Surface Modifications

16 октября, 2015

Pokraskin

Since pigment properties are dependent not only on the chemistry and solid-state properties of the pigment, but also to a large extent on the application in which the pigment is being used and how it is applied in a defined application, the interaction between a pigment and a specific application media is of the utmost importance. This interaction depends to a large part on the surface characteristics of the pigment. In order to achieve the desired properties of a pigment in a given application, the surface characteristics of the pigment must first be optimized.

1) In many cases no true solid solutions are being formed and designations like combinations or hybrid pigments are used.

The surfaces of DPP pigments have been modified to optimize their properties for both coatings and plastics applications. Many patents and some publications have appeared in the literature on this subject.[9]

In general, different types of surface modifications of DPP have been investigated and can be summarized as shown in Table 11.3.

Surface Modification References

Organic	Pigment derivative	DPP derivatives QA derivatives Perylene derivatives	[62-80] [81-85] [86, 87]
	Misc. Derivative		[88-90]
	Polymer		[91-94]
Inorganic	Metal oxide		[95]
	Metal oxide modified		[96, 97]
Grafting			[98-108]

The purpose of modifying the surface of pigments for paint applications is to improve the rheological properties of the paint millbase and thereby improve the aesthetic value (gloss) of the resulting coating [109], reduce the VOC (volatile organic compounds), and improve the economics of the paint formulations through an increase of the pigment concentration. Several DPPs with improved rheology and gloss have been introduced to the market involving C. I. Pigment Red 254, C. I. Pigment Red 264, and C. I. Pigment Orange 73.

Specific surface treatments of pigments for plastics applications can be done to improve properties like dispersibility, warping, and crystallization behavior. The warping (distortion) of polyethylene is strongly related to the crystallization of the polymer [110]. Through specific surface treatments, a reduction of the distorting properties of polyethylene can be achieved. DPPs have been surface treated to reduce the distortion [111, 112], and commercial products based on C. I. Pigment Red 254 are now present on the market.

11.6