Flocking of T-shirts and sportswear

Flocking is currently not only used for leisure activities and sports clubs but is also applied in fashion as flock print or design flocking for ladies' upper wear. This essay is to demonstrate the various flocking techniques, the necessary materials and machinery and the flocking process.

Flock produces a nice, velvety, embossed-like surface. Flock writings and designs clearly stand out from the usual textile prints. At the beginning, flock was slightly doubted due to repeated difficulties with quality but today it is a known fact that a high quality is achieved if the correct materials and machinery are used.

Flocking is currently not only used for leisure activities and sports clubs but is also applied in fashion as flock print or design flocking for ladies’ upper wear. This essay is to demonstrate the various flocking techniques, the necessary materials and machinery and the flocking process.

Besides single-coloured direct flocking, there are different ways of multi-colour flocking and flock transfers. The most important multi-colour flocking processes are listed below but we make no claim to be exhaustive.

1. Direct flocking
2. Multiple flocking
3. Covering process
4. Iris flock
5. Flock on flock
6. Multi-colour flock
7. Transfer flock - screen printing
8. Transfer flock - die-cutting
9. Transfer flock - plotting
10. Transfer flock - digital printing.

Depending on the quality demands, add-on and above all on the technical conditions, one of the above processes is selected.

Direct flocking

Adhesives

Adhesives are of crucial importance to the flock quality since they link the flock with the support and must be soft, flexible and wash fast. Today, mainly disperse adhesives on an acrylate base are used. For special cases such as e.g. coated wovens, solvent adhesives are also applied. There are cold and hot crosslinking adhesives. The cold crosslinking adhesive dries at room temperature and crosslinks within two to five days, i.e. it also becomes wash fast within this time. For crosslinking a fixing agent is added.

Depending on the type, heat-setting adhesives require a temperature of approximately 130-160øC for crosslinking and fix within approx. 5-20 minutes. We must stress that drying and fixation take place in two phases: First, the adhesive has to dry, i.e. the water contained in the adhesive must evaporate. During this time, due to physics the temperature does not rise above 100øC; it only reaches 130-160øC afterwards. The drying process is supported through an intense air movement with corresponding fresh air supply. If drying is to be done in a drying chamber with circulating air only, the air moisture is increased there up to the saturational limit. Thus, there is no longer any drying since the air can no longer absorb any moisture. Therefore, a good air circulation with the corresponding share of fresh air is important for drying.

Disperse adhesive are environmentally friendly, screens and working utensils can be cleaned with water. Only for surfaces with a water repellent coating solvent adhesives have to be used. These are mostly two component systems based on polyurethane which also produce very good fastness levels just like disperse adhesives.

CHT has various heat-setting and cold-setting disperse adhesives with the name TUBVINYL for all kinds of direct flocking.

Flock

Flock is made of shortly cut textile fibres. For design flocking of textiles a flock length of 0.5 or 1.0 mm is usually applied. Flock is made of viscose (artificial silk) and polyamide (nylon). The most common sizes are 1.7 decitex/0.5 mm and 6.7 decitex/1.0 mm for polyamide. A particularly soft handle is e.g. achieved with 1.7 decitex/1.0 mm. For flocking door mats, which is very common, a harsher and longer flock is applied: nylon 22 decitex/2.0 mm. With this flock carpets are also produced. The clearly thicker fibre is very durable and extremely fast to abrasion.

For a better comprehension the term “decitex” shall be briefly explained. This value gives the weight (g) of an individual fibre of 10 km light, i.e. if 3.3 decitex are stated, the individual fibre of 10000 m length weighs 3.3 g. Both fibre types are offered in a quality which is fast to light, washing and bleeding.

Screen printing screens

The adhesive is applied by means of screen printing screens. The gauzes are usually made of polyester since this material absorbs only little water, so that the gauze is not drawn by the disperse adhesive and by the washing off or cleaning process.

The adhesive layer which needs to be applied is quite thick (15-20 per cent of the flock length), so gauze with 21 to 39 threads per cm is used. Compared with normal screen printing these are coarse gauzes but the adhesive is paste-like and thixotropic, so it must be applied onto the fabric in a sufficient quantity. It is important that the selected outlines are not too fine to prevent saw tooth effects due to the coarse gauze and a bad adhesion of the flock. The width of lines and dots ought not be below 1.5 mm.

The adhesive amount is not only determined through the fineness of the screen gauze but also through the squeegee hardness and form. A soft, round squeegee (60 to 70 Shore A) is suited best. On both sides the squeegee ought to be 20-30 mm wider than the design.

Working procedure

The adhesive is applied with the screen printing screen. If textiles are to be flocked, the adhesive may be printed with contact or with a short off-contact. If the substrate to be flocked is not absorbent, e.g. coated woven or paper or plastic, the off-contact must be a little bit longer to prevent a squeezing of the edges. Immediately after the adhesive application, flocking is carried out.

The time between adhesive application and flocking must not be too long since otherwise a skin may form on the adhesive surface, so that the flock would no longer penetrate into the adhesive. Flocking is done purely electrostatically, i.e., the fibres are charged with high voltage and fly along the lines of electric flux to the opposite pole. If there is no adhesive on the opposite pole, they will fly back to the flock device. If the opposite pole is covered with adhesive, they will enter it vertically and be fixed and anchored there.

The flocked surface must not be touched while the adhesive is still wet. Otherwise, the vertical flock would be pressed down. The flock is not only dyed according to the fastness levels described above but it is also prepared for the electrostatic flocking, i.e. it has a certain electric conductivity, so it can quickly accept and give of electric charges. This conductivity is caused by the intrinsic conductivity of the preparation and by the relative humidity in the working room. This means that the relative humidity of the working room influences the flying behaviour of the flock.

The ideal relative humidity is 55-65 per cent. If the air is too dry, the flock will form so-called barbs during flocking, whereas it pours badly and lumps easily if the air is too humid. Particularly in the winter time, when outside temperatures are very low, there may often be a relative humidity of only 30-35 per cent in the working room. An efficient air humidifier can be of help here. If the air is too dry, the open time of the adhesive will decrease, so that a skin may form more quickly on the surface.

The adhesive is mostly applied by hand, i.e. with a manual squeegee, through a screen printing screen. We recommend to use an automatic screen printing machine for higher production numbers because the squeegee strokes are always even according to the previous adjustment.

The adhesive may either be applied with an oscillating crank on a working table or even better with a footed device on a pallet. In the ideal case, the screen printing screen may be turned aside, so that the T-shirt or sports jacket can be slightly put down and removed after the adhesive application. Afterwards, the pieces to be flocked are put on the working table. This may be a normal table but it should have a metal plate as surface which is connected via a ground cable to the ground socket of he flocking device.

A special flock working table has side walls, so that the flock remains within the actual working place. The surface is trellis shaped, so that excess flock falls first into a funnel underneath, then into a collecting vessel.

Manual flock devices are composed of a high voltage electrostatic device and the actual working device, the applicator. The flock is filled into the applicator. The bottom is connected to high voltage; a screen is installed on the front part. Through a slight shaking and high voltage, the flock flies along the lines of electric flux towards the piece to be flocked and is vertically anchored in the adhesive. Depending on the device the maximum voltage is approx. 70,000 to 100,000 Volt, but the intensity of the current is within the A range, so that it is not dangerous.

Multiple flocking

The complete procedure is carried out several times, i.e. the first shade is flocked dried and cleaned. Afterwards, the piece is drawn onto the pallet, so that the next shade is flocked. Since the material is flexible, an exact registration is only achieved in limited cases. Therefore, designs are selected which do not require an exact registration. However, this process is very expensive - a three colour flocking costs e.g. three times as much as a single-coloured flocking.

Covering process

The adhesive for the complete design is applied first. Then, those design areas which are to be flocked with the second or third shade are covered with paper or cardboard screens. The uncovered design area is flocked with the first shade. Afterwards, another design area is covered and the next shade is flocked. This is far more economical and quicker than the previous process but the design variety is highly limited. With coherent designs the outlines are not sharp unless the design is selected in a way that the different shades are at least 2 - 3 cm apart from one another. The advantage of this system is that drying and cleaning also only need to be carried out once, so this process is a lot cheaper.

Iris flock

The adhesive is applied once onto the complete design. The flock applicator contains various flock shades, separated from one another through walls. All shades are flocked simultaneously, so that there is a nice passing from one shade to the other. Very appealing designs can be selected with just a bit of fantasy, e.g. different blue shades for the sky or yellow, red and dark blue for a sunset design. The expense is not higher than for a single-coloured flocking.

Flock on flock

The adhesive is applied once for the complete design, then similar to the first process the flocking, drying, cleaning and application of the next adhesive follow with the applications being carried out on top of instead of next to each other. This facilitates sharp outlines between the individual shades and special effects through the double embossing effect. However, this process is also very expensive since each shade implies a complete working procedure from drawing the piece onto a pallet, applying the adhesive, flocking to drying and cleaning.

Multi-colour flock

This is a true multi-colour flocking where the design has very sharp outlines. This process can only be carried out on machines since highest precision is required. On the first station of a big circular printing machine the adhesive is applied onto the complete design, then the pallet moves onto the first flock shade. There, the first flock shade is flocked through a flock screen with an exact registration. It is important that there is an exact distance between fabric and flock screen. When using 1 mm flock, which is the usual length, the distance ought to be approx. 1.2 - 1.6 mm. If the distance is too small, the bottom part of the screen may be soiled with adhesive or the screen structures may become visible (which may of course look quite interesting, too). If the distance is too wide, the outlines won’t be as sharp. Underneath, the circular printing machine turns on to flock shade 2, shade 3 and shade 4. Production is almost as fast as with single-coloured flock since the pallets are flocked one after the other. Thus, if shade 1 is flocked, shade 2 will be flocked onto the previous pallet while the adhesive will be applied onto the subsequent pallet. The only more expensive part is the investment into the machine and several flock screens per design. Screen flock was also produced with this process, so all the shades were produced with the four basic colours. Both the machine and the operating staff must of course work with the highest precision. A particularly wide application field of multi-colour flock is the production of door mats. In Western Europe several millions are produced and sold each year. For door mats 2 mm long flock and special screens are used, so that far more adhesive can be applied. This is required due to the coarse substrate and the demand for an increased stability to abrasion.

Transfer flock screen printing

A special flock transfer paper is applied. The flock is anchored into this paper but can be released easily. The adhesive is printed mirrored and hot melt powder is sprinkled into the wet adhesive. After drying the design is turned and ironed onto the fabric with the hot melt side facing towards the fabric. The hot melt is bound with the fabric. The flock is released from the support paper in those areas where the adhesive was. Thus, the design is applied onto the fabric in the right way.

Multi-colour designs are also possible with this process. A white flock transfer paper which is suitable for multi-colour flocking is required. First, the colours of the design are printed and dried intermediately. Then, the adhesive is applied with the hot melt powder. It is important that the printing colours penetrate the flock completely. A slight sandwich effect/ frosting of the finished transfer indicates that the quality is poor.

CHT offers all the necessary products for this process under the name TUBITRANS.

Transfer flock, die-cutting

Letters or designs can be die-cut out of special flock transfer papers with hot melt film and then ironed onto fabrics. Since a special die-cutting tool is required for die-cutting, only designs in high production numbers are worth the expense. This process is often used for letters, trademarks, or numbers. CHT product name: TUBITHERM.

Transfer flock, plotting

Similar to the previous process a flock transfer paper with hot melt film is used. However, this film is laminated onto a transparent support paper, so that the hot melt film is on the upper side. The design is plotted mirrored and the matrix, i.e. those parts which do not belong to the design, are removed. Even smallest production numbers of flock transfers can be quickly produced with a computer and a plotter at low costs. CHT product: TUBITHERM PLT.

Transfer flock,digital printing

Today, even smallest production numbers of multi-colour flock transfers can be easily produced. Special, heat-sealable flock films can be printed wash fast with an inkjet printer and die-cut in a plotter or die-cut machine. Hybrid plotters which cut immediately after the printing process are particularly suitable. CHT product: CHIPTEX Base 1000/2000.

Comparison between transfer flock and direct flock

Now that the individual processes were described, the pros and cons of each process must be checked. In general, both processes achieve a comparable quality level provided only highest quality products are processed carefully. Directly flocked designs are softer than transfers, which is particularly advantageous in case of large surface designs. With transfers much finer details can be realised than with direct flockings. For direct flockings more machinery and production phases are required than with transfer systems since either the transfer paper or even the finished transfer can be purchased, so that it only needs to be transferred. In case of direct flocking the design size is of minor importance cost wise, whereas it goes directly into the calculation in case of transfer flocking.

A flock transfer of the size 10 x 10 cm is almost four times as expensive as a transfer of the size 5 x 5 cm. It is obvious that small writings or small signs, especially if being multi-colour, will be much cheaper if they are produced as flock transfers. An additional advantage is that the slightly higher stiffness has not such a great impact on a small design than on a large surface design. Big club writings, country names or designs with cities or sights are better realised as direct flockings.

Due to the elegant appearance and the good properties, flocking stands out very much from all the other printing techniques, so that it has established at the upper price level within recent years. Therefore, we recommend to offer flocked fabrics with washing instructions. Due to the swelling of the fibres with water contact, the wet abrasion stability is not unlimited. Moreover, the permanent turning in the washing machine drum highly strains the fabric. A possible damaging of the flock surface can be avoided if the fabrics are turned to the reverse for washing. This way, a direct abrasion during washing and thus a damaging of the flocked surface is avoided.

Flocking does not only produce positive results on textiles, T-shirts and sportswear, but it is also successfully, applied for all kinds of surface finishing and above all for many technical applications.

Source: CHT R Beitlich GmbH