Triple-roll milling

DIN ISO 8780-6-1990 Dispergieren mit einem Dreiwalzwerk. Dispersion using a triple roll mill. 

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. 

Because of their small particle size and their resulting large surface area, pigment blacks are classed as pigments, which are more difficult to disperse. Depending on the supplied form, pigment blacks can be dispersed with all grinding machines, for example sand mill, pearl mill, ball mill, triple roll mill and others. 

Processing is best done in two stages first, paste is prepared without extender and extender is added and dispersed by dissolver after paste already has been roll-milled (this comment especially applies to triple-roll milled pastes). 

Pastes containing Vinnolit extenders should not be triple-roll milled because extender resin will separate in front of nip. Instead, extender should be dispersed after the paste with all other ingredients have already been roll milled. 

The kneadable compounds are mixed on a triple roll mill or in a kneader. 

Roller mills, which have their major use in ink production, consist of a number of horizontal steel rolls placed side-by-side and moving in opposite directions, often at different speeds, with very small clearances in between. In these gaps, the pigment-resin mixture is sheared. The triple roll mill is shown in Fig. 8.5. A paste is fed in at D, is lightly sheared between rollers A and B and more severely between B and C. A scraper blade E removes the dispersion. All rollers are independently driven and run at different speeds to increase shear. The mill is particularly suitable for the production of pastes of very high pigment content. 

Dispersion in a liquid, in pasty phase, or in polymer melts takes place on extruders, calendars, kneaders, triple roll mills and attrition mills. Also, ultrasound and thermal energy based procedures are used for the production of a fine pigment powder. Inorganic pigments, due to their ionic lattice, are more readily dispersable than organic ones. 

Three-roll mill See triple roller mill. 

Three-Roll Mill See Triple Roller Mill. 

Fig. 8.49 is another schematic representation, published by one of the manufacturers (CPM), showing the typical design of a pellet mill with cylindrical die and two internal press rollers. The execution suggested by Fig. 6.4b.5 (Chapter 6), 8.40, and 8.41 with one press roller is only used in laboratory and small production machines. For structural and process reasons, the perforated concave die can not be very wide (Fig. 8.50). Therefore, to increase the capacity of a given press and more uniformly distribute the forces acting on the ring, up to three rollers (see below. Fig. 8.52) are installed. With two rollers (Fig. 8.49) the capacity of a machine doubles as compared with a single roll pellet mill and triples with three rollers from a ring loading point of view, the latter also results in the best distribution of the pressing forces.

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