dyeing of knitted fabrics

1. Dyeing Of
Knitted Fabrics
REHAN ASHRAF
NATIONAL TEXTILE UNIVERSITY

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Table of Contents
Introduction ....................................................................................2
Dyeing Process .................................................................................2
Machines used in dyeing process of knitted fabrics....................................2
Dyeing through winch dyeing machine...................................................2
Dyeing through Jet dyeing machines.....................................................3
Space dyeing of knitted fabrics..............................................................4
The effect of temperature on dyeing of knitted fabrics .................................4
Common Knit Dyeing Faults and Their Remedies .........................................4
References......................................................................................6

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Dyeing of Knitted Fabrics
In the coloring of textile goods, the nature and quality of fiber and materials in
reference to the dyes and dyestuff should be considered. Since some dyeing agents
and mordents are best suited to one fiber, other can be used equally as well with
all fibers or mixtures thereof. The details of coloring must be suited to the quality
and kind of garment.
Introduction
Manufacturing of knit goods is cheap and 100% knit good items are very comfortable
which increase the demand of knitted underwear and outerwear garments. As a
result knitting, knit dyeing and finishing industries are growing very rapidly.
Jets and winch dyeing machines are generally used as exhaust equipment for
preparation, dyeing and finishing of apparel knit fabrics. Knit fabric wet processing
is started with batching or batch preparation where fabric is weighted as per
machine capacity and the fabric is turned to inside out in case of body fabric i.e.
main fabric of garments. Interlock, rib, fleece fabrics are also turned to inside out
when those are in unbalanced structures and used as body fabric of garments. The
fabrics are usually turned to keep away from the any unaccepted incident or damage
on face side and remove edge marks, which are created due to formation of fabric
roll.
Dyeing Process
Knit dyeing is a technique of dyeing the knitted fabrics. The dyeing of knitted fabrics
occurs in the exhaust method or in batch-wise process. Generally all type of single
jersey, double jersey and their derivatives are dyed by the following process.
Machines used in dyeing process of knitted fabrics
Winch dyeing machine
Jet dyeing machine
Jig dyeing machine
Paddle dyeing machine
Soft flow dyeing machines
Dyeing through winch dyeing machine
Knit goods are generally dyed in the roller piece form and slit(To cut lengthwise into
strips) lengthwise after dyeing. Warp knits have the tendency to curl at the edges,
hence several rolls are tied together so they are dyed in tubular form. Forming a
long chain, the number of rolls to the chain being dependent on the weight of the
fabric. When dyeing of tubular fabric is carried out in winches, air bubbles are

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collected inside the tube form immediately below the jockey roll. The bubble is
continuously pushed back along the rope by the jockey roll. The dyeing machine
employed consist of a tub provided with a revolving winch on top. The winch is made
up of wood. The chains of cloth are passed over the winch and circulated through
the dye liquor in the tub below. Usually from eight to twelve chains are run in one
machine side-by-side. As the goods come up from the liquor they are passed from a
set of small squeeze rollers and then run on the revolving winch. The squeeze rollers
and the winch should be so set and run at such relative speeds that there is as little
tension on the cloth as possible, as the tension while the cloth is running in the
dyeing operation tends to stretch the goods out of shape and also materially reduce
their elasticity. The speed of the squeezing rollers is somewhat high than that of the
winch. The winch is fluted so that less surface area of the fabric touches the winch
and hence low tension is created on the fabric.
The machine employed for the dyeing process is similar in every respect to that
employed for wetting-out or scouring process. Unless a number of lots to be dyed,
the goods may be rinsed off in the machine used for dyeing, by simply running off
the dye liquor and refilling with fresh water.
Piece-Dyeing
Piece dyeing occurs in the winch dyeing machine. Most textured polyesters is piece-
dyed which are manufactured through knitting. Some continuous scouring machines
are built to handle knitted fabric with controlled tension. Although one machine is
more suitable than other, the depends on many factors, including the type of fabric
to be processed, machine tension, method of extraction and efficiency of oil and
dirt removal. This last factor is especially important.
High temperature dyeing units generally operates at temperatures between 230 and
260 F. This makes possible shorter dyeing cycles with little or no carrier cost. It also
improves quality, barre and shading piece to piece. In spite of high capital costs,
there are definite advantages to high temperature dyeing.
Dyeing through Jet dyeing machines
Jet dyeing machines resemble becks in that a continuous loop of knitted fabric is
circulated through the machine. However, the cloth transport mechanism is
dramatically different in these two types of machines. A high speed jet of dye liquid
created by a venture transports the fabric through the cloth guide tube of the jet
machine. A jet machine has a cloth guide tube for each loop of fabric being
processed. A powerful pump circulates the liquor through a heat exchanger outside
of the main vessel and back into the jet machine. The fabric travels at high velocity
of 200-800 meters per minute while it is in the cloth guide tube. The fabric leaving
the cloth guide tube enters a larger capacity cloth chamber and gradually advances
back toward the cloth guide tube. Pressurizing a jet dyeing machine provides for
high temperature dyeing capability. High temperature jet machines are especially
suitable for delicate fabrics made of texturized polyester. Some atmospheric

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machines designed for dyeing temperatures up to 100 C also use the jet circulation
principle.
Space dyeing of knitted fabrics
Polychromatic method can be used to produce a wide variety of patterns in many
shades on knitted fabrics. Two or three set of jets apply the dye liquor to the goods
passing below the jets. The individual jets can be connected with dye liquors of
different colors by means of a special dyestuff supply tube. A sheet called mirror is
placed at an angle below the jets. The angle is so adjusted that the liquid stream
coming from or two series of jets produces changes in color pattern and mixtures.
After applying a constant amount of liquor, which must be fixed beforehand by a
suitable choice of jet size, the goods are through a padder, when the final pattern
is obtained. The goods are than steamed continuously, washed and dried.
The effect of temperature on dyeing of knitted fabrics
Two fabrics are dyed A and B using standard and varied temperature respectively.
When the effect of dyeing temperature was studied, the comparisons between
samples B and A (as standard) were done. Temperatures varied 30-50 °C, applied
ultrasound frequency was 40 kHz, while the quantity of added NaCl was 60 g/dm3.
The results of color differences between samples B and A present that the sample B
is darker at temperatures of dyeing from 30 °C to 50 °C yellow and more redder at
dyeing temperature 50 °C.
The same sample is greener and bluer when the temperatures of dyeing are 40 °C
and 30 °C. When the effect of dyeing temperature was studied, the comparisons
between samples D and A (as standard) were done. Temperatures varied from 60 to
40 °C, applied ultrasound frequency was 40 kHz, while the quantity of added NaCl
was 60 g/dm3. Regarding the results of color differences between samples D and A
(not shown), it appears that the sample D is darker at temperature of dyeing from
60 °C to 40 °C; redder and more yellow (0.8) at dyeing temperature 40 °C. The same
sample is greener and bluer when the temperatures of dyeing are 60 °C and 50 °C.
Total color differences satisfy two allowed criteria M&S and CMC for applied
temperature 50 °C.
Common Knit Dyeing Faults and Their Remedies
Knit fabric dyeing process is different from yarn dyeing or woven dyeing process.
During dyeing; some dyeing faults can be occurred due to wrong operating system.
But it can be overcome by applying some techniques.
Common knit fabric dyeing faults and their way of remedies are given below.
Crack, Rope or Crease Marks
o Causes

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 Poor opening of the fabric rope.
 Shock cooling of synthetic material.
 Incorrect process procedure.
 Higher fabric speed.
o Remedies
 Pre-heat setting.
 Lower rate of rising and cooling the temperature.
 Reducing the machine load.
 Higher liquor ratio.
Pinhole
o Causes
 Due to the presence of Fe+ and Cu+ ions in water.
 Active per-oxide that is used during bleaching.
o Remedies
 Water hardness should be in limit.
 Strong sequestering agent should be used.
 Per-oxide killing should be done properly.
Fabric distortion and increase in width
o Causes
 Too high material speed.
 Low liquor ratio.
o Remedies
 By decreasing both nozzle pressure and winch speed.
 By using high liquor ratio.
Pilling
o Causes
 To high mechanical stress on the surface of the fabric.
 Excess speed during processing.
 Excess foam formation in the dye bath.
o Remedies
 By use of a suitable chemical lubricant.
 By using antifoaming agent.
 By turn/reversing the fabric before dyeing.
Running problems
o Ballooning and intensive foaming
 Causes
 Occurs in woolen or worsted fabrics which are too densely
sewn.
 Pumping a mixture of air and water.
 Remedies
 By cutting a vertical slit of 10-15 cm in length for escaping
the air.
 By using antifoaming agents.

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References
Textile Preparation and Dyeing By A. K. Roy Choudhury
Posselt’s Textile Journal the Bleaching, Dyeing and Finishing of Knit Goods.
“EFFECT OF REACTIVE DYEING AND CELLULASE TREATMENT ON THE PILLING
PROPERTIES OF COTTON KNITTED FABRIC” by C.W. Kan and K.P. Law The Hong
Kong Polytechnic University, Faculty of Applied Science and Textiles, Institute
of Textiles and Clothing, Hung Hom, Kowloon, Hong Kong
“PROCESS FOR LEVEL DYEING OF 100% COTTON KNIT FABRICS WITH REACTIVE
DYE” by Chowdhury Jony Moin and A.K.M. Mahabubuzzaman Senior Lecturer,
Department of Textile Engineering, Southeast University, Dhaka, Bangladesh
and Principal Scientific Officer, Mechanical Processing Division, Bangladesh
Jute Research Institute (BJRI), Manik Mia Avenue, Dhaka-1207, Bangladesh.
https://archive.org/details/hosieryknitgoods00hutt
http://textilefashionstudy.com/knit-dyeing-common-knit-dyeing-faults-and-
their-way-of-remedies/
http://www.textiletoday.com.bd/magazine/
http://textilefashionstudy.com/process-flow-chart-of-knit-fabric-dyeing-
with-reactive-dyes/