Semicontinuous Dyeing

1) Direct application of dye liquor by spraying, foam application, or printing. 

2) Continuous immersion of the fabric in a dyebath and removal of the excess of liquor by squeezing or suction (padding). 

Dye Fixation. On the dried fabric, the dye is only deposited on the fiber surface. It must penetrate into the fiber during a fixation step and be incorporated in the fiber by chemical reaction (reactive dyes), aggregation (vat, sulfur dyes), ion-pair formation (acid, cationic dyes), or in the form of a solid solution (disperse dyes). 

Fixation is performed by steaming under various conditions, depending on the fibers and dyes involved. Generally, saturated steam at ca. 100°C is applied. Pressure steamers permit a reduction of the steaming time. Disperse dyes are fixed in polyester fibers by the Thermosol process the fabric is heated in a infrared unit by radiation, by hot air, or with contact heat to 210-220°C for 30-60 s. Superheated steam facilitates rapid fixation at lower temperatures. 

Afterwards, fabrics are usually washed to remove unfixed dye and chemicals. Vat and sulfur dyes must be reoxidized. 

---

Semiconductor surfaces, 9 730-731 Semiconductor technology, 19 127 Semiconductor transport, 22 237-239 Semiconductor-vacuum interface, 22 241 Semicontinuous deodorizer, 10 815 Semicontinuous dyeing, 9 211-213 Semicontinuous ion-exchange systems, 14 403... 

Continuous or semicontinuous dyeing processes are uncommon because dry heat treatment (thermosol) hardens wool. Besides, application of the wool dye requires dyeing in aqueous liquor or dye fixation by steaming. 

Manu B, Chauhari S (2003) Decolorization of indigo and azo dyes in semicontinuous reactors with long hydraulic retention time. Process Biochem 38 1213-1221... 

Maas R, Chaudhari S (2005) Adsorption and biological decolourization of azo dye Reactive Red 2 in semicontinuous anaerobic reactors. Process Biochem 40 699-705... 

As a typical pattern of a multipurpose batch plant, the authors consider a plant with multiple floors that produces various products (e.g., fine chemicals or dyes) in batches and/or semicontinuously. Raw materials are entered into premixing devices and placed together in a reactor where the chemical reaction takes place. The resulting product is separated from the mother liquor by a filter press and then packaged in various types of packaging. The mother liquor is stored and eventually recycled. The same product may even take different paths through the plant by use of alternate devices or production lines. 

Pad Processes. In a continuous or semicontinuous processes, the fabric is first padded with the dye solution. The substantive adsorption of dyes during padding is avoided by employing minimum amounts of pad liquor at ambient temperatures. For even penetration of the dye, the material is then steamed without intermediate drying for 1-3 min in saturated steam (pad steam process ). Alternatively, it is heated to 80-85 °C and rolled up in a closed chamber where it is slowly rotated for 2-8 h (pad roll process). 

In the semicontinuous pad roll process, after impregnation with the pad liquor, the material is batched up and stored in an air-free steam chamber (dry and wet temperature ca. 98°C) where it is rotated slowly for about 1 h. By this procedure, the dye is almost completely fixed. Excellent penetration is obtained. 

In the thermosol pad batch process, a semicontinuous process, alkali-sensitive disperse dyes can be used if the alkali is applied after the thermosol process. Conversely, if the thermosol process is carried out after the pad batch step, the pH must be lowered before the thermosol process so that the disperse dye is not destroyed. 

Piece goods made of CA are usually dyed in a jigger, less often in a star frame or winch beck, with gentle material guidance. The piece beam is suitable for warp materials. Yam was previously dyed in hanks. Since suitable winding machines are available, CA can also be dyed on cylindrical cheeses. Woven CA fabrics are occasionally dyed semicontinuously in a pad roll system at 80-90 °C. Dyeing auxiliaries are subsequently washed out. 

Maekawa, Y. Semicontinuously producing aniline condensed dyes. U.S. Patent 4056530, 1977 Chem. 

---