How to Reduce Variables in Fiber Reactive Dyeing
I’ve been working with fiber reactive dyes for over sixty years now. Still, I get questions about variability of fiber reactive dyeing. Why the shade doesn’t repeat in dyeing from lot to lot? Why dye levels are sometimes uneven? And, how do we meet fastness requirements? New technologies came into the textile market to help determine the issue factors. Keen-eyed technicians can spot inconsistencies and improvement areas. However, one of the most effective ways to reduce variables in reactive dyeing is to start with clean fabric.
There are many new technological developments in the textile industry. Using a computer, like a spectrophotometer, to read the color hue and shade depth, gives specific color data. New chemistry in fiber reactive dyes uses less salt and offers better repeatability. But in the end, these are only tools to assist us in obtaining our final goal.
Therefore, we always start at the beginning — the fabric or yarn for dyeing. Production tends to be cost-driven. Everyone wants to shorten the process and reduce water, energy, and chemical cost. When in fact, if the fabric wasn’t well prepared, all other processes will suffer.
Cellulosic fibers contain many impurities which we need to remove. Depending on the source, we want to eliminate dirt, oils, motes, and metals, among others. My co-contributor, Angelo, speaks in-depth about the preparation of cotton cellulose fibers and removing impurities. We’ll look now at the best practices for reduce variables in fiber dyeing processes.
Monitoring Liquor Use
New machinery strives to increase process speed and lower the liquor ratios. This is all in effort to reduce water consumption and energy costs. Most all scouring, half-bleach, and bleach formulas measure by gallons per liter (g/l) for chemicals. To get desired results, you need the amount of surfactant and water at or less than the liquor ratio 1:8. The surfactant used in the preparation procedure must be multi-functional. We need to use a low-foaming detergent in preparation. An APEO-free product works best. An emulsifying package will also help here. Extracting properties to remove impurities is also necessary.
Maintaining Fiber Absorbency
The fabric is a canvas for the painting. The canvas must be absorbent and free of impurities. Choosing the right surfactant will improve absorbency of the fabric. This is how to achieve level dyeing and get repeatability. Best results come by adding alkali with a temperature of at least 80°C (175°F) to remove wax and oils. Proper rinsing will prevent redisposition of impurities on the fabric. Failing to rinse well is one of the most common mistakes made in preparation.
Once you have prepped the fabric, then we select a dye to match the desired shade. We need to remember the spectrophotometer is only a tool. The color matching programs select the best formula to match the shade based on data. They do not account for the ratio of sensitivity to liquor, diffusion coefficient, absorption, reaction rate, fastness properties, etc. of the dyes selected. A color technician can make up for these shortcomings. Working with an experienced technician will help you find the best solution for your process. Their expertise will ensure dye combinations will dye level and repeat from lot to lot.
Beware of Cheap Costs
There are formulations where no matter how you try to work them, will not repeat, dye evenly, or give the required fastness process. The most economical formulation doesn’t always give the best formulation for total process cost. This is another common mistake. Dyestuff manufacturers go to great extent to develop and produce new dyes. These are not as sensitive to variables in the actual dye process like liquor ratio, alkali and electrolyte concentration, dyeing time, and temperature. I’ll talk about these more in depth in the next post. Significant improvements came with these new chemistries. Yet, we still have to follow the basics to achieve optimum performance. It’s also worth mentioning, the most economical solution isn’t always in the best interest of the environment. This is a big concern for textile manufacturers under bluesign®, ISO, Okeo-Tex®, and other regulations.
We only discussed the fabric preparation and dye selection processes in this article. We’ll discuss further the actual variables in the dyeing process. We’ll look at rinsing, neutralization, soaping, and drying processes which are just as critical. What we can conclude so far: Preparing for fabric processing is the first step to lower costs, ensure quality, and achieve uniformity.
Looking to get started with a clean slate? Discover the best preparation formulation for you from our textile chemical portfolio.