FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
&
THE PATENTS (AMENDMENT) RULES, 2006
COMPLETE SPECIFICATION
[See Section 10; rule 13]
"PEARLESCENT PIGMENT WITH MODIFIED DENSITY OF SURFACE
CAPPING FUNCTIONAL GROUPS, PROCESS FOR PRODUCING THE SAME,
AND MIXTURES AND COMPOSITIONS THEREOF"
SUDARSHAN CHEMICAL INDUSTRIES LTD., an Indian cooperation of 162 Wellesley Road, Pune, Maharashtra, India, 411001.
The following specification particularly describes the invention and the manner in which it is to be performed:

Pearlescent Pigment with Modified Density of Surface Capping Functional Groups, Process for Producing the Same, and Mixtures and Compositions Thereof
The invention relates generally to pigments comprising one or more metal oxides, e.g., titanium dioxide, and in particular pearlescent pigments, which are coated with a multi-functional organo silane aftercoat, which coated pigments have excellent dispersability and weatherability characteristics.
BACKGROUND OF THE INVENTION
Nacreous or pearlescent pigments comprising an inorganic core coated with one or more metal. oxide layers can impart a variety of optica! effects, such as a pearlescent luster, metallic luster and/or multi-color effects to a substrate into which they are incorporated. First described in U.S. Pat. Nos. 3,087,828 and 3,087,829, pearlescent pigments have been used in a variety of . organic substrates such as polymeric coatings, plastic articles, cosmetics and the like. The core typically consists an inorganic platelet or flake and the metal'oxide layers are in the form of a thin film deposited on the surface of the core, and in many cases, on previously deposited layers. Common materials for the core of the pigment include mica, silicon dioxide, glass, aluminum oxides and the like. Commonly encountered metal oxides include, titanium oxide, iron oxide and oxides of tin, chromium and zirconium. The most common metal oxide used in pearlescent pigment layers is titanium dioxide.
The color and other optical properties of a pearlescent are due in large part to effects arising from reflection and light interference dependent on the thicknesses of the coatings. For example, thin Ti02 coatings produce a whitish reflection, which appears to be pearly or silvery. Reflection colors of gold, red, blue, green, etc. can be obtained by using progressively thicker coatings. Iron oxide has an inherently red color and the coated mica, for example, has both a reflection color arising from light interference and an absorption color arising from absorption of light. More intense color and optical effects can be obtained by using other oxide layers, metallic layers and by adding other materials, including inorganic or even organic materials to the metal oxide layers.
The widespread use of titanium dioxide layers causes significant difficulties when using pearlescent pigments in organic substrates due to photocatalytic activity associated with the Ti02, which induces weathering instability and degradation in organic substrates. Exposure of

an organic substrate, such as a polymeric article or coating matrix containing such a pigment to UV radiation in the presence of water and oxygen can cause pearlescent pigment induced accelerated breakdown of the organic compounds which make up the polymeric matrix. The UV radiation component present in sunlight is sufficient to initiate this process.
Surface modification and passivation of pearlescent pigments by applying protective coating layers to the pigment is a well known method to make them more suitable for applications where they will be exposed to UV light, for example, automobile coatings or other outdoor coatings, plastic articles, various inks, cosmetics and the like. The first used protective coatings for pearlescent pigments generally contained trivalent chromium compounds, which due to a greenish color and environmental concerns have been replaced with other metal oxides, for example oxides of cerium and/or zirconium. The onset of waterborne coatings has further aggravated the challenges of meeting the elevated performance standards for many coatings.
In addition to protective layers of inorganic oxides, pearlescent pigments have also been provided with an organic aftercoat or capping layer. In addition to enhancing the weathering stability of the pigments, incorporation of appropriate functionality into these organic aftercoats, can make the stabilized pearlescent pigments more compatible with various polymer resins, such as binder resins, in particular binder resins found in water-based pigmented coating systems. Silicon containing coupling agents bearing functionality capable of reacting with functionality found in, for example, an organic binder, have been used to create an organic capping layer which securely binds to both the surface of the pigment and also to the binder resin. These coating systems exhibit good water condensation resistance, enhanced weatherability, good rheological properties and improved pigment dispersion. Moreover, it is possible for the organic aftercoat or capping layer to positively influence the orientation behavior of pearlescent pigments in the application medium, thus enhancing their optical properties, which can be highfy dependent on geometric factors.
EP 0 141 174 discloses pearlescent pigments with improved weathering resistance which have a protective coating essentially consisting of a rare earth metal compound, e.g. a cerium compound, and a polysiloxane. Zinc, aluminum salts, or silicates can also be present in the protective coating, which is prepared in an aqueous suspension. The coating operation is carried out in aqueous suspension after which the product is dried.

U.S. Pat. No. 4,544,415 discloses a pearlescent pigment with improved weather resistance, comprising mica flakes coated with metal oxides and top coat made of a polysiloxane a rare earth metal compound, i.e., cerium oxide or cerium hydroxide.
U.S. Pat. No 5,423,912 discloses a pearlescent pigment with enhanced weather stability comprising mica coated with titanium or iron oxide which is treated with a top coat containing a combination of hydrated cerium and aluminum oxide. Also disclosed are low temperature water immersion and Q-C-T tests.
U. S. Pat. No. 5,759,255, incorporated herein by reference, discloses a metal oxide coated mica pearlescent pigment with improved humidity resistance and weatherability due to a protective coating comprising a first layer of hydrated aluminum oxide or a combination of hydrated cerium and aluminum oxide, and a second layer of one or more hydrolyzed silane coupling agents, which may be intermingled with the first layer. Silane coupling agents useful in the preparation of the second layer comprise a silicon functional group which binds to the pigment surface and organic functional groups capable of binding to the binder resin. Many of these coupling agents are known and include, e.g., aminopropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, glycidyloxypropyltrimethoxy silane, mercaptopropyltrimethoxy silane and the like.
U.S. Pat No. 5,472,491, incorporated herein by reference, discloses pearlescent pigments based on metal oxide coated, platelet shaped substrates and a top layer comprising silicon dioxide, at least one further metal hydroxide or metal oxide hydrate and at least one organic coupling agent, for example, N-2-aminoethyl-3-propyltrimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-glycidyloxypropyitrimethoxysilane The metal hydroxides or metal oxide hydrates are derived from cerium, aluminum or zirconium or mixtures thereof.
U.S. Pat No. 6,176,918 discloses modified nacreous luster pigments for water paint systems comprising a platelet-form substrate coated with metal oxides and located on the topmost metal oxide layer a top layer consisting of at least two oxides and/or mixed oxides from the group consisting of silicon dioxide, aluminum oxide, cerium oxide, titanium oxide and zirconium oxide, and a water based oligomeric silane system.
U.S. Pat. No. 8,197,591, incorporated herein by reference, discloses a variation of the weather stable pearlescent pigment of US 5,759,255, wherein the pigment has a first metal oxide

protective layer comprising cerium oxide, hydrated cerium oxide and/ or cerium hydroxide, a second silicon dioxide protective layer, and bound to the silicon dioxide layer is an organochemical aftercoating comprising at (east one alpha-silane component of the formula
-0(4-n-m)-Si(-R1)m(-CH2-Y)n wherein 1 < n+m < 3; m is 0,1 or 2; n is 1, 2 or 3; R1 is H, or a Si-C bonded C1-20 alkyl or C1-15 hydrocarbonyloxy interrupted by, e.g., -0-, -CO-, -S-, -NH-, -N-alkyl-, -N=C-, -N=N-; and Y is a functional group reactive with a binder system, e.g., acrylate, vinyl, amino, CN,NCO, COOH, epoxy, etc. Silane components of US 5,759,259, i.e., gamma silanes similar to those of the above formula, may also be present.
While a large number of possible silane aftercoats and silicon coupling agents are generically disclosed in US 8,197,591, very few are actually exemplified. The only aftercoats prepared were prepared from cyclohexylaminomethyl triethoxysilane or cyclohexylaminomethyl diethoxymethylsilane, and/or aminopropyl triethoxysilane.
Organofunctional silanes in the capping layer impart specific properties to the pigment surface depending on the functionalities chosen and capping layers containing a combination of silanes are often more efficient than a single silane system. The choice of the organic functionality depends on the chemistry required for binder resin reactivity and to some extent, the media in which a coating or article is prepared, e.g., the solvent in which a coating is prepared. Both the identities and concentrations of the selected functionalities need to be controlled for the best effects.-
A significant drawback in the art is that the preparation of the aftercoat most often relies on the availability of a precursor siloxane coupling agent containing the desired functional groups. That is, the aftercoat is generally prepared from coupling agents having structures such as
X-(CH2)n-Si-Y3, or X-(CH2)n-Si(R)-Y2, wherein X is an organic functional group covalently bonded to the central silicon atom via a carbon chain, R is an alkyl group or a second X-(CH2)n- group, and Y is a silicon bonded hydrolysable functional group, generally an alkoxy group, which results in free hydroxyl groups upon hydrolysis, that in turn hydrogen bond with, e.g., an inorganic substrate for example a pigment surface, and upon further condensation forms a stable bond between the silane and the inorganic substrate.

The organic functionality of the capping layer is therefore the X-(CH2)n- group of the coupling agent. The functional group X must therefore be stable to the conditions used to.prepare the coupling agent and the conditions encountered in the process of adhering the coupling agent to the pigment surface. However, coupling agents bearing certain substituents, particularly multi functional substituents, are neither currently available nor readily prepared. Specifically, certain aftercoats and coupling agents inferable from the generic disclosure of US 8,197,591 are not obtainable by the processes therein.
U.S. Pat. No. 4,818,614, discloses a capped titanium dioxide-coated mica pigment which is first coated with a silicon polymer containing Si-H moieties, and then the pigment bound silicon polymer is modified with a compound capable of reacting at the Si-H. This process allows for some flexibility in that functional groups can be incorporated after the protective layers and after coating have been applied, however, it is limited by the available reagents that will successfully react at Si-H.
There is, therefore, still a need for a simple process that can successfully provide a greater array of silane bound functionality in the organochemical aftercoat. A process has been identified comprising a straightforward means for effectively modifying functionality present on the organochemical aftercoat which was introduced by the silane coupling agents used in its preparation. The process gives one greater flexibility to tailor silane based aftercoats and fine tune pigment processing and performance characteristics, by allowing for the introduction of functionality that can not be introduced directly via the substituents found on a readily prepared silicon coupling agent.
SUMMARY OF THE INVENTION
The present invention overcomes aforementioned disadvantages to provide a pigment comprising one or more metal oxides which is after coated with a multi-functional capping layer prepared by first depositing on the pigment one or more coupling reagents bearing organic substituents, with at least one substituent comprising a targeted reactive organic functional group, such as a free primary amino functionality, wherein some or all of the targeted functional group is modified by an organic reagent to introduce further functionality while the coupling agent is bound to the pigment surface either through hydrogen bonding network or through a bond involving oxygen atom. For example, a targeted primary amine is reacted with a dialdehyde or diketone to create an imine group which is further substituted by carbonyl.

For example, one embodiment of the invention provides a pigment comprising one or more metal oxides which is after coated with a multifunctional organo silane surface capping layer, wherein the capping layer contains at least one silicon moiety comprising an alkyl group substituted with a functional group capable with reacting a binder resin, e.g., an aminoalkyl group, a silicon moiety comprising an polyfunctional alkyl group, e.g., an alkyl group comprising an imino group and a carbonyl substituent such as a polyfunctional group derived by a reaction between an amino-alkyl group and a dicarbonyl. In other embodiments the capping layer further
comprises one or more silicon moieties comprising an unsubstituted alkyl group, an alkyl group
'i
substituted with an organic functional group, and/or a polyfunctional alkyl group.
Particular embodiments provide pearlescent pigments coated with the organo silane capping layer above. Thecapped pearlescent pigments of the invention typically also comprise a first inorganic protecting layer comprising e.g., select metal oxides, and a second protection layer of silicon dioxide to which the capping layer is bound.
Pigments of the invention, for example, pigments coated with an organo silane capping layer comprising a silicon bound difunctional alkyl group, e.g., an alkyl group containing both a imine and ketone or aldehyde group, are made available by an inventive process whereby silicon coupling agents comprising reactive functional groups, e.g., amino groups, are bound to the surface of a pigment via a hydrogen bond or covalent bond to provide an intermediate capped pigment, and while thus bound to the pigment, all or a certain amount of reactive functional groups are modified by reaction with a difunctional reagent, e.g., a dicarbonyl compound.
The process of the invention allows for the preparation of a number of pigments, such as the imino-carbonyl alkyl silane capped pigment described, which are not obtainable by known methods, e.g., those of US 8,197,591 wherein a coupling agent comprising the final difunctional imino-carbonyl alkyl group is added to a pigment, because the required difunctional coupling agent is neither commercially available nor stable under the conditions for preparation.
The invention therefore provides the metal oxide containing pigments capped with the inventive capping layer, compositions comprising the pigments, and the process by which the pigments are prepared. Specific embodiments relate to pearlescent pigments of the invention comprising the inventive capping layer, and in particular, pearlescent pigments further comprising inorganic

protection layers of metal oxides and silicon dioxide having excellent weatherability. Furthermore, pigments coated by the process of the invention, whether layered pearlescent pigments or other pigments comprising metal oxides, also demonstrate excellent dispersability in polymers, such as thermoplastic compositions and coating binders, as well as excellent adhesion properties in water born, solvent born, or powder coatings.
Another embodiment of the invention provides mixed pigments comprising pigments of the invention wherein the density of reactive groups of the capping layer has been modified, along with pigments comprising a capping layer with unmodified density of reactive groups. For example, a mixed pigment comprising pigments capped by amino silane coupling agents, and pigments.prepared therefrom capped with imino-carbonyl siiane moieties formed by reacting the amino group with a dicarbonyl. Such mixed pigments show surprising synergy regarding certain physical properties, for example, mixed pigments are prepared which exhibit greater adhesion than either the individual pigment comprising the amino silane coupling agent or the individual modified imino-carbonyl containing pigment formed therefrom.

Scheme 1. Pathway of surface density modification of the organic coupling agent such as silane, bound to the surface of a pearlescent pigment, either via hydrogen bonding network or chemical bond through oxygen, and a blended mixture comprising pigments with' modified density of surface capping and. pigments containing unmodified density of surface capping.

DESCRIPTION OF THE INVENTION
One general embodiment of the invention provides a pigment comprising one or more metal
oxides and an organo silane capping layer, wherein the capping layer comprises
a) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-6 aminoalkyl group, e.g., a C1-3 aminoalkyl group, e.g., aminomethyl, aminoethyl or aminopropyl; and
b) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C3-24 imino-alkyl group substituted or interrupted by carbonyl, that is, a substituent containing 3 to 24 carbon atoms comprising an internal C-N double bond and a ketone or aldehyde group, e.g., a C3-12 imino-alkyl group substituted or interrupted by carbonyl.
In another embodiment, the capping layer of the above pigment further comprises
c) one or more silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one
C1-20 alkyl group;
C1-30 alkyl group substituted by one or more groups selected from OH, C1-12 carbonyloxy, COOH, amino, amido, ester or epoxy;
and/or
C1-30 alkyl group interrupted by one or more -0-, -NH-, -N(alkyl)-, -C=N- carbonyl or carboxy and optionally substituted by one or more OH,C1-12 carbonyloxy, COOH, amino, amido, ester or epoxy.
For example, a pigment as above wherein the capping layer comprises
a) at least one'silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-6 amino-alkyl group, e.g., C1-3 amino-alkyl group
b) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C3-12 imino-alky! substituted or interrupted by carbonyl, arid
c) one or more silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one

C1-12 alkyl group or
C1-30 alkyl group substituted by one or more groups selected from OH, COOH, amino, ester or epoxy, and/or interrupted by one or more -0-, -NH- or -N(alkyl)-. .
For example, a pigment wherein the capping layer comprises
a) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-3 amino-alkyl group,
b) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-14 imino-alkyl substituted or interrupted by carbonyl, and optionally
c) at least one or more silane coupling moiety attached to the pigment by a hydrogen bond or
covalent bond and substituted at silicon by at least one alky! group substituted by epoxy or giycidyloxy.
For example, the capping layer comprises
a) a group-O(4-n+m)Si (-R1)n(-R-NH2)m and
b) a group-0{4.n+m)Si(-R1)n(-R-N=C(R2')R2)m
wherein n+m= 1 or 2; n is 0 or 1; m is 1 or 2; R is C1-3 alkylene, R1 is C1-6 alkyl, R2 is a C2-5 ketone or aldehyde and R2' is H or C{1-3)alkyl.
or
a) a group -O(4-n+m)Si(-R1)n(-R-NH2)m
b) a group -O(4.n+m)Si(-R1)n(-R-N=C(R2)R2)m and
c) a group -O(4.n+m)Si(-R1)n(-R3-glycidyJoxy)m
wherein n+m= 1 or 2; n is 0 or 1; m is 1 or 2; R is C1-6alkylene, e.g., C1-3 alkylene, R1 is C1-6 alkyl, R2 is a C2-11 ketone or aldehyde, e.g., C2-5 ketone or aldehyde, R2' is H or C^alkyl, e.g., H or methyl, and R3 is C1-6 alkylene, e.g., C1-3alkylene.
In the formulas above, e.g., -O(4.n+m)Si(-R1)n(-R-NH2)mi one of the oxygen atoms may be bound to another silane group. When the other silane group is a group of one of the above formulas, it is understood that each of the silicon atoms involved are tetravalent and one of the 4-n+m oxygen atoms is shared between the two silicon groups as in the following (-0-)(3-n+m)(-R-NH2)m(-R1)nSi-0-Si(-R1)n(-R-NH2)m(-0-)(3-n+m).

While any pigment comprising a metal oxide can benefit by the improved dispersion and adhesion properties provided by the capping layer of the invention, e.g., in solvent or water born coatings, especially water born coatings, the inventive capping layer is particularly valuable for use on pearlescent pigments, i.e., pigments comprising a core platelet substrate coated with one or more metal oxide layers, especially where at least one of layers is a titanium dioxide.
Generally, when preparing a pearlescent pigment of the invention, best results, particularly in terms of weatherability, are obtained by depositing a first protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof, and a second protective layer of silicon dioxide, upon which the capping layer is adhered.
Thus, particular embodiments of the invention provide a pearlescent pigment comprising a core platelet substrate coated with one or more metal oxide layers, at least one of which is a titanium dioxide or iron oxide layer, and an organo silane capping layer as described above; for example, the pearlescent pigment which further comprises a silicon dioxide protecting layer upon which the capping layer is adhered; and more particularly a pearlescent pigment comprising a first protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof, a silicon dioxide protecting layer, and adhered to the silicon oxide protecting layer, the capping layer above.
Any pearlescent pigment can be used in the present invention, for example, a commercially available pearlescent pigment. The platelet shaped substrate of the pearlescent pigment may be made of a natural or synthetic mica, kaolin, glass, talc, aluminum oxide, etc, which is coated with metal oxides such a titanium dioxide, iron oxides, titanium dioxide mixed with iron oxides, tin dioxide, zinc oxide, etc. Pigments of this type include, for example, those that are commercially available under the name Sumica® (manufacturer: Sudarshan Chemical Industries Ltd.)
Specific embodiments of the invention therefore provide pearlescent pigments comprising a platelet or flake shaped core substrate, one or more metal oxide layers, at least one of which is a titanium dioxide layer, and
a first.protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof,

a second protective layer comprised mainly of silicon dioxide, upon which silicon dioxide is adhered a capping layer comprising
a) a group -0(4.n+m)Si(-R1)n(-R-NH2)m
b) a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and optionally
c) a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m wherein
n+m= 1 or 2, typically 1; n is 0 or 1, typically 0; m is 1 or 2, typically 1;
R is C1-6 alkylene, e.g.,C1-3 alkylene such as methylene, ethylene or propylene;
R1 is C1-12 alky], for example C1-6 alkyl such as methyl, ethyl, propyl, butyl, pentyl, hexyl, or
cyclohexyl;
R2 is a C2-n ketone or aldehyde, e.g., C2-5 ketone or aldehyde,
R2' is H or C(1-3)alkyl, e.g., H or methyl, and
R3 isC1-6 alkylene, e.g., C1-3 alkylene such as methylene, ethylene or propylene.
. The relative amounts of the components a), b) and c) in the capping layer can be varied depending on the exact properties desired. In general, 25 to 99 mole%, and in certain embodiments 100 moi% of the silane capping layer are components a) and b), in some embodiments, 25 to 75 mol%, e.g., 30 to 70 mol%, is comprised by these two components and 25 to 75 mol %, e.g., 30 to 70 mol%, by component c). In some embodiments 50 to 100 mol% is comprised by components a) and b), and 0 to 50 mol % by component c), and in one particular 50% is comprised by components a) and b), and 50 mol % by component c).
For example, the aftercoat is a capping layer wherein
1 to 99 mol %, e.g., 1 to 99 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-
NH2)m
1 to 99 mol %, e.g., 1 to 99 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-
N=C(R2')R2)m and
0 to 75 mol %,e.g., 1 to 75 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R3-
glycidyloxy)m
for example,
5 to 60 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-NH2)m
10 to 65 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and
30 to 60 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m

or
1 to 49 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-NH2)m
1 to 49 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and
40 to 50 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m
The relative amounts-of the silane moieties present in the capping layer are readily controlled by the process for forming the capping layer. The process comprises: a) adding to a pigment suspended in an appropriate liquid media, e.g., water, an alcohol, alcoholic water, or other organic or aqueous solvents, one, two or more coupling agents of the general formula
(R'0-)pSi(-R")q(-RY)r
wherein p+q+r = 4, p is 2 or 3; q is 0 or 1, and r is 1 or 2;
R is an alkylene group, typically comprising 1 to 6 carbon atoms, e.g., 1 to 3 carbon
atoms;
R' is an alkyl group typically comprising 1 to 6 carbon atoms;
R" is an alkyl group of 1 to 6 carbon atoms e.g., 1 to 3 carbon atoms; and
Y is an organic functional group capable of reacting with an organic binder polymer, provided that at least one coupling agent comprises a group (RY) wherein Y is a group such as primary amino, which group which is targeted for further modification in a subsequent reaction, to form an intermediate capped pigment, followed by
b)modifying the intermediate capped pigment at the targeted group Y, e.g., primary amino group, by reaction with an organic'reagent, typically a difunctional or polyfunctional reagent such as a dicarbonyl compound, to form the pigment of the invention.
The pigment after surface capping with organofunctional silanes in step a) can be filtered off, washed and dried, or it can be used directly in step b) without isolation. This pigment is called the pigment with unmodified density of surface capping, i.e., PUDSC. The pigment produced by modification of the PUDSC in step b) is called the pigment with modified density of surface capping, i.e., PMDSC.
Of course if the intermediate capped pigment is isolated it is re-suspended in an appropriate solvent, i.e., aqueous, organic or mixed solvent before modification. Organic solvents include, for example, ethers, esters, alcohols etc. Alternately the intermediate capped pigment can be

isolated and used as a standalone pigment or conveniently mixed or blended with other pigments of the invention, in particular pigments formed by the above modification of the same intermediate capped pigment, to form another product of this invention.
Examples of common coupling agents useful in the invention include those of the above formula wherein R is methylene, ethylene or propylene; R' is methyl, ethyl, propyl or butyl; R" is methyl, ethyl, propyl or butyl; Y is primary amino, methylamino. ethylamino, propylamino, cylohexylamino, glycidyloxy, carboxylic ester, acryloyl, aniline and the like. For example, certain pigments of the invention comprise a capping layer prepared using the coupling agents aminopropyltriethoxysilane, and 3-glycidoxypropyltriethoxysilane, wherein a portion of the amino groups are subsequently modified with a dialdehyde of the formula 0=CH-(CH2)n-CH=0 where n is 0-6. an aromatic dialdehyde, a diketones of the formula: 0=CR-(CH2)n-CR=0 where n is 0-6 and R is alkyl or aryl or an aromatic diketones.

Scheme 2. Exemplified pathway using two organofunctional silanes bound to a pigment wherein the modification of the aminopropyl functionality is realized through reaction with dialdehyde, generating a pigment with modified density of aminopropyl functionality.

Alternate embodiments of the invention can be readily envisioned wherein a targeted silane-bound amino group can be reacted to form an amide derivative or reacted with an epoxide reagent forming a hydroxy amine; or where an epoxy group as Y is targeted for modification and is reacted, e.g., with an amine, alcohol, polyamine, polyol, polyetheralcohol, amino acid etc.
The amount of components a) plus b) present in the capping layer of the final modified pigment, PMDSC, for example, in the sequence above wherein the targeted functional group is aminopropyl, is determined by the amount of aminopropyl silane coupling agent relative to the other silane coupling agents reacted to form the PUDSC. The relative amount of a) to b) is determined by the amount of primary amine groups that react with the dicarbonyl.
Other coupling agents may also be employed in this process, and any of the organo silicon coupling agents of the art may be used. Examples of available organo silane coupling agents useful in the present invention can be found in the art, e.g., U.S. Pat. No. 8,197,591 and references cited therein. Multiple silanes comprising different functional groups can be metered in simultaneously or one after another during step a) and more than one functional group can be targeted for further modification, including mixtures of e.g. alpha- and gamma amines. Appropriate selection of the amounts and mode of addition of the coupling agents allows one to prepare PUDSC capping layers with preselected ratios and densities of various silane moieties on the intermediate capped pigment. The final make up of the modified capping layer of the PMDSC is determined by the amount and identity of organic reagent or reagents used in the modification step.
It is also possible to use as a portion of the coupling agent compounds that do not comprise reactable functional groups, however, these are typically not the major portion of the coupling agents used.
As stated above, particular pigments of the invention are prepared from pearlescent pigments which comprise a platelet shaped core coated by one or more metal oxide layers, most notably wherein at least one of the metal oxide layers comprises titanium dioxide. Such pigments typically comprise a first protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof, and a silicon dioxide protecting layer upon which the capping layer above adhered. These two inorganic layers are applied according to procedures known in the art, e.g., US Pat. No. 8,197,591 already incorporated by reference, which is followed by the

incorporation of the capping layer as described above. Specific embodiments of the overall process are shown in the appended Examples.
The optical effects of pearlescent pigments are greatly influenced by the thickness of the various metal oxide layers that are chosen to coat the core. One therefore needs to be sure that the protective layers, e.g., metal oxide layers, applied in the practice of the invention are not of a thickness that would alter the optical properties of the pigments, while still being thick enough to provide the desired protection. Due to the processes by which the layers of the invention are deposited on the pigment, it is possible to correlate and control the thickness of the layer with the amount of material deposited,
Thus, the amount of the organochemical aftercoat employed in the invention is from 0.1% to 6%, by weight, e.g., from 0.2% to 5%, by weight, based on the total weight of the pigment.
The amount of the oxides, hydroxide or oxide hydrate of Ce or Zr, or W or Mo or mixtures thereof in the first protection layer is between 0.1% to 5%, generally between 0.2% to 1% by weight. For example, when cerium is employed in the first protection layer, the amount of cerium oxide and/or hydrated cerium oxide and/or cerium hydroxide deposited in order to provide a good balance between UV stabilization and impact on optical effects is from 0.1% to 3.0%, by weight, and often from 0.1% to 1.0%, by weight based on the total weight of the pigment. Meta! oxidelayers, in addition to the first protective layer may also be added, e.g. a zirconium oxide layer, and such a layer will be of a similar weight.
Despite the low refractive index of Si02, the pigments usually have a very good luster even when relatively thick layers are applied, while on the other hand, even thin layers Si02 improve UV stability. However, no additional benefit is seen by adding an excessive amount of Si02, for example, the amount of silicon dioxide or other silicates in the protective layer is less than 8% by weight, often less than 5% by weight and in many cases the amount of deposited Si02 is from 0.1 to 5%, from 0.1 to 1%, or from 0.5 to 1% by weight based on the total weight of the pigment. In addition to Si02 there may also be present hydroxides, suboxides and/or hydrated oxides of silicone in the Si02.
In individual cases, the proportion by weight of the layers of the invention depend on the fineness and, concomitantly, on the specific surface area of the pearlescent pigment and the

thickness of Ti02 layer. Fine pigments or thicker Ti02 layers can demand a higher content of, e.g., cerium oxide and/or cerium hydroxide and/or hydrated cerium oxide, and/or higher amounts of Si02 per Weight of pigment.
One embodiment of the invention is a pearlescent pigment prepared by: i) depositing by precipitation onto the pigment surface at 50 to 90°C, e.g.,75 to 85°C, and a pH of from 3 to 6, approximately 0.1% to 5%, generally 0.2% to 1%, an oxide, hydroxide and/or hydrated oxide Ce or Zr, or W or Mo or mixtures thereof;
II) raising the pH to from 7 to 9.5, generally from 7.5 to 8.5, and adding sodium silicate or . tetraethyl orthosilicate, e.g., a 30 % solution of sodium silicate or 28% tetraethyl orthosilicate, to deposit a silicate or Si02 layer, typically between 0.1 to 5%, generally 0.5% to 1% as Si02, wherein all the metal hydroxides or oxide hydrates are already completely precipitated; Ilia) surface capping the pearlescent pigment thus obtained at pH of from 7 to 9.5, e.g., 7.5 to 8.5 with a separate layer containing from 1 to 10% by weight, e.g. from 1 to 5% by weight, of organofunctional silanes wherein at least one silane contains primary amino functionality to obtain the PUDSC, and
IIIb) modifying the targeted functional groups of the PUDSC, partially or completely, with a reactive agent comprising a dialdehyde or diketone forming an carbonyl substituted alkyl imine, i.e., Schiff base substituent on the organofunctional silane bound by means of oxygen bond (when PUDSC is isolated and dried prior to modification), or pigment bound by hydrogen bonding network to the pigment surface (in case of wet cake PUDSC), after which the pigment is isolated and dried, e.g. at elevated temperatures. Hydrogen bound silane moieties become covalently bound during the drying process.
A partial modification of the PUDSC is modification of 0.1 to 50% of the existing targeted functionality, typically 5 to 50% of said functionality; and total modification is modification of more than 50%, preferably more than 80% of the targeted functional groups.
it has been found that modification of amino by reaction with, e.g., a dialdehyde, in presence of the pigment as in the invention can be used to generate a mono-imine product as opposed to a bis-imine product Significantly it has been found that in the absence of adherence to the pigment surface, modification of the silane amino function to a mono-imino alkyl group further comprising an aldehyde does not proceed as above, rather such reactions using an uncomplexed silane coupling agent invariably result in disilyl-bis-imino products plus other

unidentified byproducts (see, e.g., comparative example 6). Thus, the novel pigments of the invention, comprising certain specific surface capping aftercoats, especially with highly reactive functionality, e.g., aldehydes, or more particularly difunctional organic substituents, e.g., carbonyl substituted imino-alkyl groups, are generally not available by conventional methods, because the silane starting materials needed to prepare the products of the present invention are unavailable.
Pearlescent pigments which can be employed in the invention include the commercially available pigments. Examples of pearlescent pigments can be found, e.g., in U.S. Pat. No. 8.197,591. Pearlescent pigments typically contain a platelet-shaped substrate, generally selected from the group consisting of mica, talc, sericite, kaolin and Si02, glass, graphite, Al203 platelets and mixtures thereof. For example, natural or synthetic micas, Si02, glass, or Al203 platelets, whose standard deviation of the thickness distribution is lower than 20%, preferably lower than 15%, e.g., lower than 10%. These substrates have particularly smooth surfaces. Particularly color-intense pearlescent pigments with strong color flops can therefore be prepared using these substrates. Glass platelets may be used with a mean thickness of the glass platelets of up to 1 micron, e.g., less than 500 nm e.g., less than 350 nm. Glass platelets coated on both sides with semitransparent metal layers are known such as layers of silver, aluminum, chromium, nickel, gold, platinum, palladium, copper, zinc, and mixtures and alloys thereof. The thicknesses of the semitransparent layers preferably range from about 2 nm to about 30 nm, more preferably from about 5 nm to about 20 nm.
A wide variety of inorganic layers, such as layers comprising metal oxides, metal hydroxides, hydrated metal oxides, metal suboxides and metal sulfides, metal fluorides, metal nitrides, metal carbides, and mixtures thereof are known. Often a multilayer system comprises at least one highly refractive layer, at least one poorly refractive layer. Most often highly refractive and poorly refractive and again highly refractive layers are present in that order as regarded from the inside to the outside of the layer system. The refractive index of the metaf oxide layer required to afford a good pearlescent effect, is greater than 1.8, preferably greater than 2.2, more preferably greater than 2.3, even more preferably greater than 2.4,-and very preferably 2.5 or greater.
Examples of commercially available pearlescent pigments include: mica pigments coated with Ti02 and/or iron oxide are commercially available, for example, under the name PHOENIX (Eckart). Al203 flakes coated with Ti02 and/or Fe203 are supplied by, e.g., Merck under the

trade name XIRALL1C, and correspondingly coated Si02 flakes under the trade name COLORSTREAM: glass flakes coated with Ti02 and/or iron oxide are available, for example, from Engelhard, USA under the name FIREMIST, or by Merck, Darmstadt under the name MIRAVAL Multilayer interference pigments are described, for example, in DE 19618569, consisting of a carrier coated with alternating layers of metal oxides of low and high refractive index. Each of these pigments and others can be aftercoated according to the invention.
Qther specific embodiments of the invention include blended mixtures of pigments with unmodified density of surface capping (PUDSC) and pigments according to the invention wherein the density of surface capping is modified (PMDSC) in varying ratios. The final mixture of pigment may comprise either two or more parts of identical or non-identical platelet shaped-substrates. For example, the PUDSC and PMDSC are blended together at temperature of at 20 to 70°C e.g., 20 to 50°C, in a blender apparatus or as in the form of slurry made in water to get blended mixtures. Two types of mixtures are obtained. One mixture has homogeneous amount of at least one unmodified silane group(s), other than those bearing amino functionality, present on each part(s) of the mixture and the other that consists of non-homogenous amount of at least one unmodified silane group(s), other than those bearing amino functionality, present on each part(s) of the mixture.
Pearlescent pigments prepared according to the invention exhibit improved weathering, passivated photocatalytic activity, and superior adhesion after humidity exposure in both solvent and water borne coating systems. Surprisingly, the homogeneous (in terms of % surface unmodified functional group) blend of the PUDSC & PMDSC equal or more pronounced. . improvements. The mechanism underlying this improved adhesion over the standalone surface density unmodified pigment remains to be elucidated, perhaps it is due to an increase in the network of hydrogen bonding and the presence of finely tuned non-identical functionalities could possibly be an operative pathway.
The pigments of the invention, including pearlescent pigments, mixed pigments or standalone single pigments, are well suited for use in, e.g., polymeric coatings, including water born, solvent born, powder coatings and inks, plastic articles, and cosmetic formulations. In particular, the coated pearlescent pigments of the invention are used as weather-resistant pearlescent pigments in automobile lacquers and powder-based pigmented coating systems and other coatings for external applications.

EXAMPLES
Example 1
In1 lit flask 40 gm of Sumica® iridescent blue pigment (titanium dioxide coated mica pigment)
are suspended in 266 ml demineralised water with stirring and the slurry is heated to 80°C. The
pH of the slurry is then adjusted to 3 using HCI (3.6% HCI) and 1.3 gm of the 20% Ce(N03)3
solution is added to the slurry. The mixture is stirred for 30 minutes after which the pH is adjusted to 6 using 3.5% NaOH solution and 0.75 g of tetraethyl orthosilicate (28% Si02) is added while maintaining the pH of the slurry at 8.5. The mixture is stirred for a further 20 minutes at pH 8.5 and then 0.57 gm of gamma-aminopropyltrimethoxysilane silane is added. The mixture is stirred at pH 8.5 at 80°C for 60 minutes, the product is subsequently filtered, washed and dried at 120°C for 12 hours.
Example 2
In 1 lit flask 40 gm of Sumica® iridescent blue pigment (titanium dioxide coated mica pigment) are suspended in 266 ml demineralised water with stirring and the slurry is heated to 80°C. The pH of the slurry is then adjusted to 3 using HCI (3.6% HCI) and 1.3 gm of the 20% Ce(N03)3 solution is added to the slurry. The mixture is stirred for 30 minutes after which the pH is adjusted to 6 using 3.5% NaOH solution and 0.75 g of tetraethyl orthosilicate (28% Si02) is added while maintaining the pH of the slurry at 8.5. The mixture is stirred for a further 20 minutes at pH 8.5 and then 1.14 gm of garnma-aminopropyltrimethoxysilane silane is added. The mixture is stirred at pH 8.5 at 80°C for 60 minutes, after which the product is filtered, washed and re-slurried in 300 mi demineralised water. The temperature of the constantly stirred slurry is maintained at 70-80C. The pH is adjusted to 6.5 and 1.14 gm of glutarldehyde (50% w/w in water) is added to the slurry and stirred for 30 min. The pigment is filtered, washed and dried at 120°C for 12 hours.
Example 3
A 1:1 mixture of the pigment according to Example 1 and a pigment according to Example 2 is made in a blender assembly. This is a mixture of pigment having homogenous composition of gamma-glycidoxy propyl trimethoxy silane.

Example 4
In 1 lit flask 40 gm of Sumica® iridescent blue pigment (titanium dioxide coated mica pigment) are suspended in 266 mL demineralised water with stirring and the slurry is heated to 80°C. The pH of the slurry is then adjusted to 3 using HCI (3.6% HCI) and 1.3 gm of the 20% Ce(N03)3 solution is added to the slurry. The mixture is stirred for 30 minutes after which the pH is adjusted to 6 using 3.5% NaOH solution and 0.75 g of tetraethyl orthosilicate (28% Si02) is added while maintaining the pH of the slurry at 8.5. The mixture is stirred for a further 20 minutes at pH 8.5 and then 0.6 gm gamma-glycidoxy propyltrimethoxy silane is added followed by 0.6 gm of gamma-aminopropyltrimethoxysilane. The mixture is stirred at pH 8.5 at 80°C for 60 minutes, the product is subsequently filtered, washed and dried at 120°C for 12 hours.
Example 5
In 1 lit flask 40 gm of Sumica® iridescent blue pigment (titanium dioxide coated mica pigment) are suspended in 266 mL demineralised water with stirring and the slurry is heated to 80°C. The pH of the slurry is then adjusted to 3 using HCI (3.6% HCI) and 1.3 gm of the 20% Ce(N03)3 solution is added to the slurry. The mixture is stirred for 30 minutes after which the pH is adjusted to 6 using 3.5% NaOH solution and 0.75 g of tetraethyl orthosilicate (28% Si02) is added while maintaining the pH of the slurry at 8.5. The mixture is stirred for a further 20 minutes at pH 8.5 and then 0.6 gm of gamma-glycidoxy propyltrimethoxy silane is added followed by 0.6 gm of gamma-aminopropyltrimethoxysilane. The mixture is stirred at pH 8.5 at 80°C for 60 minutes, after which the product is filtered, washed and re-slurried in 300 mL demineralised water. The temperature of the constantly stirred slurry is maintained at 70-80C. The pH is adjusted to 6.5 and 1.2 gm of glutarldehyde (50% w/w in water) is added to the slurry and stirred for 30 min. The pigment is filtered, washed and dried at 120°Cfor 12 hours.
Comparative Example 1
Sumica® iridescent blue standalone serves as a comparative to example 1 without any
protective layers.
Comparative Example 2
In a 1 liter flask 40 gm of Sumica® iridescent blue (titanium dioxide coated mica pigment) is suspended in 266 mL demineralised water and the slurry is heated to 80C at a pH of 8.5 and 1.6 gm of gamma-aminopropyl trimethoxy silane is added. The mixture is stirred at pH 8.5 at

80°C for 60 minutes, then fiitered and washed. The pigment obtained is dried at 120 C for 12 hours.
Comparative Example 3
\n a 1 liter flask 40 gm of Sumica® iridescent blue (titanium dioxide coated mica pigment) is
suspended in 266 mL demineralised water and the slurry is heated to 80C at a pH of 8.5 and
2.4 gm of gamma-aminopropyl trimethoxy silane is added. The mixture is stirred at pH 8.5 at
80°C for 60 minutes, then filtered and washed. The pigment obtained is dried at 120 C for 12
hours.
Comparative Example 4
In 500 mL flask, 20 gm of pigment prepared according to comparative example 2 is suspended in 135 mL demineralised water and the slurry is heated to 80°C at 6.5 and 0.6 gm of glutaraldehyde (50% w/w in water) is added. The mixture is stirred at pH 6.5 at 80°C for 30 minutes, then filtered and washed. The pigment obtained is then dried at 120 C for 12 hours.
Comparative Example 5
A 1:1 mixture is.made as a water based slurry in de-mineralized water using one part as per comparative example 3 and the other as per comparative example 4 in flask. The final pH of the slurry is adjusted to 6.5 and stirred at 70°C for 1 h. The homogeneous mixture obtained is filtered and dried at 120°C for 12 h.
Comparative Example 6
In 100 mL flask, 1.2 gm of gamma-aminopropyl trimethoxy silane diluted with 30 mL of a 1:1 ethanol water mixture. To this was added 0.6 gm of glutarldehyde (50% w/w in water) and the . mixture was stirred at ambient temperature for few minutes. During this time the color of the mixture turned yellow and then dark red, finally resulting in a red colored gel. The product was dried in a vacuum desiccator to get a resinous material.
The preceding examples 1-3 can be repeated with similar success with specified reactants or by generic substituent and/or operating conditions of this invention.
The pigment, and the mixtures thereof are tested by the following test methods:

Water resistance - Pressurized Hot Water Test (PHWT)
The test is performed in a pressure apparatus. The apparatus is equipped with a pressure release weight (55 gm) and a safety valve (melt pressure of 3 kgs. per. sq.'cm.). The operating pressure of the apparatus using water is 1.03 bar over the atmospheric pressure with intermittent release of the excess pressure. At 1.03 bar over the atmospheric pressure the boiling point of the water inside the vessel is 121 °C. Thus the water inside the vessel is a pressurized hot water having substantially elevated boiling point. These conditions are therefore best termed as most harsh water exposure conditions to which a coating system can be exposed.
Water resistance - Three Hour Boiling Water Test (3HBWT)
The test is performed in water bath set at a temperature to continuously boil the water. These .
conditions are milder than that of pressurized hot water test conditions.
The pigment samples were incorporated into both solvent borne and water borne coating systems. The test panels were prepared by spray application. FOR THE PHWT the panels were fully dipped in water inside the pressure apparatus and exposed to the pressurized hot water conditions for 25 minutes during which time the pressure intermittently is released as per the weight applied. Upon completion of the duration of the test the panels are removed from the vessel, wiped with a clean cloth and allowed to stand until ambient temperature is reached.
FOR THE 3HBWT the test panels were fully dipped in water inside the water bath. The panels were exposed to boiling water conditions for 3 hours. Upon completion of the duration of the test the panels are removed from the bath, wiped with a clean cloth and allowed to stand until ambient temperature is reached.
Water resistance -10 Day Humidity Test (1ODHT)
The test is performed as per the ISO 6270-2. The panels were removed after the exposure to
humidity for 240 hours and let stand for 1 hour.
The degree of blistering was assessed visually in accordance with ASTM D714-87 (F is few, M is medium, MD is medium dense, D is dense, 1 is worse, 10 is no blister). As soon as the panels reached ambient temperature a 2 mm cross hatch cut was performed for the 3HBWT PHWT and 10DHT using BYKO-Cut Universal film gauze (cat. No. PG 3430) as per DIN EN

ISO 2409 and the adhesion test was performed using 3M 898 tape in accordance with GMW14829. The adhesion is rated as per ISO class (0 is intact 5 is more than 65% exposed). Table 1 shows the results in solvent borne coating system and Table 2 shows the results of the selected candidates in water borne coating system.
Table 1: results on the test paint panels made in solvent base system and exposed to various
humidity conditions.
10DHT* 3HBWIT* PHWT*
Comparative
Example 15 5 5
Example 11 4 4
Example 2 1 1 5
Example 3 1 13
Note: None of the panels show blistering. *cross hatch test using 2 mm cross hatch tool, performed after 1 hour post exposure period
Table 2: results on the test paint panels made in water base system and exposed to various humidity conditions.
10DHT* 3HBWIT*
Comparative
Example 1 4 5
Example 1 1 2
Example 2 11
Example 3 11
Note: None of the panels show blistering. *cross hatch test using 2 mm cross hatch tool, ,
performed after 1 hour post exposure period
. It is evident from the results obtained as shown in Table 1 and 2 that compared to Comparative Example 1 and Example 1 the products as per example 2 and 3 exhibited superior performance. Moreover, a synergistic advantage is seen in example 3, i.e. a 1:1 blend of example 1 and example 2.

Discoloration Resistance Test
The test is performed in accordance with the description mentioned in U.S. Pat. No. 5688314. The Db values were calculated for the assessment of resistance to discoloration. The lesser the Db values the better is the product for discoloration resistance. Table 3 gives the Db values.
Table 3: Db values for the assessment of resistance to discoloration
Db
Comparative 1 1.937
Example 1 0.294
Example 2 0.126
Example 3 0.215
Relative to the pigment with surface modification completely absent as per comparative example 1 all products as per example 1, 2 and 3 showed reduced photocatalytic behavior. The product of example 2 and the 1:1 blend of example 3 are superior in terms of reduced photocatalytic activity than example 1.
Identification of free carbonyl and amino groups on the pigment surface. To estimate semi-quantitatively the amount of free amino groups originating from the pigment surface bound silane, Rimini's test is performed. The pigments with higher concentrations of the amino functionality were employed for these purposes (comparative examples 1-6). Typically, a 2 g pigment is added to 5 ml DM water, 5 mi acetone (L.R grade) and 20 ml (0.13M) sodium nitroprusside solution. The developed color stayed with the pigment. Development of violet red color confirms presence of primary amine group on the pigment. Although the developed color is unstable for temperature and fades with time, it provided sufficient time to work up the reacted pigment and incorporate into a nitrocellulose lacquer to perform a pull down. The color assessment is made on .the nitrocellulose film to determine the color change to semi-quantitatively know the concentration of amino group. Table 4 shows the color analysis.
Table 4: L, a, b, C & H values obtained from the NC lacquer film containing the pigment that's
been treated with Rimini's reagent. The pigment loading in lacquer is 10%
Name (Rimini's test) illu L* a* b* C* H
Comparative example 1 D65 89.28 -0.743 3.597 3.673 101.675

Comparative example 2 D65 88.27 0.238 2.652 2.663 84.867
Comparative example 3 D65 87.902 0.605 2.294 2.372 75.218
Comparative example 4 D65 88.495-0.6614.12 4.172 99.113
Comparative example 5 D65 88.773-0.704 3.878 3.941 100.28
It is evident from the 'a' values of Comparative example 2 & 3 that as the concentration of amino grouping increases the 'a' value increases. When the amino function is reacted with glutaraldehyde as per comparative example 4 the 'a' value is almost equivalent to that of Comparative example 1 that does not have any amino function, indicating residual levels of amino groups present on this product. A 1:1 blend of comparative example 3 & 4 (comparative example 5) indicates rise in the level of amino function as compared to the comparative example 1.
On the other hand, since the amino grouping is reacted with glutaraldehyde it is important to understand if the dialdehyde reacts to generate a mono or a bis product. If the glutaraldehyde reacts with the pigment bound amino groups in bis manner then the free carbonyl test would be negative whereas if it is condensing in a mono manner then the free carbonyl test would be positive. To semi-quantitatively test for the existence of a free carbonyl, 2,4-Dinitrophenyl hydrazine was used as a carbonyl selective reagent. Typically, 2 g pigment was added to 5 ml water containing 5 ml methanol and 10 ml 0.1 M 2,4 DNP reagent. Development of yellow-red precipitate or yellow-red color on the pigment confirms the presence of free carbonyl group on pigment. Table 5 shows the color analysis.
Table 5: L, a, bt C & H values obtained from the NC lacquer film containing the pigment that's been treated with 2,4 DNP reagent. The pigment loading in lacquer is 10%
2,4DNP test illu L* a* b* C* H
Comparative example 1 D65 89.216-0.705 3.835 3.899 100.421
Comparative example 2 D65 88.867-0.699 3.831 .3.895 100.335
Comparative example 3 065 88.934-0.735 3.892 3.961 100.698
Comparative example 4 D65 86.97 -0.219 10.32210.32591.214
Comparative example 5 D65 88.164-0.754 7.085 7.125 96.078

The 'a' and 'b' values of Comparative Example 1, 2 and 3, are consistent with absence of carbonyl, while the pigment of comparative example 4 shows significant shift towards yellow-red as indicated by 'a' and 'b' values, showing the presence of carbonyl establishing that the dtaldehyde reacts in a mono-manner with one aldehyde group being free.

What is claimed
1. A pigment comprising one or more metal oxides and an organo silane capping layer wherein
the capping layer comprises
a) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-6 aminoalkyl group, and
b) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C3-24 imino-alkyl group substituted or interrupted by carbonyl.
2. The pigment according to claim 1 wherein the capping layer further comprises
c) one or more silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one
C1-20 alkyi group;
C1-30 alkyl group substituted by one or more groups selected from OH, C1-12 carbonyloxy, COOH, amino, amido, ester or epoxy;
and/or
C1-30 alkyl group interrupted by one or more -0-, -NH-, -N(alkyl)-, -C=N- carbonyl or carboxy and optionally substituted by one or more OH, C1-12 carbonyloxy, COOH, amino, amido, ester or epoxy.
3. The pigment according to claim 2 wherein the capping layer comprises
a) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-6 amino-alkyl group,
b) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C3-12 imino-alkyl substituted or interrupted by carbonyl, and
c) one or more silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one
C1-12 alkyl group or
C1-30 alkyl group substituted by one or more groups selected from OH, COOH, amino, ester or epoxy, and/or interrupted by one or more -O-, -NH- or -N(alkyl)-.

4. The pigment according to claim 2 wherein the capping layer comprises
a) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-3 amino-alkyl group,
b) at feast one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-14 imino-alkyl substituted or interrupted by carbonyl, and
c) at least one or more silane coupling moiety attached to the pigment by a hydrogen bond or
covalent bond and substituted at silicon by at least one afkyl group substituted by epoxy or glycidyloxy.
5. The pigment according to claim 1 wherein the capping layer comprises
. a) a group -O(4.n+m)Si(-R1)n(-R-NH2)mand
b)'a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m
wherein n+m= 1 or 2; n is 0 or 1; m is 1 or 2; R is C1-3 alkylene, R1 is C1-6 alkyl, R2 is a C2-5
ketone or aldehyde and R2' is H or C(1-3)alkyl.
6. The pigment according to claim 2 wherein the capping layer comprises
a) a group -O(4.n+m)Si(-R1)nC-R-NH2)m
b) a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and
c) a group -O(4.n+m)Si(-R1)n(-R3-glycidyioxy)m
wherein n+m= 1 or 2; n is 0 or 1; m is 1 or 2; R is C1-3 alkylene, R1 is C1-6 alkyl, R2 is a C2-.5 ketone or aldehyde, R2' is H or CC1-3 alkyl and R3 C1-3 alkylene.
7. The pigment according to claim 1 which is a pearlescent pigment comprising a core platelet substrate coated with one or more metal oxide layers, at least one of which is a titanium dioxide or iron oxide layer and the organo silane capping layer.
8. The pearlescent pigment according to claim 7 further comprising a first protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof, and a silicon dioxide protecting layer upon which the capping layer is adhered.

9.. The pigment according to claim 2 which is a pearlescent pigment comprising a core platelet substrate coated with one or more metal oxide layers, at least one of which is a titanium dioxide or iron oxide layer and the organo silane capping layer.
10. The pearlescent pigment according to claim 9 further comprising a first protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof, and a silicon dioxide protecting layer upon which the capping layer is adhered. -
11. The pigment according to claim 3 which is a pearlescent pigment comprising a core platelet substrate coated with one or more metal oxide layers, at least one of which is a titanium dioxide' or iron oxide layer and the organo silane capping layer.
12. The pearlescent pigment according to claim 11 further comprising a first protective layer comprising a metal hydroxide or oxide of the metals Al, Ce, Zr, W, Mo or mixtures thereof, and a silicon dioxide protecting layer upon which the capping layer is adhered.
13. The pearlescent pigment according to claim 8 wherein the capping layer comprises
a) at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-3 amino-alkyl group,
bj at least one silane coupling moiety attached to the pigment by a hydrogen bond or covalent
bond and substituted at silicon by at least one C1-14 imino-alkyl substituted or interrupted by
carbonyl,
and optionally
c) at least one or more silane coupling moieties attached to the pigment by a hydrogen bond or
covalent bond and substituted at silicon by at least one alkyl group substituted by epoxy or
glycidyloxy.
14. The pearlescent pigment according to claim 13 wherein the capping layer comprises
a) a group -O(4.n+m)Si(-R1)n(-R-NH2)m
b).a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m
and optioinalfy
c) a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m
wherein n+m= 1 or 2; n is 0 or 1; m is i or 2; R is C1-3 alkylene, R1 is C1-6alkyl, R2 is a C2-5
ketone or aldehyde, R2' is H or C(1-3)alkyl and R3 C1-3 alkylene.

15. The pearlescent pigment according to claim 14 wherein the capping layer comprises
a) a group -O(4.n+m)Si(-R1)n(-R-NH2)
m
b) a group -0(4.n+m)Si(-R\(-R-N=C(R2)R2)m and
c) a group -0(4.n+m)Si(-R1)n(-R3-glycidyloxy)m wherein
n+m= 1 or 2; n is 0 or 1; m is 1 or 2;
R is methylene, ethylene or propylene;
R1 is methyl, ethyl, propyl, butyl, pentyl, hexyl, or cyclohexyl;
R2 is aC2-5 ketone or aldehyde,
R2' is H or methyl and
R3 is methylene, ethylene or propylene.
16. The pearlescent pigment according to claim 15 wherein in the capping layer
1 to 98 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-NH2)m
1 to 98 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and
0 to 75 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m.
17. The pearlescent pigment according to claim 16 wherein in the capping layer
5 to 60 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-NH2)m
10 to 65 mol % of the silane capping moieties is a group - -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and 30 to 60 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m
18. The pearlescent pigment according to claim 17 wherein in the capping layer
1 to 49 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-NH2)m
1 to 49 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R-N=C(R2')R2)m and
40 to 50 mol % of the silane capping moieties is a group -O(4.n+m)Si(-R1)n(-R3-glycidyloxy)m
19. The pigment according to claim 1 prepared by a process-comprising
a) adding to a pigment suspended in an appropriate liquid media, one or more coupling agents of the general formula
(R'0-)pSi(-R")q(-RY)r
wherein p+q+r = 4, p is 2 or 3; q is 0 or 1, and r is 1 or 2;
R is an alkylene group, comprising 1 to 6 carbon atoms;

R' is an alky! group comprising 1 to 6 carbon atoms;
R" is an alkyl group of 1 to 6 carbon atoms;'and
Y is an organic functional group capable of reacting with an organic binder polymer, provided that at least one coupling agent comprises a group (RY) wherein Y is a group targeted for further modification in a subsequent reaction, to form an intermediate capped pigment, followed by
b) modifying the intermediate capped pigment at the targeted group Y group by reaction with a difunctional or polyfunctions) organic reagent.
20. The pearlescent pigment according to claim 16 prepared by a process comprising
I) depositing by precipitation onto the pigment surface at 50 to 90°C and a pH of from 3 to 6, approximately 0.1% to 5%, by weight based on the total weight of the pearlescent pigment, an oxide, hydroxide and/or hydrated oxide of Ce or Zr, or W or Mo or mixtures thereof; 11) raising the pH to from 7 to 9.5 and adding sodium silicate or tetraethyl orthosilicate to deposit a silicate or Si02 layer, between 0.1 to 5% by weight based on the total weight of the pearlescent pigment, wherein all the metal hydroxides or oxide hydrates are already completely precipitated;
Ilia) surface capping the pearlescent pigment thus obtained at pH of from 7 to 9.5 with a separate layer containing from 1 to 10% by weight, by weight based on the total weight of the pearlescent pigment, of organofunctional silanes wherein at least one silane contains primary amino functionality to obtain the PUDSC, and
lilb) modifying the targeted functional groups of the PUDSC, partially or completely, with a reactive agent comprising a dialdehyde or diketone forming an carbonyl substituted alkyl imine, substituent on the organofunctional silane pigment bound by means of oxygen bond or pigment bound by hydrogen bonding network to the pigment surface after which the pigment is isolated and dried at elevated temperatures.
21. A mixed pigment comprising a pearlescent pigment prepared according to the process of claim 20 and a pearlescent pigment corresponding to the intermediate capped pearlescent pigment obtained after step Ilia) of the process.
22. A plastic article, polymeric coating or cosmetic formulation containing a pigment according to claim 16.

23. A plastic article, polymeric coating or cosmetic formulation containing a mixed pigment according to claim 21.