Flocking is the process of depositing many small fiber particles (called flock) onto a surface. It can also refer to the texture produced by the process, or to any material used primarily for its flocked surface. Flocking of an article can be performed for the purpose of increasing its value in terms of the tactile sensation, aesthetics, color and appearance. It can also be performed for functional reasons including insulation, slip-or-grip friction, and low reflectivity.
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, thus creating an even, textile surface. Due to the adhesives used today, flocking is very hard-wearing and abrasion-resistant. Depending on the fiber thickness and length, a velvety to hard- abrasive surface can be created depending on the desired function, appearance or feel.
Historians write that flocking can be traced back to circa 1000 B.C.E., when the Chinese used resin glue to bond natural fibers to fabrics. Fiber dust was strewn onto adhesive coated surfaces to produce flocked wall coverings in Germany during the Middle Ages. In France, flocked wall coverings became popular during the reign of Louis XIV of France.
Fibers or yarns form the basis for flock fibers. They are cut by machine and coated in water with various salts and tannins so that they have electrical conductivity and flowability 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 hatchet. The random cut takes place on a machine that is like a fan with knife blades. This method is cheaper and faster, but is also particularly suspected – in addition to the salts – the so-called flock (worker) lung – rather as a “flock worker’s lung” known – to evoke.
In principle, all textile fibers can be processed into flock, but their use depends on the area of application. For example, polyester is ideal for outdoor use, but has limited kink resistance. Viscose is mostly used on soft surfaces such as textiles and foams, but polyamide is generally used due to its positive properties.
Flock is specified by the type of fiber, the fiber length, the fiber thickness and the color. Common cutting lengths are 0.3 to 2.0 mm, the fiber thickness is given in the unit decitex (dtex) (grams per 10,000 meter 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 difficult to process. The following also applies: the thinner the lines or the more delicate 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.
Flocking is used in many ways. One example is in model building, where a grassy texture may be applied to a surface to make it look more realistic. Similarly, it is used by model car builders to get a scale carpet effect. Another use is on a Christmas tree, which may be flocked with a fluffy white spray to simulate snow. Other things may be flocked to give them a texture similar to velvet, velveteen, or velour, such as t-shirts, wallpaper, gift/jewelry boxes, and upholstery.
Besides the application of velvety coatings to surfaces and objects there exist various flocking techniques as a means of color and product design. They range from screen printing to modern digital printing in order to refine for instance fabric, clothes or books by multicolor patterns. Presently, the exploration of the flock phenomenon can be seen in the fine arts. Artist, Electric Coffin, is known for their many colorful flocked works, including a 50-foot piece in Facebook’s Seattle headquarters.
Flocking in the automotive industry is used for decorative purposes and may be applied to a number of different materials. Many rally cars also have a flocked dashboard to cut down on the sun reflecting through the windscreen. A view on the present state-of-the-art of flocking can be found in the first international exhibition “Flockage: the flock phenomenon” in the Russell-Cotes Art Gallery & Museum in Bournemouth.
In the photographic industry, flocking is one method used to reduce the reflectivity of surfaces, including the insides of some bellows and lens hoods. It is also used to produce light-tight passages for film such as in 135 film cartridges.
Flock consists of synthetic fibers that look like tiny hairs. Flock print feels somewhat velvet and a bit elevated. The length of the fibers can vary in thickness which co-determines the appearance of the flocked product. Thin fibers produce a soft velvety surface, thicker fibers a more bristle-like surface.
High-quality model cars are known to use flocking for decorative purposes. Premium model maker AUTOart is well known for its use of flocking in their model cars.
Flocking is defined as the application of fine particles to a previously glued surface. Nowadays, this is generally done by the application of a high voltage electric field. In a flocking machine, the floc has a negative charge, while the receiving medium is grounded. The fibers are directed in the direction of the electrostatic field created and are planted in the non-dry glue. A number of different substrates can be flocked: fabrics, paper, PVC.
After the glue has dried, a final cleaning must be planned to remove the excess fibers. In fact, the part is largely flocked so that the entire bonded area is covered with flock. A brush, compressed air or an industrial vacuum cleaner are used for this.
A flocked finish gives the surface a decorative and / or functional character. The variety of materials that can be applied to many surfaces by different methods of flocking, creates a wide range of finished products. The flocking process is used on items ranging from everyday consumer goods to products with high-tech military applications.
Manual flocking, where the flock is simply sprinkled, is done in certain circumstances where the support cannot be passed through an electric field, for example on the nails in Nail Art. In the particular conditions of a tree, a fluffy white is flocked with a spray to simulate snow on a Christmas tree.
An adhesive layer is first applied to the substrate, for example by screen printing, a spray gun or an immersion bath. The surface of the material to be finished must be smooth or only slightly embossed or grooved.
The fibers are applied electrostatically to the wet adhesive. For this purpose, 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 prevents the fibers from falling out in an uncontrolled manner through a plastic sieve. On the opposite side of the opening, a metal plate is attached as an anode. The cathodeforms the substrate or the adhesive. The applicator is held with the opening to 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.
Flocking is defined as the application of fine particles to adhesive coated surfaces, usually by the application of a high-voltage electric field. In a flocking machine the “flock” is given a negative charge whilst the substrate is earthed. Flock material flies vertically onto the substrate attaching to previously applied glue. A number of different substrates can be flocked including textiles, fabric, woven fabric, paper, PVC, sponge, toys, and automotive plastic.
The majority of flocking done worldwide uses finely cut natural or synthetic fibers. A flocked finish imparts a decorative and/or functional characteristic to the surface. The variety of materials that are applied to numerous surfaces through different flocking methods create a wide range of end products. The flocking process is used on items ranging from retail consumer goods to products with high technology military applications.
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 being deformed.
Grids or very thin lines are hardly feasible, since the fibers bulge and do not form razor-sharp edges, so small font sizes are not recommended.
Flock of 1 mm or longer can result in the processing of the flocked sheets being impaired, for example when punching. It is also not possible to cut several sheets at the same time. The material begins to float due to the flock. Only with a very short flock can up to 10 sheets be cut exactly.
Types of flocking
Flocking of molded parts: Flocking of molded parts means 3-dimensional parts that are not flat or flat. For example, these have curves and recesses.
Surface flocking: Surface flocking means all parts that are flat and flat.
Design flocking: Design flocking means patterns, logos, lettering etc. that are applied using a template (similar to screen printing).
Electrostatic flocking: It is used for flocking flat, flat or bulging parts such as bottles or flower pots.
Electrostatic-pneumatic flocking: A process used for flocking all shapes, curves or recesses in parts. The electrical shielding of the cavities can be overcome by the additional use of compressed air.
Flocking of cavities
When flocking cavities in objects (e.g. glove box) there is the problem that the charge runs off on 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 addresses this problem with compressed air- the “electrostatic-pneumatic flocking” – against. The flock is accelerated more 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 almost similar to that on an outer surface. The trick is to create an optimal flock picture in the corners too, which is achieved, 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 thermoformed films or using the in-mold process to incorporate a flocked film into the production process.
During the 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. This requires special, thermally activatable 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 is carried out mirror-inverted by the hot melt adhesive up to the surface of the transfer film. All commercially available cutting plotters in drag knife mode or tangential cut mode can be used for this. Only the cutting knife has to be changed for 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 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 s. 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 obtained by a preliminary test with the desired textile, since the settings of the thermal transfer press may have to be corrected.
With multicolor flock, the adhesive is first applied to the full motif area and then certain areas are successively flocked with the desired flock through a sieve. The sequence of different sieves creates multicolored graphic motifs (see screen printing). Another approach is the new UnikatFlock technology, which creates a color effect that is dependent on the viewing angle and results from the three-dimensional character of the flocked surface.
Flocking can expose workers to small nylon particulates, which inhaled can cause flock worker’s lung, a type of interstitial lung disease. Other exposure in the flocking industry can include acrylic adhesives, ammonium ether of potato starch, heat transfer oil, tannic acid, and zeolite.