The confusion of color fastness of polyester fabric: [discussion、learning and communication on printing and dyeing,], with the pursuit of high—quality life, polyester spandex fabric has become more and more popular, especially polyester spandex knitted fabric has many advantages, such as good sag, soft coating, soft wrapping with little tightness when chasing the fashion at the same time,  good permeability and so on. However, this trend has improved the technical threshold for the printing and dyeing enterprises. But, we can not avoid the problem of fastness of how to make six fiber fastness to 4.5 degrees, and immersion color fastness 4-5 degree, this is a rather big problem!
 
How to solve the 4.5 grade fastness of polyester spandex red fabric
How to make polyester spandex fabric, especially spandex in more than 8% of the fabric to achieve six fiber dip color fastness 4.5, and immersion color fastness level 4~5, is the issues that every technical director of each dyeing factory now or once considered.

For this difficult problem, we should gather the experience of production and to sum up a set of processes, then we explore together.
Some suggestions to define the production engineering:
I. Pretreatment:  Because of the polyester spandex fabric in the process before spinning accumulates a large number of chemical auxiliary agent oil will disperse dyes in the dyeing process and form the condensation product, thus occurring many problems such as color and design. Therefore, it is necessary to do some pretreatment with scouring agent. Because many manufacturers of pure polyester generally do not have habits to act before treatment, it is suggested that polyester spandex fabric should be in pre-processing.

II. A predetermined type: because the elasticity of spandex in the weaving process will have a lot of residual elastic which is not fully released, a predetermined type is very necessary; otherwise it will affect the subsequent problems with width, weight, fold, etc.

III. Staining. The primary choice for dyeing is a dye. Let's take red for example: in the past, the bright red GS (R-153) we usually use is the most used by everyone, although GS can not meet the requirements of a class of environmental protection. But GS has the advantage of bright colors, high strength, and low cost. On the other hand,  in the high water wash fabric, the bright red GS' s performance is definitely not up to the mark. Then we have pure polyester, often all of the red XF, it is good performance when in pure polyester washing fastness, and the economy is good, but in polyester spandex, it will be in very poor performance. Then to choose the newest bright red PUD.
With 6% depth, pure polyester and polyester/spandex, have a reduction effected diagram in alkaline cleaning for once and acid alkali reduction cleaning for twice. The diagram shows a difference of washing fastness between alkaline cleaning for once and acid alkali reduction cleaning for twice.

Comparison of fastness towards six fibers of pure polyester, polyester and ammonia fabric with scarlet GS, scarlet XF, scarlet PUD at different concentrations
Under differ

▼ At a concentration of 4%

▼At a concentration of 6%


We have a good selection of dyes, which means that we should have a reasonable dyeing process. In order to make high washing dye PUD series of excellent performance and more stable, we must firstly control dyeing pH in 4, because of the composition of high water dye is relatively complex, and PH will make a group of properties of the dye have bias, causing the dye not stable. Secondly, it is the heating rate, we should control at 0.8 degrees C/min, because the high water dye is basically high polymer, warming up too fast will cause color flowers. The holding time is controlled according to the color depth of the 40min-60min. Cooling rate is controlled at 1.5 degrees C/min because the molecular weight of high water dye is generally relatively large, and some of the cooling processes also has a little color. What’s more, cooling rate will make bright colors become more plump.

IV. reductive cleaning: the polyester and spandex fabric's reductive cleaning is not the ordinary one. And whether it is the good or not, will directly affects the textile fabric wash fastness. Because the disperse dyes is unavoidable to dye the spandex, if you do not wash off the floating color, and then a good high water dye can not show the wash fastness as itself. If you do acidic and alkaline for twice, it is impossible to make it with 4.5 red, like using a net reduction cleaning of special Li TM.

Suggestions
Reduction cleaning is being under in acidic conditions, PH:4-6, so after that the dyeing can go on without drainage, and can only be cooled to about 85 DEG C. It will be done after opening the cylinder directly into the heat preservation after 20 minutes, the drainage and water cleaning once, and adding one last point. To supplement for the last point, the setting of the temperature should not be too high, and the setting of  speed can not be too slow. Because of the need to consider the thermal migration of disperse dyes, it can produce floating color again, which is believed to downgrade when washing fastness of polyester spandex fabric has been settled down.