Pigments are insoluble in water and are used in a dispersed state to maintain a stable crystal configuration and particle size distribution during coloring to improve coloring strength, vividness, hiding, transparency, and the like. Pigment for inkjet printing ink, need to be modified by hydrophilic, in order to get high concentrations, high mobility and stability of good, do not plug the nozzle of the water-based ink.
To this end, the major dyestuffs and ink companies to do a lot of research institutions, these work focused on how to prepare microemulsion ink, the synthesis of new dispersion of excellent pigment and pigment modification and so on. Particle size, shape, particle size distribution and unique surface area parameters not only affect the stability of the dispersion system, but also the particle size and color are also directly related. Pigment The light absorption properties of the molecules in the solid and solution are different. Molecules in the general solid Compared to the molecules in the solution absorb short wavelengths of light, the size of the primary particles determines the color of the pigment, turbidity and other properties. The color of the pigment With these properties of the particles, there is a significant difference in refractive index between the particles and the dispersion medium, Pigment and the small particle size contributes to the production of good gloss and light transmission.
In addition, when the particle size is about half (0.2 to 0.4 m) of the wavelength of light, the viscosity of the pigment dispersion has a maximum value. Lattice stacking different, resulting in the phenomenon of pigment polycrystalline, different crystal form of the same pigment, Pigment shade different. The copper phthalocyanine of the alpha crystal is blue, while the copper phthalocyanine of the β crystal is cyan (green); the quinacridine of the v crystal is red and the quinacridine of the beta crystal is purple The
Pigment synthesis of the original ecological particle size larger, can not be used directly. Intermediates are soluble in the reaction medium, water or organic solvents, the beginning of the pigment is insoluble in the nucleus of the media, and then in the pigment synthesis process to be added in order to get dispersible pigment, at the same time, in the pigment particles Dispersing, including wetting, crushing and dispersion stability of the three processes that pigment, dispersant and various additives added to a certain amount of water, adjust to the required viscosity of grinding, and then in the conventional three-roll mill or ball mill repeated grinding, Until the required fineness is reached, Pigment transferred to the mixer, and water is added to the amount of water required for the recipe.
This processing method to obtain the pigment particle size generally can only reach 2 ~ 10μm, obviously can not meet the requirements of inkjet printing ink. Advanced pigment ink requires particle size <0.4μm, if the use of sanding process, the minimum particle size of the pigment can be <0.4μm, but the pigment particle size varies, the distribution of large dispersion, the need to use and cost higher. The dispersion stability of the pigment after ultrafine pulverization is also one of the problems of water-based pigment ink production. When the pigment particles reach 50nm or less, the smaller the particles, the greater the surface energy, Pigment the particles in the water to attract each other, there is a tendency to re-aggregate into large particles, ink shape is very unstable. In the past, the surface active agent used in the grinding and dispersing process of the pigment, as a wetting agent and a dispersant, is limited by the molecular weight, and it is impossible to prepare a superfine pigment dispersion system. On the basis of the classical chemical structure of surfactants, some polymer dispersants have been developed and developed. Their molecules contain adjustable lipophilic polymer chains, and the surface of the anchors and pigments are adsorbed by multi-point and firmly bonded to the pigment Surface, can significantly reduce the desorption, in the dispersion, crushing, grinding by adding polymer dispersant can be water self-dispersing ultra-fine pigments.
Commonly used polymer dispersants are styrene-maleic anhydride (SMA), polyvinylpyrrolidone, styrene ethyl acrylate-a-methacrylic acid ethyl ester (J-68). The particle size of the pigment particles treated with J-68 was 0.3 μm. In order to improve the dispersibility of the pigment, the surface of the pigment particles can also be chemically modified. Such as the introduction of hydrophilic or water-soluble groups: the carbon black with silicone coupling agent modified, and then the introduction of a variety of hydrophobic or anionic, Pigment cationic groups; carbon black with oxidative acid treatment to the surface of the pro- Water-based functional groups or grafted on their surface polyurethane, polyacrylic acid. There are also patent reports in the carbon black dispersion process, the addition of amino naphthalenesulfonic acid and aniline coupling reaction, the product adsorption deposition on the surface of carbon black, the product obtained by centrifugal separation, remove large particles after use.