WO2006128793A1 - Dispersible silica particles - Google Patents

Dispersible silica particles

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Publication number
WO2006128793A1
WO2006128793A1 PCT/EP2006/062406 EP2006062406W WO2006128793A1 WO 2006128793 A1 WO2006128793 A1 WO 2006128793A1 EP 2006062406 W EP2006062406 W EP 2006062406W WO 2006128793 A1 WO2006128793 A1 WO 2006128793A1
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WO
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Prior art keywords
silica
sol
particles
silane
according
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PCT/EP2006/062406
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French (fr)
Inventor
Jan-Erik Otterstedt
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Small Particle Technology Gbg Ab
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    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; MISCELLANEOUS COMPOSITIONS; MISCELLANEOUS APPLICATIONS OF MATERIALS
    • C09CTREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES; PREPARATION OF CARBON BLACK; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28Compounds of silicon
    • C09C1/30Silicic acid
    • C09C1/3063Treatment with low-molecular organic compounds
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00Nanotechnology for materials or surface science, e.g. nanocomposites
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUSE OF INORGANIC OR NON-MACROMOLECULAR ORGANIC SUBSTANCES AS COMPOUNDING INGREDIENTS
    • C08K5/00Use of organic ingredients
    • C08K5/54Silicon-containing compounds
    • CCHEMISTRY; METALLURGY
    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; MISCELLANEOUS COMPOSITIONS; MISCELLANEOUS APPLICATIONS OF MATERIALS
    • C09CTREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES; PREPARATION OF CARBON BLACK; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28Compounds of silicon
    • C09C1/30Silicic acid
    • C09C1/3081Treatment with organo-silicon compounds
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01PINDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00Particle morphology
    • C01P2004/60Particles characterised by their size
    • C01P2004/62Submicrometer sized, i.e. from 0.1-1 micrometer
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01PINDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00Particle morphology
    • C01P2004/60Particles characterised by their size
    • C01P2004/64Nanometer sized, i.e. from 1-100 nanometer

Abstract

1. Object of the invention is a process for making silica particles, comprising the following steps: 1) An alkali stabilized silica sol with a particle size in the range from 8 to 250 nm is diluted to at most 30 % SiO2 with water and/or a water-soluble organic solvent 2) A silane and/or an organic compound, selected from polyols und dicarboxylic acids, is pumped into the agitated sol of step 1, which is maintained at a temperature between 20 and 75 °C, 3) The sol of step 2 is deionized by contacting it with anion and cation exchange resins 4) The silylated, deionized sol of step 3 is dried by evaporating the water, preferably under vacuum or in an air stream, 5) optionally, the dried sol of step 4 is milled to a fine powder, whereby at least two of the steps 2), 3) and 4) may be carried out in a different order.

Description

DISPERSIBLE SILICA PARTICLES

Field of the invention

The present invention relates to particles or a powder of colloidal particles of amorphous silica having an average diameter of 8 to 250 nanometers in which the particles have hydrocarbon radicals chemically attached to surface silicon atoms. The invention is further directed to processes for preparing powders, the ultimate particles of which have been made organophilic by the reaction of the surface of the particles with hydrocarbon- substituted silanols. It also relates to making nanocomposites with superior mechanical properties by incorporating a powder of colloidal silica particles as reinforcing filler in polymers.

Description of prior art

The definition of filler in the sense relating to plastics is an inert solid substance, which is added to a polymer to modify its properties. Fillers are used extensively to reduce cost, but may in some cases actually upgrade the compound. Carbon black, e.g. greatly improves the strength of rubbers.

The effect of fillers on the mechanical properties of polymers depends on their specific surface area, which is inversely proportional to particle size. Generally, fillers with particle size larger than about 1 μm, e.g. clays, mica, talc and baryte, tend to reduce tensile strength, elongation, and low temperature flexibility, while increasing specific gravity and hardness. Fillers with particle size smaller than 1 μm, e.g. very fine clays, some types of silica and carbon black, and provided they are very well dispersed in the polymer matrix, will increase tensile strength and modulus but still reduce elongation.

In colloid chemistry, the chemical composition of the particles of the dispersed phase is naturally of major importance, but the nature of the surfaces of the particles of the dispersed phase becomes a significant behaviour factor, which must be taken into account. When particles of solids are supercolloidal in size, and the specific surface area exceeds a certain minimum value, the nature of the surfaces is then the major behaviour factor, although the internal nature and structure of the particle is still important. Specific surface area is the ratio of exposed surface to the mass of the particle and is usually expressed as square meters per gram (m2/g). Surface phenomena of solids become more and more important as the specific surface area increases. A specific surface area of about one m2/g can be considered as a threshold value, below which we may disregard surface phenomena. For dense, non-porous, siliceous particles of substantial spherical shape, this corresponds to an average particle diameter of about 2-3 microns. As the particle diameter of such particles decreases, the specific surface area increases. When the specific surface area reaches 25 m2/g, or above, the nature of the surface becomes quite significant and may, for instance interact strongly with the molecular chains of polymers.

Colloidal particles of siliceous particles have found wide utility in many fields. Among other uses, they have been used to fill, extend, thicken and reinforce various organic materials, such, for example, as plastics, resins, rubber, oils, etc.

U. S Patent 2,727,876 discloses a silica powder consisting of aggregates of spherical particles with diameters as low as 5 to 7 nm, the surface of which is esterified, readily dispersible in natural rubber and that the elastomers thus obtained give vulcanizates with extremely high tensile strength, tear resistance and elongation. U.S. Patent 2,974,105 describes stable organosols of amorphous, dense, substantially non-aggregated silica spheroids 5 to 130 nm in diameter, which preferably are surface esterified, dispersed in alkoxy-substituted ethanols. The organosols can be used to incorporate very fine silica particles as fillers in polymers, particularly of the polyester type.

U.S. Patent 2,786,042 claims alkalistabilized aquasols and organosols of colloidal particles of amorphous silica having an average diameter of from 10 to 150 nanometers, the particles having monovalent hydrocarbon radicals chemically attached directly to at least 5 % of the surface silicon atoms. The organosols form a vehicle by which the colloidal silica can be dispersed into polymers to act as a filler to improve tensile and compression and shear strength.

European Patent Application 1 236 765 A1 discloses organosols of colloidal particles of amorphous silica having an average diameter of from 3 to 50 nanometers in polyols, polyamines, linear or branched polyglycol ethers, polyesthers and polylactones and the use of such organosols to make polymers with improved mechanical properties

PCT application WO 01/05883 A1 discloses compact or cellular polyurethane elastomers containing from 0.01 to 20 weight % discrete, non-aggregated particles of silica having an average diameter from 1 to 500 nanometers. The silica filler is incorporated into the PUR elastomer by mixing a silica aquasol or an organosol of silica particles in solvents such as for instance alcohols, low molecular weight diols and alkanes with higher molecular weight polyhydroxyl compounds and/or low molecular weight chain extenders and/or crosslinking agents and removing water and/or the organic solvent by for instance distillation. European Patent Application 0 236 945 A2 discloses a monodispersed glycol suspension, comprising a monodispersed suspension in a glycol of spherical fine particles of an amorphous inorganic oxide, e.g. silica, having an average diameter of 0.05 to 5 micrometers prepared in a three-step procedure. In the first step, a hydrolyzable organometallic compound, e.g. tetramethylorthosilicate, (CH3O)4Si, in an aqueous solution of an alcohol, which may include a glycol, to be used in the second step to obtain a glycol suspension of an amorphous hydrated inorganic oxide, e.g. silica, in the alcoholic solution. In the second step, a glycol is substituted for the alcoholic solvent of the suspension to obtain a glycol suspension of the fine particles. In the third step, the glycol suspension is heat treated to yield a monodispersed glycol suspension of fine inorganic oxide particles. The product of the invention is claimed to be useful as a raw material for the production of a polyester film with improved slipperiness.

U.S. Patent 6,136,912 and U.S.Patent Application U.S. 2001/0027223 disclose fluid silico- acrylic compositions polymerizable thermally or by radiation and containing a multifunctional acrylic monomer, a silane and silica in the form of discrete particles with an average diameter between 5 and 100 nm. Polymerizing, e.g. by radiation, a mixture of an organosol of such silica particles in an acrylate, e.g. tripropylene glycol diacrylate, and a polyether acrγlate modified amine oligomer results in transparent, clear films with excellent scratch and abrasion resistance.

Summary of the Invention

It is therefore an object of the present invention to provide methods for making polymeric materials containing silica particles in the form of powders or pastes, which are readily dispersible in liquid or molten organic compounds. Another object is to provide methods for making such particles and powders in which the silica particles are present in the form of dense ultimate particles from 8 to 250 nm in diameter. Yet another object is to provide such particles and powders in which the silica particles and in which the particle surface has been modified so as to change its chemical nature in a controlled manner, e.g. by reacting the surface silanol groups of the particles with silanes and/or adsorbing high-boiling organic liquids onto the particle surface.

The particles and powder are used as reinforcing filler in polymers. It may be dispersed in polyols, isocyanates, carboxylic acids and other raw materials used for making polyurethanes, polyamides and polyesters. It may also be directly dispersed in molten thermoplastics by use of extruders. - A -

In yet other embodiments of the invention the particles or powder is incorporated in nanocomposites of polyurethanes, polyesters and polyamides. Especially important embodiments of the invention are nanocomposites of the powder and urethane-, ester-, and amide-based thermoelastomers, in which the soft segment blocks dominate over the hard segment blocks in the domain structure characterizing the phase-separated systems of these multiblock polymers.

Other polymer properties can also be improved by using particles and powders of this invention. Thus, for instance, are polyester films widely used in magnetic tapes, optical photography, capacitors and packaging materials, but poor slipperiness of the films causes problem during manufacture, handling and use. The slipperiness of polyester films can be improved by use of particles and powders of this invention.

In other embodiments of the invention the particles and powders can be introduced in a wide variety of organic media. They may be mixed with liquid lubricants, such as hydrocarbon oils, fluorocarbon oils, silicone oils, vegetable oils and polyether oils to give improved viscosity, wetting power, body, water resistance, and the like in many of the uses of these materials.

Another object of this invention is to improve fuels, e.g. diesel fuels, by having silica dispersed therein by means of these powders because it provides a catalytic surface for combustion and also keeps the combustion chamber clean.

In yet another embodiment of the invention, waxes, especially those used in coating paper, can be improved by addition of these silica powders. They have more body when hot, permitting thicker coatings by a single dip, and prevent blocking during hot weather. Wax compositions containing organic solvents such as paste waxes and waxes dissolved or suspended in naphtha, can advantageously be modified by powders as herein described.

Detailed Description of the Invention

The process for making silica particles, comprises the following steps:

1) An alkali stabilized silica sol with a particle size in the range from 8 to 250 nm is diluted to at most 40, preferred 30 % SiO2 with water and/or a water-soluble organic solvent, preferably at a pH of the diluted sol between 9.0 and 10.5,

2) A silane and/or an organic compound, selected from polyols und dicarboxylic acids, is pumped into the agitated sol of step 1, which is maintained at a temperature between 20 and 75 0C, 3) The sol of step 2 is deionized by contacting it with anion and cation exchange resins preferably to a pH below 10.0,

4) The silylated, deionized sol of step 3 is dried by evaporating the water, preferably under vacuum or in an air stream,

5) Optionally, the dried sol of step 4 is milled to a fine powder.

The above indicated sequence of steps 2 to 4 can be varying from the order, as disclosed below.

Silica Particles

The sources of the silica particles of the present invention are commercial silica sols. Such sols are aqueous dispersions of silica particles and the particles are uniform spheres of silica, which have no internal surface area or detectable crystallinity. They are usually dispersed in an alkaline medium, which reacts with the silica surface to produce a negative charge. Because of the negative charge, the particles repel one another resulting in a stable product.

There are also silica sols in which the particles have a positive charge and are dispersed in an acidic solution. The solids content depends on the particle size and varies from about 15 % per weight silica for the smallest particles, 4 to 5 nm, to about 50 % per weight silica for larger particles, > 20 nm. The surface of the particles in aqueous silica sols is covered with surface hydroxyl groups, silanol groups.

Stabilization of commercial silica sols is accomplished by adjusting the pH of the sol to between 8.0 and 10.0 by addition of alkali, usually a solution of sodium hydroxide. The sols also contain small amounts of other electrolytes such as sodium chloride and sodium sulfate. The stability of highly concentrated silica sols, aqueous sols as well as organosols, is very sensitive to the presence of electrolytes. The electrolyte concentration can be reduced to a minimum by deionising the sols. This can be accomplished by subjecting a silica aquasol to contact with a cation-exchange resin, which will remove cations, primarily sodium ions, or a mixture of anion- and cation-exchange resins, which will remove both anions and cations. The art is familiar with techniques for effecting such deionisation. Sols of this type may be made in quite concentrated form and because of their high purity are especially suitable for some purposes of the present invention.

When commercial silica sols are dried by removing the water the resulting dried sol in the form of flakes or a powder cannot be redispersed in water or organic solvents. Commercial silica sols are sold under different trade names, e.g. Bindzil® from EKA Chemicals Sweden, Ludox® from DuPont, U.S.A., Nalcoag® from Nalco, U.S.A., Baykisol® from Bayer, Germany, Klebosol from Clariant, France, and Snowtex® from Nissan, Japan.

Silanes

The general formula of the organosilane coupling agents used in this invention shows two types of functionality

YnSiX(4-n)

where n is an integer < 4. Both ends of the silane molecule may undergo chemical modification, either separately or simultaneously. The X groups can be exchanged or hydrolyzed without altering the Y group, or the Y group may be modified while maintaining the X group. In some cases the Y group is modified in an aqueous environment such that the X groups are hydrolyzed. Chemical modification of the Y group may precede application to a surface or may take place at the surface after silylation.

The X group is involved in the reaction with the hydroxyl groups on the surface of an inorganic substrate. The bond between X and the silicon atom in coupling agents is replaced by a bond between the inorganic substrate and the silicon atom. X is a hydrolysable group, typically alkoxy, acyloxy, amine, or chlorine. The most common alkoxy groups are methoxy and ethoxy, which give methanol and ethanol as byproducts during coupling reactions. Since chlorosilanes generate hydrogen chloride as a byproduct during coupling reactions, they are generally utilized less than alkoxysilanes.

Y is a nonhydrolyzable group that may be organo-reactive or nonorgano-reactive. If it is organo-reactive it enables the coupling agent to bond with organic resins and polymers. Organosilanes may have one, two or three organic substituents. Most widely used are those with one organic substituent.

In most cases the silane is subjected to hydrolysis prior to the surface treatment of a substrate. Following hydrolysis a reactive silanol group is formed, which can condense with other silanol groups, for example those on the surface of siliceous fillers, to form siloxane linkages. Stable condensation products are also formed with other inorganic oxides such as those of aluminum, zirconium, tin, titanium and nickel, which have hydroxyl groups on their surfaces. Water for hydrolysis may come from several sources. It may be added, it may be present on the substrate surface, or it may come from the atmosphere.

Reaction of silanes involves several steps. Initially, the hydrolysis of the labile X groups attached to silicon occurs. Condensation between hydrolyzed silanes to oligomers or condensation with hydroxyl groups on the substrate surface follow. If oligomer formation predominates oligomers will then hydrogen bond with OH groups of the substrate. Finally, during drying or curing, a covalent linkage is formed with the substrate with concomitant loss of water.

Some commercially available organo-reactive silanes are shown in Table 1.

Table 1. Organo-Reactive Silanes

Some commercially available nonorgano-reactive silanes are shown in Table 2.

Table 2. Nonorgano-Reactive Silanes

Trialkoxysilanes, RSi(OR)3, and dialkoxysilanes, R2Si(OR)2, hydrolyze stepwise in water to give the corresponding silanols, which ultimately may condense to siloxanes. Increased organic substitution enhances hydrolysis rate, i.e. (Me)3SiOMe>(Me)2Si(OMe)2>MeSi(OMe)3. The rate of hydrolysis of the alkoxy groups are generally related to their steric bulk. A methoxysilane, for instance, hydrolyzes at 6-10 times the rate of an ethoxysilane. The rate of acid hydrolysis is significantly higher than base hydrolysis and is minimally affected by other carbon bonded substituents. The rates of condensation of alkoxysilanols depend on the degree of organic substitution and follow the same trends as the rate of hydrolysis of the corresponding organically substituted alkoxysilanes. Reaction rates are strongly dependent upon pH, but under commonly used conditions, pH 3.5-5.5, the hydrolysis is relatively fast(minutes)while the condensation reaction is much slower(hours).

Deposition from an aqueous alcohol solution is the most facile method for preparing silylated surfaces of conventional fillers such as clays. A 95% ethanol-5% water solution is adjusted to pH 4.5-5.5 with e.g. acetic acid. Silane is added with stirring to yield a 2% final concentration. Five minutes should be allowed for hydrolysis and silanol formation. Particulate fillers and glass fiber are silylated by stirring them in the silane solution for 2-3 minutes and then decanting the solution.

Deposition from aqueous solutions is employed for most commercial fiberglass systems. The alkoxysilane is dissolved at 0.5-2.0% concentration in water. For less soluble silanes, 0.1% of a non-ionic surfactant is added prior to the silane and an emulsion rather than a solution is prepared. If the silane does not contain an amine group the solution is adjusted to pH 5-5 with acetic acid. The solution is either sprayed onto the substrate or employed as a dip bath. Silanes are commercial products available from for instance Dow Corning in the U.S.A., and Degussa, Germany.

Modifying the surface of silica particles with silanes and/or organic compounds

The silylation or the adsorption of organic compounds on the surface of small silica particles according to the present invention is a quite different process compared with the silylation of the surface of conventional fillers such as clays and fibreglass. The colloidal silica used in the present invention is a dispersion of discrete, non-aggregated, uniformly sized, spherical silica particles in water. The silylation procedure must be carried out under such conditions of pH, concentration, rate of addition of silylating solution and temperature that the silica particles do not aggregate by forming non-reversible siloxane bonds with one another.

The stability of silica sols towards gelling decreases with increasing concentration of silica, SiO2. Commercial silica is manufactured with the highest possible silica content, which depends on the particle size, commensurate with long-term stability towards gelling. Although the silylation procedure can be carried out at silica concentrations approaching those of commercial silica sols it is preferred to use less concentrated silica sols. In silica sols containing about 15 % SiO2 the average distance between particles is one particle diameter, which ensures only moderate interaction between the particles and good stability towards gelling.

Before the silane is added to the solution of the silica particles the solution is diluted to at most 40 % by weight, preferred 30 % by weight SiO2 in the solution. The solution is preferably diluted with water and/or an organic solvent. The pH of the diluted sol is preferably between 9.0 and 10.5. Preferred organic solvents are lower alcohols, preferably aliphatic alcohols with 1 to 6 carbon atoms in the chain. Most preferred are methyl alcohol, ethyl alcohol and mixtures of these compounds.

The silylating solution comprises using a silane as such, or in a mixture of water and a water- soluble organic solvent, e.g. an alcohol such as methyl alcohol or ethyl alcohol, or in a water- soluble organic solvent, preferred methyl alcohol or ethyl alcohol. The concentration of silane is limited by the requirement that the silane molecules should not have time to hydrolyse and condense to polysiloxanes during the time frame of the silylation procedure. In the present invention, and also in commercial applications of silanes as silylating agents, it has been found that about 2%by weight of silane is a suitable concentration, but higher concentrations can be used and are sometimes preferred. In one process for making silica particles and powder of the present invention undiluted silane is added to the silica sol to be silylated.

The pH of the system during the silylation procedure should be such that the silane, hydrolysed to the corresponding silanol, readily reacts with the OH groups on the silica particle surface but does not destabilize the silica sol. In the art of conventional silica technology it is well known that the size of the particles of a silica sol can be increased by having the silanol groups of the particle surface react with monomeric silicic acid. Such buildup of particle size takes place best at pH above 8, preferably between pH 9 and 10. Similarly, the silanol groups of silica particles readily react with the hydroxy I groups of hydrolyzed silanes at pH above 7 to form a coating of the particle surface by organic groups without compromising the stability of the silica sol during the time frame of the silylation procedure. In conventional silane technology the surface of such fillers as clays and fibreglass is readily modified by reacting hydroxyl groups on the filler surface with silanols at a pH between 3.5 and 5.5. If the silane contains amine groups the pH of the system must be alkaline, e.g 9-10, to ensure proper alignment of the silane molecule with the particle surface, i.e. the silanol molecule must approach the particle with the OH groups closest to the surface. In an acid environment, amine groups are positively charged and amine-containing silanols would therefore approach the particles with the amine group closest to the mildly positively charged particle surface and condensation between the OH groups of the silanol molecules and the particle surface would not occur.

The condensation reaction, like any chemical reaction, increases with temperature whereas the stability of silica sols decreases with temperature. A temperature of 20-750C, preferably 20-500C, ensures rapid and efficient reaction of the silane with the particle surface without compromising the stability of the silica sol.

Silylation of the surface of particulate fillers by deposition from, for instance, aqueous alcohol solutions occurs readily and is accomplished by stirring the filler particles in the silylating solution for 2-3 minutes. Silylation of colloidal silica according to the present invention also occurs readily and can be accomplished in a few minutes. It is preferred, however, so as not to compromise the stability of the colloidal silica, to adjust the rate of addition of silylating solution to the suspension of colloidal silica particles so that silylation of the particle surface takes place over a period of hours instead of minutes.

The degree of silylation, expressed as number of silane molecules per square nanometer of particle surface, required to yield a dispersible powder depends on the chemical structure of the silane, but falls in the range from 1.0 to 7.0, preferably 3.0 to 4.0, silane molecules per square nanometer particle surface.

Dispersible particles of silica can be prepared by, in addition to or instead of silylating the particle surface, adsorbing organic molecules, e.g. polyols, preferably with a molecular weight of from 62 to 10000 g/mol, most preferred a polyether polyol, diamines or dicarboxylic acids, onto the particle surface. The organic compound, e.g. a polyol, or a solution of the organic compound is added to the de-ionized silica sol or the de-ionized, silylated silica sol.

Removal of the liquid phase, consisting of water or a mixture of water and an alcohol such as methanol or ethanol, must take place under such conditions of pH and temperature that formation of irreversible siloxane bonds between particles is prevented or reduced to a minimum.

The amount of organic liquid or compound, e.g. a polyol, should correspond to at least 10 % by weight based on the weight of silica in the de-ionized silica sol or the de-ionized, silylated silica sol.

Drying of the modified silica particles

Removal of water and alcohols, e.g. methanol or ethanol, from the suspension of silylated silica particles must take place under such conditions of pH and temperature that formation of irreversible siloxane bonds between particles is prevented or reduced to a minimum.

The rate of formation of siloxane bonds between particles increases with pH, i.e. with increasing concentration of hydroxyl ions. The rate of formation siloxane bonds also increases with temperature.

Water and alcohol, e.g. methanol or ethanol, must therefore be removed at a pH preferably below 10, most preferred from 2.0 to 3.0 for colloidal silica particles, and at moderate temperatures, preferably not higher than about 750C. By the application of vacuum, water and alcohol, e.g. methanol or ethanol, can be rapidly evaporated even at temperatures below 500C.

Low pH and low electrolyte concentration will prevent or minimize destabilization, caused by siloxane bond formation between particles or aggregation of particles, of the silylated sol during the drying stage, i.e. the removal of the liquid phase, consisting of water and/or alcohol, from the sol. So as to ensure maximum stability of the silylated sol in the sense of not forming siloxane bonds during the drying operation it is subjected to contact with an anion- and a cation-exchange resin until completely deionized. The art is familiar with techniques for effecting such deionization, the methods described in U.S. Patent 2,577,485 being suitable. As the anion exchange resin one can use, for example, a strong base resin in the hydroxyl form and as the cation exchange resin one can use, for instance, a strong acid resin in the hydrogen form. The silylated silica sol can be passed first through a column of a cation-exchange resin in the hydrogen form and then through a column of an anion- exchange resin in the hydroxyl form, or alternatively, passed through a column of the mixed resins. The exchange cycle can be repeated two or more times if desired. Another alternative is to stir the silylated sol with a mixture of the anion- and cation-exchange resins.

When modifying the surface of the silica particles with organic compounds, as polyols, dicarboxylic acides or diamines it is preferred to add the organic compounds after the deionization of the diluted solution of the silica particles.

After the silylated silica particles have been dried to constant weight, the resulting cake can be ground to a fine powder, for instance in a ball mill. When polyols used for modifying the silica particles mostly a sticky paste results after drying, which is mostly used as paste or as a masterbatch with polyols.

Organic compounds - liquids or molten solids

Organic compounds such as polyols, isocyanates or carboxylic acids, which may be liquids or solids at room temperature, are used in the manufacture of many types of polymers, e.g. polyurethanes, polyamides and polyesters. The powder of silylated silica particles can readily be dispersed in such organic compounds by techniques well known in the trade.

Polvols

Polyols, which are used according to the present invention to prepare polyurethanes including urethane-based thermoelastomers, are organic compounds containing two or more hydroxyl groups.

The term polyol is used for low-molecular substances containing two or more hydroxyl groups, e.g. ethylene glycol(1,2-ethanediol) and glycerol(1,2,3-propanediol) as well as for polymeric compounds containing terminal hydroxyl groups, e.g. polyester polyols and polyether polyols with molecular weights of up to several thousand.

Polyols may be divided into two classes; those used for making rigid foams, rigid solids and stiff coatings and having a molecular weight range of 400-1000 and a functionality 3-8, and those used for making flexible foams and elastomers and having a molecular weight range of 1000-6500 and a functionality 2-3.

Polyols, which are used according to the present invention are of polyether type, polyester type or based on acrylics.

The polyester polyols and polyether polyols used in the present invention can have molecular weights ranging from low values, corresponding to diols and triols of monomer type, to high values of many thousand.

Polyols, which are used to manufacture nanocomposites according to the present invention, are commercial products sold under different trade names, e.g. Arcol from Lyondell, Caradol from Shell, Voranol from Dow, Daltolac from Huntsman, Baycoll and Desmophen from Bayer, and Lupranol from BASF.

Polyether polyols

Polytetramethylene glycol polyols, PTMEG, which are prepared by acid-catalyzed polymerization of tetrahydrofurane, THF, polypropylene glycol polyols, which can be based on propylene oxide only, a mixture of ethylene oxide and propylene oxide or a mixture of propylene oxide, ethylene oxide and double metal cyanide catalysts, DMC, polymer modified polyols, and amine terminated polyether polyols, which are really not polyols but polyamines, are the four different main types of polyether polyols used to make polyurethane polymers.

Polyester polyols

Polybutanediol adipates, polycaprolactone polyols and polyethylene terephthalate polyols are three important types of polyester polyols. Polyester polyols can be linear or branched and the branching can be weak, moderate or extensive. Polyester polyols can be modified by incorporating saturated, fatty acids of low molecular weight into their structure.

Acrylic polyols

Acrylic polyols are prepared by polymerisation of hydroxyl-containing monomers such as hydroxyethyl methacrylate, hydroxypropyl methacrylate and allyl alcohol propoxylate and copolymers such as methyl methacrylate, styrene, butyl acrylate, 2.ethylhexyl acrylate, acrylic acid, methacrylic acid and acrylonitrile.

Polyester and polyether polyols are characterized by their hydroxyl functionality, which is related to the average number of hydroxyl groups per polyol molecule and usually falls in the range from about 2 to almost 4. Acrylic polyols have functionalities ranging from 2 to 8.

Polyols of diol type, which are used in the present invention to prepare e.g. ester-based thermoelastomers, are acyclic and alicyclic dihydroxy compounds. Preferred are diols with 2- 15 carbon atoms such as ethylene, propylene, tetramethylene, pentamethylene, 2,2'- dimethyl-trimethylene, hexemethylene, and decamethyleneglycols, dihydroxy cyclohexane, cyclohexane dimethanol, etc. Especially preferred are aliphatic diols containing 2-8 carbon atoms. Equivalent ester-forming derivatives of diols are also useful, e.g. ethylene oxide or ethylene carbonate can be used in place of ethylene glycol.

Other polyols

Castor oil polyols, polycarbonate polyols and polybutadiene polyols are other less commonly used polyols.

The silica powder of the present invention can readily be dispersed in the polyols described herein by techniques well known in the trade.

lsocyanates

The other important class of chemicals used in the commercial preparation of polyurethanes, including urethane-based thermoelastomers, is the polyisocyanates, especially the diisocya nates. The two most important groups of diisocyanates are toluenediisocyanates, TDI's, and methylenebis(phenyl isocyanates), MDI's.

In addition to MDI, HDI, hexamethylene diisocyanate, IDPE, isoprene diisocyanate, and NDI, naphthalene diisocyanate, are used to form hard segments in urethane-based thermoelastics.

Diisocyanates and other isocyanates used in the preparation of polyurethanes, including urethane-based thermoelastomers, are commercial products sold under various trade names by, e.g. Huntsman, Shell, Bayer, and BASF, Rhodia, and Dow. The diisocyanates will react with and add to any chemical compound containing active hydrogen, e.g. the hydrogens of the hydroxyl groups in polyols and water, of the hydroxyl groups on the surface of silylated silica particles or of the NH-groups in primary and secondary amines.

The silica powder of the present invention can readily be dispersed in the isocyanates described herein, and other isocyanates, by techniques well known in the trade. The isocyanate will then chemically modify the particle surface by reacting with the surface silanol groups. The resulting particles have a chemically active surface which can react with polyols, isocyanates and other components in formulations for making polyurethanes, polyesters and polyamides.

Carboxylic acids

Dicarboxylic acids of both aliphatic and aromatic types are used in the preparation of polyamides and polyesters, including amide-based and ester-based thermoelastomers.

Aliphatic carboxylic acids, as the term is used herein, refer to carboxylic acids having two carboxyl groups each attached to a saturated carbon atom. If the carbon atom to which the carboxyl group is attached is saturated and is in a ring, the acid is cycloaliphatic. Aliphatic or cycloaliphatic acids having conjugated unsaturation often cannot be used because of homopolymerization. However, some unsaturated acids, such as maleic acid, can be used.

Representative aliphatic and cycloaliphatic acids, which can be used to prepare amide-based and ester-based thermoelastomers in this invention, are sebacic acid, 1 ,3-cyclohexane dicarboxylic acid, 1,4- cyclohexane dicarboxylic acid, adipic acid, glutaric acid, succinic acid, carbonic acid, oxalic acid, azelaic acid, diethylmalonic acid, allylmalonic acid, 4-cyclohexene- 1 ,2-dicarboxylic acid, 2-ethylsuberic acid, 2,2,3,3-tetramethylsuccinic acid, cyclopentane dicarboxylic acid, decahydro-1,5-naphthalene dicarboxylic acid, 4,4'-bicyclohexyl dicarboxylic acid, decahydro-2,6-naphthalene dicarboxylic acid, 4,4'- methylenebis(cyclohexane carboxylic acid), 3,4-furan dicarboxylic acid, and 1 ,r-cyclobutane dicarboxylic acid. Preferred aliphatic acids are cyclohexane dicarboxylic acids and adipic acid.

Aromatic dicarboxylic acids, as the term is used herein, are dicarboxylic acids having two carboxyl groups attached to a carbon atom in an isolated or fused benzene ring. It is not necessary that both functional carboxyl groups be attached to the same aromatic ring and where more than one ring is present they can be joined by aliphatic or aromatic radicals or radicals such as -O- or -SO2-.

Representative aromatic dicarboxylic acids, which can be used to prepare amide-based and ester-based thermoelastomers in this invention, include terephatalic, phtalic and isophatalic acids, bibenzoic acid, substituted dicarboxy compounds with two benzene nuclei such as bis(p-carboxyphenyl)methane, p-oxy(p-carboxyphenyl) benzoic acid, ethylene-bis(p- oxybenzoic acid), 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,7- naphthalene dicarboxylic acid, phenanthrene dicarboxylic acid, anthracene dicarboxylic acid, 4,4'-sulfonyl dibenzoic acid, and CrCi2 alkyl and ring substitution derivatives thereof, such as halo, alkoxy, and aryl derivatives. Hydroxyl acids such as p(β-hydroxyethoxy) benzoic acid can also be used providing an aromatic dicarboxylic acid is also present. Aromatic dicarboxylic acids are a preferred class for preparing ester-based thermoelastomers in this invention. Among the aromatic acids, those with 8-16 carbon atoms are preferred, particularly the phenylene dicarboxylic acids, i.e. terphthalic, phthalic and isophthalic acids.

The silica powder of the present invention can readily be dispersed in the carboxylic acids described herein by techniques well known in the trade.

Chain extenders, branching agents or cross-linking agents

Chain extenders, branching agents or cross-linking agents are compounds present in relatively small amounts, less than 10 % by weight and often less than 5 % by weight, in formulations for preparing polyurethane polymers, including urethane-based thermoelastomers, ester-based thermoelastomers and amide-based thermoelastomers, so as to modify the properties of the polymers.

Diols, such as ethylene diol, 1 ,3- propane diol, 1 ,4-butane diol, 1 ,5-pentane diol and 1,6- hexane diol, and diamines, such as 4,4'-diaminodiphenylmethane, 3,3'-dichloro-4,4'- diaminodiphenylmethane, benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 3,3'- dichlorobenzidine and p-phenylenebenzidine, are used as chain extenders in polyurethane polymers, including urethane-based thermoelastomers, ester-based thermoelastomers and amide-based thermoelastomers.

Triols, such as glycerol, 1 ,1,1 -trimethylol propane, tris(2-hydroxyethyl) isocyanurate pentaerythritol, trimellitic acid, pyromellitic acid and poly(ethylene oxide) and polypropylene oxide) triols of about 400-3000 molecular weight are used as branching agents or crosslinking agents in polyurethane polymers, including urethane-based thermoelastomers, ester-based thermoelastomers and amide-based thermoelastomers. The silica powder of the present invention can readily be dispersed in the chain extenders, branching agents or cross linking agents described herein by techniques well known in the trade.

Dispersion of modified silica particles in organic liquids

Any stirring equipment can be used for mixing the silica powder of the present invention with organic compounds used to manufacture different types of polymers, but, so as to ensure as perfect dispersion as possible, that is dispersing the powder to a dispersion of the ultimate silica particles in the organic liquid, the equipment used should therefore be chosen from among the more efficient mixing machines; e.g high speed mixers

It is essential to ensure complete de-aeration of the dispersion since air bubbles may cause porosity in the finished product. In the production of some polymers, e.g. polyurethanes, it is also important to lower the water content to below a certain critical level, e.g. less than 0.1% by weight. It is therefore often advantageous to carry out the whole mixing procedure in vacuum.

Polymers made of components containing well dispersed silica particles and powder

Polvurethanes

The chains of polyurethane polymers contain the urethane linkage, -NH-CO-O-. The easiest and commercially most useful method for the production of the urethane linkage is the reaction of the urethane radical, -N=C=O, in e.g. diisocyanates, with a hydroxyl radical in e.g. polyols. The simplest form of a polyurethane polymer is the linear one, where the polyol and the isocyanate each have a functionality of two. Linear polyurethanes are used as thermoplastics, e.g in the form of fibers.

By incorporating materials with functionality greater than two, polymers can be produced with various degrees of cross-linking ranging from a few to many branches. Hence, they can give rise to polyurethanes, which vary in properties from soft elastomers to rigid thermosetting plastics similar to phenolics. It is possible to further modify the properties of polyurethanes by varying the ratio of polyol, which provides the soft segment of the polymer, to isocyanate, which provides the hard segment of the polymer, in the formulation. Higher ratios give softer, more flexible materials because the tensile strength and modulus will decrease whereas the elongation at break increases. The unusual effect of the particles and powder of the present invention to simultaneously increase tensile strength and elongation at break of polyurethanes is particularly pronounced at high ratios of polyol to isocyanate; i.e. polyurethanes, in which the soft segment blocks, consisting of polyesters or polyethers, predominate over the hard segment blocks, consisting of polyisocyanates and chain extenders.

The great diversity of structure in polyurethanes accounts for the tremendous variation in physical properties, making polyurethane polymers the group of polymers with the widest range of applications, e.g. as thermoplastics, elastomers and thermosetting plastics, and in the production of flexible and rigid foams, fibers, coatings and adhesives.

Urethane-based thermoelastomers

Urethane-based thermoelastomers are prepared by reacting a diisocyanate with a short- chain diol, e.g. 1 ,4-butane diol, and a long-chain diol. The hard segments of the thermoelastomer are formed when the diisocyanate reacts with the short-chain diol, which acts as a chain extender. The soft segments of the thermoelastomer are formed when the long-chain diol reacts with the diisocyanate.

In general, urethane-based thermoplastic elastomers are made by reacting the ingredients together at temperatures above 800C. The reaction can be carried out in different ways. The so-called "one-shot method" involves mixing all the ingredients together. In the "prepolymer method, the polyol is reacted first with the diisocyanate to give an isocyanate containing prepolymer, which is then reacted with the chain extender, i.e. a low molecular weight polyol.

The silica particles and powder of the present invention can readily be incorporated into polyurethanes by having the particles and powder well dispersed in one, several or all of the components used for producing polyurethanes, so as to make nanocomposites of polyurethanes with superior mechanical properties.

The unusual effect of the particles and powder of the present invention to simultaneously increase tensile strength and elongation at break of polyurethanes is particularly pronounced at high ratios of polyol to isocyanate; i.e. polyurethanes, in which the soft segment blocks, consisting of polyesters or polyethers, predominate over the hard segment blocks, consisting of polyisocyanates and chain extenders.

In nanocomposites of polyurethane of the present invention, the dependence of polymer properties on the ratio of hard segments to soft segments can therefore be relaxed, thus making it possible to combine high tensile strength with for instance high impact strength and excellent low temperature properties.

Ester-based thermoelastomers

Like urethane-based thermoelastomers, ester-based thermoelastomers form 2-phase structures consisting of crystalline and amorphous domains. The hard phase of crystalline domains, is usually made up of lamellarly packed segments of polybutylene terephthalate, which form crystallites with melting points as high as 220 0C. The soft, flexible phase of amorphous domains consists of polybutyleneglycol ether, which has a glass transition temperature of -50 0C when the number of monomer units in the ether is 12-16.

Ester-based thermoelastomers can be made by ester exchange of a long-chain polyol and a short-chain polyol with the methylester of a dicarboxylic acid. The polymerization is carried out in the presence of an alkyl titanate, e.g. butyl titanate, and often in combination with alkaline earth acetate. The short-chain polyol is in excess and the product is driven to high molecular weight by its evaporation. Usually, an ester prepolymer is first formed by gradually heating the catalyzed mixture to about 200 0C as methanol is removed by distillation. The ester prepolymer is driven to high molecular weight by evaporation of the original excess polyol under vacuum, less than 1 mm Hg, and at temperatures between 240 0C and 250 0C." Ester-based thermoelastomers contain the ester linkage, -CO-O-.

The silica powder of the present invention can readily be incorporated into ester-based thermoelastomers by having the powder well dispersed in one, several or all of the components used for producing ester-based thermoelastomers, so as to make nanocomposites of ester-based thermoelastomers with superior mechanical properties. The unusual effect of the powder of the present invention to simultaneously increase tensile strength and elongation at break of ester-based thermoelastomers is particularly pronounced for ester-based thermoelastomers, in which the soft segment blocks, consisting of for instance polybutyleneglycol ether, predominate over the hard segment blocks, consisting of for instance polybutylene terephthalate and chain extenders.

In nanocomposites of ester-based thermoelastomers of the present invention, the dependence of polymer properties on the ratio of hard segments to soft segments can therefore be relaxed, thus making it possible to combine high tensile strength with for instance high impact strength and excellent low temperature properties. Amide-based thermoelastomers

Amide-based thermoelastomers are also 2-phase structures consisting of crystalline and amorphous domains. The hard phase of microcrystalline domains is based on polyamide 11 and polyamide 12, but may also contain segments of polyamide 6, polyamide 66 or copolymers of polyamide 6 and polyamide 11. The soft, flexible phase of amorphous domains is most commonly based on poly(tetramethylene oxide) glycol, but may also be based on polyethylene glycol or polypropylene glycol.

The three important types of amide-based thermoplastic elastomers are designated polyesteramides(PEAs), polyetheresteramides(PEEAs), and polycarbonate- esteramides(PCEAs), respectively.

The formation of the amide group is the reaction occurring during the polymerisation of monomers into the PEAs, the PEEAs, and the PCEAs. Polyamides are typically synthesized by the condensation reactions of either diamines with dicarboxylic acids or by the ring opening polymerization of cyclic lactams.

PEA, PEEA, and PCEA elastomers are synthesized by the condensation of the aromatic diisocyanate, MDI, with aliphatic dicarboxylic acids and a polyester or polyether prepolymer with a molecular weight of 500 to 5000 and terminated with aliphatic carboxylic acid.

The polymerisation is usually carried out homogeneously in a polar solvent, which is nonreactive with isocyanates at elevated temperatures (200 0C to 280 0C), by the controlled addition of the diisocyanate to a solution of the other monomers. The added dicarboxylic acid serves as the hard segment chain extender and forms the semiaromatic hard segment with the MDI. It is analogous to the 1,4-butanediol used to increase the length of the urethane block in urethane-based thermoplastic elastomers.

Polyester, polyether, or polycarbonate prepolymers terminated with aliphatic carboxylic acids form the soft segments for PEA, PEEA, AND PCEA, respectively. These prepolymers are obtained by the esterification reaction of dihydroxyl-terminated polyols with an excess of aliphatic carboxylic acid, or directly by the reaction of a short chain diol with an excess of a carboxylic acid.

Amide-based thermoelastomers can be prepared by reacting a low molecular polyamide, such as low molecular weight polyamide 6, polyamide 66 or copolymers of polyamide 6 and polyamide 11 , with excess dicarboxylic acid at 230 0C and high pressure, >2.5 MPa. The polyamide is next reacted with a polyether at 230-280 0C under vacuum and in the presence of a titanate catalyst.

Amide-based thermoelastomers contain the amide linkage, -NH-CO-.

The silica powder of the present invention can readily be incorporated into amide-based thermoelastomers by having the powder well dispersed in one, several or all of the components used for producing amide-based thermoelastomers, so as to make nanocomposites of amide-based thermoelastomers with superior mechanical properties. The unusual effect of the powder of the present invention to simultaneously increase tensile strength and elongation at break of amide-based thermoelastomers is particularly pronounced for amide-based thermoelastomers, in which the soft segment blocks, consisting of for instance poly(tetramethylene oxide) glycol, predominate over the hard segment blocks, consisting of fer instance polyamide 11 or polyamide 12.

In nanocomposites of amide-based thermoelastomers of the present invention, the dependence of polymer properties on the ratio of hard segments to soft segments can therefore be relaxed, thus making it possible to combine high tensile strength with for instance high impact strength and excellent low temperature properties.

Dispersion of silica particles in thermoplastics by compounding or master batching.

Compounding is the process by which additives, for instance the silica particles and powder of the present invention, are added to the basic thermoplastics material. This usually involves melting the thermoplastics material then mixing it with the required additive material, for instance the silica particles and powder of the present invention, in an extruder. The polymer melt is then extruded and chopped into pellets as it cools, which can then be used directly by the plastics processor. An associated process is master batch. This is where a high concentration of additives, for instance the silica particles and powder of the present invention, are dispersed in a carrier medium which can then be used directly by the processor in small quantities to pigment or modify the virgin polymer material.

The invention will be better understood by reference to the following illustrative examples.

Examples

A. Methods of making silica particles and powder dispersible in polyols, isocyanates, carboxylic acids and other compounds used for making polyurethane polymers, including urethane-based thermoelastomers, and esterbased thermoelastomers and amide-based thermoelastomers, and in thermoplastics. Example A1.

To 360 g of an alkali stabilized silica sol, having a particle size of 100 nm and a concentration of 50% SiO2 (Nyacol 9950 from Eka Nobel), was added 320 g of methanol. pH of the metanolic sol was 9.75. 7.2 g of dimethyldimethoxysilane (silane Z-6194 from Dow Corning) was dissolved in 200 g of methanol. The silane solution was added to the diluted sol at a rate of 14 g per hour. The temperature of the diluted sol was kept at 270C during the time of addition of the silane solution. After completed addition, the silylated sol was agitated for 3 hours at 270C. The silylated sol, having a pH of 10.74, was deionized to pH 2.91 by adding a mixture of 74 g of strong cation exchange resin and 22 g of strong anion exchange resin. 841 g of deionized, silylated sol was recovered and dried by removing the liquid phase, consisting of mixture of methanol and water, under vacuum at a temperature not higher than 100C to yield 188 g of dry silylated sol. The dried, silylated sol was milled in ball mill to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A2

As in Example 1, but the dried silylated sol was ground in a mortar to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A3

As in Example 1, but the deionized, silylated silica sol was dried by evaporating the liquid phase in the air stream from a fan at 80C. The dried silylated sol was ground in a mortar to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A4

As in example 1 , but the silane used was methyltrimethoxysilane (silane Z-6070 from Dow Corning).

Example A5

As in example 1, but the silane used was trimethylmethoxysilane Example A6

As in example 1, but the silane used was isobutyltrimethoxysilane (silane Z-2306 from Dow Corning).

Example A7

As in example 1, but the silane used was n-octyltriethoxysilane (silane Z-6341 from Dow Corning).

Example A8

As in example 1 , but the silane used was Aminoethylaminopropyltrimethoxysilane (silane Z- 6020 from Dow Corning).

Example A10

As in example 1 , but the silane used was aminopropyltriethoxysilane (silane Z-6011 from Dow Corning).

Example A11

As in example 1 , but the silane used was vinyltrimethoxysilane (silane Z-6300 from Dow Corning).

Example A12

As in example 1 , but the silane used was 3-glycidoxipropyltrimethoxysilane (silane Z-6040 from Dow Corning).

Example A13

As in example 1, but the silane used was 3-methacryloxipropyltrimethoxysilane (silane Z- 6030 from Dow Corning). Example A14

150 g of an alkali stabilized silica sol, having a particle size of 100 nm and a concentration of 50% SiO2, was diluted to 12% SiO2 with 475 g water and decationized to pH 3.5 using a strong acid cation resin. 2.25 g of dimethyldimethoxysilane (silane Z-6194 from Dow Corning) was dissolved in 110 g of methanol and partially hydrolyzed by adding 0.23 g water. The silane solution was added to the diluted sol at a rate of 28 g per hour. The temperature of the diluted sol was kept at 250C during the time of addition of the silane solution. After completed addition, the silylated sol was agitated for 1 hour at 250C. The silylated sol was poured on two baking trays and the liquid phase, consisting of methanol and water, was evaporated in the air streams of two fans at 250C to yield 77 g of dry silylated sol. The dried, silylated sol was milled in ball mill to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A15

2003-09-19, 2. 75 g of an alkali stabilized silica sol, having a particle size of 100 nm and a concentration of 50% SiO2, was diluted to 12% SiO2 with 238 g water and decationized to pH 3.5 using a strong acid cation resin. 1.50 g of dimethyldimethoxysilane (silane Z-6194 from Dow Corning) was dissolved in 50 g of methanol. The silane solution was added to the diluted sol at a rate of 21 g per hour. The temperature of the diluted sol was kept at 350C during the time of addition of the silane solution. After completed addition, the silylated sol was agitated for 1 hour at 350C. The silylated sol was poured on a baking tray and the liquid phase, consisting of methanol and water, was evaporated in an oven with air circulation at 750C to yield 39 g of dry silylated sol. The dried, silylated sol was ground in mortar to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A16

To 200 g of an alkali stabilized silica sol, having a particle size of 22 nm and a concentration of 40% SiO2, was added 200 g of methanol. pH of the metanolic sol was 9.75. 6.24 g of dimethyldimethoxysilane (silane Z-6194 from Dow) was dissolved in 225 g of methanol. The silane solution was added to the diluted sol at a rate of 10 g per hour. The temperature of the diluted sol was kept at 250C during the time of addition of the silane solution. After completed addition, the silylated sol was agitated for 3 hours at 250C. The silylated sol, having a pH of 10.74, was deionized to pH 2.91 by adding a mixture of 88 g of strong cation exchange resin and 26 g of strong anion exchange resin. 592 g of deionized, silylated sol was recovered and dried by pouring it on two baking trays and removing the liquid phase, consisting of mixture of methanol and water, in air streams from two fans at a temperature not higher than 1O0C to yield 80 g of dry silylated sol. The dried, silylated sol was ground in a mortar to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A17

To 267 g of an alkali stabilized silica sol, having a particle size of 12 nm and a concentration of 30% SiO2 (Bindzil 30/220 from Eka Nobel), was added 133 g of methanol. pH of the metanolic sol was 9.86. 12.2 g of dimethyldimethoxysilane (silane Z-6194 from Dow Corning) was dissolved in 300 g of methanol. The silane solution was added to the diluted sol at a rate of 14 g per hour. The temperature of the diluted sol was kept at 250C during the time of addition of the silane solution. After completed addition, the silylated sol was agitated for 3 hours at 250C. The silylated sol, having a pH of 10.81 , was deionized to pH 2.95 by adding a mixture of 100 g of strong cation exchange resin and 30 g of strong anion exchange resin. 670 g of deionized, silylated sol was recovered and dried by removing the liquid phase, consisting of mixture of methanol and water, under vacuum at a temperature not higher than 100C to yield 80 g of dry silylated sol. The dried, silylated sol was milled in ball mill to a fine powder, which was readily dispersible in polyols and isocyanates to a clear dispersion.

Example A18

To 80 g of an alkali stabilized silica sol, having a particle size of 100 nm and a concentration of 50% SiO2 (Nyacol 9950 from Eka Nobel), was added 350 g of methanol. The methanolic sol, having a pH of 10.51 , was deionized to pH 2.98 by adding a mixture of 31 g of strong cation exchange resin and 14 g of strong anion exchange resin. 408 g of deionized, methanolic sol was recovered and dried by evaporating the liquid phase, consisting of mixture of methanol and water, in the air stream from a fan at 250C. The dried sol was ground in a mortar to a fine powder, which was dispersible in polyols and isocyanates to an opaque dispersion.

Example A19

To 80 g of an alkali stabilized silica sol, having a particle size of 100 nm and a concentration of 50% SiO2 (Nyacol 9950 from Eka Nobel), was added 350 g of methanol. The metanolic sol, having a pH of 9.75, was dried by evaporating the liquid phase, consisting of mixture of methanol and water, in the air stream from a fan at 250C. The dried sol was ground in a mortar to a fine powder, which was dispersible in polyols and isocyanates to an opaque dispersion. B. Mechanical properties of polyurethanes reinforced with small particles of silica.

The preparation of the samples for mechanical testing was carried out by the practices commonly used in the polyurethane industry. The raw materials used for preparing the polymeric materials in the examples are defined in table 4.

The diisocyanate was added to the well mixed and homogenized blend of the polyol, with or without silica particles, and the other ingredients of formulations for making polyurethane polymer. The formulations were poured into a mould and reacted and cured to a 150x150x5 mm sheet. The mechanical properties of the polyurethanes were determined upon dog bone- shaped pieces cut from these slabs. Measurements were made by procedures commonly used for testing polyurethane polymers. The stress-strain measurements were made on a MECMESIN AFC-M 2500N tensile tester.

The tensile strengths at break are recorded in table 3 in MPa. The elongation at break is recorded as percent of the original length of the sample. In the table, the compositions of the polymer samples prepared in the patent examples are also shown. The polyols and the isocyanates are designated by abbreviated trade names, which are explained in table 4. MDI refers to the isocyanate used in the particular preparation and the number designations are explained in table 4. The blending ratio is the polyol: isocyanate weight ratio. Included in the amount of polyol in the blending ratio are BDO and OH-containing organic solvents (e.g. for the catalyst) and dispersants (e.g.for the zeolite). The left column in table 5 shows a typical formulation for a referens PUR, example B13, and the right column shows the formulation for a PUR containing 10.8% particles, example B14. The index is given the value 100 when polyol(including BDO and OH-containing solvents and disperants) and isocyanate are present in stoichiometric amounts; systems with indices below and above 100 are under- crosslinked and over-crosslinked, respectively. The particle size and the concentration of the silica particles are also shown in the table.

The results in table 3 show that nanocomposites of polyurethane polymers and small particles of silica from a powder of the present invention, having improved tensile strength combined with unchanged or increased elongation and resulting in remarkably large increases of the energy at break, can be prepared from many different polyols and isocyanates. The largest improvements of tensile strength, elongation and energy at break were obtained by using high molecular weight polyols. Unexpectedly, the degree of improvement went through a maximum with increasing silica concentration and in some systems the maximum was reached at surprisingly low silica contents. Example B1

Reference sample of polyurethane was made from Arcol 1004 and Suprasec 5025 with index 90.

Example B2

Polyurethane was made from Arcol 1004, containing 16.0 % by weight of powder from example A17, and Suprsec 5025 with index 90. The finished polyurethane contained 10.8 % by weight of SiO2.

Examples B3a-c

Reference samples of polyurethanes were made from Voranol 4711 and Suprasec 2018 with indices 90, 105 and 120.

Example B4

Polyurethane was made from Voranol 4711, containing 16.0 % by weight of powder from example A17, and Suprasec 5025 with index 90. The finished polyurethane contained 10.8 % by weight of SiO2.

Examples B5a-c

Polyurethane was made from Voranol 4711 , containing 8.0 % by weight of powder from example A17, and Suprasec 5025 with index 90, 105 and 120. The finished polyurethane contained 5.4 % by weight of SiO2.

Examples B6a-c

Reference samples of polyurethanes were made from Caradol 28-02 and Suprasec 2018 with indices 90, 105 and 120.

Example B7 Polyurethane was made from Caradol 28-02, containing 8.0 % by weight of powder from example A17, and Suprsec 2018 with index 120. The finished polyurethane contained 5.4 % by weight of SiO2.

Example B8

As in example B7 but the polyol contained 16.0 % by weight of powder from example A17 and the index was 105. The finished polyurethane contained 10.8 % by weight of SiO2.

Examples B9a-c

Polyurethanes were made from Caradol 28-02, containing 16.0 % by weight of powder from example A16, and Suprsec 2018 with index 90, 105 and 120. The finished polyurethane contained 10.8 % by weight of SiO2.

Examples B10a-c

As in examples B9a-b but the polyol contained 5.4 % by weight of powder from example A16.

Examples B11a-c

Polyurethanes were made from Caradol 28-02, containing 16.0% by weight of powder from example A3, and Suprsec 2018 with index 90, 105 and 120. The finished polyurethane contained 10.8 % by weight of SiO2.

Examples B12a-c

As in examples B11a-b but the polyol contained 5.4 % by weight of powder from example A3

Example B13

Reference sample of polyurethane was made from Voranol 4711 and Suprasec 2018 with index 105. Example B14

Polyurethane was made from Voranol 4711, containing 16.0 % by weight of powder from example A14, and Suprasec 2018 with index 105. The finished polyurethane contained 10.8 % by weight of SiO2.

Example B15

Polyurethane was made from Voranol 4711, containing 16.0 % by weight of powder from example A15, and Suprasec 2018 with index 105. The finished polyurethane contained 10.8% by weight of SiO2.

Example B16

Reference sample of polyurethane was made from Lupranol 2090 and Lupranat 134-7 with index 105.

Example B17

Polyurethane was made from Lupranol 2090, containing 16.0 % by weight of powder from example A3, and Lupranat 134-7 with index 105. The finished polyurethane contained 10.8% by weight of SiO2.

Example B18

Reference sample of polyurethane was made from Lupranol 2090 and Lupranat 134-7 with index 105.

Example B19

Polyurethane was made from Lupranol 2090, containing 8.0 % by weight of powder from example A16, and Lupranat 134-7 with index 105. The finished polyurethane contained 5.9% by weight of SiO2.

Example B20

Reference sample of polyurethane was made from Lupranol 2090 and Lupranat 134-7 with index 105. Example B21

Polyurethane was made from Lupranol 2090 and Lupranat 134-7, containing 10.0 % by weight of powder from example A3, with index 105. The finished polyurethane contained 2.1% by weight of SiO2.

Example B22

Reference sample of polyurethane was made from PTHF 1000 and Lupranat 134-7 with index 105.

Example B23

Polyurethane was made from PTHF 1000, containing 15.0 by weight of powder from example A3, and Lupranat 134-7 with index 105. The finished polyurethane contained 3.2 by weight of SiO2.

Example B24

Reference sample of polyurethane was made from PTHF 1000 and MET with index 105.

Example B25

Polyurethane was made from PTHF 1000 and MET, containing 15.0 % by weight of powder from example A3, with index 105. The finished polyurethane contained 4.7% by weight of SiO2.

Example B26

Reference sample of polyurethane was made from PTHF 2000 and Lupranat 134-7 with index 105.

Example B27

Polyurethane was made from PTHF 2000, containing 15.0 % by weight of powder from example A3, and Lupranat 134-7 with index 105. The finished polyurethane contained x% by weight of SiO2. Example B28

Reference sample of polyurethane was made from Lupranol 2090 and Suprasec 2018 with index 105.

Example B29

Polyurethane was made from Lupranol 2090, containing 16.0 % by weight of powder from example A18, and Suprasec 2018 with index 105. The finished polyurethane contained 10.8% by weight of SiO2.

Example B30

Polyurethane was made from Lupranol 2090, containing 16.0 % by weight of powder from example A19, and Suprasec 2018 with index 105. The finished polyurethane contained 10.8% by weight of SiO2.

Table 3. The Effect of Small Particles of Silica and Index on the Mechanical Properties of Polyurethane Polymers

Table 4 Polyols and lsocyanates used in the Examples

Claims

Claims
1. A process for making silica particles, comprising the following steps:
1) An alkali stabilized silica sol with a particle size in the range from 8 to 250 nm is diluted to at most 40 % SiO2 with water and/or a water-soluble organic solvent,
2) A silane and/or an organic compound, selected from polyols und dicarboxylic acids, is pumped into the agitated sol of step 1, which is maintained at a temperature between 20 and 75 0C,
3) The sol of step 2 is deionized by contacting it with anion and cation exchange resins
4) The silylated, deionized sol of step 3 is dried by evaporating the water, preferably under vacuum or in an air stream,
5) optionally, the dried sol of step 4 is milled to a fine powder,
whereby at least two of the steps 2), 3) and 4) may be carried out in a different order.
2. A process according to claim 1, wherein the silane is used in a mixture of water and or a water-soluble solvent.
3. A process according to claim 1 or 2, wherein the silane is dissolved in a lower aliphatic alcohol.
4. A process according to any of claims 1 to 3, wherein the pH of the diluted sol of step 1 is between 8.0 and 10.5.
5. A process according to any of claims 1 to 4, wherein the pH in step 3 is below 10.0.
6. A process according to any of claims 1 to 5, wherein the silane in step 2 has the general formula RSiX3 and where R is a non-hydrolyzable group that may be organo- reactive or nonorgano-reactive and X is a methoxy or an ethoxy group.
7. A process according to any of claims 1 to 5, wherein the silane in step 2 has the general formula R2SiX2 and where R is a non-hydrolyzable group that may be organo- reactive or nonorgano-reactive and X is a methoxy or an ethoxy group.
8. A process according to any of claims 1 to 5, wherein the silane in step 2 has the general formula R3SiX and where R is a non-hydrolyzable group that may be organo- reactive or nonorgano-reactive and X is a methoxy or an ethoxy group.
9. Silica particles obtainable by a process according to any of claims 1 to 8.
10. Silica particles according to claim 9, comprising amorphous, dense, essentially non- aggregated silica spheroids with a diameter of 8 - 250 nm.
11. Silica particles according to claim 9 or 10, wherein the surface of which having been modified by having organic molecules attached to the particle surface.
12. Silica particles according to claim 11 , wherein said organic molecules are adsorbed onto the particle surface.
13. Silica particles according to claim 11 or 12, wherein said organic molecules are polyols, dicarboxylic acids or diamines.
14. Silica particles according to any of claims 11 to 13, wherein said organic molecules are silane groups chemically bonded to the particle surface.
15. A method for the manufacture of a polymeric material, comprising reacting a) a first component with b) a second component and optionally other components, characterized in that said first component is a polyol, said second component is an isocyanate, dicarboxylic acid or a diamine and that c) small particles of silica from a dispersible silica powder according to any of claims 9 to 14, are mixed into at least one of the said components prior to the reaction.
16. A method according to claim 15, in which the polymeric material is polyurethane, including urethane-based thermoplastic elastomers.
17. A method according to claim 15, in which the polymeric material is polyester, including ester-based thermoplastic elastomers.
18. A method according to claim 15, in which the polymeric material is polyamide, including amide-based thermoplastic elastomers.
19. A method according to any of claims 15 to 18, wherein said small particles of silica constitutes up to 25 % of said polymeric material.
20. A method according to any of claims 15 to 19, wherein said polymeric material is selected from the group consisting of urethane based polymers, including urethane based thermoelastomers, and polyurea polymers containing urethane groups.
21. A method according to any of claims 15 to 20, wherein said other components are chain extenders, branching agents, cross-linking agents, catalysts, foaming agents and/or defoaming agents.
22. A polymeric material obtainable by a method according to any of claims 15 to 21.
23. A method for the manufacture of a thermoplastic polymer comprising incorporating the powder, in the molten polymer, preferably in an extruder.
24. The use of particles or powder of silica, according to any of claims 9 to 14 as filler for the production of polymeric material.
25. The use of particles or powder of silica, according to any of claims 9 to 14, as filler for liquid lubricants, fuels or waxes.
26. The use of a polymeric material according to claim 22 for the production of flexible and rigid foams, fibers, coatings and cast elastomers.
27. The use of according to claim 25, wherein the polymeric material is a polyurethane material.
PCT/EP2006/062406 2005-06-01 2006-05-18 Dispersible silica particles WO2006128793A1 (en)

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