EP0566832A2 - Method and device for mercerising - Google Patents

Abstract

In modern mercerising processes, strong liquor is applied to the moist, mechanically dewatered cloth by the addition method and becomes mixed with the water already in the cloth to produce a liquor which has the desired concentration. The recirculating strong liquor is replenished by admixture with fresh liquor of a high concentration and with weak liquor from downstream stages. The object of the invention is to reduce the consumption of caustic while maintaining an exactly uniform loading density. To this end, the moist or dry cloth is preimpregnated with weak liquor before the strong liquor is applied. The loading density of the preimpregnated cloth is continuously measured, as are the volume stream of weak liquor being added while the volume of the strong liquor is kept constant, and the concentration of the weak liquor. The volume stream of the high-concentration liquor to be added is controlled according to the NaOH balance on the basis of the measurements obtained.

Description

The invention relates to a method for the mercerization of textile webs according to the preamble of patent claim 1 and a system suitable for carrying out the method according to the preamble of patent claim 4.

In known mercerization processes, the web is impregnated with an alkali solution in a first stage, usually with sodium hydroxide solution. For example, it is sprayed with the lye or passed through a lye bath. The duration of the treatment is such that the lye completely wets the goods with a predetermined concentration. The product wetted with the lye has a strong tendency to shrink. In order to prevent the shrinkage, a bound guidance of the goods is necessary. After the goods have been completely wetted, they are fed to a second stage via a squeezer, in which the lye is removed from the goods again. The stabilization takes place in a first sub-stage, which the goods also pass through in tied guidance. Here, the lye is washed out, for example by spraying water, to such an extent that the goods then no longer shrink. This produces a dilute lye. The goods are then freed from the remaining lye in at least one further sub-stage in an unbound state by steam leaching and / or by washing.

The manufacturers and operators of mercerising systems strive to keep treatment times as short as possible in order to enable high throughput speeds with short machine lengths. From DD-267 636 A3 it is known to apply a strong alkali to the material web to be mercerized in the inlet-side part of the mercerizing field, the concentration of which is higher than the target concentration. The starch liquor is sprayed into the gusset with a spray tube, which the moist goods form when they run onto a first roller. It collects in a drip pan into which several rollers wrapped in the product are immersed and is brought onto the product again via another spray tube. The goods are then subjected to an alkali in the outlet-side half of the mercerizing field, the concentration of which is lower than the concentration of the strong alkali, but higher than the target concentration. In this process, the mass transfer, with which the water already contained in the goods is replaced by lye, is accelerated by the high concentration gradient between the lye and the material web.

EP-A1-0 339 438 describes a so-called addition method. Strong liquor is applied to the damp, mechanically dewatered material web with a platen roller. It penetrates into the goods during a passage through the subsequent web and adds to the moisture already present in the goods, so that the desired target concentration is established. It is emphasized in the document as a particular advantage that the free path which the material web travels from the impregnation to the first roller of the dwell path in the unbound state is shortened.

Another addition method was described in DE-Z '' Melliand '' Textilberichte 9/1991, pages 753 to 756. The preambles of claims 1 and 4 are based on this article. After a pre-washing process, the web passes through a high-performance crushing unit. In accordance with the squeezing effect, sodium hydroxide solution with a controlled concentration is applied evenly to the fabric web on both sides with a special addition device, so that after a short diffusion distance in the fabric sets the desired alkali concentration. The circulated sodium hydroxide solution is supplemented by concentrated or fresh alkali and by rinsing liquor, which is obtained during the stabilization and washing process. Concentration and level control devices are used.

From DE-AS 14 60 463 it is known to feed the amounts of lye to various aggregates of the de-leaching section of a mercerization system back to the de-leaching section and the mercerization field. In particular, it is also known to feed the return liquor to the web in an impregnation field designed similar to a stabilization field and upstream of the mercerization field, into which the goods enter without alkali. The main impregnation takes place in an elongated mercerising field, where the strong liquor applied in a conventional manner displaces the moisture contained in the goods by mass transfer.

The invention has for its object to improve a method according to the preamble of claim 1, so that exactly a uniform loading density is maintained with reduced alkali consumption. A second task is to create a mercerizing system which is particularly suitable for carrying out the method.

The first object is solved by the characterizing features of claim 1. The reduction of the alkali consumption is achieved in that a part of the weak liquor, which occurs especially during stabilization, is used according to the first feature of the label to apply a certain amount of alkali to the goods even before the starch liquor is applied. The amount of starch liquor that has to be added in order to achieve the desired loading density is reduced accordingly. As a result of the pre-impregnation, however, it is very difficult, especially with the addition process, to always achieve a uniform, exact loading density in the subsequent main impregnation even if the predetermined moisture values are not exactly adhered to in the preceding or subsequent mechanical dewatering. These difficulties will be overcome by the further characterizing features of claim 1.

Due to the feature of claim 2, the penetration of the applied strong liquor into the goods is evened out and accelerated.

The feature of claim 3, on the one hand, achieves a good washing effect, and, on the other hand, the highest possible concentration of the dilute alkali produced during stabilization.

The second object is achieved by the characterizing features of claim 4.

In addition to the advantages mentioned in connection with claim 2, the features of claim 5 additionally achieve that the material web is transferred from the main impregnation field into the subsequent field without leaving the bound guide.

The features of claim 6 enable the method specified in claim 3 to be carried out.

• Figur 1 zeigt den mechanischen Aufbau des einlaufseitigen Teils der Mercerisieranlage.
• Figur 2 zeigt das Stabilisierfeld.
• Figur 3 veranschaulicht das Leitungssystem der Gesamtanlage für die verschiedenen Laugen.
• Figur 4 zeigt das Hauptimprägnierfeld mit meß- und regeltechnischen Einrichtungen.

The drawing serves to explain the invention on the basis of a simplified, schematic representation of a plant for carrying out the method according to the invention.

• Figure 1 shows the mechanical structure of the inlet-side part of the mercerizing system.
• Figure 2 shows the stabilizing field.
• Figure 3 illustrates the piping system of the entire system for the different alkalis.
• Figure 4 shows the main impregnation field with measuring and control equipment.

The mercerization system consists of several fields that are continuously traversed by the web to be treated, namely a pre-impregnation field 1, a main impregnation field 2, a penetration field 3, a dwell field 4, a stabilization field 5 and a washing field 6.

The pre-impregnation field 1 comprises a roller skid compartment of conventional design. It is divided into a number of chambers 8 in the floor area by a plurality of partitions 7. The separating bulkheads 7 are alternately provided with passage openings which are not visible in the drawing, so that the weak liquor supplied on the outlet side flows through the individual chambers 8 transversely to the direction of travel of the goods and is guided zigzag from chamber to chamber. The chamber 8a adjacent to the goods inlet is delimited by an overflow weir 9 which determines the fill level. In the individual chambers 8 immersion rollers 10 are accommodated, to which upper rollers 11 are assigned. The material web is alternately guided in the form of vertical loops over the dipping rollers 10 and the top rollers 11. A pendulum roller 12 for tension control is arranged on the outlet side. Behind the roller skid compartment, the web passes over a spreader roller 13 to a vertical crushing unit 14 and from there over another pendulum roller to the main impregnation field 2.

The main impregnation field 2 comprises a horizontal crushing unit, consisting of two rollers 15, 16, over which distributor channels 17, 18 are attached for the alkali. The bottom under the rollers 15, 16 is designed as a collecting trough. It is provided at its deepest point with a drain 19 which leads to a pump template 20. A line 21, which is guided via a circulation pump 22 and a heat exchanger 23, connects the pump supply 20 to the distributor channels 17, 18. A conductivity measuring device 24 for measuring the loading density of the incoming pre-impregnated goods is arranged at the goods inlet of the main impregnation field 2.

In the subsequent penetration field 3, a plurality of lower rollers 25, 26, 27 are arranged at short intervals, the axes of which lie at the same height and parallel to the axes of the rollers 15, 16. Upper rollers 28, 29 are arranged in a gap with the lower rollers, so that the upper rollers 28, 29 are supported on two lower rollers each. At the transition between the main impregnation zone 2 and the penetration zone 3, an upper roller 30 is arranged, which is supported on the one hand on the roller 16 of the horizontal crushing unit, on the other hand on the lower roller 25 on the inlet side, and thus ensures the transition of the goods from the main impregnation zone 2 to the penetration zone 3 in bound guidance. No devices for supplying liquid are normally provided in the penetration field 3. Under the lower rollers 25, 26, 27 there is a collecting trough 35 with drain 36, which is led to a pump receiver 37.

The dwell field 4 comprises a similar roller arrangement which directly adjoins the roller arrangement of the penetration field 3. The first two lower rollers of the dwell field 4 are cooled. A vertical crushing unit 38 is arranged at its outlet. Devices for supplying liquid are not provided in the dwell field 4. A drain 39 leads to the pump receiver 37 from the bottom designed as a collecting trough.

The stabilizing field 5, which is shown separately in FIG. 2, is configured analogously to the two preceding fields with respect to the arrangement of the rollers, it being understood that the number of bottom and top rollers in the individual fields can be different, depending on the desired dwell times. On the outlet side, the stabilizing field 5 is separated from the subsequent washing field 6 by a vertical crushing unit 40. To supply the washing liquid, a spray tube 41 is arranged directly in front of the vertical crushing unit 40 and is directed into the roll wrap of the vertical crushing unit 40. The bottom of the stabilizing field 5 is designed as a collecting trough 42, which is divided by transverse dividing plates 43, 44. Accordingly, the stabilizing field 5 consists of the sections 45, 46, 47.

The outlet-side section 47 also includes the vertical crushing unit 40. Each section has its own washing liquid circuit. The washing liquid circuit of section 47 comprises an outlet 48, a pump receiver 49, a pump 50, a circulation line 51 and a spray tube 52 which is arranged in an intermediate space between two top rollers 53, 54. The washing liquid circuits of the sections 45, 46 are constructed analogously. The pump templates 55, 56, 49 are arranged similarly to the steps of a staircase rising in the direction of travel and separated from one another by overflow plates 57, 58, so that the liquid flows from step to step in a countercurrent to the direction of travel of the web. A branch line 60 leads from the circulation line 59 of the section 45 on the inlet side and is led to the pump receiver 37.

The subsequent washing area 6 has no particular reference to the invention and therefore does not require a detailed description. It should only be noted that in the washing area 6, bound goods guidance is no longer required. A vertical crushing unit 61 is arranged behind the washing area 6. An outflow opens into a pump receiver 62. The associated pump 63 is connected on the pressure side by a line 64 to the spray tube 41 of the stabilizing field 5.

The material web runs dry into the pre-impregnation field 1 and is guided therein over a number of guide rollers which are immersed in a lye bath made from dilute weak lye. The weak liquor has a concentration of about 80 - 130 g / l. The weak liquor is impregnated into the goods and then squeezed to about 70% moisture by the vertical squeeze mechanism 14 (% by weight of liquid, based on the weight of the dry goods). The loading density is around 70 - 100 g / kg (g NaOH per kg goods).

In another process variant, the goods already run into the pre-impregnation field 1 with a moisture content of about 70%. This moisture is displaced by weak liquor as it passes through the caustic bath of the pre-impregnation field 1. Through the Ouetschwerk 14, the moisture content again reduced to 70%. The goods therefore leave the pre-impregnation field 1 with the same moisture with which they entered. However, instead of the water originally present, it absorbed weak liquor. The loading density corresponds approximately to the process variant described first.

Strong liquor is applied to the pre-impregnated goods in the gusset between the rollers 15, 16 on both sides. The concentration of the strong liquor is around 400 - 500 g / l. In the heat exchanger 23, the starch liquor is heated to the temperature of 50-80 ° C. required for the hot mercerization. The rolls 15, 16 squeeze the goods to a moisture level which is significantly higher than the moisture level remaining behind the vertical crushing unit 14. It therefore leaves the main impregnation zone 2 with a 30 to 40% higher humidity, e.g. with a humidity of approx. 100%. With the additionally applied moisture, the desired amount of NaOH is applied, so that the goods leave the main impregnation zone 2 e.g. has a NaOH loading density of 250-300 g / kg.

Without leaving the bound guide, the goods subsequently enter the penetration zone 3, where the starch liquor applied to the goods penetrates into the goods and mixes with the weak liquor, which has already been introduced into the goods in the pre-impregnation zone 1. No new alkali is applied to the goods in the penetration field 3. In this field, therefore, no alkali cycle is required. The outlet 36 only serves to drain off any dripping liquid, the amount of which is generally very small. In the event, however, that appreciable amounts of lye drip off the goods, a lye circuit, not shown in the drawing, can be provided. It only serves to return the drained liquid to the goods so that the loading density remains unchanged. The temperature of the goods remains almost constant in the penetration field.

When entering the subsequent dwell area 4, the temperature of the goods is reduced by contact with cooled rollers. This accelerates swelling.

The goods also remain in the dwell area 4 without contact with liquid. At its exit, the moisture is reduced in the ouetschwerk 38 as much as is possible in the swollen state of the goods, i.e. about 80 - 90%. The dripping liquid flows to the pump receiver 37.

In the stabilizing field 5, the loading density of the goods is reduced to about 50-70 g / kg by spraying them repeatedly with washing liquid in countercurrent. On the one hand, this results in a good washing effect, and on the other hand a relatively high concentration of the weak liquor that flows into the pump receiver 37.

The entire route from the main impregnation field 2 to the exit of the stabilization field 5 is traversed by the goods, which tends to shrink due to the high loading density, e.g. - As shown in Figures 1 and 2 - along a meandering path over closely adjacent rollers. However, the goods can also be transported on the entire route or on partial routes, e.g. in the stabilizing field 5, bound between tension chains.

The goods are passed through the washing area unbound. In this field, the goods are washed out with hot water, so that the residual load density is less than 0.5 g / kg. Flowing washing liquid is fed to the stabilizing field 5.

As can be seen in particular from FIG. 3, the alkali circuits of the individual fields are linked to one another. In the pump receiver 37, the dilute alkali accumulating in the stabilization field 5, the alkali squeezed off in the vertical squeeze mechanism 38, and possibly a very small amount of drained alkali from the penetration field 3 are collected. A partial amount of the alkali thus formed is fed to the pre-impregnation field 1 as a weak alkali by a pump 65 via a line 66. When the goods arrive dry, the amount of weak liquor supplied is controlled by a level controller so that the liquor level in the pre-impregnation field 1 remains constant. In this way, exactly the amount of weak liquor replaced by the Goods are picked up. However, if the goods already have a moisture content of approx. 70% runs in and leaves the pre-impregnation field 1 with approximately the same moisture, it merely causes a reduction in the concentration of the alkali bath. In this case, the amount of weak liquor supplied is controlled by means of a flow controller so that the required concentration is not undercut. Corresponding to the amount of weak liquor supplied, liquor depleted in NaOH runs off via an overflow 67.

In the main impregnation zone 2, the strong liquor is circulated and continuously supplemented by metered addition of highly concentrated lye and weak lye. The admixture takes place via a static mixer 68, which is connected on the output side to the pump supply 20. On the inlet side, highly concentrated sodium hydroxide solution, preferably at a concentration of about 700 g / l, is fed to it from a storage tank 69 via a line 70. In addition, weak liquor is fed to him from the pump receiver 37 via a line 71 and strong liquor via a line 72, which is branched off from the line 21 of the pump circuit.

wobei die Symbole folgende Bedeutung haben:

b

Beladungsdichte nach der Vorimprägnierung in g/kg

B

Vorgebene Beladungsdichte nach der Hauptimprägnierung in g/kg

M

''Warengewicht'' (eigentlich Masse pro laufenden Meter Ware) in kg/m

w

Durchlaufgeschwindigkeit in m/s

c

Konzentration der Schwachlauge in g/l

C

Konzentration der hochkonzentrierten Lauge in g/l

v̇

Volumenstrom der Schwachlauge in l/s

V̇

Volumenstrom der hochkonzentrierten Lauge in l/s

Auf der linken Seite des Gleichheitszeichens sind die NaOH-Mengen aufgeführt, die mit der vorimprägnierten Ware, mit der Schwachlauge und mit der hochkonzentrierten Lauge in das System eingebracht werden, auf der rechten Seite die mit der Ware aus dem System ausgetragene NaOH-Menge. Aus der Stoffbilanz errechnet das Gerät 75 die zuzuführende Menge an hochkonzentrierter Lauge:

$$\dot{\text{V}}\text{=}\frac{\text{1}}{\text{C}}\text{[(B-b) · M · w - c ·}\dot{\text{v}}\text{]}$$

Entsprechend dem ermittelten Wert wird mittels eines Stellventils 83, welches durch das Gerät 75 betätgit wird, die hochkonzentrierte Lauge dosiert.With the arrangement shown in Figure 4, the added amounts of alkali are dosed so that exactly the specified loading density of the goods is achieved. The conductivity measuring device 24 continuously measures the loading density which the incoming material web 73 brings with it from the pre-impregnation field 1. The measured value is transmitted to a computing and control unit 75 via a line 74. Likewise, the speed of the roller 15, which is a measure of the throughput speed of the goods, is signaled to the device 75 via a line 76. With a valve 77, the inflow of the weak liquor via the line 71 is influenced via a symbolically illustrated controlled system 78, so that the liquid level in the pump reservoir 20 is kept at a constant level. The volume flow of the weak liquor flowing in is continuously measured with a flow meter 79 and the concentration thereof with a measuring device 80. The measurement signals are transmitted to device 75 via lines 81, 82. In addition, the predetermined loading density and the weight of the goods are input into the device 75, ie the Mass per linear meter of goods. The device 75 draws up the mass balance for the NaOH. This is:

$\text{bMw + c}\dot{\text{v}}\text{+ C}\dot{\text{V}}\text{= B · M · w}$

where the symbols have the following meaning:

b

Loading density after pre-impregnation in g / kg

B

Specified loading density after the main impregnation in g / kg

M

'' Goods weight '' (actually mass per running meter of goods) in kg / m

w

Throughput speed in m / s

c

Concentration of weak liquor in g / l

C.

Concentration of the highly concentrated lye in g / l

v̇

Volume flow of the weak liquor in l / s

V̇

Volume flow of the highly concentrated lye in l / s

On the left side of the equal sign are the quantities of NaOH that are introduced into the system with the pre-impregnated product, with the weak liquor and with the highly concentrated alkali, and on the right side with the quantity of NaOH discharged from the system with the product. From the material balance, the device 75 calculates the amount of highly concentrated alkali to be fed:

$$\dot{\text{V}}\text{=}\frac{\text{1}}{\text{C.}}\text{[(Bb) · M · w - c ·}\dot{\text{v}}\text{]}$$

According to the determined value, the highly concentrated alkali is metered by means of a control valve 83 which is actuated by the device 75.

Claims (6)

Process for the mercerization of textile material webs in a continuous run
a moist web of material is first dewatered mechanically,
whereupon a strong lye is applied to the mechanically dewatered material web in a main impregnation field,
the web then passes through further treatment fields, in particular a stabilizing field in which it is brought into contact with a washing liquid,
whereby the starch liquor is circulated and continuously supplemented by the controlled admixture of highly concentrated caustic and weak liquor, which is produced in the other treatment fields,
characterized,
that the damp or dry material web is pre-impregnated with weak lye before dewatering and applying the strong lye,
that the loading density of the pre-impregnated goods is measured continuously,
that the volume flow of the weak liquor flowing in while the strong liquor is kept constant and its concentration are measured continuously and
that the volume flow of the highly concentrated liquor to be supplied is calculated and controlled on the basis of the measured values obtained according to the NaOH material balance. A method according to claim 1, characterized in that the starch liquor is applied on both sides in the gusset of a roll nip and that the goods are immediately squeezed off in the roll nip. A method according to claim 1 or 2, characterized in that
that the stabilization is carried out in several stages,
that the web is brought into contact with circulated washing liquid in each stage and
that the washing liquid is passed in countercurrent to the direction of travel of the web from stage to stage. Plant for the mercerization of textile webs according to one of claims 1 to 3,
with a device for mechanical dewatering of the moist web,
with a device for applying strong alkali to the mechanically dewatered web,
with subsequent treatment fields, in particular a stabilization field,
with a circulation system for the strong liquor, which comprises a pump template, a line and a circulation pump,
with lines for the controlled supply of highly concentrated lye and weak lye to the circulation system,
featured
through a pre-impregnation field (1) connected upstream of the mechanical dewatering device (14),
by a conductivity measuring device (24) for measuring the loading density of the pre-impregnated web (73),
through lines (70, 71) for supplying highly concentrated lye and weak lye to the circulation system (20, 21, 22),
by a flow measuring device (79) and a concentration measuring device (80) for the weak liquor flowing in at a constant level in the pump reservoir (20) and
by means of a computing and control device (75) acting on a control valve (83) of the line (70) and calculating and controlling the volume flow of the supplied highly concentrated alkali according to the NaOH material balance. Installation according to claim 4, characterized in that the device for applying strong liquor is a horizontal squeeze mechanism with two rollers (15, 16) forming a gusset and in that the transition between the horizontal squeeze mechanism and the roller arrangement is bridged by an upper roller (30) which is bridged is supported on the one hand on a roller (16) of the horizontal crushing unit and on the other hand on a roller (25) belonging to the roller arrangement. System according to claim 4 or 5, characterized in that
that the stabilizing field (5) comprises a plurality of sections (45, 46, 47) arranged one behind the other,
that each section has its own pump circuit (49, 50, 51, 52) for the Has washing liquid and
that the pump templates (55, 56, 49) form a cascade falling against the direction of travel of the goods.

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