Flock Manufacture consists of three production cycles:
- Monofilament's cutting or milling
- Processing or activation (with the special mixture giving flowability and electrical conductivity to flock)
2.1. Cutting or milling
There are two ways of flock manufacture
- Exact cutting of parallel stacked bundles of fibres (a professional term: a tow). In this case the cut flock is dealt with.
- Grinding (a professional expression — milling) of initial raw material with different length and thickness. In this case the milled flock is dealt with.
The milled flock can be produced from fibre remains on spools. But it is also possible to use a high-quality tow. In any case the manufacture of cut flock demands the use of tow from parallel monofilaments with the same thickness. The cut flock is considered of high quality if its filaments are straight, with identical length and if they are not fusion-spliced at the end.
The cut and milled flock are the most widespread types of flock in Europe. The so-called «curved flock» is produced in Japan. In this case the idea is about flock made of unstraight fibres. In this flock some filaments are straight, and some can be greatly curved at any place.
The colour of flock is a key characteristic, especially for visible surfaces of details. Flock is dyed in different colours. The dyed flock possesses the following characteristics:
- Light resistance
- Colour fastness
- Washing resistance
- Resistance to other external actions (friction, sweat, perfumery …).
Flock of different colour meets the set of above-listed requirements in a different degree. A certain property can be intentionally improved. But, as a rule, it leads to the price increase or to other qualities loss. Thus, it is only necessary to change the dyeing composition in case of urgency if it is demanded by operating conditions of end product.
There are two ways of flock dyeing:
1. Fibre dyeing (at the stage: after tow cutting);
2. Dyeing of raw polyamide (spun dyeing at the stage: before tow manufacturing).
At fibre dyeing the milled or cut flock, as well as usual textile, is dyed in the vat.
During spun dyeing polymeric fusion is dyed before extrusion. In such a way parameters of light resistance substantially increase. When dyeing polymeric fusion the minimal loading of initial raw material is great, therefore the method is economically not so effective. Besides, it is difficult enough to precisely set a certain colour.
Black spun dyed flock possesses the highest light resistance. When dyeing they use gas black, which does not change its colour under influence of light. During other colours production less stable dyes are used. Therefore the spun dyed flock, as a rule, possesses the best light resistance.
Besides the darker colour of flock is, the higher light resistance it possesses. In dark colours there are quantitatively more colouring matters, than in light ones.
2.3. Processing (activation)
After dyeing fibres are processed. The processing reagent consists of salts, surfactants and tannin.
The purposes for activation:
1. To impart to flock a certain electrical conductivity along the length of a filament. Fibres should be charged not only by means of a high-voltage electrode, but also by each other. The charged flock only flies to the grounded surface, which should be coated with poil.
2. To provide a filament with a dipole. The filaments with distributed charge are only situated parallel to the electrostatic field lines, i.e. perpendicular to the flocked surface.
3. To impart flowability to flock to make it divide in the poil-feeding system and in the metering device.
4. To provide flock with optimal wettability.
The perfectly dry salts do not conduct current. They only get conductivity in the water solution. Thus, flock conductivity increases when relative air humidity rises. On the other hand, the more moisture accumulates on a filament, the more adhesive the surface is. The separability worsens, flock crumples and becomes unsuitable for processing. Flock slugging is very harmful: a flock blob, being in adhesive, do not allow other flock items to fix near by in the adhesive layer. It leads to the bald spots and coat non-uniformity. Therefore it is necessary to flock in the humidity range which conductivity is sufficient and flowability is still kept.
The quality of flock processing can be spoiled by many factors (by moisture, temperature…). Some damages can be corrected, some cannot. The spoiled flock can be processed again if it has no foreign matters. The recovered flock is as good as a new one.