What can we do to improve the aesthetics or the resistance of a product? How can we improve a tissue? It depends on the fibers of the that is composed, we will perform before and after operations of the spinning process in one form or another.
To be able to dye, print or add finishes to the fabric, it is essential to carry out the so-called “preparation operations”. We must remove impurities and anything that may make it difficult for the application of dyes or finishes.
There are two types of impurities that can be found in fibers: natural ones, which are those that the plant of origin carries or those that the animal produces, and added ones, which are those that are added in the spinning process (gums, oils…).
The vegetable origin fibers, you can make a singeing in which the fibres protruding from the fabric are removed (the lint) bringing the fabric closer to a flame. We can also desizing (remove impurities added by us to the tissues) and desizing (eliminate impurities that cannot be dissolved in water). As we have commented in the section of fibers, cotton can be made a mercerized, so that the thread is brighter, dyed better and is inflate the fibers, thus improving their resistance.
On the other hand, animal origin fibres such as wool or silk need to remove fat and waxes with detergents and de-caking agents before dyeing or weaving.
All fabrics made with natural fibres need to be bleached to be able to dye them in light or white colours (let’s imagine that we want a white or beige jute fabric, we must bleach it first, as the natural colour of the jute is brown.
We have all heard of the “optical white”, which we distinguish from the “natural white” if we take an ultraviolet light (the first will shine and the second will not). Optical brightening aims to improve the degree of white.
An important improvement we can make to the textile material is dyeing. We can dye the fibres, the thread, the fabric or the finished garment. There are two ways of doing this:
- By exhaustion: The textile material is put in contact with the dye until it is exhausted.
- By impregnation: A garment is impregnated with dye and then passed through two cylinders to drain the excess dye. Finally, the fabric is washed.
Parameters such as pH, speed, temperature or time influence the dyeing. The dye depends on these and more parameters, so it is very frequent that there are defects in it. What are the most common? Lack of uniformity, local stains, light spots…
If we only want a localised coloration, instead of dyeing the entire fabric, we use the technique of stamping.
What steps must be taken to get a good stamping?
- Prepare the fabric (mercerized, bleached, degreased…)
- Prepare the colored paste that we are going to use.
- Prepare the machine and spread color.
- Fixation (by heat, vaporized or other method) of the color.
- Washing and operations according to the stamping process.
In order to stamp the pastes correctly, it is very important that it has a correct viscosity, since otherwise the pattern may not be well profiled, or it may filter through the fabric if it is too liquid. This parameter can be measured with the viscometer.
We can stamp manually (each template will be in a frame), with a machine (mold, rollers, templates) or digitally, always stamping dark colors before light ones, and glitters etc …
The main stamping systems are as follows:
- The main stamping systems are as follows:
- Stamping by colorless or colored corrosion: usually used corrosive dyes to make a pattern on dark fabrics.
- Reserve printing: a paste is applied that prevents the penetration of dyes to later dye the entire fabric.
- Stamping by sublimation or transfer: the drawing is stamped in a paper, which is then transferred to the fabric (preferably polyester) by applying heat.Reserve printing: a paste is applied that prevents the penetration of dyes to later dye the entire fabric.
- Digital stamping.
Thanks to the stamping we can see textiles with flocked, inflatable, laminated, glitter…
Finally, when we have the fabric washed, bleached and dyed or stamped, we can apply sizing (chemical) and finishing (mechanical).
The mechanical finishes apply heat, pressure, tension… by means of machines created for it. Some mechanical finishes are: calendering (applying tension, temperature and humidity) to increase shine or ironing; embossing, in which an engraved design is engraved on the cylinder applying pressure and temperature; grinding, which consists of sanding the fabric to give a peach skin effect or raising, which increases the hairiness of the fabric.
The chemical finishes or sizing improve some property of the fabric applying chemical products. Some of the most commonly used finishes are: waterproof, antibacterial, fireproof, fungicide, ultraviolet or antistatic.