In many cases a backstaining or redeposition of blue indigo is undesirable. Either the inside pockets are not pretty white, the cast of the jeans is too blue daubed or the used areas do not show nice “pepper and salt”-contrast, a part of the locker indigo turned back to the cotton and “re-dyed” it.
What to do to avoid that?
Of course it’s all about the quality of the used fabric but in Garment Wet Processing are some useful solutions to improve the results. One way could be to spray the garments before washing with a special auxiliary to deepen the color and improve the rubbing fastness, such as the Atrix system of CHT-Tübingen, Germany. This product has to be applied by spray and afterwards immediately glazed manual with a brush or rubber gloves. Subsequent put the garments in a curing oven, dry them at 80 to 90 °C and fix them at 150 °C.
Additionally to that a fixation of the indigo during washing is possible. Usually fixing agents are cationic products and accumulated to the fiber. Per temperature it will be linked to the fiber. A well known product is the Rotta Fix 1545 from ROTTA/DYSTAR which you apply in a bath with liquor ratio of 1:10 at 30 °C for 3-5 min and then heat up to 60 °C for further more 10-15 min runtime. Of course other products are available on the market but normally they are all cationic products and work more or less in the same way as above described. Important is to keep the pH at 6 to 7 all time.
These are two options which could be done before the wash process is started. During the several wash steps especially during desizing and stonewash appears a high backstaining/redeposition. The desizing with an Amylase should not run too long time, in many cases a short desize with 5 to 8 min at 40 °C is enough to clean the garments sufficient and avoid the “Re-dyeing”. Here it should be applied already very strong detergents together with some “backstaining-blocker”. Some warm and cold rinses afterwards will help for sure. These products must be used during stonewash processes as well. Sometimes it’s necessary to run stonewash in two or three phases to avoid too long runtime with high backstaining rate. First phase might be shorter like 15 to 25 min and then next phase with a bit longer runtime as 25 to 35 min and so on and so fort, with rinses in between.
The best anti-backstaining-agent chemistry to use nowadays is a combination of the usage of an ethoxylate and polyesterpolyglycol products. Commercially speaking chose from DYSTAR Lava Sperse CPOS together with Lava Sperse KDS f.i.
If the garments are still not clean enough, even after some rewashes with cleaning auxiliaries, a short “bleach” with Laccase at 50 to 70 °C will help much. Because the Laccase reduces first the locker indigo on the surface of the garments and turns the cast generally from blue to grey, means the jeans won’t look blue daubed. Hereby it is important to rinse and spin the jeans well and dry the jeans in a tumbler on the left side (inside out) with high temperature and possible short run time.
A very successful method, fast and low cost, is to clean the jeans by using Ozone. The advantage is that you do not need to put the garments again in a washer, rinse,soften, spin and dry them in a tumbler. Dry garments can be placed in the Ozone machine and the result is seen immediately. Just let them run once more for a short time in a tumbler at temperature to destroy the rest of Ozone.
Backstaining of Indigo is unavoidable consequence of stoning or bio-stoning. Laccase treatment after these processes is basically a process for lightening blue denim as well as removal backstaining simultaneously. Accurate control of bleaching process so as to discriminate between removal of backstaining without effecting denim is impossible. No chemical process can differentiate between the indigo trapped in the pocket cloth and the indigo in the warp.
Here are just a few options shown and short explained. If you are interested for further information please do not hesitate to contact us either by phone (0049 173 431 41 21) or mail (Ingo.firstname.lastname@example.org).
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