Self-Dispersing Pigments

A self-dispersing pigment can be prepared by physical or chemical treatment hy grafting a hydrophilic group onto the surfaces of the pigment particles (22). 

For the physical treatment, a vacuum plasma treatment may be performed. For the chemical treatment, a wet oxidation may be performed to oxidize the surfaces of the pigment particles with an oxidizing agent. 

Further, an aminobenzoic acid derivative may be bound to the surfaces of the pigment particles so as to bind the carboxyl group onto the surfaces with a phenyl group in between. For example, sulfanilic acid, p-aminobenzoic acid, or 4-aminosalicylic acid may be bound to the surface of the pigment (22). 

On the other hand, if the ink composition is used as a black ink, from the viewpoint of high color developability, it is preferable that the self-dispersing pigment is surface-treated by the oxidation with a h5/pohalous acid or its salt, ozone, or persulfuric acid or a persulfate. 

In order to disperse the pigment in water, a polymer may be used (22). A copol mer of benzyl acrylate, cyclohexyl acrylate or their mixture and acrylic acid is suitable. As an alternative to the acrylic acid, cD-carboxy-polycaprolactone monoacrylate, phthalic acid hy dr oxyethyl acrylate, or a dimeric acrylate may be used. Other monomers are summarized in Table 4.5. 

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W.L. Anton and A.W. Kluth, Self-dispersing pigment dispersions and ink jet inks containing them, US Patent 8 562124, assigned to E. 1. Du Pont de Nemours and Company (Wilmington, DE), October 22,2013. 

Pigments are stabilized by dispersing agents such as pol5mieric dispersants or surfactants. Also, so-caUed self-dispersible or self-dispersing pigments have been developed. As the name imphes, these types are dispersible in water, or aqueous vehicle, without dispersants. 

N. Shimomura, A. Shinohara, E. Watanabe, and Y. Kurabayashi, Selfdispersion pigment, production process of self-dispersion pigment, ink set and inkjet recording method, US Patent 8 282725, assigned to Canon Kabushiki Kaisha (Tokyo, JP), October 9,2012. 

Takada, Y. Hakamada, S. Tsujimura, M. Akasaka, A. Nito, Y Mishina, S. Ink compositions containing self-dispersible pigments and acrylic polymers, ink sets therefrom, and method and apparatus for ink jet printing therewith. Jpn. Kokai Tokkyo Koho IP 2006160930, 2006 Chem. Abstr. 2006,145, 64649. 

In special applications, it is desirable to increase the hydrophilic properties of fillers and pigments for easy dispersion in water. With polyetherfiinctional silanes, it is possible to obtain, for example, self-dispersing iron oxide pigments [38]. Furthermore, the polyether silanes display a very significant reduction in the viscosity of unsaturated polyester systems [47] when high filler loadings are required. 

A black pigment may be stabilized to be self-dispersing by a treatment with dispersant in the traditional way, or by some combination of surface treatment and dispersant. 

Yellow chromophtal GTAD (Ciba) is an anthraquinone-based material and is self-dispersing in resins and polyolefin fibres. Unlike classic pigments, it recrystallizes on return to ambient temperature and so offers a high thermal stability (up to 28()°C). The pigment is also transparent and non-warping. 

During roller-blending to disperse iron red pigment (iron(III) oxide) into plasticised cellulose nitrate, the mixture became a gel after 15 passes and tended to self-ignite. 

Today, there are a number of manufacturers who offer color-matched, predispersed, pigment sugar-coating concentrates. These concentrates are easily incorporated into the bulk of the syrup-coating solution. The convenience of these concentrates and the ability of the manufacturers to reproduce color batch after batch make these products an attractive alternative to self-preparation of dispersions. 

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