WO2010043638A2

WO2010043638A2 - Curable epoxide formulation containing silica

Info

Publication number: WO2010043638A2
Application number: PCT/EP2009/063381
Authority: WO
Inventors: Alexander Traut; Norbert Wagner; Andreas FECHTENKÖTTER; Chih-Cheng Peng; Malik Jamal Jaffar Ali; Lily-Liqi Yang
Original assignee: Basf Se
Priority date: 2008-10-15
Filing date: 2009-10-14
Publication date: 2010-04-22
Also published as: WO2010043638A3

Abstract

The present invention provides novel curable epoxy coating formulations containing silica, methods for their preparation and their use.

Description

Curable epoxide formulation containing silica

Description

Field of Invention:

The present invention provides novel curable epoxide coating formulations containing silica, methods for their preparation and their use.

Description of the Related Art

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 non uniformly 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.

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 epoxy resin which already comprises inorganic particles is therefore sought.

US 2005/008865 A1 , US 2004/101688 A1 , US 2004/102529 A1 , US 2004/138343 A1 and US 2005/049334 A1 describe methods to incorporate SiC>₂ nanoparticles into epoxy resins for different applications. However, a disadvantage of these method is without a proper acidification procedure of SiO₂ sols, the SiO₂ loading in the epoxy composition is either very low or the final coatings are not suitable for applications which require optical transparency.

US-A-3699049 describes the removal of water by distillation at from 50 to 100 ⁰C 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 290 ⁰C at atmospheric pressure. This prevents removal of the solvent under gentle conditions.

EP 1236765 A1 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. 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 A1 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.

US-A-6210790 describes a method to functionalize SiO₂ nanoparticles with trialkoxysilane in the presence of ion exchange resin, where the ion exchange resin serves as a catalyst for the hydrolysis and condensation of trialkoxysilane. A disadvantage of this method is that without a proper removal of metal ion from the SiO₂ dispersion, instead of reacting with silanol groups on SiO₂ surface the hydrolyzed trialkoxysilane tends to condense with each other. It usually leads to a lower degree of surface modification.

WO 2007/146521 A1 describes a method to formulate surface modified SiO₂ into epoxy resin for adhesive applications. In there the native alkaline SiO₂ nanoparticle dispersion is acidified with ion exchange resin. However, in order to transfer the modified SiO₂ into epoxy resin, a water miscible solvent must be added to the system prior to the removal of water. A disadvantage of this method is that the choice of epoxy resin is therefore limited to its compatibility to water miscible solvent only.

Summary of the Invention

The present invention refers to a method for the preparation of curable epoxide coating formulations containing silica comprising the steps of

a) providing a dispersion of silica nanoparticles in an aqueous medium b) acidifying the silica nanoparticles preferably by ion exchange c) addition of at least one organosilane S d) addition of at least one organic solvent L or a mixture of solvents L during or preferably before the addition of the organosilane S wherein at least one solvent L is miscible with the epoxide and water e) optionally adding at least one water-immiscible solvent K which is miscible with the epoxide f) functionalizing the silica nanoparticles by reaction with the organosilane S preferably at 10 to 30 ⁰C and preferably at the pH of 2 to 3 g) optionally removing water and /or solvent L h) optionally removing metal ions from the silica sol prior to functionalizing preferably by ion exchange and i) mixing the functionalized silica nanoparticles with a curable epoxide in the presence of solvent L and/or the water-immiscible solvent K and j) optionally removing at least part of the solvent and the water.

Silica in the context of the present invention is silicon dioxide including its sol and silicic acid.

A typical curable epoxide coating formulation according to the present invention con- tains preferably 1 to 60 weight-% (based on the total weight of the formulation) of silica nanoparticles wherein the silica nanoparticles are modified by an organosilane and an epoxy resin or precursor thereof, e.g. an aliphatic, cycloaliphatic or aromatic epoxide and optionally at least one of the following ingredients: an UV photo initiator, a monothiol or polythiol, a solvent and optionally other additives.

Preferred curable epoxides are:

1. Aliphatic epoxy resins including long-chain diol modified epoxides, such as the d i g l y c i d y l e t h e r of p o l y p ro p y l e n e g l y c o l [σ, ω-bis(2,3-epoxy- propoxy)poly(oxypropylene)] or diglycidyl ether of polyethylene glycol [σ, ω- bis(2,3-epoxyethoxy)poly(oxyethylene)]. Polyglycidyl ethers or esters of sorbitol, glycerol, and pentaerythiol can be used as aliphatic epoxy resins.

2. Cycloaliphatic epoxy resins are well known to the art and, as described herein, are compounds that contain at least about one cycloaliphatic group and at least one oxirane group. More preferred cycloaliphatic epoxides are compounds that contain about one cycloaliphatic group and at least two oxirane rings per mole- c u l e . S p e c i f i c e x a m p l e s i n c l ude 3-cyclohexenylmethyl-3- cyclohexenylcarboxylate diepoxide, 2-(3,4-epoxy)cyclohexyl-5,5-sp/ro-(3,4- epoxy)cyclohexane-m-dioxane, 3,4-epoxycyclohexylalkyl-3,4-epoxycyclohe- xanecarboxylate, S^-epoxy-θ-methylcyclohexylmethyl-S^-epoxy-θ-methylcy- clohexanecarboxylate, vinyl cyclohexanedioxide, bis(3,4-epoxycyclohexyl- methyl)adipate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, exoexo bis(2,3-epoxycyclopentyl)ether, endo-exo bis(2,3 epoxycyclopentyl) ether, 2,2- bis(4-2,3-(epoxypropoxy)cyclohexyl)propane, 2,6-bis(2,3-epoxypropoxycy- cyclohexyl-p-dioxane), 2,6-bis(2,3-epoxypropoxy)norbornene, the digly- cidylether of linoleic acid dimer, limonene dioxide, 2,2-bis(3,4- epoxycyclohexyl)propane, dicyclopentadiene dioxide, 1 ,2-epoxy-6-(2,3- epoxypropoxy)hexahydro-4,7-methanoindane, p-(2,3-epoxy)cyclopentylphenyl- 2,3-epoxypropylether, 1 -(2,3-epoxypropoxy)phenyl-5,6-epoxyhexahydro-4,7- methanoindane, o-(2,3-epoxy)cyclopentylphenyl-2,3-epoxypropyl ether), 1 ,2- bis(5-(1 ,2-epoxy)-4,7-hexahydromethanoindanoxyl)ethane, cyclopentenylphenyl glycidyl ether, cyclohexanediol diglycidyl ether, and diglycidyl hexahydrophtha- late. Typically, the cycloaliphatic epoxy resin is 3-cyclohexenylmethyl-3- cyclohexenylcarboxylate diepoxide.

3. Aromatic epoxy resins may also be used with the present invention. Examples of aromatic epoxy resins useful in the present invention include bisphenol-A epoxy resins, bisphenol-F epoxy resins, phenol novolac epoxy resins, cresol- novolac epoxy resins, biphenol epoxy resins, biphenyl epoxy resins, 4,4'- biphenyl epoxy resins, polyfunctional epoxy resins, divinylbenzene dioxide, and 2-glycidylphenylglycidyl ether. When resins, including aromatic, aliphatic and cycloaliphatic resins are described throughout the specification and claims, either the specifically-named resin or molecules having a moiety of the named resin are envisioned.

4. Numerous commercially available epoxy resins can be utilized. In particular, epoxides that are readily available include octadecylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide, glycidol, glycidyl methacrylate, diglycidyl ethers of Bisphenol A (for example, EPON 828, EPON 825, EPON 1004, and EPON 1001 from Resolution Performance Products, Houston, TX as well as DER 221 , DER 332, and DER 334 from Dow Chemical Co., Midland, Ml), vi- nylcyclohexene dioxide (for example, ERL 4206 from Dow Chemical, Midland, Ml), 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexene carboxylate (for exam- pie, ERL 4221 , CYRACURE UVR 61 10, and CYRACURE UVR 6105 from Dow

Chemical), 3,4-epoxy-6-methylcyclohexylmethyl-3,4- epoxy-6-methyl-cyclohe- xene carboxylate (for example, ERL 4201 from Dow Chemical), bis(3,4-epoxy- 6-methylcyclohexylmethyl) adipate (for example, ERL 4289 from Dow Chemical), bis(2,3-epoxycyclopentyl) ether (for example, ERL 0400 from Dow Chemi- cal), aliphatic epoxy modified from polypropylene glycol (for example, ERL 4050 and ERL 4052 from Dow Chemical), dipentene dioxide (for example, ERL 4269 from Dow Chemical), epoxidized polybutadiene (for example, OXIRON 2001 from FMC, Corp.), silicone resin containing epoxy functionality, flame retardant epoxy resins such as brominated bisphenol-type epoxy resins (for example, DER 580 from Dow Chemical), 1 ,4-butanediol diglycidyl ether of phenol formaldehyde novolak (for example, DEN 431 and DEN 438 from Dow Chemical), re- sorcinol diglycidyl ether (for example, KOPOXITE from Koppers Company, Inc.), bis(3,4-epoxycyclohexyl)adipate (for example, ERL 4299 or CYRACURE UVR 6128 from Dow Chemical), 2-(3,4-epoxycyclohexyl-5, 5-spiro-3,4- epoxy) cyclohexane-meta-dioxane (for example, ERL-4234 from Dow Chemical), vinyl- cyclohexene monoxide, 1 ,2-epoxyhexadecane (for example, CYRACURE UVR- 6216 from Dow Chemical), alkyl glycidyl ethers such as alkyl Cs-Ci₀ glycidyl ether (for example, HELOXY MODIFIER 7 from Resolution Performance Products), alkyl C₂-C₄ glycidyl ether (for example, HELOXY MODIFIER 8 from Reso- lution Performance Products), butyl glycidyl ether (for example, HELOXY

MODIFIER 61 from Resolution Performance Products), cresyl glycidyl ether (for example, HELOXY MODIFIER 62 from Resolution Performance Products), p- tert-butylphenyl glycidyl ether (for example, HELOXY MODIFIER 65 from Resolution Performance Products), polyfunctional glycidyl ethers such as diglycidyl ether of 1 ,4-butanediol (for example, HELOXY MODIFIER 67 from Resolution

Performance Products), diglycidyl ether of neopentyl glycol (for example, HELOXY MODIFIER 68 from Resolution Performance Products), diglycidyl ether of cyclohexanedimethanol (for example, HELOXY MODIFIER 107 from Resolution Performance Products), trimethylol ethane triglycidyl ether (for ex- ample, HELOXY MODIFIER 44 from Resolution Performance Products), trimethylol propane triglycidyl ether (for example, HELOXY 48 from Resolution Performance Products), polyglycidyl ether of an aliphatic polyol (for example, HELOXY MODIFIER 84 from Resolution Performance Products), polyglycol diepoxide (for example, HELOXY MODIFIER 32 from Resolution Performance Products), bisphenol F epoxides (for example, EPON 1138 from Resolution Performance Products and GY-281 from Ciba-Geigy Corp.), and 9,9-bis[4-(2,3- epoxypropoxy)-phenylfluorenone (for example, EPON 1079 from Resolution Performance Products).

In a preferred embodiment the nanoparticles are prepared and functionalized according to the following steps 1 ) - 3):

1. Silica sol

The SiO₂ nanoparticle dispersion (sol) used 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 SiO₂, is from 10 to 60 wt% by weight, preferably from 20 to 55 % by weight, particularly preferably from 25 to 40 wt%. 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 SiO₂ nanoparticle dispersion (sol) which, if appropriate, can be stabilized to a slight extent with alkali metal, alkaline earth metal, ammonium, aluminum, iron(ll), iron (III) 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. 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.

2. Acidification

The acidification of native SiO₂ nanoparticle dispersion can be performed, 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 preparation of the silica sols 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 preparation of the silica sols from waterglass by acidification, for example with an ion exchanger, or by addition of a mineral acid is also conceivable. A waterglass preferably used for this purpose is potassium and/or sodium silicate, which particularly preferably has a ratio of 1 - 10 mol of SiO₂ to 1 mol of alkali metal oxide, very particularly preferably 1 .5 - 6 and in particular 2 - 4 mol of SiO₂ to 1 mol of alkali metal oxide.

3. Functionalizing

Functionalizing the surface of the SiO₂ 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 organosilane (S), preferably before or during and particularly preferably before the reaction with the organosilane.

Organosilane S

Functionalizing in the context of the present invention means that the surface of the silica nanoparticles is modified by adsorbing and/ or reacting with functionalizing organosilanes S which have an affinity to said surface. Without limiting the present invention this might be an adsorption, a coordinative or chemical bond.

Preferred organosilanes S correspond to the following formula:

(R)_mSi(R¹)_4-m

wherein the substituents have the following meaning: R reactive group or alkyl, aryl or alkoxy which may be substituted by at least one reactive group

m 1 or 2

R¹ each R¹ is independently selected from the group consisting of H or alkoxy, especially CrC₄-alkoxy, especially methoxy or ethoxy; acyloxy, especially acetoxy; amino; halogene, especially Cl; wherein at least one of the groups R¹ is hydrolysable and is especially methoxy or ethoxy.

A hydrolysable group in the context of the present invention is a group which reacts with water or a hydroxyl group.

Examples of 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. Preferred examples of d- to C₄-alkyl are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl and tert-butyl. Preferred radicals are methyl, ethyl, n-butyl and tert-butyl, particularly preferably methyl and ethyl.

Reactive groups are preferably those which have a group identical or complimentary to the binder/cross-linking agent combination of organic coating material to be used according to the present invention. Preferred reactive groups are primary amino, secondary amino, amide, hydrazide, imidazoles, thiol, carboxylic acid, anhydride, hydroxyl. In a very preferred embodiment the reactive group means hydroxyl, epoxy, amino or acid groups in the case of epoxy resins or melamine/formaldehyde resins, hydroxyl, amino or isocyanate groups in the case of polyurethane resins or groups capable of free radical polymerization in the case of radiation-curable resins. Groups capable of free radical polymerization are, for example, allyl ether, vinyl ether, acrylate or methacrylate groups, preferably vinyl ether, acrylate or methacrylate groups and particularly preferably acrylate or methacrylate groups, which are referred to for short as (meth)acrylate groups in this document. These reactive groups are as a rule linked to the silyl groups by spacer groups. Such spacer groups are divalent organic radicals having 1 to 20 carbon atoms, for example alkylene or arylene groups, preferably alkylene groups. Examples of these are methylene, 1 ,2-ethylene (-CH₂-CH₂-), 1 ,2- propylene (-CH(CHs)-CH₂-) and/or 1 ,3-propylene (-CH₂-CH₂-CH₂-), 1 ,2-, 1 ,3- and/or 1 ,4-butylene, 1 ,1-dimethyl-1 ,2-ethylene, 1 ,2-dimethyl-1 ,2-ethylene, 1 ,6-hexylene, 1 ,8- octylene or 1 ,10-decylene, preferably methylene, 1 ,2-ethylene, 1 ,2- or 1 ,3-propylene, 1 ,2-, 1 ,3- or 1 ,4-butylene, particularly preferably methylene, 1 ,2-ethylene, 1 ,2- and/or 1 ,3-propylene and/or 1 ,4-butylene and very particularly preferably methylene, 1 ,2- ethylene, 1 ,2- and/or 1 ,3-propylene.

Preferred compounds (S) are 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4- epoxycyclohexy^ethyltrimethoxysilane, isooctyltrimethoxysilane, N-(3-triethoxysilyl- propyl)methoxyethoxyethoxyethyl carbamate (PEG3TES), N-(3-triethoxysilylpropyl)- methoxyethoxyethoxyethyl carbamate (PEG2TES), 3-(methacryloyloxy)propyl- trimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-(methacryloyloxy)propyl- triethoxysilane, 3-(methacryloyloxy)methyltriethoxysilane, 3-(methacryloyloxy)ethyl- triethoxysilane, 3-(methacryloyloxymethyl)methyldimethoxysilane, 3-(methacryloyloxy- methyl)methyldiethoxysilane, 3-(methacryloyloxy)propylmethyldimethoxysilane,

3-(acryloyloxypropyl)methyldimethoxysilane, 3-(methacryloyloxy)propyldimethyl- ethoxysilane, 3-(methacryloyloxy)propyldimethylethoxysilane, vinyldimethylethoxy- silane, vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltrimethoxysilane, vinyltriphenoxy- silane, vinyltri-tert-butoxysilane, vinyltrisisobutoxysilane, vinyltriisopropenoxysilane, vinyltris(2-methoxyethoxy)silane, 3-(N-allylamino)propyltrimethoxysilane, 3-(N-allyl- amino)propyltriethoxysilane, styrylethyltrimethoxysilane, 3-aminopropyltrimethoxy- silane, 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 (S) are preferably 3-(methacryloyloxy) propyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-(methacryloyloxy)propyltriethoxysilane or 3-(methacryloyloxy)propylmethyldimethoxysilane and isobutyltriethoxysilane.

The amount of organosilane used can be adjusted according to its compatibility to specific epoxy resin, which is typically in the range of 1 to 50 wt% (based on the amount of the silica sol used).

Organic solvent (L)

In a preferred embodiment solvent L is used as an addition solvent to improve the miscibility of water and solvent (K). 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 wt% (based on the prepared water/solvent mixture), preferably at least 50 wt% and particularly preferably at least 80 wt%. If the miscibility is too low, one can select another organic solvent (polar or non-polar) to improve the compatibility between the organic solvent (L) and epoxy resin. For example, in order to transfer SiO₂ into butyl acetate, a certain amount of isopropanol (here refer to L) can be a good solvent both for the surface modification for SiO₂ and improving the compatibility between water and butyl acetate.

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. 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.

Water-immiscible solvent K

In a preferred embodiment less than 2 g of Solvent K are soluble in water at 20 ⁰C. The solvents K which can be used include aromatic hydrocarbons, halogenated aromatic hydrocarbons, and ketones, acetates, ethers, esters and and the like. The type and amount of solvent used can be selected according to its compatibility to specific epoxy resin and the final system viscosity. A preferred solvent K is butyl acetate especially for water-immiscible epoxy resins.

Acidifying by ion exchange

Acidifying the silica nanoparticles by ion exchange is preferably performed with anionic ion exchange resins which are able to remove the cationic counter ions in the native silica dispersions.

Additives

Any suitable additives known for coating formulations may be used additionally, pref- erably initiators, photoinitiators, polythiols, flame retardants and stabilizers. Any suitable photoinitiator can be used in the present formulations. In many embodiments, the photoinitiator is a single-component system such as an ultraviolet cationic photoinitiator. Suitable ultraviolet cationic photoinitiators often include a sulfonium salt or an iodonium salt. Exemplary triarylsulfonium salts include triarylsulfonium hexafluorophosphate and triarylsulfonium hexafluoroantimonate such as those commercially available from Dow Chemical Co., Midland, Ml under the trade designation CYRACURE (UVI-6976, UVI-6992, UVI-6974, or UVI-6990) and from Sartomer, Exton, PA under the trade designation SARCAT (Kl 85 or SRIOIO). Exemplary iodonium salts typically are diaryliodonium salts such as those further described in U.S. Patent Nos. 4,494,403 (Smith), 4,250,053 (Smith), 3,808,006 (Smith), 3,741 ,769 (Smith), and 3,729,313 (Smith). The iodonium salts can be a simple salt containing an anion such as Cl^", Br^", I^", or C₄H₅SO₃ ^" or a metal complex salt containing an anion such as SbF₆ ^", PF₆ ^", BF₄ ^", tetrakis(perfluorophenyl)borate, SbF₅OH^", or AsF₆ ^". The cation of the iodonium salt is often diphenyliodonium. Mixtures of iodonium salts can be used, if de- sired.

Examples of a polythiol compound which may be combined include aliphatic polythiol compounds such as methanedithiol, ethanedithiol, 1 ,1-propanedithiol, 1 ,2- propanedithiol, 1 ,3-propanedithiol, 1 ,6-hexanedithiol, 1 ,2,3-propanetrithiol, 1 ,1- cyclohexanedithiol, 1 ,2-cyclohexanedithiol, 2,2-dimethylpropane-1 ,3-dithiol, 3,4- dimethoxybutane-1 ,2-dithiol, 2-methylcyclohexane-2,3-dithiol, 1 ,1-bis(mercapto- methyl)cyclohexane, bis(2-mercaptoethyl) thiomalate, 2, 3-dimercapto-1-propanol (2- mercaptoacetate), 2,3-dimercapto-1-propanol (3-mercaptopropionate), diethyleneglycol bis(2-mercaptoacetate), diethyleneglycol bis(3-mercaptopropionate), 1 ,2-dimercapto- propyl methyl ether, 2,3-dimercaptopropyl methyl ether, 2,2-bis(mercaptomethyl)-1 ,3- propanedithiol, bis(2-mercaptoethyl) ether, ethyleneglycol bis(2-mercaptoacetate), ethyleneglycol bis(3-mercaptopropionate), trimethylolpropane bis(2-mercaptoacetate), trimethylolpropane bis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercapto- acetate), pentaerythritol tetrakis(3-mercaptopropionate) and tetrakis(mercapto- methyl)methane; aromatic polythiol compounds such as 1 ,2-dimercaptobenzene, 1 ,3- dimercaptobenzene, 1 ,4-dimercaptobenzene, 1 ,2-bis(mercaptomethyl)benzene, 1 ,3- bis(mercaptomethyl)benzene, 1 ,4-bis(mercaptomethyl)benzene, 1 ,2-bis(mercapto- ethyl)benzene, 1 ,3-bis(mercaptoethyl)benzene, 1 ,4-bis(mercaptoethyl)benzene, 1 ,2,3- trimercaptobenzene, 1 ,2,4-trimercaptobenzene, 1 ,3,5-trimercaptobenzene, 1 ,2,3- tris(mercaptomethyl)benzene, 1 ,2,4-tris(mercaptomethyl)benzene, 1 ,3,5-tris(mercapto- methyl)benzene, 1 ,2,3-tris(mercaptoethyl)benzene, 1 ,2,4-tris(mercaptoethyl)benzene, 1 ,3,5-tris(mercaptoethyl)benzene, 2,5-toluenedithiol, 3,4-toluenedithiol, 1 ,3-di(p- methoxyphenyl)propane-2,2-dithiol, 1 ,3-diphenylpropane-2,2-dithiol, phenylmethane- 1 ,1-dithiol and 2,4-di(p-mercaptophenyl)pentane; aromatic polythiol compounds con- taining a sulfur atom in addition to a mercapto group such as 1 ,2- bis(mercaptoethylthio)benzene, 1 ,3-bis(mercaptoethylthio)benzene, 1 ,4-bis(mercapto- ethylthio)benzene, 1 ,2,3-tris(mercaptomethylthio)benzene, 1 ,2,4-tris(mercaptomethyl- th io)benzen e, 1 , 3 , 5-tris(mercaptomethylthio)benzene, 1 ,2,3-tris(mercaptoethyl- thio)benzene, 1 ,2,4-tris(mercaptoethylthio)benzene and 1 ,3,5-tris(mercaptoethyl- thio)benzene as well as their nuclear alkylated derivatives; sulfides such as bis(mercaptomethyl) sulfide, bis(mercaptoethyl) sulfide, bis(mercaptopropyl) sulfide, bis(2-mercaptoethylthio)methane, bis(3-mercaptopropylthio)methane, 1 ,2-bis(2-mer- captoethylthio)ethane, 1 ,2-bis(3-mercaptopropylthio)ethane, 1 ,3-bis(2-mercapto- ethylthio)propane, 1 ,3-bis(3-mercaptopropylthio)propane, 1 ,2,3-tris(2-mercapto- ethylthio)propane, 1 ,2,3-tris(3-mercaptopropylthio)propane, 1 ,2-bis[(2-mercapto- ethyl)thio]-3-mercaptopropane, 4,8-dimercaptomethyl-1 ,1 1-dimercapto-3,6,9-tri- thiaundecane, 4,7-dimercaptomethyl-1 ,1 1-dimercapto-3,6,9-trithiaundecane, 5,7-di- mercaptomethyl-I J I-dimercapto-S.Θ.Θ-trithiaundecane, tetrakis(2-mercaptoethylthio- methyl)methane, tetrakis(3-mercaptopropylthiomethyl)methane, bis(2,3-dimercapto- propyl) sulfide, bis(1 ,3-dimercaptopropyl) sulfide, 2,5-dimercapto-1 ,4-dithiane, 2,5-di- mercaptomethyl-1 ,4-dithiane-, 2,5-dimercaptomethyl-2,5-dimethyl-1 ,4-dithiane, bis(mercaptoethyl) disulfide and bis(mercaptopropyl) disulfide as well as their thioglyco- lates and mercaptopropionates; aliphatic polythiol compounds containing a sulfur atom in addition to a mercapto group such as hydroxymethylsulfide bis(2-mercaptoacetate), hydroxymethylsulfide bis(3-mercaptopropionate), hydroxyethylsulfide bis(2-mercapto- acetate), hydroxyethylsulfide bis(3-mercaptopropionate), hydroxypropylsulfide bis(2- mercaptoacetate), hydroxypropylsulfide bis(3-mercaptopropionate), hydroxymethyldi- sulfide bis(2-mercaptoacetate), hydroxymethyldisulfide bis(3-mercaptopropionate), hy- droxyethyldisulfide bis(2-mercaptoacetate), hydroxyethyldisulfide bis(3-mercapto- propionate), hydroxypropyldisulfide bis(2-mercaptoacetate), hydroxypropyldisulfide bis(3-mercaptopropionate), 2-mercaptoethylether bis(2-mercaptoacetate), 2-mercapto- ethylether bis(3-mercaptopropionate), 1 ,4-dithiane-2,5-diol bis(2-mercaptoacetate), 1 ,4- dithiane-2,5-diol bis(3-mercaptopropionate), bis(2-mercaptoethyl) thiodiglycolate, bis(2- mercaptoethyl) thiodipropionate, bis(2-mercaptoethyl) 4,4-thiodibutyrate, bis(2- mercaptoethyl) dithiodiglycolate, bis(2-mercaptoethyl) dithiodipropionate, bis(2- mercaptoethyl) 4,4-dithiodibutyrate, bis(2,3-dimercaptopropyl) thiodiglycolate, bis(2,3- dimercaptopropyl) thiodipropionate, bis(2,3-dimercaptopropyl) dithiodiglycolate and bis(2,3-dimercaptopropyl) dithiodipropionate; heterocyclic compounds containing a sulfur atom in addition to a mercapto group such as 3,4-thiophenedithiol and 2,5- dimercapto-1 ,3,4-thiadiazole; and compounds containing a hydroxy group in addition to a mercapto group such as 2-mercaptoethanol, 3-mercapto-1 ,2-propanediol, glyceryl di(mercaptoacetate), i-hydroxy-4-mercaptocyclohexane, 2,4-dimercaptophenol, 2- mercaptohydroquinone, 4-mercaptophenol, 3,4-dimercapto-2-propanol, 1 ,3-di- mercapto-2-propanol, 2,3-dimercapto-1-propanol, 1 ,2-dimercapto-1 ,3-butanediol, pen- taerythritol tris(3-mercaptopropionate), pentaerythritol mono(3-mercaptopropionate), pentaerythritol bis(3-mercaptopropionate), pentaerythritol tris(thioglycolate), dipenta- e ryth rito l pentakis(3-mercaptopropionate), hydroxymethyl-tris(mercaptoethylthio- methyl)methane and i-hydroxyethylthio-3-mercaptoethylthiobenzene. These compounds may be halogenated (e.g., chlorinated or brominated).

Examples

Example 1

Preparation of silica sol

5.0 g of a strongly acid cation exchanger (Amberjet^®1200H) was mixed with 10O g of colloidal SiO₂ (Levasil^®200) containing 30 weight-% 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 7.08 g of isobutyltriethoxy- silane 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

Dispersion of modified silica sol into Epoxy resin

25.0 g of epoxy resin was weighed in a round bottomed flask and mixed with 35 g of isopropanol and stirred strongly. Then 20.0 g of modified silica solution as described in example 1 was added into it and mixed very well. Water and isopropanol was removed from the mixture using rotary evaporator operated at 4O⁰C and 50 mbar vacuum. Finally, flowable transparent epoxy resin containing SiO₂ solid content of 25.0 % which has only 0.2 % water content and stable for at least 6 months was obtained.

Example 3

Dispersion of modified silica sol into Epoxy resin

25.0 g of epoxy resin was weighed in a round bottomed flask and mixed with 340.0 g of isopropanol and stirred strongly. Then 180.00 g of modified silica solution as described in example 1 was added into it and mixed very well. Water and isopropanol was removed from the mixture using rotary evaporator operated at 4O⁰C and 50 mbar vac- uum. Finally, flowable transparent epoxy resin containing SiC>₂ solid content of 50 % which has only 0.2 % water content and stable for at least 6 months was obtained.

Example 4

Dispersion of modified silica sol into epoxy resin

20.0 g of epoxy resin was weighed in a round bottomed flask and mixed with 20.0 g of butyl acetate. Separately 18.00 g of modified silica solution as described in example 1 was taken and mixed with 30.0 g of isopropanol and it was added to the epoxy solution and mixed very well. Then water and isopropanol was removed from the mixture using rotary evaporator operated at 4O⁰C and 50 mbar vacuum. Finally, flowable epoxy resin containing SiO₂ solid content of 10 % which stable for at least 6 months was obtained.

Example 5

Dispersion of modified silica sol into butylacetate:

30.0 g of butylacetate was weighed in a round bottomed flask and mixed with 52.0 g of isopropanol and stirred strongly. Then 27.00 g of modified silica solution as described in example 1 was added into it and mixed very well. Water and isopropanol was removed from the mixture using rotary evaporator operated at 4O⁰C and 50 mbar vacuum. Finally, transparent dispersion of modified silica nanoparticle in butyl acetate containing SiO₂ solid content of 10 % which has only 0.2 % water content and stable for at least 6 months was obtained.

Example 6

Dispersion of silica nanoparticle in butylacetate into Epoxy Resin

30.0 g of Epoxy resin was weighed in a round bottomed flask and mixed with 15.0 g of butyl acetate to reduce the viscosity. Then 30.0 g of butyl acetate containing silica nanoparticle prepared as explained in example 2 was mixed very well. Then the butyl acetate was removed using rotary evaporator operated at 4O⁰C and 40 mbar vacuum. Finally, flowable epoxy resin containing SiO₂ solid content of 10 % which stable for at least 6 months was obtained. Scratch resistance:

An epoxy-SiO₂ hybrid coating containing the composition given in example 4 was prepared using a doctor blade of a thickness of 24.0 μm. The coating was then tested using a 5135 Abraser (TABER Industries) following the ASTM 4060 standard method. As a benchmark comparison, similar tests were done with three commercial epoxy-SiO₂ hybrid resins C 450, C 460 and C 620 (NanoResins^®). The the test results are shown as the following table.

As can be seen the composition of example 4 according to the present invention uses a low concentration of 10 % of SiO₂ provides for much better or similar resistance to mass abrasion as compared with the state of the art comprising 4 times as much SiO₂.

Claims

1. Method for the preparation of curable epoxide coating formulations containing silica comprising the steps

2. Method according to claim 1 wherein the solvent L is isopropanol.

3. Method according to at least one of the preceding claims wherein the organosilane S is

3-(methacryloyloxy)propyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-(methacryloyloxy)propyltriethoxysilane

3-(methacryloyloxy)propylmethyldimethoxysilane or isobutyltriethoxysilane.

4. Method according to at least one of the preceding claims wherein solvent L is isopropanol and wherein the isopropanol and water are removed after mixing the functionalized nanoparticles with a curable epoxide.

5. Method according to claim 1 wherein the solvent comprises butylacetate and isopropanol and wherein isopropanol and water are removed before step i).

6. Method according to at least one of the preceding claims wherein the curable epoxide is an aliphatic epoxy resin.

7. Method according to at least one of the preceding claims wherein the curable epoxide is a compound that contains at least about one cycloaliphatic group and at least one oxirane group.

8. Method according to at least one of the preceding claims wherein the curable epoxide is an aromatic epoxy resins , preferably bisphenol-A epoxy resins, bisphenol-F epoxy resins, phenol novolac epoxy resins, cresol-novolac epoxy resins, biphenol epoxy resins, biphenyl epoxy resins, 4,4'-bi, epoxy resins, poly- functional epoxy resins, divinylbenzene dioxide or 2-glycidylphenylglycidyl ether.

9. Method according to at least one of the preceding claims wherein the water - immiscible solvent K is an aromatic hydrocarbon, ketone, acetate, ether or ester.

10. Curable Composition comprising a curable epoxy resin and organosilane modified silica nanoparticles obtainable by a method according to at least one of the preceding claims.

1 1. Composition according to claim 10 comprising additionally at least one of the following compounds

a photoinitiator a polythiol a stabilizer.

12. A process for coating substrates wherein a composition according to claim 10 comprising at least a photoinitiator and, if appropriate further additives typical for coatings is applied to a substrate and exposed to UV-radiation preferably under inert gas.

13. A process for coating substrates wherein at least one composition according to claim 10 comprising at least one thiol and, if appropriate further additives typical for coatings is applied to a substrate under curing conditions.

14. Articles containing substrates coated according to claims 12 and/or 13.