Spin dyeing

The technique of spin dyeing chemical fibers may be located somewhere between the textiles and the plastics area. In contrast to textile coloration, the material which is to be extruded is colored before the fiber is made. The requirements to be met by pigments are therefore similar to those which apply to the coloration of 

Three different methods are available for spin dyeing [40]  

As a rule, pigment preparations for this application are based on a carrier material which is identical or similar to the polymer which is to be extruded. 

Wet spinning. This technique is characterized by spinning a filtered viscous polymer mass, dissolved in a suitable solvent, into contact with a precipitation or coagulation bath. Polyacrylonitrile, polyvinyl acetate, cellulose acetate, and other materials are processed by this method. Thermal requirements for pigments are less stringent than for melt spinning but pigments are expected to be fast to the solvents and chemicals used. 

Dry spinning. The polymer, dissolved in a suitable solvent and filtered, is pressed through spinnerettes and, in an oxygen-free atmosphere, pulled by vacuum through a heated shaft, where the polymer solidifies as the solvent evaporates. The requirements of this process regarding the heat stability of pigments are much less 

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The dispersibility of an organic pigment which is to be incorporated in a polyolefin is of particular importance. This is especially true for the coloration of extrusion films and for HDPE or PP ribbon made from stretched blown film or from sheeted extrusion film, as well as for the coating or melt spin dyeing. 

P.Y.62 is thermally stable up to 250°C. It has a considerable effect on the shrinkage of HDPE and other partially crystalline polymers. The pigment is an equally suitable colorant for polystyrene and polyurethane and lends color to polypropylene spin dyeing products with minimal application requirements. 

The textiles printing industry has an appreciable interest in P.Y.17 and applies it in the form of pigment preparations. Where its fastness properties satisfy the specifications and where the use requirements are not too demanding, the pigment is also utilized for spin dyeing purposes. Manufacturer recommendations include media such as polyacrylonitrile and cellulose acetate fibers, on which 1/3 SD pigment prints exhibit a lightfastness which is equal to step 5 on the Blue Scale. 

The high quality of the fastness properties is the basis for frequent pigment use in textile printing. Dry cleaning with perchloroethylene or washing has almost no effect on the color. P.Y.83, sometimes in the form of a preparation, is used for viscose spin dyeing, secondary acetate, and polyacrylonitrile. 

Rigid PVC is one of the polymers which are sometimes colored by P.R.112. Transparent systems (0.1% pigment) equal step 8 on the Blue Scale for lightfastness while the lightfastness of white reductions is only step 5-6. The spin dyeing industry employs P.R.142 for viscose rayon and viscose cellulose, in which the pigment exhibits excellent lightfastness and performs, if not perfectly, then almost satisfactorily. 

Due to the disadvantage of comparatively poor migration resistance, P.R.5 is not used in plasticized PVC, but it can be applied in rigid PVC. Its lightfastness is excellent in this medium, transparent and opaque colorations (up to 0.01% pigment + 0.5% TiOz) equal step 7 and, respectively, step 6-7 on the Blue Scale. Dispersed pigment preparations are available for the mass coloration of viscose films as well as for spin dyeing of viscose rayon and viscose cellulose. 

P.R.170 is not always heat stable enough to allow application in polyolefins. In HDPE systems formulated at 1/3 SD, the pigment tolerates exposure to 220 to 240°C for one minute. Its tinctorial strength, on the other hand, is excellent. P.R.170 is also occasionally used in polypropylene and polyacrylonitrile spin dyeing in the latter medium, it satisfies the specifications of the clothing and home textiles industries. Besides, P.R.170 lends color to viscose rayon and viscose cellulose it is used for the mass coloration of semisynthetic fibers made of cellulose last but not least, it colors yarns, fibers, and films made of secondary acetate. 

P.O.38 is also used in spin dyeing, where it colors filament, fibers, and films made of secondary acetate. The pigment possesses excellent fastness properties in this medium. 

P.B1.25 is only produced in small volume in Europe, Japan, and the USA. It is used for the spin dyeing of secondary acetate, lends color to rubber, and is found in inks for packaging purposes. 

Various benzimidazolone pigments are heat stable enough to be used in polypropylene spin dyeing. Several types find extensive use in the spin dyeing of other fibers, such as polyacrylonitrile, viscose reyon, and vicose cellulose, or secondary acetate. 

P.Y.151, like 154 and 175, lends itself to polypropylene spin dyeing. This is particularly true for polymer types whose flow behavior makes it possible to work at temperatures between 210 and 230°C. P.Y.151 is very lightfast in these media. 

P.O.62 also lends itself to polypropylene spin dyeing, especially at temperatures up to approximately 230°C. This makes it a suitable colorant for PP types which exhibit good flow behavior. 

P.O.72 is used for melt spin dyeing of polypropylene, in which 1/3 SD (1% TiOz) affords 0.2% pigment. The lightfastness of PP colorations with 0.3%... 

P.R.175 is also used in polypropylene spin dyeing, where it satisfies the lightfastness requirements. The pigment is an interesting colorant for polystyrene and for polyester (PETP). These systems are utilized to make bottles and other products. 

P.R.176 provides very lightfast polyacrylonitrile spin dyeing products. The samples equal step 6-7 on the Blue Scale. Dry and wet crocking may affect the objects to a certain extent. P.R.176 is also used in polypropylene spin dyeing, especially for coarse textiles, such as carpet fibers, split fibers, filaments, bristles, or tape, but also for finer denier yams. A special pigment preparation for this purpose is commercially available. 1/3 SD samples tolerate exposure to up to 300°C for one minute or up to 290°C for 5 minutes. In terms of lightfastness, 0.1% colorations equal step 5-6 on the Blue Scale, while 2% samples match step 7. 

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