Washing knitwear in spray - dwelling compartments

Transcription

1 J. Ströhle, G. Schramek /Benninger AG, CH Uzwil / Switzerland Washing knitwear in spray - dwelling compartments 1. Summary This paper describes washing of knitwear in spray - dwelling compartments. Efficient washing is of central importance during textile finishing and is defined by the factors mechanical action, time, temperature and water. By logical implementing the process requirements BENNINGER has realized a concept for washing after dyeing and printing that is particularly economical on water and energy consumptions. The concepts described impress with a high level of reliability and a wide range of applications. However, the concepts are also specifically matched to small batch sizes. 2. Introduction Impregnation, reaction and washing define the chemical finishing of textiles. Often, reference is only made to bleaching, mercerizing, dyeing, printing and resin finishing. Nevertheless, apart from resin finishing, each of these processes is related to a washing process the key to each textile finishing process. The objective of each washing process is to remove the soiling from the substrate and irreversibly transfer it to the washing solution. Every washing process is defined by four factors: Mechanical washing action Temperature Time Water Depending on the washing task the weighting of the individual factors varies (see Figure 1). Often the term washing is only associated with the washing out of caustic soda. This important washing process comes under the term dilution wash as does, e.g., the washing out of salts, residual chemicals and pre-emulsified oils. The success of a dilution wash essentially depends on the water temperature and mechanical washing action. On the other hand, reaction processes, e.g., de-mineralisation, oxidation, neutralisation and emulsification, require a specific amount of time for the chemical reactions to take place. The fastness wash for obtaining wear-fastness (fastness when washed, in water, on abrasion, etc.) falls under the term diffusion wash. Objective of this washing process is to bring the unfixed residual dye in the core of the fibres to the fabric surface and to remove it. Here time and temperature are key factors.

2 Weighting of the factors that affect textile washing processes Fresh water Temperature Time Dilution wash caustic soda, salts, H2O2, emulsified oils Fastness wash (diffusion wash) reactive dye, etc. Reaction processes demineralisation, oxidation, neutralisation, emulsification Mechanical washing action Figure 1: Weighting of the factors for textile washing processes 3. Machinery-related requirements and equipment for the diffusion wash Diffusion washing processes cannot be undertaken satisfactorily using common drum washing systems; the investment required is also excessive. Drum washing machines are particularly well suited to thorough dilution washing processes and the surface wash. Although BENNINGER has already achieved a fabric content of 9 m using the double TRIKOFLEX washing compartment (the majority of competitors are significantly below this figure with 3-5 m fabric content), this content is not sufficient, for instance, to perform a soaping process for 2 or more minutes. At a processing speed of 40 m/min some 9 washing compartments would be necessary. Time-consuming washing processes can be performed significantly better in dwelling compartments. Therefore often underliquor accumulators are used. They have, however, significant disadvantages: 1.) The fabric is continuously moved through the same contaminated liquor. 2.) There is practically no liquor movement. Mechanical reorientation of the fibre or knitwear structure does not take place. 3.) Large liquor volume. 4.) The fabric often tends to swim off and shifts to one side. For diffusion washing and reaction processes BENNINGER relies on roller bed dwelling compartments with additional spraying areas. The washing principle applied by BENNINGER is based on the principle of seeping wash, where liquor is applied to the textile substrate and slowly seeps through the fabric. Hereby, gravity produces a forced flow. Combined with such a dwelling compartment, knitwear can be washed with very low tension. The knitwear is placed horizontally on the roller bed in small loops and moves forwards

3 continuously. Water sprayed onto the fabric seeps through the pile, is re-collected, heated and sprayed onto the fabric again with a circulating pump. For a genuine counterflow wash, the dwelling compartment is separated into several circulation circuits. During washing there are practically no longitudinal tensile forces acting on the knitwear. The knitwear lies freely and with low tension in the dwelling section and can relax at the same time. Unlike storage racks, accumulator belts or chains, the roller bed used by BENNINGER has the major advantage that the pile of fabric is continuously in motion and is passed from roller to roller. Laymarks are therefore reliably avoided. The relative motion within the individual fibres and threads improves the penetration of the capillary spaces by the seeping water. Two units are available from BENNINGER for the seeping wash. TRIKOFLEX small accumulator - Combined dwelling and washing unit This special new product, a combination of dwelling and drum washing compartment, is the result of the logical implementation of process requirements in a machine. A seeping washing process is immediately followed by a drum washing process to wash out diffused hydrolysate from the surface. A machine for washing after dyeing and printing is shown in Figure 2. Fig. 2: BENNINGER machine for washing after dyeing and printing The fabric is placed in each of the two dwelling zones for 2 4 min and sprayed with boiling water. At the outlet of the washing compartment there is a washing drum. The washing result is improved by an intermediate rinsing process during the soaping; with the fabric fully straightened and at full width. Figure 3 shows the washing range:

4 Fig. 3: BENNINGER multiple flexible Trikoflex Washing range REACTA washing steamer - combined washing and steaming unit This unit comprises a roller bed section and is combined with a TRIKOFLEX drum washing compartment. The roller bed section is of modular design and can be configured to suit the required reaction times. As for the seeping wash washing principle, the fabric is sprayed with circulating washing water. The REACTA washing steamer can also be used for PAD STEAM bleaching processes. Such a machine concept is shown in Figure 4. Fig. 4. BENNINGER machine concept for PAD STEAM pre-treatment and washing after dyeing The first small accumulator is used for de-mineralisation during pre-treatment processes, for rinsing after reactive dyeing or for dwelling thickeners during washing after printing. The REACTA washing steamer (in the middle of the machine) can be used as a steaming unit for bleaching (15 25 min) when fed with saturated steam. During the soaping of reactive dyes, the fabric is continuously sprayed using multiple circuit circulation systems. Each circulation system sprays water onto the fabric at 1000 l/min to ensure that the hydrolysate migrates to the surface with the seeping water (Fig. 5). Final washing is done both during bleaching and during washing after dyeing and printing in the following TRIKOFLEX drum washing compartments. As already mentioned, this process has the advantage that knitwear is fully opened (no curled in selvedges) with the emphasis on mechanical action. If the washing is only performed using the principle of seeping wash, the familiar problems with yellow fabric selvedges arise (due to residual alkali in the curled in selvedges) or poor fastnesses (water-, washing-, chlorine- or rubbing fastnesses) occurs in the edge areas (with significant cutting loss). Prior to leaving the machine, there is a minute long

5 neutralisation process in a small accumulator with subsequent final rinsing in the integrated drum washing machine. Fig. 5: BENNINGER Seep washing with 1000 l/min spray water per circulation 4. Results and outlook Thanks to the seeping wash it is possible to perform diffusion washing processes economically and with an optimised process. The most important parameters in the units available from BENNINGER are listed in Table 1. Table 1: Technical data on TRIKOFLEX small accumulator and REACTA washing steamer TRIKOFLEX small accumulator REACTA washing steamer Conventional unit Fabric content m m 3-9 m drum washing machine Reaction time min 4-30 min min Liquor content 90 l/m 90 l/m and circulation circuit 2000 l/m underliquor accumulator Fabric tension tension-free tension-free 5-15 N/m Application Diffusion wash Short reaction processes Diffusion wash Long reaction processes Drum washing machine: high-performance dilution wash Removal of surface soiling The dwelling compartments described are integral components in a machine concept with a well thought out process. In future flexible machines will be required for the production of the highest possible fabric quality combined with the lowest possible water and steam consumption. Particularly important is the achievement of wear-fastness as assessed by the end customer on a daily basis. BENNINGER machine concepts meet these requirements due to highly efficient washing technology with minimum longitudinal tensile forces and minimized selvedge cutting losses.