AUTOMATED COLOR ANALYSIS AND COLOR CONTROL OF DYEING INDUSTRY

AUTOMATED COLOR ANALYSIS AND CONTROL OF DYE HOUSE

It is worth remembering that in the past the assessment of color reproduction was exclusively entrusted to the ability and to the experience of the eye of highly skilled operators working on the color kitchen, whose judgment, however, could be influenced by a number of physical, physiological and psychological restrictions. The success and the development of electronics have deeply transformed the color control task thanks to the introduction of new measuring instruments, which have allowed definitely scientific and objective assessment.

All the systems currently available on the market have basically the same fundamental structure and differ only in their performance and in the algorithms adopted for color analysis. These systems generally feature:

1. A spectrophotometer, which measures the different spectral components of the sample analyzed. Today the measurement is carried out by means of a xenon flash, a prism separating the chromatic components and a CCD sensor (of the type used for modern solid state television cameras that have only a single row of light-sensitive elements or pixels), which reads the intensity of all the components simultaneously;

2. A standard computer, connected to a spectrophotometer like a simple peripheral unit.

The software carries out the processes and defines the functions of the system. It represents an interesting field of competition and makes the real difference between the various systems.

In brief, the software includes the following functions:

- Algorithms for color analysis (processing of the data measured by the spectrophotometer to recognize the colorimetric features);

- Preparation of recipes, i.e. the combination of several base dyestuffs to obtain the desired color by accurately mixing and distributing them; the color to be matched is suggested to the computer by reading the reference sample with the spectrophotometer;

- Assessment of the color differences, i.e. the assessment of the distance between the colours of the two samples in the colour table, expressed in different systems of coordinates;

- Correction of the recipes, i.e. the analysis of the difference between the colour obtained with the machine and the reference colour, and the calculation of dye distributions to improve the dyeing result;

- Control and storage of references and recipes for future retrieval;

- Control and storage of dyestuffs and textile substrates;

- Different types of algorithms to match the colour table to visual assessment and to the type of source used (so that the differences that the human eye has perceived as matching can generate assessments of the same degree);

- Selection of the recipe which better matches the sample, the costs and fastness;

- Other valuable functions;

Automatic devices for the preparation of recipes are now considered crucial for all well organized and efficient dyeing mills.

BENEFITS

Repeatability of procedures

Reduction of sampling times

Reduction of sampling costs

Reduction of dyestuff consumption

Possibility to assess the dyeing efficiency

Impartiality of the assessment

Better control of colour archives

Cost control

Quality improvement

LIMITS

Integration problems

Need for special training

Needs for organizational changes

Need for preparation steps

There are really many reasons justifying the investments in automation which can be carried out at different levels and consequently having different costs; it is worth remembering that even the most sophisticated automated systems applied to any production cycle, turn out to be useless if the information coming from the laboratory is scarcely reliable or even incorrect.

To obtain reliable indications, the laboratory and the production units must first of all be equipped with machines and tools working on the basis of the same operating concept (i.e. the laboratory must be in a condition to reproduce the same operating conditions as during the production process).

With reference to the above-mentioned considerations, it is worth mentioning that manufacturers of color matching systems have studied the reproducibility of measures, based on very precise and repeatable calibrating procedures. The dyestuffs must be accurately dosed both in the laboratory and in the dye house. As far as this latter is concerned, no real innovations have been introduced, due also to the high technological level reached by modern automatic colour kitchens; the only real innovations have generated an uninterrupted improvement of the dosing techniques for dyestuffs in different forms (liquid, powder, paste), leading to very accurate results also on large quantities.

The multi-pipette volumetric dosing system is meeting with success in modern automated dyeing laboratories since it eliminates all the residual limits of the standard single-pipette volumetric system.

Here are the main benefits ensured by multi-pipette systems:

1. The elimination of intermediate pipette washing when changing the dye or the substrate, which considerably reduces the operating times necessary for each single dosing procedure and, at the same time, up to a 40/50% increase in productivity (compared to single-pipette systems).

2. The thorough elimination of any residual contamination risk, which could occur in particular with some products and dyes even after accurate washing of the pipette.

Very important also are the benefits deriving from the use of special pipettes studied for the particular properties of some products (viscosity, precision, speed) which give excellent technical results. Another important issue is also represented by the application of a gravimetric system for dosing testing, which completely eliminates any residual doubt concerning the quantities delivered during each single delivery of the pipettes. Operating data are registered by means of a printer, while an automatic self-calibrating system guarantees a continuous check-up of each single pipette.

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