DE1952538A1 - Lead chromate pigments improvement of - light and heat - fastness - Google Patents

Abstract

The pigments are coated at 10-100 degrees C with (A) SiO2 by treatment with alkali silicate or pH 7-10, and (B) Sb3+, Zn2+ and/or Sn2+ or pH 4-7, with repetition of stage (A), or of stages (A) and (B), or of stages (A) and (B)(zinc). The treated pigments contain SiO2 5-40%, and added metal 2-16%. The products are especially suitable for PVC compositions.

Description

Process for improving the light and temperature resistance of lead chromate-containing pigments The invention relates to a process for the preparation of light- and temperature-resistant pigments containing lead chloride.

Pigrente containing lead chloride, such as chrome yellow, which is made from lead chromate or lead chromate lead sulfate mixed crystals or molybdate red, mixed crystals from lead chromate, lead sulfate, lead molybdate, have long been known and are used for Pigmentation of paints, varnishes and printing inks and plastics.

The process according to the invention uses bleach-containing as starting materials Pigments made by any of the methods known per se, e.g. by joint precipitation of the components from their solutions.

To improve the light and weather resistance of these pigments, numerous suggestions have already been made.

Of the previously proposed methods for improving the light and weather resistance are particularly noteworthy those who focus on the addition from different HilS; substances during or after the precipitation of the chromium-containing Pigments relate. Among other things, lead chromate-containing pigments are caught by being noticed of hydroxides or oxides or by treatment with reducing substances such as sodium sulfide, Sodium polysulphides, tin (II) and antimony (III) compounds treated. These Substances can be used on their own and sometimes in combination as well Light stabilizers of chromate-containing pigments described (cf. e.g.

U.S. Patent 2.) 16,244; 2139,753; British Patent No. 568.072 and DAS 1.224.858).

The use of a pigment in plastics is not only about light resistance also good compatibility of pigment and plastic at the processing temperature necessary. These requirements are met by the post-treated ones known up to now pigments containing lead chromate not to the full satisfaction.

It has now been found that the light and especially the temperature resistance of chromate-containing pigments, especially when used in thermoplastics, especially in those based on PVC can be significantly improved if the aftertreatment the pigments takes place in several stages.

In this way, chromate-containing pigments with a content are obtained from 5 to 40 percent by weight silo; 2 to 16 percent by weight antimony and / or tin and optionally zinc oxide - each based on the solid substance. The implementation of the method according to the invention is carried out by adding the substances to be precipitated either in solution or in solid form to a pigment suspension. Here is opposite the previously known methods both the increased amount and the sequence the protective layers of importance for the process.

As a first process step, a pigment slurry in one the hydrolysis promoting solvent, preferably water with an alkali silicate solution or a silica sol and deposited 5102 on the pigment. Afterward the pigment suspension with a water-soluble antimony (III) -, tin (II) - and / or Treated zinc compound.

The aftertreatment is preferably carried out with an alkali silicate solution, e.g. B. with a water glass solution carried out. When generating the SiO2 precipitation lies the pH of the suspension between 7 and 10. As antimony (III), tin (II) and zinc compounds such compounds come into question, which react acidic in aqueous solution, so preferably the corresponding metal salts of strong acids, such as. B. halides, Sulfates, nitrates or phosphates. The post-treatment with the metal compounds takes place in weakly acidic solution at pH values between 7 and 4. The pH values can go through Addition of protons or OH ions supplying substances, such as. B. dilute sulfuric acid or soda solution.

This procedure can now be repeated several times.

A surprisingly good stabilization of the pigments is already achieved the deposition of three consecutive protective layers, one SSO2-J one Sb2O3- SnO or ZnO layer and, in turn, a SiO2 layer. The alternating Precipitation of 5102 and metal compounds are of particular importance. The temperature the pigment suspension is during the aftertreatment between about 10 and 1000C, preferably between 20 and 70 0C held.

The aftertreatment can preferably be carried out in the following form by stirring are: A water glass solution with z. B.

28 ffi SiO2 and 8.3% Na2O in an amount of 2 to 15 percent by weight Silicic acid with an antimony (III) or tin (II) compound on top, z. B. SbFD, SbCl3 or SnCl2 in solid form or in solution in an amount of 1 to 8 percent by weight Sb2O3 or SnO and then at least one more time Water glass solution in an amount of 2 to 15 percent by weight SiO2, based on each case on the dry solid substance, added. If necessary, a Zinc salt solution in an amount of 1 to 8 percent by weight ZnO and another one Water glass solution was added in an amount of 2 to 15 percent by weight SiO2. in the Following the aftertreatment, the pigment is washed free of salt and washed at 11,000 dried.

The pigments aftertreated in this way are subjected to a test for thermal resistance in PVC and a test for light resistance in an alkyd resin binder system. To test the temperature resistance, 1.6 parts of pigment are mixed with 100 parts of polyvinyl chloride powder - either emulsion PVC with a K value of 70 (K value according to DIN 53 726 or ISO-R 174) or suspension PVC with a K- Value 70 (Vinnol E 100/70 or Vinnol H 100/70 from Wacker-Chemie, Munich) - as well as with 0.5 part of lubricant, a metal soap-free ester wax (Hoechst-Wachs E) and with 1.0 part of stabilizer, a dialkyltin mercaptide (17 M from Deutsche Advance Production GmbH, Marienberg near Bensheim), rolled out at 17500 on a pair of heated rollers to give a 0.2 mm thick rigid PVC skin. Samples are taken every 10 minutes up to 70 minutes of rolling time. The temperature resistance is shown in the lesser or greater discoloration of the pigmented rigid PVC films from bright yellow to brownish-green, dirty shades. A reflectance photometer (Elrepho from Zeiss, Oberkochen) is used to measure the lightness value as reflectance value with an Rg filter on the PVC films, which are arranged in 8 layers to achieve an optically infinite layer thickness. (Light reference value A according to DIN 5033, sheet 1, item 12). The percentage decrease in the lightness value of the 50, 60 or 70 minute rolled sample of a pigmentation compared to the practically not yet discolored sample that has been rolled for 10 minutes is used as a measure of the temperature resistance, e.g. the relative decrease in brightness in PVC after 50 minutes is: To determine the fastness to light and weather, the pigment is exposed to accelerated weathering in an opaque layer on a test plate in an atlas weatherometer in a fatty acid-modified, long-oil alkyd resin binder system (Alkydal F 67 from Farbenfabriken Bayer AG, Leverkusen) at a pigment volume concentration of 15%. The relative decrease in the lightness Ry of the coating in percent, measured with the mentioned reflectance photometer with Y filter, after 80 hours of weathering in the Weatherometer is used as a measure of the light resistance: The invention will be explained in more detail with the aid of the examples listed below: Example 1 359 parts of a customary chrome yellow pigment which is still filter-moist in terms of its solution (parts by weight in each case based on dry weight). were slurried in 6000 parts of water and stirred to form a uniform suspension. 54 parts of a water glass solution (28% SiO2; 8.3% Na2O) were stirred into this solution in about 5 minutes. The mixture was then stirred for a further half an hour, then 21.5 parts of anti: ron trifluoride in solid form1 were added and the mixture was stirred for a further 10 minutes. The slurry was adjusted to pH 7 with concentrated soda solution. The pigment was filtered off, washed free of salts with water and dried at 110.degree.

This pigment with good light stability, but unsatisfactory heat resistance when incorporated into PVC, subsequently served as a comparison pigment and possesses the characteristic values: a) Relative decrease in brightness after 80 weatherometer hours: 1.8 % b) Relative decrease in brightness in PVC at 175 ° C. after 50 minutes of rolling time: 30.9 %.

Example 1a 359 parts of a chrome yellow pigment were as in Example 1 in aqueous suspension with 54 parts of water glass solution (28% SiO2, 8.3% Na2O) and treated with 21.5 parts of antimony trifluoride and stirred for 10 minutes. Afterward the suspension was heated to 600C, and then within 5 minutes with 54 parts of the above water glass solution were added. With 10% soda solution was the pH adjusted to 8.0. After stirring for 30 minutes at 60 ° C was diluted with Sulfuric acid adjusted to pH 7.0. After cooling, the pigment was filtered off with suction, with Washed salt-free water and dried at 110 ° C.

Resistance to light and temperature: a) Relative decrease in brightness after 80 weatherometer hours: 0.5%.

b) Relative decrease in brightness in PVC at 175 ° C after 50 min.

Rolling time: 20.7%.

Example ib 359 parts of a chrome yellow pigment were in aqueous suspension as in Example 1 with 54 parts of water glass solution (28% SiO2, 8.3% Na2O) and with 21.5 parts of antimony trifluoride were added and stirring was continued for 10 minutes. Afterward the suspension was heated to 60.degree. C., in about 5 minutes with 54 parts of the above Water glass solution is added and immediately adjusted to pH 8.0 with 10% soda solution, then stirred for a further 30 minutes, then with 28 parts of ZnCl dissolved in 100% Parts of water are added, the mixture is stirred for a further 10 minutes and adjusted to pH 7.0 with soda solution and cooled down. The pigment was filtered off with suction, washed free of salt with water and at Dry at 110 ° C. Resistance to light and temperature: a) Relative decrease in brightness after 80 weatherometer hours: 1.2.

b) Relative decrease in brightness in PVC at 175 ° C after 50 minutes of rolling: 16.2%.

Example le 359 parts of a common chrome yellow pigment are with Slurried 6000 parts of water and heated to 600C.

79 parts of a water glass solution (28 % SiO2; 8.3?, Na 2 O) was added in about 5 minutes.

The suspension was then stirred for a further half an hour at 60 ° C, 21.5 parts of solid antimony trifluoride are added, the mixture is again stirred for 10 minutes, mixed with 79 parts of the above water glass solution, with 10 of a soda solution pH 8, adjusted, again stirred for 30 minutes, with 28 parts of zinc chloride, dissolved in 100 parts of water. again stirred for 10 minutes, with 79 parts of the above water glass solution mixed with soda solution adjusted to pH 8.0, again stirred for a further 30 minutes, and finally with dilute sulfuric acid adjusted to pH 7.0. The Pig @ ent was filtered off and washed salt-free with water and dried at 110 ° C.

Resistance to light and temperature: a) Relative decrease in brightness after 80 weatherometer hours: 1.0%.

b) Relative decrease in brightness in PVC at 1750C - after 50 minutes of rolling time: 15.0%.

Example 2 359 parts of a common chrome yellow pigment were used in 6000 Slurried parts of water and stirred to form a uniform suspension. The suspension was heated to 600C, with 54 parts of soda water glass (28% SiO2; 8.3% Na20) offset in about 5 minutes. Stirring for a further 30 minutes, dissolved with 27 parts of SnCl2 in ethanol, and at the same time mixed with so much concentrated soda solution that the pH value has not fallen below 5. The suspension was then 10 minutes stirred further, mixed with 54 parts of the above waterglass solution. Continue stirring for 30 minutes, adjusted to pH 7 with dilute sulfuric acid (and cooled). The pigment was filtered off, washed salt-free with water and dried at 110.degree.

This pigment exhibited an unsatisfactory resistance to light, with good light resistance Thermal resistance when incorporated into PVC: a) Relative decrease in brightness after 80 weatherometer hours: 2.9%.

b) Relative decrease in brightness in PVC at 17500 and 50 minutes rolling time: 75.7%.

Example 2a 359 parts of a conventional chrome yellow pigment were used in 6000 parts of water slurried and stirred into a uniform suspension. The suspension was heated to 6000, 54 parts of soda water glass were added, Stirring for a further 30 minutes, with 27 parts of SnCl2, dissolved in ethanol, and at the same time so much soda solution is added that the pH does not fall below 5. The suspension stirring was then continued for 10 minutes, 54 parts of water glass were added, 30 minutes stirred further. then 28 parts of ZnCl2 dissolved in 100 parts of water are added. Stirring was continued for 10 minutes, adjusted to pH 7 with soda solution and cooled. That The pigment was filtered off, washed free of salt with water and dried at 110.degree.

Resistance to light and temperature: a> Relative decrease in brightness after 80 weatherometer hours: 3.8%.

b) Relative decrease in brightness in PVC at 17500 and rolling time: 19.4 % Example b 359 parts of a conventional chrome yellow pigment were in 6000 parts of water slurried and stirred into a uniform suspension. The suspension was heated to 600C, mixed with 54 parts of soda water glass, stirred for a further 30 minutes, with? 7 parts of SnCl2 dissolved in ethanol, and at the same time mixed with enough soda solution, that pH 5 is not fallen below. The suspension was then stirred for a further 10 minutes, 54 parts of water glass are added, stirring is continued for 30 minutes, with 28 parts of ZnCl2, dissolved in 100 parts of water, added, stirred for 10 minutes, then finally mixed with 54 parts of water glass, stirred for a further 30 minutes, with diluted sulfuric acid adjusted to pH 7 and cooled. The pigment was filtered off, Washed salt-free with water and dried at 110 ° C.

Resistance to light and temperature: a) Relative decrease in brightness after 80 weatherometer hours: 2.6%.

b) Relative decrease in brightness in PVC at 175 ° C and 50 minutes of rolling time: 13.7%.

Example 3 330 parts (based on dry weight) of a known type Made from lead nitrate, potassium chromate, sodium sulfate and ammonium molybdate Molybdate red pigments were suspended in 6000 parts of water while still filter-moist and stirred into a uniform suspension. To this slurry were Room temperature 54 parts of sodium water glass (28 S SiO2; 8.3 ß Na20) were added and then Stirred for another 30 minutes. The suspension was then mixed with 21.5 parts of antimony trifluoride in solid form, stirred for a further 10 minutes, again with 54 parts of sodium silicate solution added, stirred for a further 30 minutes, then adjusted to pH 7 with dilute sulfuric acid and filtered. The salt-free washed pigment cake was dried at 110.degree.

Resistance to light and temperature: a) Relative decrease in brightness after 80 weatherometer hours: o, 6, c '.

b) Relative decrease in brightness in PVC at 175 ° C and 50 minutes of rolling time: o.6%.

For comparison, the light and temperature resistance became the same Molybdate red pigment without the one described Post-treatment listed: a) Relative decrease in brightness after 80 weatherometer hours: 10.1.

b) Relative decrease in brightness in PVC at 1750C and 50 minutes of rolling time: 31.6%.

Claims (7)

Patent claims: 1) Process for stabilizing pigments containing lead chromate in aqueous suspension by post-treatment at temperatures between about 10 up to 1000 C with Si02-containing solutions as well as with antimlon (III), zinc and / or tin (II) compounds, with the pigment SiO2 in amounts of 5 to 40 percent by weight and the metals in an amount of 2 to 16 percent by weight, calculated as oxide, are noticeable thereby characterized in that the aftertreatment is carried out in several stages. 2) Method according to claim 1, characterized in that as SiO2-containing Solution silica sols and / or alkali silicate solutions can be used. 3). Method according to one of Claims 1 to 2, characterized in that that the aftertreatment of the pigments with the SiO2-containing solutions at pH values between 10 and 7 and the post-treatment with the antimony (III) -, tin (II) - and / or Zinc compounds occur at pH values between 7 and 4. 4) Method according to one of claims 1 to 3, characterized in that that the aftertreatment of the pigments first with a sodium silicate solution, then with an antimony (III), tin (II) and / or zinc compound and in turn with a Sodium silicate solution is made. 5) Method according to one of claims 1 to 3, characterized in that that the aftertreatment of the pigments alternates twice with a sodium silicate solution each time and an antimony (III), zinc and / or tin (II) compound. 6) Method according to one of claims 1 to 9, characterized in that that the pigments a) with a sodium silicate solution, b) with an antimony (III) - and / or Tin (II) -containing solution, c) again with a sodium silicate solution and d) with treated with a zinc-containing solution. 7) Use of the pigments prepared according to Claims 1 to 6 for pigmenting thermoplastics, preferably those based on PVC.