Analysis of the factors influencing rubbing resistance colour fastness

2023-02-24 | Textile Fabric Knowledge

  Colour fastness to rubbing refers to the degree of colour loss of dyed fabrics after rubbing, and is an assessment of the resistance of dyes to mechanical rubbing, divided into dry and wet rubbing. The principle of the specified size of the textile specimen with clamping device to fix the specimen in the friction test instrument platform, and then respectively with a dry friction cloth and a wet friction cloth friction, and finally the degree of white cloth staining as the basis for evaluation, against the standard grey sample card, a total of five levels, the greater the level, said the better the friction fastness, friction fastness of poor fabric will seriously affect its use. Many factors affect the friction fastness of the fabric, I collected for you to analyse the following factors.

Influence of the surface morphology of the fabric

  As a result of unconsolidated dyestuff is the main cause of poor friction colour fastness, in dry conditions, for the surface rough or abrasive down, pile fabric, hard such as hemp fabrics, denim fabrics and paint printing fabrics, if dry friction is very easy to the fabric surface pile of dyestuff, paint or other coloured material grinding down, or even cause part of the coloured fibres to break and form coloured particles, so that the dry friction colour fastness further decline. For abrasive or pile fabric, the fabric surface of the pile and friction cloth surface is a certain angle, and not parallel, so that the friction head in the reciprocal movement of friction resistance increases, so that such fabrics dry friction fastness decreased.

Influence of fabric structure

  Not much attention has been paid to the influence of the fabric structure and the surface form of the fabric on the colour fastness to rubbing. The surface of light fabrics (usually synthetic fibres or silk fabrics), which have a relatively loose fabric structure, slip partially under pressure and friction with the movement of the friction head when dry rubbing is carried out, resulting in increased friction resistance and higher friction efficiency. However, when wet friction is carried out, the situation is completely different from that of cellulose fibres. Due to the extremely low moisture absorption or water swelling effect of the fibres and the presence of water acting as a lubricant, this makes the colour fastness of such fabrics to wet rubbing significantly better than to dry rubbing, which is in marked contrast to the commonly held notion that the colour fastness of textile products to dry rubbing should be better than to wet rubbing, and often causes confusion. As a result, it is not uncommon for certain fabrics to have better colour fastness to wet rubbing than to dry rubbing. In this case, the variety of dyestuff chosen, the properties of the dyestuff, the dyeing and finishing process conditions, etc., although they also have an impact on the colour fastness to rubbing, are not very important compared to physical factors such as the fabric's structure and surface form. The statistics show that it is still mostly dark colours, such as black, red and navy, where this occurs. Of course, for fabrics such as corduroy, chinos and paint prints, the colour fastness to wet rubbing under wet conditions is usually class 2 or even lower, and not better than its colour fastness to dry rubbing, due to the dyestuffs and printing and dyeing processes used in their own right.

Influence of the chemical structure of reactive dyes

  The colour fastness of cellulosic fabrics dyed with reactive dyestuffs to wet rubbing can be affected by two factors: firstly, the water-soluble dyestuff is transferred to the rubbing fabric when rubbing, causing the original sample to fade and staining the rubbing fabric; secondly, some of the dyed fibres break when rubbing, forming tiny coloured fibre particles which are transferred to the rubbing fabric, causing colour staining. Therefore, the factors that may affect the colour fastness of reactive dyestuff to wet rubbing are: the structure and characteristics of the reactive dyestuff itself; the nature of the fabric; the effect of pre-treatment, fabric breakage and surface finish; the dyeing process and the effect of soaping after dyeing; the effect of colour fixing treatment after dyeing the fabric; the effect of finishing the dyed fabric, etc. The study showed that although there were some differences in the strength of the covalent bonds formed between the reactive dyes of different chemical structures and cellulose fibres, the bond stability and adhesion, there were no significant differences in the effect on the colour fastness of dyed fabrics to wet rubbing. When dyed fabrics are rubbed wet, the covalent bonds formed between the dye and the fibres do not break and produce floating colours. The dyestuffs that are transferred are usually supersaturated, not covalently bonded to the fibres, and are only adsorbed by van der Waals forces, i.e. the so-called floating colours.

  Research has also proved that the wet rubbing fastness of reactive dye-dyed fabrics is closely related to the depth of dyeing, i.e. when wet rubbing is carried out, the amount of colour transfer is nearly in a good linear relationship with the depth of dyeing, which is the most important factor when dyeing the supersaturated dyestuff, when dyeing dark colours, the concentration of dyestuff used is higher, but cannot greatly exceed the saturation value, because the excess dyestuff does not combine with the fibres, but only In the fabric surface accumulation and the formation of floating colours, seriously affecting the fabric's resistance to wet rubbing colour fastness.    In addition, the cotton fibres without special treatment are swollen under wet conditions, friction increases and the strength of the fibres decreases, all of which create good conditions for the fracture, shedding and colour transfer of coloured fibres. Therefore, appropriate pre-treatment of cellulose fibres before dyeing, such as mercerisation, burnt wool, cellulose enzyme brightening treatment, boiling, bleaching, washing and drying, can improve the surface finish and gross effect of the fabric, reduce friction resistance and floating colours, thus effectively improving the colour fastness of the fabric to wet rubbing.

Influence of softeners

  Improves the colour fastness of reactive dye prints by softening the finish. Softeners have a lubricating effect and reduce the coefficient of friction, thus preventing dye shedding. Cationic softeners can also form a colour deposit with anionic dyes, which makes the dyes less likely to fall off. At the same time, the colour precipitate makes the dye less soluble and can improve wet friction fastness. However, the softener with hydrophilic groups is not conducive to the improvement of wet friction fastness. In production practice, colour fixing agents can be used to close the water-soluble groups of the dyestuff, control the pH of the finished coloured fabric, remove floating colours and improve the smoothness of the fabric, thus improving the wet rubbing fastness of the fabric. Proper pre-drying of the front section can prevent the dyestuff from "swimming". The first two are closely related to the degree of hydrolysis of the dyestuff and the last two are directly related to the floating colour of the dyed product. The dyed fabric, especially the long car rolling dye, should be washed and soaped sufficiently to remove the floating colours and unreacted and hydrolysed dyes on the surface of the fibres, so as not to affect the colour fastness, which will result in very poor colour fastness if no attention is paid to the post-treatment of the dye, while the colour light will also become shrivelled and dark.



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