WO2015040477A1

WO2015040477A1 - A modifier for a coating composition

Info

Publication number: WO2015040477A1
Application number: PCT/IB2014/001874
Authority: WO
Inventors: Swapan DUTTA; Soumen Sensarma; Someshwarnath PANDEY; Trupti NIRMALE
Original assignee: Tata Chemicals Limited
Priority date: 2013-09-19
Filing date: 2014-09-18
Publication date: 2015-03-26
Also published as: IN2013MU03027A

Abstract

A modifier for improving the surface properties of a coating composition is disclosed. More particularly, a modifier comprising inorganic nanoparticles bonded to a crosslinking agent, which is further crosslinked to a polydialkylsiloxane diol is disclosed. A method for preparing the said modified is also disclosed.

Description

A MODIFIER FOR A COATING COMPOSITION

The present invention relates to a modifier for improving the surface properties of a coating composition. More particularly, the present invention relates to a modifier comprising inorganic nanoparticles bonded to a crosslinking agent, which is further crosslinked to a polydialkylsiloxane diol.

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 are made possible in this procedure. One of the disadvantage 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 Ureclear clear coat. The inorganic organic hybrid mixture thus produced gives automotive coating system which gives scratch resistance. The nano particles thus produced require substantial amount of silica nanoparticles 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 monopolydimethylsiloxane hydride coupled with vinyl trimethoxysilane. It also teaches the reaction of silaplane based compound with caprolactone based monomers 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).

WO 2006/1 14420 describes the modification of silica nanoparticles with the use of low chain polydimethylsiloxane and tetraethylorthosilicate and use the same for acrylic melamine and 2 based polyurethane system. The invention describes use of very low amount of silica in the final resin system to get the required surface hardness. However, incorporation of silica nanoparticles into the 2K based resin system develops craters and also the gloss of coating at 20 Deg reduces while comparing with blank system. Further, for the reduction of crater formation and maintaining gloss of coatings it is essential that the crosslinked polydimethylsiloxane network carrying modified silica nanoparticles must be compatible with the matrix. With the use of known crosslinkers such as tetraethylorthosilicate, octyl-triethoxy silane etc. there is no improvement in the reduction of crater formation without compromising on desired properties.

Thus, there is a need to devise modifier systems for coating compositions which exhibit scratch and mar resistance without embrittlement, haziness, crater formation. It is also desired that such coatings have properties such as recoatability while requiring lesser loading of inorganic particles. It is further desirable that such modifier system exhibits the afore-said properties with both the 1 (one-component) and 2 (two-component) coating compositions based on polyurethane/ acrylic melamine or epoxy resin etc.

SUMMARY

The present invention is directed to a modifier for improving the surface properties of a coating composition. The said modifier comprises of an inorganic nanoparticle having atleast one hydroxyl functional group covalently bonded to a crosslinking agent. Herein, the crosslinking agent has a general formula (I):

Z [YR₂XR,Si(R)₃]2 (I)

Where:

R = OMe, OEt, OBu;

Ri = (CH₂)x ,where x = 1 to 4;

X = NHCOO;

R₂ = alkyl substituent having 5 to 7 carbon atoms, polyether, polyester; Y= COOZO;

Z = -(CH^-O-fCH^— or— (CH₂)_n- or

CH₃

H2C CH2~

CH₃

where m, z= 3, 4; n= 6 to 9

The said crosslinking agent is obtained by reacting polycaprolactone diol having a molecular weight less than 550 Daltons and an isocyanatosilane having a general formula (II):

X,R,Si(R)₃, (II)

where:

X,= OCN

Ri = (CH₂)x , where x = 1 to 4

R = OMe, OEt, OBu. The crosslinking agent is further crosslinked with a polydialkylsiloxane diol having a molecular weight less than 450 Daltons.

The present invention is also directed towards a modifier kit for a coating composition. The said modifier kit comprises a first component comprising of the aforesaid modifier and a second component comprising a polyether-modified polydialkylsiloxane, such that the first component and the second component are to be added to the coating composition to obtain a modified coating composition. DETAILED DESCRIPTION

To promote an understanding of the principles of the invention, reference will be made to the 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 disclosure generally relates to a modifier for improving the surface properties of a coating composition. The modifier of the present disclosure comprises an inorganic nanoparticle having atleast one hydroxyl functional group covalently bonded to a crosslinking agent. Herein, the crosslinking agent has a general formula (I):

Z[YR₂XR,Si(R)3]₂ (I)

Where:

R = OMe, OEt, OBu;

R , = (CH₂)x ,where x = 1 to 4;

X = NHCOO;

R₂ = alkyl substituent having 5 to 7 carbon atoms, polyether, polyester; Y= COOZO; Z = -(CH₂)^ 0-(CH₂)— or— (CH₂)_n- or

CH₃

H2C CH2^—

CH₃

where m, z= 3, 4; n= 6 to 9

X,R,Si(R)₃, (II)

where:

Xi= OCN

Ri = (CH₂)x , where x = 1 to 4

R = OMe, OEt, OBu.

The crosslinking agent is further crosslinked with a polydialkylsiloxane diol having a molecular weight less than 450 Daltons.

Herein, the hydroxyl groups present in the polycaprolactone diol react with the isocyanate group present in the isocynatopropyltrimethoxysilane having general formula II to form alkoxysilane encapped polycaprolactone, the crosslinking agent having the general formula I. The alkoxysilane groups present on both the terminals of the crosslinking agent then reacts with the hydroxyl functional groups present in the inorganic nanoparticles as well as that on the polydialkyl siloxane to obtain crosslinked polycaprolactone- polydialkyl siloxane network with embedded inorganic nanoparticles, the modifier disclosed herein. For the sake of simplicity, the crosslinked polycaprolactone- polydialkyl siloxane network with embedded inorganic nanoparticles will now be referred to as "modified nanoparticles". The reaction scheme 1 illustrates the preferred embodiment of the present invention wherein the crosslinking agent is formed by reacting polycaprolactone diol (A) with isocyanatopropyltrimefhoxysilane (B), which is further crosslinked to polydimethylsiloxane diol i.e. PDMS diol (C) and silica nanoparticles to obtain crosslinked polycaprolactone- polydialkyl siloxane network with embedded silica nanoparticles.

i ossliiiked polyt npiolactoue-pdin s uetwork wit erab dded sili< a unnopai tides

Scheme 1

In accordance with an aspect, the modifier further comprises a polyether modified polydialkylsiloxane for addition to the coating composition. In accordance with a preferred embodiment, the polyether-modified polydialkylsiloxane is polyether- modified polydimethylsiloxane. In accordance with a related embodiment, when the modifier is added to the coating composition, the amount of polyether-modified polydialkylsiloxane is 0.02% to 0.5% of total weight. The polyether-modified polydialkylsiloxane serves to reduce the surface_ tension of the ; j;oatjng _.. composition, upon _.curing._ The modified . nanoparticles when used along with polyether modified polydimethylsiloxane exhibits synergistic action to render complete mar resistance to the cured coating composition at 0 hour.

In accordance with an embodiment, polydialkylsiloxane diol has an alkyl substituent having 1 to 8 carbon atoms. The polydialkylsiloxane diol has an average number of siloxane groups (r) between 1 to 10. In accordance with a preferred embodiment, polydialkylsiloxane diol is polydimethylsiloxane diol having 1 <_ r _< 10 having the general formula (III):

The polydialkylsiloxane diol may be prepared by any known method or may be obtained from any commercial source. Herein, polydialkylsiloxane diol having a molecular weight less than 450 Daltons is used. Using a low molecular weight polydialkylsiloxane enables achieving higher crosslinking density, as desired in the present invention.

In accordance with an aspect, low molecular weight polycaprolactone diol having a molecular weight less than 550 Daltons is used in the present invention. Use of shorter polycaprolactone diol or low molecular weight polycaprolactone diol provides a better reaction with isocyanatosilane and allows achieving higher crosslinking density when reacted with polydialkylsiloxane diol.

In accordance with an embodiment, two molar equivalents of isocyanatosilane are reacted with polycaprolactone diol. In accordance with another embodiment, the isocyanatosilane may be selected from 3-isocyanatopropyltrimethoxysilane and 3- isocyanatopropyltriethoxysilane ^" and is more preferably 3- isocyanatopropyltrimethoxysilane. It is preferred that three reactive groups are present on the isocyanatosilane. Thus the resultant crosslinking agent has six reactive groups present thereon. This provides higher crosslinking density when the crosslinking agent prepared by reacting polycaprolactone diol and isocyanatosilane is cured with polydialkylsiloxane diol.

In accordance with a related embodiment, the molar ratio of the crosslinking agent and the polydialkylsiloxane diol is in a range of 0.1 to 1.4. In accordance with an aspect, due to the presence of polycaprolactone which is a soft polymer there is increase in flexibility of the crosslinked polydialkylsiloxane network and reduction in the crater formation on the surface when blended with 1K/2 coating system. The present invention describes the use of flexible polycaprolactone based crosslinker and soft polymer based on siloxane i.e. polydialkylsiloxane which introduces softness in the resultant coating and thus prevents the brittleness of the final coating. There is increase in homogeneity of the coating composition on the surface. Polycaprolactone renders further advantages such as the long chain of polycaprolactone leads to the phase separation between the inorganic nanoparticle and polycaprolactone. Further, the absence of true chemical bonding between the inorganic nanoparticles and coating matrix leads to migration of nanoparticles toward the surface of the coating and hence renders glass like properties to the coating thereby providing abrasion resistance, mar resistance and scratch resistance to the coating. The inorganic nanoparticle(s) migrates toward the coating surface also because of low bulk density. Migration of nanoparticle to surface of coating during curing provides further advantages such as lesser amount of nanoparticles in the range of 1 to 6 wt% is required to achieve the desired surface properties. Further, the nanoparticles present on surface of coating provide anchoring points thereby allowing ability to recoat the surface with the coating composition. In accordance with an embodiment, the inorganic nanoparticle is selected from the group comprising of silica, alumina, titania, zirconia, clay and mixtures thereof. In accordance with a preferred embodiment, the inorganic particle is silica. Further, the nano particles may be present either in powder or solution form. In accordance with a related embodiment, silica nanoparticles may be obtained from commercial source. Preferably, sols of silica are used. It could be aqueous based silica sol (aquasol) or any polar/ non- polar solvent based silica sol. The polar solvent may be any alcohol and non-polar solvent can be butyl acetate, methoxy propyl acetate, heptanone, Methyl ether ketone. In accordance with a related embodiment, silica nanoparticles have a particle size in the range of 1 - 60 nm and is preferably 5-20 nm. The pH of aqueous based sol which is used in the present invention may range from 2 to 4 with particle size distribution (PSD) of 5 to 60 nm and silica loading of 20 to 35 wt%. The alcohol based silica sol could have pH 3 to 4 with PSD of 5 to 60 nm and silica loading of 20 to 35 wt%. The non polar solvent based silica sol has a PSD of 5 to 60 nm with silica loading of 20 to 35 wt%. Alternatively, silica nanoparticles may be obtained by controlled hydrolysis of tetraethylorthosilicate, methyl trimethoxy silane, ethyl trimethoxy silane or any other suitable derivative of siloxane compounds in presence of mild acid. In accordance with an aspect, silica sol containing silica nanoparticles having free hydroxyl groups is used. In accordance with a preferred embodiment, the hydroxyl groups on the silica nanoparticles are made hydrophobic by at least partial esterifi cation with organic solvents such as ethanol, butanol etc. Any known technique may be used to esterify silica nanoparticles.

In accordance with a further aspect, a method of preparing a modifier of the present invention is disclosed. The said method comprises of adding to a dispersion of inorganic nanoparticle(s). the crosslinking agent and the polydialkyl siloxane in the desired molar ratio, followed by heating the reaction mixture so obtained at the 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 130°C for 3 hours. Herein, the dispersion of inorganic nanoparticles is prepared by first esterifying the inorganic nanoparticles with an organic solvent followed by dispersion in a desired solvent. In accordance with a further preferred embodiment, the molar ratio of the crosslinking agent and the polydialkylsiloxane diol is in a range of 0.1 to 1.4.

The crosslinking agent of the present invention is prepared by reacting polycaprolactone diol with an isocyanatosilane in the presence of dibutyltin dilaurate (DBTDL) at an elevated temperature in the range of 60 to 100 °C and preferably at 85 °C for a predetermined time period. Preferably, the reaction is carried out for two hours.

The modifier once prepared may be dispersed in water, solvents etc. to obtain a dispersion thereof or separated in the form of solid particles such as powder, flakes etc. for storage and transportation.

In accordance with an aspect, a modifier kit for a coating composition is also disclosed. The said modifier kit comprises a first component comprising of the modified nanoparticles, as described above and a second component comprising a polyether- modified polydialkylsiloxane, such that the first component and the second component are to be added to the coating composition to obtain a modified coating composition. In accordance with a further aspect, a method of preparing a coating composition comprising the modifier, described above is also disclosed. The said method comprises of adding to the coating composition, the first component and the second component in a predetermined quantity. In accordance with a preferred embodiment, the amount of first component added to the coating composition is in the range of 3 to 20 % by weight based on the total weight and that of the second component is in the range of 0.02% to 0.5% % by weight based on the total weight.

The modifier as described in the present disclosure may be used with any coating composition including but not limited to thermally, radiation curable I K / 2 coating' , compositions. In accordance with an embodiment, the modifier may be used as filler for any polypropylene, polyurethane, nylon, polybutylene terephthalate (PBT), Polyimide, Polyether ether ketone, Polyethylene terephthalate, PPT, polyesters, polyamide, polyacrylate, polyether, polysulphone based polymer systems. The coating composition may further comprise one or more of certain additives such as UV-absorbers, defoamers, plasticizers, adhesion promoters, light stabilizers, anti-oxidants, colouring agent, flow controllers/ enhancers, catalysts, wetting agents, leveling agents, sag control agent, organic solvent etc.

The coating composition according to the invention may be used for coating automotive parts, various other substrates including but not limited to wood, metal, alloys, ceramic, plastic. Any known method of coating the coating composition prepared in accordance with the present invention may be used. 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. The coating composition prepared in accordance with the present invention may be cured at any temperature in the range of 70- 150 °C. The coa'dng composition prepared in accordance with the present invention when coated on plastics generally cure at 70°C and at 120-140 °C for metallic parts. 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 modifier for a coating composition comprising an inorganic nanoparticle having atleast one hydroxyl functional group covalently bonded to a crosslinking agent, the crosslinking agent having a general formula (I):

Z[YR₂XR,Si(R)₃]₂ (I)

Where:

R = OMe, OEt, OBu;

Ri = (CH₂)_X ,where x = 1 to 4;

X = NHCOO;

R₂ = alkyl substituent having 5 to 7 carbon atoms, polyether, polyester;

Y= COOZO;

Z = -(CH₂^0-(CH₂^— or—(CH₂)_n- or

CH₃

H₂C CH₂ ^—

CH₃

where m, z= 3, 4; n= 6 to 9

obtained by reacting polycaprolactone diol having a molecular weight less than 550 Daltons and an isocyanatosilane having a general formula (II):

X,R,Si(R)₃, (II)

where:

X,= OCN

Ri = (CH₂)x ,where x = 1 to 4

R = OMe,OEt, OBu,

the crosslinking agent further crosslinked with a polydialkylsiloxane diol having a molecular weight less than 450 Daltons. Such a modifier for a coating composition further comprising polyether modified polydialkylsiloxane for addition to the coating composition.

Such a modifier for a coating composition wherein the polydialkylsiloxane diol has an alkyl substituent having 1 to 8 carbon atoms.

Such a modifier for a coating composition wherein the isocyanatosilane is 3- isocyanatopropyl-trimethoxysilane.

Such a modifier for a coating composition wherein the molar ratio of the crosslinking agent and the polydialkylsiloxane diol is in a range of 0.1 to 1.4.

Such a modifier for a coating composition wherein the inorganic nanoparticle is selected from the group comprising of silica, alumina, titania, zirconia, clay and mixtures thereof.

Such a modifier for a coating composition wherein when the modifier is added to the coating composition, the amount of polyether-modified polydialkylsiloxane is 0.02% to 0.5% of total weight.

Such a modifier for a coating composition wherein the polyether-modified polydialkylsiloxane is polyether- modified polydimethylsiloxane.

A modifier kit for a coating composition comprising a first component comprising an inorganic nanoparticle having atleast one hydroxyl functional group covalently bonded to a crosslinking agent, the crosslinking agent having a general formula (I):

Z[YR2XRl Si(R)3]2 (I)

Where:

R = OMe, OEt, OBu;

Ri = (CH₂)_x ,where x = 1 to 4;

X = NHCOO;

Z = (CH₂)r_iO-(CH₂)_z— or— (CH₂)_n- or

where m, z= 3, 4; n= 6 to 9

X. R|Si(R)₃, (II)

where:

Xi= OCN

Ri = (CH₂)x ,where x = 1 to 4

R = OMe,OEt, OBu, the crosslinking agent further crosslinked with a polydialkylsiloxane diol having a molecular weight less than 450 Daltons; a second component comprising a polyether- modified polydialkylsiloxane, such that the first component and the second component are to be added to the coating composition to obtain a 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 modified nanoparticles in accordance with the present invention:

Materials used:

1. Polycaprolactone diol (Mn ~ 400, Perstorp, UK);

2. Bis(3-hydroxypropyl) polydimethylsiloxane (Mn -380, Nanjing SiSiB Silicoes Co., Ltd.);

3. Isocyanatopropyltrimethoxysilane (Gelest);

4. dibutyltin dilaurate (DBTDL,95%, Aldrich);

5. Aqueous silica sol (Snowtex-O, pH=2-4, 21 -23 wt % sillica,Nissan Chemical America corporation);

6. Polyether modified polydimethylsiloxane (BYK-333, BYK chemie Co.). 7. Thinner. Lacquer (acrylic / polyester polyol) and Hardner (HMDI) obtained from commercial source.

8. Absolute Ethanol (Merck), Isopropanol (Merck) and Butanol (sd-fine chemicals), methoxypropyl acetate from commercial source.

9. Modaflow acrylic flow additive

10. 10% BYK 310 in Methoxy propyl acetate (MP A)

Example 1 : Preparation of modified nanoparticles (Molar ratio polycarprolactone diol and Isocyanato-propyl trimethoxy silane - 1 :2)

The synthesis of modified nanoparticles was carried out in three steps:

Step 1 : Dispersion of aqueous silica sol into an organic solvent such as methoxy propyl acetate after esterification with alcohols such as butanol etc.

20 grams of aqueous silica sol was taken in a 100 milliliter round bottom flask. The assembly was circulated with nitrogen gas through schlenk line. To the round bottom flask were added 60 grams of isopropanol and 40 grams of butanol along with addition of 0.03 grams of n-propyltrimethoxysilane. The solution was evaporated using rotavapor at 30 °C to make volume of solution around 40 grams. Further 30 grams of methoxy propyl acetate was added to the round bottom flask and heated at 130 °C for one hour. The solution was further concentrated to 36 grams using rotavapor.

Step 2: Preparation of crosslinking agent

0.788 grams of polycaprolactone was taken in a preheated 25 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 connected to schlenk line for maintaining the nitrogen atmosphere. 15 milligrams of 10% DBTDL in heptanone was added to the flask and 0.81 grams 3-isocyanatopropyltrimethoxysilane 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. Step 3: Reaction of the sol formed in step 1 with a mixture of crosslinking agent prepared in the Step 2 and polydimethylsiloxane diol (PDMS diol) to obtain modified nanoparticles of the present invention.

In a round bottom flask, 36 grams of the dispersion of silica nanoparticles in methoxy propyl acetate and 1.138 grams of crosslinking agent formed in step 2 was added along with 0.62 grams of PDMS diol maintaining the molar ratio of 0.9. The reaction was carried out at 130 °C for 2 hours. Further the reaction product was concentrated to 20 grams on a rotavapor and centrifuged to obtain modified nanoparticles of the present invention. Amount of solid silica in the sol is 23 wt%, viscosity 10 cps.

Example 2: Preparation of modified nanoparticles (Molar ratio polycarprolactone diol and isocyanatopropyl trimethoxy silane - 1 : 1 )

Step 1 : Dispersion of aqueous silica sol into an organic solvent such as methoxy propyl acetate after esterifi cation with alcohols such as butanol etc.

The procedure adopted herein is similar to that used in Example 1 . In a 1 Litre round bottom flask 100 grams of colloidal silica was brought together with 300 grams isopropanol and 200 grams of n-butanol along with the addition of 0.06 grams of n- propyltrimethoxysilane. From the mixture, water was azeotropically removed by distillation under reduced pressure at 30° C until a mass of 140 grams colloidal dispersion was reached. To this solution 150 grams of 1 -methoxyisopropyl acetate was added and then heated at 90° C for 1 hour under nitrogen atmosphere and again concentrated to 213 grams. Step 2: Preparation of crosslinking agent.

About 4 grams o polycaprolactonc diol ^"and 2.05 grams of Isocynatopropyltrimethoxy silane were added in a 50 milliliters two neck round bottom flask with 36 milligrams of 1 0% DBTDL solution and whole solution was heated at 90° C for 90 minutes with continuous stirring under nitrogen atmosphere.

Step 3: Reaction of the sol formed in step 1 with a mixture of crosslinking agent prepared in the step 2 and polydimethylsiloxane diol (PDMS diol) to obtain modified nanoparticles of the present invention. The nanoparticles prepared in Step 1 were mixed with 3.14 grams of prepared crosslinking agent and 2.2 grams of polydimethylsiloxane diol. The mixture was stirred well and heated at 130° C for about 2 hours and kept overnight. Then the mixture was concentrated at 50° C under reduced pressure to 100 grams. The mass was centrifuged at 4000 rpm for 20 minutes at room temperature to remove some unreacted material. A clear colloidal dispersion of modified nanoparticles was obtained.

Preparation of coating composition including modifier of present invention Example 3: Testing on 2 k component polyurethane based system: The modifier of the present inventior has been used for preparing 2K Polyurethane Clear Lacquer comprising of Acrylic Polyol and Polyisocyanate.

2K Polyurethane (P T) metallic base coat:

2K PU base coat with blazing silver contains mixture of two acrylic polyol resins with one having the solid content of 54.5% and other one having¹50%. Hydroxyl value of one of the film forming polyol resin is 80 and other one is 30 respectively. Apart from these, the formulation also contains component of wax dipersion, Cellulose acetate butyrate and anti-settling additives. Hexamethylene diisocyanate (HMD I) was used as hardener and thinner used was a mixture of xylene, solvent C9 and butyl acetate in ratio of 55:30: 15. Mixture of non-leafing type aluminum pigments were used to get desired color such as silver effect or sparkling effect.

Top Clear coat formulation:

The top clear coat was formed using the following materials:

Polyacrylate polyol : 73.2 g;

Defoamer : 0.09g;

HALS : 0.37 g;

UV absorber: 0.73g;

Glycol ether ester solvent: 1 1.0 g;

Butyl diglycol acetate: 1.83g;

Duranate 22A/75PX (NCO content 16.5% and 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 2 coating system to Acrylonitrile Butadiene Styrene (ABS) and metal sheet (MS) panels

ABS and metal sheet panels were washed with iso-propanol and allowed to dry. The

2K polyurethane metallic base coat comprising metallic silver was applied on both the. panels with thickness 20 to 25 microns followed by flash off time of 5 minutes. Then top clear coat as prepared above (application viscosity 22 sec) was sprayed on the panels to achieve thickness 25 to 35 micron. After flash off time of 5 minutes, the panels were baked at 80 °C for 30 minutes.

Various samples of the above coating composition were prepared to determine and compare the effect of the modifier of the present invention on various properties of the resulting coating composition.

Perfomance analysis - Instruments Used

Pencil hardness was tested using Mitsubishi Uni-H pencil (pressure proofed high density lead). Scratch / mar behavior was tested using automatically electrically operated model as per BS-3900 part Es l.S. 101-1964. Pencil Hardnesss was tested using 720 N pencil scratch hardness tester from Sheen using pencils 9B to 9H (ISO 15184 / BS 3900 - El 9). Scratch test was carried out by using 'SHEEN' UK Make Automatic Electric operated Scratch Hardness Tester (Ref: 705).

The following samples were prepared:

Sample I. (Blank): 92 grams of acrylic polyoL lacquer-is taken and 1.5.9 grams, of. hardener is mixed to it along with 35 grams of thinner and mixed well. The coating was drawn on metal sheet as well as ABS panel. ^'

Sample 2: 92 grams of acrylic polyol lacquer was mixed with 15.9 grams of hardener (Duranate 22A) along with 35 grams of a thinner (mixture of xylene and butyl acetate (85: 15 w/w). To the above formulation 8.5 grams of dispersion of modified nanoparticles (prepared in Example 1 ) and 0.068 grams of polyether modified polydimethylsiloxane (BYK 333) is added^ maintaining the concentration of the silica content on dried polyurethane film to be 4.01 % and mixed well.

Sample 3: 92 grams of acrylic polyol lacquer with silicone flow additive and acrylic flow additive both were mixed with 15.9 grams of hardener (Duranate 22A) along with 35 grams of a thinner (mixture of xylene and butyl acetate- 85: 15 w/w). To the above formulation 8.5 grams of dispersion of modified nanoparticles (prepared in Example 1 ) along with 0.068 grams of Polyether modified polydimethylsiloxane (BYK 333) is added, maintaining the concentration of the silica content on dried polyurethane film to be 4.01 % and mixed well.

Tables 1 , 2 and 3 illustrate the findings of the test after 24 hours, 48 hours and 72 hours of curing, respectively. As shown in Tables 1 , 2 and 3, the coatings obtained using the modifier of the present invention exhibit improved characteristics in terms of pencil hardness and also nail mark and thus has a distinct role in improving Surface Hardness. Also, the modifier of the present invention does have any negative effect on coating performance.

Table 1 : performance after 24 hours maturation in air at room temperature of the cured film at 80°C/30 minutes ( 25 minutes curing and 5 minutes heat up of the panel).

Table 2: performance after 48 hours maturation in air at room temperature of the cured film at 80°C/30 minutes ( 25 minutes curing and 5 minutes heat up of the panel).

Table 3: performance after 72 hours maturation in air at room temperature of the cured film at 80°C/30 minutes ( 25 minutes curing and 5 minutes heat up of the panel).

Example 4: Testing on lk Coating system

Sample 4 (Blank)

10 grams of Acrylic Polyol Resin, Melamine Formaldehyde Resin was spray coated on a metal plate pretreated with isopropanol and base coated with blazing silver having a thickness of 20 micron. After a flash off time of 8 minutes the coating plate was baked at 130 °C for 25 minutes.

Sample 5 (With modifier)

About 92 grams of Acrylic Polyol Resin, Melamine Formaldehyde Resin was mixed along with 8.5 grams of dispersion of modified silica nanoparticles of the present invention and 0;068 grams of Polyether modified polydimethylsiloxane (BYK 333) and kept for 5 minutes. A metal plate was pretreated with isopropanol and base coat with blazing silver was applied with thickness of 20 micron. Then clear I lacquer as prepared above was applied on the pretreated metal plate to obtain thickness of 22 microns. After a flash off time of 8 minutes the coating plate was baked at 130 °C for 25 minutes.

The two samples prepared above were tested for determining the surface hardness. Table 4 illustrates the findings of the tests. Table 4: Comparison of performance Of Thermosetting Acrylic (TSA) Clear Lacquer with and without modifier of the present invention

INDUSTRIAL APPLICABILITY

The above disclosed modifier can be used in various types of coating compositions including but not limited to polyurethane, acrylic or epoxy based I K/ 2 coating compositions. Further, the coating compositions comprising the modifier of the present invention may be used on any substrate including but not limited to metals, wood, glass, plastic, ceramics. This can be also used in UV or thermally curable resin system to obtain remarkable surface properties. Addition of modifier results in obtaining coating compositions having desired surface properties such as improved anti-scratch, mar resistance, recoatability, high gloss retainability, barrier properties. Using the modifier of the present invention, results in obtaining complete mar resistance at 0 hour after baking the film at 70 to 150 °C and sustaining pencil hardness. The coating obtained by using this modifier leads to elimination of haziness and formation.

Claims

WE CLAIM:

1. A modifier for a coating composition comprising:

an inorganic nanoparticle having atleast one hydroxyl functional group covalently bonded to a crosslinking agent, the crosslinking agent having a general formula (I):

Z[YR₂XR,Si(R)₃]₂ (I)

Where:

R = OMe, OEt, OBu;

R i = (CH₂)x , where x = 1 to 4;

X = NHCOO;

R.2 = aikyl substituent having 5 to 7 carbon atoms, polyether, polyester;

Y= COOZO;

Z = -(CH₂)^0-(CH₂)_z— or— (CH₂)_n- or

CH₃

H₂C j CH₂ ^—

CH₃

where m, z= 3, 4; n= 6 to 9,

obtained by reacting polycaprolactone diol having a molecular weight less than 550 Daltons and an isocyanatosilane having a general formula(II):

X|R,Si(R)₃, (II)

where:

X,= OCN

Ri = (CH₂)x , where x = 1 to 4

R = OMe, OEt, OBu,

the crosslinking agent further crosslinked with a polydialkylsiloxane diol having a molecular weight less than 450 Daltons.

2. A modifier for a coating composition further comprising polyether modified polydialkylsiloxane for addition to the costing composition. A modifier for a coating composition as claimed in claim 2 wherein the polydialkylsiloxane diol has an alkyl substituent having 1 to 8 carbon atoms.

A modifier for a coating composition as claimed in claim 1 wherein the isocyanatosilane is 3-isocyanatopropyl-trimethoxysilane.

A modifier for a coating composition as claimed in claim 1 , wherein the molar ratio of the crosslinking agent and the polydialkylsiloxane diol is in a range of 0.1 to 1.4.

A modifier for a coating composition as claimed in claim 1 , wherein the inorganic nanoparticle is selected from the group comprising of silica, alumina, titania, zircotiia, clay and mixtures thereof.

A modifier for a coating composition as claimed in claim 1 wherein when the modifier is added to the coating composition, the amount of polyether-modified polydialkylsiloxane is 0.02% to 0.5% of total weight.

A modifier for a coating composition as claimed in claim 1 wherein the polyether- modified polydialkylsiloxane is polyether- modified polydimefhylsiloxane.

A modifier kit for a coating composition comprising:

a first component comprising an inorganic nanoparticle having atleast one hydroxyl functional group covalently bonded to a crosslinking agent, the crosslinking agent having a general formula (I):

Z[YR₂XR, Si(R ]₂ (1)

Where:

R = OMe, OEt, OBu;

Ri = (CH₂)_X ,where x = 1 to 4;

X = NHCOO;

R₂ = alkyl substituent having 5 to 7 carbon atoms, polyether, polyester;

Y= COOZO; Z = - (CH^O-tCH^— or— (CH₂)_n- or

CH₃

— H₂C-)-CH2- CH₃

where m, z= 3, 4; n= 6 to 9,

Xi Ri Si(R)₃, (II)

where:

X,= OCN

Ri = (CH₂)x ,where x = 1 to 4

R = OMe, OEt, OBu,

the crosslinking agent further crosslinked with a polydialkylsiloxane diol having a molecular weight less than 450 Daltons;

a second component comprising a polyether-modified polydialkylsiloxane, such that the first component and the second component are to be added to the coating composition to obtain a modified coating composition.