Wednesday, September 1, 2010

Garment Dyeing - Part-3 - Chemicals and Auxiliary Chmicals - Selection and Analysis

In garment processing we are using a lot of basic chemicals, auxiliary chemicals, enzymes and natural resources such as water. All the above said ingredients play its own important role.

  • Water plays the key role in any textile wet processing. The quality of water decides the quality of your product and rework percentage.  In all climatic condition no water quality would remain same. Rainy season will bring more turbidity and mineral content in running water (river) and more soft and less saline water in bore wells. Providing a good quality water for processing is the basic requirement for any processing unit. How to test and treat water and make it suitable for dyeing is a separate line of discussion.

  • Basic Chemicals: In garment processing we are using the following basic chemicals. The purity of these chemicals is also very important from the point of dyestuff behavior and economy. Some examples are:
      • Common Salt - Common salt is used in reactive, direct and sulphur dyeing processes as a dye exhausting agent. The high impurities present in salt will precipitate on the garment being processed during the addition alkali (soda or caustic) in to the dyeing bath. The unwanted metal ions present in the contaminated salt, like Calcium, Magnesium, Manganese, Iron, Aluminium etc some time replaces the metal ions present in the dyestuff and make the shade appear duller and different in tone. By using a good quality salt like Galuber's salt (Na2SO4) or pure vacuum salt (common salt purified), would save you from these problems. While selecting a basic chemical, buy it from reputed manufacturer and ask them provide you purity certificates. If necessary you can also test the purity of chemicals.
      • Soda Ash - Purity testing of soda ash is very important because the concentration decides the correct pH requirement for fixation of reactive dyes.
      • Hydrogen Peroxide - Hydrogen Peroxide is being sold under two concentrations viz., 35% and 50%. According to the strength the dosage in bleaching varies. Being water like adulteration very easily possible and this decides the batch whiteness. If whiteness between varies, then the final shade also will vary in tone and depth.
      • Acetic Acid - Acetic Acid is used as a neutralizing  agent in two stages of processing, viz., after bleaching and after dyeing. Both stages are very important to achieve the required results. Improper neutralization before dyeing leads to patchy dyeing and after dyeing results in fastness related problems and tonal variations of many shades.
  • Auxiliary Chemicals  - inclusion of too many products for processing leads to loading of effluent and creates complications in treatment. Moreover poor quality products purchased only with the aim to reduce cost of production ends up in many quality problems. If you have a simple analytical lab you can test all auxiliary chemicals at your end itself as a standard practice. We can suggest you the optimum number of essential products for any type of dyeing or finishing.

    Garment Dyeing - Part-2 - Dyestuff Selection - Shade matching

    Different dyes for different colors/effects:

    Selecting Dyes

    There are several different types of dye available for garment dyeing including reactives, pigments, and direct dyes. Dyes are selected based on the fabric (or combination of fabrics) to be dyed, the garment type, and the desired color, consistency, texture, and feel of the finished garments.

    The type of dye selected can also impact the shade range and light fastness of the finished garment. Therefore, it is important to consider the function of the finished garment. For example, light fastness would be an important consideration for summer tanks to be worn in the sun consistently, whereas, light fastness may not be an issue for under garments.

    For your information, following is a table describing some of the factors to be taken into consideration when selecting dye types.

    We would be happy to consult with you when it comes time to dye your garments!

    The table gives fairly a working idea for dyestuff selection. But this is not the final. For example if you opt to select reactive dyes, you still have to make your correct decision which group of reactive dyestuff you have to select.

    There are cold brand (room temperature dyeing), Vinylsulphone, Bifunctional, High Exhaust and so on. Similar is the case with direct and pigment dyes. We have pleasure in advising for proper selection of dyestuff with respect to quality, economy and application ease.

    Garment Dyeing - Part-1 - Check List for PFD garments

    Well prepared is half dyed! - this is a dyers' slogan.

    Quality Assurance is a defense mechanism that protects us from flaws and problems that may sprout out after dyeing and finishing. A thorough inspection by qualified people will save a lot. We at Nuchem suggest our clients to make the following tests before starting Garment Dyeing.

    What you need to know before dyeing your garments?:

    •      Some dyeing processes may cause unseen garment flaws to become apparent subsequent to processing; such as pin holes, bad seams, and optical spots. As these flaws are inherent in the garments prior to processing, which the dyer cannot be responsible for.
           Because each garment costs more and job dyers are very much responsible for any fault after processing,  a pre-inspection  of greige garments in a dark room equipped with UV lights may proves effective to locate optical brightener spots, oil marks and even sewing thread variations.

    •      Many garments are cut and sewn from previously prepared/finished fabrics (such as water repellants, fire retardants, fluorocarbon, silicone softeners or resins), which may impact the dying process.
           This is a typical case and all garment dyers would regularly face this type of incidents. A better solution is to dye one or two random pieces in a sample garment dyeing machine and get the party's approval.

    •      Many garments are assembled using several different types of fabric. Dye saturation levels and shrinkage may differ between fabric types (even if it is all cotton, as in Greige cotton and bleached cotton combinations) causing unpredictable results.
           As told for the earlier point the only suggestion to  make a sample dyeing and find out the final effect and get the approval of the concerned party.

    •      The garment dyer has no idea in most cases what is present on the garment or how it will behave in the dyeing process. Even on well prepared cloth there will be residual oils, fats, waxes, sizes on woven goods, spinning oils, etc, all of which should be removed to be able to dye successfully.
    •      Also to be taken into consideration is the shrinkage, creases, threads, labels and buttons.
    Open seams, wrong stitching techniques, non- matching threads, and missing stitches, improper creasing of the garment, erroneous thread tension and raw edges are some of the sewing defects which can affect the garment quality adversely. During processing the quality control section needs to check each prepared article against these defects.