DE2135435C3 - Process for the production of molybdate orange and molybdate red pigments resistant to sulfur dioxide - Google Patents

Description

Molybdate orange and molybdate red have long been in use as inorganic pigments as they are characterized by brilliant colors, good coverage and a relatively low price. Disadvantageous for but a wider use of these pigments is their low light and weather resistance as well poor resistance to air pollutants, especially sulfur oxide. One Significant improvements in the resistance to light and weather have recently been achieved as a result can be achieved that one varied the manufacturing process and stabilizing additives such. B. aluminum, Titanium, antimony, silicon hydroxides or oxide hydrates, alone or in combination with one another or together with other compounds, such as ß. Rare earth salts, on the pigments notices. Regarding the resistance to the increasing pollution of the atmosphere with Sulfur dioxide, which causes an undesirable change in color in these pigments, was able to counter this only gradual improvements can be achieved.

The invention relates to a process for the production of molybdator orange and red pigments resistant to sulfur dioxide by precipitation of antimony (III) hydroxide or oxide hydrate and silicon oxide hydrate in the presence of fluorine ions in aqueous suspension, the pigments thus treated from the The suspension is filtered off, washed and dried, which is characterized in that on d ^; s Pigments are noticeable in the suspension after the precipitation of antimony (III) hydroxide or oxide hydrate and silicon oxide hydrate with the addition of an aqueous solution of a calcium compound to the calcium fluoride suspension.

It is already known from German Auslegeschrift 12 53 384, molybdate red or molybdate orange pigments to stabilize against sulfur dioxide by treating these pigments after their precipitation with antimony III ions, Fluorine ions and silicate ions are added, followed by a pH of 8 to 8.5 with alkalis adjusts. Surprisingly, however, the additional component according to the invention makes calcium fluoride a significant improvement in the resistance to sulfur dioxide is achieved.

The precipitation of these compounds can take place immediately after the precipitation reaction of the pigment, however, it is expedient to first wash the pigment suspension free of electrolytes. To the Aqueous solutions of water-soluble antimony, Silicon, calcium and optionally fluorine compounds. After each addition of the antimony and Silicon compounds, the pH of the suspension is to be adjusted in each case so that the elements mentioned precipitate in the form of their hydroxides. The pH of the suspension after precipitation of all of the compounds mentioned is most advantageously between 6 and 8. For the implementation of the invention All water-soluble compounds that contain the elements antimony, silicon, Provide calcium and fluorine, such as sodium fluoride, antimony chloride, antimony fluoride, sodium silicate, Sodium tetrafluorosilicate and calcium chloride. The use of antimony trifluoride is advantageous together with sodium silicate and calcium

»5 chloride.

The amounts of the precipitated compounds can vary within wide limits. They are preferably 1 to 5 percent by weight antimony hydroxide, calculated as Sb2G * 3, 1 to 5 percent by weight silicon hydroxide, calculated as S1O2 and 1 to 6 weight percent calcium fluoride calculated on the basis CaO. Of course, smaller or larger amounts of these compounds can also be applied to the Pigments are noticeable, although there may be changes in the color strength and opacity can result.

example

A suspension containing 90 g of molybdate red in 3 liters of water is added over the course of 15 minutes Solution of 15 g of sodium silicate solution (27.2% S1O2) in 150 ml of water. Then you give a nitric acid Solution of 5 g of antimony fluoride in 200 ml of water within 1 h, whereby the pH by adding a dilute sodium hydroxide solution to 5.5 nail. The suspension is subsequently stirred for 1 hour then gives a solution of 7 g calcium chloride (CaCb - 2H2O) in 100 ml water within 15 min to. The pH is then adjusted to 8 with sodium hydroxide solution and the mixture is subsequently stirred for 1 h. The so The treated pigment suspension is filtered off, washed and dried at 95.degree. C. in the customary manner.

After grinding and grinding, e.g. B. in a melamine resin varnish, you get a stoving varnish that even after more than three cycles in the Kesternich test device according to DIN 50018 SFW 2.0 only very little Shows changes in hue or gloss. A molybdate red pigment with equally good properties is obtained if, in the above example, the pigment is used in small amounts after the precipitation a sulfated castor oil treated as a crystallization inhibitor and the pigment suspension before Stabilize by decanting, washes electrolyte-free.

Claims (1)

Claim: Process for the production of molybdate orange and red pigments resistant to sulfur dioxide by precipitation of antimony (III) hydroxide or oxide hydrate and silicon oxide hydrate in the presence of fluorine ions in aqueous suspension, the pigments thus treated filtered off from the suspension, washed and dried, characterized in that that on the pigments in the suspension after the precipitation of antimony (III) hydroxide or oxide hydrate and silicon oxide hydrate with the addition of an aqueous solution of a calcium compound calcium fluoride is noticeable in the suspension.