METHOD FOR IMPREGNATING A TEXTILE MATERIAL
FIELD OF THE INVENTION This invention relates to a process for the continuous impregnation of textiles, more particularly wet textiles, in an impregnation compartment containing liquor through which the textile is passed, the impregnation liquor contains as an impregnation medium a lye, more particularly soda lye, or a lye, more particularly soda lye, and furthermore an oxidizing bleaching agent, more particularly hydrogen peroxide, part of the impregnation liquor is derived or branched, more particularly continuously, to Through a bypass, it is filtered and supplied to one or more detectors to determine the concentration of the impregnation medium. After filtration, that part of the impregnation liquor that has been derived is preferably further subjected to the treatment in a particular manner before being supplied to the detectors. BACKGROUND OF THE INVENTION Such a process is known from an article of the magazine Int. Dyer, August 1997, pages 20-22. In this case, the concentration of hydrogen peroxide is measured continuously in a bleaching liquor. Samples are continuously removed from the bleaching process, ie, from the impregnation compartment, through a bypass and returned after their removal. The sample removed or removed is first filtered to remove coarse impurities from the solution. For the determination of hydrogen peroxide, a buffer solution is introduced to adjust the pH to 7 because it is necessary for the measurement. The sample is then automatically supplied to the detector. To calibrate the detector, calibration solutions for two-point calibration are supplied to the detector at cyclic intervals. After the amplification of the detector signal, the concentrations are calculated from it and are shown. The values obtained can be used to drive a metering unit for hydrogen peroxide and / or soda lye. The data is stored on a personal computer and is available for printing. The invention is particularly indicated for the continuous wet-wet impregnation as commonly used in the textile industry. In this process, the wet or moaned textile is continuously fed to the impregnation compartment. Since the water is continuously introduced into the impregnation compartment, the problem is to maintain the concentration of the constant impregnation medium in the impregnation compartment. The concentration in the impregnation compartment can be measured periodically, as is standard in practice, and the impregnation means is replenished accordingly. Alternatively, the necessary amount of the impregnation means to be added can also be determined on the basis of the weight of the textile introduced in the impregnation compartment. In the case of wet-dry impregnation wherein the dried textile material is introduced into the impregnation compartment, the liquor in the impregnation compartment can not be diluted so that it is merely necessary in this case to add impregnation liquor with the same concentration.
However, the aforementioned continuous wet wet impregnation is generally practiced in the textile industry. The particular problems in determining the amount of impregnation medium to be added arise whenever the type of textile is changed. Another problem lies in the delay between the measurement of the concentration existing in the impregnation compartment and the resulting addition of the impregnation means. This is due, in the present, because concentration is always determined in practice by the titration manual. In general, the titration is carried out at 30 minute intervals. The shorter titration intervals are very rare and involve a lot more personnel.
Since the textile material passes through the impregnation bath at high speeds and since the type of material is often changed, the concentration in the impregnation compartment has changed significantly in the aforementioned half hour. The process mentioned in the above mentioned article in Int. Dyer is in principle a distinct improvement in the existing practice of the textile industry because it allows the concentration of the impregnation medium, hydrogen peroxide, in the impregnation compartment to be determined quickly and continuously so that the necessary amount of the impregnation medium can be added to virtually the same time. Accordingly, an automatic control system can be built based on this process that continuously monitors the concentration in the impregnation compartment and adjusts accordingly. Unfortunately, considerable problems arise in the practical application of the process described in the journal article. The filters used for the filtration stage of the sample preparation are blocked relatively quickly. On the other hand, if the filtration is not carried out, the analysis system and especially the detectors are plugged by the fine residual particles present in the impregnation liquor, which are dragged by the textile material in the impregnation compartment and which emanate from treatments previous of the fibers and the textile material. The particular damage is caused by the starch constituents, which represent the main component of the sizes used in the weaving process. It was found in the development of the process according to the invention that the starch which coagulates at low temperatures and which is soluble at high temperatures is mainly responsible for the blocking of the filters having a pore size of the order of 0.2 μ. DESCRIPTION OF THE INVENTION Accordingly, the problem addressed by the present invention was to achieve the replacement or continuous, uninterrupted and exact supply of the impregnation medium, more especially soda lye or a combination of lye of soda and hydrogen peroxide, in the process mentioned at the beginning. According to the invention, the solution to this problem in the process mentioned at the beginning is characterized in that the part of the impregnation liquor that is derived or branched is heated before filtering. The heating prevents the coagulation of the starch constituents in the impregnation liquor and the coagulated starch particles are redissolved. In the tests conducted during the development of the process according to the invention, it was found that the problems that otherwise occur through the blocking of the filters, are no longer observed when the impregnation liquor is heated to a suitable minimum temperature. The operation not interrupted for a long period of time is guaranteed in this way. In a particular embodiment of the invention, the portion of the branching impregnation liquor is heated before filtration to a temperature in the range of 30 to 60 ° C and more particularly to a temperature of approximately 40 ° C. The tests according to the invention have shown that this temperature range is particularly advantageous for the uninterrupted and exact determination of the concentration of the impregnation medium for prolonged periods of time.
Another embodiment of the invention is characterized by the cyclic automatic rinsing of the filtration unit, more particularly with heated process water. The effect of this rinse is that residues of the impregnation liquor remaining in the filters that can not be dissolved by heating as the starch constituents are regularly washed in the waste water pipe. Uninterrupted filtration thus extends significantly. In another embodiment of the invention, the enrometric and / or potentiometric detectors are used to determine the concentration of the impregnation medium, the branched part of the impregnation liquor is optionally diluted for an adjustment pH of approximately pH 7 - in line with the requirements of the hydrogen peroxide detector - before its concentration is determined and galvanically separated from the remaining part of the liquor. impregnation. The mentioned detectors are known from the prior art and can be obtained commercially. The dilution of the impregnation liquor is necessary only for the determination of the hydrogen peroxide because the corresponding detector can only be used for hydrogen peroxide concentrations that are well below the typical concentrations in the impregnation liquor. The galvanic separation that can be carried out by a drip mechanism is of advan to obtain reliable results with certainty. This is because, with the above mentioned detectors, even a small current leak or a small vol error can lead to an error in the determination of the concentration. Other advanous embodiments of the invention are covered by the other subsidiary or dependent claims. Finally, in order to use the measured concentration values to automatically maintain the required concentration, the signals of the detectors corresponding to the measured concentrations are supplied to a control unit to replenish or replenish the impregnation means. The control unit operates advanously based on the following correlations discovered by the inventors. Whenever the fabric is changed, that is, whenever the textile to be impregnated is changed, there is generally a change in the concentration of the impregnation medium in the impregnation mixture. The change in concentration detected after 5 minutes can be used to calculate the concentration in the new equilibrium because the difference in equilibrium concentrations according to the observations and tests according to the invention is about 8 times larger than the change in concentration in the first 5 minutes. The concentration in the new equilibrium is obtained in this way and can be used to estimate the additional amount of the impregnation medium that needs to be added or the degree to which the amount of the impregnation medium to be added should be reduced. If the concentration of the impregnation medium in the new equilibrium after a change of the textile material is to be determined even more accurately, it is favorable to calculate this concentration using an exponential formula that is a function of time.The advantages of the invention lie in particular in the following: 1. Constant textile qualities are achieved through the invention because the concentration of the impregnating liquor can be maintained substantially constant, even when the textile is changed. 2. For documentation purposes, the reports can be prepared and printed or the stored data can be processed accordingly so that, for example in case of possible errors detected later, the cause can be easily located. 3. The process can be carried out with known facilities because such facilities can easily be modified. 4. The textiles produced have few defects than in the prior art because there is no more an over-concentration of hydrogen peroxide in the impregnation liquor or from here in the textile. An example of the embodiment of the invention is described in detail in the following with reference to the sole drawing. Figure 1 schematically illustrates a suitable installation for carrying out the process according to the invention and a corresponding flow diagram without the tubes and the parts without relevance for the invention. The process according to the invention can be divided into three main stages. First, the sample to be measured has to be eliminated and prepared. Then comes the measurement. Third, the liquor to be introduced is dosed based on the results obtained so that a constant concentration of the particular impregnation medium is always maintained in the impregnation compartment. The articles of the equipment for carrying out the first two mentioned stages are shown in the installation illustrated in figure 1. The last stage of the process according to the invention can be constructed in a known manner using standard elements. The liquor to be measured is removed from the impregnation compartment 1 through a bypass line 2 and heated in a heat exchanger 3 to a temperature of about 40 ° C to avoid coagulation of the residual constituents of the size in the following membrane filters 4, 5 to which the heated sample is supplied by a flow inductor 6. The part of the unfiltered excess of the liquor is returned to the impregnation compartment 1 through a bypass return line 2a. The impurities > 0.2 μp? they are removed from the sample in membrane filters 4, 5. The remaining impurities remain behind in both filters are eliminated by cyclic rinsing of the filters. For this purpose, water is introduced through a process water connection 29 into a heater 30 where it is heated to a temperature of about 60 ° C and immediately transported inside the two filters by an inductor 6 of the flow . The washed impurities are removed from the system through a waste water connection 31. The filtrate from the first membrane filter 4 is used to determine the concentration of hydrogen peroxide. The filtrate flows through a level measuring tank 7 to two dilution stations between which a pressure equilibrating the chamber 8 is arranged. The distilled water is supplied to the sample solution from a storage tank 9a through the pipe 10 while a buffer solution is supplied from a storage tank 9b through the pipe 11 so that the sample is in the range of the pH and concentration range suitable for the detector. In addition, flow inductors 12, 13 are provided at those locations where distilled water and buffer solution are introduced for the first and second dilutions. In addition, for two-point calibration of the detector, calibration solutions can be fed into the pipe from two storage tanks 14, 15, one solution having a low concentration and the other solution a high concentration of hydrogen peroxide. If the calibration does not take place, the calibration solutions are introduced in a particular order. Between the introduction of the two calibration points, the drip chamber 16 is quickly emptied at a particular time by means of the membrane pump 16a to prevent mixing of the solutions and thus accelerate the calibration. The sample now diluted twice is then supplied via a drip chamber 16 used for the galvanic separation to the detector 17 for hydrogen peroxide. The sample is then supplied by a flow inductor 18 to a collection tank 28 for the waste solution. The detector 17 is a molecularly selective, amperometric chemodetector and is commercially available from Zabs GmbH. In the detector 17, the peroxide continuously decomposes in a platinum electrode. The electric current obtained represents the measured value which is compared with the calibration values previously obtained in a following electronic device (not shown). To determine the concentration of the soda lye in the impregnation liquor, the filtrate of the second membrane filter 5 is supplied through the first channel 19a of the flow inductor and a drip chamber 20 used for the galvanic separation to a detector 21. for sodium ions and their reference system 22. The two storage tanks 24, 25 are used for the calibration of the detector, the corresponding calibration solutions are supplied to the detector 21 from the tanks 24, 25. The detector 21 is a potentiometric, ion-selective chemodetector. The concentration of the soda lye is measured via the membrane potential. After the measurement, the sample solution is supplied through the second channel 19b of the flow inductor to the aforementioned collection tank 28 for the waste solution. In addition, a reference solution of the potassium chloride has to be fed via the reservoir 23 to the reference system 22 of the sodium ion detector 21 from another storage tank 26 by means of a flow inductor 27. This solution of potassium chloride represents the reference solution for the analysis and therefore is supplied with only. If the described system is not used for the analysis, stand-by operation is essential to avoid drying and salification of the detectors 17, 21. For this purpose, a standby circulation pipe containing a standby container 35 is constructed. , inside the analysis section of detector 17 of hydrogen peroxide. From the container 35, the buffer solution is supplied continuously through the detector 17 of the hydrogen peroxide and back to the container 35 during the waiting phase. The standby operation of the soda lye detector 21 is effected by the permanent supply of the sodium chloride solution from a storage tank 36 in place of the sample solution. To ensure the operation of the soda lye detector 21 for long periods, the reference system 22 of the detector 21 has to be cleaned at regular intervals. For this purpose, the distilled water instead of the sodium chloride solution is transported through the reference system 22 from a storage tank 32, the potassium chloride deposit 23 is controlled by means of two valves 33, 34 of constriction to accelerate the rinsing procedure. In order to maintain the required concentration of the impregnation medium in the impregnation compartment at a constant level, a stronger, ie more highly concentrated, solution of the impregnation means must be continuously added. Since each textile material is different in relation to the liquor content and the liquor exchange with the moisture already adhered to the textile, the concentration of the impregnation liquor - for a constant addition - approaches a certain concentration value, which differs from according to the particular textile, until an equilibrium is reached. Other parameters, such as the mechanics, temperature and chemicals used, can also produce changes in the equilibrium concentration value of the impregnation medium. However, since these other parameters remain the same in most, they only play a minor role. Accordingly, a different amount of the impregnation means always has to be added independently of the treated textile to ensure a constant concentration in the impregnation compartment. Changes in concentration can be determined as a function of time using an exponential equation so that the equilibrium concentration can be calculated. Accordingly, there is no need for the trial and error method normally applied in practice. Whenever there is a change in the textile material, the necessary amount of concentrated liquor to be added can be calculated at a few more minutes. For this purpose, the weight of the textile material per meter (weight of fabric passing through the bath in kg / m) has to be indicated. The compensation liqueur (Q2) transported by the textile from the impregnation compartment is calculated. The amount of water (Ql) carried by the textile within the impregnation compartment is generally known or can easily be determined. Another parameter, the exchange factor (f), can be determined (by iteration) very quickly as a function of time and concentration of development. The following equation is used for this purpose:
Kt = Ko - Mc * Kc / (Ql * f * M * v + Me) * exp. { -t * ((Ql * f * M * v + Me) / Mbo)} + Mc * Kc / (Ql * f * M * v + Me), where; Kt is the concentration after a time of t minutes, Ko is the concentration at the entrance to time t = 0 minutes, Kc is the concentration of the liquor of total concentration increase (1/1), Me is the difference of the liquor by unit of time (1 / min),
Mbo is the volume of the bath, Ql is the amount of water introduced into the impregnation compartment (1 / kg), M is the weight of the textile (kg / m), v is the traveling speed of the textile (m / min) , F is the exchange factor. Once the factor f has been determined, the necessary amount of liquor of concentration increase is calculated based on the following equation: Addition (1 / min) = M * v * (Q2 - Ql + Ql * f) / Rf where :
Ql is the amount of water introduced into the impregnation compartment (1 / kg), Q2 is the transported liquor (1 / kg), Rf is the ipso of concentration increase (concentration in the liquor of concentration / concentration increase required, the total concentration increase is calculated as Dq = Ql -02), M = textile weight (kg / m), v = travel speed (m / min), f = exchange factor. Since the control can be performed continuously, the required concentration of the impregnation means in the impregnation compartment can be kept constant, even when the textile material is changed.
LIST OF REFERENCE NUMBERS 1 impregnation chamber 2 bypass line 2a bypass return line 3 heat exchanger (40 ° C) 4 first membrane filter 5 second membrane filter 6 flow inductor 7 level 8 chamber measuring tank pressure equalization 9a storage tank for distilled water 9b storage tank for buffer solution 10 pipe for distilled water 11 pipe for buffer solution 12 flow inductor 13 flow inductor 14 storage tank for calibration solution (low concentration of H2O2) 15 storage tank for calibration solution (high concentration of H202) 16 drip chamber 16a membrane pump 17 detector for hydrogen peroxide 18 flow inductor 19a first channel of the flow inductor 19b second channel of the flow inductor 20 drip chamber 21 sodium lye detector 22 detector reference system for l Soda 23 tank for the potassium chloride solution
24 storage tank for the calibration solution (low NaOH concentration) 25 storage tank for the calibration solution (high concentration of NaOH) 26 storage tank for the potassium chloride solution 27 flow inductor 28 collection tank 29 process water pipe 30 heater (60 ° C) 31 waste water connection 32 storage tank for distilled water
33 constriction valve 34 constriction valve 35 holding container 36 storage tank for the sodium chloride solution.