Colour can be defined as the effect on the brain of an observer when an object is viewed in the presence of a light source.
In textile industries, the desired color is obtained by mixing three or four dyes. The most important problem in the industry is how to arrive at the perfect match to the customer’s samples using the minimum amount of chemicals and dyes.
This job is normally attended by an expert dyeing master who decides the three or four dyes color recipe to reproduce a given shade. The dyeing master maintains the record of his experience in “shade Bank” and selects one of the color recipes, which may be close to the standard.
He, then, makes necessary changes by trial and error method to obtain the exact match.most appropriate recipe depending on the cost of production and quality of the products required. This technique is known as Computer Aided Color Matching.
A computer color matching system comprises of,
- A spectrophotometer.
- A personal computer.
- A color matching software.
A spectrophotometer is an instrument which measures the color of an object. To measure the color of an object we use reflectance spectrophotometer. The spectrophotometer consists of the light source, integrating sphere, dispersion device, detector, signal processor or microprocessor.
The light source illuminates the specimen. The light source used in spectrophotometers are tungsten halogen, xenon flash, light emitting diode, emits the light in the visible region.
It is coated with barium sulfate, to simulate the conditions of daylight
Dispersion device (prism): in Toit splits the into various colors.
A sensor which detects the energy of the light source that is reflected back by an object.
Signal processor or microprocessor:
I n optical sensor the electrical signal is generated proportional to light energy reflected from the sample. These electrical signals corresponding to different wavelengths are fed to the microprocessor.
The microprocessor converts the analog signal from the optical sensor into digital form to compute and displays several color parameters following CIE recommendations. (CIE- Commission International del’Eclairage or International Commission on Illumination). For textile Samples, the measurements in a spectral range from 400 to 700nm at the 20nm interval is used.
The colour matching software consist of the following modules / programmes:
All QA applications involve comparing batches against a standard.
QA functions in the following applications.
-colour difference assessment for approved standard and a batch
-whiteness / yellowness index for assessing whiteness of OBA treated samples and yellowness for white textile substrates.
-pass / fail status for batch production
K/S Data generation:
Generate K/S data using representative substrates and processes. Analyses K/S data outputs for various colorant properties
Match new as well as current shades and obtain formulation for cost saving. It performs colour matching for a given target using selected dyes.
Use batch correction for laboratory and production correction. It will help in reducing trail and error method.
Use colour maker program for generating new shades.
Stores all lab and productions shades into computer.
Use file management for creating a user data. keep back up of data files using this program.
Select instrument using setup. Calibrate spectrophotometer and set communication codes between computer and instrument.the final delta E value calculated by ccm software.