Flocking attracts due to its delightful and silky appearance. Today flocking is used every where including t-shirts, sports clubs and leisure wear, car glove boxes, floor coverings and on many other products.
Flocking process
The flocking method covers applying short monofilament fibers, normally nylon, rayon or polyester right away on a substrate that has been formerly layered with an adhesive. So, by flock we mean short-cut textile fibers. For making flocking on textiles, generally we apply flock lengths of 0.5 or 1.0 mm of viscose or polyamide (Nylon). The most used sizes for polyamide are 3.3 dtex/0.5 mm and 6.7dtex/1.0 mm, and for viscose 3.3 dtex/0.5 mm and 5.6 dtx/1.0 mm. An enormously soft touch is achieved with 3.3 dtex/1.0 mm, but this flock is not effective as wear-resistant as the other sizes as described above. Furthermore, flocking with this flock occasionally makes troubles for the strength of the fiber in proportion to its length, is obviously low-grade and may decrease the flock's siftability. The value dtex points out the weight in grams of one individual fiber being 10 km long. So 3.3 dtex means that one fiber, 10 km long, has a weight of 3.3 g. Both types of fibers are presented with light-fast, washable and considered against bleeding. The washing capability of polyamide is superior to that of viscose, since polyamide absorbs a maximum of 6 percent humidity against 13 percent in viscose.
Because of the humidity, the fiber swells up faintly which of course decreases its tight embedding in the glue. For the flocking of door mats a longer and harder flock Nylon 22 dtex/2.0 mm is used. In the production of carpets the same type of flock is used. This thicker fiber has very hard-wearing and extremely abrasion resistant properties.
Adhesives
Adhesives create most favorable effect on the quality of flocking. They make the link between the flock and the substrate. They are preferred to be soft, flexible and wash-proof. Today acrylate based dispersions are significantly applied for special application, like waterproof jackets or other coated fabrics; solutions can be applied as well.
Dispersion glues are distinguished between low and high temperature curing glues. At room temperature curing within two to five days, the low temperature glue dries. This denotes, after this time has passed the garment can be washed. A fixing agent has to be applied for curing. It is critical to understand the producer's instructions concerning the mixing ratio and blend the fixing agent homogeneously into the glue.
With a temperature between 120 and 140 degree Celsius, high temperature curing glue needs 5 - 10 minutes fixing time. It has to be stressed that drying and curing is achieved in to two stages. In the first stage the glue has to get dry, i.e., the water included in the glue has to evaporate. During this time, by virtue of physical law, the temperature does not go over 100 degrees Celsius. Then only 120 or 140 degree Celsius is achieved.
The drying process is provided by concentrated air circulation with combination of fresh air. If a drying oven performs only with circulating air then the air humidity will be raised to its peak limit without any further drying outcome, here the air cannot absorb further humidity. Hence, healthy air circulation with an appropriate share of fresh air has to be obtainable. Dispersion glues are eco-friendly, the stencils and utensils are washed out with water. In case of water-resistant surfaces solutions should be applied, normally a polyurethane-based two-component system is used. Fastnesses are superior, just like those achieved with dispersions.
Printing Screens
The adhesive is used by screen printing. Normally, we apply a screen mesh prepared by polyester as it absorbs only less water and does not covered by the dispersion glue and in cleaning. Screen meshes of 24 T to 40 T are applied (standing for 24 to 40 threads per cm) as the adhesive layer is comparatively thick. In against ordinary screen printing these meshes are proved to be relatively rough, but the glues are paste like up to thixotropic, and an enough amount has to be used on the substrates. It is essential that the contours or lines are not extremely fine. The rough mesh would make saw tooth appearance, and, as not sufficient glue could be used, the flock would not restrain very well. Lines and dots in the design are kept at a minimum width of 1.5 mm. The needed quantity of adhesive is not only decided by the screen mesh, but also by the toughness and shape of the squeegees. Soft squeegees (60 to 70shore) with a rounded edge and a square edge have showed to be most excellent. The squeegee should extend beyond the design by at least 20 to 30 mm.
Operation Method
The adhesive is fixing to the printing screen. The first squeegee stroke should be achieved with high pressure so the adhesive can some extent enter in to the fabric. Two to four strokes with the curved edge should crushed in an adequate amount of glue by the screen. And, in the final stroke, with the pointed edge, the surface of the screen should be washed out by applying as little pressure as needed. The outcome is a silky surface and an adhesive layer of circa 0.1 to 0.2 mm achieved after the pulling up of screen. After eliminating the screen the adhesive is replenish with the curved edge to evade desiccation of the screen. The adhesive can be imprinted with contact or small off-contact distance in textile flocking.
The off-contact distance should be kept slight higher so the material edges will not get compressed in coated fabrics, paper, or plastic materials. Flocking goes after straight away subsequent to adhesive application.
This is significant, for, if intense time delivers between adhesive utilization and flocking, the adhesive might obtain a film, maintaining the flock fibers from entering. Flocking is achieved simply by electrostatics, the fibers are charged with high tension and fly, relating to the lines of force, vertically to the counter pole. They will get discharged and go back to the flocking machine if they do not locate adhesive there. When they are been linked with the adhesive, they will fix there vertically and are set in. As long as the adhesive stays wet the flocked surface must not be contacted to not press the fibers in placing upright.
The flock is not exactly dyed relating to the color fastnesses mentioned before, but it also experiences a particular cure which provides it a particular electrical conductivity permitting it to take up and give off loads rapidly. For one thing, this conductivity composes of the preparation's own conductivity, but also of the comparative air humidity in their atmosphere. This denotes that the comparative air humidity in the work-room also affects the flock's motion in the electrical field.
The ideal relative air humidity ranges between 55 and 65 percent. The flock makes so-called "whiskers" or "beards", and, if the humidity is too high, the flock's siftabiliy is poor and it tends to become lumpy, and it has happened if the air is too dry. Especially in winter when outside temperatures are very low, it often happens that the comparatively air humidity in the work-room is only 30 - 35 percent. An adapted humidifier will be helpful. If the air is too dry the "open" time of the adhesive decreases and the danger of getting a film raises.
Machines and Equipment
In majority situations the adhesive is used manually. It is applied by the printing screen with a hand squeegee. It is recommending the use of an automatic screen printer in case of larger batches. Their benefit is that the squeegee pressure stays constant as pre-adjusted.
Adhesive utilized are promising either with a table printer, or if possible, with a stationary device on a palette. Perfectly, the printing stencil is swivelling so the T-shirt or sports jacket may be effortlessly applied and detached after adhesive application. Subsequently the parts to be flocked are put on a worktable. A regular table enclosed by a metal plate which is attached with the ground socket of the flocking machine via a ground cable is used. A particular flock table has lateral walls to keep the flock from straying.
The top provided with the outline of a grid so the surplus flock drops into a funnel underneath and from there into a flock hopper. Hand flocking units cover a high-tension generator and the working utensil, called applicator. The flock is spread out into the applicator whose bottom is linked to high tension. It is put near by a screen. When shaking the applicator a little during the high tension, it is turned on and the flock spurts into the object to be flocked following the electrical field lines, and is inserted vertically in the glue. The high tension produced by the different generators ranges between 70.000 to100.000 volt, whereas, the amperage resides within the safe A range.
The RF 500 flocking machine permits automatic flocking in combination with a carousel printing table. The RF 500 covers the high-tension generator, the control unit and the flocking unit with a circular flock container and rotating brush. The rotating speed of the brush, as well as the dosing time, the intensity of high tension, and the duration of high tension, they all can be set separately.
After adhesive treatment, the garment put on the palette of the rotating table and has been shifted under the flocking station; the functions are being achieved by a foot pedal. High tension and flock feeding are started. According to the size of the design and the flock's ability, the flock is fed for 5 to 15 seconds while high-tension is turned on. After treatment of this period, the feeding made closed, while the high tension stays on for about 5 seconds to permit the surplus flock, which is still shifting in the electrical field and to get it also fixed in the glue. After stoppage the high tension, the carousel continues to shifting and the working process starts with a new phase.
To transform flock colors the flock hopper with the dosing brush can be simply detached and washed. For effective production it is suggested to apply an independent flock hopper for each flock color, or, at least, use independent hoppers for light and dark colors. This decreases machine standstill periods when shifting flock colors.
The garment is detached after flocking and the main part of the excess flock is removed before it is put into a tray cart for drying. As described earlier, drying is achievable at room temperature or in a drying oven or channel. After drying, the garment should experience a final washing treatment by heavy shaking, beating or vacuuming, or most capably, particularly in a T-shirt cleaning device. An extremely robust exhauster automatically appeals to the shirt. With brushes on top and bottom of the placed slot the surface gets brushed completely because of a special powerful air guiding system pneumatic vibration of the fabric is effected, comparable to a flag flapping in the wind. The surplus flock is vacuumed and gathered in a bag. This machine permits precise cleaning within seconds. On other hand, single-color direct flocking numerous tools of multi-color flocking and flock transfers are to be preferred.
The methods are mentioned as below:
.Multiple flocking
.Cover-up flocking
.Iris flock
.Flock-on-flock
.MC flocking.
Multiple Flocking
The entire working process is done repeatedly in this method, i.e. the first color is flocked, dried, and washed. And the garment is put on the palette again, and the next color is flocked, etc. Registration cane achieved merely to a certain extent as the fabrics are flexible. Hence this method is useful only for designs where exact registration is not needed. It is very labor-intensive; hence the cost for three-color flocking is three times as much as for single-color products.
Cover-Up Method
In this process the adhesive is used at once for the complete design. After that the applied parts of the design which are to be flocked in the second or third color are enclosed with paper or cardboard stencils. Simply the remain part of the design is flocked with the first color. After that another part of the design is uncovered before flocking the next color. This process is more economical than multiple flocking, but here, too, the range of appropriate designs is very less. If a design appears with closest colors, contours between the colors will not be darker. Various colors in a design should if possible be set in a distance of about 2 - 3 cm. The benefit of this process is that adhesive application, drying and cleaning have to be functions only once, creating the method very economical.
Iris Flock
The adhesive is layered at in one process over the whole design. Various flock colors are placed into the flock applicator, divided by dividing walls. All colors are flocked in single operation creating good-looking moves from one color to another. With some concepts, appealing designs like different blues for a sky, or a sunset atmosphere by using yellow, red and navy blue colors are made. The cost of the process is the same as in single color flocking.
Flock-On-Flock
It is similar to the multiple flocking methods; the adhesive is applied, then flock, dry, clean, and apply more adhesive. In this case not next to the first layer, fasten top of it. By these method sharp contours achieved and the double relief character will give special effects. Though, this also is an extremely complicated method, for each color needs the entire procedure: loading the garment on a palette, adhesive application, flocking, drying and cleaning.
MC Flocking
It is a true multi-color flocking process where the design has sharp contours. It stresses intense precision, and hence must be made by machines.At the first stage of a big carousel machine the adhesive is used over the complete design. After that the palette is shifted for the first flock color. Here the first color is flocked with precise registration by a printing screen. The distance between the garment and the flocking screen must be place closest. When applying the 1 mm flock, as is generally completed, the distance should be circa 1.2 to 1.6 mm. If the distance is moreover less, there is the risk that the bottom of the screen becomes soiled by the glue, or that the screen texture shows (of course, this may also be a very interesting side-effect). If the distance is at extreme the sharpness of the contours will be decreased. The carousel remains rotating while flocking color 2, color 3, and color 4. Since the palettes always go after each other(i.e. while the adhesive is applied at the first station, color 1 2 get flocked at station 2 3, etc.) the fabrication speed is approximately as fast as in single-color flocking.
In this process the outlay cost for the machine and for a number of flocking screens per design will be greater. By this method halftone MC flock has been made, which shows that with the four basic colors all colors can remake. This process stresses maximum precision in both from the machine and in the from the machine workers. MC flocking covers a broad field of uses in making the door mats. In Western Europe many million door mats are made and sold every year. They apply 2 mm flock and exclusive screens to permit the uses of a lot more adhesive, due to the coarse surface, and for a higher abrasion resistance.
Transfer Flock
In this process the idea is to iron flocked logos on a fabric piece and is similar to transfer printing. There are many possibilities to do the same. The easy form is to flock hot-melt foils and punch out letters or logos which are afterward ironed onto the fabric. Though this process needs costly punching tools, only larger batches of a logo can be done. The process is generally applied for the manufacturing of letters, digits and firms' logos.
Reverse Method, single color
In this process a special transfer flock paper is used, where the flock is fixed in a simply detachable way. A mirror image of the design is made with the adhesive. After that hot-melt powder is applied over the adhesive when it is wet. After it becomes dry, the design is overturned, i.e. it is put on the fabric with its hot-melt powder side onto the fabric and is afterward ironed on. The hot-melt powder mixes with the fabric, and in the part where the adhesive was imprinted the flock releases from the mover material. By this method design is made on the fabric with the accurate side. Particularly for small designs this method use cost effective tool than direct flocking, even if the superiority generally is not as precise. A normal screen printing business only needs a screen printer (which they already have anyway), a dryer and a transfer cleaning machine to make flock transfers are the benefits. For utilization of the relocation on the fabric (cut-piece fabric or finished garment) it just needs a transfer press without any supplementary needs.
Reverse Method, multicolor
This process is similar to the reverse method, single color but here need a transfer paper of simple white one. In this process, first the colors of the design are embossed, and then the adhesive with the hot-melt powder is applied. It is essential that the printing ink actually enters in to the flock. Delicate grayness on the finished transfer will make deprived quality.
LEXTRA Transfers
LEXTRA Transfers is multicolor flocking methods, it is a blend of MC flocking and transfers. The flock is used on the transfer paper, or on the mover foil, not selected singles colored, but the whole design as mirror image. Pursued by flocking and dry-in, adhesive and hot-melt powder is used. This technology carries the nearly all brilliant colors and very dark contours, as, of course, a foil is yet superior, capable for MC flocking than a fabric.
Evaluation of Transfer Flock and Direct Flocking
After the discussing a variety of process it is time to evaluate the advantages and disadvantages of the various process, granted that only the best materials are applied and effort is carried out carefully.
Normally, the quality of direct flocking will to some extent exceed that of transfer flocking, particularly in larger designs. For indirect flocking more tools and more process phases are needed in against transfer flocking, as here the transfer paper, or the finished transfer, can be procured for application with a transfer press.
In direct flocking, the size of the design performs a somewhat less important roll in price calculations, while it is a vital factor in transfer flocking. A transfer 10 x 10 cm costs almost four times as much as a transfer 5 x 5 cm, this obviously proves that small logos or letterings, particularly if multicolored, are more logically priced. The relative stiffness of the transfer is not as disturbing as in large designs, is another benefit of small transfers. Large club logos, nationalities, or designs of tourist temptations are made by direct flocking. A company that needs to present the entire range to its customers should have both possibilities.
In evaluating the quantities of single and multicolor prints, flocking will forever maintain just a small fraction of the market. Its well-designed appearance and good wearing characteristics create flocking better to other technologies, and as the past years have showed, prices are ranging high. As described earlier, this technology doesn't obtain market shares with low-price merchandise but with better quality. No quality is sufficient that it could not be broken by inappropriate handling. Of course, this also uses to flocked articles. Hence it is suggested to stick washing instructions to flocked garments. Since the fibers are swelling up in the water, their abrasion resistance is low. Constant spinning in the washing machine is rather hard on the fibers.
Hence it is recommended to turning the garments inside out before putting them into the washing machine. By this, there will be no straight away grazing of the fibers whilst the washing effect stays as it is. Relevant washing guidance can save you a lot of effort. Flocking is not only used on textiles, T-shirts and sportswear, but it is applied in all fields of surface treatment, and, above all, for many technical applications.
Source: Maag Flockmaschinen GmbH
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