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WO2015170163A2 - A modified coating composition - Google Patents

A modified coating composition Download PDF

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Publication number
WO2015170163A2
WO2015170163A2 PCT/IB2015/000655 IB2015000655W WO2015170163A2 WO 2015170163 A2 WO2015170163 A2 WO 2015170163A2 IB 2015000655 W IB2015000655 W IB 2015000655W WO 2015170163 A2 WO2015170163 A2 WO 2015170163A2
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WO
WIPO (PCT)
Prior art keywords
coating composition
modified coating
modifier
modified
solvent
Prior art date
Application number
PCT/IB2015/000655
Other languages
French (fr)
Other versions
WO2015170163A8 (en
WO2015170163A3 (en
Inventor
Soumen Sensarma
Someshwarnath PANDEY
Ramesh Kumar VERMA
Original Assignee
Tata Chemicals Limited
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Publication date
Application filed by Tata Chemicals Limited filed Critical Tata Chemicals Limited
Publication of WO2015170163A2 publication Critical patent/WO2015170163A2/en
Publication of WO2015170163A8 publication Critical patent/WO2015170163A8/en
Publication of WO2015170163A3 publication Critical patent/WO2015170163A3/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/61—Polysiloxanes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L51/00—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
    • C08L51/06—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers grafted on to homopolymers or copolymers of aliphatic hydrocarbons containing only one carbon-to-carbon double bond
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
    • C08G18/4266—Polycondensates having carboxylic or carbonic ester groups in the main chain prepared from hydroxycarboxylic acids and/or lactones
    • C08G18/4269—Lactones
    • C08G18/4277—Caprolactone and/or substituted caprolactone
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/62—Polymers of compounds having carbon-to-carbon double bonds
    • C08G18/6216—Polymers of alpha-beta ethylenically unsaturated carboxylic acids or of derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
    • C08G18/71—Monoisocyanates or monoisothiocyanates
    • C08G18/718—Monoisocyanates or monoisothiocyanates containing silicon
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
    • C08G18/72—Polyisocyanates or polyisothiocyanates
    • C08G18/73—Polyisocyanates or polyisothiocyanates acyclic
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
    • C08L33/04—Homopolymers or copolymers of esters
    • C08L33/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, which oxygen atoms are present only as part of the carboxyl radical
    • C08L33/062—Copolymers with monomers not covered by C08L33/06
    • C08L33/066—Copolymers with monomers not covered by C08L33/06 containing -OH groups
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
    • C09D175/04—Polyurethanes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2227—Oxides; Hydroxides of metals of aluminium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/002—Physical properties
    • C08K2201/003—Additives being defined by their diameter
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • C08K3/36—Silica
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/54—Silicon-containing compounds
    • C08K5/541—Silicon-containing compounds containing oxygen
    • C08K5/5415—Silicon-containing compounds containing oxygen containing at least one Si—O bond

Definitions

  • the present invention relates to a modified coating composition. Specifically, the present invention relates to a modified coating composition having improved surface properties.
  • inorganic particles in coating compositions is widely known to improve the surface properties of the coatings. Such coating compositions however are subjected to drawbacks such as - haziness, crater formation, brittleness etc. in the final coating. It is further desired that such coatings exhibit mar-resistance and resistance to environmental etching.
  • Several methods of modifying the coating compositions have been devised to achieve one or more of these properties. To be commercially successful, a coating should provide as many favorable characteristics as possible. Accordingly, it is most preferable to produce a coating that has an optimum mix of characteristics with regard to various forms of damage resistance.
  • One of such techniques employs modification of the inorganic particles such as silica by coating the particle surface with crosslinked polysiloxane coating.
  • the inorganic particles are for example, grafted with a polysiloxane coating via a crosslinking agent.
  • the existing techniques represent a compromise, usually one or more properties are partially/ completely sacrificed to increase the other.
  • EP 0832947 describes formation of a film forming binder system with improved scratch resistance.
  • the binder system consists of a crosslinkable resin and crosslinking agent.
  • the nanoscale fillers are made surface reactive by the use of dual functional crosslinking agent (carbamate or glycidyloxy silane) having reactive end groups which are reactive to the polymeric phase.
  • dual functional crosslinking agent carbamate or glycidyloxy silane
  • US 5853809 describes use of silica particle modified with carbide molecules and used in clear coats.
  • the inorganic organic hybrid mixture thus produced gives automotive coating system which gives scratch resistance.
  • the nano particles thus produced require substantial amount of nano silica particles to obtain antiscratch property while curing the film above 130 °C.
  • Nano particles were modified with suitable functional agent and resin matrix binds chemically with nano particles which often lead to the brittleness in final coating.
  • US 7641972 describes modification of nano particles by use of trimethyl terminated polydimethylsiloxane hydride coupled with vinyl trimethoxysilane. It also teaches the reaction of silaplane based compound with caprolactone based monomer followed by further functionalization with isocyanatopropyltrimethoxysilane.
  • the nano particles thus prepared is used for polyurethane based resin systems.
  • the particle thus produced shows substantial enrichment of nano particles on the surface of the final film but unable to provide substantial surface hardness to obtain anti-scratch property at a relatively low temperatures.
  • the film thus obtained also fails to exhibit , in particular, 0 hour mar resistance (i.e. immediately after baking).
  • Another limiting factor often encountered in the prior art is that silica requires higher temperature of approx. 120 °C for curing. This poses a problem specifically for automotive components made with plastics which require baking at lower temperatures.
  • Silica requires higher temperature (> than 120 °C) to obtain solid and glassy silica network at the surface of the final coated film.
  • curing a coating composition comprising silica nanoparticles at a temperature less than or equal to 80 °C does not provide the required hardness.
  • modifier systems for coating compositions which could exhibit scratch and mar resistance without embrittlement, haziness, crater formation while being curable at low temperatures. It is also desired that such coating compositions exhibit said properties while requiring less percentage loading of inorganic particles. It is further desirable that such modifier system exhibits said properties with both the IK (one- component) and 2K (two-component) coating compositions based on polyurethane/ acrylic melamine or epoxy resin etc.
  • a modified coating composition comprises a coating composition, a modifier, atleast one dispersing agent, atleast one solvent and at least one binder, wherein the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder are collectively ground to obtain nanoparticles of the modifier dispersed therein.
  • the modifier in accordance with the present invention, comprises of mixed oxide particles bonded to a silane crosslinking agent.
  • the mixed oxide particles comprise alumina and silica in a weight ratio between 30:70 and 40:60.
  • the present invention relates to a modified coating composition having improved surface properties.
  • the modified coating composition comprises-
  • the modifier comprising mixed oxide particles bonded to a silane crosslinking agent, the mixed oxide particles comprising alumina and silica in a weight ratio between 30:70 and 40:60;
  • coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder are collectively ground to obtain nanoparticles of the modifier dispersed therein.
  • milling is done to collectively ground the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder to obtain nanoparticles of the modifier dispersed therein. Milling breaks down the large agglomerates of the modifier to desired particle size.
  • milling is carried out in a milling machine including any high energy milling device.
  • ball milling is carried out.
  • the ball milling may comprise a first ball milling step followed by at least one more subsequent ball milling step, and/or other processing as appropriate.
  • the ball milling is carried out with yttrium- stabilized zirconium dioxide (YSZ) milling balls.
  • YSZ yttrium- stabilized zirconium dioxide
  • the milling balls may have a diameter in the range of 0.05 to 4 mm and preferably in the range of 0.1 to 2.3 mm.
  • ball milling is carried out with milling balls having a diameter of 0.5 mm or a combination of milling balls having diameter of 1 mm and 2.3 mm.
  • the percentage filling of the milling machine may vary from 40 to 80 % by volume and is preferably in the range of 60% by volume.
  • milling is carried at a temperature in the range of 25 to 40 °C. Preferably, milling is carried out at around 25 °C.
  • milling is carried out for a time period of 30 minutes -24 hours and preferably for 2-6 hours and more preferably for 3 hours.
  • the weight ratio of alumina and silica may be modified depending on the refractive index of the coating composition in which the modifier is to be incorporated.
  • the mixed oxide particles have an effective refractive index which is closely approximated as a volume average of the refractive indices of alumina and silica.
  • the refractive index of silica is 1.46 and that of alumina is 1.66.
  • the refractive index of the mixed oxide particles when dispersed in a coating composition may vary between 1.46 and 1.66, depending on the weight ratio of alumina and silica.
  • the weight ratio of alumina and silica may vary between 30:60 and 40:60.
  • alumina and silica are in the weight ratio of 35:65.
  • amorphous alumina having a refractive index of about 1.66 and silica having a refractive index of about 1.46 mixed in the weight ratio of 35:65 would have a refractive index of approximately 1.52 -1.54.
  • nanoparticles of the modifier when dispersed in the coating composition have a mean diameter in the range of 17 to 60 nm.
  • the dispersion of nanoparticles of modifier in the coating composition has a d90 value less than 58 nm. Keeping the particle size as well as the refractive index of the modifier in the desired range prevents interaction of incident light with the nanoparticles of the modifier. This prevents reduction of transparency of the coating compositions. It is specifically significant for clear coating compositions.
  • the shape of the mixed oxide particles may vary depending upon the intended application.
  • the nanoparticles of the modifier may be spherical, cubic, platy, or acicular (elongated or fibrous).
  • the nanoparticles of the modifier are substantially spherical in shape.
  • the mixed oxide particles may comprise a homogeneous mixture or solid state solution of alumina and silica.
  • Mixed oxide particles of alumina and silica may be prepared by any commonly known method.
  • the mixed oxide particles are prepared by mixing fumed silica powder and fumed alumina powder, followed by calcination thereof. The calcination may be carried out at a temperature in the range of 80 to 200 °C and is preferably carried out at 130 °C.
  • the silane crosslinking agent is selected from a group consisting of a reaction product of a polycaprolactone diol and an isocyanatoalkyl- trialkoxysilane, a reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride and hydroxyl terminated polydimethylsiloxane, and a combination thereof.
  • the reaction product of polycaprolactone diol and an isocyanatoalkyl-trialkoxysilane is used as the silane crosslinking agent.
  • the hydroxyl groups present in the polycaprolactone diol react with the isocyanate group present in the isocynatopropyl-trimethoxysilane to form alkoxysilane encapped polycaprolactone.
  • the said silane crosslinking agent is prepared by reacting polycaprolactone diol with an isocynatopropyl-trimethoxysilane in the presence of dibutyltin dilaurate (DBTDL) at an elevated temperature in the range of 60 to 100 °C and preferably at 90 °C for a predetermined time period. Preferably, the reaction is carried out for 90 minutes with continuous stirring.
  • DBTDL dibutyltin dilaurate
  • low molecular weight polycaprolactone diol having a molecular weight less than 550 Daltons is used in the present invention.
  • the use of a shorter polycaprolactone diol or a low molecular weight polycaprolactone diol provides a better reaction with isocyanatoalkyl-trialkoxysilane and allows achieving higher crosslinking density.
  • isocyanatoalkyl-trialkoxysilane is reacted with polycaprolactone diol in a molar ratio in the range of 1 :1 to 2: 1.
  • isocyanatoalkyl-trialkoxysilane is reacted with polycaprolactone diol in a molar ratio of 2: 1.
  • the isocyanatoalkyl-trialkoxysilane may be selected from 3-isocyanatopropyl- trimethoxysilane and 3-isocyanatopropyl-triethoxysilane and is more preferably 3- isocyanatopropyl-trimethoxysilane. It is preferred that three reactive groups are present on the isocyanatoalkyl-trialkoxysilane.
  • the resultant silane crosslinking agent has six reactive groups present thereon. This provides higher crosslinking density when the modifier comprising crosslinking agent prepared by reacting polycaprolactone diol and isocyanatoalkyl-trialkoxysilane is cured with the coating composition.
  • a reaction product of vinyltrimethoxysilane, polydialkylsiloxane hydride and hydroxyl terminated polydimethylsiloxane is used as the silane crosslinking agent.
  • vinyltrimethoxysilane and polydialkylsiloxane hydride are reacted to form alkoxysilane encapped polydialkylsiloxane, which is further crosslinked with hydroxyl terminated polydimethylsiloxane to obtain the desired silane crosslinking agent.
  • the said silane crosslinking agent is prepared by reacting vinyltrimethoxysilane with polydialkylsiloxane hydride in the presence of hexachloroplatinic acid at an elevated temperature in the range of 60 to 100 °C and preferably at 80 °C for a predetermined time period. Preferably, the reaction is carried out for 2 hours with continuous stirring.
  • the reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride is reacted with hydroxyl terminated polydimethylsiloxane in a predetermined molar ratio to obtain the silane crosslinking agent.
  • vinyltrimethoxysilane is reacted with the polydialkylsiloxane hydride in a molar ratio in the range of 2:1.
  • the reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride is reacted with hydroxyl terminated polydimethylsiloxane in a molar ratio of 0.67.
  • the polydialkylsiloxane hydride has an alkyl substituent having 1 to 8 carbon atoms.
  • the polydialkylsiloxane hydride has an average number of siloxane groups (n) between 1 to 10.
  • the polydialkylsiloxane hydride has two terminal hydride groups attached thereon.
  • the polydialkylsiloxane hydride is polydialkylsiloxane hydride having the general formula (I), where 1 ⁇ n ⁇ 10:
  • the polydialkylsiloxane hydride may either be prepared by any known method or obtained from any commercial source.
  • low molecular weight polydialkylsiloxane hydride having a molecular weight equal to or less than 450 Da is used in the present invention.
  • Use of a shorter polydialkylsiloxane hydride or a low molecular weight polydialkylsiloxane hydride with alkene group provides a rapid transfer of hydride group onto the double bond of vinyltrimethoxysilane. It also allows achieving a higher crosslinking density when reacted with hydroxyl terminated polydimethylsiloxane.
  • the hydroxyl terminated polydimethylsiloxane has an average number of siloxane groups (r) between 1 to 10 and has a general formula (II), where 1 ⁇ r ⁇ 10:
  • the hydroxyl terminated polydimethylsiloxane may either be prepared by any known method or obtained from any commercial source.
  • the hydroxyl terminated polydimethylsiloxane having a molecular weight equal to or less than 450 Da is used.
  • Using the low molecular weight hydroxyl terminated polydimethylsiloxane further enables achieving higher crosslinking density, as desired in the present invention.
  • the use of a flexible polycaprolactone or polydialkylsiloxane based crosslinking agent introduces softness in the resultant coating and thus prevents the brittleness in the final coating.
  • polycaprolactone and/or polydialkylsiloxane increases flexibility of the crosslinked polysiloxane network. This causes a substantial reduction in the crater formation in the final coating. Also, there is increase in homogeneity of the coating composition on the surface of the final coating.
  • Polycaprolactone and polydialkylsiloxane renders further advantages such as their long chain leads to the phase separation between the inorganic nanoparticle and polycaprolactone/ polydialkylsiloxane. Further, the absence of true chemical bond between the inorganic nanoparticles and matrix of coating composition leads to migration of inorganic nanoparticles towards the surface of the final coating.
  • the inorganic nanoparticles migrate towards the coating surface also because of low bulk density. Migration of inorganic nanoparticles to surface of final coating during curing provides a further advantage that a lesser amount of inorganic nanoparticles in the range of 1 to 3 % by weight based on total weight is required , to achieve the desired surface properties. Further, the inorganic nanoparticles present on the surface of final coating provide anchoring points thereby allowing ability to re-coat the substrate with the coating composition.
  • the mixed oxide particles and the silane crosslinking agent are in a weight ratio between 20:1 and 30: 1. Preferably, the mixed oxide particles and the silane crosslinking agent are in a weight ratio of 25: 1.
  • the modifier is added to the coating composition in powdered form. This enables the curing of the coating composition at low temperature of around 80 °C, once the modifier is dispersed in the coating composition.
  • the solvent is a non-polar solvent or could be mixture of solvents.
  • the solvents are selected from a group consisting of methoxy propyl acetate, xylene, butylacetate, ethylacetate and combinations thereof.
  • the solvent is methoxy propyl acetate.
  • the solvent is present in the coating composition in an amount in the range of 55 to 80 % by weight of the total weight of the modified coating composition.
  • the binder is selected from a group consisting of polyacrylate polyol, polyetherpolyol, polyesterpolyol, polyamidepolyol, polyurethanepolyol, polysiloxanepolyol etc.
  • the binder is polyacrylate polyol.
  • the binder is present in the coating composition in an amount in the range of 10 to 20% by weight of the total weight of the modified coating composition.
  • the binder is present in the coating composition in an amount in the range of 12 to 18 % by weight of the total weight of the modified coating composition.
  • the dispersing agent is present in the coating composition in an amount in the range of 2 to 7 % by weight of the total weight of the modified coating composition.
  • the dispersing agent is BYK- 9077, commercially available from Byk-Chemie.
  • the modifier is present in the modified coating composition in an amount in the range of 0.005 to 0.01 % by weight of the total weight of the modified coating composition.
  • the coating composition may include polypropylene, polyurethane, nylon, PBT, polyimide, polyether ether ketone, Polyethylene terephthalate, PPT, polyesters, polyamide, polyacrylate, polyether, polysulphone based polymer systems.
  • the coating composition may further comprise certain additives such as UV-absorbers, defoamers, plasticizers, adhesion promoters, light stabilizers, anti-oxidants, metallic or non-metallic colouring agent, flow controllers/ enhancers, catalysts, wetting agents, leveling agents, sag control agent, organic solvent etc.
  • the modified coating composition according to the invention may be used for coating automotive parts, and other substrates including but not limited to wood, metal, alloys, ceramic and plastic.
  • the modified coating composition may be applied to a substrate as a clear or pigmented coating composition as known to those skilled in the art.
  • a method of preparing the modifier of the present invention comprises the steps of separately preparing the mixed oxide particles comprising of alumina and silica in a desired ratio, and the silane crosslinking agent; blending the mixed oxide particles with the silane crosslinking agent; heating the reaction mixture so obtained at an elevated temperature in the range of 80 to 150°C for a time period in the range of 30 minutes to 4 hours.
  • the reaction mixture is heated at 90°C for 2 hours.
  • a method of preparing the modified coating composition comprising the modifier described above is also disclosed.
  • the said method comprises of adding to the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder in a predetermined quantity and subjecting the mixture thus obtained to a milling step. Milling is carried out by ball milling the mixture with milling balls for predetermined time period. Modified coating composition is obtained once the milling is over. Milling balls are separated from the modified coating composition by filtration. The modified coating composition thus obtained may be subjected to further processing as desired.
  • any known method of coating may be used for coating the modified coating composition prepared in accordance with the present invention. These include, for example, spray coating, dip coating, roll coating, curtain coating, and the like. Although various methods of curing may be used, heat curing is preferred. Curing agents may also be added to the modified coating composition. Preferably, isocyanate based curing agents are used. Curing agents may include hexamethylene diisocyanate, toluene diisocyanate, polymer modified isocyanate, isophorone diisocyanate. One or more catalysts may also be used to accelerate the curing of the modified coating composition.
  • the coating composition prepared in accordance with the present invention can be cured at a temperature in the range of 25-140 °C.
  • the curing time will vary depending on the particular components used, and physical parameters such as thickness of the layers etc.
  • a modified coating composition comprising-
  • the modifier comprising mixed oxide particles bonded to a silane crosslinking agent, the mixed oxide particles comprising alumina and silica in a weight ratio between 30:70 and 40:60;
  • coating composition, the modifier, the at least one dispersing agent, the binder and the at least one solvent are collectively ground to obtain nanoparticles of the modifier dispersed therein.
  • Such a modified coating composition wherein the silane crosslinking agent is selected from a group comprising of a reaction product of a polycaprolactone diol and an isocyanatoalkyl-trialkoxysilane, a reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride and hydroxyl terminated polydiemethylsiloxane and a combination thereof.
  • the silane crosslinking agent is selected from a group comprising of a reaction product of a polycaprolactone diol and an isocyanatoalkyl-trialkoxysilane, a reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride and hydroxyl terminated polydiemethylsiloxane and a combination thereof.
  • Such a modified coating composition wherein alumina and silica are in the weight ratio of 35:65.
  • Such a modified coating composition wherein the nanoparticles of the modifier have a mean diameter in the range of 17 to 60 nm.
  • Such a modified coating composition wherein the mixed oxide particles and the silane crosslinking agent are in a weight ratio between 20: 1 and 30:1.
  • Such a modified coating composition wherein the modifier is added to the coating composition in powdered form.
  • Such a modified coating composition wherein the dispersing agent is BYK-9077.
  • Such a modified coating composition wherein the solvent is a non-polar solvent or a mixture of solvents.
  • Such a modified coating composition wherein the binder is polyacrylate polyol.
  • Such a modified coating composition wherein the modifier is present in the modified coating composition in an amount in the range of 0.005 to 0.01 % by weight based on total weight of the modified coating composition.
  • Such a modified coating composition wherein the dispersing agent is present in the modified coating composition in an amount in the range of 2 to 7 % by weight based on total weight of the modified coating composition.
  • Such a modified coating composition wherein the solvent is present in the modified coating composition in an amount in the range of 55 to 80 % by weight based on total weight of the modified coating composition.
  • 2K PU base coat blazing silver contains mixture of two acrylic polyol resins with one having the solid content of 54.5% and other one having 50%. Hydroxyl value of one of the film forming polyol resin is 80 and other one is 30 respectively. Apart from these, the formulations also contains component of wax dipersion, Cellulose acetate butyrate and antisettling additives. Hexamethylene diisocyanate (HMDI) was used as hardener and thinner used was a mixture of xylene, solvent C9 and butyl acetate (55:30:15). Mixture of non leafing type aluminum pigments are used to get desire color such as silver effect or sparkling effect.
  • HMDI Hexamethylene diisocyanate
  • Polyacrylate polyol 73.2 g;
  • UV absorber 0.73 ' g
  • BYK 310-Silicon flow additive 0.094 g
  • Modaflow Acrylic flow additive 0.013 g
  • ABS and metallic panels were washed with iso-propanol and allowed to dry.
  • the base coat comprising metallic silver was applied on both the panels with thickness 20 to 25 microns followed by 5 minutes flash off time.
  • clear coat as prepared above application viscosity 22 sec was sprayed on the panels with thickness 25 to 35 micron. After flash off time 5 minutes, the panels were baked at 80 °C for 30 minutes.
  • Pencil hardness was tested using Mitsubishi Uni-H pencil (pressure proofed high density lead). Scratch test (Automatically electrically operated model as per BS-3900 part Es I.S. 101-1964) mar resistance as compared to the coating composition without the modifier of the present invention. Pencil Hardnesss was tested using 720 N pencil scratch hardness tester from Sheen using pencils 9B to 9H (ISO 15184 / BS 3900 - E19). Scratch test was carried out by using 'SHEEN' UK Make Automatic Electric operated Scratch Hardness Tester (Ref: 705).
  • Example 1 Preparation of modified coating composition and coating thereof on glass plate (Silane Crosslinking agent: reaction product of polycarprolactone diol and Isocyanatopropyl- trimethoxy silane in a molar ratio of 1 :2)
  • Silane Crosslinking agent reaction product of polycarprolactone diol and Isocyanatopropyl- trimethoxy silane in a molar ratio of 1 :2)
  • the success of the reaction was confirmed by the disappearance of the isocyanate peak at 2270 cm "1 in the Infrared (IR) spectra of the product
  • Step 2 About 65 grams of fumed silica powder was brought together with 35 grams of fumed alumina powder followed by heating at 130 °C for 3 hours. 4 grams of silane crosslinking agent prepared in step 1 was mixed with the powder mixture thus obtained. This mixture was blended in a kitchen blender followed by heating at 90 °C for 2 hours.
  • Step 3 The following day 0.75 grams (i.e 1.5 wt%) of above powder mixture was mixed with 50 grams of top coat clear lacquer . To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
  • MMI Desktop Planetary Ball Miller
  • Example 2 1.5 grams (i.e. 3 wt %) of powder mixture mentioned in step 2 of Example 1 was mixed with 50 grams of top coat clear lacquer. To this solution about 168 grams of zirconia balls of sizes 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 h on a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
  • MMI corporation Desktop Planetary Ball Miller
  • IR Infrared
  • Step 2 About 65 grams of fumed silica powder was brought together with 35 grams of fumed alumina powder followed by heating at 130 °C for 3 hours. 4 grams of silane crosslinking agent prepared in step 1 was mixed with the powder mixture thus obtained. This mixture was blended in a kitchen blender followed by heating at 90 °C for 2 hours.
  • Step 3 The following day 0.75 grams (i.e. 1.5 wt %) of above powder mixture was mixed with 50 grams of top coat clear lacquer . To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at
  • Table 1 illustrates the coating characteristics of modified coating compositions prepared in aforesaid example 1, 2 and 3.
  • Table 2 illustrates the findings of the scratch test after 24 hours of curing.
  • Example 4 About 7.5 grams of modifier prepared in example 1 was added to 31.5 grams of methoxy propyl acetate along with lgram of BYK 9077 and 10 grams of polyacrylate polyol with OH value of 56. To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
  • MMI corporation Desktop Planetary Ball Miller
  • Example 5 About 7.5 grams of modifier prepared in example 1 was added to 37.5 grams of methoxy propyl acetate along with 1 gram of BYK 9077 and 4 grams of polyacrylate polyol obtained from Surya coating, Nasik with OH value of 80 (solid resin 60%). To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
  • MMI Desktop Planetary Ball Miller
  • Example 6 About 7.5 grams of modifier prepared in example 1 was added to 39 g methoxy propyl acetate along with 1 gram of BYK 9077 and 2.5 grams of polyacrylate polyol obtained from Surya coating, Nasik with OH value of 80 (solid resin 60%). To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
  • MMI Desktop Planetary Ball Miller
  • Example 7 18.75 grams of Alumina-Silica powder prepared in example 1 was added to 73.72 g methoxy propyl acetate along with 7.73 gram of BYK 9077 and 24.90 grams of polyacrylate polyol obtained from Surya coating, Nasik with OH value of 80 (solid resin 60%). The mixture was taken in a 500 ml alumina jar containing equal volume (150 mL) of zirconia balls of diameter 1 mm and 2.3 mm. 150 mL of zirconia ball of size 1 mm corresponds to 495 g weight and 150 mL of zirconia balls of size 2.3 mm corresponds to 535g weight.
  • composition coating example 4 (2.7 wt%) prepared in example composition
  • Table 3 illustrates the findings of the scratch test after 24 hours of curing.
  • Step 2 About 65 grams of fumed silica powder was brought together with 35 grams of fumed alumina powder followed by heating at 130 °C for 3 hours. 4 grams of silane crosslinking agent prepared in step 1 was mixed with the powder mixture thus obtained. This mixture was blended in a kitchen blender followed by heating at 90 °C for 2 hours.
  • Step 3 The following day 0.75 grams (i.e. 1.5wt %) of above powder mixture was mixed with 50 grams of clear lacquer . To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
  • MMI Desktop Planetary Ball Miller
  • IK lacquer acrylate-melamine formaldehyde system
  • thinner mixture of alcohols
  • modifier prepared in example 1 5 grams was mixed with 1 gram of thinner (mixture of alcohols) and 0.43 grams of the modifier prepared in example 1, in order to maintain the concentration of modifier in the lacquer at around at around 2.34% after drying.
  • This mixture was mixed properly to form a homogeneous mixture and was cast on a steel plate cleaned with isopropanol. This steel plate was left for 5 minutes for flash off and baked at 140°C for 25 minutes.
  • the surface properties of the modified coating composition prepared above were compared with a coating composition prepared without the modifier. Table 5 illustrates the findings of the tests.
  • the above disclosed modifier can be used in various polyurethane, acrylic/melaimine 2K or IK coating compositions. This can be also used in UV or thermally curable resin system to obtain remarkable surface properties.
  • the modified coating compositions prepared in accordance with the present invention exhibits desired surface properties such as improved anti-scratch, mar resistance, recoatability, high gloss retainability, barrier properties, while being curable at low temperature of around 80 °C.
  • the coating obtained by using this modifier leads to elimination of haziness and formation of crater in the final coating which is clearly not acceptable for the coating industries.

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Abstract

A modified coating composition is disclosed. Said modified coating composition comprises a coating composition, a modifier, at least one dispersing agent, at least one solvent and at least one binder, wherein the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder are collectively ground to obtain nanoparticles of the modifier dispersed therein. The modifier, in accordance with the present invention, comprises of mixed oxide particles bonded to a silane crosslinking agent. Herein, the mixed oxide particles comprise alumina and silica in a weight ratio between 30:70 and 40:60.

Description

A MODIFIED COATING COMPOSITION
FIELD OF INVENTION
The present invention relates to a modified coating composition. Specifically, the present invention relates to a modified coating composition having improved surface properties.
BACKGROUND
The use of inorganic particles in coating compositions is widely known to improve the surface properties of the coatings. Such coating compositions however are subjected to drawbacks such as - haziness, crater formation, brittleness etc. in the final coating. It is further desired that such coatings exhibit mar-resistance and resistance to environmental etching. Several methods of modifying the coating compositions have been devised to achieve one or more of these properties. To be commercially successful, a coating should provide as many favorable characteristics as possible. Accordingly, it is most preferable to produce a coating that has an optimum mix of characteristics with regard to various forms of damage resistance. One of such techniques employs modification of the inorganic particles such as silica by coating the particle surface with crosslinked polysiloxane coating. Herein, the inorganic particles are for example, grafted with a polysiloxane coating via a crosslinking agent. However, because the existing techniques represent a compromise, usually one or more properties are partially/ completely sacrificed to increase the other.
For example, EP 0832947 describes formation of a film forming binder system with improved scratch resistance. The binder system consists of a crosslinkable resin and crosslinking agent. The nanoscale fillers are made surface reactive by the use of dual functional crosslinking agent (carbamate or glycidyloxy silane) having reactive end groups which are reactive to the polymeric phase. Thus the covalent attachment of the nanoscale fillers to the polymer matrix is made possible in this procedure. One of the disadvantages of this process is that high loading of the reactive nanoscale fillers is required for gaining improved scratch resistance which also leads to high cost and brittlement of the coating.
US 5853809 describes use of silica particle modified with carbide molecules and used in clear coats. The inorganic organic hybrid mixture thus produced gives automotive coating system which gives scratch resistance. The nano particles thus produced require substantial amount of nano silica particles to obtain antiscratch property while curing the film above 130 °C. Nano particles were modified with suitable functional agent and resin matrix binds chemically with nano particles which often lead to the brittleness in final coating. US 7641972 describes modification of nano particles by use of trimethyl terminated polydimethylsiloxane hydride coupled with vinyl trimethoxysilane. It also teaches the reaction of silaplane based compound with caprolactone based monomer followed by further functionalization with isocyanatopropyltrimethoxysilane. The nano particles thus prepared is used for polyurethane based resin systems. The particle thus produced shows substantial enrichment of nano particles on the surface of the final film but unable to provide substantial surface hardness to obtain anti-scratch property at a relatively low temperatures. The film thus obtained also fails to exhibit , in particular, 0 hour mar resistance (i.e. immediately after baking). Another limiting factor often encountered in the prior art is that silica requires higher temperature of approx. 120 °C for curing. This poses a problem specifically for automotive components made with plastics which require baking at lower temperatures. Silica requires higher temperature (> than 120 °C) to obtain solid and glassy silica network at the surface of the final coated film. Thus, curing a coating composition comprising silica nanoparticles at a temperature less than or equal to 80 °C does not provide the required hardness.
Thus, there is a need to devise modifier systems for coating compositions which could exhibit scratch and mar resistance without embrittlement, haziness, crater formation while being curable at low temperatures. It is also desired that such coating compositions exhibit said properties while requiring less percentage loading of inorganic particles. It is further desirable that such modifier system exhibits said properties with both the IK (one- component) and 2K (two-component) coating compositions based on polyurethane/ acrylic melamine or epoxy resin etc.
SUMMARY
A modified coating composition is disclosed. Said modified coating composition comprises a coating composition, a modifier, atleast one dispersing agent, atleast one solvent and at least one binder, wherein the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder are collectively ground to obtain nanoparticles of the modifier dispersed therein. The modifier, in accordance with the present invention, comprises of mixed oxide particles bonded to a silane crosslinking agent. Herein, the mixed oxide particles comprise alumina and silica in a weight ratio between 30:70 and 40:60.
DETAILED DESCRIPTION
To promote an understanding of the principles of the invention, reference will be made to a particular embodiment and specific language will be used to describe the same. It will nevertheless be understood that no limitation of scope of the invention is thereby intended, such alterations and further modifications in the described product and such further applications of the principles of the inventions as disclosed therein being contemplated as would normally occur to one skilled in art to which the invention relates:
The present invention relates to a modified coating composition having improved surface properties. Specifically, the modified coating composition comprises-
- a coating composition;
- a modifier; the modifier comprising mixed oxide particles bonded to a silane crosslinking agent, the mixed oxide particles comprising alumina and silica in a weight ratio between 30:70 and 40:60;
- atleast one dispersing agent;
- atleast one solvent;
- at least one binder;
wherein the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder are collectively ground to obtain nanoparticles of the modifier dispersed therein.
In accordance with an aspect, milling is done to collectively ground the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder to obtain nanoparticles of the modifier dispersed therein. Milling breaks down the large agglomerates of the modifier to desired particle size. In accordance with an aspect, milling is carried out in a milling machine including any high energy milling device. Preferably, ball milling is carried out. In accordance with an embodiment, the ball milling may comprise a first ball milling step followed by at least one more subsequent ball milling step, and/or other processing as appropriate. In accordance with an aspect, the ball milling is carried out with yttrium- stabilized zirconium dioxide (YSZ) milling balls. In accordance with an aspect, the milling balls may have a diameter in the range of 0.05 to 4 mm and preferably in the range of 0.1 to 2.3 mm. By way of a specific example, ball milling is carried out with milling balls having a diameter of 0.5 mm or a combination of milling balls having diameter of 1 mm and 2.3 mm.
In accordance with an aspect, the percentage filling of the milling machine may vary from 40 to 80 % by volume and is preferably in the range of 60% by volume. In accordance with an aspect, milling is carried at a temperature in the range of 25 to 40 °C. Preferably, milling is carried out at around 25 °C.
In accordance with an aspect, milling is carried out for a time period of 30 minutes -24 hours and preferably for 2-6 hours and more preferably for 3 hours.
In accordance with an aspect, the weight ratio of alumina and silica may be modified depending on the refractive index of the coating composition in which the modifier is to be incorporated. The mixed oxide particles have an effective refractive index which is closely approximated as a volume average of the refractive indices of alumina and silica. The refractive index of silica is 1.46 and that of alumina is 1.66. Thus, the refractive index of the mixed oxide particles when dispersed in a coating composition may vary between 1.46 and 1.66, depending on the weight ratio of alumina and silica.
In accordance with an aspect, the weight ratio of alumina and silica may vary between 30:60 and 40:60. In accordance with a preferred embodiment, alumina and silica are in the weight ratio of 35:65. Thus, amorphous alumina having a refractive index of about 1.66 and silica having a refractive index of about 1.46 mixed in the weight ratio of 35:65 would have a refractive index of approximately 1.52 -1.54. In accordance with an aspect, nanoparticles of the modifier when dispersed in the coating composition have a mean diameter in the range of 17 to 60 nm. In accordance with a preferred embodiment, the dispersion of nanoparticles of modifier in the coating composition has a d90 value less than 58 nm. Keeping the particle size as well as the refractive index of the modifier in the desired range prevents interaction of incident light with the nanoparticles of the modifier. This prevents reduction of transparency of the coating compositions. It is specifically significant for clear coating compositions.
In accordance with an aspect, the shape of the mixed oxide particles may vary depending upon the intended application. The nanoparticles of the modifier may be spherical, cubic, platy, or acicular (elongated or fibrous). Preferably, the nanoparticles of the modifier are substantially spherical in shape.
In accordance with an aspect, the mixed oxide particles may comprise a homogeneous mixture or solid state solution of alumina and silica. Mixed oxide particles of alumina and silica may be prepared by any commonly known method. Preferably, the mixed oxide particles are prepared by mixing fumed silica powder and fumed alumina powder, followed by calcination thereof. The calcination may be carried out at a temperature in the range of 80 to 200 °C and is preferably carried out at 130 °C.
In accordance with an aspect, the silane crosslinking agent is selected from a group consisting of a reaction product of a polycaprolactone diol and an isocyanatoalkyl- trialkoxysilane, a reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride and hydroxyl terminated polydimethylsiloxane, and a combination thereof.
In accordance with an aspect, the reaction product of polycaprolactone diol and an isocyanatoalkyl-trialkoxysilane is used as the silane crosslinking agent. Herein, the hydroxyl groups present in the polycaprolactone diol react with the isocyanate group present in the isocynatopropyl-trimethoxysilane to form alkoxysilane encapped polycaprolactone. The said silane crosslinking agent is prepared by reacting polycaprolactone diol with an isocynatopropyl-trimethoxysilane in the presence of dibutyltin dilaurate (DBTDL) at an elevated temperature in the range of 60 to 100 °C and preferably at 90 °C for a predetermined time period. Preferably, the reaction is carried out for 90 minutes with continuous stirring.
In accordance with an aspect, low molecular weight polycaprolactone diol having a molecular weight less than 550 Daltons is used in the present invention. The use of a shorter polycaprolactone diol or a low molecular weight polycaprolactone diol provides a better reaction with isocyanatoalkyl-trialkoxysilane and allows achieving higher crosslinking density. In accordance with an aspect, isocyanatoalkyl-trialkoxysilane is reacted with polycaprolactone diol in a molar ratio in the range of 1 :1 to 2: 1. Preferably, isocyanatoalkyl-trialkoxysilane is reacted with polycaprolactone diol in a molar ratio of 2: 1. The isocyanatoalkyl-trialkoxysilane may be selected from 3-isocyanatopropyl- trimethoxysilane and 3-isocyanatopropyl-triethoxysilane and is more preferably 3- isocyanatopropyl-trimethoxysilane. It is preferred that three reactive groups are present on the isocyanatoalkyl-trialkoxysilane. Thus the resultant silane crosslinking agent has six reactive groups present thereon. This provides higher crosslinking density when the modifier comprising crosslinking agent prepared by reacting polycaprolactone diol and isocyanatoalkyl-trialkoxysilane is cured with the coating composition.
In accordance with an embodiment, a reaction product of vinyltrimethoxysilane, polydialkylsiloxane hydride and hydroxyl terminated polydimethylsiloxane is used as the silane crosslinking agent. Herein, vinyltrimethoxysilane and polydialkylsiloxane hydride are reacted to form alkoxysilane encapped polydialkylsiloxane, which is further crosslinked with hydroxyl terminated polydimethylsiloxane to obtain the desired silane crosslinking agent.
The said silane crosslinking agent is prepared by reacting vinyltrimethoxysilane with polydialkylsiloxane hydride in the presence of hexachloroplatinic acid at an elevated temperature in the range of 60 to 100 °C and preferably at 80 °C for a predetermined time period. Preferably, the reaction is carried out for 2 hours with continuous stirring. The reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride is reacted with hydroxyl terminated polydimethylsiloxane in a predetermined molar ratio to obtain the silane crosslinking agent. In accordance with an aspect, vinyltrimethoxysilane is reacted with the polydialkylsiloxane hydride in a molar ratio in the range of 2:1. The reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride is reacted with hydroxyl terminated polydimethylsiloxane in a molar ratio of 0.67.
In accordance with an embodiment, the polydialkylsiloxane hydride has an alkyl substituent having 1 to 8 carbon atoms. The polydialkylsiloxane hydride has an average number of siloxane groups (n) between 1 to 10. The polydialkylsiloxane hydride has two terminal hydride groups attached thereon. In accordance with a preferred embodiment, the polydialkylsiloxane hydride is polydialkylsiloxane hydride having the general formula (I), where 1 < n< 10:
Figure imgf000008_0001
The polydialkylsiloxane hydride may either be prepared by any known method or obtained from any commercial source. In accordance with an aspect, low molecular weight polydialkylsiloxane hydride having a molecular weight equal to or less than 450 Da is used in the present invention. Use of a shorter polydialkylsiloxane hydride or a low molecular weight polydialkylsiloxane hydride with alkene group provides a rapid transfer of hydride group onto the double bond of vinyltrimethoxysilane. It also allows achieving a higher crosslinking density when reacted with hydroxyl terminated polydimethylsiloxane.
In accordance with an aspect, the hydroxyl terminated polydimethylsiloxane has an average number of siloxane groups (r) between 1 to 10 and has a general formula (II), where 1 < r< 10:
Figure imgf000008_0002
The hydroxyl terminated polydimethylsiloxane may either be prepared by any known method or obtained from any commercial source. Herein, the hydroxyl terminated polydimethylsiloxane having a molecular weight equal to or less than 450 Da is used. Using the low molecular weight hydroxyl terminated polydimethylsiloxane further enables achieving higher crosslinking density, as desired in the present invention. In accordance with an aspect, the use of a flexible polycaprolactone or polydialkylsiloxane based crosslinking agent introduces softness in the resultant coating and thus prevents the brittleness in the final coating. The use of polycaprolactone and/or polydialkylsiloxane increases flexibility of the crosslinked polysiloxane network. This causes a substantial reduction in the crater formation in the final coating. Also, there is increase in homogeneity of the coating composition on the surface of the final coating. Polycaprolactone and polydialkylsiloxane renders further advantages such as their long chain leads to the phase separation between the inorganic nanoparticle and polycaprolactone/ polydialkylsiloxane. Further, the absence of true chemical bond between the inorganic nanoparticles and matrix of coating composition leads to migration of inorganic nanoparticles towards the surface of the final coating. This renders glass like properties to the coating thereby providing abrasion resistance, mar resistance and scratch resistance to the coating. The inorganic nanoparticles migrate towards the coating surface also because of low bulk density. Migration of inorganic nanoparticles to surface of final coating during curing provides a further advantage that a lesser amount of inorganic nanoparticles in the range of 1 to 3 % by weight based on total weight is required , to achieve the desired surface properties. Further, the inorganic nanoparticles present on the surface of final coating provide anchoring points thereby allowing ability to re-coat the substrate with the coating composition. In accordance with an aspect, the mixed oxide particles and the silane crosslinking agent are in a weight ratio between 20:1 and 30: 1. Preferably, the mixed oxide particles and the silane crosslinking agent are in a weight ratio of 25: 1.
In accordance with an aspect, the modifier is added to the coating composition in powdered form. This enables the curing of the coating composition at low temperature of around 80 °C, once the modifier is dispersed in the coating composition. In accordance with an aspect, the solvent is a non-polar solvent or could be mixture of solvents. Preferably, the solvents are selected from a group consisting of methoxy propyl acetate, xylene, butylacetate, ethylacetate and combinations thereof. Preferably, the solvent is methoxy propyl acetate. In accordance with an aspect, the solvent is present in the coating composition in an amount in the range of 55 to 80 % by weight of the total weight of the modified coating composition.
In accordance with an aspect, the binder is selected from a group consisting of polyacrylate polyol, polyetherpolyol, polyesterpolyol, polyamidepolyol, polyurethanepolyol, polysiloxanepolyol etc. Preferably, the binder is polyacrylate polyol. In accordance with a related aspect, the binder is present in the coating composition in an amount in the range of 10 to 20% by weight of the total weight of the modified coating composition. Preferably, the binder is present in the coating composition in an amount in the range of 12 to 18 % by weight of the total weight of the modified coating composition.
In accordance with an aspect, the dispersing agent is present in the coating composition in an amount in the range of 2 to 7 % by weight of the total weight of the modified coating composition. In accordance with an aspect, the dispersing agent is BYK- 9077, commercially available from Byk-Chemie.
In accordance with an aspect, the modifier is present in the modified coating composition in an amount in the range of 0.005 to 0.01 % by weight of the total weight of the modified coating composition. In accordance with an embodiment, the coating composition may include polypropylene, polyurethane, nylon, PBT, polyimide, polyether ether ketone, Polyethylene terephthalate, PPT, polyesters, polyamide, polyacrylate, polyether, polysulphone based polymer systems. The coating composition may further comprise certain additives such as UV-absorbers, defoamers, plasticizers, adhesion promoters, light stabilizers, anti-oxidants, metallic or non-metallic colouring agent, flow controllers/ enhancers, catalysts, wetting agents, leveling agents, sag control agent, organic solvent etc. The modified coating composition according to the invention may be used for coating automotive parts, and other substrates including but not limited to wood, metal, alloys, ceramic and plastic. The modified coating composition may be applied to a substrate as a clear or pigmented coating composition as known to those skilled in the art.
In accordance with an aspect, a method of preparing the modifier of the present invention is disclosed. The method comprises the steps of separately preparing the mixed oxide particles comprising of alumina and silica in a desired ratio, and the silane crosslinking agent; blending the mixed oxide particles with the silane crosslinking agent; heating the reaction mixture so obtained at an elevated temperature in the range of 80 to 150°C for a time period in the range of 30 minutes to 4 hours. Preferably, the reaction mixture is heated at 90°C for 2 hours.
In accordance with a further aspect, a method of preparing the modified coating composition comprising the modifier described above is also disclosed. The said method comprises of adding to the coating composition, the modifier, the at least one dispersing agent, the at least one solvent and the binder in a predetermined quantity and subjecting the mixture thus obtained to a milling step. Milling is carried out by ball milling the mixture with milling balls for predetermined time period. Modified coating composition is obtained once the milling is over. Milling balls are separated from the modified coating composition by filtration. The modified coating composition thus obtained may be subjected to further processing as desired.
Any known method of coating may be used for coating the modified coating composition prepared in accordance with the present invention. These include, for example, spray coating, dip coating, roll coating, curtain coating, and the like. Although various methods of curing may be used, heat curing is preferred. Curing agents may also be added to the modified coating composition. Preferably, isocyanate based curing agents are used. Curing agents may include hexamethylene diisocyanate, toluene diisocyanate, polymer modified isocyanate, isophorone diisocyanate. One or more catalysts may also be used to accelerate the curing of the modified coating composition.
The coating composition prepared in accordance with the present invention can be cured at a temperature in the range of 25-140 °C. The curing time will vary depending on the particular components used, and physical parameters such as thickness of the layers etc.
SPECIFIC EMBODIMENTS ARE DESCRIBED BELOW
A modified coating composition comprising-
- a coating composition;
- a modifier; the modifier comprising mixed oxide particles bonded to a silane crosslinking agent, the mixed oxide particles comprising alumina and silica in a weight ratio between 30:70 and 40:60;
- atleast one dispersing agent;
- atleast one solvent;
- at least one binder;
wherein the coating composition, the modifier, the at least one dispersing agent, the binder and the at least one solvent are collectively ground to obtain nanoparticles of the modifier dispersed therein.
Such a modified coating composition, wherein the silane crosslinking agent is selected from a group comprising of a reaction product of a polycaprolactone diol and an isocyanatoalkyl-trialkoxysilane, a reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride and hydroxyl terminated polydiemethylsiloxane and a combination thereof.
Such a modified coating composition, wherein alumina and silica are in the weight ratio of 35:65.
Such a modified coating composition, wherein the nanoparticles of the modifier have a mean diameter in the range of 17 to 60 nm. Such a modified coating composition, wherein the mixed oxide particles and the silane crosslinking agent are in a weight ratio between 20: 1 and 30:1. Such a modified coating composition, wherein the modifier is added to the coating composition in powdered form.
Such a modified coating composition, wherein the dispersing agent is BYK-9077.
Such a modified coating composition, wherein the solvent is a non-polar solvent or a mixture of solvents.
Such a modified coating composition, wherein the binder is polyacrylate polyol.
Such a modified coating composition, wherein the modifier is present in the modified coating composition in an amount in the range of 0.005 to 0.01 % by weight based on total weight of the modified coating composition. Such a modified coating composition, wherein the dispersing agent is present in the modified coating composition in an amount in the range of 2 to 7 % by weight based on total weight of the modified coating composition.
Such a modified coating composition, wherein the solvent is present in the modified coating composition in an amount in the range of 55 to 80 % by weight based on total weight of the modified coating composition.
Examples
The following examples are provided to explain and illustrate the preferred embodiments of the process of the present invention and do not in any way limit the scope of the invention as described and claimed:
Synthesis of modifier in accordance with the present invention
Materials used:
1. Polycaprolactone diol (Mn ~ 400, Perstoph, UK);
2. Bis(3-hydroxypropyl) polydimethylsiloxane (Mn -380, Nanjing SiSiB Silicoes Co., Ltd.);
3. Isocyanatopropyltrimethoxysilane (Gelest); 4. dibutyltin dilaurate (DBTDL,95%, Aldrich);
5. Polyether modified polydimethyl siloxane (BYK-333, BYK chemie Co.).
6. Thinner, Lacquer (acrylic / polyester polyol) and Hardener (HMDI) obtained from commercial source, Berger Paints India limited.
7. Methoxypropyl acetate from commercial source.
8. Vinyltrimethoxy silane from Gelest
9. Hydride terminated polydimethylsiloxane (mol. Wt 400 to 500 ) from Gelest
10. HexaChloroplatinic acid hydrated
11. Alumina, Alu C From Evonik
12. Aerosil 200 fume silica
13. Modaflow acrylic flow additive
14. 10% BYK 310 in Methoxy propyl acetate (MPA)
15. Acrylic formaldehyde melamine (AFM) resin from Berger Paints India limited termed as lk
16. Thinner for lk mixtures of alcohol
Coating Compositions
2K Polyurethane (PU) metallic base coat:
2K PU base coat blazing silver contains mixture of two acrylic polyol resins with one having the solid content of 54.5% and other one having 50%. Hydroxyl value of one of the film forming polyol resin is 80 and other one is 30 respectively. Apart from these, the formulations also contains component of wax dipersion, Cellulose acetate butyrate and antisettling additives. Hexamethylene diisocyanate (HMDI) was used as hardener and thinner used was a mixture of xylene, solvent C9 and butyl acetate (55:30:15). Mixture of non leafing type aluminum pigments are used to get desire color such as silver effect or sparkling effect.
Top Clear coat formulation:
Polyacrylate polyol : 73.2 g;
Defoamer : 0.09g;
HALS : 0.37 g;
UV absorber : 0.73'g;
Glycol ether ester solvent : 1 1.0 g; Butyl diglycol acetate : 1.83 g;
Duranate 22A/75PX (NCO content 16.5% & solid content 75%) as catalyst used stoichiometrically
BYK 310-Silicon flow additive: 0.094 g;
Modaflow Acrylic flow additive : 0.013 g
Silica sol : 8.5 g in methoxypropyl acetate;
BYK 333 (polyether-polydimethylsiloxane) : 0.069 g;
Dibutyltin dilaurate : 0.009 g . Application of 2K coating system to Acrylonitrile Butadiene Styrene (ABS and metal sheet (MS) panels
ABS and metallic panels were washed with iso-propanol and allowed to dry. The base coat comprising metallic silver was applied on both the panels with thickness 20 to 25 microns followed by 5 minutes flash off time. Then clear coat as prepared above (application viscosity 22 sec) was sprayed on the panels with thickness 25 to 35 micron. After flash off time 5 minutes, the panels were baked at 80 °C for 30 minutes.
Performance analysis - Instruments Used
Pencil hardness was tested using Mitsubishi Uni-H pencil (pressure proofed high density lead). Scratch test (Automatically electrically operated model as per BS-3900 part Es I.S. 101-1964) mar resistance as compared to the coating composition without the modifier of the present invention. Pencil Hardnesss was tested using 720 N pencil scratch hardness tester from Sheen using pencils 9B to 9H (ISO 15184 / BS 3900 - E19). Scratch test was carried out by using 'SHEEN' UK Make Automatic Electric operated Scratch Hardness Tester (Ref: 705).
Various samples of the above coating composition were prepared to determine and compare the surface properties of the modified coating composition of the present invention. Synthesis of modifier in accordance with the present invention
Example 1: Preparation of modified coating composition and coating thereof on glass plate (Silane Crosslinking agent: reaction product of polycarprolactone diol and Isocyanatopropyl- trimethoxy silane in a molar ratio of 1 :2) Step 1: About 5.94 grams of polycaprolactone diol (Molecular Weight = 400 g/mole) and 6.1 grams of Isocynatopropyl-trimethoxysilane were added with 36 miligrams of 10% DBTDL solution in heptanone and whole solution was heated at 90 °C for 90 minutes with continuous stirring under nitrogen atmosphere to prepare the silane crosslinking agent. The success of the reaction was confirmed by the disappearance of the isocyanate peak at 2270 cm"1 in the Infrared (IR) spectra of the product obtained upon completion of reaction.
Step 2: About 65 grams of fumed silica powder was brought together with 35 grams of fumed alumina powder followed by heating at 130 °C for 3 hours. 4 grams of silane crosslinking agent prepared in step 1 was mixed with the powder mixture thus obtained. This mixture was blended in a kitchen blender followed by heating at 90 °C for 2 hours.
Step 3: The following day 0.75 grams (i.e 1.5 wt%) of above powder mixture was mixed with 50 grams of top coat clear lacquer . To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
Coating on glass plate: About 10 milliliters of grinded lacquer mixture as prepared above was mixed with 1.7 grams of hexamethylene diisocynato and thinner (xylene and butyl acetate) in a sample bottle, to which 36 miligrams of 10% BYK 333 in heptanone was added. A thin film having thickness of 30 microns was prepared on a glass plate which was cured at 70 °C for 30 minutes. A clear transparent film was observed.
Example 2: 1.5 grams (i.e. 3 wt %) of powder mixture mentioned in step 2 of Example 1 was mixed with 50 grams of top coat clear lacquer. To this solution about 168 grams of zirconia balls of sizes 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 h on a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
Coating on glass plate: About 10 milliliters of grinded lacquer mixture as prepared above was mixed with 1.7 grams of hexamethylene diisocynato and thinner (xylene and butyl acetate) in a sample bottle, to which 36 miligrams of 10% BYK 333 in heptanone was added. A thin film having thickness of 30 microns was prepared on a glass plate which was cured at 70 °C for 30 minutes. A clear transparent film was observed. Example 3: Preparation of modified coating composition and coating thereof on glass plate (Silane Crosslinking agent: reaction product of polycarprolactone diol and Isocyanatopropyl- trimethoxy silane in a molar ratio of 1 :1)
Step 1: About 4 grams of polycopralactone diol (Molecular Weight = 400 g/mole) was taken in a preheated 50 milliliter two necked round bottom flask with a magnetic pellet. Nitrogen was flushed for 2 minutes through the flask and it was connected to dried condenser with nitrogen inlet which was further connected to schlenk line for maintaining the nitrogen atmosphere. About 35 miligrams of 10 % DBTDL in heptanone was added to the flask and 2.05 grams of 3-isocyanatopropyl-trimethoxysilane was further added drop-wise over 15 minutes maintaining temperature of the reaction mixture at 85°C. The reaction was carried out over a period of two hours. The success of the reaction was confirmed by the disappearance of the isocyanate peak at 2270 cm'1 in the Infrared (IR) spectra of the product obtained upon completion of reaction.
Step 2: About 65 grams of fumed silica powder was brought together with 35 grams of fumed alumina powder followed by heating at 130 °C for 3 hours. 4 grams of silane crosslinking agent prepared in step 1 was mixed with the powder mixture thus obtained. This mixture was blended in a kitchen blender followed by heating at 90 °C for 2 hours.
Step 3: The following day 0.75 grams (i.e. 1.5 wt %) of above powder mixture was mixed with 50 grams of top coat clear lacquer . To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at
580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
Coating on glass plate: About 10 milliliters of grinded lacquer mixture as prepared above was mixed with 1.7 grams of hexamethylene diisocynato and thinner (xylene and butyl acetate) in a sample bottle, to which 36 miligrams of 10% BYK 333 in heptanone was added- A thin film having thickness of 30 microns was prepared on a glass plate which was cured at 70 °C for 30 minutes. A clear transparent film was observed.
Table 1 illustrates the coating characteristics of modified coating compositions prepared in aforesaid example 1, 2 and 3.
Figure imgf000018_0001
Table 1
Table 2 illustrates the findings of the scratch test after 24 hours of curing.
Performance After 24 Hrs Maturation In Air At Room Temperature Of The Cured Film At 80°C/30 Minutes ( 25 Minutes Curing & 5 Minutes Heat Up Of The PaneD-
Scratch Resistant Performance Additive
Figure imgf000018_0002
Figure imgf000019_0001
Table 2
Example 4: About 7.5 grams of modifier prepared in example 1 was added to 31.5 grams of methoxy propyl acetate along with lgram of BYK 9077 and 10 grams of polyacrylate polyol with OH value of 56. To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
Example 5: About 7.5 grams of modifier prepared in example 1 was added to 37.5 grams of methoxy propyl acetate along with 1 gram of BYK 9077 and 4 grams of polyacrylate polyol obtained from Surya coating, Nasik with OH value of 80 (solid resin 60%). To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
Example 6: About 7.5 grams of modifier prepared in example 1 was added to 39 g methoxy propyl acetate along with 1 gram of BYK 9077 and 2.5 grams of polyacrylate polyol obtained from Surya coating, Nasik with OH value of 80 (solid resin 60%). To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
Example 7 : 18.75 grams of Alumina-Silica powder prepared in example 1 was added to 73.72 g methoxy propyl acetate along with 7.73 gram of BYK 9077 and 24.90 grams of polyacrylate polyol obtained from Surya coating, Nasik with OH value of 80 (solid resin 60%). The mixture was taken in a 500 ml alumina jar containing equal volume (150 mL) of zirconia balls of diameter 1 mm and 2.3 mm. 150 mL of zirconia ball of size 1 mm corresponds to 495 g weight and 150 mL of zirconia balls of size 2.3 mm corresponds to 535g weight. Whole mixture was stirred well and then grinded at 300 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (Fritschz, Germany) at room temperature 25 °C. The balls were separated by filtration. The dispersion was allowed to stand for further study. No sedimentation was observed even after 35 days.
Particle size distribution: 24 to 123 ran and d90 < 51 nm, viscosity 14.9 cps with Spindle S 18, rpm = 100 and % torque = 49.6 Table 3 illustrates the coating characteristics of modified coating compositions prepared in aforesaid example 4, 5 and 6. Sample No 1 ( performance additive have been evaluated in PU Top Coat)
ABS panel cleaned with IPA PU Base Coat Blazing Silver - Flash off 5 minutes
System
- PU Top Coat -» Flash Off 5 minutes -» Baking 80 Deg C 30 min
Modified coating Modified coating Modified composition prepared in composition coating example 4 (2.7 wt%) prepared in example composition
SI No Test Items
5 (2.7 wt%) prepared in example 6 (2.5 wt%)
A Liquid Paint Properties -
1.0 Supply Viscosity 80 sees 79-sec
2.0 Specific Gravity 1.0 1.01
Slightly hazy, Slightly hazy, Slightly hazy,
3.0 Appearance homogenous & uniform. homogeneous and homogeneous uniform and uniform
Application
4.0 22 sees 22 sec 23 sec
Viscosity
Mixture of xylene+BA Mixture of xylene Mixture of
5.0 Thinner Used and butyl acetate xylene and butyl acetate
6.0 Thinner intake 55 % ( V/V) 55 (v/v) 55 (v/v)
22 sees to 26 sees after 4 25 sec after 4h 25 sec after 4
7.0 Pot Life
hrs. h aliphatic isocyanide aliphatic isocyanide aliphatic
8.0 Catalyst Used
isocyanide
9.0 Mixing Ratio 100:15 100 : 15 100 : 15
Table 3 Table 4 illustrates the findings of the scratch test after 24 hours of curing.
Performance After 24 Hrs Maturation In Air At Rt Of The Cured Film At 80°C/30 Minutes ( 25 Minutes Curing & 5 Minutes Heat Up Of The PaneP-Scratch Resistant
Performance Additive
Figure imgf000022_0001
Table 4 Example 8: Preparation of modified coating composition and coating thereof on glass plate (Silane Crosslinking agent: reaction product of hydride terminated polydimethylsiloxane and vinyl trimethoxy silane)
Step 1: About 10 grams of hydride terminated polydimethylsiloxane (MW= 450 g/mole) and 6.8 grams of vinyltrimethoxysilane were added with 12 milligrams of hexachloroplatinic acid. The whole solution was heated at 80°C for 2 hours with continuous stirring under nitrogen atmosphere to obtain the silane crosslinking agent. The success of the reaction was monitored by dissappearace of Si-H peak in the IR spectra at 2163 cm-1
Step 2: About 65 grams of fumed silica powder was brought together with 35 grams of fumed alumina powder followed by heating at 130 °C for 3 hours. 4 grams of silane crosslinking agent prepared in step 1 was mixed with the powder mixture thus obtained. This mixture was blended in a kitchen blender followed by heating at 90 °C for 2 hours.
Step 3: The following day 0.75 grams (i.e. 1.5wt %) of above powder mixture was mixed with 50 grams of clear lacquer . To this solution about 168 g of zirconia balls of diameter 1 mm and 2.3 mm were added. Whole mixture was stirred well and then grinded at 580 rpm for 3 hours in a SFM-1 Desktop Planetary Ball Miller (MTI corporation) at room temperature 25 °C.
Coating on glass plate: About 10 mL of ground lacquer mixture as prepared above was mixed with 1.7 grams of hexamethylene diisocynato and thinner (xylene and butyl acetate) in a sample bottle, to which 36 miligrams of 10% BYK 333 in heptanone was added. A thin film was prepared on a glass plate which was cured at 70 °C for 30 minutes. Slight hazy film was observed. Example 8: Performance of Alumina-silica dispersion in lk resin system
5 grams of IK lacquer (acrylate-melamine formaldehyde system) was mixed with 1 gram of thinner (mixture of alcohols) and 0.43 grams of the modifier prepared in example 1, in order to maintain the concentration of modifier in the lacquer at around at around 2.34% after drying. This mixture was mixed properly to form a homogeneous mixture and was cast on a steel plate cleaned with isopropanol. This steel plate was left for 5 minutes for flash off and baked at 140°C for 25 minutes. The surface properties of the modified coating composition prepared above were compared with a coating composition prepared without the modifier. Table 5 illustrates the findings of the tests.
Figure imgf000024_0001
Figure imgf000025_0001
Table 5
INDUSTRIAL APPLICABILITY
The above disclosed modifier can be used in various polyurethane, acrylic/melaimine 2K or IK coating compositions. This can be also used in UV or thermally curable resin system to obtain remarkable surface properties. The modified coating compositions prepared in accordance with the present invention exhibits desired surface properties such as improved anti-scratch, mar resistance, recoatability, high gloss retainability, barrier properties, while being curable at low temperature of around 80 °C. The coating obtained by using this modifier leads to elimination of haziness and formation of crater in the final coating which is clearly not acceptable for the coating industries.

Claims

WE CLAIM:
1. A modified coating composition comprising-
- a coating composition;
- a modifier; the modifier comprising mixed oxide particles bonded to a silane crosslinking agent, the mixed oxide particles comprising alumina and silica in a weight ratio between 30:70 and 40:60;
- atleast one dispersing agent;
- atleast one solvent;
- at least one binder;
wherein the coating composition, the modifier, the at least one dispersing agent, the binder and the at least one solvent are collectively ground to obtain nanoparticles of the modifier dispersed therein.
2. A modified coating composition as claimed in claim 1, wherein the silane crosslinking agent is selected from a group comprising of a reaction product of a polycaprolactone diol and an isocyanatoalkyl-trialkoxysilane, a reaction product of vinyltrimethoxysilane and polydialkylsiloxane hydride and hydroxyl terminated polydiemethylsiloxane and a combination thereof.
3. A modified coating composition as claimed in claim 1, wherein alumina and silica are in the weight ratio of 35:65.
4. A modified coating composition as claimed in claim 1 , wherein the nanoparticles of the modifier have a mean diameter in the range of 17 to 60 nm.
5. A modified coating composition as claimed in claim 1, wherein the mixed oxide particles and the silane crosslinking agent are in a weight ratio between 20:1 and 30:1.
6. A modified coating composition as claimed in claim 1, wherein the modifier is added to the coating composition in powdered form.
7. A modified coating composition as claimed in claim 1, wherein the dispersing agent is BYK-9077.
8. A modified coating composition as claimed in claim 1, wherein the solvent is a non-polar solvent or a mixture of solvents.
9. A modified coating composition as claimed in claim 1, wherein the binder is polyacrylate polyol.
10. A modified coating composition as claimed in claim 1, wherein the modifier is present in the modified coating composition in an amount in the range of 0.005 to 0.01 % by weight based on total weight of the modified coating composition.
11. A modified coating composition as claimed in claim 1, wherein the dispersing agent is present in the modified coating composition in an amount in the range of 2 to 7 % by weight based on total weight of the modified coating composition.
12. A modified coating composition as claimed in claim 1, wherein the solvent is present in the modified coating composition in an amount in the range of 55 to 80 % by weight based on total weight of the modified coating composition.
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