CN1095863C - Metal oxide coated titanium dioxide lamellas - Google Patents

Abstract

Colored pearl luster pigments, consisting of a core of platelet-like particles of titanium dioxide and one or more other metal oxides or metal oxide hydrates, obtainable by curing thermally degradable titanium in a continuous band An aqueous solution of the compound, separating the _resulting layers, and, without an intervening drying step, adding one or more other metal oxides or metal oxide hydrates _, such as _Fe2O3 , _Fe3O4 , FeOOH or _Cr2 O ₃ The resulting titanium dioxide flakes are coated by a wet process, separated, the resulting material is dried and, if necessary, the resulting material can be calcined.

Description

Titanium dioxide flake particles coated with metal oxides

The present invention relates to very thin pearlescent pigments based on platelet-shaped titanium dioxide coated with metal oxides or coated with metal oxide hydrates.

Pearlescent pigments based on mica are known which have an additional metal oxide layer on top of the titanium dioxide layer. U.S. Patents 3 087 828 and 3 087 829 propose aluminum oxide, zirconium oxide, zinc oxide and tin oxide as colorless oxides of the second metal oxide layer, iron oxide, nickel oxide, cobalt oxide, copper oxide and chromium oxide As an oxide with intrinsic color. The deposition of the second metal oxide on the titanium dioxide hydrate layer results in a significant stabilization of the photosensitivity of this layer. Especially titanium dioxide pigments containing iron oxide have been used successfully for many years.

US Pat. No. 30 87 828 describes that by depositing an Fe ₂ O ₃ -layer on a TiO ₂ layer, golden mica pigments can be obtained, said golden pigments exhibiting a reddish hue when calcined.

US Patent 3 874 890 describes a process for the preparation of golden pearl luster pigments in which mica pigments coated with TiO ₂ and/or ZrO ₂ are first coated with iron(II) hydroxide and then oxidized to Fe ₂ O ₃ .

U.S. Patent 4 744 832 describes pearlescent pigments based on platelet-shaped substrates coated with metal oxides, in particular mica, said metal oxide layers containing titanium and iron, said pigments having a multilayer structure, having a rutile type The first layer of _TiO2 is coated with a layer of pseudobrookite and a layer of iron oxide.

Mica pigments are widely used in the printing and coatings industry as well as in the cosmetics and polymer processing industries. They can be identified by interference color and high gloss. However, in order to form an extremely thin coating, mica pigments are not suitable because the thickness of mica itself, which is the matrix of the metal oxide layer of the pigment, is 200 to 1200 nm. A further disadvantage is that the thickness of the mica platelets in a certain size range determined by the platelet size in some cases varies considerably around the mean value. In addition, mica is a naturally occurring mineral that is mixed with exotic ions. Furthermore, it technically requires highly complex and time-consuming steps, including pulverization and classification in particular.

Due to the thickness of the edges, pearlescent pigments based on thick mica platelet particles coated with metal oxides have a pronounced scattering rate, especially in the case of finer particle size distributions below 20 μm.

As an alternative to mica, the use of thin glass flakes, which can be obtained by rolling a glass melt followed by grinding, has been proposed. Interference pigments based on such materials exhibit color effects superior to those of conventional mica-based pigments. However, the disadvantage is that said glass flakes have a very large average thickness, ie 10-15 μm, and a very broad thickness distribution (typically 4-20 μm), whereas the thickness of interference pigments is generally not greater than 3 μm.

EP 0,384,596 describes a method in which the hydrated alkali metal silicate is subjected to air jets at 480-500°C to form thin-walled bubbles; Silicate matrix. However, said process is complicated and the thickness distribution of the resulting tabular grains is broad.

DE 11 36 042 describes a continuous-band process for the preparation of flake or scintillation oxides or hydrated metal oxides of groups IV and V of the periodic table and of the iron group. In this method, in order to facilitate the subsequent separation of the metal oxide layer, a continuous web is first applied, if desired, with a release layer comprising, for example, a polysiloxane coating. Then apply a liquid film comprising a solution of a hydrolyzable metal compound that can be converted to the desired oxide, dry the film, and then apply a shock Device detached. Although no specific example of this method is cited, the layer thickness of the obtained tabular particles is 0.2-2 μm.

EP 0,240,952 and EP 0,236,952 propose a continuous belt process for the preparation of different sheet-like materials including silica, alumina and titania. In this method, a thin liquid film of a defined thickness of said sheet material precursor is applied to a smooth belt by means of a roller system; said liquid film is dried and removed from said Separation on the belt to form flaky particles. The particles are then calcined, ground and classified if desired.

The thickness of the platelets obtained according to the method described in EP 0 240 952 is better determined because the liquid film is very uniformly applied to the continuous belt by a roller system. In the examples given, the layer thickness of the tabular grains is 0.3-3.0 μm. According to Example 1, the first roller is wetted with the precursor used by partial immersion of the roller in a stock container filled with said precursor. Said film is transferred from this roller to a second co-rotating roller which is in very intimate contact with the first roller. Finally, the film is slid off the second roll onto the continuous belt.

However, a disadvantage is the use of very expensive precursor materials, especially when organometallic compounds are used, and increased requirements regarding plant safety have to be met. Complete chemical conversion of the precursors to the desired coating material generally requires intense heating of the film and tape material. In addition to the high thermal stresses this creates on the material of the strip, the high energy consumption and the limitation of the processing speed are very unfavorable for the economics of the method.

WO 93/08 237 describes flaky particle pigments consisting of a flaky matrix comprising silica, which may contain soluble or insoluble colorants, and are covered with one or more metal oxides or metal reflective layer. The tabular particle matrix is prepared by solidifying water glass on a continuous belt.

DE 1 273 098 describes the preparation of a mother-of-pearl pigment by vapor deposition of thin films of ZnS, MgF ₂ , ZnO, CaF ₂ and TiO ₂ on a continuous strip. However, this method has a very high equipment expense similar to the method described in US Patent 4,879,140, in which flake-like particle pigments with layers of Si and _SiO2 are obtained by plasma deposition from _SiH4 and _SiCl4 .

Despite various attempts, it has hitherto not been possible to develop any economical process for the preparation of very thin plate-like particle titanium dioxide pigments with a layer thickness of less than 500 nm.

The object of the present invention is to provide high-gloss, pearlescent titanium dioxide-containing pigments with a layer thickness of less than 500 nm and a layer thickness tolerance of less than 10%.

According to the invention, this object is achieved by a pearl luster pigment having a multilayer structure, that is, a layer of another metal oxide or metal oxide hydrate is coated on the platelet-shaped particle titanium dioxide core, said multilayer Structured pearlescent pigments can be obtained by solidifying an aqueous solution of a thermally hydrolyzable titanium compound on a continuous strip, separating the resulting layers, and, without drying in between, by wet processing with another The metal oxide coats the resulting titanium dioxide platelets and the resulting material is isolated, dried and, if desired, calcined.

Other metal oxides or metal oxide hydrates coated on said titanium dioxide are Fe ₂ O ₃ , Fe ₃ O ₄ , FeOOH, Cr ₂ O ₃ , CuO, Ce ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , BiVO ₄ , NiTiO ₃ , CoTiO ₃ and antimony-doped, fluorine-doped or iodine-doped tin oxide.

In a particular embodiment of said novel pigments, a third layer of a further metal oxide or metal oxide hydrate is present on top of a second layer of another metal oxide or metal oxide hydrate. Such additional metal oxides or metal oxide hydrates are alumina _or alumina hydrate, _silica or silica hydrate, _Fe2O3 , _Fe3O4 , FeOOH, _ZrO2 , _{Cr2O 3} and antimony-doped, fluorine-doped or iodine-doped tin oxide.

The aqueous solution of the thermally hydrolyzable titanium compound used for the preparation of the titanium dioxide tabular particles on the continuous belt is preferably an aqueous solution of titanium tetrachloride.

The concentration of titanium salt in these solutions is 7-30 wt%, preferably 8-15 wt%.

This object can additionally be achieved according to the invention by a process for the preparation of said novel pigments, wherein

- application of an aqueous solution of a heat-hydrolyzable titanium compound in the form of a thin film onto a continuous strip,

- said liquid film is cured by drying during which titanium dioxide is produced from said precursor by chemical reaction,

- the resulting layer is subsequently separated from said tape and washed,

- suspending the resulting platelets of titanium dioxide in water with or without intermediate drying and coating with another metal oxide and, if desired, another metal oxide,

- The coated titanium dioxide flakes are separated from said aqueous suspension, dried and, if necessary, calcined.

In addition, the coating of said titanium dioxide flake particles, after intermediate drying, can also be carried out by gas phase coating (such as CVD method) with metal oxide or metal oxide hydrate in a fluidized bed reactor, for example , can utilize the method for preparing pearl gloss pigment proposed in EP 0,045,851 and EP 0,106,235.

In addition, the invention relates to the use of the pigments according to the invention for pigment paints, printing inks, plastics, cosmetics and glazes for ceramics and glass.

For this purpose, it is possible to use mixtures of the pigments according to the invention with commercially available pigments, such as inorganic and organic light-absorbing pigments, metallic effect pigments and LCP pigments.

The new pigments in question are based on platelet-shaped particles of titanium dioxide. The thickness of these tabular particles is between 10nm and 500nm, preferably between 40nm and 150nm. The two other dimensions range between 2 and 200 μm, especially between 5 and 50 μm.

The layer of another metal oxide applied to said titanium dioxide platelets has a thickness between 5 and 300 μm, preferably between 5 and 150 μm.

The novel pigments are prepared by a three-stage process. In the first stage, titanium dioxide tabular particles are produced by means of a continuous belt.

First, the so-called continuous band method will be explained with reference to FIG. 1. FIG.

A continuous web 1 guided by a roller system 2 passes through a coater unit 3, wherein said continuous web 1 is coated with a thin film of said precursor. Suitable applicator units are either roll applicators or flow-type units. Said belt speed is 2-400m/min, preferably 5-200m/min.

In order to achieve uniform wetting of the plastic tape, it is best to add commercially available wetting agents to the coating solution, or by flame treatment, corona discharge treatment or ionization Activate said strip surface.

The coated strip then passes through a drying section 4 in which the coating is dried at a temperature between 30 and 200°C. As the dryer, for example, commercially available infrared, circulating air jet and ultraviolet dryers can be used.

After passing through the drying section, the belt passes through a separation tank 5 containing a suitable separation medium, such as deionized water, in which tank the dry layer is separated from the belt. Said separation process is assisted by additional devices, such as air jets, brushes and ultrasonic devices.

In the subsequent dryer 6, the tape is dried before it is coated again.

In order to ensure a sufficient service life and a high drying temperature, the continuous belt should be manufactured from a chemically and thermally stable plastic. Suitable materials for the tape include polyethylene terephthalate (PET) or other polyesters and polyacrylates.

The width of said film is generally between a few centimeters and two meters or more. Said thickness is between 10 μm and several millimeters, these two parameters are optimized according to specific needs.

Further details of the continuous belt method can be learned from US 3 138 475, EP 0 240 952 and WO 93/08 237.

In a second operating stage, the previously undried titanium dioxide platelets separated from the belt are coated with another metal oxide according to a known method.

When coating with hematite ( _{Fe2O3 )} , the starting material can be, for example, iron(III) salts as described in US 3 087 828 and US 3 087 829, but also in US 3 874 890 Iron(II) salts, the initially formed iron(II) hydroxide coating can be oxidized to iron(III) oxide hydrate. Iron salts (III) are preferably used as starting material. For this purpose, a solution of iron(III) chloride is dosed to a water-based suspension of titanium dioxide tabular particles at a temperature of 60-90° C. and a pH value of 2.5-4.5. The pH is kept constant by simultaneous addition of 32% sodium hydroxide solution. After completion, and after drying at 110°C, a red pigment was obtained.

Magnetite (Fe ₃ O ₄ ) coating is performed by hydrolysis of a solution of an iron(II) salt, such as iron(II) sulfate, at a pH of 8.0 in the presence of potassium nitrate. A specific example of precipitation is described in EP 0,659,843. After completion, and after drying at 100°C, a black pigment was obtained.

It is also preferred to coat the titanium dioxide platelets with the yellow FeO(OH) used in the goethite modification. In this case, an aqueous solution of FeSO ₄ was dosed at 70°C under a nitrogen atmosphere to the suspension of titanium dioxide tabular particles. The pH was then adjusted to 4 with 10% _Na2CO3 solution and oxygen was bubbled through the suspension _. After completion, and after drying at 110°C, a yellow pigment was obtained. For precise precipitation conditions reference is made to EP 0,659,843.

In order to better bond the iron oxide layer with the titanium dioxide flakes, it is preferred to first apply a tin oxide coating. In this way, the _SnCl4 solution treated with hydrochloric acid was quantitatively added to the suspension of titanium dioxide platelet particles to adjust the pH value to 1.8, while adding 32% sodium hydroxide solution to keep the pH value constant. Iron oxide hydrate can be applied immediately after the tin dioxide hydrate layer has settled.

Another metal oxide that is preferably deposited on the titanium dioxide platelets is chromium oxide.

Said precipitation can be easily carried out by thermal hydrolysis which occurs when ammonia gas is volatilized from the aqueous solution of hexaammine chromium(III) derivative or by thermal hydrolysis of chromium salt solution buffered with borax. Methods for applying chromium oxide are described in US 3 087 828 and 3 087 829.

The novel pigments mentioned do not necessarily have to be calcined in every case. For some applications, drying at 110°C to 150°C, preferably 110°C, is sufficient. If the pigment is calcined, the temperature is determined to be between 400°C and 1000°C, with a preferred range between 400°C and 700°C.

In addition, the novel pigments can be coated with tightly bound low solubility inorganic or organic colorants. Preference is given to using color precipitation pigments, in particular aluminum precipitation pigments. For this purpose, an aluminum hydroxide coating is applied by precipitation and colored with color-precipitated pigments in a second step. This procedure is described in more detail in DE 24 29 762 and DE 29 28 287.

As described in EP 0 141 173 and DE 23 13 332, also preferred are other pigments coated with complex salts, especially ferricyanide complexes, such as Prussian blue and Turnbull blue.

According to DE 40 09 567, said new pigments can also be coated with organic dyes, especially with phthalocyanine or metallophthalocyanine and/or indanthrene dyes. For this purpose, a suspension of the pigment in a dye solution is prepared and this suspension is then mixed with a solvent in which the dye has little or no solubility.

For a further coating, it is also possible to use metal chalcogenides or metal chalcogenide hydrates and carbon black.

In addition, the pigments can be post-coated or post-treated to further increase the light stability, weather resistance and chemical stability or to facilitate the processing of the pigments, especially their incorporation into different media . Suitable post-coating techniques are those described in DE-C 22 15 191 , DE-A 31 51 354 , DE-A 32 35 017 or DE-A 33 34 598 . Since the properties of the new pigments in question are already very good without these additional measures, these optional additional coating substances represent only about 0-5% by weight of the total pigment, in particular about 0-3% by weight.

In terms of thickness, said new pigments represent the best that can be obtained with pearlescent pigments, since they consist only of optically functional layers, without other conventional carrier materials, such as mica or glass shards. Due to the thickness of the mica, the mica pigment is up to 25 times thicker for a given thickness of the functional layer. In terms of technical use, this yields intrinsic advantages that cannot be obtained with other conventional pearl luster pigments. For example, the coating layer can be made thinner and the amount of pigment required can be reduced since said pigment is more optically active in the absence of said carrier material "filler".

The examples given below illustrate but do not limit the invention.

Example 1

A 20% solution of titanium tetrachloride was applied by passing an endless belt of polyethylene terephthalate (0.3 m wide, speed 20 m/min) through a counter-rotating applicator roller. The coating solution contained 0.3% by weight of a surfactant (DISPERSE-AYD W-28, manufacturer: DANIEL PRODUCTS COMPANY). In the drying section the water film on the belt was dried by passing it through hot air at 70°C, and the formed layer was separated from the belt in a separation tank filled with deionized water. The flaky titanium dioxide particles were filtered and washed with deionized water. Said flake particles have silvery luster and a layer thickness of 100±10nm. For coating another metal oxide, they can be redispersed in deionized water. 2 liters of said suspension (solids content: 15 g of TiO ₂ ) were heated to 75° C. and adjusted to pH 1.8 with dilute hydrochloric acid.

4.3 g of SnCl ₄ ·5H ₂ O were dissolved in 29 ml of HCl, the solution was diluted to 290 ml with deionized water and stirred for 10 minutes.

The _SnCl4 solution was added to the _TiO2 suspension at a rate of 3 ml/min, during which time the pH was kept constant at 1.8 with 32% NaOH solution. The suspension was stirred for 15 minutes at constant temperature and pH after coating with _SnO2 .

Then adjust the pH value to 3.0 with 32% NaOH solution, add a kind of 8% iron (III) chloride aqueous solution quantitatively with the speed of 3ml/min, add said NaOH solution simultaneously and keep pH constant. The _FeCl3 is added continuously until the desired interference color is obtained. The resulting pigment was filtered off, washed with deionized water and dried at 110°C for 12 hours. Said pigment has the desired interference color and has a red overall color.

Claims (10)

1, colored pearl colour lustre pigments, nuclear by a kind of platy shaped particle titanium dioxide is formed with one or more layers other metal oxide or metal oxide hydrate, can obtain by following process: but one continuously with on solidify the aqueous solution of the titanium compound of thermal hydrolysis, separating obtained layer, during do not have to be selected from Fe with one or more under the situation of drying step ₂O ₃, Fe ₃O ₄, FeOOH, Cr ₂O ₃, CuO, Ce ₂O ₃, Al ₂O ₃, SiO ₂, BiVO ₄, NiTiO ₃, CoTiO ₃, the metal oxide of stannic oxide of antimony dopant, fluorine or iodine or the metal oxide hydrate titanium dioxide lamellas by wet method coating gained, if desired, be selected from aluminum oxide or hydrated alumina, silicon-dioxide or Silicon dioxide, hydrate, Fe with one or more ₂O ₃, Fe ₃O ₄, FeOOH, ZrO ₂, Cr ₂O ₃And the metal oxide of the stannic oxide of antimony dopant, fluorine or iodine or metal oxide hydrate apply by wet method the titanium dioxide lamellas of above-mentioned coated layer of metal oxide compound or metal oxide hydrate again, and separate, the material of dry gained, if necessary, can calcine the material of gained.

2,, be characterised in that said other metal oxide or metal oxide hydrate are Fe according to the pearlescent pigment of claim 1 ₂O ₃, Fe ₃O ₄, FeOOH or Cr ₂O ₃

3, according to the preparation method of the pearlescent pigment of claim 1～2, characteristics are:

-but a kind of aqueous solution of titanium compound of thermal hydrolysis is coated to one with the form of film be with continuously, form a liquid film thus,

-by the said liquid film of dry solidification, in this process, from solution, produce titanium dioxide by chemical reaction,

-subsequently the layer of gained is separated and washing from said being with,

-during do not have under the situation of drying step, be suspended in the titanium dioxide lamellas of gained in the water and apply one or more metal oxides,

-coated titanium dioxide lamellas to be separated from said aqeous suspension, drying if necessary, is calcined.

4, according to the method for claim 3, characteristics are that the said titanium compound aqueous solution that can thermal hydrolysis is titanium tetrachloride aqueous solution.

5, according to the method for claim 3 and 4, characteristics are that other used metal oxide or metal oxide hydrate are Fe ₂O ₃, Fe ₃O ₄, FeOOH and Cr ₂O ₃

6, according to any method of claim 3～5, characteristics are that said pigment is at 110～150 ℃ temperature drying.

7, according to any method of claim 3～6, characteristics are that said pigment is 400～700 ℃ temperature calcining.

8, according to any method of claim 3～7, characteristics be a fluidized-bed by the CVD method with described one or more metal oxide coated to said titanium dioxide lamellas.

9, the purposes that is used for the glaze of pigment coating, printing-ink, plastics, makeup and pottery and glass according to the pigment of claim 1 or 2.

10, according to the purposes of claim 9, characteristics are that said pigment is to use with the form of the mixture of commercial available pigment.

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