| The melt-spinning process used for production of | | | | yarn that causes the Zebra effect is a well-known |
| synthetic fibers such as polyamides, polyester and | | | | problem to melt spinners of polyamides. With |
| others is a well-established and long-existing | | | | elastic yarns like spandex, the problem is even |
| technology in the industry.For many years | | | | more difficult to resolve.Uneven yarn is not |
| attempts have been made by the industry | | | | acceptable in fine-denier spandex used, for |
| experts to produce an elastic spandex yarn using | | | | example, in hosiery, even if the spandex is |
| a similar process by melt spinning TPU | | | | covered by nylon yarn before circular knitting |
| polymers.We all know that Dry spinning is the | | | | since the Zebra effect will show on the final |
| most traditional and common way of producing | | | | product, thus downgrading its quality.The solution |
| spandex. However, one of the major drawbacks | | | | to this Zebra effect problem involves finding the |
| of this method is the heavy investment required | | | | right spinning conditions, such as manifold and |
| in construction of a commercial-scale production | | | | spinning head temperature, spinneret design, |
| plant of, for example, 3000 to 5000 tons per | | | | quench-air temperature, relative humidity, blowing |
| year. At a 40-denier average, the overall | | | | speed and uniformity of air stream, and aging of |
| investment is in the range of US$ 40 million to | | | | yarn packages after winding.High-uniformity, |
| US$ 50 million which is quite high. The same is true | | | | melt-spun spandex yarns of perfect evenness for |
| for constructing a wet-process plant. Moreover | | | | hosiery applications are being produced today |
| dry and wet spinning also involve dealing with a | | | | after finding the spinning conditions necessary to |
| toxic solvent recovery process and, in the case | | | | meet this quality requirement.Another problem is |
| of the dry process, traces of the solvent remain | | | | that the recovery of melt-spun spandex is in |
| in the final yarn produced. In the melt spinning | | | | many cases below 90% versus a desired |
| method, no solvent is involved.The preparation | | | | recovery level of more than 95%. Modulus of |
| process for polymer in both dry and wet spinning | | | | around 1 gram/den for 40-denier yarn at 300% is |
| start by making the pre-polymer, the same used | | | | often found, and this is more than double the |
| in melt spinning, and sometimes called a | | | | desired level. These two elastic characteristics of |
| crosslinker. Wet-process plants are only | | | | the yarn stem from the type of raw materials |
| economical in producing coarser yarns of 400 | | | | used, NCO percentage, the amount and mixing of |
| denier and above, due to the limited underwater | | | | the pre-polymer, residence time within the |
| spinning speeds of a maximum of 200 meters | | | | manifold, and spinning conditions. High recovery |
| min.Melt Spinning: A competitive New ProcessIn | | | | and 300% modulus of 0.5 gr/den for 40-denier |
| recent years, very low cost melt-spinning | | | | are now being produced after all of these spinning |
| equipment has been developed and is offered | | | | conditions have been optimised.Role of Raw |
| today in Asia for a price that is 20% of that of a | | | | Material Suppliers is VitalThe low melting point of |
| dry/wet plant of equivalent production capacity. | | | | melt-spun spandex depends solely on the raw |
| This new process attracted many newcomers | | | | materials used. This issue is best solved by the |
| into the spandex production field.In addition, recent | | | | raw materials suppliers, as it is up to them to |
| developments brought more adequate TPU | | | | alter the mix of materials used in their production |
| polymers and the introduction of pre-polymer into | | | | of TPU to arrive at higher yarn melting point. One |
| the melt stream of TPU to improve the elastic | | | | leading supplier is already delivering a higher |
| characteristics of the produced yarns. All these | | | | melting point raw material and a second major |
| developments have further pushed this process | | | | supplier is developing an improved raw material |
| forward.Still there are drawbacks in producing | | | | having a higher melting point as well.With PTG and |
| melt-spun spandex. Among them are the short | | | | MDI market prices of less than $2/kg, raw |
| lifetime of spinneret, repeated cleanings of | | | | material suppliers of TPU and pre-polymer mainly |
| manifold; non-uniformity of the yarn that causes a | | | | made by these two raw materials must decide |
| zebra effect in the end product; recovery of less | | | | whether they wish to support further expansion |
| than 90% and a high (300%) modulus; a low | | | | of the spandex melt spinning into deniers such as |
| melting point and the limited range of deniers that | | | | 40 where selling prices are much lower in |
| can be economically produced. In spite of these | | | | comparison with 15 or 20 denier by selling their |
| drawbacks, melt-spun spandex production facilities | | | | raw material at prices that will give spandex melt |
| continue to expand, particularly in China where | | | | spinners the margins they need to justify making |
| demand for spandex yarns is still growing, with | | | | these products.In case of one leading TPU and |
| imports amounting to more than 30,000 tons in | | | | pre-polymer supplier, who is also supplying the |
| 2002.For the above reasons, a lot of attention has | | | | PTG to dry-spinning process users, this is a |
| been given to equipment, raw materials and | | | | strategic issue this supplier must address. In |
| technology to further improve the melt-spinning | | | | conclusion, it seems that the melt spinning of |
| process for spandex.Overcoming the | | | | spandex will grow substantially in the near future |
| DrawbacksThe drawbacks of using melt spinning | | | | mainly due to the low entry investment involved, |
| process can be overcome by taking some basic | | | | shorter installation time, and ease of operation.No |
| necessary steps. Selection of raw materials with | | | | doubt a faster acceptance of melt-spun spandex |
| the right specifications is the key and most | | | | yarns will much depend on the overall quality of |
| important point.TPU and pre-polymer, or | | | | this sophisticated high-priced yarn. Once the |
| crosslinker, (made by PTG and MDI) are available | | | | drawbacks are taken care there is no doubt that |
| from a number of sources. Process stability and | | | | it will have a huge acceptance in the market as |
| final yarn quality are affected by a variety of | | | | the price will be much less as compare to those |
| factors: the NCO percent of the pre-polymer | | | | produce from conventional methods.To read |
| used and the amount of pre-polymer added in the | | | | more articles on Textile, Fashion, Apparel, |
| process; the manner in which this low-viscosity | | | | Technology, Retail and General please visit If you |
| material is introduced into the high-viscosity, | | | | wish to download/republish the above article to |
| high-pressure melt of TPU; the mixing of these | | | | your website or newsletters then please include |
| two streams in and after the extruder by various | | | | the "Article Source". Also, you have to make it |
| mixing techniques; and the residence time within | | | | hyperlinked to our site.Copyright © |
| the manifold. The spinneret is also crucial to the | | | | 2006Fibre2fashion has emerged as a distinctive |
| quality of the final yarn produced. The design of | | | | B2B platform for global Textile, Apparel, Fashion |
| the spinneret assembly including hole diameter, | | | | and Retail and allied industries. offers business |
| hole layout within the spinning head and filtering of | | | | solutions, news, articles and information that help |
| the melt all play a major role in the life of the | | | | to survive and sustain in the most hostile and |
| spinneret and spinning efficiency. | | | | competitive business environment. |
| Solving the Zebra EffectThe non-uniformity of | | | | |