0’
`
`Europaisches Patentamt
`European Patent Office
`Office européen des brevets
`
`63 Publication number:
`.
`.
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`'
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`O 263 428 '
`A2
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`®
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`EUROPEAN PATENT APPLICATION
`
`@ Application number: 871142535
`
`@ Int. 01.4; C090 3/82 , 009D 3/84
`
`@ Date of filing: 30.09.87
`
`'
`
`@ Priority: 03.10.86 us 914856
`03.10.86 us 914857
`03.10.86 us 914858
`03.10.86 us 914859
`03.10.86 us 914860
`03.10.86 us 914920
`03.10.86 us 915344
`03.10.86 US 915346
`
`@ Date of publication of application:
`_ 13.04.88 Bulletin 88/15
`
`Designated Contracting States:
`DEESFR GBITNLSE
`
`® Applicant: PPG INDUSTRIES, INC.
`One PPG Place
`
`Pittsburgh Pennsylvania 15272(US)
`
`(72) Inventor: Lin, Chia-Cheng
`3273 Cramlington Drive
`Gibsonia, Pa. 15044(US)
`Inventor: Yoldas, Bulent Erturk
`1605 Jamestown Place
`
`.
`
`-
`
`Pittsburgh, Pa. 16201 (US)
`Inventor: Hunia, Robert Michael
`FLD. 7, Box 46
`
`Kittanning, Pa. 16201 (US)
`Inventor: Basil, John Darwin
`504 Rainier Drive
`
`Pittsburgh, Pa. 15239(US)
`Inventor: Falleroni, Charlene Ann
`152 Melwood Drive
`
`New Kenslngton. Pa. 15068(US)
`
`Representative: Stemagel, Hans-Ganther, Dr.
`et al
`
`Patentanwalte Dr. Michael Hann Dr. H.-G.
`Sternagel Sander Aue 30
`D-5060 Bergisch Gladbach 2(DE)
`
`
`
`@ Organoslloxane/metal oxide coatings.
`
`(57) An organoalkoxysilane/alumina sol-gel composition and method for its production are disclosed whereby an
`aluminum alkoxide is hydrolyzed in water to form a sol. to which is added a hydrolyzable organoalkoxysilane of
`the general formula
`N FixSi(OR') a,
`wherein F1 is an organic radical, R' is a low molecular weight alkyl radical. and x is at least 1 and less than 4.
`”The composition is dried and cured to form an organosiloxane/alumina monolith or coating on a substrate. An
`Norganoalkoxysilane/metal oxide sol-gel composition and method for its production are disclosed whereby an
`Vorganoalkoxysiiane is partially hydrolyzed in organic solution and reacted with alkoxide of the general formula M-
`m(OR")4 wherein M is aluminum, titanium. zirconiu. etc. or mixtures thereof and R' is a lower alkyl radical. The
`@composition is hydrolyzed. dried and condensed to form an organosiloxane/metal oxide abrasion-resistant
`coating on a substrate. An ultraviolet radiation resistant coating is disclosed comprising cerium oxide in an
`cinorganic oxide matrix formed by the hydrolysis and condensation of an alkoxysilane and/or other metal alkoxide.
`A method is disclosed for making an organoalkoxysilane/metal oxide sol-gel composition in an essentially
`maqueous medium by partially hydrolyzing an organoalkoxysilane with a limited amount of water which is
`essentially completely consumed in the hydrolysis reaction, adding a metal alkoxide of titanium or zirconium to
`the essentially anhydrous partially hydrolyzed organoalkoxysilane, completely reacting the metal alkoxide with
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`0 263 428
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`the partially hydrolyzed organoalkoxysilane to form an oxide network and then completely hydrolyzing the
`composition in water. A method of removing residual organic material from inorganic polymers prepared from
`alkoxides by a sol-gel process is disclosed, wherein the dried gel is treated with aqueous fluid to effect solid-
`state hydrolysis of residual alkoxy groups. Organic-inorganic hybrid polymers and a method of making them by
`reaction of organic monomers with organofunctional alkoxysilanes are disclosed. A composition and method are
`disclosed for forming an oxide film containing silicon and tin on a» substrate surface involving a composition
`comprising a partially hydrolyzed alkoxysilane and an organotin compound, and thermal reaction thereof.
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`0 263 428
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`ORGANOSILOXANE/METAL OXIDE COATINGS
`
`Field i th invention
`
`The present invention relates generally to the art of abrasion-resistant coatings. and more particularly to
`the art of abrasion-resistant inorganic coatings on abrasion-prone organic substrates.
`
`Background
`
`_
`
`A number of patents to Yoldas and other dislose sol-gel compositions containing various components.
`U.S. Patent Nos. 3,941,719 and 3,944,658 to Yoldas relate to alumina sol-gels. U.S. Patents No. 4,208,475
`and 4,244,986 to Paruso and Yoldas describe a liquid polymer formed from organometallic sodium and
`aluminum compounds.
`U. S. Patent No. 4,271,210 to Yoldas discloses a method of forming an optically clear, porous metal
`oxide layer having a low refractive index on a glass substrate by dipping the substrate into a clear colloidal
`solution of metal alkoxide.
`,
`_
`-
`US. Patent No. 4,278,632 to Yoldas discloses a method of forming a clear vitreous gel of silica-titania
`binary by preparing a clear organic solvent solution of partially hydrolyzed alkoxide of either silicon or
`titanium and then adding the other element in the form of alkoxide or a clear organic solvent solution of
`partially hydrolyzed alkoxide. The components are reacted. additional water is added to complete hydrolysis
`and the resulting product is then dried and heated to remove residual organic material.
`U. S. Patent No. 4,286,024 to Yoldas discloses a high temperature resistant transparent monolithic
`member or coating consisting of aluminum and silicon in a ratio of about 2:1 and in reacted oxide form,
`formed by reacting precursor alkoxides of aluminum and silicon in the presence of water to form a clear
`solution, gelling the reacted precursors, and drying the gel in the form of a monolithic member ‘or coating
`on a substrate. The dried material is then heated to evolve all residual hydrogen, carbon and water and to
`eliminate porosity.
`'
`U.S. Patent No. 4,346,131 to Yoldas discloses polymerized solutions for depositing optical oxide
`coatings prepared by reacting metal alkoxide with a mixture of critical amounts of water and/or acid in an
`alcohol medium. The alkoxides may be titanium, tantalum and/or silicon.
`According to these patents, hydrolytic polycondensation of metal alkoxides produces polymeric species
`containing alkoxy and hydroxyl pendent and terminal groups. Typical sol-gel compositions contain about 10
`to 40 percent by weight organic and hydroxyl components. Heat treatment is carried out at sufficiently high
`temperature, generally around 500°C. to remove residual organic material.
`Optical quality abrasion resistant coated plastic materials generally require a coating that protects the
`substrate from the damaging effects of ultraviolet
`(UV) radiation. Protection from ultraviolet radiation is
`especially important
`for polycarbonate. since hydrolytic degradation is apparently accelerated by UV
`exposure. Conventional UV stabilizers do not
`impart sufficient protective capacity to abrasion resistant
`coatings. as sufficient amounts of most typical organic UV absorbers cannot be added to abrasion resistant
`coatings without adversely affecting hardness and adhesion of the coating. Moreover, typical UV absorbers
`may gradually become deactivated after prolonged exposure, and also may gradually be leached from the
`composition.
`
`Summary at me invention
`
`The present invention provides an abrasion-resistant coating composition comprising an organoalkox-
`ysilane and a hydrolyzable compound of a metal such as titanium or zirconium. Such a composition is
`formed by producing active soluble and polymerizable titanium or zirconium species from titanium or
`zirconium alkoxides and dispersing or polymerizing the titanium or zirconium species into silicon-oxygen
`networks of organosiloxane polymers via reaction with silanol groups. The presence of titanium or zirconium
`in the polymer network modifies such. properties as the hardness and refractive index of the polymer. When
`such a titanium or zirconium modified polymer coating is applied to a plastic substrate surface. the coating
`increases the chemical resistance, index of refraction and blocking of ultraviolet radiation. in addition to the
`abrasion resistance.
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`The present invention also involves the preparation of silane/alumina sol-gel compositions by adding an
`organoalkoxysilane into an aqueous alumina sol prepared from a hydrolyzable aluminum alkoxide. The
`organoalkoxysilane hydrolyzes and condenses with the hydrolyzed aluminum alkoxide to form a
`siloxane/alumina copolymer with an organic constituent. The organosiloxane/alumina compositions of the
`present invention may further comprise a pigment or blend of pigments in order to form a non-porous
`durable paint which can be applied by conventional methods and cured conveniently at temperatures as low
`as 80°C.
`
`The present invention. in addition to providing abrasion resistance, involves also optimizing a variety of
`properties such as alkali resistance. adhesive strength. chemicai resistance. water stability and index of
`refraction for optical coatings. The present invention. encompasses a multi-cornponent system combining an
`organoalkoxysilane composition with a combination of other components such as hydrolyzable alkoxides of
`aluminum. titanium, tantalum. hafnium and the like to form an inorganic oxide polymer network optimizing
`overall performance. The organoalkoxysilane/mixed metal alkoxides composition can be coated on glass,
`metals and ceramics. as well as on plastics. not only for abrasion resistance, but also for chemical
`resistance, 6.9.. to alkali or oxidation. The organoalkoxysilane/mixed metal alkoxides composition may also
`function as a carrier and binder for pigments to form opaque and/or colored coatings. An important feature
`of the present invention is that the proportion of metal alkoxides can be selected to produce a coating with
`_a desired refractive index, e.g., to match a transparent substrate.
`The present invention provides protection for underlying plastic substrates such as polycarbonate from
`damaging ultraviolet radiation by means of transparent coatings containing cerium oxide, a stable strongly
`ultraviolet absorbing species. The transparent cerium Oxide containing UV protective coatings of the present
`invention are formed from aqueous sols containing colloidal cerium oxide in addition to alkoxides of silicon
`and/or other metals which hydrolyze and polymerize by condensation to form a film in which the cerium is
`incorporated in the oxide network of the coating.
`The present invention further provides a method for incorporating metal such as titanium or zirconium
`into the polymer network structure of an organoalkoxysilane in an aqueous medium. The method of the
`present invention involves initial partial hydrolysis of the organoalkoxysilane, reaction of a metal alkoxide of
`titanium or zirconium with essentially anhydrous partially hydrolyzed organoalkoxysilane, and final complete
`hydrolysis of the sol-gel composition. The aqueous compositions of the present invention deposit harder,
`more abrasion-resistant. and higher optical quality coatings than organic solvent compositions.
`The present invention provides for the removal of residual organic material from sol-gel compositions
`by means of chemical reaction at or near ambient temperature by treating a formed gel monolith or thin film
`with water, containing a catalyst if needed, to effect solid-state hydrolysis of residual organic groups. By
`avoiding removal of organic material from sol-gel compositions by means of thermal decomposition, the
`present invention prevents gel degradation and carbon deposits which adversely affect sol-gel composi-
`tions. Further. since high temperatures are avoided. application of sol-gel compositions is not limited to high
`temperature resistant substrates in accordance with the present invention. Furthermore. polymerization and
`densification continues in the solid state under the conditions of the present invention.
`Organic-inorganic hybrid polymers in accordance with the present invention are prepared by poly-
`merizing an organic monomer in the presence of an inorganic oxide sol comprising an organoalkoxysilane
`having an organic functional group capable of reacting with said organic monomer.
`Transparent oxide films containing silicon and tin are applied to glass by spraying on a hot glass
`surface an alcohol sol containing partially hydrolyzed alkoxysilane and an organotin compound in accor-
`dance with the present invention.
`
`
`Detailed Description o_f the Preferred Embodiment
`
`A sol-gel system for producing an organosiloxane/alumina composition may be prepared in the
`following manner. First, an aluminum alkoxide is hydrolyzed using water as solvent. The temperature is
`preferably maintained at about 80°C during hydrolysis to prevent the formation of insoluble bayerite.
`Various hydrolyzable aluminum alkoxides may be used to form a sol
`in accordance with the present
`invention. Preferably. aluminum alkoxides are of the general formula Al(0Fl)3. wherein R is preferably an
`alkyl radical of the general formula CannH wherein n is from 2 to 4. Aluminum isopropoxide is a
`particularly preferred aluminum alkoxide. Preferably, aluminum isopropoxide is added to water which has
`been heated to 80°C. followed by an acid hydrolyzing agent. Various acids may be used in accordance
`with the present invention; both inorganic acids. such as nitric and hydrochloric acids, and organic. such as
`acetic and dichloroacetic acids. The basic hydrolysis reaction is illustrated below.
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`O 263 428
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`AI(OR)3 + szO-°Al(OR)3.y(OH)y + yFtOH
`The condensation reaction. may involve alkoxy and/or hydroxyl groups. and produce water or alcohol
`according to either of the following reactions.
`-
`2 Al(OR)3.y(OH)y-°(HO)y(RO)3_,_.Al-O-AI(OR) “(OHM + ROH
`or
`
`2 Al(OFl)3.y(OH)y-°(H0)y.1(RO)3.yAl-O-AI(OR) 3.5,(OH),,.1 + H20
`The hydrolysis and condensation reactions continue until substantially all of the alkoxy groups are
`hydrolyzed. and condensation yields a composition of aluminum-oxygen network containing pendent and
`terminal hydroxyl groups. having the empirical formula AIO(OH).
`In one preferred embodiment of the present invention. the aluminum alkoxide is added to 80°C water in
`a pressure vessel. After the acid is added. the vessel is sealed. and the mixture is heated under pressure.
`Using aluminum isopropoxide. heating to 125°C for two hours. the pressure reaches about 50 psi. A clear
`sol
`is formed in hours under pressure, compared with days at ambient pressure. and precipitation of
`insoluble aluminum hydroxide is avoided.
`In a preferred embodiment of this invention. an alumina sol condenses to form a gel which is weakly
`crosslinked. such that when the gel is heated to approximately 60°C in a closed container, it converts back
`to a clear sol. The reformed sol will gel again within about 72 hours at room temperature. This reversible
`characteristic provides an alumina sol-gel composition with a relatively long shelf life.
`After preparation of the alumina sol. an organoalkoxysilane is added. The organoalkoxysilane reacts with
`the hydrolyzed alumina sol to form a silicon-oxygen-aluminum network according to the folI0wing general
`reaction.
`‘
`
`AIO(OH) + RxSi(OR’)4-x-°'O'AI'O‘Sin(ORI)4-x-1 + Fl'OH
`In an aqueous alumina sol. the remaining alkoxy groups of the organoalkoxysilane are hydrolyzed according
`to the following general reaction
`‘
`-O-Al-0-Sin(OR’)4.,...
`4- (4-x-1)HzO-e-O-Al-O-Sin(OH)4.,.., + (4-x-1)R'OH
`Various organoalkoxysilanes may be used in accordance with the present invention. Organoalkoxysilanes of
`the general formula Fl,.Si(OFi’)...x wherein x is less than 4 and preferably is one. R is an organic radical. and
`R' is a low molecular weight alkyl radical are preferred. R is preferably a low molecular weight. preferably
`from one to six carbon. alkyl or vinyl. methoxyethyl. phenyl, y-glycidoxypropyl or rmethacryloxypropyl. R’
`is preferably a two to four carbon alkyl group. Particularly preferred organoalkoxysilanes are those wherein
`R is methyl and R’ is ethyl; a most preferred organoalkoxysilane is methyl triethoxysilane. The organoalkox-
`ysilane is preferably added in an amount such that the molar ratio of silica (SiOz) to alumina (A1203) is from
`about 10:1 to about 1:1. more preferably from about 6:1 to 3:1. The resulting organosiloxane/alumina sol is
`useful as a coating composition for application to a substrate surface.
`In one embodiment of
`the present
`invention. a transparent. colorless organoalkoxysilane/alumina
`composition may be applied to a plastic transparency by any of a variety of methods such as spinning.
`spraying. dipping or flowing to form a continuous coating. Upon drying and curing at about 100°C. a
`durable. glassy coating is formed which improves the surface properties of the plastic transparency.
`Preferred coating thickness is in the range of about
`1
`to 20 microns. A coating about 5 microns thick
`provides a protective surface comparable to a glass surface in abrasion resistance. Bayer abrasion testing
`of the coated surface involves abrading the coated surface with 1000 grams of quartz sand in the 6 to 14
`mesh size range for 300 cycles according to ASTM F-735 and comparing the transmittance and haze
`before and after abrasion.
`
`the
`to
`added
`be
`pigments may
`invention.
`present
`the
`of
`embodiment
`another
`In
`organoalkoxysilane/alumina sol, which may be applied. dried and cured as a translucent or opaque paint on
`a variety of substrates. Preferably pigments include inorganic oxides such as colored metal oxides and
`titania coated mica. Appropriate temperatures for curing the coating depend on the substrate. Preferably. if
`the coating is applied to acrylic.
`the temperature is held at about 80°C to 85°C. For coatings on
`polycarbonate. temperatures of 120°C to 130°C are preferred. Less temperature sensitive substrates. such
`as glass and metal. can be coated and cured at temperatures in the range of 250°C to. 600°C. The higher
`the temperature. the faster the cure. Preferably. the oragnoalkoxysilane/alumina composition may contain
`fillers such as talc or mica to adjust the thermal expansion of the coating to match that of the substrate in
`order to avoid cracking of the coating or crazing of the substrate. A preferred additive is mica in theoretical
`3000 mesh particle size of 5 to 10 microns in diameter by 0.5 micron thickness available as Micro Mica C-
`3000 from The English Mica Co.. Stamford, Connecticut.
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`0 263 428
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`Preferred organoalkoxysilane/alumina compositions for use as architectural coatings on glass comprise
`an alumina sol which is between 3 and 16 percent solids, and sufficient organoalkoxysilane to provide a
`molar ratio of about 10:1 to 1:1. preferably 6:1 to 3:1, silica (Si02) to alumina (Ales). Pigments and fillers
`may be added up to about a 50 percent solids level. The resulting coating composition is preferably
`sprayed or flow coated onto a glass sub strate surface. The coated surface may be heated in an oven or
`under infrared heaters. preferably to at least about 250° F (about 121 °C), more preferably to about 500°F
`(about 260° C). to cure the coating All of the water and organic solvent is removed,
`leaving an oxide-
`containing network containing pigments and fillers, which is sufficiently dense to survive a durability test
`consisting of immersion for 24 hours in boiling water. The finish of the coafing may be matte if Inorganic
`oxide pigments are used. such as the metal oxide pigments available from the Shepherd Chemical Co. A
`glossyIfinish may be obtained by using titaniaocoated mica pigments, such as the Afflair series from E. 8: M.
`Chemical Company- A matte color finish may be made glossy with a clear glassy overcoat of a transparent
`silane-alumina composition in accordance with the present invention. Preferred opaque coatings on glass
`range from 7.5 to 12 microns in thickness.
`A multi-component organoalkoxysilane/mixed metal alkoxides composition is prepared in accordance
`with the present invention in order to provide a coating with superior abrasion resistance. as well as alkali
`resistance and chemical resistance, which can be pigmented and coated on metal. ceramic and glass
`surfaces. as well as on plastics, and the refractive index of which may be matched to that of a transparent
`substrate for optical applications.
`Preferably an organoalkoxysilane is first at least partially hydrolyzed by adding a less than equivalent
`quantity of water to an organoalkoxysilane in solution, preferably in alcohol. The organoalkoxysilane
`preferably has the general formula
`RXSKOR' 4.,
`Wherein R is an organic radical, Fi’ is low molecular weight alkyl radical, and x is at least one and less than
`4; preferably x is 1. so that the organoalkoxysilane has three hydrolyzable sites. The organic radical R is
`preferably a lower (CI,
`to Ca) alkyl or vinyl. methoxyethyl, phenyl. y-glycidoxypropyi or y-methacrylox-
`ypropyl. Preferably. R' is selected from the group consisting of methyl. ethyl, propyl and butyl. Preferred
`organoalkoxysilanes include those wherein R is methyl and R’ is ethyl. particularly methyl triethoxysilane.
`Another preferred organoalkoxysilane is y-glycidoxypropyl trimethoxysil‘ane. Mixtures of organoalkoxysilanes
`may also be preferred. Preferably about one mole of water per mole or organoalkoxysilane is added in
`alcohol medium to partially hydrolyze the organoalkoxysilane according to the general reaction
`RxSi(OR’)M + szo-rR x Si(OFi’)‘.,._,,(OH)y + yR'OH
`After the organoalkoxysilane is partially hydrolyzed. additional metal ions are incorporated in the composi-
`tion by adding hydrolyzable metal alkoxides to the partially hydrolyzed organoalkoxysilane. Preferably.
`these additional metal alkoxides include alkoxides of the general formula
`l\«1(0l=i")z
`wherein M is a metal selected from the group consisting of aluminum titanium. zirconium and mixtures
`thereof. 2 is the valence of M and R' is a low molecular weight alkyl radical. preferably ethyl, propyl or
`butyl.
`In addition to aluminum, titanium and/or zirconium, other metal alkoxides including such metals as
`tantalum. hafnium. etc., may be employed. The metal alkoxide may include an alkyl or aryl group or be in
`dimer or higher condensed form so long as hydrolyzable alkoxy groups remain reactive with silanol groups
`of the partially hydrolyzed organoaikoxysilane to copolymerize.
`When metal alkoxides or alkylalkoxides are introduced into the partially hydrolyzed organoalkoxysilane,
`the hydrolyzable alkoxy groups react with the hydroxyl bonds of the partially hydrolyzed organoalkox-
`ysilane. condensing to form an inorganic oxide network and producing alcohol according to the general
`reaction:
`
`_
`
`IR'
`st
`_R
`
`_
`
`i’R'
`-
`n _
`n
`_
`OH + R o M(OR )2-1 a I31
`R
`
`_=
`
`=_
`n
`n
`0 M(0R )Z_1 + R on
`
`Once the metal alkoxide is reacted with the organoalkoxysilane by this reaction, the composition may be
`fully- hydrolyzed by the addition of water, converting the alkoxy groups OR’ and OR” to hydroxyl groups
`without precipitation of insoluble metal hydroxides. Condensation polymerization proceeds to extend the
`inorganic oxide network. The composition may then be diluted with either water. alcohol or other suitable
`solvent to the concentration desired for applying a coating to a substrate. Using titanium alkoxides in
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`conjunction with zirconi urn. aluminum and silicon alkoxides in various ratios provides coatings with
`refractive indices within the range of 1.4 to 1.85 for optical coating applications.
`In a preferred embodiment of the present invention. an alkoxide is partially hydrolyzed before adding an
`aqueous sol of colloidal cerium oxide. Preferably, the alkoxide is an alkoxysilane of the general formula Ftx
`Si(OR')¢,. wherein R is an organic radical, R’ is selected from the group consisting of low molecular weight
`alkyl radicals, and x is less than 4 and may be zero. The organic radical of Ft is preferably alkyl. vinyl.
`methoxyethyl, phenyl. Tglycidoxypropyl. or rmethacryloxypropyl. The alkoxide hydrolyzes according to
`the general reactions
`
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`
`-
`l=i,.Si(OR').ax + szO R xSi(OR‘)4.,..y(OH)y + yR'OH.
`Condensation of the hydrolyzed alkoxide proceeds according to the general reaction
`
`Y
`'
`l
`ZRxSi(OR )4_x_y(0H)y-9»Rxs1(0R )4-x-y(OH)y-l + R OH
`
`0l
`
`RxSi(OR')4_
`
`x-y-l
`
`(0H)y
`
`'
`I
`ZRxSi(OR )4_x_y(0H)Y-€>Rxfi(0R )4_x_y<0H)y_l + 320
`o
`I
`RxSi(OR )4.X_y(oa)y_1
`
`Further hydrolysis and condensation follow.
`The pH and/or degree of condensation of the alkoxides may be adjusted. if necessary. to prevent haze
`or precipitation upon mixing with the ceria sol. The cerium oxide sol preferably comprises about 10 to 30
`percent by weight colloidal cerium oxide in water. with the colloidal cerium oxide particle size sufficiently
`small to minimize scattering of visible light. preferably less than 30 to 40 nanometers. most preferably less
`than 10 nanometers. Alkoxides of titanium and/or zirconium may also be included in compositions of the
`present
`invention. as well as colloidal silica for abrasion resistance. The ultraviolet radiation protection
`provided by the cerium oxide containing coating of the present invention may be determined by measuring
`the UV absorbence spectrum of the coating applied on a quartz substrate.
`An aqueous composition of organoalkoxysilane and metal alkoxide is prepared by first partially
`hydrolyzing an organoalkoxysilane with water. A less than equivalent quantity of water is added to an
`organoalkoxysilane of the general formula RxSi(OFl’)4.xwherein R is an organic radical. R’ is a low molecular
`weight alkyl radical. and x is at least one and less than four. Preferably x is one. so that the organoalkox-
`ysilane has three hydrolyzable sites. Partial hydrolysis requires. in this case. less than three moles of water
`per mole of monomeric organoalkoxysilane. Preferably. about one mole of water is added to partially
`hydrolyze the preferred organoalkoxysilane according to the following general reaction
`RxSi(OFl')4.x + yH20~R xSilOFl’).._,..,.(OH)y + yR’OH
`Because the organoalkoxysilane and water are immiscible. a small amount of cosolvent is preferably added.
`Preferably. a small amount of alcohol is added to promote miscibility and. if necessary, a small amount of
`catalyst such as nitric acid to accelerate hydrolysis. Preferred organoalkoxysilanes are those wherein x is 1.
`R is selected from the group consisting of lower (preferably one to six carbon) alkyl or vinyl. methoxyethyl.
`phenyl. y-glycidoxypropyl and Tmethacryloxypropyl and R’ is selected from the group consisting of methyl.
`ethyl. propyl and butyl. Mixtures of organoalkoxysilanes may be preferred. It is crucial to the practice of the
`invention that during the initial partial hydrolysis of the organoalkoxysilane, essentially all of the water is
`consumed in the hydrolysis step. It is also crucial that the partially hydrolyzed organoalkoxysilane cannot be
`allowed to stand so long that the condensation polymerization reactions
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`
`.
`7
`V
`2Rxsl(0R )4_x_y(OH)y-fi RXS'HOR )4-X-y(OH)y—1 + H20
`
`0l
`
`RxSi (0R
`
`'
`
`) 4-x-y
`
`(
`
`on
`
`)y_1
`
`V
`V
`(omyfi RxsiCOR )4_x__y_1(oa)y + R OH
`
`O l
`
`R SiCOR')
`x
`
`4-x-y(
`
`0H
`
`) y— 1
`
`_
`
`or
`
`5
`
`1D
`
`15
`
`I
`ZRXSHOR )
`
`4-x-y
`
`proceed to eliminate active silanol groups needed for reaction with the titanium or zirconium alkoxides to be
`added.
`'
`~
`ions into the organoalkoxysilane network by the
`The second step involves incorporation of metal
`2H addition of a metal alkoxide of the general formula MlOR’)z wherein M is preferably titanium or zirconium.
`Ft“ is a low molecular weight alkyl radical, preferably containing two to four carbons. and z is the valence of
`M“ The metal alkoxide may comprise an alkyl or aryl radical and may be in dimer or higher condensed form
`so: long as the alkoxide contains hydrolyzable groups reactive with silanol groups to copolymerize Because
`titanium and zirconium alkoxides also hydrolyze in water. and form insoluble hydroxide species which
`25, precipitate from an aqueous medium, the titanium or zirconium alkoxide must be added to the partially
`hydrolyzed organoalkoxysilane in the essential absence of water. The addition of titanium or zirconium
`alkoxide to the partially hydrolyzed organoalkoxysilane results in the copolymerization of an inorganic oxide
`network wherein titanium or zirconium ions are interspersed with silicon according to the following general
`reaction
`
`30'
`
`35
`
`4a
`
`45
`
`50
`
`55
`
`Y
`1'
`II
`RxSiCOR )4—x-yy(OH) + M(OR )4——)RXIS'.1'.(OR')4_._x_y(Oi:I)y_l + R OH .
`‘I’
`M(OR") z-
`
`The copolymerization reaction must proceed essentially to completion. i..e essentially all the titanium or
`zirconium alkoxide must be reacted into the polymer network. TItanium or zirconium may also be
`introduced into the partially hydrolyzed organoalkoxysilane in the form of clear polymer solutions wherein
`hydrolyzable alkoxy groups remain reactive with silanol groups of the partially hydrolyzed organoalkox-
`ysilane.
`The final step involves addition of a large quantity of water to essentially completely hydrolyze the
`composition. i.e., all remaining hydrolyzable groups of either the silane or the titanium or zirconium alkoxide
`are hydrolyzed according to the general reaction:
`
`R Si(OR')
`x3)
`H
`l
`M(OR )z_1
`
`4-x—y
`
`+ H O ———> RxS|i(OH)
`(in excess)
`x0
`I
`Mwlil)?”1
`
`4 X y
`
`+ R'OH + R"OH
`(in various quantities)
`
`Because any unincorporated titanium or zirconium alkoxide would hydrolyze to form insoluble hydroxides
`which would precipitate from the aqueous medium. the water must be added in the essential absence of
`unreacted titanium or zirconium alkoxide.
`
`The resultant composition is an essentially aqueous organoalkoxysilane/metal oxide sol-gel composition
`which may be dried and cured to form an inorganic oxide network according to the following condensation
`polymerization reaction
`
`

`

`0 263 428
`
`2R Si OH
`xi
`(
`0
`
`)4—x-y""' ?
`
`M(OH) z_ 1
`
`‘?
`.°
`9
`‘i
`R Si-O-M—O—Si—O-M-O-
`XI
`l
`|
`l
`0
`O
`0
`0
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`the oxide network. The
`ions are proportionately dispersed throughout
`wherein silicon and metal
`siloxane/metai oxide polymer may be in the form of a monolithic article, or may be applied as a coating
`composition to the surface of a substrate to form a glassy film. Applied to a plastic substrate such as
`polycarbonate or acrylic. a silane/metal oxide coating of the present invention has superior abrasion
`resistance to that of a silane/aiumina or other organic solvent based abrasion resistant coating.
`Preferably.
`the fully hydrolyzed composition is applied by any conventional procedure such as
`spraying. dipping or flow coating onto a surface of a substrate. The coating composition is dried to remove
`alcohol and water solvents. and then heated to promote the continued condensation polymerization of the
`composition. and curing to a dense glassy abrasion resistant film.
`,
`However. the inorganic polymer still contains some residual alkoxy groups. When the composition is
`subsequently fired to density the inorganic polymer, and residual organic material will be eliminated by
`thermal decomposition. However, thennal decomposition of residual organic material may result in carbon ,
`deposits which blacken the inorganic polymer and degrade the integrity of the metal/oxide network.
`In accordance with the present invention. the dried gel. whether in monolithic or coating form, is treated
`with water or other aqueous solvent, such as inorganic acid or hydrogen peroxide. to remove residual
`organic material by solid-state hydrolysis before the gel
`is fired. Thus.
`the inorganic polymer is not
`blackened or degraded by carbon deposition. When the composition is dried to remove the solvent. the
`alcohol and water formed in the hydrolysis and condensation reactions are removed as well.
`Substrates which can be improved in their abrasion resistance and other properties with the
`organoalkoxysilane/metal oxide compositions of the present invention include polycarbonate and acrylic,
`particularly as used for vehicle transparencies. Abrasion resistance is measured by ASTM F-735 abrasion
`testing (Bayer abrasion) using 1000 grams of quartz sand of 6 to 15 mesh size range for 300 cycles.
`Coating compositions of the present invention may also be used on nonplastic susbtrates such as glass,
`ceramics and metals to improve corrosion resistance or other properties.
`Organic-inorganic hybrid polymers in accordance with the present invention are prepared by poly-
`merizing an organic monomer in the presence of an inorganic oxide sol comprising an organoalkoxysilane
`having an organic functional group capable of reacting with said organic monomer. The functional group of
`R is selected in accordance with the organic monomer to be subsequently polymerized. A preferred
`functional group is acryloxy’ for reaction with an acrylic monomer capable of polymerization to an acrylic
`polymer. A preferred organoalkoxysilane for producing hybrid polymers is 7—methacryloxypropyl trimethox-
`ysilane.
`
`A coating composition