Source: The Stitch Times
Abstract: The garments produced from woven fabrics have in creased many problems, and experience has shown that existing styles as developed for piece-dyed fabric cannot be just assembled from grey fabric and thrown into the dyeing machine, unless they have been engineered from the original design stage for garment dyeing. To obtain a high quality final Garment there should be a thorough coordination between fabric supplier, accessories supplier, garment manufacturer and garment processor.
The recent surge in export of garments has created a challenging opportunity for the garment processing industry because of:
- Short pipeline necessary for quick response.
- Reduced losses from dyed fabric waste.
- No subsequent shrinkage. Reduced inventory.
- Lower energy, water and labour costs.
- Ability to produce small batches.
- Most importantly to produce uniformly dyed garments with no variations in shade of the different parts of the garment, which is a major problem for garment manufacturers using piece-dyed fabric because of sort-to-sort variations.
Structure of the Garment Dyeing and Finishing Sectors
1) Conventional Finishers
Traditional finishing plants that have adopted garment dyeing in addition to their conventional production.
2) Laundries/Dry Cleaners
These establishments do garment dyeing as an additional profitable activity to give a new lease of life to garments with no guarantees offered on the final appearance of fastness.
3) Garment Dyers
Composed of fully established fashioned dyers.
Quality Control in Garment Processing
The garments produced from woven fabrics have produced many problems, and experience has shown that existing styles as developed for piece-dyed fabric cannot be just assembled from grey fabric and thrown into the dyeing machine, unless they have been engineered from the original design stage for garment dyeing. Care should be taken that the grey fabrics dye-up identical in shade and if necessary must be adequately pretreated before dyeing.
The other major areas for control are: Seams, elasticated areas, waist bands, cuffs. Shrink behaviour, Chafe marks/creases, Accessories, Sewing thread, Foreign substances, Inter linings and Care labeling depending on the fastness requirement, being the most important of them all.
Elasticated areas, waist bands and cuffs, must be fairly slack, and seams should not be too tight or bulky, otherwise poor penetration of dyestuff occurs especially with heavy articles and heavily swelling fibres like cotton. However the problem can be solved by using suitable dyes and the right process control.
The use of a high application temperature dyes not only ensures that the migration potential is fully realized, it also offers several additionaI advantages. Higher temperatures mea ns better diffusion, better penetration and better running of the cloth facilitating liquor flow. These benefits assume particular significance in garment dyeing, especially in garments that have multilayered seams of woven fabrics (pockets, lapels, zips etc) or tight elasticated waists and ribs.
Thus a short period at high temperature i.e. 950C before cooling for fixation with reactive dyes has overcome even the most difficult seam penetration problems.
Shrink Behavoiur is important because of excessive shrinkage of the article or uneven shrinkage where knitted and woven fabric are mixed which leads to seam puckering, when it becomes important for pre-relax knitted fabric and the pre-treated woven fabric must be fully pre-shrunk by giving the various shrink-proofing treatment for high quality fabrics. To rule out the possibility of later complaint, it is advisable to carry out a blank dyeing.
Chafe Marks and Creases are a problem particularly for delicate articles due to the mechanical stress in drum dyeing machines which have a negative influence on the final product. Articles which are prone to chafe marks or pilling effects should be turned inside out and dyed with the addition of a non-foaming lubricant while adopting the shortest possible dyeing process.
With woven fabrics certain types of weaves are liable to creasing and breaks. One preventive measure from the outset is to avoid overloading the dyeing drum.
Accessories: Care must be taken with the selection of zips and metal accessories, such as buttons and studs. Ferrous metal must be avoided, and good quality components fabricated from nickel or its alloys must be used if breakdown through corrosion in bleaching or reactive dyeing, with its high concentration of electrolyte and alkali, is to be avoided.
The composition of buttons can be a difficult
choice. Those buttons, such as made of casein and cellulose, break up under the
dyeing conditions, while polyester buttons do not dye at all and must be used
either of a neutral colour, capable of co-ordinating with a range of shades or
be purchased ex-stock. Nylon buttons can be coloured in the garment dyeing
process, but it is difficult procedure to control to obtain consistent results.
Elastomerics, either natural rubber or polyurethane fibres such as Lycra, are used in ribs and both types can give rise to problems. Natural rubber is adversely affected by ceratin metals, and for this reason it is important to use dyestuffs that do not contain copper. Polyurethane fibres are seriously weakened in presence of strong oxidizing agents such as chlorine, but hydrogen peroxide bleaching can be used with the polyester type of elastomeric fibre. Hence it is very important to specify the correct Lycra tape to avoid breakdown in dyeing.
To prevent the major problems due to the metal accessories, corrosion protection agents must be used.
An anionic, organic corrosion inhibitor protects
metal accessories such as buttons, zip fastners etc. made of non-ferrous and
white metals (but not aluminium) from oxidation and tarnishing. It prevents the
metal ions from attacking sensitive dyes and, when added in the last rinsing
bath, prevents corrosion when wet goods are left lying.
Sewing Thread is undeniably one of the most vital components to be found in countless articles we use. It is a component taken for granted and the demands on the threads we use are so many that it must satisfy a wide range of needs.
Properties desirable for sewing threads are that
- It must be strong and yet fine enough to produce a neat seam and last for the whole life of the product and
- Considering the modern high speed sewing machines where the speeds of the machines are as high as 6000 stitches/min, the thread is accelerated at over 100miles/hr and hence must be designed to withstand these speeds. An additional lubricant is required to reduce friction between the thread, needle, and thread guides and the fabric and also protect synthetic fibre threads against needle heating.Therefore before dyeing these lubricants have to be removed, otherwise it will inhibit dye uptake by the sewing thread.
For garment dyeing, the thread and the fabric have to be of the same fibre type, however, this is suitable mainly for cotton as sewing threads are not produced in all fibre types because of their dyestuff specific nature.
Precautions in Stitching
In sewing fabrics made from cotton, heavier cotton threads must be used in order to obtain equivalent seam strengths. Further, it is necessary to keep sewing tensions to a minimum on lockstitch and chain stitch operations, deliberately producing slack stitches, since otherwise pucker will be introduced owing to shrinkage of the thread during subsequent garment dyeing.
All these factors would slow down the production speed for garments to be post-dyed and hence coatings should be carefully adjusted.
Whichever thread is selected, ultimately it will be a trial and error situation and hence sampling is essential before bulk dyeing.
To reduce value loss it is better to prevent the foreign substances such as stains due to oil, grease and other lubricating agents used during the course of manufacturing. Further proper handling and good house keeping also would reduce the stains.
Other foreign substances could be sizes and resins containing additives such as elastomers and oil repelling agents which would cause poor appearance of the final goods and hence must be taken care of before dyeing.
The purpose of an interlining, whether fusible or non-fusible, is to stabilize and add body to the outer fabric. With the introduction of post dyed garments, certain special properties had to be introduced into interlinings to ensure that they performed satisfactorily.
The special properties required are :
- It must take up dye from the bath to a similar level as that of the outer fabric.
- The adhesive bonding of the outer fabric to the interlining base must remain intact during and after the dyeing operation.
- The handle after dyeing should be one that is the customer.
- There should be no adverse colouration caused by dye absorption in the fusible resin used in the fusible.
The three main components of any fusible which should have the above properties are:-
- base fabric
- base fabric finish and
- the fusible resin coating
The best choice for the base fabric is cotton as it would not cause problems during dyeing.
The base fabric finish is also important. Resin could be used, however they take up the normal hydroxyl sites needed resin and mechanical shrinkage has to be done to get even dye absorption and prevent the differential shrinkage.
The fusible resins used must be resistant to breakdown during dyeing and hence they should have the following properties:
- Should be hydrophobic,
- Inertto pH changes,
- Have high melting points,
- Method of coating-Scatter coating is economic but gives poorer results, whereas -dot coatings give smootherfinish.
- Rapid cross-linking and no
subsequent cross-linking during storage.
The garment dyed goods generally have fastness properties inferior to the normal piece dyed goods. Their major properties are:
- Dimensional stability
- Colour fastness to washing
- Colourfastness to rubbing
Based on the various physical and colour fastness, properties a suitable care label is arrived at, which tells the customer the precautions he should take when cleaning or washing the garment.
The various "care labeling" systems used are: American, E u r 0 pea n , British and Canadian.
The labels are designed in such a manner that they must give specific instructions with respect to the method of washing, bleaching, drying, ironing, suitability for dry cleaning and other relevant parameters.
Except for the American system which is based on written instructions, all other care labelling systems are based on symbols. The objective is to inform the consumers on the correct care labeling of textiles.
Thus, it is seen that garment processing and manufacturing is not without problems. To obtain satisfactory results an absolute teamwork is required between the garment fabric supplier, accessories supplier, garment manufacturer, garment processor.
Taking all the necessary precautions during making and processing of a garment, the export earnings can be tremendously increased.
Originally published in The Stitch Times: February 2010
About the Author
The author is M.Sc (Tech) Gold Medalist & Textile Consultant