Flock fiber

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Flocked T-shirt with a velvety print

As a flock fiber (short Flock ) are fibers (about 1 to 5 mm) indicates short length. With electrostatic flocking , these millions of fibers are applied in an electric field to a substrate coated with adhesive . The field lines ensure that all fibers are aligned vertically and thus create a uniform, textile surface. The adhesives used today make flockings very hard-wearing and abrasion-resistant. Depending on the fiber thickness and length , a velvety-soft to hard- abrasive surface can be created, depending on the desired function, look or feel .

Manufacturing

Fibers or yarns form the basis for flock fibers. They are machine-cut and coated with various salts and tannins in water so that they are electrically conductive and free-flowing after drying and sieving. When cutting / manufacturing, a distinction is made between the so-called precision cut and the random cut. The first method provides more precise, easier to process fibers and is made using a kind of guillotine. The random cut is made on a machine that resembles a fan with knife blades. This method is cheaper and faster, but is particularly suspected - in addition to the salts - of causing so-called flock (worker) lungs - more commonly known as “flock worker’s lung”.

sorts

In principle, all textile fibers can be processed into flock, but their use depends on the area of ​​application. So is polyester suited for outdoor use, but has a limited kink stability. Viscose is mostly used on soft surfaces such as textiles and foams, but due to its positive properties, polyamide is usually used.

Flock is specified by the fiber type, fiber length, fiber thickness and color. Common cut lengths are 0.3 to 2.0 mm, the fiber thickness is given in the unit decitex (dtex) (grams per 10,000 meters of length). Fibers with a thickness of 0.9 to 22 dtex are commercially available. The ratio of fiber length to thickness determines the look of the flock pile - the thinner the fibers are in relation to their length, the softer the surface feels, but they are also more difficult to process. Furthermore, the thinner the lines or the more filigree the motifs, the shorter the flock should be. A line width of 0.5 mm, for example, can only be achieved with a short flock.

application

First, an adhesive layer is applied to the substrate , for example by screen printing , spray gun or immersion bath. The surface of the material to be finished must be smooth or only very slightly embossed or grooved.

The fibers are applied electrostatically to the wet adhesive. To do this, the fibers are placed in the applicator, which consists of a plastic chamber into which the flock is filled. The flock can emerge from an opening which, through a plastic sieve, prevents the fibers from falling out in an uncontrolled manner. On the opposite side of the opening, a metal plate is attached as an anode . The cathode forms the substrate or the adhesive. The applicator is held with the opening facing the substrate and a voltage is applied. Due to the electrostatic effect, the flock fibers shoot into the adhesive and are fixed there. The electrostatic charge ensures that all fibers are stuck vertically in the adhesive, as this is the only way to achieve the typical, velvety to bristly consistency.

The durability of the flock can be influenced by the processing company optimally coordinating the substrate, adhesive and flock. For example, polyamide flock can withstand high pressure and the fibers straighten up again after deformation.

Grids or very thin lines can hardly be implemented, as the fibers bulge and do not form razor-sharp edges, which is why small font sizes are not recommended.

Flock of 1 mm or longer can adversely affect the machine processing of the flocked sheets , for example when punching. It is also not possible to cut several sheets at the same time. The material begins to float through the flock. Only with a very short flock can up to 10 sheets be cut exactly.

Types of flocking

  • Molded part flocking: Molded part flocking means 3-dimensional parts that are not even or flat. These have curves and depressions, for example.
  • Surface flocking: Surface flocking is understood to mean all parts that are flat and flat.
  • Design flocking: Design flocking means patterns, logos, lettering, etc. that are applied using a stencil (similar to screen printing).
  • Electrostatic flocking: It is used for flocking flat, level or outwardly curved parts such as bottles or flower pots.
  • Electrostatic-pneumatic flocking: A process that is used for flocking all shapes, curves or indentations in parts. With the additional use of compressed air, the electrical shielding of the cavities can be overcome.

Flocking of cavities

When flocking cavities in objects (e.g. glove boxes), there is the problem that the charge runs off the outside of the object and thus attracts the charged fibers more strongly ( Faraday cage ). This can be particularly noticeable in the inner corners of the object between the side wall and the floor due to the lower flock density. The industry counteracts this problem with compressed air - the "electrostatic-pneumatic flocking". The flock is accelerated more strongly and reaches the bottom of the inside of the objects despite the electrical attraction of the outer walls. The air currents allow a flock pattern that is almost similar to that on an outside surface. The trick is to create an optimal flock image even in the corners, which is done, for example, through mechanical support and a high electrostatic field potential with external support. For objects that are not too deep, there is also the option of using prefabricated flocked thermoforming foils or incorporating a flocked film in the production process using the in-mold method.

Flock transfer

Knife setting for flock film

With flock transfer, a special film or paper is flocked and then cut out or plotted . The motif can then be transferred to a textile by ironing it on. This requires special, thermally activated hot melt adhesives , which form a permanent bond with the textile after the thermal transfer.

The plotting (cutting out a vector graphic with the cutting plotter ) of the flock film takes place in mirror image through the hot melt adhesive down to the surface of the transfer film. All commercially available cutting plotters in drag knife mode or tangential cutting mode can be used for this. Only the cutting knife has to be changed on individual cutting plotters for flock material. In practice, a 60 ° knife is used and the knife tip protrudes 0.3–0.5 mm above the knife holder. The cutting speed is usually a maximum of 60 cm / s. After the cutting process, the elements of the transfer film that are not to be printed are removed (weeded).

Depending on the nature of the textile to be processed and depending on the manufacturer, commercially available thermal transfer presses are set to a flock temperature of 140–180 ° C. At an average pressure of approx. 2-3 bar, the pressing process then takes between 10 and 20 seconds. Depending on the manufacturer, the carrier film is removed hot or cold. In practice it has been found that the best possible result can only be achieved through a preliminary test with the desired textile, since the settings of the thermal transfer press may have to be corrected.

Multicolor

With multi-color flock, the adhesive is first applied to the entire motif surface and then certain areas are flocked with the desired flock through a sieve. The succession of different screens creates multicolored graphic motifs (see screen printing ). Another approach is the new unique flock technology, which creates a color effect that is dependent on the viewing angle and originates from the three-dimensional character of the flocked surface.

use

All materials and workpieces to which the adhesive sticks can be flocked, from T-shirts to glove boxes.

In the case of textile flocking, a flock film with a motif is plotted and transferred to the textiles while hot. In this way, all textiles made of 100% cotton and cotton blends can be flocked with polyester or acrylic. Nylon fabrics and fabrics with a water-repellent impregnation are not suitable for heat transfer. Textile flocking is a very high quality textile print variant. It is characterized by its high wash resistance and lightfastness. As a rule, these prints last significantly longer than the actual textile to be printed.

literature

  • Martin Kaimer: Waterproof, water vapor permeable flocked membranes and fabrics. Dissertation at the University of Stuttgart, 1992, OCLC 831869882 .
  • F. Kassack: flocking. Textile surface refinement through flocking. Paint factories Bayer, Leverkusen 1963, OCLC 313209932 .
  • Herbert Vogler: From medieval fiber prints to modern electrostatic flocking. In: Journal for the entire textile industry 67, 1965, pp. 819–826.
  • Michel Sieroff: The possible uses of flocculation in the textile sector. In: Lenzinger reports. 38, March 1975 ( lenzing.com PDF) pp. 108-119.

Web links

Individual evidence

  1. ↑ L. Zell: The flock workers lung - background of a new pneumological occupational medical disease picture. In: Pneumology. 54, pp. 43-47, doi: 10.1055 / s-2000-9061 .
  2. ^ David G. Kern, III, Charles Kuhn, E. Wesley Ely, Glenn S. Pransky, Curtis J. Mello, Armando E. Fraire, Joachim Müller: Flock worker's lung. Broadening the spectrum of clinicopathology, narrowing the spectrum of suspected etiologies . In: Chest . tape 117 , no. 1 , January 2000, ISSN  0012-3692 , p. 251-259 , doi : 10.1378 / chest.117.1.251 ( chestnet.org ).
  3. ↑ Types of flocking. schuster-beflockung.de, accessed on September 8, 2016 .