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