A new era for Bangladesh is yarn printing. As like as the normal printing process it has some similarity like localized dyeing or space dyeing, color fixing; though no printing paste with thickener is used here. It is a process where printing is done with dye solution and applied on yarn in soft wounded package form. The printing is done by bobbin injection method. Time, temperature and pressure are the main controlling points in the process. After the production of printed yarn, fabric is produced through knitting. The fabric has mélange, slub, irregular color effects which can produce value added garments.
In two dimensional fabrics mainly in regular formation there are four types of fabric- knit, woven, nonwoven and braiding. All development in these fabrics are done with the design variation of yarn structure and in fabric.
Mixing, blending, different coloration process also impact in this fashionable purpose. Different types of finishes also give a different touch in the appearance of required product. Finishes are for improve the appearance (color, pattern, sheen), change the texture (embossing, brushing and smoothing), improve the feel (soften, crisper, firmer), improve the drape (how the fabric hangs) –weighted, improve wearing qualities (crease resistance, stain resistance, flammability, water proof etc), modify care requirements (easy wash, quicker drying time, colorfast, less shrinkage) etc. Some products have extra technical function and technical properties that meet up some solution which cause extra benefit for not to use extra cloths over it. Here there is a discussion about the new possible way to meet up special design by printing the yarn. This technology can be used to produce beautiful effects in knitted fabric and garments with extra value addition.
2.0 Materials and machines
100% cotton, PC, PVC, viscose, rayon, grey mélange and other cellulosic yarn or other blended yarn can be used. Fineness 20’s – 60’s cotton, 20D-170D polyester etc.
Machine required for this process are Soft winding machine, Yarn package dyeing machine, Bobbin injection machine, Steaming machine, Hydro extractor, Drying machine, Hard winding machine, Knitting machine.
Process flows are showed step by step in ascending order
- Soft winding
- Bleaching or white dyeing (100oC X 30 min)
- Peroxide killing (60oC X 20 min)
- Neutralization (50oC X 20 min)
- Hydro extractor
- Bobbin inject (cold brand 40oC/ Hot brand 80oC)
- Steaming (80oC X 30 min)
- Neutralization (50oC X 20 min)
- Soaping (95oC X 20 min)
- Fixing (40oC X 20 min)
- Finishing (50oC X20 min)
- Hydro extractor
- Hard winding
Soft winding, Yarn dyeing, hydroextracting, drying, garments manufacturing are well known to all. Printing machine and printing procedure are discussed here in details.
4.0 Yarn printing machine
Sample m/c type : Yarn Printing
Brand : LAIP
Origin : Italy
Capacity : 2 Packages (at a time)
Package weight : 1 kg (each)
Color Used : 4 ( maximum)&2 (minimum)
Mixing tank : 4 (1for each color)
Color storage capacity : 300L/tank
Fiber used : Cotton mainly
Dye type : Reactive mainly used
Temperature : (40-50) °C
Storage cylinder no : 8
Cylinder storage capacity : 1 L
Yarn printing machine consists of dyes tank, dyes cylinder, oil box, printing device, panel boards etc. Key elements of the machine are discussed below.
Tank: Preparing the dyes mixture is the first task of the printing process. 4 tanks for having four colors at a time and the require chemicals that use for comfort dyeing facility. There are stirring motor and the steaming bulb helps agitation and heating as required.
Printing cylinder: To keep required amount of dye liquor for each injection no of cylinder are 4 times multiple of each printing head. In this machine one cylinder is attached to 2 cylinder and for two head total no of cylinder is 8. Capacity of each cylinder is 1.5 liters. Printing amount that have to be injected is stored in the cylinder temporary. For one printing 1kg package 4 liters dye is used.
Bobbin holder: Help to keep the package in firm space of the yarn at upper side.
Needle head: It is adjusted with the color supply pipe. For one package 4 needle head is used which covers the whole circumference of the package. Each needle head contains 4 needle for top to bottom that will penetrate into the package to discharge the dye.
Printing needle: The machine has 32 needles. Each needle contains 5 pores which pass the liquor to the package by air pressing system. The frontier pointed head helps to easily penetrate through the package.
Hydraulic press: All operation or movement of this machine is done by hydraulic pressure and this is done by oil which is in the oil box beneath the machine.
5.0 Mechanism of the printing process
5.1 Coloration process:
4 pipe lines come from the mixing tanks & carry color solution to the 2 cylinders (2 pipe lines for each cylinder).Thus 8 cylinders contain total of 4 colors ( 2 cylinders per color). Here color solution is injected to the package which is fixed by a pressure head. Dye injection is done by some perforated needles with the help of air pressure. Color solution passes through 4 pipe lines for each cylinder & extrudes through 4 needles connected with these pipe lines. 4 needles are set in a holding plate which holds the bobbin during printing by pressing. Here total 4 pressing plate used for each bobbin coloring.
As 2 packages printed at a time total 4 color cylinders are used to dye one package. The needles pass air pressure for 30 seconds after passing of the dye solution is done as for the uniform dye absorbing. When dyeing is done then the extra color solution is removed by a perforated suction nozzle by the reverse flow of air pressure on which the package bobbin is set. Thus maximum 2 packages of a maximum 4 colors can be found after the dyeing is done from this machine.
5.2 After treatment processes
Following yarn bobbin printing, necessary after treatments steaming (80°C for 30 minutes), washing (using core neutralizer, soaping agent, fixing agent and softener), hydro-extracting and drying was carried out.
6.0 Machine setting
Dark shade: Double punch system, here for courser yarn punching is done in cylinder for two times for having a dark shed. One punching is enough for dark shed in normal fine yarn.
Light shade: Single injection with single punch is available for all kind of shade.
Double inject: For having a slub effect in the fabric after first injection, 2nd injection is done with a fully different color by rotating the package with 45o angle. With 40 percent setting.
Setting inject Cylinder: This refers time and percentage. Different percentage like 90 %, 100% setting system determines the amount of dye injected from the cylinder in the package for a specific time.
Brand: LISKY Machine type: Single jersey Model: LFS/96 No of feeder: 114 Specification: 36” X 24E
8.0 Benefits of yarn printing
Highly fashionable irregular and contrast fabric can be developed. There is no limitation of color choice in yarn printing system. Slub effect can easily be earned in yarn printing by double inject system, here don’t have to dye the polyester part and the cotton part separately to make the slub yarn effect. Terry effect effect can be achieved in double jersey if loop side is done with these printing yarn appearances can be achieved like offset jersey, ottoman rib and terry towel etc.
Yarn printing is faster process than any other dyeing technology. Yarn printing system can also be a replacement of discharge printing which is very expensive and there is color or shade limitation. Resist printing effects also can be achieved by yarn printing technology.
9.0 Problems and remedies
For analysis printing and shade variation in the injected package a small quantity can be knityed in a sample making machine for a particular package, marking 6 layer yarn of the packages the prominancy of variation can be examined.
In the figure problem 1 to 3 shows the outer layer yarn to inner yarn printing variation. Problem 1 shows the circumference yarn problem 2 shows inner surfaced yarn. If the shade is ok then the printing variation problem will not be prominant in the fabric when following things could be incorporated.
- Larger dia knitting machine like 22 to 36 inch.
- Proper set up of cone in creel system can reduce problems.
- Inserting other solid dye yarn and printing yarn in a alternative manner. Last 10 percent yarn can be cut out from the package when hard winding for more accuracy.
- Some package become more lighter than standard shade. It happens If dyeing is done on a grey yarn or on lower absorbancy properties of yarn is used. Otherwise storage of dyes in the tank may occur hydrolisis and create this problem.
- Sometimes undyed spaces come in fabric because of improper absorbancy property of yarn, if bleacing and souring is not done properly then it may occur. But it is not found for light shade design.
- Some times reddish tone or browinsh tone come on the fabric if the template and the printing parts and needles are not washed clearly after every batch.
- Shade becomes more darker around the needle ( specially for light shade). This may occur if the dye solution store for a long time and If the agitation doesnot work properly when mixing.
- Inner layer and outer layer of one package become lighter than the middle layer.
During knitting, yarn breakage is occurred because 16 needles punch a package at a time. This penetration of the needles frequently weaken the yarn where it is placed.
10.0 Comparison between dyeing and printing:
Precision winding and DIGI winding all are applicable in yarn dyeing process but only DIGI soft winding process is applicable for yarn printing because in this winding the density of yarn in soft winding package is less than precision winding package which is suitable for proper dye injection process. Single coloration process of yarn packages is done in yarn dyeing technology whether multiple coloration is injected in a same yarn package at a time in yarn printing process.
Yarn printing for each package requires only 2 minutes whether other process requires long time. PH of the dye solution reduced for the time being for storage in the tank in yarn printing but this doesn’t happen in the yarn dyeing process. Steaming is required for dye fixation in the yarn printing process but alkali medium with perfect PH is responsible for dye fixing in the yarn dyeing process. 30 percent less shade is occurred when washing off because less fixing of dyes for storage in the tank when printing but this is not occurred in the yarn dyeing process.
If any problem is created in printing or shade variation, reprocess can be done in yarn dyeing system but not possible in yarn printing. In yarn dyeing process no particular design can be provided but in yarn printing it is possible.
Table: Typical cost of yarn printing
|Shade||Dye %||Cost $/kg|
|Special||2.5 – above||5|
Cost analysis of yarn printing depends on their shade. When a solid dyed T-shirt value is $2, then T-shirt from dyed yarn is $5, but T-shirt from printed yarn price is $10.
12.0 Disadvantage of the process:
No reprocess system can be done here. If we find any fault then we have to cut out the faulty part or use it for any other purpose. After washing a lot of dyes are wasted away from cone and wastage of dyestuff is occurred.
This study reveals that there are many more horizons of technology and arts that helps fusion of many steps which cause hassle, instead these we can use the shortest potential one way- yarn printing. This is a modification of yarn dyeing process but replacement of other multifunctional printing system and gives a clear outline and contrast printing appearance. Garment using printed yarn is an empirical study of value addition to increase foreign currency by exporting ready-made clothing.
- Knit Concern Yarn Dyeing Ltd.
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