EP0319361B1 - Method and apparatus for monitoring a dye bath - Google Patents

Description

The invention relates to the treatment, in particular textile, in continuous scrolling by passage through a colored impregnation bath. It relates more particularly to the dyeing of textile fabrics offshore by padding a dye bath and then fixing the dyes.

The treatments of materials in continuous movement, by passing said materials through an impregnation bath, are commonly used in all kinds of industry. Some of these treatments aim to give the materials a certain homogeneous and uniform coloring over their entire length. For example in document DE.A. 1,610,995 the impregnation bath is continuously and automatically supplied with a concentrated solution and the overall concentration of the bath is continuously adjusted, by metric pH, using a dilute bath.
However, it has been observed, in particular when dyeing off a piece of a textile material, a heterogeneity in the coloring of the material between the start and the rest of the piece, and this while the colored impregnation bath is identical and renewed throughout the dyeing period. This heterogeneity which can be easily corrected leads to eliminating, during certain dyes, the beginning of the pieces thus dyed, which can go up to several hundred meters of fabric.
this phenomenon can be explained by a difference in the substantivity of certain colored constituents used in the impregnation bath for the material. Thus at the start of the impregnation, one of the constituents would rise in greater quantity on the material compared to the other constituents, the material would then have a more marked coloring in this constituent while, in the opposite direction, the concentration of the bath impregnation in this constituent would decrease; the contribution of renewed bath and the reduction of the concentration of the bath in this constituent would lead, after a certain time, to an equilibrium, or at least to deviations whose result would be less than the perception of the eye.

However, we have found, and this is what is the subject of the invention, a method of regulating a colored impregnation bath for the treatment of a material in continuous movement which overcomes the drawback observed.

As is known from document FR.A. 2,307,074 this method consists in measuring by photocolorimetry a value proportional to the concentration of the bath - the transparency in the case of the aforementioned document - at determined time intervals and in comparing the values obtained with reference values corresponding to the initial bath before impregnation of the material.

Characteristically according to the invention, said value is measured proportional to the concentration of the bath or the concentration itself for each colored constituent, and the values obtained for each colored constituent are compared with the reference values corresponding to the initial bath before impregnation of the material, and when the difference found for a given colored constituent reaches a certain threshold, a predetermined quantity of a correction solution is added to the impregnation bath.

When the difference observed is negative, that is to say when the concentration of the bath at a given instant is lower than that of the initial bath, the correction solution consists in a concentrated solution of the colored component.

When the difference observed is positive, that is to say when the concentration of the bath at a given instant is higher than that of the initial bath, the solution consists in a dilute solution of the colored constituent, even a solution free of colored constituent .

Thus when the impregnation bath undergoes a variation for one of its colored constituents, due to a difference in the substance of the material passing through the bath, for said constituent, the concentration of the bath in this constituent is immediately corrected by adding correction solution to the bath. The correction in question depends on the one hand on the threshold corresponding to the minimum value of the difference measured and on the other hand on the predetermined quantity of the solution of correction. Each of these parameters is determined so that the correction occurs so that there is no visual variation in coloring on the material.

As we have been able to understand on reading what has just been said, the objective of the process is to make the concentration of the bath in each of the colored constituents as constant as possible, and from the start of the impregnation.

Preferably, the measurement of the concentration of the bath or of a value proportional to the concentration of the bath is carried out by conversion into an electrical signal of a light flux passing through a volume of circulating bath. The electrical signal is notably obtained by, at least, a photodetector placed at the output of a filter illuminated by the light flux passing through the volume of the circulating bath. It was determined that the measurement of the bath or of a value proportional to the concentration of the bath was carried out under good, reproducible conditions, when it was based on the measurement of four electrical signals coming from the photodetectors placed at the outlet of four filters. , whose transmission spectra have maximum peaks which together cover the range of wavelengths between 400 and 700 nanometers.

The method of the invention applies in particular when the colored bath is a dyeing bath of a textile material, comprising several dyes, at least one of which has, for said material, a substantivity, at low temperature, greater than the other.

It may be advantageous, in particular for the correction to be faster, to carry out the measurement on the colored bath corresponding to the excess bath, intended to be recycled, after the impregnation of the material. This excess bath is, for example, the bath recovered immediately after passage of the tissue between the squeezing cylinders and before return of said bath to the impregnation tank. This excess bath is that which, having been carried away by the tissue, is extracted from it; it is therefore the bath which is the most depleted in the colored constituent (s) having the most substantivity for the fabric.

It is another object of the invention to protect a device specially designed for carrying out the aforementioned process. As is known from document FR.A. 2,307,074, this device comprises a photocolorimetric sensor comprising a measurement chamber in which the colored bath circulates, an optical unit consisting at least of a white light source placed on one side of the chamber and processing means capable of measuring, from the light flux transmitted by the colored bath, a value proportional to the concentration of the bath, and means for comparing the measured value at determined time intervals with respect to the reference value corresponding to the initial bath.

Typically, according to the invention, the processing means are capable of measuring said value proportional to the concentration of the bath or else the concentration itself in each colored component; the comparison means are capable of carrying out the comparison of the measured value for a given component with respect to the reference value of the same component; in addition, the device comprises injection means, actuated when the comparison carried out by the comparison means shows for a colored constituent a difference equal to or greater than a certain threshold, and controlling the injection into the colored bath of a quantity solution of a correction solution.

According to a preferred embodiment of the device of the invention, the optical unit comprises a set of four filters, the transmission spectra of which have maximum peaks which together cover the range of wavelengths between 400 and 700 nanometers.

The invention will be better understood on reading the description which will now be made of an embodiment of the preferred version of the regulation device, illustrated by the appended drawing in which the single figure is a schematic view of said device.

The fabric 1, coming from a food not shown, plunges into the dye bath 2, contained in the bacholle 3; it is supported by the three detour rollers, the first 4 at the entrance, the second 5 at the bottom of the bacholle 3 and the third 6 at the exit. The fabric 1, impregnated with the dye bath 2, then passes between the two expressing cylinders 7,8, between which pressure is exerted by any known means. The coating of the rolls 7, 8 and the pressure exerted are defined so that the fabric 1, after expressing, comprises a determined quantity of the dye bath 2, this quantity being uniform over time and homogeneous throughout the width of the fabric 1. After this impregnation, the fabric is directed into a heat treatment and / or vaporization enclosure where the dyes are fixed to the material constituting the fabric.

The most downstream part of the bacholle 3, in the direction of movement of the fabric 1 represented in the figure by the arrow D, is terminated by a bend 9 in the form of a gutter extending near the lower cylinder 8. This gutter 9 is intended to collect the excess bath, after expressing, carried away by the tissue 1.

Just at the entrance of the expressing cylinders, at the level of the lower cylinder 8 and under the plane of the fabric 1, a ramp 10 has been placed transversely, the bottom of which is slightly inclined up to the conduit 11 connecting said ramp 10 and the bacholle 3. Thus the excess weight of the fabric 1 during the expression is collected at least in part in the ramp 10, flows naturally in the conduit 11 and returns to the bacholle 3.

The conduit 11 passes into a measurement chamber 12. This chamber 12 is connected by a double set 13, 14 of optical fibers to a block optics 15, comprising two parts 16 and 17. In the first part 16, a white light source 18 and its associated optics 19 illuminate the input 20 of the first set of fibers 13. In the second part 17, the output 21 of the second fiber set 14 is directed to four filters, each one associated with photodiodes and converters, transforming the light flux transmitted through the corresponding filter into an electrical signal.

The four filters are chosen so that their transmission spectra have maximum peaks which together cover the range of wavelengths between 400 and 700 nanometers.

The measurement chamber 12 comprises the conduit 11 which passes through it, the outlet 22 of the first set of fibers 13 and the inlet 23 of the second set of fibers 14. The outlet 22 and the inlet 23 are positioned opposite one of the other and enter the duct 11.

The converters are connected to an assembly 24 for processing electrical signals, the operation of which will be explained later, which controls the use of one and / or the other of the three injection nozzles 25, 26, 27, each nozzles is directed towards the inside of the bacholle 3 and is supplied with the aid of a concentrated colored solution, corresponding to one of the dyes entering into the composition of the dye.

In practice, it may be advantageous to provide five nozzles, corresponding, for a three-color dye, to the three concentrated solutions for the three basic dyes, to a concentrated solution of the shading dye and to a dilution solution free of dye.

The implementation of the method of the invention and the operation of the device will be described in the following example of dyeing a piece of cotton fabric using an impregnation bath 2 comprising three direct dyes including light yellow diazol 2JS. This dye has a very important substantivity for cotton at low temperature, which results, when the fabric is immersed in such an impregnation bath, by a rise in light diazol yellow 2JS on the fabric more important than the concentration of this dye in the bath.

The piece of fabric 1 is engaged in the bacholle 3 and plunges into the bath 2 passes between the expressing cylinders 7 and 8, where it is expressed so as to carry around 40% of its weight in the dye bath. The excess bath carried away by the fabric and coming from the pressing by the cylinders 7 and 8 is collected in the ramp 10 and flows into the conduit 11.

The light source 18 associated with its optics 19 sends to the input 20 of the first set of optical fibers 13 a light flux which is directed into the measurement chamber 12. In the chamber 12, this flux, coming from the output 22 of the set of fibers 13 passes through the dye bath which circulates in the conduit 11; the incident luminous flux undergoes an absorption which is a function of the dye concentration of the bath, for a given wavelength of light. The flow after passing through the bath, is taken up by the second set of fibers, is separated into four separate channels where it passes through each of the four filters. The purpose of passing over the filters is to reveal the specific luminous flux of each dye contained in the bath as a function of its wavelength. The photodetectors, the converters and the processing unit 24 convert the light intensities into standardized currents (from 4 to 20 mA).

Before and before any passage of the fabric, the initial dye bath 2 was introduced into the conduit 11. The values of the currents obtained, proportional to the concentration of the bath in each of its dyes, were the reference values.

During the dyeing, the recycling bath originating from the tissue expression is depleted in light diazol yellow 2JS. This depletion is noted by a variation in the value of the current corresponding to this dye. When the difference observed between the measured value, at a given instant, and the reference value reaches a predetermined threshold, for example 0.5%, the processing assembly 24 controls the injection by the nozzle 25 of a solution colored containing only dye yellow diazol light 2JS and at a higher concentration than that of bath 2. This injection increases the concentration of bath 2 in yellow diazol light 2JS and thereby corrects the depletion observed.

The exact parameters are to be determined for the skilled person for an installation as a function of the volume of bath in the bacholle 3, of the take-up rate after passage between the expressing cylinders 7,8 and for a dye pass according to the composition of the dye bath. It is important that the correction of the bath, by injection of a concentrated dye solution having a greater substantivity for the tissue, take place before the difference observed has resulted in a variation in the color of the tissue perceptible to the eye.

The invention is not limited to the embodiment which has just been described by way of example. In particular, the measurement of the bath can be made directly on the bath 2 contained in the bacholle 3, and not on the excess recycling bath. Likewise, what has been said for the dyeing of fabrics is also valid for the dyeing of threads in continuous movement using other means of impregnation and other means of expression.

The invention is also not limited to the use of a colored impregnation bath, one of the colored constituents of which is more substantial than the others for the material to be treated. It applies whenever, for this reason or for another, the colored impregnation bath varies in the concentration, in one or the other of its colored constituents. This may be the case when the means of expression are means using compressed air, which is charged with moisture and concentrates the recycling bath; the solution to be injected must then be a solution having a concentration lower than that of the initial bath, or even a solution free of dye.

Claims (10)

1. Process for controlling a coloured impregnating bath (2) for the treatment of a material passing through continuously, according to which a value proportional to the concentration of the bath (2) is measured by photocolorimetry at determined time intervals and the values obtained are compared with the reference values corresponding to the initial bath before impregnation of the material, characterised in that the said value which is proportional to the concentration of the bath or the concentration of the bath itself is measured in the case of each coloured constituent, the values obtained for each coloured constituent are compared with the reference values corresponding to the initial bath and when the difference found in the case of a given coloured constituent reaches a certain threshold a predetermined quantity of a correcting solution is added to the impregnating bath (2).
2. Process according to Claim 1, characterised in that when the difference found is negative the correcting solution is a concentrated solution of the said coloured constituent.
3. Process according to Claim 1, characterised in that when the difference found is positive the correcting solution is a dilute solution of the said coloured constituent or a solution free from the said constituent.
4. Process according to one of Claims 1 to 3, characterised in that the measurement of the concentration of the bath (2) or a value proportional to the concentration of the bath (2) is performed by converting into an electrical signal a luminous flux passing through a volume of bath (2) in circulation.
5. Process according to Claim 4, characterised in that the electrical signal is obtained by at least one photodetector placed at the exit of a filter illuminated by the luminous flux passing through the volume of bath in circulation (2).
6. Process according to Claim 5, characterised in that the measurement of the concentration of the bath (2) or of a value proportional to the concentration of the bath (2) is based on the measurement of four electrical signals originating from the photodetectors placed at the exit of four filters whose transmission spectra exhibit maximum peaks which together cover the wavelength range of between 400 and 700 nanometres.
7. Process according to Claim 1, characterised in that the coloured bath is a bath for dyeing a textile material, comprising a number of dyes at least one of which exhibits in the case of the said material a substantivity, at low temperature, greater than the others.
8. Process according to Claim 1, characterised in that the coloured bath in which the measurement is performed at determined time intervals corresponds to the excess bath intended to be recycled after impregnation of the material.
9. Controlling device for making use of the process according to Claim 1, which comprises a photocolorimetric sensor comprising a measuring chamber (12) in which the coloured bath circulates, an optical block (15) consisting of at least one source of white light (18) placed at one side of the chamber (12) and processing means capable of measuring, from the luminous flux transmitted by the coloured bath, a value proportional to the concentration of the bath and, on the other hand, means for comparing the measured value at determined time intervals in relation to the reference value corresponding to the initial bath, characterised in that the processing means are capable of measuring the said value which is proportional to the concentration of the bath or the concentration itself in each of the coloured constituents, in that the means of comparison are capable of performing the comparison of the measured value in the case of a given constituent in relation to the reference value of the same constituent and in that it comprises injection means (25) actuated when the comparison performed by the means of comparison reveals in the case of a given constituent a difference which is equal to or greater than a certain threshold, and commanding the injection into the coloured bath of a predetermined quantity of a correcting solution.
10. Device according to Claim 9, characterised in that the optical block (15) comprises a set of four filters, whose transmission spectra exhibit maximum peaks which together cover the wavelength range of between 400 and 700 nanometres.

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