Zirconium silicate occlusion pigments with spinel occlusions, their preparation and their use.

p0001The invention relates to inclusion pigments based on zirconium silicate as enveloping substance of cobalt-free and spinels as discretely encapsulated colored compound and a process for their preparation and use.

p0002Color body spinel such as CoAl₂O₄, CuCr₂O₄, ZnFe₂O₄, because of their often brilliant colors have long been used for coloring glazes and as part of decorative paints. Although some color pigments from Spinelltypus to aggressive fluxes are largely stable with respect to their color, it comes with other spinels, particularly iron-containing spinels, when used in glazes to unwanted color changes. A disadvantage of most spinels is also the so-called bleeding effect. The interaction of the pigment with the glass flux, the pigment is more or less dissolved strong, ie, components of the pigment migrate into the glass flux surrounding it and color it if necessary. This "bleeding" prevented the sharply defined contours decors.

p0003To increase the stability of color pigments during baking ceramic decorations, some color bodies were enclosed in transparent crystals of glaze stable substances - see DE-AS 23 12 535. As a shell substance has zirconium, which includes the color-producing particles, proven. The Zirkoniumsilikatbildung and the inclusion of colored particles carried thereby in a solid state reaction at 750 - 1400^OC from a source of silica and a source of zirconia, usually directly from SiO₂ and ZrO₂, in the presence of mineralizing agents. With the method described in DE-AS 23 12 535 all conceivable colored compounds during the formation process of zirconium silicate can not be included into this in sufficient for pigment purposes amount. The coloring components or their starting compounds can in fact in many cases delay or prevent the formation of ZrSiO₄ of SiO₂ and ZrO₂, or the colored compounds are not encased and thus does not reach the desired pigment properties.

p0004In DE-AS 23 12 535 also pointed to an attempt after which obtained from SiO₂, ZrO₂ and Thenard, a spinel of formula CoAl₂O₄, a light blue inclusion pigment. It has now been found that cobalt-containing spinels of formula CoAl₂O₄, CoFe₂O₄ and CoCr₂O₄ in a conventional pigment grade either as such, by in-situ formation of spinels from CoO and Al₂O₃, Fe₂O₃ or Cr₂O₃ in the production of the inclusion, if any, so only at a very low inclusion rate, can include in a zirconium silicate. Be the use of the pigments obtained in decorative paints to each show distinct history traces and no bleeding when the decoration is baked in an oblique fire. The no bleeding attributable to the release of cobalt in the glaze.

p0005There is a special interest, the range of pigments based on zirconium silicate - cf. Chemikerzeitung 101 (1977), pp 319-323, DE-OS 37 19 051, DE-OS 39 06 818, DE-OS 39 06 819. DE-OS 39 06 821 - to expand. Of such pigments is expected that toxic heavy metals contained therein can not escape from the ZrSiO₄ crystal, and Ausblutungserscheinungen and color changes can be reduced or avoided during the glaze firing. A restriction on zirconium silicate as enveloping component would also have the advantage of being able to work in decoration process, for example screen printing, with a single paste-forming medium for all pigments. Since the range of black, gray and brown shades is still limited, it was an object of the invention to provide such pigments based on zirconium silicate inclusion pigments. In addition, the inclusion pigments in high color intensity should be accessible and be substantially free of unvaccinated or incompletely enveloped colorant compound. Another object is directed to the preparation of the pigments, which measures about separation should spare non-enveloped colorant compound itself.

p0006Found inclusion pigments based on zirconium silicate as enveloping substance and spinels as discretely enclosed colored compound, which are characterized in that the entrapped spinels are cobalt-free.

p0007The entrapped Spinels have the general formula AB₂O₄, wherein A represents a divalent and a trivalent metal ion B, or vice versa. Divalent metal ions are, in particular Ni, Zn, Mg, Mn and Fe, trivalent metal ions, in particular Al, Cr, Fe and Mn. The inclusion pigments according to the invention are black, gray and brown and have the required color stability and Ausblutungsresistenz on. Preferred pigments include aluminum-free spinels, particularly preferred pigments ferrous spinels as ZnFe₂O₄, NiFe₂O₄ and Fe (Fe, Cr) ₂O₄.

p0008The inclusion pigments based on zirconium silicate as enveloping substance and spinels as discretely enclosed compound can be prepared by mixing or a mixture of a source of zirconia such as ZrO₂, Zirkonyloxidhydrate and a source of silica, as SiO₂, SiO₂-rich zeolites, alkoxysilanes siloxanes in ZrSiO₄-forming molar ratio, raw materials of entrapped colored compound and customary mineralizers at 800 to 1300 ^OC glows within 0.5 to 8 hours and as necessary aufmahlt the annealed product. Annealing can be carried out under reducing, but preferably mostly oxidizing conditions. As raw material for the entrapped colored compound are cobalt-free oxides or precursors of the oxides, such. As hydroxides or carbonates, used in spinellbildender composition. According to a preferred embodiment, the spinel-forming oxides have an average particle diameter (D₅₀ value, as determined by laser diffraction) of less than 2 microns. The mixture to be calcined contains preferably 10 to 20 wt .-% of spinel oxides. As raw materials for ZrSiO₄ ZrO₂ and SiO₂ are preferred. ZrO₂ and SiO₂ are preferably used with an average grain diameter in the range of 1 to 10 microns. As Mineralizers particular fluorides and chlorides of alkali and / or alkaline earth metals and halides Alkalisilikofluoride are well suited. After annealing, the annealed product to be ground in the usual manner and, if desired, removed by a wet treatment of the mineralizing agents.

p0009The spinellhaltigen inclusion pigments of the invention generally D₅₀ values ​​ranging from large 2 to 20 .mu.m, in particular from 8 to 15 .mu.m. They are suitable for coloring glazes, enamels, decorative paints and the sharply defined contours of ceramic decorations which lead during firing no color change and do not bleed. The inclusion pigments according to the invention can also be in other substrates, such as plastics, paints and printing inks used.

p0010Preferred inclusion pigments are characterized by a narrow particle size spectrum, each less than 5% are less than 3 microns and greater than 20 microns.

p0011The inclusion pigments according to the invention are distinguished by their glaze and color stability under usual decoration firing conditions, their Ausblutungsresistenz and environmental friendliness.

p0012With respect to the entirely unsatisfactory production possibility of ZrSiO₄-inclusion pigments with inclusions of cobalt-containing spinels was not foreseeable that other spinels, particularly iron-containing spinels, can be safely contained in a Zirkonsilikathülle when the spinel from suitable starting materials in situ during formation of the Einschlußpigments is only formed.

p0013Surprisingly, the majority of the spinels formed in situ and is wrapped so that the known disadvantages not trapped spinels fail; a separate means for removing non-enveloped spinels is thus not required.

example 1

p0014An offset consisting of <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="char" char=",">51.4 g</entry><entry namest="col2" nameend="col2" align="left">ZrO₂</entry></row><row><entry namest="col1" nameend="col1" align="char" char=",">20.0 g</entry><entry namest="col2" nameend="col2" align="left">SiO₂</entry></row><row><entry namest="col1" nameend="col1" align="char" char=",">9.6g</entry><entry namest="col2" nameend="col2" align="left">Fe₂O₃</entry></row><row><entry namest="col1" nameend="col1" align="char" char=",">4.8g</entry><entry namest="col2" nameend="col2" align="left">ZnO</entry></row><row><entry namest="col1" nameend="col1" align="char" char=",">6.6g</entry><entry namest="col2" nameend="col2" align="left">KCl</entry></row><row><entry namest="col1" nameend="col1" align="char" char=",">4.8g</entry><entry namest="col2" nameend="col2" align="left">MgF₂</entry></row><row><entry namest="col1" nameend="col1" align="char" char=",">2.8 g</entry><entry namest="col2" nameend="col2" align="left">Na₂SiF₆</entry></row></tbody></tgroup></table></tables> is mixed for 20 minutes in a Bloch-Rosetti-ball mill. The annealing is performed at 1100^OC. for 2 hours in covered fireclay crucibles in electric chamber furnace. The annealed material is subsequently ground. In the resulting beige-brown pigment of the colorant included spinel ZnFe₂O₄ is by X-ray detectable.

p0015A decoration with the inclusion pigment prepared above was compared to non-entrapped ZnFe₂O₄ spinel with a Prüfglasur (40 wt .-% PbO, 40 wt .-% SiO₂, 7 wt .-% Al₂O₃, 6 wt .-% B₂O₃, 5 wt .-% CaO, 2 wt .-% K₂O) overglazed and tested in oblique fire. Each pigment equivalent amounts (based on the spinel) were with a conventional paste-forming medium pasted (weight ratio 8: 2), transmitted by screen printing on a ceramic substrate, glazed with Prüfglasur and then at 1050^OC burned in oblique fire.

p0016The decor with the inclusion pigment remains sharp contours and retains its natural color (L = 61, a = 16, b = 28, measured in the CIE Lab system according to DIN 66131. ​​In contrast, the decor with the spinel unwrapped runs almost completely unrecognizable; also changed the color of beige-brown yellow brown to dirty.

example 2

p0017An offset in accordance with Example 1, was replaced with the ZnO by 4.8 g NiO, provides a reddish brown inclusion pigment with X-ray diffraction proven NiFe₂O₄ spinel. The color values ​​were in the test according to Example 1 L = 20, a = 11, b = 14th

p0018The tested as a comparison non-enclosed spinel results in the release of Fe and Ni ions and a color change after gelbolivbraun.

example 3

p0019An offset according to Example 1, wherein the ZnO was replaced by 4.8 g of Cr₂O₃, provides a black inclusion pigment which is ausblutungsresistent. In the same decor Spinellkonzentration in that includes with the pigment according to Example 3 of the invention, a higher color intensity than the one with the non-enclosed spinel.