Method for the production of pigment granules
Dispersible pigment granules are produced by mixing an aqueous suspension of an organic pigment with an aqueous emulsion of a wax-like additive. The aqueous emulsion is then allowed to coagulate and the resulting aqueous dispersion is spray dried.
1. A process for producing a readily dispersible granular wax-coated pigment particle having a particle size distribution in the range from 0.05 to 5.0 mm, said process comprising
a) mixing an aqueous suspension of an organic pigment with an aqueous emulsion of a waxy additive to form an aqueous emulsion mixture,
b) coagulating the aqueous emulsion mixture to form an aqueous dispersion wherein the waxy additive is partially or fully disposed on the organic pigment,
c) diluting the aqueous dispersion with water and homogenizing to form a homogenized suspension, and
d) spray drying the homogenized suspension to form a dustless and free-flowing, readily dispersible wax-coated pigment granule comprising from 50 to 99 percent by weight of the organic pigment and from 1 to 50 percent weight of the waxy additive based on said pigment particle, wherein the process uses no organic solvents.
2. A process as claimed in claim 1 , wherein the organic pigment is an azo pigment selected from the group consisting of monoazo pigments, disazo pigments, Naphtol pigments, metal complex pigments, and polycyclic pigments selected from the group consisting of isoindolinone pigments, isoindoline pigments, anthanthrone pigments, thioindigo pigments, quinophthalone pigments, anthraquinone pigments, dioxazine pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, perinone pigments, diketopyrrolopyrrole pigments and azomethine pigments.
3. A process as claimed in claim 1 wherein the organic pigment is a laked azo pigment.
4. A process as claimed in claim 1 , wherein the waxy additive is a wax or a thermoplastic polymer of waxy character.
5. A process as claimed in claim 1 , wherein the waxy additive is a natural wax, a partly synthetic wax or a wholly synthetic wax.
6. A process as claimed in claim 1 , wherein the waxy additive is a polyolefin wax.
7. A process as claimed in claim 1 , wherein the aqueous suspension of the organic pigment contains the organic pigment in an amount from 3 to 20% by weight.
8. A process as claimed in claim 1 , wherein the aqueous emulsion of the waxy additive contains the waxy additive in an amount of 5 to 40% by weight and an emulsifier in an amount from 0 to 40% by weight, each percentage being based on the weight of the aqueous emulsion.
9. A process as claimed in claim 1 , wherein 50 to 98 parts by weight of the aqueous suspension of the organic pigment are mixed with 50 to 2 parts by weight of aqueous emulsion of the waxy additive.
10. A process as claimed in claim 1 , wherein the aqueous suspension of the organic pigment is mixed with the aqueous emulsion of the waxy additive at a temperature of between 20 and 95° C.
11. A process as claimed in claim 1 , wherein the coagulating step is accomplished by one or more of the steps selected from the group consisting of changing the pH, adding salts and adding a coagulation assistant.
12. A granular wax-coated pigment particle having a particle size distribution in the range from 0.05 to 5.0 mm made in accordance with the process of claim 1 .
13. An article colored with the granular pigment particle of claim 12 .
14. The process of claim 1 , wherein the homogeneous suspension comprises water and from 5 to 40 wt-% of the organic pigment and the waxy additive.