Patent Application
20140251202
This application is directed to improved methods of generating synthetic zinc phlogophite platelets of high aspect ratio via hydrothermal conditions; the phlogopite obtainable by said method and to the phlogophite platelet per se of high aspect ratio. Further the use of habit modifiers during hydrothermal synthesis of phlogopite to form high aspect ratio platelets is disclosed and claimed.
Natural mica is mined in the presence of sand, kaolin, feldspar and other silicates and will contain various impurities such as iron oxides and heavy metals. Because of the presence of these additional impurities, mica is often discolored. This discoloration is of course, an undesired characteristic of the natural material particularly when the mica is used as a platelet, core or substrate for interference pigments, barrier coatings and the like.
Furthermore, natural mica must be ground to produce flakes. This grinding does not allow for tight control of the smoothness of the mica surface, stepped characteristics and the thinness of the flake. Accordingly, the flakes often have imperfect edges and faces and less specular reflection (edge scattering).
Thus, natural mica mining and grinding does not favor the production of large diameter, thin flakes resulting in high aspect ratio platelet.
As a result, synthetic alternatives have long been desired which would provide good purity and high aspect ratio. Synthetic mica containing fluoride is well known in the art and is most commonly prepared via a melt reaction method. Synthetic fluorine containing mica powder of high purity has been prepared by mixing compounds containing oxides and/or fluorides of potassium, sodium, magnesium, aluminum and silicon at a predetermined ratio, melting, crystallizing, cooling, and then mechanically pulverizing. However, even synthetic mica prepared via solid phase synthesis is problematic. The solid phase synthesis requires grinding and the grinding process leads to stepping, lack of flake thickness control and variability of plate diameter size. The natural or synthetic mica normally consists of platelets having a thickness of about 500 to 600 nm and a defined particle size distribution.
Ideally, a synthetic pathway is needed which would lead directly to mica characterized by low thickness parameters and large diameter (high aspect ratio) and less specular reflection (edge scattering).
It is known to prepare synthetic phlogopite hydrothermally at high pressures and temperatures. For example, Yoder H. S. et al., Geochimica et Cosmochimica Acta, 1954, Vol. 6, pp. 157-185 teaches the formation of synthetic phlogopite at 1080° C. and 75,000 psi water vapour pressure. Frondel, C et al., The American Mineralogist, Vol. 51, 1966 teaches the formation of small particle size zinc containing micas via hydrothermal crystallization at high pressure (1000-3000 bars) and high temperatures (250° C. to 650° C.).
It is also known to prepare synthetic hydroxyl containing mica via lower temperature hydrothermal methods. For example, Komarneni, S. et al., Clays and Clay Minerals, Vol. 51. p. 693 and Perrotta, A. et al., J. American Mineralagist, Vol. 60, p. 152 describe hydrothermal methods of forming a zinc containing mica of the hydroxyl phlogopite type. Korean Patent Publication No. 20070111271 teaches hydrothermal preparation of magnesium phlogopite. However, the processes presented therein are unsatisfactory in regard to the diameter size of the platy surface and thickness of the platy material, smoothness of the crystal, transparency, the purity of crystal formation, the length of preparation times, aspect ratio and temperatures and pressures required.
Accordingly, there is a pressing need in the art to devise a method for preparing synthetic mica, especially zinc phlogopite production wherein single crystals are produced (no grinding necessary) and the major dimensions of the mica platelets, especially zinc phlogopite such as thickness and platelet diameter (aspect ratio) can be adequately controlled and to carry out this method using low temperatures and pressures.
The present applicants have successfully discovered a method for producing a synthetic zinc phlogophite hydrothermally at low temperatures and pressures which meet the above needs.
Further the present method is capable of producing a novel platelet of synthetic zinc phlogophite which is distinguished from synthetic phlogophite made by other methods by its aspect ratio, that is the synthetic zinc phlogophite is characterized by a high aspect ratio (ratio of diameter to thickness).
This application embodies a synthetic phlogopite platelet or substrate of formula (1)
IZn3(AlSi3O10)(X)2 (1)
IZn3(AlSi3O10)(X)2 (1)
This application further embodies a synthetic zinc phlogopite platelet of formula (1) obtainable by the process described above which synthetic zinc phlogopite platelet is further characterized by an aspect ratio (diameter/thickness) ranging from about 50 to about 2000, preferably about 100 to about 2000, especially about 150 to about 1500.
The above zinc phlogopite platelet is envisioned as an effect pigment wherein the platelet is coated with at least one metal oxide layer.
The inventors also claim the use of a habit modifier to increase the aspect ratio of a synthetic zinc phlogopite platelet during hydrothermal synthesis of the synthetic platelet, wherein the habit modifier is a weak organic acid or inorganic acid, salt or hydrate thereof or a sugar.
Thus this disclosure embodies a method of increasing the aspect ratio of a synthetic zinc phlogopite platelet during hydrothermal synthesis comprising the step of adding to a hydrothermal reaction mixture a habit modifier, wherein the habit modifier is a weak organic acid or weak inorganic acid, salt or hydrate thereof or a sugar.
The term “hydrothermal process” as used herein means a process that allows platelets of material such as synthetic zinc phlogopite to grow in a solvent at temperatures and pressures which allow for the at least partial dissolution or dispersion of precursor materials.
The reaction vessel may be sealed or not sealed.
The terms “synthetically derived” means the zinc phlogopite is formed synthetically, i.e. by a controlled chemical reaction, specifically a hydrothermal reaction. The hydrothermal reaction conditions disclosed herein are those characterized by low temperature and low pressures.
The terms “low temperature” and “low pressure” when used to describe the hydrothermal process conditions means for purposes of this application temperatures ranging from 125 to about 250° C., preferably 150° C. to about 225° C. and pressures ranging from about 50 to about 400 psi, and preferably about 100 psi to about 220 psi.
The term “platelet, platy, plate-like and flakey” are typical terms used in the art and is understood to mean that the platy substrates have a diameter which is greater than the thickness of the substrate, such as platelets (flakes).
The term “aspect ratio” refers to the ratio of the maximum dimension (diameter or d50) to the minimum dimension (thickness) of a particle. In other words when the term “aspect ratio” is used herein the ratio of diameter/particle thickness is meant.
The diameter is defined for example as the d50 particle size distribution determined via static light scattering using a Malvern Mastersizer® Hydo2000S. The thickness of the platelet is determined via Scanning Electron Microsope (SEM).
High aspect ratio means for purposes of this disclosure a ratio of diameter/particle thickness ranging from about 50 to about 2000, preferably about 100 to about 2000, especially about 150 to about 1500.
The reaction mixture will typically be an aqueous dispersion, solution, slurry or gel of the starting materials.
Bulk density is a property of powders or granules and other “divided” materials such as the platy zinc phlogopite substrates formed by the process disclosed herein. This bulk density is defined as the weight of a unit volume of the powder usually expressed as grams per cubic centimeter.
This is also sometimes referred to as the apparent density. It accounts for the powder and the voids between particles as well as voids within and on the surface of the particles.
For example the bulk density of zinc phlogophite may vary from about 35 g/cm3 to about 65 g/cm3.
The term “habit” when used in reference to a crystalline substance is a well known term in the art. Crystal habit modifiers have been studied qualitatively since the turn of the century. It is generally understood that faces of crystals can grow at different rates, giving rise to different shapes. If a modifier interacts more readily with some faces than others, thus altering the growth rate of those faces relative to others, it will affect the habit.
Crystal habit modification is a part of many industrial processes. For example habit modification alters the grain geometry and therefore properties of the photosensitive silver halides.
Habit modifiers are known for use in modifying the habit of zeolites. For example, Lupulescu A. I et al, Angew. Chem. Int. Ed. 2012, 51, 3345-3349 and U.S. Publication No. 2012/0202006 teach spermine as a growth modifier for tailoring the crystal habits of zeolites. US2012/0202006 teaches many zeolite growth modifiers. See Table 1 of US '2006. The methods for forming the zeolite materials include binding or otherwise adhering one or more zeolite growth modifiers to the surface of a zeolite crystal, which results in the modification of crystal growth rates along different crystallographic direction, leading to the formation of zeolites having tailored crystal habits.
The crystalline habit of phlogopite, like other micas, has a layered structure of magnesium aluminum silicate sheets weakly bonded together by layers of potassium ions (or sodium or lithium). These potassium ion layers produce the perfect cleavage. A modifier of the phlogopite habit alters the geometric structure in such a way as to speed the growth of a lattice plane.
The applicants have discovered that agents effective for habit modification of zinc phlogopites during hydrothermal synthesis are weak organic acids or weak inorganic acids salts or hydrates thereof or sugars.
However, the present application embodies the use of weak organic acids or weak inorganic acids, hydrates or salts thereof or sugars, as habit modifiers during hydrothermal preparation of synthetic zinc phlogopite.
The term weak organic acids means for purposes of this application that the weak organic acid (salt or hydrate) thereof comprises at least one carboxylic acid (salt or hydrate thereof), preferably at least two carboxylic acids (salts or hydrates thereof).
The weak organic acid salts or hydrates thereof as habit modifiers may be defined by formula (1)
when m+p is 1:
A is branched or unbranched, substituted or unsubstituted C1-C10 alkyl, branched or unbranched, substituted or unsubstituted C2-C10 alkenyl, substituted or unsubstituted C7-C9 phenylalkyl or substituted or unsubstituted C6-C10 aryl,
wherein the linear or branched unsubstituted C1-C10 alkyl, the linear or branched C2-C10 alkenyl may be substituted by C(O)OH, C(O)O−X+, NH2, halogen, OH, —C(O)H or interrupted by —O—, —NR2— or —C(O)—,
the C7-C9 phenylalkyl or the C6-C10 aryl includes substitution by one or more C(O)OH, C(O)O−X(+)n, NH2, halogen, OH or —C(O)H,
wherein R is hydrogen or RO is O−X(+)n,
R2 is hydrogen or linear or branched C1-C10-alkyl one or more substituted by C(O)OH, C(O)O−X(+)n, halogen, NH2, —C(O)— or OH; n is 1-3,
and
X(+)n is a cation, X(+)n is a organic or inorganic cation, for example ammonium, substituted ammonium, such as, for example methylammonium, dimethylammonium, trimethylammonium, ethanolammonium, metal cations, for example metal cations for example alkali metal cation, alkaline earth metal cation or other metal cations, for example Na+, Li+, K+, Cs+, Rb+, Fr+, Mg++, Sr++, Ba++, Be++, Ca++, Al+++, B+++ or P+++;
when m+p is two or more,
A is branched or unbranched, substituted or unsubstituted C1-C10 alkylene, branched or unbranched, substituted or unsubstituted C2-C10 alkylidene, substituted or unsubstituted C7-C9 alkylphenylene or C6-C10 arylene,
wherein C7-C9 alkylphenylene or C6-C12 arylene may include one or more substitution by NHR2, OH, COOH, halogen, COO−X(+)n or —C(O)H,
and the linear or branched C1-C10 alkylene, the linear or branched C2-C10 alkylidene may be substituted by C(O)OH, C(O)O−X+, NH2, halogen, OH, —C(O)H and/or interrupted by —O—, —NR2— or —C(O)—,
with R, RO, R2 and X(+)n as defined above.
Preferably m+p is two or more.
C1-C10 alkyl having up to 10 carbon atoms is a branched or unbranched radical, for example methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, 2-ethylbutyl, n-pentyl, isopentyl, 1-methylpentyl, 1,3-dimethylbutyl, n-hexyl, 1-methylhexyl, n-heptyl, isoheptyl, 1,1,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl, 2-ethylhexyl, nonyl and decyl.
C2-C10 alkenyl having up to 10 carbon contains at least one unsaturated carbon-carbon bond. For example, alkenyl is a version of alkyl, for example isopropenyl, propenyl, hexenyl, heptenyl, and the like.
C7-C9phenylalkyl is, for example, benzyl, α-methylbenzyl, α,α-dimethylbenzyl or 2-phenylethyl. For example benzyl and α,α-dimethylbenzyl.
C6-C10 aryl is for example phenyl or naphthyl, but also comprised are hydroxy, halogen NH2, C(O)H, COOH, COO—X(+)n substituted phenyl or naphthyl. For example benzoic acid, phthalic acid and terephthalic acid or halogen substituted benzoic acid.
C1-C10alkylene is a branched or unbranched radical, for example methylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, decamethylene, dodecamethylene or octadecamethylene. For example C1-C12alkylene, for instance preferably C1-C8alkylene or C1-C6 alkylene.
C2-C10alkylene interrupted by oxygen, NR2 or C(O) is, for example, —CH2—O—CH2—, —CH2—NR2CH2—, —CH2—N(CH3)—CH2—, —CH2—O—CH2CH2—O—CH2—, —CH2—(O—CH2CH2—)2O—CH2—, —CH2—(O—CH2CH2—)3O—CH2—, —CH2—(O—CH2CH2—)4O—CH2—, —CH2CH2—N(CH2CH2OH)—CH2CH2—, —CH2CH2C(O)CH2CH2—.
C2-C10 alkylidene having from 2 to 20 carbon atoms is, for example, ethylidene, propylidene, butylidene, pentylidene, 4-methylpentylidene, heptylidene, nonylidene, tridecylidene, nonadecylidene, 1-methylethylidene, 1-ethylpropylidene or 1-ethylpentylidene. For example C2-C5alkylidene.
C7-C9 alkylphenylene is for example, CH2-Ph-CH2 (Ph is phenyl), CH2—CH2-Ph-CH2—.
C6-C12 arylene is for example
X(+)n wherein n is 1, 2 or 3.
X(+)n is a organic or inorganic cation, for example ammonium, substituted ammonium, such as, for example methylammonium, dimethylammonium, trimethylammonium, ethanolammonium, metal cations, for example metal cations for example alkali metal cation, alkaline earth metal cation or other metal cations, for example Na+, Li+, K+, Cs+, Rb+, Fr+, Mg++, Sr++, Ba++, Be++, Ca++, P+++, B+++ or Al+++,
Preferred for formula (I) salt or hydrates thereof are
when m+p is two or more,
A is branched or unbranched, substituted or unsubstituted C1-C8 alkylene,
substitution of the branched or unbranched C1-C8 alkylene includes one or more substitution by OH, COOH, COO−X(+)n as defined above, preferably OH and COOH, COO−X(+)n substitution.
Suitable weak organic acid habit modifiers would include formic acid, acetic acid, acrylic acid, oxalic acid, benzoic acid, phthalic acid, isothalic acid, terephthalic acid, malonic acid, sorbic acid, ascorbic acid, methyl malonic acid, succinic acid, lactic acid, aspartic acid, glutaric acid, adipic acid, pimelic acid, malic acid, maleic acid, tartaric acid, tartronic acid, mucic acid, gluconic acid, citric acid, isocitric acid, acetyl citric acid, suberic acid, sebacic acid, azelaic acid, 1,2,3-propanetricarboxylic acid, 1,1,3,3-propanetetracarboxylic acid, 1,1,2,2-ethane tetracarboxylic acid, 1,2,3,4-butantetetracarboxylic acid, 1,2,2,3 propanetetracarboxylic acid, 1,3,3,5 pentanetetracarboxylic acid, ethylenediamine tetraacetic acid, ethyleneglycolbis-tetraacetic acid, diglycolic acid, ethylenediamine tetrapropionic acid, iminodiacetic acid, 1,2-propylenediaminetetraacetic acid, N-methyl, -ethyl, -propyl and -butyl iminodiacetic acid, 1,3-propylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, diethylenetriaminepentaacetic acid, amino acids such as glycine, alanine, valine, leucine, tyrosine, thoreonine, serine, glutamic acid, lysine, and salts or hydrates thereof.
A preferred listing of suitable weak organic acids is malic acid, adipic acid, tartronic acid, citric acid, isocitric acid, pimilic acid, azelaic acid, oxalic acid, digycolic acid, mucic acid, malonic acid, methyl malonic acid, glutaric acid, succinic acid, tartaric acid, aspartic acid, suberic acid, sebacic acid, glutamic acid, salts or hydrates thereof.
A most preferred listing of suitable weak organic acids is malic acid, tartaric acid, oxalic acid, citric acid, isocitric acid, mucic acid and salts or hydrates thereof.
Weak inorganic acids are for example boric acid, phosphoric acid (H3PO4) and pyrophosphate, salts or hydrates thereof.
Sugars are also envisioned as habit modifiers including mono and disaccharides. For example sugars would include glucose, fructose, galactose, sucrose, maltose, sorbitol, lactose mannitol, inositol, xylitol, threitol, erythritol, adonitol(ribitol), arabitol(lyxitol), dulcitol(galactitol), maltitol, isomalt, ribose, xylose and mannose.
The most preferred habit modifiers are weak organic acids or weak inorganic acids such as citric, tartaric and boric acids, salts and hydrates thereof. For example tri-sodium citrate dehydrate, tartaric acid salts and sodium tetraborate decahydrate come to mind.
The amount of habit modifier (sugars or weak organic or weak inorganic acids) required during the hydrothermal processing of the zinc phlogopite of formula (1) will range from about 0.5 to about 10% mmol, preferably about 1 to about 7% mmol, and most preferably about 1.5 to about 5% mmol based on the theoretical calculated product (phlogopite).
This disclosure envisions the use of a habit modifiers to alter the lateral dimensions or aspect ratio of the mica platelet during its hydrothermal formation. For example, the habit modifier may be used to alter the aspect ratio of any of the micas listed below:
phlogopite KMg3(AlSi3O10)(F,OH)2, KZn3(AlSi3O10)(F,OH)2,
annite KFe3(AlSi3O10)(OH,F)2,
clintonite Ca(Mg, Al)3AlSi3O10(OH)2,
siderophyllite KFe2Al(Al2Si2)O10(F,OH)2,
easonite (KMg2Al(Al2Si2)O10(OH)2),
paragonite (NaAl2(AlSi3O10)(OH)2),
margarite (CaAl2(Al2Si2)O10(OH)2),
lepidolite KLi2Al(AlSi3)O10(F,OH)2,
muscovite KAl2(AlSi3O10)(OH,F)2,
biotite K(Mg,Fe)3AlSi3O10(OH,F)2,
aspidolite NaMg3AlSi3O10(OH)2,
celadonite K(Mg, Fe+2)Fe3+(Si4O10)(OH)2
ephesite LiNaAl2(Al2Si2O10)(OH)2
ferro-aluminoceladonite K(Fe2+,Mg)(Al,Fe3+)(Si4O10)(OH)2
ferro-celadonite K(Fe2+,Mg)(Fe3+,Al)(Si4O10)(OH)2
glauconite (K,Na)(Fe3+Al,Mg)2 (Si,Al)4O10(OH)2
hendricksite K(Zn,Mg,Mn)AlSi3O10(OH)2
illite (K, H2O)(Al,Mg,Fe)2(Si,Al)4O10(OH)2, K0.65Al2.0(Al0.65Si3.35O10)(OH)2
montdorite (K,Na)2(Fe2+, Mn2+, Mg)5(Si4O10)2(OH,F)4
norrishite KLiMn23+(Si4O10)O2
polylithionite KLi2Al(Si4O10)(F,OH)2
preiswerkite NaMg2Al(Al2Si2O10(OH)2
shirokshinite KNaMg2(Si4O10)F2
shirozulite K(Mn2+,Mg)3 (AlSi3O10)(OH)2
tainiolite KLiMg2(Si4O10)F2
tetraferriphlogophite KMg3(Fe3+, Si3O10)(OH,F)2
trilithionite K(Li,Al)3AlSi3O10(F,OH)2
yangzhumingite KMg2.5(Si4O10)F2
Zinwaldite KLiFe2+Al(AlSi3O10)(F,OH)2
The method of preparation of the synthetic mica platelet comprises the step of adding to a hydrothermal reaction mixture a habit modifier, wherein the habit modifier is a weak acid, salt or hydrate thereof or a sugar.
Phlogopite
Phyllosilicates are silicate mineral having the tetrahedral silicate groups linked in sheets, each group containing four oxygen atoms, three of which are shared with other groups so that the ratio of silicon atoms to oxygen atoms is two to five. Mica is a subset of phyllosilicates. Phlogopite is a subset of mica and zinc phlogopite is a subset of phlogopites.
Phlogopite is a mica which has a layered structure most commonly comprising magnesium aluminum silicate sheets weakly bonded together by layers of alkali ion (sodium, lithium or potassium ions). For example, potassium containing phlogopite (KMg3AlSi3O10(F,OH)2 has potassium ions weakly bonding the magnesium aluminum silicate sheets.
The most preferred mica of formula (I) is zinc containing phlogopite. For example, KZn3AlSi3O10(OH)2, KZn3AlSi3O10(OH,F) and KZn3AlSi3O10(F)2 and may be made by the hydrothermal process herein disclosed.
Furthermore, the formation of large platelets of zinc phlogopite of high aspect ratio using habit modifiers during the hydrothermal process disclosed is of particular importance.
As described above one of the embodiments of this application is directed to a synthetic zinc phlogopite platelet of formula (1)
IZn3(AlSi3O10)(X)2 (1)
wherein
I is an interlayer monovalent cation selected from the group consisting of K+, Na+, NH4+ and Li+, preferably K+ and Na+;
and
X is independently fluoride, hydroxide or fluoride and hydroxide, preferably hydroxide;
of an aspect ratio ranging from about 50 to about 2000, preferably about 100 to about 2000, wherein the aspect ratio is determined by the diameter of the platelet divided by the thickness of the platelet.
The diameter is defined as the d50 particle size distribution determined via static light scattering using a Malvern Mastersizer® Hydo2000S. The thickness of the platelet is determined via cross sectional Scanning Electron Microsope (SEM).
The synthetic zinc phlogopite platelet is substantially transparent, that is it transmits at least 92% light, preferably 95% light and most preferably 98% light.
Identification of the Crystal Form of the Phyllosilicate Crystals
Identification of the zinc phlogopite crystals are confirmed via X-ray diffraction. The Powder X-ray scan (PXRD) is performed using CuKα radiation source.
The aspect ratio has been briefly discussed above and defined as the diameter/thickness dimensions.
It is presently preferred that the diameter of the hydrothermally prepared zinc phlogopite, range from about 4 microns to about 1 mm, about 5 microns to about 1 mm, with a more preferred range of about 6 microns to about 60 microns, especially about 6 microns to about 50 microns.
The thickness of the zinc phlogopite will for example range from about 10 nm to about 500 nm, preferably about 20 nm to about 400 nm. For example the thickness may range most preferably from about 10 nm to about 150 nm, especially about 15 nm to about 100 nm or about 15 nm to about 80 nm.
Thus, the aspect ratio of the hydrothermally produced mica will range from about 50 to about 2000, preferably about 100 to about 2000, most preferably about 150 to about 1500.
A particularly useful means of characterizing the size distribution of a mass of synthetic platelets produced is by specifying the platelet size of the lowest 10 vol. %, 50 vol. %, and 90 vol. % of platelets along the Gaussian curve. This classification can be characterized as the d10, d50, and d90 values of the platelet size distribution. Thus, a platelet having a d10 of a certain size means that 10 vol. % of the platelet particles has a size up to that value. Thus, the size distribution of the mica-based platelets can be described as follows: 10 volume % of the platelets have a size of up to and including 10 microns, 50 volume % of the platelets have a size up to and including 22 microns, and 90 volume % of the platelets have a size up to and including 45 microns for example.
For example the synthetically derived zinc phlogopite platelets are preferably characterized by a d50 ranging from about 5 to about 60 microns, most preferably about 7 to about 50 microns, especially the synthetically derived zinc phlogopite platelets may be characterized by a d50 of at least 8 or a d50 of at least 9.
The platelet may of course be classified by means of various methods, such as gravity sedimentation, sedimentation in a decanter, sieving, use of a cyclone or hydrocylone, spiral classifying or a combination of two or more these methods. A method such as sieving, for example, may also be used in a plurality of successive steps. Classification may shift the distribution of platelet toward larger or smaller diameters.
As explained above the term “hydrothermal process” as used herein means a process that allows crystals of mica platelet or zinc phlogopite platelet to grow in a solvent at low temperature and low pressure.
The solvent is typically water.
The reaction mixture may be a slurry, solution, dispersion or gel in water.
Thus the preparation of the synthetic zinc phlogopite platelet,
comprises the steps of:
The base may for example be derived from common inorganic bases such as potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium carbonate, lithium carbonate, ammonium hydroxide, and potassium carbonate and organic bases such as tripropylammonium hydroxide, tetramethyl ammonium hydroxide, triethanolamine and diethanolamine.
Preferably the base is an inorganic base and is selected from the group consisting of potassium hydroxide, lithium hydroxide, lithium carbonate, sodium hydroxide, ammonium hydroxide, sodium carbonate and potassium carbonate.
This base may provide the hydroxide source when present during the hydrothermal synthesis of the phlogopite of formula (1).
The initial reaction mixture should be basic. Typically the pH of the initial reaction mixture will range from about 9 to about 14, preferably the pH will range from about 12 to about 14, and most preferably will range for about 12.5 to about 14.
As explained above is an interlayer monovalent cation selected from the group consisting of K+, Na+, NH4+ and Li+, preferably K+ and Na+. The source for this cation may be from the base used to ensure basic reaction conditions of the hydrothermal process. For example, bases which would provide a K+, Na+, Li+, NH4+ may be potassium hydroxide, sodium hydroxide, Na2O, lithium hydroxide, ammonium hydroxide, sodium carbonate, lithium carbonate, Li2O, potassium carbonate and K2O
Preferably the interlayer monovalent cation is K+,
The aluminum source may be selected from elemental aluminum Al0, salts of aluminum (organic or inorganic), oxide and hydrates thereof. For example, the aluminum source may be selected from the group consisting of Al(NO3)3(aluminum nitrate), K2Al2O4(potassium aluminate), Na2Al2O4 (sodium aluminate) Al(OH)3(aluminum hydroxide), Al2O3, pseudoboehmite, aluminum isopropoxide, Al(C2H3O2)3, AlBr3, AlCl3, Al(C6H6O7) (aluminum citrate), AlF3, Al(CHO2)3 (aluminum formate), Al2(SO4)3, AlOOH (aluminum hydroxide oxide) and hydrates thereof.
Preferably the aluminum source is selected from Al(NO3)3(aluminum nitrate), Al2(SO4)3K2Al2O4(potassium aluminate), Na2Al2O4, Al(OH)3, AlOOH and hydrates thereof and especially Al2(SO4)3K2Al2O4 (potassium aluminate).
The most preferable aluminum source is potassium aluminate (K2Al2O4).
The silica sources are typically derived from hydrates of SiO2, colloidal SiO2, sodium metasilicate, sodium silicate, potassium metasilicate, potassium silicate, lithium metasilicate, lithium silicate, kaolin, fumed silica, talc, H2SiO3 and tetraethyl orthosilicate.
Colloidal SiO2 is most preferred.
The zinc source may be elemental, any salt (organic or inorganic), hydrate or oxide thereof. The zinc source may be selected from the group consisting of Zn0, ZnSO4, Zn(NO3)2, ZnCl2, Zn(C2H3O2)2 (zinc acetate), ZnCO3, Zn(CHO2)2 (zinc formate), ZnBr2, zinc oxide, ZnI2 and hydrates thereof.
The optional fluoride source is for example HF, NH4F, NaF, K2SiF6, KF and MgF2.
It is preferable not to include a fluoride source.
The hydroxide source may come from the bases such as potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide, and organic bases such as tripropylammonium hydroxide and tetramethyl ammonium hydroxide.
It is preferable to have a hydroxide source. As explained above this may come from the base.
The water content during the hydrothermal reaction may vary from about 60 to about 98 wt. percent. Thus the wt. % reagents will normally range from about 2 wt. % to about 40 wt. percent, preferably from about 4 wt. % to about 35 wt. % and most preferably about 5 wt. % to about 30 wt. %. The weight % is based on the total weight of the reaction mixture.
Seeding of the hydrothermal reaction may be desirable with a previously formed mica. The amount of seeding making up the reaction mixture may range from about 1 to 6 wt. % of the calculated phlogopite product. For example if the product intended is a zinc phlogopite, the hydrothermal reaction may be seeded with a wt. % of phlogopite seed crystal ranging from about 0.1 to about 10 wt. %, preferably 0.5 to about 8 wt. %, most preferably 1 to about 6 wt. % of the theoretical product formed.
The hydrothermal reaction mixture is typically heated to the appropriate temperature, about 150 to about 250° C., then held at the appropriate temperature from about 2 to about 100 hours, more typically about 10 to 90 hours or most typically about 20 to about 85 hours.
The pressure conditions for carrying out the hydrothermal reactions will vary depending upon the platelet but will typically vary from about 50 psi to about 400 psi, more typically about 75 psi to about 300 psi, most typically from about 85 to about 250 psi.
The hydrothermal process for production of the mica may be done under static or stirring/mixing conditions.
The hydrothermal preparation of the zinc phlogopite can be done under stoichiometric conditions or non-stoichiometric conditions. It is preferable that the reaction is run under stoichiometric conditions.
Stoichiometric conditions means for purposes of this application, that the starting materials, in particular zinc source, silicon source, and aluminum source are present at the start of the reaction at the same molar ratios of the final product, the zinc phlogopite.
The applicants have discovered that stoichiometric conditions make a very significant different in the size, shape and size distribution of the hydrothermally formed zinc phlogopite platelets.
There are many applications for the presently disclosed zinc phlogopite. For example, mica is an excellent insulator, reinforcement material, solid lubricant, cosmetic extender, substrate or core for effect and interference pigments, barrier in packaging and paper applications and filler in resins providing heat resistance.
When the term “synthetic zinc phlogopite” is use in the follow passages, what is meant is the inventive synthetic phlogopite formed via the herein disclosed hydrothermal method or the hydrothermally produced phlogopite disclosed herein. These products give platelet of an aspect ratio varying from about 50 to 2000 which is likely to lead to special visual effects.
Effect pigments and their use in paints, ink-jet printing, for dyeing textiles, for pigmenting coatings, printing inks, plastics, cosmetics, glazes for ceramics and glass is well known in the art.
Such pigments having a core comprising of a transparent carrier material, such as, for example, natural, or synthetic mica, SiO2, or glass, are known. Reference is made, for example, to Gerhard Pfaff and Peter Reynders, Chem. Rev. 99 (1999) 1963-1981.
The presently formed substrate, the synthetically derived phlogopite, is an especially suitable substrate, core or platelet for formation of an effect pigment.
One of the objects of the present invention is to develop pearlescent pigments on the basis of the presently hydrothermally produced zinc phlogopite with the disclosed aspect ratio (50 to 2000). The presently coated synthetic zinc phlogopite would exhibit the advantages of mica pigments (e.g. good application properties in a variety of binder systems, environmental compatibility and simple handling) with the possibility of realizing superior optical effects, i.e. to provide interference pigments, having high color strength and/or color purity because of the high aspect ratio of the substrate.
This objective has been solved by pigments, comprising a plate-like substrate of the hydrothermally produced platelets of zinc phlogopite of aspect ratio about 50 to about 2000, and
(a) a dielectric material, especially a metal oxide, having a high index of refraction; and/or
(a) a metal layer, especially a thin semi-transparent metal layer.
Thus the application is directed to a pigment, comprising the synthetic zinc phlogopite platelet of formula (1) the various embodiments of the application.
The pigment may comprise a synthetic zinc phlogopite according to formula (1), wherein the pigment further comprises in addition to layer (a) having a high refractive index and/or (b) a metal layer, an oxide layer (c) of low refractive index and a layer (d) of high refractive index, wherein the difference of the refractive indices between the high and low refractive indexes is at least 0.1.
The above pigment will preferably comprise a metal oxide of layer (a) of high refractive index is TiO2, ZrO2, Fe2O3, Fe3O4, Cr2O3, ZnO, a mixture of these oxides, an iron titanate, an iron oxide hydrate, a titanium suboxide or a mixture and/or mixed phase of these compounds.
The pigment particles (coated core of synthetically produced phlogopite) generally have a diameter of from 5 microns to 5 mm, and an average thickness of <1 micron, and contain a core of synthetically derived phlogopite, having two substantially parallel faces, the distance between which is the shortest axis of the core. The core is either coated with a dielectric material, especially a metal oxide, having a high index of refraction, or a metal layer, especially a thin semi-transparent metal layer. Said layers can be coated with additional layers.
Suitable metals for the (semi-transparent) metal layer are, for example, Cr, Ti, Mo, W, Al, Cu, Ag, Au, or Ni. The semi-transparent metal layer has typically a thickness of between 5 and 25 nm, especially between 5 and 15 nm.
According to the present invention the term “aluminum” comprises aluminum and alloys of aluminum. Alloys of aluminum are, for example described in G. Wassermann in Ullmanns Enzyklopädie der Industriellen Chemie, 4. Auflage, Verlag Chemie, Weinheim, Band 7, S. 281 to 292. Especially suitable are the corrosion stable aluminum alloys described on page 10 to 12 of WO00/12634, which comprise besides of aluminum silicon, magnesium, manganese, copper, zinc, nickel, vanadium, lead, antimony, tin, cadmium, bismuth, titanium, chromium and/or iron in amounts of less than 20% by weight, preferably less than 10% by weight.
The metal layer can be obtained by wet chemical coating or by chemical or physical vapor deposition, for example, gas phase deposition of metal carbonyls. The substrate is suspended in an aqueous and/or organic solvent containing medium in the presence of a metal compound and is deposited onto the substrate by addition of a reducing agent. The metal compound is, for example, silver nitrate or nickel acetyl acetonate (WO03/37993).
According to U.S. Pat. No. 3,536,520 nickel chloride can be used as metal compound and hypophosphite can be used as reducing agent. According to EP-A-353544 the following compounds can be used as reducing agents for the wet chemical coating: aldehydes (formaldehyde, acetaldehyde, benzalaldehyde), ketones (acetone), carbonic acids and salts thereof (tartaric acid, ascorbinic acid), reductones (isoascorbinic acid, triosereductone, reductine acid), and reducing sugars (glucose). However, it is also possible to use reducing alcohols (allyl alcohol), polyols and polyphenols, sulfites, hydrogensulfites, dithionites, hypophosphites, hydrazine, boron nitrogen compounds, metal hydrides and complex hydrides of aluminium and boron. The deposition of the metal layer can furthermore be carried out with the aid of a CVD method. Methods of this type are known. Fluidised-bed reactors are preferably employed for this purpose. EP-A-0741170 describes the deposition of aluminium layers by reduction of alkylaluminium compounds using hydrocarbons in a stream of inert gas. The metal layers can furthermore be deposited by gas-phase decomposition of the corresponding metal carbonyls in a heatable fluidised-bed reactor, as described in EP-A-045851. Further details on this method are given in WO93/12182. A further process for the deposition of thin metal layers, which can be used in the present case for the application of the metal layer to the substrate, is the known method for vapour deposition of metals in a high vacuum. It is described in detail in Vakuum-Beschichtung [Vacuum Coating], Volumes 1-5; Editors Frey, Kienel and Löbl, VDI-Verlag, 1995. In the sputtering process, a gas discharge (plasma) is ignited between the support and the coating material, which is in the form of plates (target). The coating material is bombarded with high-energy ions from the plasma, for example argon ions, and thus removed or atomised. The atoms or molecules of the atomised coating material are precipitated on the support and form the desired thin layer. The sputtering process is described in Vakuum-Beschichtung [Vacuum Coating], Volumes 1-5; Editors Frey, Kienel and Löbl, VDI-Verlag, 1995. For use in outdoor applications, in particular in the application in vehicle paints, the pigments can be provided with an additional weather-stabilising protective layer, the so-called post-coating, which simultaneously effects optimum adaptation to the binder system. Post-coatings of this type have been described, for example, in EP-A-0268918 and EP-A-0632109.
If pigments with metallic appearance are desired, the thickness of the metal layer is >25 nm to 100 nm, preferably 30 to 50 nm. If pigments with colored metal effects are desired, additional layers of colored or colorless metal oxides, metal nitrides, metal sulfides and/or metals can be deposited. These layers are transparent or semi-transparent. It is preferred that layers of high index of refraction and layers of low index of refraction alternate or that one layer is present, wherein within the layer the index of refraction is gradually changing. It is possible for the weathering resistance to be increased by means of an additional coating, which at the same time causes an optimal adaption to the binder system (EP-A-268918 and EP-A-632109).
In one preferred embodiment of the present invention, the interference pigments comprise materials having a “high” index of refraction, which is defined herein as an index of refraction of greater than about 1.65, and optionally materials having a “low” index of refraction, which is defined herein as an index of refraction of about 1.65 or less. Various (dielectric) materials that can be utilized including inorganic materials such as metal oxides, metal suboxides, metal fluorides, metal oxyhalides, metal sulfides, metal chalcogenides, metal nitrides, metal oxynitrides, metal carbides, combinations thereof, and the like, as well as organic dielectric materials. These materials are readily available and easily applied by physical, or chemical vapor deposition processes, or by wet chemical coating processes.
Optionally a SiO2 layer can be arranged between the inventive phlogopite substrate and the materials having a “high” index of refraction. By applying a SiO2 layer on the substrate the mica surface is protected against chemical alteration, such as, for example, swelling and leaching of mica components. The thickness of the SiO2 layer is in the range of 5 to 200 nm, especially 40 to 150 nm. The SiO2 layer is preferably prepared by using an organic silane compound, such as tetraethoxy silane (TEOS). The SiO2 layer can be replaced by thin layers (thickness 1 to 20 nm) of Al2O3, Fe2O3 or ZrO2.
Furthermore, the SiO2-coated, or TiO2-coated synthetic mica flakes may, as described in EP-A-0 982 376, be coated with a nitrogen-doped carbon layer. The process described in EP-A-0 982 376 comprises the following steps:
(a) suspending the SiO2, or TiO2 coated synthetic mica flakes in a liquid,
(b) where appropriate adding a surface-modifier and/or a polymerization catalyst,
(c), before or after step (b), adding one or more polymers comprising nitrogen and carbon atoms, or one or more monomers capable of forming such polymers,
(d) forming a polymeric coating on the surface of the flakes,
(e) isolating the coated flakes and
(f) heating the coated flakes to a temperature of from 100 to 600° C. in a gaseous atmosphere.
The polymer may be a polypyrrole, a polyamide, a polyaniline, a polyurethane, a nitrile rubber or a melamine-formaldehyde resin, preferably a polyacrylonitrile, or the monomer is a pyrrole derivative, an acrylonitrile, a methacrylonitrile, a crotonitrile, an acrylamide, a methacrylamide or a crotonamide, preferably an acrylonitrile, methacrylonitrile or crotonitrile, most preferably an acrylonitrile.
Preferably, the flakes are heated in step (f) initially to from 100° C. to 300° C. in an oxygen-containing atmosphere and then to from 200 to 600° C. in an inert gas atmosphere.
The present invention therefore relates also to pigments based on the synthetic mica flakes according to the invention comprising over the entire surface of the silicon oxide, or titanium oxide coated synthetic mica flakes a layer consisting of from 50 to 95% by weight carbon, from 5 to 25% by weight nitrogen and from 0 to 25% by weight of the elements hydrogen, oxygen and/or sulfur, the percentage by weight data relating to the total weight of the layer (PAN).
The thickness of the nitrogen-doped carbon layer is generally from 10 to 150 nm, preferably from 30 to 70 nm. In said embodiment preferred pigments have the following layer structure:
Synthetic mica substrate/TiO2/PAN, synthetic mica substrate/TiO2/PAN/TiO2, synthetic mica substrate/TiO2/PAN/SiO2/PAN.
In an especially preferred embodiment, the interference pigments on the basis of the synthetic mica substrate comprise a layer of a dielectric material having a “high” refractive index, that is to say a refractive index greater than about 1.65, preferably greater than about 2.0, most preferred greater than about 2.2, which is applied to the entire surface of the synthetic mica substrate. Examples of such a dielectric material are zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO2), titanium dioxide (TiO2), carbon, indium oxide (In2O3), indium tin oxide (ITO), tantalum pentoxide (Ta2O5), chromium oxide (Cr2O3), cerium oxide (CeO2), yttrium oxide (Y2O3), europium oxide (Eu2O3), iron oxides such as iron(II)/iron(III) oxide (Fe3O4) and iron(III) oxide (Fe2O3), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO2), lanthanum oxide (La2O3), magnesium oxide (MgO), neodymium oxide (Nd2O3), praseodymium oxide (Pr6O11), samarium oxide (Sm2O3), antimony trioxide (Sb2O3), silicon monoxides (SiO), selenium trioxide (Se2O3), tin oxide (SnO2), tungsten trioxide (WO3), or combinations thereof. The dielectric material is preferably a metal oxide. It being possible for the metal oxide to be a single oxide or a mixture of oxides, with or without absorbing properties, for example, TiO2, ZrO2, Fe2O3, Fe3O4, Cr2O3 or ZnO, with TiO2 being especially preferred.
It is possible to obtain pigments that are more intense in colour and more transparent by applying, on top of the TiO2 layer, a metal oxide of low refractive index, such as SiO2, Al2O3, AlOOH, B2O3 or a mixture thereof, preferably SiO2, and optionally applying a further TiO2 layer on top of the latter layer (EP-A-892832, EP-A-753545, WO93/08237, WO98/53011, WO9812266, WO9838254, WO99/20695, WO00/42111, and EP-A-1213330). Nonlimiting examples of suitable low index dielectric materials that can be used include silicon dioxide (SiO2), aluminum oxide (Al2O3), and metal fluorides such as magnesium fluoride (MgF2), aluminum fluoride (AlF3), cerium fluoride (CeF3), lanthanum fluoride (LaF3), sodium aluminum fluorides (e.g., Na3AlF6 or Na5Al3F14), neodymium fluoride (NdF3), samarium fluoride (SmF3), barium fluoride (BaF2), calcium fluoride (CaF2), lithium fluoride (LiF), combinations thereof, or any other low index material having an index of refraction of about 1.65 or less. For example, organic monomers and polymers can be utilized as low index materials, including dienes or alkenes such as acrylates (e.g., methacrylate), polymers of perfluoroalkenes, polytetrafluoroethylene (TEFLON), polymers of fluorinated ethylene propylene (FEP), parylene, p-xylene, combinations thereof, and the like. Additionally, the foregoing materials include evaporated, condensed and cross-linked transparent acrylate layers, which may be deposited by methods described in U.S. Pat. No. 5,877,895, the disclosure of which is incorporated herein by reference.
Accordingly, preferred interference pigments comprise besides (a) a metal oxide of high refractive index in addition (b) a metal oxide of low refractive index, wherein the difference of the refractive indices is at least 0.1.
Pigments on the basis of the synthetic mica substrates, which have been coated by a wet chemical method, in the indicated order are particularly preferred:
TiO2, (SnO2)TiO2 (substrate: synthetic mica; layer: (SnO2)TiO2, preferably in the rutile modification), titanium suboxide, TiO2/titanium suboxide, Fe2O3, Fe3O4, TiFe2O5, FeTiO3, Cr2O3, ZrO2, Sn(Sb)O2, BiOCl, Al2O3, Ce2S3, MoS2, Fe2O3—TiO2 (substrate: synthetic mica; mixed layer of Fe2O3 and TiO2), TiO2/Fe2O3 (substrate: synthetic mica; first layer: TiO2; second layer: Fe2O3), TiO2/Berlin blau, TiO2/Cr2O3, or TiO2/FeTiO3. In general the layer thickness ranges from 1 to 1000 nm, preferably from 1 to 300 nm.
In another particularly preferred embodiment the present invention relates to interference pigments containing at least three alternating layers of high and low refractive index, such as, for example, TiO2/SiO2/TiO2, (SnO2)TiO2/SiO2/TiO2, TiO2/SiO2/TiO2/SiO2/TiO2, Fe2O3/SiO2/TiO2, or TiO2/SiO2/Fe2O3.
Preferably the layer structure is as follows:
(a) a coating having a refractive index>1.65,
(b) a coating having a refractive index≦1.65,
(c) a coating having a refractive index>1.65, and
(d) optionally an outer protective layer.
The thickness of the individual layers of high and low refractive index on the base substrate is essential for the optical properties of the pigment. The thickness of the individual layers, especially metal oxide layers, depends on the field of use and is generally 10 to 1000 nm, preferably 15 to 800 nm, in particular 20 to 600 nm.
The thickness of layer (A) is 10 to 550 nm, preferably 15 to 400 nm and, in particular, 20 to 350 nm. The thickness of layer (B) is 10 to 1000 nm, preferably 20 to 800 nm and, in particular, 30 to 600 nm. The thickness of layer (C) is 10 to 550 nm, preferably 15 to 400 nm and, in particular, 20 to 350 nm.
Particularly suitable materials for layer (A) are metal oxides, metal sulfides, or metal oxide mixtures, such as TiO2, Fe2O3, TiFe2O5, Fe3O4, BiOCl, CoO, Co3O4, Cr2O3, VO2, V2O3, Sn(Sb)O2, SnO2, ZrO2, iron titanates, iron oxide hydrates, titanium suboxides (reduced titanium species having oxidation states from 2 to <4), bismuth vanadate, cobalt aluminate, and also mixtures or mixed phases of these compounds with one another or with other metal oxides. Metal sulfide coatings are preferably selected from sulfides of tin, silver, lanthanum, rare earth metals, preferably cerium, chromium, molybdenum, tungsten, iron, cobalt and/or nickel.
Particularly suitable materials for layer (B) are metal oxides or the corresponding oxide hydrates, such as SiO2, MgF2, Al2O3, AlOOH, B2O3 or a mixture thereof, preferably SiO2.
Particularly suitable materials for layer (C) are colorless or colored metal oxides, such as TiO2, Fe2O3, TiFe2O5, Fe3O4, BiOCl, CoO, Co3O4, Cr2O3, VO2, V2O3, Sn(Sb)O2, SnO2, ZrO2, iron titanates, iron oxide hydrates, titanium suboxides (reduced titanium species having oxidation states from 2 to <4), bismuth vanadate, cobalt aluminate, and also mixtures or mixed phases of these compounds with one another or with other metal oxides. The TiO2 layers can additionally contain an absorbing material, such as carbon, selectively absorbing colorants, selectively absorbing metal cations, can be coated with absorbing material, or can be partially reduced.
Interlayers of absorbing or nonabsorbing materials can be present between layers (A), (B), (C) and (D). The thickness of the interlayers is 1 to 50 nm, preferably 1 to 40 nm and, in particular, 1 to 30 nm. Such an interlayer can, for example, consist of SnO2. It is possible to force the rutile structure to be formed by adding small amounts of SnO2 (see, for example, WO93/08237).
In this embodiment preferred interference pigments have the following layer structure:
The metal oxide layers can be applied by CVD (chemical vapour deposition) or by wet chemical coating. The metal oxide layers can be obtained by decomposition of metal carbonyls in the presence of water vapour (relatively low molecular weight metal oxides such as magnetite) or in the presence of oxygen and, where appropriate, water vapour (e.g. nickel oxide and cobalt oxide). The metal oxide layers are especially applied by means of oxidative gaseous phase decomposition of metal carbonyls (e.g. iron pentacarbonyl, chromium hexacarbonyl; EP-A-45 851), by means of hydrolytic gaseous phase decomposition of metal alcoholates (e.g. titanium and zirconium tetra-n- and -iso-propanolate; DE-A-41 40 900) or of metal halides (e.g. titanium tetrachloride; EP-A-338 428), by means of oxidative decomposition of organyl tin compounds (especially alkyl tin compounds such as tetrabutyltin and tetramethyltin; DE-A-44 03 678) or by means of the gaseous phase hydrolysis of organyl silicon compounds (especially di-tert-butoxyacetoxysilane) described in EP-A-668 329, it being possible for the coating operation to be carried out in a fluidised-bed reactor (EP-A-045 851 and EP-A-106 235). Al2O3 layers (B) can advantageously be obtained by controlled oxidation during the cooling of aluminium-coated pigments, which is otherwise carried out under inert gas (DE-A-195 16 181).
Phosphate-, chromate- and/or vanadate-containing and also phosphate- and SiO2-containing metal oxide layers can be applied in accordance with the passivation methods described in DE-A-42 36 332 and in EP-A-678 561 by means of hydrolytic or oxidative gaseous phase decomposition of oxide-halides of the metals (e.g. CrO2Cl2, VOCl3), especially of phosphorus oxyhalides (e.g. POCl3), phosphoric and phosphorous acid esters (e.g. di- and tri-methyl and di- and tri-ethyl phosphite) and of amino-group-containing organyl silicon compounds (e.g. 3-aminopropyl-triethoxy- and -trimethoxy-silane).
Layers of oxides of the metals zirconium, titanium, iron and zinc, oxide hydrates of those metals, iron titanates, titanium suboxides or mixtures thereof are preferably applied by precipitation by a wet chemical method, it being possible, where appropriate, for the metal oxides to be reduced. In the case of the wet chemical coating, the wet chemical coating methods developed for the production of pearlescent pigments may be used; these are described, for example, in DE-A-14 67 468, DE-A-19 59 988, DE-A-20 09 566, DE-A-22 14 545, DE-A-22 15 191, DE-A-22 44 298, DE-A-23 13 331, DE-A-25 22 572, DE-A-31 37 808, DE-A-31 37 809, DE-A-31 51 343, DE-A-31 51 354, DE-A-31 51 355, DE-A-32 11 602 and DE-A-32 35 017, DE 195 99 88, WO 93/08237, WO 98/53001 and WO03/6558.
The metal oxide of high refractive index is preferably TiO2 and/or iron oxide, and the metal oxide of low refractive index is preferably SiO2. Layers of TiO2 can be in the rutile or anastase modification, wherein the rutile modification is preferred. TiO2 layers can also be reduced by known means, for example ammonia, hydrogen, hydrocarbon vapor or mixtures thereof, or metal powders, as described in EP-A-735,114, DE-A-3433657, DE-A-4125134, EP-A-332071, EP-A-707,050, WO93/19131, or WO06/131472.
For the purpose of coating, the substrate particles are suspended in water and one or more hydrolysable metal salts are added at a pH suitable for the hydrolysis, which is so selected that the metal oxides or metal oxide hydrates are precipitated directly onto the particles without subsidiary precipitation occurring. The pH is usually kept constant by simultaneously metering in a base. The pigments are then separated off, washed, dried and, where appropriate, calcinated, it being possible to optimise the calcinating temperature with respect to the coating in question. If desired, after individual coatings have been applied, the pigments can be separated off, dried and, where appropriate, calcinated, and then again re-suspended for the purpose of precipitating further layers.
The metal oxide layers are also obtainable, for example, in analogy to a method described in DE-A-195 01 307, by producing the metal oxide layer by controlled hydrolysis of one or more metal acid esters, where appropriate in the presence of an organic solvent and a basic catalyst, by means of a sol-gel process. Suitable basic catalysts are, for example, amines, such as triethylamine, ethylenediamine, tributylamine, dimethylethanolamine and methoxy-propylamine. The organic solvent is a water-miscible organic solvent such as a C1-4alcohol, especially isopropanol.
Suitable metal acid esters are selected from alkyl and aryl alcoholates, carboxylates, and carboxyl-radical- or alkyl-radical- or aryl-radical-substituted alkyl alcoholates or carboxylates of vanadium, titanium, zirconium, silicon, aluminium and boron. The use of triisopropyl aluminate, tetraisopropyl titanate, tetraisopropyl zirconate, tetraethyl orthosilicate and triethyl borate is preferred. In addition, acetylacetonates and acetoacetylacetonates of the afore-mentioned metals may be used. Preferred examples of that type of metal acid ester are zirconium acetylacetonate, aluminium acetylacetonate, titanium acetylacetonate and diisobutyloleyl acetoacetylaluminate or diisopropyloleyl acetoacetylacetonate and mixtures of metal acid esters, for example Dynasil® (Hüls), a mixed aluminium/silicon metal acid ester.
As a metal oxide having a high refractive index, titanium dioxide is preferably used, the method described in U.S. Pat. No. 3,553,001 being used, in accordance with an embodiment of the present invention, for application of the titanium dioxide layers.
An aqueous titanium salt solution is slowly added to a suspension of the material being coated, which suspension has been heated to about 50-100° C., especially 70-80° C., and a substantially constant pH value of about from 0.5 to 5, especially about from 1.2 to 2.5, is maintained by simultaneously metering in a base such as, for example, aqueous ammonia solution or aqueous alkali metal hydroxide solution. As soon as the desired layer thickness of precipitated TiO2 has been achieved, the addition of titanium salt solution and base is stopped. Addition of a precursor for Al2O3 or MgO in the starting solutions is a way for improving the morphology of the TiO2 layer.
This method, also referred to as the “titration method”, is distinguished by the fact that an excess of titanium salt is avoided. That is achieved by feeding in for hydrolysis, per unit time, only that amount which is necessary for even coating with the hydrated TiO2 and which can be taken up per unit time by the available surface of the particles being coated. In principle, the anatase form of TiO2 forms on the surface of the starting pigment. By adding small amounts of SnO2, however, it is possible to force the rutile structure to be formed. For example, as described in WO 93/08237, tin dioxide can be deposited before titanium dioxide precipitation and the product coated with titanium dioxide can be calcined at from 800 to 900° C.
In an especially preferred embodiment of the present invention the synthetic mica flakes are mixed with distilled water in a closed reactor and heated at about 90° C. The pH is set to about 1.8 to 2.2 and a preparation comprising TiOCl2, HCl, glycine and distilled water is added slowly while keeping the pH constant (1.8 to 2.2) by continuous addition of 1M NaOH solution. Reference is made to European patent application PCT/EP2008/051910. By adding an amino acid, such as glycine, during the deposition of the TiO2 it is possible to improve the quality of the TiO2 coating to be formed. Advantageously, a preparation comprising TiOCl2, HCl, and glycine and distilled water is added to the substrate flakes in water.
The TiO2 can optionally be reduced by usual procedures: U.S. Pat. No. 4,948,631 (NH3, 750-850° C.), WO93/19131 (H2, >900° C.) or DE-A-19843014 (solid reduction agent, such as, for example, silicon, >600° C.).
Where appropriate, an SiO2 (protective) layer can be applied on top of the titanium dioxide layer, for which the following method may be used: A soda waterglass solution is metered into a suspension of the material being coated, which suspension has been heated to about 50-100° C., especially 70-80° C. The pH is maintained at from 4 to 10, preferably from 6.5 to 8.5, by simultaneously adding 10% hydrochloric acid. After addition of the waterglass solution, stirring is carried out for 30 minutes.
It is possible to obtain pigments that are more intense in colour and more transparent by applying, on top of the TiO2 layer, a metal oxide of “low” refractive index, that is to say a refractive index smaller than about 1.65, such as SiO2, Al2O3, AlOOH, B2O3 or a mixture thereof, preferably SiO2, and applying a further Fe2O3 and/or TiO2 layer on top of the latter layer. Such multi-coated interference pigments comprising a synthetic mica substrate and alternating metal oxide layers of with high and low refractive index can be prepared in analogy to the processes described in WO98/53011 and WO99/20695.
It is, in addition, possible to modify the powder colour of the pigment by applying further layers such as, for example, coloured metal oxides or Berlin Blue, compounds of transition metals, e.g. Fe, Cu, Ni, Co, Cr, or organic compounds such as dyes or colour lakes.
In addition, the pigment according to the invention can also be coated with poorly soluble, firmly adhering, inorganic or organic colourants. Preference is given to the use of colour lakes and, especially, aluminium colour lakes. For that purpose an aluminium hydroxide layer is precipitated, which is, in a second step, laked by using a colour lake (DE-A-24 29 762 and DE-A-29 28 287).
Furthermore, the pigment according to the invention may also have an additional coating with complex salt pigments, especially cyanoferrate complexes (EP-A-141 173 and DE-A-23 13 332).
To enhance the weather and light stability the (multilayer) synthetic mica flakes can be, depending on the field of application, subjected to a surface treatment. Useful surface treatments are, for example, described in DE-A-2215191, DE-A-3151354, DE-A-3235017, DE-A-3334598, DE-A-4030727, EP-A-649886, WO97/29059, WO99/57204, and U.S. Pat. No. 5,759,255. Said surface treatment might also facilitate the handling of the pigment, especially its incorporation into various application media.
In a preferred embodiment of the present invention is directed to pigments which contain a core of synthetic mica and comprise a mixed layer of Al2O3/TiO2. The mixed layer can contain up to 20 mol % Al2O3. The mixed layer of Al2O3/TiO2 is obtained by slowly adding an aqueous aluminum and titanium salt solution to a suspension of the material being coated, which suspension has been heated to about 50-100° C., especially 70-80° C., and maintaining a substantially constant pH value of about from 0.5 to 5, especially about from 1.2 to 2.5, by simultaneously metering in a base such as, for example, aqueous ammonia solution or aqueous alkali metal hydroxide solution. As soon as the desired layer thickness of precipitated Al2O3/TiO2 has been achieved, the addition of titanium and aluminum salt solution and base is stopped.
The thickness of the mixed layer of Al2O3/TiO2 is in general in the range of 20 to 200 nm, especially 50 to 150 nm. Preferably the pigments comprise a TiO2 layer on top of the mixed layer of Al2O3/TiO2 having a thickness of 1 to 50 nm, especially 10 to 20 nm. By varying the thickness of the mixed layer of Al2O3/TiO2 the flop of the pigments can be enhanced and controlled as desired.
In another preferred embodiment of the present invention is directed to pigments which contain a core of the high aspect ratio synthetic mica and consist of subsequent layers of TiO2/SnO2/TiO2, wherein the TiO2 layer next to the synthetic mica substrate has a thickness of 1 to 20 nm and is preferably prepared by using titanium alcoholates, especially tetraisopropyl titanate.
The platelet-like substrate (core) of the pigments of the present invention consists of high aspect ratio synthetic zinc phlogopite.
Metallic or non-metallic, inorganic platelet-shaped particles or pigments are effect pigments, (especially metal effect pigments or interference pigments), that is to say, pigments that, besides imparting colour to an application medium, impart additional properties, for example angle dependency of the colour (flop), luster (not surface gloss) or texture. On metal effect pigments, substantially oriented reflection occurs at directionally oriented pigment particles. In the case of interference pigments, the colour-imparting effect is due to the phenomenon of interference of light in thin, highly refractive layers.
The (effect) pigments according to the invention can be used for all customary purposes, for example for colouring polymers in the mass, coatings (including effect finishes, including those for the automotive sector) and printing inks (including offset printing, intaglio printing, bronzing and flexographic printing), and also, for example, for applications in cosmetics, in ink-jet printing, for dyeing textiles, glazes for ceramics and glass as well as laser marking of papers and plastics. Such applications are known from reference works, for example “Industrielle Organische Pigmente” (W. Herbst and K. Hunger, VCH Verlagsgesellschaft mbH, Weinheim/New York, 2nd, completely revised edition, 1995).
When the pigments according to the invention are interference pigments (effect pigments), they may be goniochromatic and result in brilliant, highly saturated (lustrous) colours. They are accordingly very especially suitable for combination with conventional, transparent pigments, for example organic pigments such as, for example, diketopyrrolopyrroles, quinacridones, dioxazines, perylenes, isoindolinones etc., it being possible for the transparent pigment to have a similar colour to the effect pigment. Especially interesting combination effects are obtained, however, in analogy to, for example, EP-A-388 932 or EP-A-402 943, when the colour of the transparent pigment and that of the effect pigment are complementary. The pigments according to the invention can be used with excellent results for pigmenting high molecular weight organic material.
The high molecular weight organic material for the pigmenting of which the pigments or pigment compositions according to the invention may be used may be of natural or synthetic origin. High molecular weight organic materials usually have average weight average molecular weights of about from 103 to 108 g/mol or even more. They may be, for example, natural resins, drying oils, rubber or casein, or natural substances derived therefrom, such as chlorinated rubber, oil-modified alkyd resins, viscose, cellulose ethers or esters, such as ethylcellulose, cellulose acetate, cellulose propionate, cellulose acetobutyrate or nitrocellulose, but especially totally synthetic organic polymers (thermosetting plastics and thermoplastics), as are obtained by polymerisation, polycondensation or polyaddition. From the class of the polymerisation resins there may be mentioned, especially, polyolefins, such as polyethylene, polypropylene or polyisobutylene, and also substituted polyolefins, such as polymerisation products of vinyl chloride, vinyl acetate, styrene, acrylonitrile, acrylic acid esters, methacrylic acid esters or butadiene, and also copolymerisation products of the said monomers, such as especially ABS or EVA.
From the series of the polyaddition resins and polycondensation resins there may be mentioned, for example, condensation products of formaldehyde with phenols, so-called phenoplasts, and condensation products of formaldehyde with urea, thiourea or melamine, so-called aminoplasts, and the polyesters used as surface-coating resins, either saturated, such as alkyd resins, or unsaturated, such as maleate resins; also linear polyesters and polyamides, polyurethanes or silicones.
The said high molecular weight compounds may be present singly or in mixtures, in the form of plastic masses or melts. They may also be present in the form of their monomers or in the polymerised state in dissolved form as film-formers or binders for coatings or printing inks, such as, for example, boiled linseed oil, nitrocellulose, alkyd resins, melamine resins and urea-formaldehyde resins or acrylic resins.
Depending on the intended purpose, it has proved advantageous to use the effect pigments or effect pigment compositions according to the invention as toners or in the form of preparations. Depending on the conditioning method or intended application, it may be advantageous to add certain amounts of texture-improving agents to the effect pigment before or after the conditioning process, provided that this has no adverse effect on use of the effect pigments for colouring high molecular weight organic materials, especially polyethylene. Suitable agents are, especially, fatty acids containing at least 18 carbon atoms, for example stearic or behenic acid, or amides or metal salts thereof, especially magnesium salts, and also plasticisers, waxes, resin acids, such as abietic acid, rosin soap, alkylphenols or aliphatic alcohols, such as stearyl alcohol, or aliphatic 1,2-dihydroxy compounds containing from 8 to 22 carbon atoms, such as 1,2-dodecanediol, and also modified colophonium maleate resins or fumaric acid colophonium resins. The texture-improving agents are added in amounts of preferably from 0.1 to 30% by weight, especially from 2 to 15% by weight, based on the end product.
The (effect) pigments according to the invention can be added in any tinctorially effective amount to the high molecular weight organic material being pigmented. A pigmented substance composition comprising a high molecular weight organic material and from 0.01 to 80% by weight, preferably from 0.1 to 30% by weight, based on the high molecular weight organic material, of an pigment according to the invention is advantageous. Concentrations of from 1 to 20% by weight, especially of about 10% by weight, can often be used in practice.
High concentrations, for example those above 30% by weight, are usually in the form of concentrates (“masterbatches”) which can be used as colorants for producing pigmented materials having a relatively low pigment content, the pigments according to the invention having an extraordinarily low viscosity in customary formulations so that they can still be processed well.
For the purpose of pigmenting organic materials, the effect pigments according to the invention may be used singly. It is, however, also possible, in order to achieve different hues or colour effects, to add any desired amounts of other colour-imparting constituents, such as white, coloured, black or effect pigments, to the high molecular weight organic substances in addition to the effect pigments according to the invention. When coloured pigments are used in admixture with the effect pigments according to the invention, the total amount is preferably from 0.1 to 10% by weight, based on the high molecular weight organic material. Especially high goniochromicity is provided by the preferred combination of an effect pigment according to the invention with a coloured pigment of another colour, especially of a complementary colour, with colorations made using the effect pigment and colorations made using the coloured pigment having, at a measurement angle of 10°, a difference in hue (ΔH*) of from 20 to 340, especially from 150 to 210.
Preferably, the effect pigments according to the invention are combined with transparent coloured pigments, it being possible for the transparent coloured pigments to be present either in the same medium as the effect pigments according to the invention or in a neighbouring medium. An example of an arrangement in which the effect pigment and the coloured pigment are advantageously present in neighbouring media is a multi-layer effect coating.
The pigmenting of high molecular weight organic substances with the pigments according to the invention is carried out, for example, by admixing such a pigment, where appropriate in the form of a masterbatch, with the substrates using roll mills or mixing or grinding apparatuses. The pigmented material is then brought into the desired final form using methods known per se, such as calendering, compression moulding, extrusion, coating, pouring or injection moulding. Any additives customary in the plastics industry, such as plasticisers, fillers or stabilisers, can be added to the polymer, in customary amounts, before or after incorporation of the pigment. In particular, in order to produce non-rigid shaped articles or to reduce their brittleness, it is desirable to add plasticisers, for example esters of phosphoric acid, phthalic acid or sebacic acid, to the high molecular weight compounds prior to shaping.
For pigmenting coatings and printing inks, the high molecular weight organic materials and the effect pigments according to the invention, where appropriate together with customary additives such as, for example, fillers, other pigments, siccatives or plasticisers, are finely dispersed or dissolved in the same organic solvent or solvent mixture, it being possible for the individual components to be dissolved or dispersed separately or for a number of components to be dissolved or dispersed together, and only thereafter for all the components to be brought together.
Dispersing an effect pigment according to the invention in the high molecular weight organic material being pigmented, and processing a pigment composition according to the invention, are preferably carried out subject to conditions under which only relatively weak shear forces occur so that the effect pigment is not broken up into smaller portions.
Plastics comprising the pigment of the invention in amounts of 0.1 to 50% by weight, in particular 0.5 to 7% by weight. In the coating sector, the pigments of the invention are employed in amounts of 0.1 to 10% by weight. In the pigmentation of binder systems, for example for paints and printing inks for intaglio, offset or screen printing, the pigment is incorporated into the printing ink in amounts of 0.1 to 50% by weight, preferably 5 to 30% by weight and in particular 8 to 15% by weight.
The colorations obtained, for example in plastics, coatings or printing inks, especially in coatings or printing inks, more especially in coatings, may be distinguished by excellent properties, especially by extremely high saturation, outstanding fastness properties, high color purity and high goniochromaticity.
When the high molecular weight material being pigmented is a coating, it is especially a speciality coating, very especially an automotive finish.
The effect pigments according to the invention are also suitable for making-up the lips or the skin and for colouring the hair or the nails.
The invention accordingly relates also to a cosmetic preparation or formulation comprising from 0.0001 to 90% by weight of a pigment, especially an effect pigment, according to the invention and from 10 to 99.9999% of a cosmetically suitable carrier material, based on the total weight of the cosmetic preparation or formulation.
Such cosmetic preparations or formulations are, for example, lipsticks, blushers, foundations, nail varnishes and hair shampoos.
The pigments may be used singly or in the form of mixtures. It is, in addition, possible to use pigments according to the invention together with other pigments and/or colorants, for example in combinations as described hereinbefore or as known in cosmetic preparations.
The cosmetic preparations and formulations according to the invention preferably contain the pigment according to the invention in an amount from 0.005 to 50% by weight, based on the total weight of the preparation.
Suitable carrier materials for the cosmetic preparations and formulations according to the invention include the customary materials used in such compositions.
The cosmetic preparations and formulations according to the invention may be in the form of, for example, sticks, ointments, creams, emulsions, suspensions, dispersions, powders or solutions. They are, for example, lipsticks, mascara preparations, blushers, eye-shadows, foundations, eyeliners, powder or nail varnishes.
If the preparations are in the form of sticks, for example lipsticks, eye-shadows, blushers or foundations, the preparations consist for a considerable part of fatty components, which may consist of one or more waxes, for example ozokerite, lanolin, lanolin alcohol, hydrogenated lanolin, acetylated lanolin, lanolin wax, beeswax, candelilla wax, microcrystalline wax, carnauba wax, cetyl alcohol, stearyl alcohol, cocoa butter, lanolin fatty acids, petrolatum, petroleum jelly, mono-, di- or tri-glycerides or fatty esters thereof that are solid at 25° C., silicone waxes, such as methyloctadecane-oxypolysiloxane and poly(dimethylsiloxy)stearoxysiloxane, stearic acid monoethanolamine, colophane and derivatives thereof, such as glycol abietates and glycerol abietates, hydrogenated oils that are solid at 25° C., sugar glycerides and oleates, myristates, lanolates, stearates and dihydroxystearates of calcium, magnesium, zirconium and aluminium.
The fatty component may also consist of a mixture of at least one wax and at least one oil, in which case the following oils, for example, are suitable: paraffin oil, purcelline oil, perhydrosqualene, sweet almond oil, avocado oil, calophyllum oil, castor oil, sesame oil, jojoba oil, mineral oils having a boiling point of about from 310 to 410° C., silicone oils, such as dimethylpolysiloxane, linoleyl alcohol, linolenyl alcohol, oleyl alcohol, cereal grain oils, such as wheatgerm oil, isopropyl lanolate, isopropyl palmitate, isopropyl myristate, butyl myristate, cetyl myristate, hexadecyl stearate, butyl stearate, decyl oleate, acetyl glycerides, octanoates and decanoates of alcohols and polyalcohols, for example of glycol and glycerol, ricinoleates of alcohols and polyalcohols, for example of cetyl alcohol, isostearyl alcohol, isocetyl lanolate, isopropyl adipate, hexyl laurate and octyl dodecanol.
The fatty components in such preparations in the form of sticks may generally constitute up to 99.91% by weight of the total weight of the preparation.
The cosmetic preparations and formulations according to the invention may additionally comprise further constituents, such as, for example, glycols, polyethylene glycols, polypropylene glycols, monoalkanolamides, non-coloured polymeric, inorganic or organic fillers, preservatives, UV filters or other adjuvants and additives customary in cosmetics, for example a natural or synthetic or partially synthetic di- or tri-glyceride, a mineral oil, a silicone oil, a wax, a fatty alcohol, a Guerbet alcohol or ester thereof, a lipophilic functional cosmetic active ingredient, including sun-protection filters, or a mixture of such substances.
A lipophilic functional cosmetic active ingredient suitable for skin cosmetics, an active ingredient composition or an active ingredient extract is an ingredient or a mixture of ingredients that is approved for dermal or topical application. The following may be mentioned by way of example:
The preparations in stick form are preferably anhydrous but may in certain cases comprise a certain amount of water which, however, in general does not exceed 40% by weight, based on the total weight of the cosmetic preparation.
If the cosmetic preparations and formulations according to the invention are in the form of semi-solid products, that is to say in the form of ointments or creams, they may likewise be anhydrous or aqueous. Such preparations and formulations are, for example, mascaras, eyeliners, foundations, blushers, eye-shadows, or compositions for treating rings under the eyes.
If, on the other hand, such ointments or creams are aqueous, they are especially emulsions of the water-in-oil type or of the oil-in-water type that comprise, apart from the pigment, from 1 to 98.8% by weight of the fatty phase, from 1 to 98.8% by weight of the aqueous phase and from 0.2 to 30% by weight of an emulsifier.
Such ointments and creams may also comprise further conventional additives, such as, for example, perfumes, antioxidants, preservatives, gel-forming agents, UV filters, colorants, pigments, pearlescent agents, non-coloured polymers as well as inorganic or organic fillers. If the preparations are in the form of a powder, they consist substantially of a mineral or inorganic or organic filler such as, for example, talcum, kaolin, starch, polyethylene powder or polyamide powder, as well as adjuvants such as binders, colorants etc.
Such preparations may likewise comprise various adjuvants conventionally employed in cosmetics, such as fragrances, antioxidants, preservatives etc.
If the cosmetic preparations and formulations according to the invention are nail varnishes, they consist essentially of nitrocellulose and a natural or synthetic polymer in the form of a solution in a solvent system, it being possible for the solution to comprise other adjuvants, for example pearlescent agents.
In that embodiment, the coloured polymer is present in an amount of approximately from 0.1 to 5% by weight.
The cosmetic preparations and formulations according to the invention may also be used for colouring the hair, in which case they are used in the form of shampoos, creams or gels that are composed of the base substances conventionally employed in the cosmetics industry and a pigment according to the invention.
The cosmetic preparations and formulations according to the invention are prepared in conventional manner, for example by mixing or stirring the components together, optionally with heating so that the mixtures melt.
Thus the present application envisions cosmetics, coatings, inks, paints, and plastic composition containing the effect pigment formed from a coated phlogopite of aspect ratio ranging from about 50 to about 2000, preferably 100 to about 2000.
Barrier Applications of the Hydrothermally Produced Mica
The synthetically derived zinc phlogopite platelets produced via the hydrothermal process above may be used to effect gas barriers such as water vapor, oxygen barriers and CO2 barriers when present in paper coatings, coatings on packaging films or melt blended in films or containers used in packaging.
The platelets formed by the presently disclosed process may be used to form layered structures on or in such substrates such as paper, plastic packaging or as component within a coating. The layered structures of mica materials, for example, may be used to provide a barrier packaging film with a low moisture vapor transmission rate (MVTR), and/or a low oxygen transmission rate (OTR).
It is well known to use layered silicates to improve the flame retardant properties of flammable substrates. For example the zinc phlogopite platelet formed by the present hydrothermal process, may be used in polymeric composites for improving the flame retardant properties of the composite by increasing the barrier properties of the composite, and increased char formation upon ignition of the composite.
Equipment: Scott Volumeter equipped with a 16 or 40 mesh screen, metal funnel and baffle box. 1 inch3 density cup with capacity of 1.000±0.002 in3
Final powder to be tested should be free flowing and not contain lumps. The sample is poured onto the screen and the powder flows down through the baffle box and into the cup until the cup is completely filled to overflowing on all sides of the cup. Then without disturbing the cup rotate the baffle box and funnel out of the way. Remove excess powder by scoring the top of the cup diagonally with a spatula. Tap cup gently to settle powder and weigh. Repeat test with fresh sample powder for duplicate comparisons.
The starting reagents are potassium aluminate, zinc sulfate heptahydrate, potassium hydroxide, and colloidal silica. A 6M KOH solution is added to zinc sulfate heptahydrate and the mixture is stirred for approximately five minutes. 6M KOH is added to potassium aluminate and the contents are swirled to mix. The two mixtures are combined and water and trisodium citrate dihydrate are added. The reaction mixture is transferred to a Parr reactor and the colloidal silica is added forming a gel. The Parr reactor is sealed and placed in an oven at 200° C. for 24 hours. Upon cooling to room temperature, the reaction is filtered and washed with D.I. water yielding a white powder.
The starting reagents are potassium aluminate, zinc sulfate heptahydrate, potassium hydroxide, and colloidal silica. A 6M KOH solution is added to zinc sulfate heptahydrate and the mixture is stirred for approximately five minutes. 6M KOH is added to potassium aluminate and the contents are swirled to mix. The two mixtures are combined and water and trisodium citrate dihydrate are added. The reaction mixture is transferred to a stirred Parr reactor and the colloidal silica is added forming a gel. The Parr reactor is sealed and the stir-rate is set to 100 rpm. The reactor is heated to 200° C. and kept at temperature for 24 hours. Upon cooling to room temperature, the reaction is filtered and washed with D.I. water yielding a white powder.
The starting reagents are potassium aluminate, zinc sulfate heptahydrate, potassium hydroxide, and colloidal silica. A 16M KOH solution is added to zinc sulfate heptahydrate and the mixture is stirred for approximately five minutes. 16M KOH is added to potassium aluminate and the contents are swirled to mix. A colloidal silica solution is weighed into a beaker. The trisodium citrate dihydrate is dissolved in water and added separately to each of the zinc sulfate heptahydrate solution, potassium aluminate solution, and colloidal silica solution. All three solutions are spatula stirred and allowed to stand for five minutes, then combined. The combined reaction mixture is transferred to a stirred Parr reactor with additional water to completely transfer the reagents. The Parr reactor is sealed and the stir-rate is set to 400 rpm. The reactor is heated to reach a temperature of 200° C. and kept at temperature for 24 hours. Upon cooling to room temperature, the reaction is filtered and washed with D.I. water yielding a white powder.
1Sample 7 is characterized by a d50 of 9.978, d10 of 2.632 and a d90 of 22.137 μm.
2Sample 8 is characterized by a d50 of 13.989, d10 of 5.166 and d90 of 26.963 microns.
The zinc phlogopite from example 7 are coated with TiO2 according to well known methods of the prior art.
This application is a divisional application which claims the benefit of U.S. provisional application Ser. No. 61/776,228 filed Mar. 11, 2013 both incorporated entirely by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61776228 | Mar 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14204244 | Mar 2014 | US |
| Child | 14204366 | US |
