Dyeing Stages and Options for Fibre Dyeing

Dyeing Stages and Options for Fibre Dyeing could describe bellow:
For aesthetic reasons the dyeing process forms an essential step in virtually all manufacturing routes for textile materials destined for use as apparel or household furnishings. The point at which dyeing is applied depends on various economic and technical factors, including considerations of fashion trends and customer demand. The significant manufacturing steps in which dyeing can be achieved. The choice is wider for synthetic fibres than for natural fibres. The selection of a suitable dyeing method (excluding yarn, fabric or garment dyeing) for the main fibre types is summarised. Some of the important factors to be taken into consideration when deciding which dyeing route to adopt for a given textile product are outlined
 

Mass dyeing fits neatly into the production of melt-spun synthetic fibres, involving the relatively simple Incorporation of insoluble coloured pigment particles into the molten polymer before extrusion. This technique results in a product of exceptionally high all-round fastness suitable for numerous end-uses. Mass dyeing does not allow for rapid reaction to changes in fashion, however, the time-scale from dyeing to garment manufacture being several months. If the consumption data for individual colours in a typical shade range for a conventional end-use are analysed, It is usually found that 80 to 90% of the total consumption can be represented by only 8 tol2% of the colours In the range, often including brown, deep red, green, navy and black. The remaining 10 to 20% of total volume comprises fashion-oriented shades, including pastel tones, that consume only small amounts of colour.
 

Production levels for mass-coloured polyester and nylon variants have been In slow decline for decades because of the low flexibility of colour selection but the process remains most Important for polypropylene, which cannot he dyed readily by conventional exhaust or continuous dyeing methods. Gel dyeing is the favoured route in the manufacture of producer-coloured acrylic fibres and this method represents the outstanding performer in terms of lowest dyeing cost per kg of fibre. It satisfies the traditional requirements of those major retailers operating with a limited range of standard large-volume shades supplemented by a fluctuating series of fashion colours in smaller volumes. The cost of gel dyeing is essentially a dye-only cost plus a small standard cost for in-plant charges. Conventional dyeing costs, incorporating contributions for labour, chemicals, water and energy, are viitually absent from the gel dyeing approach.
 

Tow dyeing mainly provides worsted-spinning systems with coloured staiting materials, whereas loose fibre dyeing processes yield those required for cotton, semi-worsted and woollen spinning systems. Dyers of tow and loose fibres therefore provide a service to yarn spinners and must offer dyed material designed to undergo yarn and fabric manufacture without causing stoppages of production. To achieve this, the dyer must be clearly away of the fibre or tow finish to be applied to ensure that the dyed material performs satisfactorily. When drying, the dyer must conform to strict limits of moisture content. Considerations of colour fastness must include the effects of known subsequent textile process conditions that the dyed goods have to withstand. This places a responsibility on the dyer to select dyes of adequate fastness to all subsequent processing and ultimate end-use.
 

The continuous dyeing of synthetic fibre tow provides a consistent quality for conversion into a combed top. Costing is highly competitive and costs of labour and energy are low. Equipment costs are high, however, so that effective utilisation is essential to achieve adequate return on investment. Where smaller amounts of dyed tow in each colour are required, batchwise methods of tow dyeing are available. The economics can be made competitive even allowing for a re-packing system after the dyeing process.
Top dyeing remains the most expensive of the processing routes available but provides a high-quality product for sophisticated end-uses. The needs of fancy yarn manufacture are best met by this dyeing method. Processing costs are high because of the care necessary to preserve the configuration of the top throughout dyeing, to ensure ease of subsequent processing of the dyed yarn.
 

Batchwise and continuous methods are available for the dyeing of acrylic or polyester tow. Both fibres, and also wool, may be dyed in the form of tops or as loose stock by batchwlse or continuous methods. Loose cotton, linen, viscose, silk or nylon fibres are normally batch dyed. Circulating-liquor machines are used for all of these, but the dyeing temperature varies according to the fibre and the class of dyes selected. High-temperature dyeing equipment is required for polyester or acrylic fibres hut the other fibres can all be dyed at an atmospheric boll or at lower temperatures in most Instances.
 

Continuous dyeing systems for wool, acrylic or polyester materials in these forms entail pad application of the dye liquor, steam fixation, washing-off and rea pplication of a finish to the dyed substrate. The variable factors Include the choice of appropriate dyes and pad-liquor additives, fixation conditions, washing- off sequence and type of surface finish. An important advantage of continuous dyeing Is the scope for dry-to-dry operation, with dry undyed fibre entering the range and dry dyed fibre emerging from the delivery end. Important criteria for successful continuous dyeing of these materials include:
1. Dyes should be compatible, with similar substantivity and diffusion properties, to avoid variations in colour during the run
2. The pad liquor must have optimum viscosity to ensure uniform application and to avoid ‘frostiness’ arising from dye migration
3. Pad-liquor additives should be compatible and must not give rise to unlevel dyeing by interaction with specific dyes
4. The fixation unit must be of adequate length to ensure satisfactory fixation of all dyes applied
5. The washing-off sequence and finish re-application must give satisfactory results with all dyes applied
6. The drying equipment should be capable of drying the dyed material adequately and preserving the physical quality of the loose fibre, tow or top.