2 to 4,

- addition of the polyolic binder component (B) to the mixture thus obtained and - at least partial distillation of the organic solvent (L) , wherein the solvent (L)

- exhibits a water solubility of at least 200 g/l at 25 ⁰C,

- has a boiling point of less than 80⁰C at 50 hPa, and

- is capable of dissolving at least 200 g/l of the polyolic binder component (B) at 25 ⁰C, and wherein a solution of 200 g polyolic binder component (B) in 1000 g solvent (L) exhibits a viscosity at 25°C of not more than 500 mPa-s (according to DIN EN ISO 3219 in cone-and-plate rotational viscometer at a sheer gradient of 100 s-¹).

2. Process according to Claim 1 , characterized in that compound (C) is selected from the group consisting of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4- epoxycyclohexyl)ethyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, n-butyltrimethoxysilane, isooctyltrimethoxysilane, N-(3- (trimethoxysilyl)propyl)ethylenediamine, 1-(3-(trimethoxysilyl)propyl)diethylene- triamine, bis(3-(methylamino)propyl)trimethoxysilane, N-beta-(aminoethyl)- gamma-aminopropyl-trimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl- dimethoxysilane, gamma aminopropyltrimethoxysilane, 3-(N-styrylmethyl-2- aminoethylamino) propyl trimethoxysilane, N-phenyl aminomethyl triethoxy silane and bis-(gammatrimethoxysilyl propylamine, 3-[Bis(2-hydroxyethyl)amino] propyl triethoxysilane] or 3-(2-aminoethylamino)propyl) trimethoxysilane, 3- aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3- aminopropylmethyldimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3- aminopropyldimethylmethoxysilane, 3-aminopropyldimethylethoxysilane, N-(2'- aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2'-aminoethyl)-3- aminopropylmethyldiethoxysilane, N-(2'-aminoethyl)-3-amino- propylmethoxysilane, N-(2'-aminoethyl)-3-aminopropylethoxysilane, 3- mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3- mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3- glycidyloxypropyltriethoxysilane and 3-glycidyloxypropyltrimethoxysilane.

3. Process according to any of the preceding claims, characterized in that component (B) is a polyacrylate polyol or polyester polyol.

4. Process according to any of the preceding claims, characterized in that solvent (L) is selected from the group consisting of halogenated hydrocarbons, ketones, esters, alcohols, and ethers.

5. Process according to any of Claims 1 to 3, characterized in that solvent (L) is selected from the group consisting of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 1-chloro-2-propanol, cyclopentanol, cyclohexanol, 1 ,4-dioxane, tetrahydrofuran, 1-methoxy-2-propanol, 1-ethoxy-2- propanol, 2-ethoxyethanol, 2-methyl-2-propanol, 2-methoxyethanol, dimethylformamide, acetonitrile and acetone.

6. Process for the preparation of a two-component polyurethane coating composition, characterized in that at least one isocyanate component (A) and at least one polyolic binder (B) according to any of the Claims 1 to 3 are mixed with one another in a molar ratio of isocyanate groups to isocyanate-reactive groups of 0.1 :1 to 10:1 , and, if appropriate, further typical coatings constituents mixed in, and the final composition is applied to the substrate.

7. Use of a coating component according to Claim 6 for coating wood, wood veneer, paper, paperboard, cardboard, textile, film, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials or metals, which may optionally have been precoated and/or pretreated.

8. Use of a coating component according to Claim 6 for coatings on (large) vehicles and aircraft, and industrial applications, decorative coatings, bridges, buildings, power masts, tanks, containers, pipelines, power stations, chemical plants, ships, cranes, posts, sheet piling, valves, pipes, fittings, flanges, couplings, halls, roofs, and structural steel, furniture, windows, doors, woodblock flooring, can coating and coil coating, for floor coverings, and in automobile finishes as OEM and refinish application.