Dr. N.N. Mahapatra
CText FTI (Manchester)
Business Head (Dyes)
Shree Pushkar Chemicals & Fertilisers Ltd,
301/302, 3rd Floor, Atlanta Center, Sonawala Road,
Goregaon (East) Mumbai MH 400063
In India, spinning of dyed fibres is more important as compared to other countries. Spinning of grey fibres is easy as compared to dyed fibres. Spinning of dyed fibres may be of different blends. For example polyester fiber dyed blended with dope dyed viscose or own dyed viscose. Otherwise dyed polyester fibre blended with dyed cotton fiber or dyed acrylic fibre. In some mills spinning of 100% dyed polyester or 100% TBL (Trilobal) fibres or 100% own dyed viscose fibre or 100 % dyed cotton fibre are also done.
Dyed fibres are classified into two types:
Dope dyed.
Own dyed.
Dope dyed means where different colour pigments are added during the fibre manufacturing stage. Polyester and viscose fiber are available in dope dyed form.
Reliance and Indorama manufactures dope dyed polyester black fibre which is used in all spinning mills to make black p/v yarn. Polyester fibre is not dyed in black shade in dyehouse. because dope dyed black polyester is cheaper as compared to own dyed black polyester. Another advantage of dope dyed black polyester fibre is its spinnability. The spinners are happy in running dope dyed black polyester fibre. It will run as it is 100 % or mixed with dope dyed viscose fibre. The reason is the finish application. It is applied in tow form in the drawing m/c during the fibre manufacturing stage. The application of finish is very uniform on the fibre. That is why it runs very well in spinning. IOC manufactures dope dyed polyester fibre in few shades like navy, coffee, green, royal blue etc. The shades are limited and due to the cost factor it has not been accepted by the spinning mills. If they can manufacture more shades (like Grasim, Nagda (M.P) then it will be of help to the spinning mills. It should be cost effective. It should be cheaper or at par with own dyed polyester fibre dyeing cost.
Depending upon the dyestuff used and the depth of the shade, the polyester fibre undergoes changes in the following characteristics:
The fibre denier becomes coarser by 4 – 5 %.
The fibre tenacity decreases by 10 -15 %.
The breaking elongation of fibres increases by 16 – 30 %.
Reduction in the level of crimp.
Arising out of the above, the strength of the blend yarn, normally polyester –viscose, spun from own dyed fibres is lower than that from grey fibres.
On blending polyester fibres with viscose, the physical properties change substantially depending upon the temperature and humidity in spinning which normally varies according to place and season in India. Added to this the above changes taking place in the polyester fibre properties after dyeing. The efficiency of the spin finish and its application is never the same as a virgin fibre, which affects its processability in spinning after dyeing. Since the controls of all the above stated parameters are difficult, the problems in spinning are as below.
Loading of cards.
Generation of neps.
Fly generation.
Powder deposits (sticky material) in blowroom, carding, drawframe, speedframe).
More autoconer cuts (in heavy dark shades like navy, coffee, red and maroon) e g. 17-20 cuts per 10 kms.
More imperfections (in heavy dark shades as above)
Most of the spinning mills are situated away from the coast and therefore relatively humidity varies substantially in summer. Further, it is also found that high speed at spinning preparatory and ring spinning leads to high fly generation which in turn gives yarn faults. Fly generation is typically attributed to the poor cohesion as polyester is hydrophobic and viscose is hydrophilic in nature. In such case 2152P has to be increased slightly in finish spray to increase cohesion. Nowadays the spinning mills are using LV 40 and 2152P of different manufacturers. A fibre finish has little role to play in cuts. It is the staple fibre property like less crimps and short fibre generation. All these tests should be conducted by R & D dept at randomly. The dark shades having percentage more than 6 % depth in navy, red, maroon, coffee will create problem in spinning due to high molecular weight which cause harsh feel. But if the depth is less than 6 % (total) then there is no problem in working of navy, coffee, red and maroon shade. In other words navy and maroon shades are typically problematic above 6 % shade because higher molecular weight has limitation on dye penetration inside fibre structure there by more sort of surface coating of dye is observed. In such case dyehouse does double reduction cleaning /soaping etc to minimize the problem in spinning.
The finish solution should have pH between 6.5 to 7.5. Soft water is preferred (below 50 ppm) since most of the spin finish are unstable in hard water. During winter the temperature has to be maintained at 40 deg c. heating lamps are providing in the spinning finish oil room. Hot water is arranged by Geysor. It is better if a softening water line is provided to the mixing room.
The humidity and temperature plays a major role in spinning mills. Following are the parameters to be checked for polyester/viscose blends.
Opening – temperature – 85 – 90 deg F relative humidity – 60 –65 %
Roving – temperature reqd is 85 – 90 deg F, relative humidity is 55- 60 %
5.Ring spinning – temperature reqd is 85 – 90 deg F, relative humidity is 50 –57 %
In every dyed spinning mill in India there is tussle between the dyehouse and the spinning dept. The spinning dept wants the own dyed polyester blends to run smoothly like grey polyester or dope dyed black polyester blends, which is not possible due to the above changes taking place in polyester fibre properties after fibre dyeing. Still then some spinning mills they have studied the process control parameters to improve the spinning of polyester/viscose yarn or polyester/acrylic yarn.
In fibre dyehouse the polyester fibre and acrylic fibre should be dyed as per the dyeing cycle. No short cut in dark and heavy dark shades, after dyeing the reduction cleaning of polyester fibre is done in single stage or double stage (red, maroon, navy, and coffee). The application of finish should be done at the end of dyeing. The non –ionic antistatic cum finishing agent is used for polyester. The amount used varies from place to place. In some mills it is used 1 % on weight of fibre and in few mills it is used 0.5 % on weight of fibre. All the spinning mills should try with various finishes and check the compatability of dyehouse finish with spinning finish during different seasons of the year. It will give better results. But the retention in the fibre is only 10 %. the rest finish goes as waste. In some mills dyehouse finish reuse been done. It is good in light and medium shades. For example if you add 0.5 % the retention in dyed fibre is 0.05 %. This is based on modified polyglcol ether. It reduces the fibre to fibre and fibre to metal friction. This varies from mill to mill. In one mill in north India they don’t use any finish in dyehouse after dyeing of polyester fibre. This dyehouse finish application should be studied thoroughly.
There should be proper coordination and understanding between dyehouse and spinning dept to get good results in spinning of dyed fibres. The process control parameters at both dyehouse and spinning should be maintained to improve the spinning of p/v or p/a blends. A job card system should be introduced for each and every shade.
Suppose for any shade 5-10 lots are dyed in dyehouse. Each lot should be tested for washing, sublimation; finish retention, cold DMF test (at least for heavy dark and problematic shades) pH and hardness of water used for mixing should be checked. In Rajasthan water hardness is on the higher side so sequestering or metal chelating agent is added to control hardness due to heavy metals, effectively before adding spin finishes. After addition of the above agent pH and hardness is checked again and then spin finish is added. After spraying the finish on polyester it is conditioned first for 8 to 16 hours and then blended with viscose. Otherwise finish will be absorbed more by viscose than polyester. Humidity in the mixing room is checked. The nozzle and pump of the spray machine is checked. Process control study is carried out in which analysis of short fibre generation of each lot is carried out. The charge decay time of the fibres to be checked on the card, drawframes and ring frames occasionally to confirm the effectiveness of the spin finish applied on the fibre as against that of the virgin fibre. It should be done by the R & D dept. it has been found that fibre-fibre friction and fibre-machine friction vary with various fibres of different origin and machine manufacturers.
It varies from fibre to fibre manufacturers. Hence spinners to insist on specific spin finish to be developed with regard to their processing conditions and not accept a general spin finish formulation. The level of spin finish add-on and nature of spin finish (cohesiveness and moisture content levels) should be varied from season to season and place to place to achieve same processing efficiency in spinning. The crimp and spin finish have to be suitably modified to reduce loading and lapping tendency and effective movement of selvedge fibres during drafting which causes fly. Higher speeds cause friction and thereby generate more fly. Therefore the finish formulation has to be adjusted.
For this problem to be solved or minimized the spinner and dyer have to work hand in hand.
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
