It is a big pleasure to follow after more than 25 years, the actual and sudden interest to improve the quality of measurements from the coloration of a dye bath in order to obtain the so called "exhaustion curves" or to see graphically the kinetical behavior of the dyes during a dyeing process as function of the dyeing process parameters, normally temperature. That means the recognition of the relationship kinetic <-> levelness…

At the end of the 60ies we have tried to convince the industry about the importance of the rate of adsorption of the dyes in relation with the final levelness of the dyed material. This relation was – and is – crucial for dyeing processes in which no classical migration happens. With my team in Basle, we have proposed the called "Sandocryl calculator" for prediction of the adjustment of dyeing processes (heat period) in the dyeing of Acrylic fibers with cationic dyes.

In this time, actual promoters of measurements of exhaustion curves insisted on the fact that for Acrylic fibers, the levelness depends of the degree of fiber saturation, and Beckmann from Bayer was proposing methods for calculation of retarders quantities, using Factors, and not paying attention to our claims concerning kinetics. The approach of Beckmann was to add to the dyeing system the biggest possible quantity of cationic retarders, defining the limits on order to avoid addition of cations – proceeding of the dyestuffs as well as of the retarders – overpassing the saturation limits of the used fibers. Hoffmann tries today to find a compromise…

Our next step was "Suproma strategy" for dispersed dyes on Polyesther fibers, first at all developed for the dyeing with bigmolecular dyestuffs, presenting the best sublimation properties, but not presenting sufficient migration properties. The answer was again: controlled adsorption.

The reaction has been called "Resolin S Process" with some link to kinetical approach.

Our next step was "The CONTACT" as unit to be used in the place of time, in order to get common parameters for each kind of dyeing machine.

A very good approach (Rüttiger from BASF) was the so-called "critical rate of dyeing" related to each type of dyeing machines. He was very close to the meaning of CONTACT.

From this time and as logical consequence, I have developed more accurately the way to design mathematically (in order to achieve automatically in a computer a dyeing process with a profile adjusted to the behavior of each dyeing system - fiber/dye class). The main goal has been: give me a good kinetical curve and I will predict you which have to be the parameters to be inserted in the dyeing program.

The question was which kind of measurement method could represent the best balance between practical use for industrial purposes and enough accuracy in order to represent the relationship "energy introduced in the system" and "impact on the kinetic of the dye adsorption".

Following facts have been very significant this respect:

1. Off-line Photometrical control of dye bath after very short dyeing cycles (user for pantyhose, stocks, sockets, etc.) allowing the calculation of bath reinforcements. Used on machines of Bellmann as well as on the Teintofix dyeing machine by Helliot.
2. The big success in the market of the automatic on line dye bath survey with photoelectric cells giving on-line orders managing the rate of heating (Colorex by Hanau, Teintoprog by Comeureg, Termoregulateur by Leanord). Specially used for dyeing Acrylics.
3. Off-line Photometrical survey of Padding Liquors in order to manage the dye additions in the continuous dyeing processes (TRIATEX). Specially used with vat dyes.
4. Direct spectrophotometrical measurement of dye bath in exhaustion dyeing processes, taking samples, diluting with solvents and assuring a correct calculation at constant (room) temperature of the real dye quantity, based on calibration values characteristics for the dyes analyzed (Color-Analyzer from DATACOLOR).
5. Analysis of Dye Bath using Capillary Electrophoresis (Leeds)
6. Real Time Data Acquisition in Batch Dyeing using a FIA [Fluid Injection Analyzer for taking and keeping to constant temperature and pH dye bath samples] together with a HP Spectrophotometer and a Mathis Labor Piece Dyeing Machine. (NCSU-Raleigh)
7. On-line Color measurement of dye bath using the pulsing direct Photoacustic-spectroscopy. It takes advantage of the photothermical Effect. Actually in collaboration with THEN (Institute of the Gerhard-Mercator-Uni-Duisburg,DTNW-Krefeld).
8. Nobbs, Leeds University, has developed the first generation of a Longclose Yarn Dyeing laboratory Machine with direct colorimetric measurement of dye bath, with the goal online control of processes during the dyeing. In some sense, moving again in the same direction as 10-20 years ago with the devices 2
9. Scottish College of Textiles: using the dyeing machine mentioned under 8, working with the same final goal as 8. Till now good results with cationic dyes on acrylics, as we know from the devices 2.

 The devices 1-3 are simple colorimetric devices, working with filters.

The devices 1 and 3 working off-line, have allowed to use, in some cases, solvents for allowing to be near to the Lambert and Beer law (getting near monomolecular solutions).

The devices under 2 don’t need calibration data from the used dyes, working by computation between blank and colored dye bath samples. For quantitative determination of real dye concentration they don't respond to the Lambert and Beer law, but industrially have satisfied a lot of requirements. The success of these devices used controlling on line dyeing processes, specially batch dyeing on acrylics have been very well accepted in a lot of dye houses. It was indubitable that the commands elaborated by the variations in Color measurement were very useful. The life of these devices was related with the importance of acrylic dyeing in Europe, especially in Germany and Italy.

The collaboration Comeureg and Institute Textile de France, with my personal support, has allowed to check the possibility to use the sensor of the Teintoprog for on line measurements of dye bath. A complete development program has been realized in order to compare dyeing processes calculated on basis of these measurement values with dyeing processes calculated using spectrophotometrical measurements of the same dyeing samples. Using complex regression analysis has been possible to correct the direct measurement values in such a way, that the profiles of the corresponding dyeing cycles have been equivalent. The big advantage of the system is the fact that no calibration values are necessary and, as consequence, from dye baths - even which unknown dye composition - have always been possible to predict the parametering of an optimized dyeing processed. My software has been adapted in order to be used also going out from such kind of measurement. The new device for the on line measurement of dyeing baths, including my software for correction of the measurements has been called TEINTOLAB.

An additional new approach has been introduced in the TEINTOLAB: in order to overcome all the limitations presented by the devices working with 3 light filters (the typical approach in order to be able to measure trichromies…) concerning recipes avoiding metamerism, the TEINTOLAB works analyzing the dye bath with 4 filter. In this way, "dyestuffs" will be not direct analyzed, but "colorations", as real responsible for the homogeneity of Colors on textiles (leveling).

Special attention has been also paid to the use of this measurement device for dye baths with disperse dyes on synthetic fibers, especially Polyesther fibers. The whole strategy has been based on the fact that the Teintolab is able to measure particles, allowing additionally to measure UV-absorbers, Optical brighteners, etc. Analog to calibration curves for the spectrophotometrical measurement, reference curves have been calculated and used for on line process parametering, once the composition of the corresponding dyeing recipe has been calculated by Color matching.

The methods resp. devices 4-7 are based on real spectrophotometrical calculations, using previous memorized data (calibration values) of the analyzed dyes. From the obtained exhaustion values of each single dye is also possible to use my software for evaluation in order to establish the parametering of the corresponding optimized dyeing process.

In each case (devices 2 or 4-7 [see below]), the parametering can include not only temperature profiles, but much more important, including dosing profiles for dyes, chemicals, etc., provided the original dyeing process for conducting the measurements, fulfills the necessary requirements, using the corresponding metering devices and keeping the relationship between quantity of thermal/chemical energy supplied to the system and degree of exhaustion achieved.

The device 4 has been able to dissolve each sample with adequate solvents in order to allow a very good calculation of the real dye concentration in each sample. Problem: if samples will be taken in very short time periods, big changes of liquor ratio could influence negatively the validity of the analyzed kinetics. If the sampling time will be reduced, a lot of information could be lost in the more important "no-sampling" periods. But it was possible for the first time (not using Flow Injection Analysis, as Beck and McGregor claim) to calculate on-line dye concentrations in a dye bath with disperse dyes. It was an very interesting device for R&D purposes, not really to be used in the automation of dye houses.

The methods and devices used in 5-7 allow to use very small samples, with the corresponding low impact in the variation of liquor ratio, even taking samples at very short time periods. The use of my software for parametering dyeing cycles according to the obtained exhaustion curves, provide the best method for evaluation of the measurement results, avoiding to use very subjective point of views by the observation of the obtained graphics.

The devices 8 and 9 are again trying to work on line like the devices 2. They use the temperature as only parameter for a complete control (useful for basic and acrylics), with problems in dyeing systems in which other parameters are much more important for control of the rate of adsorption (wool and polyamide with acid, sulfonated premets and reactive dyes, or cellulosic fibers in general, etc.). An additional handicap: no using the capacities of the parameter "Contact" in the place of "time" is difficult to establish limit values for the adsorption kinetic in order to ensure a tolerated leveling.

They are following main industrial situations:

The additional factor choosing the  tools 1, 2 or 3 is also the relation value added/cost of the investment as well as working cost of the adopted method, as well as the degree of knowledge concerning interpretation of exhaustion curves.

An additional remark: In order to make possible the parametering of dyeing processes going out from exhaustion curves, the most important step is the programming of the dyeing taken as basis for the measurements of the kinetical behavior of the dyes on the used substrate.

The attempt to develop a real loop system, no needing dyeing programs, but creating on the spot the necessary commands for regulation of parameters responsible of the dye adsorption is certainly very attractive from the point of view of R&D, has to face additionally to the temperature, additions of acid, alkali, electrolyte, etc. in order to offer the necessary industrial flexibility. Another aspect would be the cost of dyeing programmers with incorporated light adsorption measurement devices.

We will be glad to collaborate with each kind of method, because the final goal of all these approaches is to increase the profit of the using customer, decreasing costs. And mainly: DECREASING COST OF THE NO-QUALITY (corrections) and IMPROVING THE ON TIME DELIVERY. The CATEX parametering method and the Autoregulation use on the dyeing equipments are the way to take profit from each used measurement method.