US20190153613A1 - Method for the production of single crystalline tio2 flakes - Google Patents
Method for the production of single crystalline tio2 flakes Download PDFInfo
- Publication number
- US20190153613A1 US20190153613A1 US16/253,520 US201916253520A US2019153613A1 US 20190153613 A1 US20190153613 A1 US 20190153613A1 US 201916253520 A US201916253520 A US 201916253520A US 2019153613 A1 US2019153613 A1 US 2019153613A1
- Authority
- US
- United States
- Prior art keywords
- tio
- single crystalline
- flakes
- flake
- titanium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title abstract description 43
- 238000004519 manufacturing process Methods 0.000 title abstract description 32
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 244
- 239000013078 crystal Substances 0.000 claims abstract description 18
- 239000002245 particle Substances 0.000 claims description 35
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 25
- 239000008199 coating composition Substances 0.000 claims description 9
- 239000002250 absorbent Substances 0.000 claims description 5
- 230000002745 absorbent Effects 0.000 claims description 5
- 239000002537 cosmetic Substances 0.000 claims description 5
- 239000000976 ink Substances 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 239000003973 paint Substances 0.000 claims description 5
- 239000011941 photocatalyst Substances 0.000 claims description 5
- 239000004033 plastic Substances 0.000 claims description 5
- 229920003023 plastic Polymers 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 4
- 230000002940 repellent Effects 0.000 claims description 4
- 239000005871 repellent Substances 0.000 claims description 4
- 239000012463 white pigment Substances 0.000 claims description 2
- 239000000049 pigment Substances 0.000 abstract description 17
- 239000004408 titanium dioxide Substances 0.000 description 101
- 150000003609 titanium compounds Chemical class 0.000 description 34
- 238000001354 calcination Methods 0.000 description 31
- 239000002243 precursor Substances 0.000 description 19
- -1 titanium alkoxide Chemical class 0.000 description 15
- 238000002156 mixing Methods 0.000 description 14
- 239000000243 solution Substances 0.000 description 14
- 239000003795 chemical substances by application Substances 0.000 description 13
- 239000011574 phosphorus Substances 0.000 description 13
- 229910052698 phosphorus Inorganic materials 0.000 description 13
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- 239000002932 luster Substances 0.000 description 11
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 10
- 229910052938 sodium sulfate Inorganic materials 0.000 description 10
- 239000010936 titanium Substances 0.000 description 10
- 229910052719 titanium Inorganic materials 0.000 description 10
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 8
- 239000012736 aqueous medium Substances 0.000 description 8
- 239000007864 aqueous solution Substances 0.000 description 8
- 238000001035 drying Methods 0.000 description 8
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 8
- 230000008569 process Effects 0.000 description 7
- DCKVFVYPWDKYDN-UHFFFAOYSA-L oxygen(2-);titanium(4+);sulfate Chemical compound [O-2].[Ti+4].[O-]S([O-])(=O)=O DCKVFVYPWDKYDN-UHFFFAOYSA-L 0.000 description 6
- 239000001488 sodium phosphate Substances 0.000 description 6
- 235000011152 sodium sulphate Nutrition 0.000 description 6
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 description 6
- 238000005406 washing Methods 0.000 description 6
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000011248 coating agent Substances 0.000 description 5
- 238000000576 coating method Methods 0.000 description 5
- 150000001875 compounds Chemical class 0.000 description 5
- 239000008367 deionised water Substances 0.000 description 5
- 229910021641 deionized water Inorganic materials 0.000 description 5
- 150000003018 phosphorus compounds Chemical class 0.000 description 5
- 150000003839 salts Chemical class 0.000 description 5
- 229910000348 titanium sulfate Inorganic materials 0.000 description 5
- 239000007832 Na2SO4 Substances 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
- 238000013019 agitation Methods 0.000 description 4
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 239000007858 starting material Substances 0.000 description 4
- LWIHDJKSTIGBAC-UHFFFAOYSA-K tripotassium phosphate Chemical compound [K+].[K+].[K+].[O-]P([O-])([O-])=O LWIHDJKSTIGBAC-UHFFFAOYSA-K 0.000 description 4
- 229910000406 trisodium phosphate Inorganic materials 0.000 description 4
- 235000019801 trisodium phosphate Nutrition 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 3
- 239000000020 Nitrocellulose Substances 0.000 description 3
- FJWGYAHXMCUOOM-QHOUIDNNSA-N [(2s,3r,4s,5r,6r)-2-[(2r,3r,4s,5r,6s)-4,5-dinitrooxy-2-(nitrooxymethyl)-6-[(2r,3r,4s,5r,6s)-4,5,6-trinitrooxy-2-(nitrooxymethyl)oxan-3-yl]oxyoxan-3-yl]oxy-3,5-dinitrooxy-6-(nitrooxymethyl)oxan-4-yl] nitrate Chemical compound O([C@@H]1O[C@@H]([C@H]([C@H](O[N+]([O-])=O)[C@H]1O[N+]([O-])=O)O[C@H]1[C@@H]([C@@H](O[N+]([O-])=O)[C@H](O[N+]([O-])=O)[C@@H](CO[N+]([O-])=O)O1)O[N+]([O-])=O)CO[N+](=O)[O-])[C@@H]1[C@@H](CO[N+]([O-])=O)O[C@@H](O[N+]([O-])=O)[C@H](O[N+]([O-])=O)[C@H]1O[N+]([O-])=O FJWGYAHXMCUOOM-QHOUIDNNSA-N 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 239000004922 lacquer Substances 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229920001220 nitrocellulos Polymers 0.000 description 3
- 229940079938 nitrocellulose Drugs 0.000 description 3
- OTYBMLCTZGSZBG-UHFFFAOYSA-L potassium sulfate Chemical compound [K+].[K+].[O-]S([O-])(=O)=O OTYBMLCTZGSZBG-UHFFFAOYSA-L 0.000 description 3
- 229910052939 potassium sulfate Inorganic materials 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- DLYUQMMRRRQYAE-UHFFFAOYSA-N tetraphosphorus decaoxide Chemical compound O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000010306 acid treatment Methods 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000002609 medium Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 235000021317 phosphate Nutrition 0.000 description 2
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 2
- 239000008213 purified water Substances 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 229910000162 sodium phosphate Inorganic materials 0.000 description 2
- 235000011008 sodium phosphates Nutrition 0.000 description 2
- ISIJQEHRDSCQIU-UHFFFAOYSA-N tert-butyl 2,7-diazaspiro[4.5]decane-7-carboxylate Chemical compound C1N(C(=O)OC(C)(C)C)CCCC11CNCC1 ISIJQEHRDSCQIU-UHFFFAOYSA-N 0.000 description 2
- 150000003608 titanium Chemical class 0.000 description 2
- 229910000349 titanium oxysulfate Inorganic materials 0.000 description 2
- YONPGGFAJWQGJC-UHFFFAOYSA-K titanium(iii) chloride Chemical compound Cl[Ti](Cl)Cl YONPGGFAJWQGJC-UHFFFAOYSA-K 0.000 description 2
- 229910000404 tripotassium phosphate Inorganic materials 0.000 description 2
- 235000019798 tripotassium phosphate Nutrition 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000003637 basic solution Substances 0.000 description 1
- 230000015271 coagulation Effects 0.000 description 1
- 238000005345 coagulation Methods 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 238000004033 diameter control Methods 0.000 description 1
- NJLLQSBAHIKGKF-UHFFFAOYSA-N dipotassium dioxido(oxo)titanium Chemical compound [K+].[K+].[O-][Ti]([O-])=O NJLLQSBAHIKGKF-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000007716 flux method Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 150000002484 inorganic compounds Chemical class 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical compound [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 1
- IYVLHQRADFNKAU-UHFFFAOYSA-N oxygen(2-);titanium(4+);hydrate Chemical compound O.[O-2].[O-2].[Ti+4] IYVLHQRADFNKAU-UHFFFAOYSA-N 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910001414 potassium ion Inorganic materials 0.000 description 1
- 239000011833 salt mixture Substances 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 239000008399 tap water Substances 0.000 description 1
- 235000020679 tap water Nutrition 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Images
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- C30B1/00—Single-crystal growth directly from the solid state
- C30B1/10—Single-crystal growth directly from the solid state by solid state reactions or multi-phase diffusion
-
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- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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- A61K8/02—Cosmetics or similar toiletry preparations characterised by special physical form
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B9/00—Single-crystal growth from melt solutions using molten solvents
- C30B9/04—Single-crystal growth from melt solutions using molten solvents by cooling of the solution
- C30B9/08—Single-crystal growth from melt solutions using molten solvents by cooling of the solution using other solvents
- C30B9/12—Salt solvents, e.g. flux growth
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K2800/00—Properties of cosmetic compositions or active ingredients thereof or formulation aids used therein and process related aspects
- A61K2800/40—Chemical, physico-chemical or functional or structural properties of particular ingredients
- A61K2800/41—Particular ingredients further characterized by their size
- A61K2800/412—Microsized, i.e. having sizes between 0.1 and 100 microns
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
- C08K3/20—Oxides; Hydroxides
- C08K3/22—Oxides; Hydroxides of metals
- C08K2003/2237—Oxides; Hydroxides of metals of titanium
- C08K2003/2241—Titanium dioxide
Definitions
- the present invention relates to a method for the production of single crystalline TiO 2 flakes, to single crystalline TiO 2 flakes produced by this method as well as to the use thereof, in particular as pigments.
- Titanium dioxide (TiO 2 ) is widely used in various fields such as pigments, photo catalysts, solar cells, UV absorbents and water repellants, and various methods have been developed in order to find appropriate methods for producing TiO 2 , especially in its rutile crystal form.
- Patent Document 1 discloses a method to obtain titanium dioxide particles of the rutile type which are grown in a specific crystal axis direction, wherein potassium titanate (K 2 O.nTiO 2 ) fibers obtained by a flux method are treated with an acid resulting in needle-shaped water containing TiO 2 -particles which are, in the following, heat treated in order to give rutile TiO 2 -needles of a very small particle size.
- K 2 O.nTiO 2 potassium titanate
- Patent Document 2 discloses a method to obtain flaky titanium dioxide particles by dissolving titanium alkoxide and an organic alkaline substance in an organic solvent and forming a film on a belt by coating this solution on a smooth surface, followed by hydrolysis, drying, peeling, and calcination steps.
- Patent Document 3 discloses a method for obtaining flaky titanium dioxide by acid treatment of potassium di-titanate fibers obtained by a melting method in the presence of a fluxing agent, whereby by means of the acid treatment all of the K+ ions within the crystals are eluted, followed by heat treating the resulting particles to obtain a flake type powder.
- the obtained particle shape of the titanium dioxide particles may partly not be suitable as pigment, in particular if larger flaky shaped crystals are needed, or the production method should be further improved, especially with respect to energy efficiency, production time and cost.
- the titanium dioxide particles obtained by the method described in the Patent Document 1 exhibit a whisker type shape having an extremely fine size (particle diameter of at most 6 ⁇ m). Therefore, the use of these particles as pigments is limited, especially with regard to their potential use as highly reflective interference pigments.
- titanium dioxide particles obtained by the method described in the Patent Document 2 have a flake type shape, they exhibit a polycrystalline structure and the production method is based on organic compounds and solvents which cause high cost and technological efforts and, thus, more complications.
- titanium dioxide particles obtained by the method described in Patent Document 3 exhibit a flake type shape of an appropriate size, but the requirement of two calcination steps takes time and causes high cost and energetic waste in the production procedure.
- the aim of the present invention is to reduce energy cost of the production step and to offer a method to effectively produce single crystalline TiO 2 flakes, preferably from inorganic compounds, which are suitable for use as pigments having luster, high refractive index as well as large particle size.
- a further aim of the present invention is to provide single crystalline TiO 2 flakes produced according to said process, as well as to suggest the use thereof.
- the inventors have found that the problems described above can be solved and that single crystalline TiO 2 flakes suitable for use as pigments can be effectively produced by mixing a phosphorus compound with a titanium compound in order to form a titanium dioxide precursor, and then by calcinating the obtained precursor, and completed the present invention.
- the present invention is following.
- the fluxing agent is a compound selected from one or more of Na 2 SO 4 , K 2 SO 4 , NaCl and KCl.
- titanium containing compound is a compound selected from one or more of titanium tetrachloride, titanyl sulfate, titanium sulfate and titanium trichloride.
- the phosphorous compound is a compound selected from one or more of trisodium phosphate, phosphorous pentoxide, phosphoric acid, phosphorous acid and tripotassium phosphate.
- the method for the production of single crystalline TiO 2 flakes according to a first embodiment of the present invention contains: “a step of mixing at least a titanium compound and a phosphorous compound whereby a titanium dioxide precursor is formed”; and “a step of calcining the titanium dioxide precursor at a temperature in the range from 800° C. to 1400° C. as a single calcination step”.
- the inventors have found that single crystalline TiO 2 flakes suitable for use as pigments can be effectively produced by mixing a phosphorus compound with a titanium compound in order to form a titanium dioxide precursor and then by calcination of the obtained precursor in a single calcination step.
- the single crystalline TiO 2 flakes have a high refractive index and high luster, therefore, they are particularly suitable as highly reflective pigments, especially interference pigments.
- the production method of the present invention enables an effective production of good quality single crystalline TiO 2 flakes with the need for only a single calcination step. Therefore, this method is highly suitable for the suppression of production cost and efforts. Furthermore, it can produce single crystalline TiO 2 flakes, in which twin crystals and coagulations hardly occur and in which crystallinity is high and diameter control is possible.
- the production method of the present invention contains as the first step a step of mixing at least a titanium compound and a phosphorous compound whereby a titanium dioxide precursor is formed (hereinafter, abbreviated to the “mixing step”).
- the concrete types for the titanium compound and for the phosphorus compound as well as a concrete method for mixing are not limited to any specifics as long as a titanium dioxide precursor can be formed. Since the formation of a titanium dioxide precursor will occur even if pure titanium is used, the titanium dioxide precursor is formed independently of the kind of starting materials for the titanium compound and the phosphorous compound, respectively.
- the “titanium dioxide precursor” is considered to contain titanium oxide hydrate as the mayor component.
- the production method according to the present invention contains a step of calcining the titanium dioxide precursor at a temperature in the range of from 800° C. to 1400° C. as a single calcination step (hereinafter, abbreviated to the “calcination step”).
- Anatase type TiO 2 is transformed into the rutile type by calcination of a titanium oxid precursor at a temperature of at least 800° C. Since rutile TiO 2 flakes are preferred according to the present invention, the minimum calcination temperature in the present calcination step is 800° C. Calcination of a titanium dioxide precursor at a temperature of more than 1400° C. would result in a bar type single crystal TiO 2 , rather than in the flake type. Therefore, the calcination temperature in the present production method is usually at least 800° C., and more preferably at least 900° C. Also it is usually at most 1400° C. and more preferably at most 1250° C., leading to a preferred temperature range of from 900° C. to 1250° C.
- the calcination time should be appropriately selected according to the desired shape of the single crystalline TiO 2 flakes (particle diameter, thickness, and aspect ratio). It is usually at least 5 minutes, preferably at least 10 minutes, and more preferably at least 2 hours. Further, this value is usually at most 12 hours, preferably at most 10 hours, and more preferably at most 5 hours.
- the calcination atmosphere is not limited to any specifics as long as TiO 2 can be formed. However, in order to reliably produce the oxide, the calcination step is preferably carried out under oxygen containing atmosphere.
- the concrete method for mixing of the titanium compound and phosphorus compound at the mixing step is not limited to any specifics, however, they are preferably mixed in an aqueous medium because working in aqueous solution is comfortable and easy to handle. If the mixing step according to the present invention is executed in an aqueous medium, this variation of the present process represents the second embodiment of the present invention.
- the addition of the phosphorus compound to the aqueous medium may be carried out prior to the addition of the titanium compound, at the same time as the addition of the titanium compound, or after the addition of the titanium compound.
- the phosphorus compound is added to the aqueous medium prior to the addition of the titanium compound, the yield of the TiO 2 flakes may be increased. Therefore, the latter sequence is preferred.
- the mixing is carried out within an aqueous medium, it is preferred to hold the aqueous solution at a pH value in the region of from pH 6 to 8 in order to avoid damage to the crucible by gas generated during calcining.
- a pH value in the region of from pH 6 to 8
- an acidic titanium compound such as titanium tetrachloride
- a basic phosphorus compound such as trisodium phosphate
- the pH value may be adjusted to pH 6 to 8 by separately adding an acidic solution such as hydrochloric acid or sulfuric acid or a basic solution such as sodium hydroxide aqueous solution or sodium carbonate. Furthermore, it is desirable for the addition of the titanium compound to be carried out gradually over a longer time period in order to suppress a rapid pH variation.
- the “aqueous medium” indicates a medium mainly comprising tap water or purified water and it may also be an aqueous solution comprising another component in addition or alternatively to the pure water such as deionized water.
- a fluxing agent is added to the above mentioned starting materials prior to the calcination step.
- the “fluxing agent” indicates a type of compound, in particular a metal salt, that functions as a dissolution means in a so called “fluxing growth process”, which leads to the formation of TiO 2 from the titanium dioxide precursor at the calcination step.
- the corresponding metal salts should exhibit a melting temperature which is not less than 800° C. but does not achieve or exceed the melting temperature of the resulting TiO 2 .
- they have to be water soluble.
- metal salts such as Na 2 SO 4 , K 2 SO 4 , NaCl and KCl, either alone or in combination of two or more thereof, whereby KCl may only be used in combination with at least one of the other salts mentioned. From the view point of cost and ready availability, Na 2 SO 4 and K 2 SO 4 are preferred, and Na 2 SO 4 is particularly preferred.
- the usage amount of the fluxing agent should be appropriately selected according to the desired shape of the single crystal TiO 2 flakes (particle diameter, thickness, and aspect ratio).
- the ratio of the fluxing agent mol number against the Ti atom mol number in the used titanium compound (fluxing agent mol number/Ti atom mol number in the titanium compound), it is usually at least 1.0, and more preferably at least 3.0. Further, this value is usually at most 30, and more preferably at most 10. In case of a ratio of less than 1.0, the fluxing salt treatment effect would be insufficient. On the other hand, if the ratio would exceed the value of 30, no further improvement in the flake formation would occur and a larger scale washing step to eliminate them later would be necessary.
- the addition of the fluxing agent into the mixture of the starting materials may be executed prior to the addition of the titanium compound, at the same time as the addition of the titanium compound, or after the addition of the titanium compound.
- the fluxing agent is added after the addition of the titanium compound, the yield of the TiO 2 flakes may be increased. Therefore, the latter adding sequence is particularly preferred.
- the production method according to the present invention may preferably also contain other steps, in addition to the mixing step and calcination step. This belongs to the following steps:
- titanium compound which may be used as a starting material for the present production method
- water soluble titanium compounds are preferred, in particular in case the process is executed in an aqueous medium.
- Organic titanium compounds as well as inorganic titanium compounds may be used, but inorganic titanium compounds are clearly preferred.
- Using water soluble inorganic titanium compounds makes the production process simple and easy to handle, in combination with no need for expensive apparatuses and explosion protection.
- Inorganic titanium compounds are preferably inorganic titanium salts.
- examples of titanium salts are: titanium tetrachloride, titanium oxy sulfate, titanium sulfate and titanium tri-chloride.
- titanium tetra-chloride and titanium sulfate are preferred.
- the type of the used titanium compound is not limited to one type and at least two types may be used together.
- the usage amount of the titanium compound should be appropriately selected according to the desired amount of the single crystalline TiO 2 flakes to be produced.
- the ratio of Ti atom mol number in the single crystalline TiO 2 flakes against the mol number in the used titanium compound (Ti atom mol number in the single crystalline TiO 2 flakes/Ti atom mol number in the titanium compound)
- it is usually at least 0.3, preferably at least 0.4 and more preferably at least 0.5. Further, this value is usually at most 0.9, preferably at most 0.95 and more preferably at most 1.0.
- phosphate compounds such as phosphoric acid, phosphates, condensed phosphoric acid, and condensed phosphate may be listed, and any one can be used as long as it is water soluble. Among them, from the view point of cost and ready availability, trisodium phosphate, phosphorus pentoxide, phosphoric acid, phosphorous acid, and tri-potassium phosphate are preferred. Trisodium phosphate is particularly preferred.
- the types of the used phosphorus compound is not limited to one type and at least two types may be used together.
- the usage amount of the phosphorus compound should be appropriately selected according to the desired shape of the single crystal TiO 2 flakes (particle diameter, thickness, and aspect ratio).
- the ratio of phosphorus compound mol number against the Ti atom mol number in the used titanium compound (phosphorus compound mol number/Ti atom mol number in the titanium compound), it is usually at least 0.01, preferably at least 0.1, and more preferably at least 1.0. Further, this value is usually at most 10, preferably at most 7.0, and more preferably at most 5.0.
- a further object of the present invention is single crystalline TiO 2 flakes produced by the process mentioned above.
- the single crystalline TiO 2 flakes according to the present invention usually exhibit the shapes and sizes as described below, although they are not limited thereto.
- the average particle diameter of the TiO 2 flakes is usually at least 10 ⁇ m, preferably at least 15 ⁇ m. And this value is usually at most 200 ⁇ m, preferably at most 150 ⁇ m.
- the “average particle diameter” expresses a diameter of a circle corresponding to the largest length or width of the flake, and indicates the average value obtained from the particle size distribution based on the volume.
- the thickness of the flakes is usually at least 0.1 ⁇ m, preferably at least 0.2 ⁇ m. And this value is usually at most 2.0 ⁇ m, preferably at most 1.0 ⁇ m. As long as the thickness is within this region, pearl luster of the resulting TiO 2 flakes may occur, optionally in combination with interference colour, depending on the actual thickness of the flakes.
- the aspect ratio of the flakes is usually at least 5, preferably at least 7.5. This value is usually at most 150, preferably at most 100. A high aspect ratio leads to good orientation and thus, high luster, of the resulting TiO 2 flakes in any coating layer to which they might be added.
- the crystal structure of the TiO 2 flakes according to the present invention is preferably the rutile type.
- Rutile TiO 2 is known to exhibit a high refractive index and, since the TiO 2 particles exhibit a flaky shape, also to exhibit high luster.
- the single crystalline TiO 2 flakes have a shape as shown in FIG. 2 ( a ) “V letter” type or (b) “triangle” type.
- the single crystalline TiO 2 flakes have a “V”—letter like shape and “triangle” like shape when the largest surface of the flake is observed, as shown in FIGS. 3 and 4 . Therefore, the single crystalline TiO 2 flakes may exhibit a relatively large surface and, thus, a good orientation in the application medium.
- the single crystalline TiO 2 flakes of the present invention are suitable as pigments, particularly for paints, inks, coating compositions, plastics or cosmetics. Therefore, the use of the present single crystalline TiO 2 flakes as pigments in paints, inks, coating compositions, plastics or cosmetics also one object of the present invention. Further, as the single crystalline TiO 2 flakes of the present invention have either a higher refractive index and/or better luster than traditional TiO 2 particles or flakes, they may also advantageously be used as photo catalysts, host material for dye sensitized solar cells, UV absorbents, water repellents and in all other applications where TiO 2 flakes may usually be used.
- FIG. 1 is a SEM image of the surface of single crystalline TiO 2 flakes obtained by the production method in accordance with an embodiment of the present invention.
- FIG. 2 is a schematic view showing a formation state of the single crystalline TiO 2 flakes (V letter type and triangle type) obtained by the production method in accordance with an embodiment of the present invention.
- FIG. 3 is a SEM image of the surface of single crystalline TiO 2 flakes (V letter type) obtained by the production method in accordance with an embodiment of the present invention.
- FIG. 4 is a SEM image of the surface of single crystalline TiO 2 flakes (triangle type) obtained by the production method in accordance with an embodiment of the present invention.
- FIG. 5 is a flowchart showing the production method for single crystalline TiO 2 flakes in accordance with a preferred embodiment of the present invention.
- the obtained TiO 2 flakes have an average particle diameter of 70 ⁇ m and most of them exhibit the V-like shape. From the X-ray diffraction analysis, the main surface of the flake have the (110) orientation and the crystal structure is the rutile type. Further, the analysis with electron microscope confirms that they are single crystals.
- the obtained TiO 2 flakes are added into a usual nitro-cellulose lacquer in an amount of 5% by weight, in relation to the total weight of the mixture.
- the resulting coating composition containing the obtained TiO 2 flakes is coated onto paper, resulting in a lustreous coating after drying.
- the TiO 2 flakes prepared according to Example 1 present the strongest luster among the examples.
- the obtained TiO 2 flakes are added into the nitro-cellulose lacquer in an amount of 5% by weight, based on the total weight of the mixture.
- the obtained coating composition containing the TiO 2 flakes are coated on paper and then the luster of the dried coating is observed.
- the coating shows a sufficient luster in a somewhat smaller degree than the coating according to example 1.
- Deionized water 600 g is heated to 95° C.
- 200 g of titanium tetrachloride solution 32.0% concentration
- sodium hydroxide aqueous solution 32.0% concentration
- the pH is raised to 7.
- 130 g of sodium sulfate is added and the resulting solution is stirred and then dried.
- the resulting powder is calcined at 1000° C. for two hours.
- the obtained product is washed within warm water under agitation in order to remove chloride and sodium sulfate.
- TiO 2 particles having the rutile type crystal structure are obtained.
- the obtained particles have an average particle diameter of 6 ⁇ m and a fiber-like shape with a granular surface.
- the obtained TiO 2 particles according to the comparative example are added to the nitro-cellulose lacquer in an amount of 5% by weight, based on the total weight of the coating composition.
- the obtained coating composition containing the TiO 2 particles is coated onto paper and observed. There was no specific appearance such as luster.
- the single crystal TiO 2 flakes obtained by the production method according to the present invention can be utilized as pigments for paints, inks, coating compositions, plastics and cosmetics, and as a photo catalyst, host material for dye sensitized solar cells, UV absorbent or water repellent.
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Abstract
The present invention is related to a method for the production of single crystalline TiO2 flakes in the rutile crystal structure, to single crystalline TiO2 flakes obtained by this method as well as to the use thereof, especially as pigments in several application media.
Description
- The present invention relates to a method for the production of single crystalline TiO2 flakes, to single crystalline TiO2 flakes produced by this method as well as to the use thereof, in particular as pigments.
- Titanium dioxide (TiO2) is widely used in various fields such as pigments, photo catalysts, solar cells, UV absorbents and water repellants, and various methods have been developed in order to find appropriate methods for producing TiO2, especially in its rutile crystal form.
- For example, Japanese Unexamined Patent Application Publication No. 58-88121 (Patent Document 1) discloses a method to obtain titanium dioxide particles of the rutile type which are grown in a specific crystal axis direction, wherein potassium titanate (K2O.nTiO2) fibers obtained by a flux method are treated with an acid resulting in needle-shaped water containing TiO2-particles which are, in the following, heat treated in order to give rutile TiO2-needles of a very small particle size.
- Japanese Unexamined Patent Application Publication No. 04-144918 (Patent Document 2) discloses a method to obtain flaky titanium dioxide particles by dissolving titanium alkoxide and an organic alkaline substance in an organic solvent and forming a film on a belt by coating this solution on a smooth surface, followed by hydrolysis, drying, peeling, and calcination steps.
- Japanese Unexamined Patent Application Publication No. 07-157312 (Patent Document 3) discloses a method for obtaining flaky titanium dioxide by acid treatment of potassium di-titanate fibers obtained by a melting method in the presence of a fluxing agent, whereby by means of the acid treatment all of the K+ ions within the crystals are eluted, followed by heat treating the resulting particles to obtain a flake type powder.
- However, in the techniques described in these Patent Documents, the obtained particle shape of the titanium dioxide particles may partly not be suitable as pigment, in particular if larger flaky shaped crystals are needed, or the production method should be further improved, especially with respect to energy efficiency, production time and cost.
- For example, the titanium dioxide particles obtained by the method described in the Patent Document 1 exhibit a whisker type shape having an extremely fine size (particle diameter of at most 6 μm). Therefore, the use of these particles as pigments is limited, especially with regard to their potential use as highly reflective interference pigments.
- Further, although the titanium dioxide particles obtained by the method described in the Patent Document 2 have a flake type shape, they exhibit a polycrystalline structure and the production method is based on organic compounds and solvents which cause high cost and technological efforts and, thus, more complications.
- Further, the titanium dioxide particles obtained by the method described in Patent Document 3 exhibit a flake type shape of an appropriate size, but the requirement of two calcination steps takes time and causes high cost and energetic waste in the production procedure.
- Thus, the aim of the present invention is to reduce energy cost of the production step and to offer a method to effectively produce single crystalline TiO2 flakes, preferably from inorganic compounds, which are suitable for use as pigments having luster, high refractive index as well as large particle size. A further aim of the present invention is to provide single crystalline TiO2 flakes produced according to said process, as well as to suggest the use thereof.
- The inventors have found that the problems described above can be solved and that single crystalline TiO2 flakes suitable for use as pigments can be effectively produced by mixing a phosphorus compound with a titanium compound in order to form a titanium dioxide precursor, and then by calcinating the obtained precursor, and completed the present invention.
- The present invention is following.
- (1) A method for the production of single crystalline TiO2 flakes by the following steps:
-
- 1. mixing at least a titanium compound and a phosphorous compound whereby a titanium dioxide precursor is formed; and
- 2. calcining the titanium dioxide precursor at a temperature in the range of from 800° C. to 1400° C. as a single calcination step.
- (2) The method according to (1), wherein the mixing is executed in an aqueous medium.
- (3) The method according to any one of (1) to (2), wherein a fluxing agent is present in the mixing step.
- (4) The method according to (3), wherein the fluxing agent is a compound selected from one or more of Na2SO4, K2SO4, NaCl and KCl.
- (5) The method according to any one of (2) to (4), wherein the method comprises drying of the titanium dioxide precursor prior to the calcination step.
- (6) The method according to any one of (1) to (5), wherein the calcining is executed in an oxygen containing atmosphere.
- (7) The method according to any one of (3) to (6), wherein a product obtained in the calcination step according to (3) is treated with hot water.
- (8) The method according to any one of (1) to (7), wherein the titanium containing compound is a compound selected from one or more of titanium tetrachloride, titanyl sulfate, titanium sulfate and titanium trichloride.
- (9) The method according to any one of (1) to (8), wherein the phosphorous compound is a compound selected from one or more of trisodium phosphate, phosphorous pentoxide, phosphoric acid, phosphorous acid and tripotassium phosphate.
- (10) Single crystalline TiO2 flakes obtained by the method according to any one of (1) to (9).
- (11) Single crystalline TiO2 flakes according to (10), having a rutile crystal structure.
- (12) Single crystalline TiO2 flakes according to (10) or (11), having a particle diameter in the range of 10 to 200 μm, according to an equivalent of the corresponding circle diameter.
- (13) Single crystalline TiO2 flakes according to any one of (10) to (12), having the shape of a letter “V” when viewed at the largest surface of the flakes.
- (14) Use of single crystalline TiO2 flakes according to any one of (10) to (13) in a paint, ink, coating composition, plastic or cosmetic.
- (15) Use according to (14) as white pigment, photo catalyst, host material for dye sensitized solar cells, UV absorbent or water repellent.
- According to the present invention, a method to effectively produce single crystalline TiO2 flakes which are suitable for use as pigments can be offered.
- Hereinafter, the method for the production of single crystalline TiO2 flakes according to the present invention and the single crystalline TiO2 flakes obtained by this method will be described in detail. However, the present invention is not limited to these particular embodiments as long as the intention of the present invention is followed.
- The method for the production of single crystalline TiO2 flakes according to a first embodiment of the present invention (hereinafter, abbreviated to “the production method of the present invention”) contains: “a step of mixing at least a titanium compound and a phosphorous compound whereby a titanium dioxide precursor is formed”; and “a step of calcining the titanium dioxide precursor at a temperature in the range from 800° C. to 1400° C. as a single calcination step”.
- The inventors have found that single crystalline TiO2 flakes suitable for use as pigments can be effectively produced by mixing a phosphorus compound with a titanium compound in order to form a titanium dioxide precursor and then by calcination of the obtained precursor in a single calcination step. The single crystalline TiO2 flakes have a high refractive index and high luster, therefore, they are particularly suitable as highly reflective pigments, especially interference pigments. The production method of the present invention enables an effective production of good quality single crystalline TiO2 flakes with the need for only a single calcination step. Therefore, this method is highly suitable for the suppression of production cost and efforts. Furthermore, it can produce single crystalline TiO2 flakes, in which twin crystals and coagulations hardly occur and in which crystallinity is high and diameter control is possible.
- Therefore, single crystalline TiO2 flakes in the rutile form having an extremely high refractive index can be produced.
- Although the detailed mechanisms for the formation of single crystalline TiO2 flakes according to the present invention have not been sufficiently clarified, the inventors have confirmed that TiO2 flakes have been formed with a titanium compound under the co-existence of phosphorus ions. Hereinafter, the production method of the present invention will be described in detail.
- The production method of the present invention contains as the first step a step of mixing at least a titanium compound and a phosphorous compound whereby a titanium dioxide precursor is formed (hereinafter, abbreviated to the “mixing step”).
- In the first and most simple embodiment of the present invention, the concrete types for the titanium compound and for the phosphorus compound as well as a concrete method for mixing are not limited to any specifics as long as a titanium dioxide precursor can be formed. Since the formation of a titanium dioxide precursor will occur even if pure titanium is used, the titanium dioxide precursor is formed independently of the kind of starting materials for the titanium compound and the phosphorous compound, respectively. Here, the “titanium dioxide precursor” is considered to contain titanium oxide hydrate as the mayor component.
- As a second step, the production method according to the present invention contains a step of calcining the titanium dioxide precursor at a temperature in the range of from 800° C. to 1400° C. as a single calcination step (hereinafter, abbreviated to the “calcination step”).
- Anatase type TiO2 is transformed into the rutile type by calcination of a titanium oxid precursor at a temperature of at least 800° C. Since rutile TiO2 flakes are preferred according to the present invention, the minimum calcination temperature in the present calcination step is 800° C. Calcination of a titanium dioxide precursor at a temperature of more than 1400° C. would result in a bar type single crystal TiO2, rather than in the flake type. Therefore, the calcination temperature in the present production method is usually at least 800° C., and more preferably at least 900° C. Also it is usually at most 1400° C. and more preferably at most 1250° C., leading to a preferred temperature range of from 900° C. to 1250° C.
- The calcination time should be appropriately selected according to the desired shape of the single crystalline TiO2 flakes (particle diameter, thickness, and aspect ratio). It is usually at least 5 minutes, preferably at least 10 minutes, and more preferably at least 2 hours. Further, this value is usually at most 12 hours, preferably at most 10 hours, and more preferably at most 5 hours.
- The calcination atmosphere is not limited to any specifics as long as TiO2 can be formed. However, in order to reliably produce the oxide, the calcination step is preferably carried out under oxygen containing atmosphere.
- The concrete method for mixing of the titanium compound and phosphorus compound at the mixing step is not limited to any specifics, however, they are preferably mixed in an aqueous medium because working in aqueous solution is comfortable and easy to handle. If the mixing step according to the present invention is executed in an aqueous medium, this variation of the present process represents the second embodiment of the present invention.
- The addition of the phosphorus compound to the aqueous medium may be carried out prior to the addition of the titanium compound, at the same time as the addition of the titanium compound, or after the addition of the titanium compound. However, when the phosphorus compound is added to the aqueous medium prior to the addition of the titanium compound, the yield of the TiO2 flakes may be increased. Therefore, the latter sequence is preferred.
- When the mixing is carried out within an aqueous medium, it is preferred to hold the aqueous solution at a pH value in the region of from pH 6 to 8 in order to avoid damage to the crucible by gas generated during calcining. For example, when an acidic titanium compound such as titanium tetrachloride is added to the aqueous solution containing a basic phosphorus compound such as trisodium phosphate, this solution is neutralized fully or at least to a certain degree.
- Further, the pH value may be adjusted to pH 6 to 8 by separately adding an acidic solution such as hydrochloric acid or sulfuric acid or a basic solution such as sodium hydroxide aqueous solution or sodium carbonate. Furthermore, it is desirable for the addition of the titanium compound to be carried out gradually over a longer time period in order to suppress a rapid pH variation.
- According to the present invention, the “aqueous medium” indicates a medium mainly comprising tap water or purified water and it may also be an aqueous solution comprising another component in addition or alternatively to the pure water such as deionized water.
- According to a third embodiment of the present invention, it is preferred that a fluxing agent is added to the above mentioned starting materials prior to the calcination step. Here, the “fluxing agent” indicates a type of compound, in particular a metal salt, that functions as a dissolution means in a so called “fluxing growth process”, which leads to the formation of TiO2 from the titanium dioxide precursor at the calcination step.
- For being useful as a fluxing agent in the production process according to the present invention, the corresponding metal salts should exhibit a melting temperature which is not less than 800° C. but does not achieve or exceed the melting temperature of the resulting TiO2. In addition, they have to be water soluble. Examples are metal salts such as Na2SO4, K2SO4, NaCl and KCl, either alone or in combination of two or more thereof, whereby KCl may only be used in combination with at least one of the other salts mentioned. From the view point of cost and ready availability, Na2SO4 and K2SO4 are preferred, and Na2SO4 is particularly preferred.
- Since the addition of a fluxing agent influences the crystal growth process of the resulting pigments, the usage amount of the fluxing agent should be appropriately selected according to the desired shape of the single crystal TiO2 flakes (particle diameter, thickness, and aspect ratio). The ratio of the fluxing agent mol number against the Ti atom mol number in the used titanium compound (fluxing agent mol number/Ti atom mol number in the titanium compound), it is usually at least 1.0, and more preferably at least 3.0. Further, this value is usually at most 30, and more preferably at most 10. In case of a ratio of less than 1.0, the fluxing salt treatment effect would be insufficient. On the other hand, if the ratio would exceed the value of 30, no further improvement in the flake formation would occur and a larger scale washing step to eliminate them later would be necessary.
- The addition of the fluxing agent into the mixture of the starting materials may be executed prior to the addition of the titanium compound, at the same time as the addition of the titanium compound, or after the addition of the titanium compound. However, when the fluxing agent is added after the addition of the titanium compound, the yield of the TiO2 flakes may be increased. Therefore, the latter adding sequence is particularly preferred.
- The production method according to the present invention may preferably also contain other steps, in addition to the mixing step and calcination step. This belongs to the following steps:
-
- drying step of the titanium dioxide precursor, in order to obtain a powder of the molten salt mixture prior to the calcination step (hereinafter, abbreviated to “drying step 1”); The temperature in drying step 1 is preferably in the range of from 70° C. to 180° C., although the method is not limited to this.
- in order to remove impurities such as chloride, sulfate, etc. from the product obtained in the calcination step, a step to treat the product obtained at the calcination step with warm water (hereinafter, abbreviated to “washing step”); Warm water used at the washing step is not limited to any specifics, however, purified water and deionized water are preferred. Here, the temperature of the warm water is preferably in the range of from 40° C. to 100° C. In case that a fluxing agent is used for the present production method, such a washing step is indispensable.
- in order to separate the TiO2 flakes from the solution containing dissolved impurities after the washing step, a step to filter and separate the undissolved solids (the TiO2 flakes) after the washing step (hereinafter, abbreviated to “filtration step”); and
- in order to dry the TiO2 flakes, a step to dry the TiO2 flakes (hereinafter, abbreviated to “drying step 2”). This drying step is executed preferably in a temperature range of from 20° C. to 180° C., although the present process is not limited thereto.
- Regarding the titanium compound which may be used as a starting material for the present production method, water soluble titanium compounds are preferred, in particular in case the process is executed in an aqueous medium. Organic titanium compounds as well as inorganic titanium compounds may be used, but inorganic titanium compounds are clearly preferred. Using water soluble inorganic titanium compounds makes the production process simple and easy to handle, in combination with no need for expensive apparatuses and explosion protection.
- Inorganic titanium compounds are preferably inorganic titanium salts. Examples of titanium salts are: titanium tetrachloride, titanium oxy sulfate, titanium sulfate and titanium tri-chloride. However, from the view point of the cost and ready availability, titanium tetra-chloride and titanium sulfate are preferred. Here, the type of the used titanium compound is not limited to one type and at least two types may be used together.
- The usage amount of the titanium compound should be appropriately selected according to the desired amount of the single crystalline TiO2 flakes to be produced. As the ratio of Ti atom mol number in the single crystalline TiO2 flakes against the mol number in the used titanium compound (Ti atom mol number in the single crystalline TiO2 flakes/Ti atom mol number in the titanium compound), it is usually at least 0.3, preferably at least 0.4 and more preferably at least 0.5. Further, this value is usually at most 0.9, preferably at most 0.95 and more preferably at most 1.0.
- As the phosphorus compound, phosphate compounds such as phosphoric acid, phosphates, condensed phosphoric acid, and condensed phosphate may be listed, and any one can be used as long as it is water soluble. Among them, from the view point of cost and ready availability, trisodium phosphate, phosphorus pentoxide, phosphoric acid, phosphorous acid, and tri-potassium phosphate are preferred. Trisodium phosphate is particularly preferred. Here, the types of the used phosphorus compound is not limited to one type and at least two types may be used together.
- The usage amount of the phosphorus compound should be appropriately selected according to the desired shape of the single crystal TiO2 flakes (particle diameter, thickness, and aspect ratio). As the ratio of phosphorus compound mol number against the Ti atom mol number in the used titanium compound (phosphorus compound mol number/Ti atom mol number in the titanium compound), it is usually at least 0.01, preferably at least 0.1, and more preferably at least 1.0. Further, this value is usually at most 10, preferably at most 7.0, and more preferably at most 5.0.
- According to the present production process, single crystalline TiO2 flakes of high quality may be effectively produced. Thus, a further object of the present invention is single crystalline TiO2 flakes produced by the process mentioned above.
- The single crystalline TiO2 flakes according to the present invention usually exhibit the shapes and sizes as described below, although they are not limited thereto.
- The average particle diameter of the TiO2 flakes is usually at least 10 μm, preferably at least 15 μm. And this value is usually at most 200 μm, preferably at most 150 μm.
- As soon as the average particle diameter of the TiO2 flakes is within the region mentioned above, it is possible to obtain a pigment having high luster. Here, the “average particle diameter” expresses a diameter of a circle corresponding to the largest length or width of the flake, and indicates the average value obtained from the particle size distribution based on the volume.
- The thickness of the flakes is usually at least 0.1 μm, preferably at least 0.2 μm. And this value is usually at most 2.0 μm, preferably at most 1.0 μm. As long as the thickness is within this region, pearl luster of the resulting TiO2 flakes may occur, optionally in combination with interference colour, depending on the actual thickness of the flakes.
- The aspect ratio of the flakes is usually at least 5, preferably at least 7.5. This value is usually at most 150, preferably at most 100. A high aspect ratio leads to good orientation and thus, high luster, of the resulting TiO2 flakes in any coating layer to which they might be added.
- The crystal structure of the TiO2 flakes according to the present invention is preferably the rutile type. Rutile TiO2 is known to exhibit a high refractive index and, since the TiO2 particles exhibit a flaky shape, also to exhibit high luster.
- By means of the production method according to the present invention, for example, particles as shown in
FIGS. 1 (a) and (b) are obtained. The particles are separated by a border line as shown inFIG. 1 (c) . After being physically separated from each other, the single crystalline TiO2 flakes have a shape as shown inFIG. 2 (a) “V letter” type or (b) “triangle” type. The single crystalline TiO2 flakes have a “V”—letter like shape and “triangle” like shape when the largest surface of the flake is observed, as shown inFIGS. 3 and 4 . Therefore, the single crystalline TiO2 flakes may exhibit a relatively large surface and, thus, a good orientation in the application medium. - The single crystalline TiO2 flakes of the present invention are suitable as pigments, particularly for paints, inks, coating compositions, plastics or cosmetics. Therefore, the use of the present single crystalline TiO2 flakes as pigments in paints, inks, coating compositions, plastics or cosmetics also one object of the present invention. Further, as the single crystalline TiO2 flakes of the present invention have either a higher refractive index and/or better luster than traditional TiO2 particles or flakes, they may also advantageously be used as photo catalysts, host material for dye sensitized solar cells, UV absorbents, water repellents and in all other applications where TiO2 flakes may usually be used.
-
FIG. 1 is a SEM image of the surface of single crystalline TiO2 flakes obtained by the production method in accordance with an embodiment of the present invention. -
FIG. 2 is a schematic view showing a formation state of the single crystalline TiO2 flakes (V letter type and triangle type) obtained by the production method in accordance with an embodiment of the present invention. - In this photograph and schematic view, the single crystalline TiO2 flakes of the V letter type (a), the single crystalline TiO2 flakes of the triangle type (b) and a border line between V letter and triangle (c) are shown.
-
FIG. 3 is a SEM image of the surface of single crystalline TiO2 flakes (V letter type) obtained by the production method in accordance with an embodiment of the present invention. -
FIG. 4 is a SEM image of the surface of single crystalline TiO2 flakes (triangle type) obtained by the production method in accordance with an embodiment of the present invention. -
FIG. 5 is a flowchart showing the production method for single crystalline TiO2 flakes in accordance with a preferred embodiment of the present invention. - Hereinafter, the present invention will be described in more detail by referencing examples, however, the present invention is not limited to these examples.
- Into 1600 g of deionized water, 5.6 g of sodium phosphate is added and stirred while heating to 95° C. Into this solution, 200 g of titanium tetrachloride solution (32.0% concentration) is added over the course of two hours while adjusting the pH with sodium hydroxide aqueous solution (32.0% concentration). After adding all of titanium tetrachloride solution, the pH is raised to 7. Further, 130 g of sodium sulfate is added under stirring. Afterwards, the resulting solution is dried and, then calcined at 1000° C. for two hours. After cooling, the obtained product is washed within warm water under agitation in order to remove chloride and sodium sulfate, and the TiO2 flakes are obtained.
- The obtained TiO2 flakes have an average particle diameter of 70 μm and most of them exhibit the V-like shape. From the X-ray diffraction analysis, the main surface of the flake have the (110) orientation and the crystal structure is the rutile type. Further, the analysis with electron microscope confirms that they are single crystals.
- The obtained TiO2 flakes are added into a usual nitro-cellulose lacquer in an amount of 5% by weight, in relation to the total weight of the mixture. The resulting coating composition containing the obtained TiO2 flakes is coated onto paper, resulting in a lustreous coating after drying. The TiO2 flakes prepared according to Example 1 present the strongest luster among the examples.
- Into 600 g of deionized water, 5.6 g of sodium phosphate is added and stirred while heating to 95° C. Into this solution, 200 g of titanium sulfate solution (32.0% concentration) is added over the course of two hours while adjusting the pH with sodium hydroxide aqueous solution (32.0% concentration). After adding all of titanium sulfate solution, the pH is raised to 7. Further, 130 g of sodium sulfate is added under agitation and the resulting solution is dried. Then, the obtained powder is calcined at 1000° C. for two hours. After cooling, the obtained product is washed within warm water under agitation in order to remove sulfate and sodium sulfate, and TiO2 flakes having the rutile type crystal structure are obtained. The average particle diameter is 45 μm.
- The obtained TiO2 flakes are added into the nitro-cellulose lacquer in an amount of 5% by weight, based on the total weight of the mixture. The obtained coating composition containing the TiO2 flakes are coated on paper and then the luster of the dried coating is observed. The coating shows a sufficient luster in a somewhat smaller degree than the coating according to example 1.
- Deionized water (600 g) is heated to 95° C. Into this, 200 g of titanium tetrachloride solution (32.0% concentration) is added over the course of two hours while adjusting the pH with sodium hydroxide aqueous solution (32.0% concentration). After adding all of titanium tetra-chloride solution, the pH is raised to 7. Further, 130 g of sodium sulfate is added and the resulting solution is stirred and then dried. Then, the resulting powder is calcined at 1000° C. for two hours. After cooling, the obtained product is washed within warm water under agitation in order to remove chloride and sodium sulfate. TiO2 particles having the rutile type crystal structure are obtained. The obtained particles have an average particle diameter of 6 μm and a fiber-like shape with a granular surface.
- The obtained TiO2 particles according to the comparative example are added to the nitro-cellulose lacquer in an amount of 5% by weight, based on the total weight of the coating composition. The obtained coating composition containing the TiO2 particles is coated onto paper and observed. There was no specific appearance such as luster.
- The single crystal TiO2 flakes obtained by the production method according to the present invention can be utilized as pigments for paints, inks, coating compositions, plastics and cosmetics, and as a photo catalyst, host material for dye sensitized solar cells, UV absorbent or water repellent.
Claims (9)
1.-9. (canceled)
10. A single crystalline TiO2 flake having a rutile crystal structure and having an average particle diameter in the range of 10 to 200 μm according to the largest length or width of the flake, and having the shape of a letter “V” or a triangle when viewed at the largest surface of the flake.
11. A single crystalline TiO2 flake according to claim 10 , wherein the average particle diameter of the TiO2 flake is at least at least 15 μm and at most 200 μm.
12. A single crystalline TiO2 flake according to claim 10 , having an average particle diameter of 15 to 150 μm according to an equivalent of the corresponding circle diameter.
13. A single crystalline TiO2 flake according to claim 10 , having and aspect ratio of at least 5.
14. A composition comprising a single crystalline TiO2 flake according to claim 10 which is a paint, ink, coating composition, plastic or cosmetic.
15. A composition according to claim 14 wherein the single crystalline TiO2 flake functions as white pigment, photo catalyst, host material for dye sensitized solar cells, UV absorbent or water repellent.
16. A single crystalline TiO2 flake according to claim 13 , wherein the TiO2 flake has an aspect ratio of at least 7.5.
17. A single crystalline TiO2 flake according to claim 10 , wherein the TiO2 flake has an average thickness of 0.2 μm-1.0 μm.
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US201615038313A | 2016-05-20 | 2016-05-20 | |
US16/253,520 US20190153613A1 (en) | 2013-12-20 | 2019-01-22 | Method for the production of single crystalline tio2 flakes |
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US15/038,313 Continuation US10233560B2 (en) | 2013-12-20 | 2014-11-20 | Method for the production of single crystalline TiO2 flakes |
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US20070292339A1 (en) * | 2004-03-23 | 2007-12-20 | Kanazawa R And D Ltd. | Iron Oxide Whisker of High Aspect Ratio, Titanium Oxide Whisker of High Aspect Ratio, Structure Containing These and Process for Producing Them |
US10233560B2 (en) * | 2013-12-20 | 2019-03-19 | Merck Patent Gmbh | Method for the production of single crystalline TiO2 flakes |
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US2044941A (en) * | 1931-08-07 | 1936-06-23 | Du Pont | Titanium oxide pigment of fine texture |
GB529596A (en) * | 1939-05-24 | 1940-11-25 | British Titan Products | Improvements in and relating to the production of titanium pigments |
US3579310A (en) * | 1967-06-28 | 1971-05-18 | Du Pont | Preparation of acicular rutile tio2 |
US3650693A (en) * | 1970-09-24 | 1972-03-21 | Du Pont | Preparation of fibrous titanium dioxide |
JPS56155098A (en) * | 1980-04-24 | 1981-12-01 | Matsushita Electric Ind Co Ltd | Production of titanium dioxide |
JPS5888121A (en) * | 1981-11-19 | 1983-05-26 | Matsushita Electric Ind Co Ltd | Production of titanium dioxide |
JP2837530B2 (en) * | 1990-10-02 | 1998-12-16 | 昭和電工株式会社 | Method for producing flaky titanium dioxide |
CN1029327C (en) * | 1991-05-30 | 1995-07-12 | 秩父水泥株式会社 | Rutile single crystals and their grouth processes |
JPH072598A (en) * | 1993-05-12 | 1995-01-06 | Ishihara Sangyo Kaisha Ltd | Production of acicular titanium oxide |
JP3165875B2 (en) * | 1993-12-08 | 2001-05-14 | 株式会社クボタ | Method for producing flaky titanium dioxide |
JP3242561B2 (en) * | 1995-09-14 | 2001-12-25 | メルク・ジヤパン株式会社 | Flaky aluminum oxide, pearlescent pigment and method for producing the same |
GB9525616D0 (en) * | 1995-12-15 | 1996-02-14 | Tioxide Group Services Ltd | Rutile titanium dioxide |
DE69929593T2 (en) | 1998-05-14 | 2006-11-02 | Showa Denko K.K. | TITANIUM DIOXIDE SOL, THIN FILM AND METHOD FOR THE PRODUCTION THEREOF |
EP1125636A4 (en) | 1998-08-21 | 2002-03-06 | Ecodevice Lab Co Ltd | Visible radiation type photocatalyst and production method thereof |
JP3947464B2 (en) * | 2002-12-27 | 2007-07-18 | Tdk株式会社 | Resin composition, cured resin, cured resin sheet, and laminate |
JP4840961B2 (en) * | 2004-03-23 | 2011-12-21 | 健二 久保村 | High aspect ratio iron oxide whisker, high aspect ratio titanium oxide whisker, structure containing them, and method for producing the same |
JP5138578B2 (en) | 2006-03-07 | 2013-02-06 | 石原産業株式会社 | Titanium oxide, conductive titanium oxide and methods for producing them |
JP2009029645A (en) * | 2007-07-25 | 2009-02-12 | Nippon Chem Ind Co Ltd | Flake-like hydrous titanium oxide, production method of the same and flake-like titanium oxide |
FR2936513B1 (en) * | 2008-09-30 | 2011-08-05 | Saint Gobain Ct Recherches | PROCESS FOR PRODUCING A DERIVATIVE, HYDRATE OR ZIRCONIUM OXIDE |
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- 2014-11-20 CN CN201480068935.1A patent/CN105829586A/en active Pending
- 2014-11-20 EP EP14801934.2A patent/EP3092329B1/en not_active Not-in-force
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US20070292339A1 (en) * | 2004-03-23 | 2007-12-20 | Kanazawa R And D Ltd. | Iron Oxide Whisker of High Aspect Ratio, Titanium Oxide Whisker of High Aspect Ratio, Structure Containing These and Process for Producing Them |
US10233560B2 (en) * | 2013-12-20 | 2019-03-19 | Merck Patent Gmbh | Method for the production of single crystalline TiO2 flakes |
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EP3092329A1 (en) | 2016-11-16 |
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