CASE STUDY : Processing characteristics of micro polyester fibers in the COM4® staple fiber spinning mill

By:

Dr. Anup K. Rakshit
Vice President - PSF Product Development
Reliance Industries Limited

And

Harald Schwippl
Dipl. Ing (FH)
Head of Technology
Rieter Machine Works Ltd.

Contents

1.0 Preface

2.0 Recron TM Micro Polyester Fibres

2.1. Advantages and areas of use of micro fibres

2.2. Applications

3.0 Micro Polyester Fibres Processing in the Staple Fibre Spinning Mill

4.0 Choice of Raw Material and Experimental Plan

5.0 Processing Characteristics of Fibre Preparation

5.1. Blowroom and Card

5.2. Drawframe

5.3. Roving Frame

6.0 Yarn Final Spinning

6.1. Yarn Unevenness

6.2. Yarn imperfections

6.3. Yarn strength and elongation

6.4. Hairiness and abrasion

6.5. Yarn resistance versus mechanical influence

7.0 Conclusion

1.Preface

This publication has evolved within the scope of the cooperation between Rieter Technology and Reliance Industries for the development of know-how for processing polyester staple fibres on Rieter spinning machinery. Processing of Recron^TM microfibres on compact spinning machine-COM4, as presented below, is one of such development programs.

2.Recron^TM Micro Polyester Fibres

The most versatile and widely used fibre is polyester where the maximum number of variations in terms of physical, chemical and geometric properties are possible as compared to other synthetic fibres. Over the years there has been tremendous development of polyester fibre and today it occupies largest market share amongst all synthetic fibres. Polyester fibre generally distinguishes itself by the following advantages:

High melting point
High breaking strength in dry and wet conditions
High elongation
High abrasion resistance
Resistant to organic and mineral acids
Good dimensional stability
Easy to wash

Reliance has started world class Research & Development facilities for the development of polyester fibres. After recent acquisition of Trevira in Germany this has further strengthened. Trevira's knowledge base developed over a period of time will be complementary to Reliance's existing R&D facility, the Reliance Technology Centre. The synergy will provide comprehensive and innovative solutions for apparel and non-apparel applications of polyester to customers worldwide.

This initiative has introduced to India and the world, a high quality product range of speciality fibres and yarns under Recron TM brand. These products bring with them distinct characteristics that add more value to the ultimate woven or knitted fabric in terms of its look, feel, drape, dye-tone etc. In addition to various modifications in basic Polyethylene Terphthalate (PET)polymer, market trend is moving towards producing finer denier fibre like micro, nano, etc. Reliance Industries Ltd. developed the art of producing very fine denier fibres. For more than ten years it produces 1.12 dtex fibre and now developed 0.9 dtex microfibre.

Excellent fabrics and garments with specific textile characteristics can be produced from the microfibres. These textile characteristics, when compared to those produced from natural fibres exhibit hardly any differences or with special fibre constructions are today even superior. Thanks to microfibre, characteristics can be created which, for instance, correspond to the advantages of natural silk.

Microfibres being fine and more pliable, it facilitates compaction mechanism of fibre in compact spinning. Higher number of fibres in the yarn cross-section gives higher yarn strength, good running characteristics and enable to spin finer yarn.

2.1Advantages and areas of use of micro fibres

This is a very fine staple fibre of 0.9 dtex produced with highly sophisticated plant equipment with precise control of polymer quality and all process parameters. The chief special feature of microfibres is its cotton like soft feel. Among the other features that this finest man-made fibre offers are:
Has a fabric in all weight categories
Is resistant to wrinkling
Offers light weight comfort
Has exceptional drape
Is easy to care for
Gives a soft, silky and buttery hand

2.2 Applications

The microfibre ultimately ends in sophisticated evening wear, men's business wear, casual wear and even intimate apparel. High quality shirting, fine T-shirts, sweatshirts, sportswear, kids wear, undergarments, tracksuits, nightwear and lingerie could come from the micro fibre. Scarves, handkerchiefs, bed sheets and linen can all begin with the micro fibre, which is basically positioned in the highest segment reserved for luxury and exclusive garments.

3.Micro Polyester Fibres Processing in the Staple Fibre Spinning Mill

Results of the introduced study in the spinning mill refer to a micro fibre of0.9 dtex with a cutting length of 40 mm. In particular with spinning of micro fibres and high cutting lengths, the "pliability of the fibre" is an important criterion. The relationship of the fibre length to the fibre diameter is also described as slimness degree. The fibre diameter can be determined from round cross-sections as follows:

With a fibre density of 1.38 g/cm³ for polyester fibre, a slimness degree will be approx. 4400. Such a high slimness degree, as it occurs otherwise only in worsted spinning, necessitates very careful and gentle settings in the spinning process in order to counteract the tendency of fibre entanglement and formation of neps.

In addition, the drafting forces in the spinning process are strongly determined by the number of fibres in the cross-section.

With the use of microfibres, there are more fibres in relation to across-section than with fibres which have a conventional fibre fineness like1.2, 1.4 deniers. The drafting forces again have substantial influence on the size of production at the individual process levels in the spinning process, in particular with the card. For the production of fine yarns, microfibres offer a particular advantage for good spinning performance. A yarn count of approx. 7.4tex and a fibre count of 0.9 dtex gives with approx. 80 fibres in the cross-section a sufficient number of fibres for a stable running behavior, whereby the spinning boundaries for ring yarns are still not reached.

The Recron^TM micro fibres exhibit around cross-section. The fibre - fibre, fibre - metal friction and static generation are fundamentally determined by the spin finish and influences the processing characteristics and finally the yarn quality in the staple fibre-spinning mill.

The amount of the spin finish and its composition is a primary parameter for the friction and static conditions. The spin finish amount should remain constant across the individual process levels. Spin finish deposits within the spinning process interfere with this and can also have negative effects on the spinning ability and yarn quality. Finish coating given on Recron^TM micro fibre takes care of these problems.

4.Choice of Raw Material and Experimental Plan

Recron TM Micro fibre of 0.9 dtex and 40mm cut length was chosen for this study. It has tenacity of 6.8 - 7.0 gpd, elongation of 22 - 24 % and very low level of fibre shrinkage.

In the preparation for spinning and spinning mill following high performance Rieter spinning machines are used:

1 Unifloc A 10
2. Blending Opener B 3/3
3. Feed Chute A70
4. Card C 51 Hi - per
5. Pre-Drawframe SB - D10
6. Finisher RSB - D30
7. Roving Frame F 10
8. Ring spinning G 33
9. ComforSpin - K 44

Spinning plan for ring spinning when using microfibres to achieve best quality is determined as follows:

5.Processing Characteristics of Fibre Preparation

5.1 Blowroom and card

As the automatically bale opening with the UNIfloc ensure an even and fine fibre opening, only a storage and a blending opener (B3/3) was used for the following process steps. Depending on the type of polyester fibre up to two openings could be necessary for a sufficient opening.

For a technologically expedient fibre preparation, adjustments of the technological elements and the settings are also necessary if the production speed of the card is increased. With regard to the wire for fibre opening on the card, over the years the needle rollers on the Rieter card C 51 have proved very effective in relation to quality and quality consistency. For the whole trial range, a needle roller with 36 points / 2 inch and a needle angle of 58 deg. was used a slicker-in on the card.

In order to keep the carding force as low as possible, a cylinder wire as typically used today of 640 points and 30 deg. working angle was at this stage applied for microfibres. The beginnings of the processing of microfibres on the card showed in the 90’s the application of even finer cylinder wires, such as 1080 points per sq. inch. With time, however, it became apparent that in practice disadvantages often resulted.

The efforts to achieve a highest possible quality by higher point numbers or to keep the number of fibres in the tooth gaps constant against the coarser fibres led to excessive card force. The fibres could only reach the tooth gaps with difficulty because of the high fibre metal friction. This caused the card force to massively rise without an optimal carding being achieved.

By tracing the fibre stress over the individual process stages, it is clear that the highest attention must be paid to the Card and therefore offers the greatest challenge to increase performance in the spinning process with minimal fibre stress and good carding quality.

A too coarse wire can, on the other hand, tend towards overloading of the wire. Due to a higher number of fibres between the teeth, in the extreme case the fibres can no longer be delivered from the cylinder wire. Added to this is that with the low single-fibre mass of microfibres, the centrifugal force on the cylinder no longer suffices for a delivery as the centrifugal force reduces linear to the fibre mass.

Consequently, with fibre counts from 0.9 dtex top figures between 640 and 720 per sq. inch and 25 - 30 deg. working angle have proved successful. The optimal wire depends also on the fibre characteristics, the spin finish and the climatic conditions.

The use of 640 points shows with this raw material that the fibres do not allow an optimal delivery from the cylinder to the doffer. It was observed that the relatively fine fibre became fixed in the wire grooves. A higher cylinder revolution to achieve a higher centrifugal force was not chosen for reasons of a lowest possible fibre stress.

Therefore, the number of points on the cylinder under otherwise equal conditions was increased to 720 points per sq. inch. The running characteristics and the fleece quality were subsequently to be described as very good.

In the fibre strength the stress of the fibre appears clearly in the carding process. The fibres lose here approx 8cN/tex. The reduction in fibre elongation amounts approx. 4%.
The optimal processing climate in the spinning mill rests with 23^o Celsius and 62% relative humidity.

The card wire and climatic conditions have a great influence on the optimal card forces and the quality. In order to here substantially increase the card production with microfibres, new methods such as the reduction of the fibre volume by increase of the carding working area must be realized. That means the conventionally working wideness of 1 m must be clearly increased.

5.2Drawframe

To determine the processing characteristics, the drafting force in the main drafting field on the first and second drawing passage was measured. The values relate to the respective optimal machine settings and therefore merely relate to the feeding fibre mass. The whole drafting level of the draw frame lay respectively in a scale from 6 to 6.3 fold. To obtain a comparison of the drafting force with microfibres, two further fibre types of polyester were used.

Based on the chosen fibre measurements, no excessively high drafting forces are exhibited with microfibres. The drafting forces are here on both drawing passages with 14 to 25 N much smaller than in comparison to the two conventional fibre counts and fibre measurements. Under the assumption that the drafting force can play a decisive role for an even drafting, the feeding fibre mass in the drafting arrangement could also with Reliance microfibres quite easily amount to minimum 27 dtex. In further investigations in the area of the drafting development with the processing of microfibres, it must still be clarified, however, whether the middle drafting force for an even drafting orthe diffusion of the drafting force is the dominating factor.

5.3Roving Frame

The twist transmission from the spindle in the spinning triangle is an important criteria on the roving frame. Despite optimal roving twist of 19.7(530 tex, 27 T/m) for the following ring spinning machine drafting arrangement, attention must be paid to a good twist transmission from the spindle in the spinning triangle on the flyer. The twist must thereby be optimally transmitted from the spindle to the spinning triangle and may not show periodically any untwisted places between the flyer crown and delivery cylinder

To clarify how far a massively smaller roving force with Recron^TM The maximum roving adhesive strength was thereby reduced to a very low value of 760 cN.

The twist transmission is strongly influenced by the fibre - metal friction of the particular raw material resp. its spin finish. To this point attention must be paid with the processing of microfibres.

The following points achieve a good twist transmission:

Flyer quality which causes little fibre - metal friction

Suitable Flyer attachment crowns
Suitable climatic conditions
The best climatic conditions for the roving frame could be established at approx. 23 deg. Celsius and a relative humidity of approx. 50%.

6.Yarn Final Spinning

As final spinning machine the conventional ring spinning system and the compact system COM4 were taken. The final spinning positions are compiled in the following overview:

In order to show the influence of both final spinning methods as clearly as possible, a most gentle fibre preparation resp. card performance of 30 kg/h and under consideration of stable running characteristics on the ring spinning machine and spindle revolutions between 15500 and 16500min^-1 with a ring diameter of 38mm were selected.

According to yarn structure and yarn count, influence parameters of the spinning process play a stronger or weaker role in the measurable quality criteria of the yarn. The yarn quality values achieved are, on the one hand substantially influenced by the yarn structure and yarn count, on the other hand the influence of the fibre preparation varies according to yarn structure and yarn count. To obtain an optical impression of the various yarn structures, the yarn body with a yarn count of 10 tex is magnified 50 times.

The roving count 530 tex 19.7 shows, against those with 400 tex 17, a worsening of0.4 percent primarily with conventional ring spinning systems and fine final spinning. This means that according to the final spinning system with approx.6000 fibres in the cross-section in combination with a 19, slight quality losses are already to be reckoned with. Consequently, in the case of highest quality requirements, the number of fibres in the cross-section or the twist factor must be reduced. The tendencies are confirmed by the variation coefficient of the yarn diameter on the optical measuring module of the UT 4.

The optical unevenness, in addition to the capacitive unevenness, makes the influence of the yarn twist visible. A reduction of the yarn twist factor from108 to 97 results in a minimally higher variation of the yarn diameter resp. the optical yarn unevenness of approx. 0.2 percent. An improvement in the unevenness of COM4 yarn is attributed to the improved fibre bonding on the spinning triangle. A better bonding of the outer fibres in the yarn core favourably affects the evenness, even with this raw material. Further, the improved unevenness shows a positive effect on the IPI values through a better fibre bonding. Missing or less bonded fibres in the yarn body lead to higher thin and thick place values. In the extreme case, sporadically or inadequately bonded fibres" short thick places" also exhibit more neps in the yarn.

The differences in the yarn unevenness with the same fibre sample between both spinning systems is therefore not founded in an improved drafting performance from one to the other ring spinning machine drafting system or the drafting performance on the final spinning machine but in an improved fibre bonding in the spinning triangle resulting from the compaction. Due to the aerodynamic compaction of the fibres on the perforated cylinder, the spinning triangle is reduced to a minimum.

6.1Yarn Unevenness

On the COM4 system a better unevenness of absolute 0.3 to 0.8 percentage points according to the capacitive measurement is given depending on the yarn count of both roving variations. Thereby, it is already apparent that also with Polyester microfibres the fibre compaction has a positive influence on the fibre orientation. The yarn twist reduction from 108 to 97 on the compact system shows no negative influence on the unevenness.

This means the final spinning system can have a greater influence on the abrasion resistance than the yarn twist. This finding is remarkable and shows what potential can also exist with Polyester microfibre in the yarn structure with constant yarn twist. In addition, the surface roughness was also visually observed after the respective maximum number of cycles

The pictures clearly show with the example of a 10 tex yarn, the advantages of a yarn structure where the outer fibres are better bound into the yarn body. Next to the very great influence of the yarn twist, a good binding of the outer fibres in the yarn body exerts a clear advantage on the yarn resistance. That means the combination of a yarn twist of 108 with a good binding of outer fibres leads to an excellent yarn resistance with the Recron^TM microfibres. A lower resistance tendency is advantageous for the subsequent winding process up to the following downstream process in the values of the textile fabrics. Conditional upon the greater fibre surface with microfibres, pilling has always been a big theme especially in the past. The improved fibre binding with theCOM4 system will also here have a positive effect.

The roving adhesive strength is a significant factor for the expected drafting performance on the ring-spinning machine and influences the quality and its constancy. Use of the Rothshild measuring method allows recording of the roving quality and to a certain extent adjustments to be made for the spinning process.

If the roving adhesive strength, based on the fibre mass and the roving twist, is too great, draft disturbances in the ring spinning machine drafting zone and will result in a poor yarn quality.

If the roving adhesive strength is not constant during the drafting process, variations in the yarn quality will occur.

6.2Yarn imperfections

As expected, the thin places in the yarn were reduced due to the compact spinning system COM4. On both rovings, according to the yarn count and taking into consideration the distribution, approx. 8% - 20% fewer thin places resulted. This result can be explained, as also mentioned with the unevenness, by a better fibre bonding on the spinning triangle. Here, the unevenness aswell as the IPI values have a direct connection.

Roving with much lower drafting force of approx. max 760 cN (400 tex 17) also results in a reduction of up to 20% of the thin place values in comparison to roving with a higher drafting force of approx. max 1650 cN (530 tex 19.7). To achieve lowest thin place values, the fibre number should next be reduced from6000 fibres in the cross-section or the twist factor of 19.7 somewhat lowered.

It can be recorded that the quality influence of the roving composition in this yarn count area turns out equally as big as by the final spinning systems. This means the negative influence of the roving can be equalized by the positive influence of the final spinning system.

In the thick places, clearly improved values of up to 20% as with conventional ring yarn also result from the COM4 system. Further, with the production of the COM4 with the coarser roving (drafting power max. 1650 cN with 530 tex 19.7) as compared to the "softer roving"; no negative influence can be registered on the thick places.

This means that the conventional spinning system reacts more sensitively to the roving characteristics with the processing of microfibres than the COM4 system. The conventional ring yarn under the application of the "softer roving" has at least 10% fewer thick places. From this can be deduced that to achieve lowest values on the conventional spinning system, the number of fibres of 6000 fibres in the cross-section or the twist factor of 19.7 must be somewhat reduced.

Between the final spinning systems, no differences in the neps are apparent taking into account the distribution. By processing of the coarser roving of 530 tex, the nep values were even better than those with the soft roving. The greater roving mass results in a higher draft on the ring-spinning machine, which positively affects the number of neps.

With regard to the yarn imperfections, it has been shown that with a constant feed in the ring spinning process, the unevenness resp. thin places, followed by the thick places, represent the critical factor. This means the COM4 system with a good "draft behavior" and a good "fibre bonding in the spinning triangle", offers to these criteria interesting possibilities for the final product.

6.3Yarn strength and elongation

Despite the relatively high yarn strength which occurs from a greater number of fibres in the yarn cross-section when processing microfibres in comparison to coarser yarn count with the same yarn count, a strength increase of approx. 1cN/tex of the particular yarn counts through the better fibre bonding on theCOM4 system is, however, apparent. The elongation here is inevitably reduced due to the high strength values. The elongation difference between the two spinning systems can thereby be explained that by a very good fibre alignment and fibre bonding in the yarn thread, the fibres can assimilate fewer length changes in the fibre formation.

A lowering of the yarn twist by 10% on the COM4 shows no reduction of the average value strength. With regard to the average value strength, the twist factor of 108 to 97 could therefore be lowered which equals a production increase of the final spinning machine.

On the conventional ring spinning system, a strength increase of approx. 0.7cN/tex from the coarser roving (530 tex 19.7) to the very soft roving (400tex 17) could be recorded. With the COM4 System, the strength increase which results from the softer roving lies at approx. 0.5 cN/tex.

It can be seen that the yarn strength and elongation when using microfibres already reacts negatively to the respective roving characteristics of 530 tex, however can be still described as satisfactory.

6.4Hairiness and abrasion

The low hairiness of the yarn resulting with the COM4 system is clearly observed with Recron^TM micropolyester compared to the conventional ring spinning system, measured according to Uster UT and Zweigle 1 2 mm. With increasing yarn numbers, the differences are smaller but are still obviously lower on the COM4 depending on the yarn count when compared to conventional yarn. The coarser roving with 530 tex has a clearly negative influence on yarn hairiness.

By observing the long hairs of more than 3 mm according to Zweigle, one ascertains a very low absolute figure. Based on the low absolute figures, a statement seems inappropriate even when a clear trend to the advantage of the COM4 system is obvious.

Ideally, no dependence of the COM4 yarn to the yarn number resp. no increase in hairiness with increasing yarn numbers is shown. This means that the raw material in the yarn number area tested can be well compacted. With the yarn winding and in the subsequent winding process, a lower hairiness also has a positive effect on the nep values through lower fibre suspension.

The yarn abrasion of ring yarns continues to be an indirect measurement for the yarn hairiness. Between the yarn hairiness and the pilling behaviour, experience has shown that generally a good correlation exists. High hairiness values lead to a higher unwanted pilling behaviour. Using the Staff tester, a measuring speed of 50 m/min over a time span of 10 minutes was recorded. By observation of the yarn abrasion per yarn weight unit, the abrasion amount with yarns, which become coarser, must inevitably reduce logarithmically as the abrasion relates to the yarn weight and a smaller reference length results. As the influence of the yarn length on the abrasion is higher by far than the influence on the yarn diameter, the reference length "abrasion in mg per1000 m yarn" was selected for this reason.

Under the criteria of the yarn reference length, the abrasion values between the positions as well as with the S 3 hairiness show too low absolute numerical values, so that under these quality criteria no explicit differences between the spinning systems of the yarn twist and the roving characteristic are visible.

6.5Yarn resistance versus mechanical influence

Along with the mentioned yarn criteria, the abrasion resistance in the downstream process and the usage characteristics in the textile fabric is an important criteria. For this purpose, the delaying tendency with particular cycles of web tester tours was examined using the Reutlinger Web tester. With the assistance of this measuring method, the resistance of the most important stress on the warp threads in weaving can be simulated. At this point, the measuring values should be applied as criteria for the precision of the fibre bonding in the yarn. Here, the presumption is that an abrasion resistant yarn not only shows advantages in the weaving process but in all further processingstages up to the textile fabric.

When comparing yarns with the same twist factor of 108 it is evident that the COM4 yarn displays a much higher number of abrasion revolutions before a thread break occurs. The sagging of the yarn overstressed from cycles was already counted as yarn break.

7.Conclusion

In the context of the co-operation relationship between Rieter and Reliance, the spinning characteristics of a Recron^TM microfibre on COM4 spinning technology up to the yarn with regard to their spinning behaviour and the yarn quality are demonstrated.

The yarn usage of synthetic staple fibre increased enormously. The polyester staple fibre production alone amounts today approx. 13 million tons per year. Within the Polyester staple fibre, the microfibre has also won lot of importance over the years.

When considering the fibre stress over the individual process stages, it is clear that the highest attention must be paid to the card and therefore offers the greatest challenge to increase performance in the spinning process with minimal fibre stress and good carding quality.

With increasing card production, a somewhat lower roving force and a higher variation of the roving force through the carding process can be ascertained.

Experience has shown that Polyester represents the greatest challenge with regard to a controlled fibre feed in the compact technology on the final spinning machine. Clear advantages with the application of the final spinning technology COM4 could, however, be demonstrated.

The COM4 final spinning system shows also with the Recron ^TM microfibres used distinct advantages in the thin and thick places of the yarn thanks to the better fibre binding. The preliminary process from the card to the flyer roving significantly influences the compacting results. Despite the relatively high yarn strength resulting from the relatively high number of fibres in the cross-section, the average value strength could, however, be noticeably increased. The physically positive yarn measurements become very clearly apparent in the yarn resistance.