What can we do to improve the aesthetics or strength of a How can we improve a tissue? Depending on the fibres it is made of, we will carry out the operations before and after the spinning process in one way or another.
To be able to dye, print or add finishes to the fabric, it is essential to carry out so-called “preparation operations”. We must remove the impurities and everything that could make the application of dyes or finishing.
There are two types of impurities that can be found in the fibres: the natural ones, which are those carried by the plant of origin or those produced by the animal, and the added ones, which are those added in the spinning process (gums, oils…).
In the case of vegetable fibres, you can do a singeing in which the fibres protruding from the fabric are removed (the fuzz) bringing the tissue closer to a flame. We can also desizing (remove impurities added by us to the tissues) and scouring (remove impurities that cannot be dissolved in water). As we have commented in the section of the fibres, the cotton can be made a mercerized, so that the yarn is brighter, better dyed and swell the fibers, thus improving their resistance.
On the other hand, animal fibres such as wool or silk need to remove grease and waxes with detergents and desizing agents before dyeing or weaving.
All fabrics made of natural fibres need to be bleached in order to be able to dye them in light colours or white (let’s imagine that we want a white or beige jute fabric, we will have to bleach it first, as the natural colour of jute is brown.
We have all heard of “optical white”, which we can distinguish from “natural white” if we take an ultraviolet light (the former will shine and the latter will not). Optical bleaching aims to improve the degree of white.
One important improvement we can make to the textile material is dyeing. We can dye the fibres, the yarn, the fabric or the finished garment. There are two methods 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 it is passed through two cylinders so that the excess dye can be drained off. Finally, the fabric is washed.
Parameters such as pH, speed, temperature or time influence the dyeing. The dyeing depends on these and more parameters, so it is very common that there are defects in the dyeing. Which are the most common? Lack of uniformity, local stains, light spots…
If we only want a localised colouring, instead of dyeing the whole fabric, we use the printing technique.
What steps need to be taken to get a good print?
- Prepare the fabric (mercerizing, bleaching, degreasing…)
- Prepare the colored paste that we are going to use.
- Prepare the machine and spread color.
- Colour fixation (by heat, steaming or other method)
- Washing and operations according to the printing process.
In order to print the pastes correctly, it is very important that they have the correct viscosity, as 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 print manually (each template will be in a frame), with machine (mold, rollers, templates) or digitally, always printing the dark colors before the light ones, and glitter etc.
The main printing systems are:
- Direct printing: it consists of applying the paste on the fabric (it is the most used)
- Colourless or coloured corrosion stamping: usually used corrosive dyes to make a drawing on dark fabrics.
- Reserve printing: a paste is applied to prevent the penetration of the dyestuffs and then the whole fabric is dyed.
- Sublimation or transfer printing: the drawing is printed on a paper, which is then transferred to the fabric (preferably polyester) by applying heat.
- Digital printing.
Thanks to printing we can see textiles with flocking, inflatables, laminates, glitter…
Finally, when the fabric has been washed, bleached and dyed or printed, we can apply sizing (chemical) and finishing (mechanical).
Mechanical finishes apply heat, pressure, tension… by machines created for this purpose. Some mechanical finishes are: calendering (applying tension, temperature and humidity) to increase the shine or ironing; embossing, in which an engraved design is engraved on the cylinder by 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.
Chemical finishes or sizing improve some property of the fabric by applying chemicals. Some of the most commonly used finishes are: water-repellent, antibacterial, fire-resistant, fungicidal, ultraviolet or antistatic.