Views: 0 Author: Site Editor Publish Time: 2023-12-05 Origin: Site
In order to improve the one-time success rate of dyeing, the indicators of pre-treatment need to be controlled, such as: desizing level, de-oiling rate, fibre splitting rate, gross efficiency, deweight , whiteness and other indicators, through the indicators of the test and control, to develop and amend the pre-treatment process, the pre-treatment of the indicators after the stabilisation of the success of the dyeing is also halfway to success.
Here are six points to focus on before the dyeing process.
Ⅰ Batch management of raw blanks (or yarns):
Two parts technology, eight parts management. In the industry of dyeing and finishing, which is an applied chemistry, when the technology develops to a certain degree, the management level determines the technology and quality level of an enterprise.
Therefore, before talking about pretreatment, I am here stress on the batch management of the original blank (or yarn). The same batch should be dyed according to the same process, and when replacing the batch, there must be a sampling and tracking procedure, and after the batch of the dyed material is replaced, the process should be adjusted in time according to the comparison of the sampling situation, and the good control of batch management reflects the level of a dyeing factory.
Inadequate desizing will affect the colouring rate of the dyestuff when dyeing, or cause the fabric to feel worse.
Desizing is for sizing woven fabrics, in order to facilitate weaving, most of the woven fabrics need to be sized after weaving.
Speaking of desizing, we have to mention the textile pulp three major slurries: starch and derivatives, polyvinyl alcohol (PVA), acrylic slurries. PVA has been phased out due to environmental issues, and now most of the use of starch and acrylic slurries used in conjunction.
Four commonly used desizing methods: hot water desizing, alkali desizing, enzyme desizing, oxidation desizing. Enzyme desizing and alkali desizing are more commonly used nowadays, while enzyme desizing (amylase) is mainly used for starch slurry. The effectiveness of desizing is generally evaluated by the desizing level. Of the three major slurries, acrylic slurries are easier to remove, while both starch slurries and PVA have simple and fast test methods (e.g., iodine/potassium iodide method.).
Degreasing is mainly for chemical fabrics (or yarns), such as polyester, nylon, etc. Inadequate degreasing affects the colour of the dyes and causes problems such as oil spots and colour spots. Degreasing is generally carried out under alkaline conditions with degreasing agent at high temperature, and the selection of a good degreasing agent helps to improve the degreasing effect. Now, in order to optimize the process, there are a lot of de-oiling and dyeing baths for chemical fibre, when choosing, pay attention to the high temperature resistance and dispersing performance of the de-oiling agent in the same bath.
Fibre splitting is also for chemical fibre fabrics, such as polyester microfibre, sea island fibre, polyester brocade blended fibre open fibre, polyester splitting is also known as alkali DEWEIGHTING. The excellence of Fibre splitting affects the colour fastness of dyeing and the stability of dyeing colour and light, and the effect of Fibre splitting is generally controlled by the rate of open fibre weight loss.
Refining is mainly for natural fibres and regenerated cellulose fibres, the purpose is to remove impurities such as oil, wax and pectin on the fibres. Similarly, the refining is mostly based on alkali high temperature refining, and there are various ways such as cold stack, continuous long car, intermittent and so on. The index for assessing the refining is mainly gross efficiency, and the level of gross efficiency directly affects the colouring rate and uniformity of the dyestuff. Rolling dyeing (left middle and right), cylinder yarn (inside and outside) dyeing on the gross effect of the higher requirements.
Another index of refining is weight loss, in principle, the higher the weight loss, the better the effect of refining, but too much weight loss also brings about the reduction of the production rate and the increase of cost.
Bleaching is also for natural and regenerated cellulosic fibres, and a bath treatment with refining is what is commonly known as practice bleaching. The purpose of bleaching is to remove pigments to achieve the whiteness required for dyeing. Common bleaching processes include oxidative bleaching (hydrogen peroxide, sodium hypochlorite, etc.) and reductive bleaching (insurance powder). The measure of bleaching is whiteness. For sensitive and bright colours, the stability of bleaching whiteness is critical. The whiteness can be measured with the naked eye to compare, but also through the whiteness meter to test.
PS: Cotton seed hulls on cotton fibres cannot be completely removed by refining alone, the cotton pre-treatment which only does refining is also known as half refining, whereas after bleaching, the pigment on the cotton seed hulls (lignin) can be completely removed.
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