Common Printing Defects in Screen or Roller Printing

The following printing defects are frequently observed in screen or roller printing:

1. Scrimp

 During the printing process the fabric sometimes creases under one of the screen during the printing process. Thus the pattern is printed on the top of the screen. When the crease is removed, it leaves a large area of the fabric unprinted.

2. Misfit or Out of Registration

 A misfit is a defect caused when screens are not properly aligned. The misaligned screens can leave an area unprinted or cause the pattern overlap on one another.

3. Stick-in

A stick-in occurs when a small fiber or yarn get stuck in one of the screen openings. It can result is a small unprinted circle in the design of the size of the tip of a pen. A stick-in is very  difficult to see and often go unnoticed.

4. Wicking or Flushing

It occurs when the printed area bleeds out into the unprinted area. This results in a "haloing" or shadowing effect around the outline of the pattern design. Wicking is often caused by residual salts left in the fabric during  resign finishing or during fabric preparation.

5. Doctor Streak

It refers to a wavy white or colored streak in the fabric in the warp direction. It is called so because it is caused by damaged or improperly set doctor blade in the printing machine. A doctor blade is a metal knife that cleans or scrapes the excess dye from engraved printing rollers, leaving dye paste only in the valleys of engraved areas.

6. Mottled

It results from the color applied unevenly during printing

7. Printing Machine Stop

As a result of printing machine stop the dye sometimes is smudged along the width of the fabric.

An excellent description of defects in digital printing can be found here.

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What are Plisse and Burnout Prints

Plissé Prints

The plisse prints are created by application of strong alkali to 100% cotton fabric. The alkali is applied in a pattern. After some time ( usually several minutes) the fabric is washed so that the alkali is removed. This results in the shrinkage of fabric from those areas where alkali is applied. This shrinkage causes puckering in the areas where alkali is not applied. A seersucker type appearance can be given to the fabric by applying the print pattern in parallel stripes. The alkali can be applied using direct or resist methods. 

http://ny-image0.etsy.com

Burn Out Prints

A beautiful "burn out" effect can be created by applying strong mineral acids or acid salts in the selected areas of a cotton polyester blended fabric. The acids will cause cotton to be destroyed and the polyeste rremains. Thus very beautiful lacey designs can be imparted to the fabric. Also in the burn out paste, a disperse dye can be incorporated which will also dye the polyester which burnout is taking place. However, due to the corrosive nature of the process special protections need to be taken.

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Motifs in Patola Saris

Ratanchowk

Kesar Chandan Design

Chhabdi Bhaat

Chanda Bhaat

Naari Kunjar Design

Five Phool Bhat

Three Phool Bhat

Sarvariya Bhat

Vora Gaji

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My Notes about Textile Books: Fabric Analysis

An excellent book on fabric analysis can be found here. 

This book is unique is the sense, that it takes care to analyse the fiber contents in common fabrics.

It gives detailed explanation on the following (among others):

1. Distinguishing between cotton and silk, silk and linen
2. Distinguishing between Weighted and Normal Silk.

I haven't tested the chemical procedure described in the book. Users are advised their discretion. And yes, this book is quite old, so don't expect to find treatment on Synthetic fibers.

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Difference between Blended Fabrics and Union Fabrics

Blended Fabrics are made up of blended yarns. Blended yarns contain fibers of different composition in fixed proportions. Thus a blended fabric may be made of polyester/cotton in 67:33 ratio in both warp and weft. 

Union fabrics are the fabrics where in the fibre content of warp is different form that of  weft. Thus a Silk/Viscose union fabric may have silk in the warp and viscose in the weft. 

An excellent study on silk/viscose union fabrics can be found here. 

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Effluent Tratement- Kerosene Recovery from Pigment Printing

Effluent Treatment- Kerosene Recovery from Pigment Printing

In India about 46% of the total printing is done using pigment printing method, 27% using reactive dyes, 15% Disperse dyes, 2% napthol, 3% acid and 7% using vat colors.

In a typical pigment printing paste, 75% is keorsene, 10% is binder, 5% each is gum and water, 2% urea and 1% each of DAP and emulsifier. Kerosene water emulsion acts as a thinkner is pigment printing. Its use is prohibitied in most of the developed countries. Alternatives to kerosene are synthetic thickners but they make the printed fabric stiff.

In India alone, about 140 thousand kiloliters of kerosene per annum is consumed during the process of printing and drying. Out of the total kerosene applied, about 22% is lost at various points during this process( 1 % is left out on the fabric, 12% screen printing and wastage, 5% is before dryer, 4% is at curing machine and 78% is released or evaporated in the atmosphere during the process of drying at 120-150 deg C). It signifies a loss of precious kerosene as well as pollution in the environment.

Apart from the effluents generated during wet processing, there is a substantial amount of kerosene vapour that is released in the air in the process of pigment printing.

Any kerosene recovery process should be based on the fact that kerosene is liquid at room temperature and immiscible with water. The kerosene vapour are at 120 deg C and they have to be cooled below 40 deg Celcius. The kerosene and water will separate out in two layers, with top layer can be skimmed for reuse.

An excellent effluent treatment plant is proposed by BTRA. Average recovery is 58% whereas maximum recovery can be 85%. Read more about it here

To view the pigment printing process and alternative to kerosene, please find the link here.

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Process Flow of Effluent Treatment in a Textile Industry-1

Process Flow of Effluent Treatment in a Textile Industry

Typically the following process flow of effluent treatment is followed in a typical textile industry;

Screening

The purpose of screening is to filter out the loose impurities. Thus wood, paper plastic bags etc. can be removed by this method. A method of progressive filtering is followed where first the matter is passed through coarse screens and then through fine screens.

Oil and Grease Removal

Many units discharge water mixed with oil. The purpose of this equipment is to remove the oil. Since surface density of oil and grease is less than water, the oily substance come on the surface of the water and can be skimmed.

Cooling and Equilization

The effluent from the primary treatment is cooled ( cooling towers are employed for this purpose) and then uniformly mixed using equlisation tank. It takes in any sudden gush of effluents as well as slow rate of effluent and feeds to the subsequent processes in a uniform way.

pH Adjustment ( Acid or Alkaline Dosing)

The waste from the Textile Industry is rarely pH neutral. To increase the efficiency of biological treatment and coagulation/flocuculation a pH of 6-8 is needed. Generally Sodium hydroxide is used to neutralise acidic waste and hydrochloric acide is used to neutralize alkaline waste. Generally the effluents from the dyeing industry have high pH and hence an acid addition is required.

Aeration 

It is reuqired to control BOD. Two main methods are used: one in which water is mechanically agitated so that air from atomoshphere may enter into the water, second method is introducing the air in the water through blowers and using diffusers to diffuse the air uniformly.

Prechlorination

Generally organic matter present in the effluent takes oxygen from the water, which increases its oxygen demand, to avoid that chlorine is added to oxidise the matter.

Clarification

The purpose of clarification is to remove any suspended solids by coagulation and flocculation. It is done using flash mixer. In flash mixer, alum solution is dosed as coagulant.

The flocculated water flows upwards towards tube settler. The suspended solids settle down.

This settling can also be done using lamella filter

Lamella Filter

It achieves solid liquid separation by directing the liquid between a seris of inclined plates called lamellae. It settles suspnded solids by gravity.



To be continued

An Excellent Document on Denim Effluent Treatment Process is here

Sources:

http://www.scribd.com/doc/4678823/Etp-Manual-Std-Denim

http://www.sharpengineering.co.in/Iffluent_Equipments.aspx

http://www.jfc-cetp.com/envinfo.html

http://www.iichemrc.org/Lamella.pdf

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Effluent Generated at various Processes of Textile Manufacturing

Effluent Generated at various Processes of Textile Manufacturing

Textile manufacturing involves conversion of Fibers into garments. At each process some amount of liquid is used. However, it is not that each process leads to generation of efflents. Typically coversion to yarn involves no generation of effluents. It is the sizing and processing where most of the efflent is generated which needs to be treated. Given below is a list of the processes along with the information about effluent generated.

1. Fiber Preparation and Yarn Spinning: 

There is very little effluent generated in these processes.

2. Slashing/Sizing

The Effluent contains BOD, COd, metals, cleaning waste and size.

3. Weaving, Knitting and Tufting

There is very little effluent generated in these processes.

4. Desizing

The effluent contains BOD from water-soluble sizes, synthetic size, lubricants, biocides and anti-static compounds.

5. Scouring

The effluent contains disinfectants and insecticide resudes, NaOH, detergents, fats, oils, pectin, wax, knitting lubricants, spin finishes and spent solvents.

6. Bleaching

The effluent contains hydrogen peroxide, sodium silicate or organic stabilizer. The effluent also contains high pH.

7. Singeing and Heat Setting

There is very little effluent generated in these processes.

8. Mercerising

The effluent contains high pH and Sodium Hydroxide.

9. Dyeing

The effluent contains metals, salts, surfacftants, toxics, organic processing assistants, cationic material, color, BOD, sulfide, acidity or alkalinity and spent solvents.

10. Printing

The effluent contains suspended Solids, urea, solvents, color, metal, heat , BOD and foam.

11. Finishing

The effluent contains BOD, COD, suspended solids, toxics and spent solvents.

Read Also

Textile Effluent Treatment-1
Textile Effluent Treatment-2

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