Discharge Printing

Prepared By : Mazadul Hasan sheshirID: 201000040000813th Batch (session 2009-2013)Department : Wet Processing Technology Email: mazadulhasan@yahoo.comBlog : www. Textilelab.blogspot.com (visit)

Southeast University Department Of Textile Engineering

I/A 251,252 Tejgaon Dhaka Bangladesh

Prepared By :

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Fabrics are dyed a solid color prior to printing. When printing is done, the design is

applied by screen or roller with a chemical which removes the color of the originally

dyed fabric. Discharge prints can be made with rollers and screen methods. They are

not widely used because production costs are high.

Discharge Print

Textile printing is the process of applying colour to fabric in definite patterns or designs. In properly printed fabrics the colour is bonded with the fiber, so as to resist washing and friction.

Textile printing is related to dyeing but, whereas in dyeing proper the whole fabric is uniformly covered with one colour, in printing one or more colours are applied to it in certain parts only, and in sharply defined patterns.

In printing, wooden blocks, stencils, engraved plates, rollers, or silkscreen’s can be used to place colours on the fabric. Colourants used in printing contain dyes thickened to prevent the colour from spreading by capillary attraction beyond the limits of the pattern or design.

Traditional textile printing techniques may be broadly categorized into four styles:

Introduction

Direct printing, in which colourants containing dyes, thickeners, and the mordants or substances necessary for fixing the colour on the cloth are printed in the desired pattern.

The printing of a mordant in the desired pattern prior to dyeing cloth; the color adheres only where the mordant was printed.

Resist dyeing, in which a wax or other substance is printed onto fabric which is subsequently dyed. The waxed areas do not accept the dye, leaving uncoloured patterns against a coloured ground.

Discharge printing, in which a bleaching agent is printed onto previously dyed fabrics to remove some or the entire colour.

Resist and discharge techniques were particularly fashionable in the 19th century, as were combination techniques in which indigo resist was used to create blue backgrounds prior to block-printing of other colours.[1] Most modern industrialized printing uses direct printing techniques.

Introduction

Discharge Printing

Discharge printing is a process where printing of lighter colors is done onto fabrics having darker background. The dye in the garment is removed by replacing it with ink which leaves a soft texture on the fabric. Discharge printing works best on cotton fabrics because other fabrics are dyed in different processes and react less to discharge chemicals and therefore the dye does not break down.

Initially in discharge printing, the finished goods required steaming during the drying process which discouraged the practicing of this process. But the latest discharge ink systems react chemically and do not require steaming. These latest systems brought advancement and brought new openings in the area of screen printing.

Discharge Printing

The casino table’s graphics are done with discharge printing to avoid the hindrance of the printed line when the dice is rolled. If at all the printing is done with plastisol it would change the speed of the rolling dice. The discharge print gives a smooth run for the rolling of the dice.

Discharge printing produces vibrant, opaque colors on dark color fabrics. The depth, levelness and penetration can be controlled in discharged printing. Complex patterns and soft colors can be produced with immense clarity.Discharge printing is best observed when the four color printing is done on black 100% cotton shirts. The print appears best only when it is exposed to the heat chamber.

Discharge Screen Printing

Discharge Printing

Required Fabric for Discharge Printing Discharge printing enables a clean and transparent print than the earlier discharge addictives which were used only for water base inks. Reduction is the keyword for discharge printing.The method of discharge printing changes from fabric to fabric, but the best fabric for this method is a pure cotton one.

Discharge all over PrintingZinc-formaldehyde is used to remove the dye in the discharge process. Therefore, it is necessary to wash the t-shirts before you wear them. Zinc- formaldehyde free discharge is also available which does not need any washing before wearing it. This is proved to be a better process than the ordinary discharge printing process.Use the right kind of fabric.-      The fabric has to be 100 percent natural like cotton.-      The dye on the fabric should be easily discharged. Cotton gives wonderful results in this process.-      The fabric should be dyed right avoiding over dyeing. This generally happens when there is shortage of dye and therefore another color is dyed on top of this color. So when we try to discharge it, it results in the color which is below it.It is important to check the fabric before starting the process. The fabric should be strong enough to carry the discharge process.

Required Fabric for Discharge Printing

Discharging agents :--

Clearly, the most important methods of discharging are based on reduction. This

general method can be varied and adapted to give discharges with most classes of

dye in use and on most types of fibre. Indeed, to many printers the terms ‘reducing

agent’ and ‘discharging agent’ are synonymous.

The most widely used reducing agents are the formaldehyde sulphoxylates. The

stability of these compounds is such that only limited losses of sulphoxylate occur

during printing and prior to steaming. The use of sodium formaldehyde sulphoxylate

(CI Reducing Agent 2, sold as Formosul or Rongalite C) was established as long ago as

1905, when it was recognized that methods based on this reducing agent offered

many advantages.

Discharging agents

Importance of Discharge Styles

Discharge styles have been important since the earliest days of textile printing..With any industrial process there must be sound technical and commercial reasons for its conception and continuation. In the case of discharge printing, the following considerations determine the usefulness of the process compared with other printing techniques.

1. Printed materials with large areas of ground colour can be produced, the depth, levelness and penetration of which would be difficult, if not impossible, to obtain by a direct printing process.

2. Delicate colours and intricate patterns can be reproduced on grounds of any depth, with a clarity and sharpness that have become the hallmarks of this style. Intricate white patterns lose their crispness if left as unprinted areas in a direct, blotch print, because the print paste spreads unequally in different directions. In addition, a coloured motif fitted into a blotch print either leaves unprinted white margins or forms a third colour where fall-on occurs. In some cases such effects are acceptable, but they can be eliminated by using the discharge technique.

Importance of Discharge Styles

3. The extra processes required and the additional costs of discharge pastes mean that production costs are higher, but the aesthetically superior results give the product a higher value and enable profit margins to be maintained or even improved. The higher costs of discharge printing are often offset when applied to long-lasting designs used for scarves, ties, cravats and dressing gowns. As already indicated, in discharge styles the pattern is produced by the chemical destruction of the original dye in the printed areas. The discharging agents used can be oxidising or reducing agents, acids, alkalis and various salts. An early and, one might say, classical example is the discharge printing of cotton dyed with indigo, the characteristic colour of which can be destroyed either by oxidation or reduction.

Importance of Discharge Styles

Discharge Screen PrintingDischarge is a screen printing process where the same techniques and equipment are used but instead of normal ink, discharge inks are used, which remove the shirt's dye instead of putting a color on top of the shirt. It is somewhat similar to bleaching in a design, except it doesn't damage the fibers like bleaching would. It results in an extremely soft print, and shows the weave of the shirt. It can be used by itself, as an under base for other colors to be put on top, or with pigments added. Pigmenting discharge can be difficult to achieve exact color results, as the discharge efficacy affects the color, and what you see is not what you get when mixing the pigments, but it can still be a great way to achieve colors on dark garments.

The discharge screen printing involves the following steps:1. First the table is prepared by stretching the cloth and pinning it up on the

table.2. Now the paste is prepared to discharge the dye on the fabric. Remember to

get your discharge paste ready a few hours before the process takes place.3. Prepare the color discharge paste and apply on the fabric so that the dye

becomes soluble and comes out before the fabric is ready for steaming.

Discharge Screen Printing

1. Print the fabric and keep it for drying, steaming should be done within 24 hours to produce best results.

2. Once the steaming process is done, then wash the fabric thoroughly to get rid of the chemicals. Hang the fabric and allow it to breathe for about 30 minutes, this helps in developing color.

3. There you go!! The final wash is here. Wash the fabric in detergent to prevent loosing of any vat dye left on the fabric which helps in fixing the dye to the fiber. It is recommended to wash the fabric in slight lukewarm water.

Discharge screen printing is a long process and cannot be carried at home as there are chemicals used in this process. They have to be handled carefully by trained staff with perfection and patience.

Discharge Screen Printing

Positives of Discharge Screen Printing

1. Very cool technique that removes the dye from the shirt

2. Little to no feeling of the print on the shirt

3. Vibrant colors

4. The best way to print on dark shirts with non-traditional inks

5. Something different from screen printing "norms"

6. Still able to do a great amount of detail

7. We offer discharge printing at no additional charge. In fact, it's often

cheaper than traditional ink

Positives of Discharge Screen Printing

Negatives of Discharge Screen Printing

1. Some sizes may discharge better than others

2. Can be hard to use for photographic style or process printing

3. Only works on natural fibers, like cotton, so 50/50 can't be used

4. Not all shirt colors will discharge (royal blue never works well, for

example)

5. Process can be quirky

Negatives of Discharge Screen Printing

How Cotton & Polyester Give Discharge Printing Different Looks

How Cotton & Polyester Give Discharge Printing Different Looks

Discharge ink will not discharge polyester, but that doesn't mean we can print discharge on polyester.

With water based and discharge ink, not all fabrics were created equal. 100% cotton will give different results than a 65/35 cotton/poly blend will and a 50/50 different yet. On top of that, as well look at below, two 50/50s from the same manufacturer can yield very different results.

It’s important to know, or at least have an idea, how these different options will affect the print style used because it will vary the end look drastically.

Since discharge ink will only “discharge” cotton and not polyester, that piece of knowledge alone will be the basis for analysis here. It’s important to know that and then apply it to different scenarios. For example, let’s say we have a design which you want to print on a black shirt. Let’s look at a few shirt options and how each can yield different results.

American Apparel 2001 Black Since this is a 100% cotton shirt we know this will discharge with rather bright, bold, true colors. There shouldn’t be too many surprises here.

American Apparel BB401 Black With this shirt being a 50/50 cotton/poly blend, we need to consider the fabric makeup to decide how it will print. This shirt is both cotton dyed as well as poly dyed. That means the cotton and the poly in the shirt are both dyed, in this case both dyed black. So, we’d only be able to get a bright discharge printing result from the cotton portion of that shirt, since that’s all we can discharge. The poly portion of the shirt won’t discharge so it’s not going to give bright printing results on a black shirt. The end result on this print will be darker, faded, muted vintage look rather than the bright bold print the 2001 delivered.

American Apparel BB401 Heather Black This is the same shirt we just looked at, but this time it’s heather black, not straight black. We now have a shirt which is only cotton dyed, not poly dyed as the black BB401 is. What that means is that the cotton part of this shirt is black and the poly is nearly white. So we can discharge the black cotton to get bright print colors and the poly is white which we can get bright colors out of. Therefore, this shirt will yield rather bright, true looking colors even though its 50/50.

How Cotton & Polyester Give Discharge Printing Different Looks

This is obviously just a tip of the iceberg when it comes to shirt options yielding different looks. We didn’t touch on discharging tri-blends or 65/35 blends, both of which can be equally exciting. Overall, discharging 50/50s, 65/35s and tri-blends can be an awesome process, but it does take some experimenting.

Points to be Considered for Discharge Printing

It is necessary to know the following points:

1. You should never overlap the colors if you want to print spots on the fabric.

2. Always go for transparent colors to show the dark background on the fabric. If you want to separate colors then go for primary colors as they produce good results.

3. Discharge printing is mainly economical for all-over prints because it is done by soft hands.

Points to be Considered for Discharge Printing

Conclusion

The discharge printing process is slightly more expensive because of the inks and

chemicals used as well as a slightly more difficult process but the end result leaves

that super soft feel that everyone wants! Works great for oversize designs with a lot of

coverage so when wearing the shirt, you’re not wearing that extra unbreathable ink

since the discharge print is actually part of the garments

Conclusion

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