DE4215276A1 - Platelike pigment with high gloss - Google Patents

Abstract

Platelike pigment (I) with high gloss and high covering power or high transparency, consists of a transparent, inorganic platelike matrix (II), that may contain an additional component (III) whereby (III) is a soluble or insol. colouring agent. In order to achieve gloss (II) is coated on at leat one side with one or more thin, transparent or semi-transparent reflective metal oxide or metal layers. The prepn. of (I) is also claimed whereby the precursor of (II) is coated onto an endless band as a thin film, dried and a chemical reaction carried out to convert the solid precursor film to (II). The resulting film is sepd. from the substrate, washed and the particles opt. dried, calcined, ground and graded. The solidified film obtd. by drying is treated with an acid and the resulting film particles are coated with one or more reflective metal oxide or metal layers.

Description

The invention relates to a method for manufacturing platelet-shaped pigments with high hiding power under Using an endless band.

For certain applications, e.g. B. in cosmetics and Painting techniques are white or colored pigments with high Opacity required.

So draw yourself with one or more thin metal oxide layers coated mica pigments by interference colors, but also because of the transparent Substrate through a high transparency and thus a ver equally low hiding power. The opacity can by using colored metal oxide layers from z. B. Chromium oxide or iron oxide may be improved, however The hiding power of such pigments is often sufficient not all requirements. The opacity can continue be increased if relatively rough metal oxide layers be separated because of the increased number of litter centers the opacity increases. When using Mica as a substrate also has all the disadvantages of one naturally occurring raw material.  

In addition, mica itself has one as a substrate certain thickness, so that the training very thin, opaque Layers is not possible.

Thin glass plates are featured as a synthetic material been hit by rolling a glass melt with subsequent grinding can be obtained. Interference pigments the basis of such materials have color effects, that of conventional mica-based pigments are superior. The disadvantage, however, is that the glass plates a very large average thickness of about 10-15 microns and one very wide thickness distribution (typically between 4 and 20 µm), while the thickness of interference pigments is typically not larger than 3 µm.

EP 0,384,596 describes a method in which hydrated alkali silicate at temperatures of 480-500 ° C is subjected to an air jet, whereby bubbles with form thin wall thicknesses; the bubbles then become crushed and you get platelet-shaped alkali silicate substrates with a thickness of less than 3 µm. The procedure is complex and the thickness distribution of the obtained Tile is relatively wide.

In EP 0,240,952 and EP 0,236,952 there is a continuous Belt process for the production of various platelet-shaped Materials including titanium dioxide, aluminum oxide and Silicon dioxide has been proposed. It is about a Roll system on a smooth tape a thin liquid film  defined thickness of a platelet precursor Applied material; the film is dried and from that Ribbon detached, forming platelet-shaped particles. The particles are then optionally annealed, possibly ground and classified.

In the production of platelet-shaped SiO ₂ z. B. tetraethyl orthosilicate is used. The film is polymerized by drying and scraped off the belt using a scraper to give small platelets; these are then annealed for conversion to SiO ₂ at temperatures of 500 ° C. In addition, an SiO ₂ sol, optionally dispersed in methanol, is used as the precursor, which is applied in an analogous manner as a film, dried and annealed.

The thickness of the SiO ₂ platelets obtained by the process described in EP 0,240,952 and EP 0,236,952 is relatively well defined, since the film e.g. B. is applied very evenly to the continuous belt via a roller system. In one example, a first roll is wetted with the precursor used by partially immersing this roll in a storage container filled with the precursor. The film is transferred from this reel to a second reel rotating in the same direction, which is in very close contact with the first. Finally the film is unwound from the second roll onto the continuous belt.

However, the use of very expensive precursors is disadvantageous materials and in particular the increased requirements the job security that is involved when using organometallic connections must be made. The complete one chemical conversion of the precursor into the desired one Layer material usually makes the heating of the Film and tape material required. In addition to that considerable thermal stress on the belt materials, the high energy consumption and the Limitation of the process speed is very disadvantageous the economics of the process.

The one described in EP 0,240,952 and EP 0,236,952 The use of oxide or hydroxide sols is problematic, since the resulting films are not homogeneous, but from small ones Particles are built up. This makes treatment very high temperatures required to give the material the necessary to give homogeneity, shape accuracy and strength.

Another disadvantage of using brine in the tape procedure is the exact observance of a precisely defined Flow behavior of the precursor preparation, since it is already low deviations in the rheological behavior of the sol exact adherence to the layer thickness and the uniformity of the film can seriously affect.  

DE 11 36 042 describes a continuous belt process for Production of flake-like or flaky oxides or oxides hydrates of metals of the IV. and V. group as well as the iron Group of the periodic table described. It is on a continuous tape, if necessary, first of all a separating layer e.g. B. silicone varnish applied to the subsequent detachment of the Lighten metal oxide layer. Then a Liquid film from a solution of a hydrolyzable Connection of the metal to be converted into the desired oxide applied, the film is dried and then with replaced by a vibrator.

No. 4,879,140 describes a relatively complex process in which platelet-shaped pigments with alternating Si and SiO ₂ layers are obtained by plasma deposition of SiH ₄ and SiCl ₄ -O.

JP-A-64-9803 describes a method for the production platelet-shaped metal compounds, the dispersed fine Contain particles of metal compounds described. The products are used as light protection filters in cosmetics used. As examples, u. a. Titanium dioxide with fine Particles of silicon dioxide and silicon dioxide with disper called titanium dioxide. The procedure is thereby characterized in that one in a basic solution, the one Contains metal compound or in a sol of a metal compound fine particles of an insoluble metal compound suspended, the suspension is applied to a flat surface, the applied film dries and into a leafy form brings and the platelet-shaped metal compound, the disper contains fine particles of a metal compound, of which plan replaces area.  

This method has the disadvantage that the suspension of the Insoluble metal compound in the base solution is insufficient is. When suspending the fine particles in the base solution with ultrasound will not evenly distribute the Particle reached. Agglomerates can be seen in the light microscope bar. In addition, larger parts of the basic solution do not contain any Particle. However, this makes the covering capacity of thin layers insufficient pigment. This disadvantage can, if over at all, only balanced by an increased use of materials will.

The object of the present invention is to follow the method Develop JP-A-64-9803 so that very thin pigment platelets with an ideally smooth surface and a high Opacity can be produced.

It has been found that this object is achieved in that in the base solution with the pigment particles to be suspended Be incorporated using a bead mill.

The invention thus relates to a method for producing the provision of platelet-shaped, carrier-free pigments with high Opacity, being

• - a suspension of pigment particles and a liquid Precursor (basic solution) for a matrix material is provided,
• - an endless belt with a thin film of the suspension is occupied  
• - The tape covered with the liquid film then for formation a solid film passed through a drying section in which the film is exposed to radiation and / or mixed with reagents to form a solid film becomes,
• - The solid film separated from the tape and then against is also crushed and
• - The platelet-shaped particles are annealed and the obtained Pigment is classified to the desired particle size,

which is characterized in that in the liquid precursor the pigment particles are suspended using a bead mill will.

The invention further relates to the use of Pigments for lacquers and produced according to the invention Paints, printing inks and cosmetics and plastics.

Solutions from. Are used as precursors for the matrix material Metal compounds in the form of inorganic or salts organic acids, such as B. borates, chlorides, sulfates, Nitrates, poly- or metaphosphates or silicates are used. As metals such. B. magnesium, zinc, aluminum, silicon, Tin, titanium, zircon, iron, potassium and sodium selected will.  

A particularly preferred precursor is water glass.

The solvents to be used are of the type of Depends on metal connection. For example, are suitable Water and organic solvents, such as. B. alcohols.

The concentration of the metal compounds in the used Solution is between 0.1 and 80 wt .-%, preferably 1 to 10% by weight.

The pigment particles that are suspended in the precursor are spherical or irregularly shaped in three dimensions Particles with a maximum expansion of less than 2 µm and in particular less than 0.5 µm, with even smaller ones Particles are often preferred.

If e.g. B. commercially available pigments must be used existing agglomerates are crushed. To primary to achieve particle size is preferably a ball mill, bead mill or similar device used. The average size of the pigment particles must in any case be less than the average thickness of the matrix to the off formation of smooth, thin, gloss-generating layers enable. The term pigment particles is too broad here understand and includes white, black, colored and luminous pigments.

Stable inorganic particles are preferably used as pigment particles Pigments used with the precursor in the manufacture tion of the pigments of the invention do not react.  

Suitable inorganic pigment particles are e.g. B. white pigments such. B. titanium dioxide, barium sulfate or zinc oxide, black pigments such. B. magnetite or pigment black and colored pigments such. B. iron or chromium oxide, mixed phase oxides such. B. (Ti, Cr, Sb) O ₂ , CoAl ₂ O ₄ , (Fe, Cr) ₂ O ₃ , further sulfides such. B. CdS and other inorganic colored pigments. Inorganic luminescent pigments such as, for. B. fluoresce the silver-doped zinc oxide or phosphorescent copper-doped zinc sulfide.

In addition to inorganic pigment particles, organic Pigment particles are used, in particular tempera turstable organic pigment particles are preferred. A lot subject can the manufacturing conditions of the invention Pigments e.g. B. by reducing the drying and possibly Annealing temperature with simultaneous increase in drying or glow duration or also varied by other measures be that less stable organic pigment particles can be used. In addition, it is frequently observed that the stability of the organic pigment particles through the Incorporation into the matrix is increased.

As organic pigment particles such. B. preferably ver uses: phthalocyanines, varnishing products of basic Dyes with heteropolyacids, anthraquinones, phenazines, Phenoxazines, diketopyrrolopyrroles or perylenes.  

The pigment particles listed here are just like the procedure known for their production (see e.g. H. Kittel, Wissen society publishing company, Stuttgart 1960, G. Benzig, Pigments for paints, Expert Verlag 1988) and they are usually also commercially available. Here are these However, pigment particles are only to be understood as examples, and they are only intended to illustrate the invention without in any way a way to limit. In addition to the explicitly named Pig ment particles can be a variety of other pigment particles be used.

Ultrafine particles from organi are also preferred colored pigments such. B. phthalocyanine blue, DPP red or Aniline black. This list is only the invention explain without limiting it. Inorganic ultra fine pigments are generally preferred as they have higher annealing temperatures allow the matrix.

Under the term ultra-fine particles, small, 3-dimensional (i.e. non-platelet-shaped) particles be understood with an average diameter between 5 and 500 nm, in particular between 5 and 100 nm. This Particles can the water glass solution z. B. in powder form or also added as an aqueous or alcoholic slurry will. The choice of very small ultrafine particles is particularly important This is required if the composite has a smooth surface particle is desired and the ultrafine particles are not or protrude from the matrix only to a negligible extent should.  

In this way, platelet-shaped composite particles are obtained, consisting of a platelet-shaped, transparent SiO ₂ matrix with embedded ultrafine metal particles or inorganic or organic pigment particles. The advantage of these composite particles is that the optical properties are essentially determined by the embedded ultra-fine particles, while the mechanical properties, the dispersibility etc. are given by the much larger matrix. Ultrafine particles made of titanium dioxide, barium sulfate, aluminum oxide and carbon black are very particularly suitable.

As can be seen from Fig. 1, the desired homogeneous distribution of the pigment particles in the liquid precursor is not achieved with the method described in JP-A-64-009803 with ultrasound. Agglomerates can be seen on the light micrograph.

The particles are distributed irregularly in the precursor.

Surprisingly, however, the desired degree of distribution is achieved by using a pearl mill. Fig. 2 shows a regular distribution of the particles over the entire area.

For the light microscopic images, 1 g of TiO ₂ (Hombitan® R 506 commercial product from Sachtleben Chemie GmbH, Duisburg) was suspended in 10 ml of water with the aid of ultrasound or with the aid of a bead mill at 2500 rpm.

The suspension must remain on the film until it solidifies endless band remain stable, which z. B. through use of stabilizers, the precursor before dispersion be added is achieved. Such stabilizers are quaternary ammonium salts and polyacrylates.

The production of the pigment, which is made from a matrix material and the pigment particles distributed therein are made in a continuous process using an endless Tape, including the surface of a drum hen is. The dispersion is made using a nozzle or a Roller system applied to the belt, if necessary has already been coated with a reagent beforehand is.

Before applying the suspension, a "release layer" made of e.g. B. PVA, silicone or other materials are deposited on the endless belt. In this case, the matrix film is not removed mechanically by a detaching device, but chemically by passing the dried film through a container filled with a suitable solvent. It is also possible for the dried film to be transferred to a second belt or, for example, a roll which is in contact with the first belt ( 1 ). The second tape or the roll or a similar device is coated with an adhesive which pulls the film off the first tape ( 1 ). The film can then be detached from the 2nd tape or from the roll by applying a suitable solvent for the adhesive to the 2nd tape or roll.

As an endless band z. B. thin metal strips z. B. from Aluminum, stainless steel or the like can be used. The metal tapes are extremely flexible and stable can increase the surface quality according to conventional Procedure to be polished. Furthermore, can also be advantageous Plastic tapes from z. B. polyester or other materials be used.

The thickness of the applied film depends on several factors influenced. It depends in particular on the advance speed the quality of the tape, the angle of discharge, the quality of the waiters area of the tape and of the viscosity and / or concentrations tration of the suspension.

It is also possible to strip the film through a stripper to bring it to a defined thickness.

Spraying can also create very well-defined films with a very low layer thickness tolerance of 0.5 µm or less can be obtained. There will be a lot about that use the entire range of nozzles arranged side by side det that spray the film, creating a very even Loading of the conveyor belt is reached. Bandvor running speed and sprayed amount of precursor are to match each other in a suitable manner. It will using this method films with a very even Get layer thickness down to about 1 µm or less where the layer thickness tolerance for the very thin films is about 10% and significantly smaller for thicker films is.  

The film having a defined thickness is then transported to a drying zone consisting of one or can stand several sections b. A preferred out The design of the drying zone b consists of a predrying device in which the film with hot air of 80-150 ° C is applied, and a subsequent IR drying Facility. In addition, there are also other configurations possible in the drying zone. The total heating output of the dry zone is u. a. depending on the forward speed of the Band and is between 0.5 and 10 kW per m of bandwidth. The advance speed of the tape is between 1 and 300 m / min and in particular between 1 and 60 m / min, wob i but larger deviations from these values are also possible are. The expert can determine the heating capacity of the drying zone and the forward speed of the conveyor belt easily adapt to each other.

The dried film has a significantly smaller thickness than the original film. So one observes with Ver use a 15% water glass solution as a precursor Shrink the film to about 1/10 of the original thickness. Cracks do form as a result of drying etc., but the dried film essentially remains stick to the conveyor belt. It is crucial that the getrock nete water glass film a very uniform thickness and thickness distribution, which by the chosen concentration adjusted and adapted to the respective requirements can be.  

In the case of water glass as a precursor, the dried one Then film through an acid bath containing a mine ralic acid, transported. Particularly suitable mineral acids are hydrochloric acid, sulfuric acid, nitric acid and phosphorus acid and especially hydrochloric acid and phosphoric acid; Besides but other mineral acids are also suitable, and it mixtures of one or more acids can also be used will. The mineral acids are preferably diluted Shape applied. So z. B. the concentration of hydrochloric acid preferably between 5 and 20% and in particular between 5 and 15% chosen; but they are also lower or higher Concentrations possible.

According to the above reaction equation, the alkali ions diffuse out in the acid bath and the water glass film is converted into an SiO ₂ film. The SiO ₂ film is already partially detached from the conveyor belt, possibly even if there is no release layer.

The SiO ₂ film residues remaining on the belt are then separated off by a stripping device; this is preferably a scraping device made of metal or a thermoset which is pulled out in the form of a knife at the lower end. If a release layer is used, the stripping device can also be omitted.

However, a mechanical detachment device can also consist of a Plastic or metal cutting edges are made which are very close to the surface of the belt is brought up. Still is it is also possible to separate the solid film in that the coated tape at an acute angle over a roll is led, the flexible band, but not the solid film can follow.

The film can also be detached using a water or Air jet. Which replacement process is more appropriate chosen wisely depends on the properties of the generated Films and the work used.

When detached, the film usually breaks into smaller fragments, but usually by gentle Grinding z. B. must be further shredded under water.

The pigment detached from the belt is optionally mixed with water washed and at temperatures of 80-180 ° C for 1 to 24 hours, preferably 90 to 130 ° C, dried. Then it becomes at temperatures between 600 and 1000 ° preferably between 700 and 900 ° C, for 15 minutes to 6 hours preferably annealed for 30 to 90 minutes and on the grind and classify the desired particle size.  

Those produced by the process according to the invention platelet-shaped pigments are characterized by a drawn surface quality and a very uniform thickness out. The standard deviation plotted as thickness tolerance b is not greater than 10%. In terms of their properties, e.g. B. their opacity, they can with regard to each application can be tailored as the deck by the number of pigment particles in the matrix depends. The more pigment particles suspended in the matrix the greater the opacity.

The matrix can e.g. B. from silicon dioxide, silicates, boron tri oxide, borates, aluminum oxide, aluminates or others by visible, stable and for the absorption of pigment particles qualified materials. The platelet-shaped pig elements typically have a thickness between 0.1 and 5 µm and in particular between 0.2 and 4.5 µm. The expansion in the other two dimensions are usually between 1 and 250 µm and especially between 2 and 200 µm.

There are pigment particles in the matrix, the dimensions of which are clear are smaller than that of the matrix, i.a. randomly turned on stores. It is e.g. B. typically spherical or three-dimensional irregularly shaped particles with a maximum dimension of less than 2 µm and ins special of less than 0.5 µm, with even smaller ones Pigment particles are often preferred.  

The proportion by weight of the pigment particles incorporated, based on the weight of the matrix (SiO ₂ platelets), is typically between 0.5 and 100% and in particular between 20 and 60%. Pigments according to the invention with white or black pigments are particularly preferred, titanium dioxide or carbon black particles in particular being used here.

The color of pigments, which contain soot particles may contain, depending on the concentration of the soot particles e.g. B. from antique white to light gray, metal-colored, dark gray to range to black. Metal is particularly interesting colored and in particular aluminum colored pigments.

Those produced by the process according to the invention Pigments have a very wide range of applications.

They can be used in formulations such as paints, cosmetics or Plastics are used. The pigments can have a high aspect ratio. So you can Varnishes or plastics as a diffusion barrier, e.g. B. especially as a corrosion protection agent (diffusion barrier for Oxygen) are added.

The examples given below are intended to illustrate the invention explain without limiting it.  

example 1

47.6 g TiO ₂ (P 25, commercial product from Degussa, Frankfurt) were mixed with 750 ml water for 1 hour at 3000 rpm with the addition of 15.3 g stabilizer (Disperse Ayd w-22, commercial product from Krahn Chemie) Bead mill (Dispermat CV from VMA-Getzmann) ground. The dispersion was then mixed with 300 ml of water glass (sodium water glass; commercial product from E. MERCK, Darmstadt). The dispersion thus obtained was applied to a polyester film (Melinex® S, commercial product from ICI) in a layer thickness of approximately 2 μm. The applied film was dried, cured by treatment with HCl, detached from the belt and washed with water until free of chloride. The platelets obtained were then dried at 110 ° C. for 1 hour and then annealed at 850 ° C. for 1 hour. White, opaque platelets with a smooth surface and a layer thickness of 200 mm were obtained.

Example 2

11 g of carbon black were mixed with 62 ml of water in a bead mill (Dispermat CV from VMA-Getzmann) with the addition of 3.8 g of stabilizer lizer (Priol®, commercial product from Henkel, Düsseldorf) Ground for 1 hour at 3000 rpm. Then the Dispersion with 91 g water glass (soda water glass; commercial product from E. MERCK, Darmstadt). The so obtained Dispersion on a polyester film (Melinex® S, Handels product from ICI) applied in a layer thickness of 3 µm.  

The applied film was dried by treatment with HCl cured, removed from the belt and free of chloride with water washed. Then the obtained platelets Dried at 110 ° C for 1 hour. You got black, not translucent plates with a smooth surface and a layer thickness of 250 nm.

Claims (5)

1. Process for the production of platelet-shaped pigments with high hiding power, wherein

• a suspension of pigment particles and a liquid precursor for a matrix material is produced,
• an endless band is covered with a thin film of the suspension,
• the tape coated with the liquid film is then passed through a drying section to form a solid film, in which the film is exposed to radiation and / or reagents are added to form a solid film,
• - The solid film is separated from the tape and then optionally crushed and
• the platelet-shaped particles are annealed and the pigment obtained is classified to the desired particle size,
  characterized in that the suspension of the pigment particles and the liquid precursor is produced using a bead mill.

2. The method according to claim 1, characterized in that the suspended amount of pigment particles 0.1 to 10 wt .-%, preferably 1 to 3 wt .-%, based on the Precursor is. 3. The method according to claims 1 and 2, characterized records that as a precursor solutions of compounds of Metals magnesium, zinc, aluminum, silicon, tin, Titanium, zircon, iron, potassium and sodium in the form of Salts of inorganic or organic acids, for example as borates, chlorides, sulfates, nitrates, poly or Metaphosphates or silicates are used. 4. The method according to claim 3, characterized in that the concentration of the metal compounds in the precursor 0.1 to 50% by weight, preferably 2 to 10% by weight. 5. Use of the manufactured according to claims 1 to 4 Pigments in formulations such as paints, cosmetics or Plastics or as an anti-corrosion agent.