J. Ströhle, G. Schramek / Benninger AG, CH - 9240 Uzwil / Switzerland Optimising quality and cost of bed sheeting finishing 1. Summary For the finishing of bed sheeting, meeting technical specifications is a minor issue, compared to reaching the cost target. Today, bed linen is manufactured in large production lots and double width, up to 3400 mm wide, in Pakistan, India, Brazil and, Turkey. The market demands production lines with high speed and high operational reliability. A major problem is the crease-free processing of wide width materials. This requires solutions in machine construction details. In recent years, BENNINGER has equipped whole manufacturing plants for the finishing of bed sheeting, with the following ranges: BEN - BLEACH for continuous pretreatment, consisting of de-sizing and bleaching BEN - DIMENSA for mercerising BEN - COLOUR - PAD DRY and PAD STEAM dyeing ranges 2. Introduction Bed sheeting fabrics are clearly defined to meet the customers demands. For the finishing of these materials the following requirements must be met: Technical fabric requirements - Working width 2800 3200 mm (in exceptional cases up to 3400 mm) - weight 120 180 g/m 2 - fabric construction: Mostly plain and satin weave (incl. satin stripe) - fibre composition: 100% CO, PES - stringent requirements regarding degree of whiteness - mostly pastel colours - pigment printing - for special applications, resistance to chemicking is required - easy-care (increasingly, non-iron is also required) Commercial requirements Apart from printed materials, there is only a small potential for differentiation with bed sheeting. Therefore, price is an important criterion for sales. High production speeds (100 140 m/min), combined with low-cost finishing processes bring competitive advantages. Hence, continuous dyeing processes frequently use single-step dyeing methods. Figure 1 shows a typical production sequence for bed sheeting fabrics. Due to the high production quantities it is important to make the finishing process as continuous as possible, as semi-continuous process steps would generate additional, undesirable logistical and planning work.
Fig. 1: BENNINGER production process for the continuous finishing of bed sheeting 3. Machine concept 3.1. Pretreatment: The old dyer s adage good pretreatment makes a dyers life easy, also applies to the finishing of bed sheeting. During the first wet finishing process crease-free running must be ensured at high production speeds, in spite of differences in tensions (e.g. flapping edges) caused by the weaving process and, uncontrolled fabric shrinkage. A good pre-treatment shows no residual size and no husks. Furthermore, the so-treated fabric provides a good absorbency as well as a high degree of whiteness. With the INJECTA, bed sheeting can be de-sized in a fully continuous process directly after singing. The advantage of this method (compared to KKV de-sizing): No dwelling process (including the A-frame logistics) is required. At the same time, continuous de-sizing offers the option of size recovery and/or water recycling. The worldwide water shortage is, of course, also affecting textile finishing plants making it all the more important to reuse this precious resource. Apart from fully continuous pretreatment ranges, BENNINGER also offers, in cooperation with partner MDS, numerous options in terms of waste water management. Bleaching is carried out in a combined scouring and bleaching process. Of course, this process is continuous, without interim drying after the de-sizing process. With the IMPACTA impregnation unit, it is possible, even at high running speeds, to get the required chemicals and additives into the core of the fibre, thanks to a high liquor exchange. PC-supported chemical dosing prevents uncontrolled liquor addition as well as overdosing, which could lead to the loss of chemicals and, as a result, higher production costs. The
subsequent reaction process is carried out in combination steamers under saturated steam conditions. In the combination steamers, the material is first guided and later plated onto a roller bed; delicate articles can also be run with 100% tight-strand fabric guiding. 3.2 Mercerising In the bed linen business, lustre and improved dimensional stability are very important. An increase in dyestuff yield is not necessarily a major criterion for bed sheeting, as it is often sold in full white, in pastel shades, or as pigment print. However, there are huge cost advantages, if the width stabilisation during the mercerisation avoids an additional stenter frame procedure before further processing: With the BEN DIMENSA, the finished width is stabilised on the integrated stenter frame field (fig. 2). As double-width fabrics have to be stretched more than narrow-width material, BEN-DIMENSA comes equipped with a proportionally longer stenter frame field. Fig. 2: BENNINGER: Stabilising fabric width with patented DIMENSA mercerising concept 3.3 Dyeing As mentioned before, the main colour requirements for bed sheeting are pastel shades. Apart from reactive dyestuff, certain colour nuances can also be dyed with pure pigment dyestuff and/or vat pigments in a hot flue, simply and cost-effectively. When using reactive dyestuff for lighter colour shades, the PAD STEAM DIRECT dyeing method is also frequently used. With this method, the interim drying process, as it would be required for the PAD DRY PAD STEAM method, can be omitted. Other options are the PAD HUMIDITY FIX method or the PAD THERMOFIX method. However, neither of these two processes will bring any sig-
nificant cost benefits. BENNINGER can supply the full range. When dyeing wide width materials, applying dyestuff evenly can be quite challenging. Particularly with single-step dyeing methods, it is important that there is rapid liquor exchange with no dead zones and partially hydrolysed reactive dyestuff. When using reactive dyes with the BICOFLEX padder, the dyeing bath is mixed just in time with multi-component inductive dosing (usually in a 4:1 ratio, dyestuff to chemicals), including cooling of the dyestuff. Pressure settings monitor the pickup across the full fabric width and, if required, also control and adjust the liquor application continuously. If a high chlorine fastness is required, bed sheeting fabrics are dyed with the PAD DRY PAD STEAM method, using vat dyes. Depending on fabric quality, BENNINGER have managed, in some special cases, to achieve vat dyeing, wet in wet, on the PAD STEAM dyeing range. 3.4 Special requirements for the finishing of satin stripe Continuous open width processing of satin stripe requires special solutions in machine construction details, particularly at high production speeds. Of particular importance is the fabric run during the pretreatment. During the washing process any differences in tension must be avoided. A modified EXTRACTA wash box (shorter fabric runs between guiding elements, small module dimensions) ensures perfect fabric runs. Each fabric loop is driven by an AC motor which prevents uncontrolled fabric tension build-up. To optimise the fabric run, additional scroll rollers are integrated in the washing compartment. Bleaching can usually be carried out continuously. The guided fabric zone, which is used for even heating across the width of the fabric, is also a potential source of creasing. A shorter fabric run between the guide rollers and the use of a specially developed swing roller, with driven scroll roller, enables a crease-free fabric run of satin stripe (fig. 2), with BENNINGER equipment. For standard products, the fabric run can be changed automatically to bypass the scroll roller. Abb. 3: BENNINGER: Crease-free fabric run of satin stripe at 100 m/min After mercerising, the stripe satin is sufficiently stabilised, so that further processing on continuous dyeing ranges should be problem-free. However, the material should still be processed with controlled tension. Dyeing stripe satin on a Hotflue is straightforward. It is recommended, however, that the Hotflue is operated in line with the PAD STEAM dyeing range, as any winding process can be a potential risk with satin stripe.
4. Results and outlook In recent years, BENNINGER has installed more than 60 ranges for the finishing of bed sheeting. The ranges are characterised by high productivity, mechanical robustness and crease-free fabric runs. These properties result in the process capability, vital for the production of these fabrics. They pose more of a challenge than the actual processes and the recipes used. Competitors can copy recipes - but not process reliability and cost advantages gained by selecting the right machine. Serious price pressures on conventional bed sheeting will result in a differentiation of individual manufacturers. This can lead to further increases in productivity, but it is more likely that new fibres or processes, particularly to improve handling and care properties will be used. BENNINGER is working very closely with the finishing industry and will continue to competently support their customers on the path to new innovations with their modern textile finishing ranges.