FAQ (Frequently Asked Questions)
The Choice of the Right Flock
Available Raw Materials
Characteristics of Different Flock Types
Areas of Application
Faulty Flock, its Causes and the Elimination Thereof
Processing Fibers
What are Dezitex?
Dyeing and Preparation
The Storage of Flock
This is as important as the basic material and adhesive, as they are based on your knowledge of different raw materials, technological qualities and nature, i.e. coloration and preparation.
Flock generally describes fibers with a length of less than 10 mm.In the past couple of years, the demands on flock fibers have become more and more specific due to a broader application area. Therefore, machine manufacturers, flock and adhesive producers give specific advice to their customers.
So far, the production of flock has rarely been discussed. Everybody guards their secret.
The choice of the right flock, however, requires a specific knowledge. It is a technology which is closely linked to the textile industry.
The choice of the right raw material has a tremendous influence on the quality of the produced flock as well as on the quality of the flocked surface.
Available Raw Materials:
1. Natural fibers such as cotton
2. Semi-synthetic materials (reclaims) after the viscose, copper and acetate spinning process
3. Purely synthetic materials like polyamide 6.6 and 6, polyacrylonitrile and polyester.
Flock made of natural raw materials cannot be produced in exact lengths due to the nature of the fibers. Therefore, this material can be ground for only a short or for a prolonged time period. It can be fine or coarse, straight or slightly bent.
Semi-synthetic materials (reclaims) exist as endless tow, fibers or as waste of the fiber manufacturer and the clothing industry. The same is true for purely synthetic materials. If they exist as endless tow, both can be cut to specific lengths. Just like natural raw materials, fibers or waste can be ground for a short or prolonged period of time.
If the preparation and adhesive are not compatible, felt formation can occur (i.e. several layers are on top of each other) and the adhesive cannot bond the fibers or uneven spots occur which resemble the coat of a leopard.
Spinning and drying follow these so-called water procedures. At last, the flock is sifted and mixed. Filtering is essential in the cutting process since it helps sort out fibers of excessive length or fibers that are too short. Filtering is also important to make the materials to be ground appear more regular. This happens on drum, wobble, shake or whirl sieve machines.
Conditioning of the materials can follow the above-mentioned procedure provided that this has not already been done during the drying process.
The later use of the fibers determines the choice of the raw material, the grist or the precision of the cut, the color-fastness and preparation, the quality of the flock and therefore the price. The coloring is a huge factor in determining the price.
There is a whole array of possibilities. Therefore, only communication with the flock manufacturer can offer clarity if the machine and adhesive manufacturers have not provided a preliminary orientation.
Characteristics of Different Flock Types:
Cotton flock is pressure-sensitive and yields the so-called writing effect as it is known of suede. When cotton is dry, it is less resistant to abrasion than when it is wet. The absorption of humidity is high.
Viscose flock is very pressure-sensitive. The pressure marks remain even after the pressure discontinues. This flock has a low abrasion resistance when it is wet. Its technical use is restricted to light duty only. The absorption of humidity is very high; higher than with cotton.
Polyamide flock has a very good recuperative capacity. Pressure marks are hardly visible or not noticeable at all. Polyamide flock, however, has a very low capacity for absorbing humidity. Polyester and polyacrylamide flock have similar properties.
Areas of Application
Cotton is generally used for textiles (suede imitations) and linings. An important area of application is the flocking of latex gloves.
Viscose flock is used for articles which are not heavily used or for surfaces of a basic material that needs to be mercerized (i.e. becomes like velvet) such as certain packing materials, decorative paper, toys, some wallpapers, clothing, flock print on sports clothes, etc.
Polyamide is for articles which are used more frequently such as upholstery fabrics and for technical purposes such as wallpapers, wall flocking, carpets, casing, rubber profiles, seals and glove boxes. It is also used for flock printing decorative designs on textiles and door mats.
Usually, viscose flock is produced from a glossy tow and, on rare occasions, also from a dull tow. Polyamide, however, is half-dull or dull. Polyamide flock tends to have more of a mirror finish and to produce the moiré effect, i.e. to change appearance. These effects can be lessened by matting the flock.
Faulty Flock, its Causes and the Elimination Thereof
Bent or crooked chopped flock can make the flocking uneven and thin. The same is true for frayed or conglomerated ends of fibers. Wrong preparation or preparation that is not compatible with the adhesive causes felt formation or an uneven surface that often resembles the coat of a leopard. Poor preparation means bad conductivity (jumping ability) in the electrostatic field. This goes hand in hand with poor flocking density or a considerably longer flocking time.
A dissimilar cut, frayed ends, crooked fibers, excess lengths and bad preparation also make the
free flowing ability of the flock poor.
The appearances are the same as the ones mentioned above. The deficiencies of the flocker cannot be remedied in such cases. The following fibers are mostly used in flocking:
- Cotton, viscose and polyamide (perlon = polyamide 6 and nylon = polyamide 6.6) and for special purposes polyester and polyacrylonitrile.
- Reclaims as well as fully synthetic fibers and threads consist in different shades of matting: glossy, half-dull and dull.
We will discuss the applications of the individual types of fibers later.
Processing Fibers
Ground flock is produced from waste or from original spinning fibers of the fiber manufacturers, spinning mills and the clothing industry. Ground flock has different lengths. Its characteristics are strongly determined by the type of materials used for fibers (relatively straight, cleaned, uncleaned or very strongly bent material) as well as the machine types used in processing.
The fineness of ground flock can only be roughly met and is determined by the waste on hand. The use of pure or new fibers is generally restricted due to price limitations.
Endless tow can be cut to defined lengths. This mainly happens on cutting machines which function like guillotines or on machines with circling knives. The tow band delivered by the tow manufacturers with approx. 30,000 dtex - 500,000 dtex is multiplied to approx. 14 -20 mio. dtex.
What are Dezitex?
3.3 dezitex, for example, means that 10,000 meters of a single thread weigh 3.3 grams. The higher the dtex number, the thicker the individual fiber (a single piece of flock).
The most common fiber strengths are 0.155 / 0.9 / 1.3 / 1.7 3.3 / 5.6 / 6.7 / 10 / 17 / 22 and 27 dtex.
Thus, the endless tow on hand can be cut to a variety of lengths. Thereby, a favorable relationship between fiber length and strength must exist. If the fiber is too long with regard to its strength, it tends to bend and form knots. Under these circumstances, the manufacturing process becomes very challenging and flocking becomes time-consuming and extremely difficult. The applied flock frequently becomes uneven and thin.
Currently, the most common measurements are:
0.5 -- 0.75 mm in 0.9 dtex, 1.7 dtex and 3.3 dtex
1.0 -- 1.5 mm in 3.3 dtex, 5.0 dtex and 6.7 dtex
2.0 -- 3.0 mm, 22 dtex and 28 dtex
After the grinding and cutting process, the finishing process of the flock is done.
Dyeing and Preparation
The dyeing methods are almost the same as for textiles.
Cotton and viscose flock are substantively dyed with appropriate follow-up treatments. If fast dye is required, reactive dyestuff or indanthrene become necessary.
Polyamide is dyed with acid dyes which yield color-fastness. For the automobile industry, metal complex dyestuff is used as well to obtain the maximum amount of color-fastness.
The preparation that follows is generally influenced by the raw material, but also in part by the adhesive. It makes the fiber ready to quickly absorb and release electrical charge. Therefore, the preparation process is instrumental for high-quality flocking.
A distinction between hydrophilic and hydrophobic preparation is made. Hydrophylic preparation is particularly good for highly conductive dispersion adhesives. Hydrophobic preparation, which is used especially for polyamide, is more suitable for poorly conductive solvent adhesives and plastisols.
The Storage of Flock
Flock should be stored at a room temperature that is as constant as possible, [i.e. not below 0 degrees C (32 degrees F) and not above 25 degrees C ( 77 degrees F)]. Direct sunlight must be avoided at all cost. If the humidity is too high or too low, it can cause just as much damage as direct sunlight. Before being processed, flock should be stored in a conditioned flocking room for several hours. The most favorable humidity for storage and processing is 65 -75 % relative humidity.
If, for some reason, flock has become too dry, a household remedy for small quantities is to dampen it with a moist cloth or to carefully spray it with salt water. Huge quantities have to be dampened in a conditioned room. If the flock is too humid, it can be carefully dried but never at a temperature above 80 degrees C (176 degrees F).
If flock is too dry, whiskers or bridges are noticeable between the electrode and the flocking part. If flock is too moist, it becomes lumpy and thus jumps badly.
Of course, it is best to check the flock before processing. This is the simplest method: Put flock on a grounded metal piece and make it jump with a hand-held apparatus or applicator. The whole quantity of flock has to jump evenly from the plate. Different testing instruments are available for this purpose: A direct or indirect resistance gauge, a jumping tester and a free flowing tester. This equipment is offered by machine manufacturers pertinent to flock processing.
These explanations are supposed to provide general information, but can under no circumstances replace expert advice.
Technicals Fibers
Fiber fillers
Cotton fiber filler
Polyamide fiber fillers
Polyester fiber fillers
Jute-, sisal-, and mineral wool fiber and rock wool
Applications for fiber
Coating Compounds
Reinforcing paint
Dispersion covering color
Construction material
Asbestos replacement
Fiber fillers
Even our ancestors used reinforcement fibers to fortify concrete and other construction material like concrete, glue, bitumen and putties. In the old days, fibers such as chopped hemp, straw or flax were used to absorb rotating, bending or pressure stress in structures. These days fibers that are made from cut or ground, organic or inorganic material find a wide range of uses to strengthen rubber products, paper and fleece (non-woven) products and construction material.
The construction industry in particular uses short staple synthetic fibers with a high elasticity module to reinforce materials like latex pant, plaster, spackle, putty, glue and bitumen, and make them thixotrope. These fortified materials are applied to subsurfaces that are cracked in order to mask the crack and protect the subsurface against weathering.
Suitable for this application are:
However, the best results for this application are achieved with acrylic fiber of 6.7 dtex and a length of 2 to 12 mm. This fiber shows outstanding weather and light resistance, high alkali resistance and very high acid resistance. Its surface is coarse and therefore bonds strongly with surrounding material.
In case the alkali-resistance is particularly important, it is recommended to use high module fiber on PAC-basis or PP-splicefiber.
Depending on the construction product and its application, it is recommended to add 0.5% to 3% (solids content) of fiber as a supplement to the construction material. In addition to the reinforcement, this could also improve the decorative effect.
Aside from the regular fiber that is cut to a defined length, combinations of fiber of varying lengths (e.g. 0.5 to 2mm) are also available. These fiber supplements will make the end product thixotrope, reinforce it, and under certain circumstances will prolong the wet life.
To ensure durability of the coating, it is critical to choose an elastic binding agent and the flawless pretreatment of the subsurface.
Additional uses for these kinds of fiber are the manufacturing of batteries and rotation coating compounds on bitumen basis. The search for a replacement for asbestos building materials has created yet another application for fiber, splissed polyethylene fiber (fibrids) in varying lengths and thicknesses offer similar characteristics without the health risks. Upon request, these fibrids can be delivered as premixed compounds with mineral fillers and have successfully proven to be a suitable replacement for asbestos in many cases. Where heat resistance is a critical criterion, fiber fillers can be made with mineral wool or rock wool, oxidized polyacrylic nitril fiber or carbon fiber which are very heat resistant materials.
Fiber fillers play an important role as carrier material for duromers, in this function they can improve mechanical, electrical, and thermal values, surface finish, abrasion resistance, conductivity or processing requirements. Additionally, they can reduce water absorption, after-contraction, and thermal expansion of molding compounds on duromer basis (phenol, melamine, urea, melamine/phenol, unsaturated polyester, epoxide,
diallylphthalate, silicon, buton).
The fibers usually used in these fillers are:
- Cotton fabric cuttings
- Cotton fiber
- Polyamide
- Polyester
- Jute
- Sisal
- Rock wool
- Mineral wool
- Cellulose
- Oxidized polyacrylic nitril fiber
- Carbon fiber
Cotton fiber filler
The capillary structure of ground fiber fillers ensures that it can be soaked and tightly enclosed by resin compound, as a result, no water will be absorbed by the fiber. In spite of the filigree structure of the cotton fiber, this filler does provide a fibrous structure and thus provides stability and rigidity. Due to this characteristic and its corrosion resistance, the cotton fiber filler is a great fit even for tropicalized molding compounds if the right filler (resin) is chosen. The recommended amount is 30 to 50% for phenolic resin and 15 to 25% for polyester resin. Very fine cotton fiber fillers have successfully been used to make epoxide and polyester resins thixotrope, for example for aircraft construction.
A frequent application for cotton fabric cuttings is thermosetting molding material that is required to be highly rigid and stable. Similar characteristics can be achieved by the use of cotton threads that make the filler free flowing. The added amount for those should be dependent on the desired level or reinforcement between 15 and 40%.
Polyamide fiber fillers
The use of polyamide fiber in filler allows for good electrical values and high creep resistance in molding compounds. In the rubber industry, this fiber is used for roll covers. Additional uses for it are phenol, melamine, and polyester molding compounds, where the fiber can make up 2 to 10% of the compound.
Polyester fiber fillers
The use of polyester fiber fillers improves the impact resistance, bending strength, deformation resistance and creep resistance. They are frequently used in combination with cotton fiber fillers. The polyester filler should make up 3 to 7% of the compound if used purely, if it is used in combination with cotton fiber the fiber filler should make up 5 to 10% of the compound.
Jute-, sisal-, and mineral wool fiber and rock wool
These kinds of fiber have recently found their way back into the molding compound industry. However, their widest use is in the brake and friction pad manufacturing and as a replacement for asbestos.
For all reinforcing fiber fillers, the reinforcing effect is significantly depending on the length of the fiber. The mechanical stability is the higher, the more fibrous or laminar the fiber filler (carrier material) can be applied.
The fiber fillers made of fiber fibrids on a polyethylene basis keep gaining importance as an asbestos replacement. The highly complex fiber structure and large fiber surface of 7 to 10 m²/ g allows for high thixotropy. In practical applications, this affords the possibility to reduce the amount needed to ¼ to 1/6 of that needed with asbestos fiber.
Fiber fibrids are available from 0.2 to 1.6 mm in length and with diameters of 3 to 50 µm.Applications for fiber
Coating Compounds
The use of short cut fiber has proven successful for tank coating compounds based on epoxide resin. For this application, a combination of a transparent polyamide fiber (0, 10/4mm) and a glass fiber (3 or 6mm) is usually added to make up 6% of the total compound. Such products can be applied to the tank with a high pressure spraying method (spray valve of 1.8 to 5 mm) and stand out as very stable coating that will not drain off.
Reinforcing paint
Coatings based on synthetic resin dispersion are used to treat net-like cracks in buildings and made with 6.7dtex acrylic short cut fiber of 4 to 6 mm in length. The fiber portion is usually 1 to 2.5% and can alternatively be composed of a combination of fibers with acrylic fiber filler. The thickness of the coating should be 400 to 600 g/m². If the intended use is spackle rather than paint, the fiber portion increases to 2 to 3% and allows for the treatment of seams, wide cracks and holes.
Dispersion covering color
One layer covering colors made from synthetic resin dispersions (or silicate paint) are enhanced with 0.3 to 1.5% of an acrylic fiber filler, mineral fiber or ceramic fiber to make it thixotrope. Such a fiber enhanced paint will cover up the surface in one layer and the water regulating feature of the acrylic fiber will prolong the wet life.
Construction material
Concrete bonded construction material can effectively be reinforced by adding in polypropylene splicefiber and PAC high module fiber. This supplement will increase the impact resistance, tensile strength, and extensibility of cement and concrete. As a result, the scrap due to breakage in the first four weeks will be significantly reduced. The larger specific surface, rectangular profile and the coarse surface of the fiber will improve the anchoring of components in the end product.
Asbestos replacement
The development of high pressure polyethylene fiber fibrids introduced the first product that was comparable to the asbestos fiber and was a suitable replacement in terms of alkali and temperature resistance, high fibrillation of the structure, and specific surface which is at 7 to 10m²/g and thus higher than for most fibers. Additionally, the fibrid fiber shows strong resistance to acid and allows for a high rate of yield due to its high specific weight of 0.95 g/cm².
Depending on the desired characteristics of the product, especially in terms of thixotropy, the length of the fiber may vary significantly. Since the fiber fibrid can not fully compensate for the weight of the asbestos fiber, the replacement product will only contain 15 to 30% of fiber and the remainder will be made up of e.g. powdered stone or talcum. Alternative replacement product for the remaining 70 to 85% that have proven successful are China potash or industrial particulate matter.
As a high pressure polyethylene the fiber fibrid has a crystal melting point of 132 to 135ºC. Therefore, above 120ºC a beginning fiber shrinkage and morphologic changes up to the complete destruction of the fiber has to be expected. However, the basic material polyethylene will remain decomposition resistant for a certain time even in temperatures of up to 200ºC.