Pigment plasticizer pastes

Recrystallization too is attributable to the pigment having a specific solubility in the plastic. As in other media, it is demonstrated primarily in a change of transparency or opacity in transparent colorations and in the depth of shade in white reductions. Lack of recrystallization stability becomes evident for example in the manufacture and processing of pigment-plasticizer pastes and in various polymers at elevated processing temperatures. 

In many cases pigment-plasticizer pastes are also used for coloring PVC. Because of the mixing or embrittlement gap in the PVC-plasticizer system, which ranges from 5 to 18% for dioctyl phthalate for example, such pastes have little or no suitability for unplasticized PVC compounds. In this concentration range, which is specific for each plasticizer, no plasticizing effect is achieved, on the contrary the additive causes embrittlement of the PVC. 

Wetting out a pigment for several days by simply storing the manually prepared pigmented PVC paste (DOP content 39%) makes for almost optimum dispersion, which requires very little shear (see Fig. 88, p. 162). The wetting of the surface of the pigment particles by the plasticizer molecules thus determines the outcome of the dispersion process. 

PVC spread-coating pastes are normally manufactured in high-speed planetary mixers that can be evacuated. It is best to add the plasticizer first, stir in the pigments or pigment pastes and only then to add the solid components in portions. In pigmenting plasticized PVC compounds, on the other hand, it is necessary to mix... 

Unsaturated polyester and methacrylate resins are frequently colored with pigment-plasticizer (DIDP) pastes. They have no measurable adverse effect on the important mechanical properties of the finished article. To a small extent pigments are also dispersed directly in one part of the monomer. 

The carbon black plastic concentrates are often not prepared by the plastics processor. They may be purchased, from the pigment-black manufacturer in the form of chips, pellets, or powders. Black-plasticizer pastes (e.g., black/DOP pastes for tinting plastisols) and water- and solvent-based dispersions (e.g., for fiber manufacture) are also commercially available. 

In the past decades, the rapidly expanding automobile industry has required increasing numbers of tires, black pigmented plastics and black paints with various characteristics. This has led not only to the development of new rubber grades, but also to the development of new carbon blacks required by refined application processes and to the development of a new and better manufacturing process, the furnace-black-process. This process allows the production of nearly all types of car-... 

As mentioned, in some cases hydrochloric acid is released during processing of PVC which could attack the metallic pigments if they are not encapsulated. It is, therefore, advisable to use the encapsulated PCR or PCA aluminum pigments or the Resist bronze pigments, which are offered as powder or plasticizer pastes (Table 4). 

Pigments are available ia a number of commercial forms including dry powders (either surface treated or untreated), presscakes, flushed colors (thick pastes), fluidi2ed dispersions (pourable pastes), resia predispersed pigments (powders), and plastic color concentrates or master batches (granules) (see PiGLffiNTDISPERSIONS). 

Of the models Hsted in Table 1, the Newtonian is the simplest. It fits water, solvents, and many polymer solutions over a wide strain rate range. The plastic or Bingham body model predicts constant plastic viscosity above a yield stress. This model works for a number of dispersions, including some pigment pastes. Yield stress, Tq, and plastic (Bingham) viscosity, = (t — Tq )/7, may be determined from the intercept and the slope beyond the intercept, respectively, of a shear stress vs shear rate plot. 

Most plastics e.g. polyolefins and polystyrenes and their derivatives such as ABS (acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) are supplied by the manufacturers in ready-to-use form with most of the above-mentioned stabilizers or simply need to be additionally stabilized with other additives, e.g. antistatic agents and HALS stabilizers, as required. On the other hand, in the case of other materials (e.g. PVC) it is the end user who adds the additives, pigments or preparations. This is normally done on fluid or high-speed mixers, although in the past gravity mixers or tumble mixers were also used. The mixture is then homogenized on mixing rolls, kneaders, planetary extruders or twin-screw kneaders and further processed. 

Organic pigments can be dispersed readily in plasticizers, for example with the aid of triple-roll mills. However, the throughput here is low because of the lack of smoothness of such pastes compared to other systems such as letterpress or offset inks, which is why attrition mills are better. 

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