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Dyeing And Printing

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Dyeing & Printing

color is one of the most significant factors in the appeal & marketability of textile productsmanner in which color is added to a textile and the chemical nature of the colorant contribute to productsappearanceperformancerate of response to fashion changequalitycost

DyesNatural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources, for example:- Indigo. The dyes that are obtained from animal sources are called Cochineal, and those that are got from minerals are Ocher. Historically, natural dyes were used to color clothing or other textiles, and by the mid-1800's chemists began producing synthetic substitutes for them. By the early part of this century only a small percentage of textile dyes were extracted from plants. Lately there has been increasing interest in natural dyes, as the public becomes aware of ecological and environmental problems related to the use of synthetic dyes. Use of natural dyes cuts down significantly on the amount of toxic effluent resulting from the synthetic dye process.

Natural dyesDyes obtained from natural sources such as vegetables, animals and minerals. These are difficult to obtain and are very expensiveVegetable dyes- These are obtained from the leaves ,flowers ,fruits,bark,and branches of plants and trees.They are obtained from jamun, henna turmeric, saffron blue plants etc.

Animal dyes-Dyes obtained from insects, fishes etc. This dye is very expensive.Mineral dyes-These are obtained from minerals .

Tyrian purple(fish)

Synthetic dyesSynthetic Dyes Synthetic dyes are classified based upon their chemical composition and the method of their application in the dyeing process. Acid Dyes A class of dyes used on wool, other animal fibers, and some manufactured fibers. Acid dyes are not used on cotton or linen . Acid dyes are widely used on nylon when high washfastness is required. These dyes are cheap and lustrous.

Basic (Cationic) Dyes Basic dyes are water-soluble and are mainly used to dye acrylic fibers. They are mostly used with a mordant. A mordant is a chemical agent which is used to set dyes on fabrics by forming an insoluble compound with the dye. With mordant, basic dyes are used for cotton, linen, acetate, nylon, polyesters, acrylics and modacrylics. Other than acrylic, basic dyes are not very suitable for any other fiber as they are not fast to light, washing or perspiration. Thus, they are generally used for giving an after treatment to the fabrics that have already been dyed with acid dyes

Neutral DyesThese dyes do not have the qualities of both acid and basic dyes.Direct (substantive) Dyes these dyes are used on cotton , linen , cotton, rayon and artificial fibers. these fibers can be dyed easily and at low cost, but colors are not fast and are not fast and durable. These colors can not resist sunlight and washing. Normally cheap fabrics are dyed with these dyes

Sulphur DyesThese dyes are used on cellulose fabrics because excessive alkalies are used in coloring with these dyes . These dyes have sulphur and are expensive. Dull colors like navy blue, brown,black,etc are coloured with these dyes. Vat DyesAny type of fabric can be dyed with vat dyes. These colors are fast and durable and can resist light, sweat, acid, base, washing, etc. Therefore fabrics which are washed regularly are colored with these dyes.

Developed Dyes These Dyes Are Also Used For Dyeing Cotton, Linen, Rayon And Artificial Fibres. Special Chemical Processes Are Used On These Dyes For Fast Coloring. These Dyes Are Expensive.

Stages of dyeingIn skein dyeing the yarns are loosely wound into hanks or skein and then dyed. The yarns have good dye penetration, but the process is slow and comparatively more expensive.Stock dyeing is dyeing raw fibers, also called stock, before they are aligned, blended, and spun into yarns.Fabric dyeing, also known as piece dyeing, is dyeing fabric after it has been constructed. It is economical and the most common method of dyeing solid colored fabrics. The decision regarding color can be made after the fabric has been manufactured. Thus, it is suitable for quick response orders. Dye penetration may not be good in thicker fabrics

Methods of dyeingSimple dyeing- In this method,the fabric to be dyed is dipped in clean water.It is now dipped in coloured solution after squeezing.For fast colouring of the fabric ,it is boiled in the coloured solution.The cloth is dyed evenly in this method.Cross Dyeing: This is a very popular method in which varied color effects are obtained in the one dye bath for a cloth which contains fibers with varying affinities for the dye used. For example, a blue dyestuff might give nylon 6 a dark blue SHADE, nylon 6, 6 a light blue SHADE, and have no affinity for polyester area unscathed or white

Batik Dyeing: This is one of the oldest forms known to man. It originated in Java. Portions of the fabric are coated with wax so that only un-waxed areas will take on the dye matter. The operation may be repeated several times and several colors may used for the bizarre effects. Motifs show a mlange, mottled or streaked effect, imitated in machine PRINTING.

Tie and dye- Tie-dye is a way of creating patterns of color by folding, tying, stitching, crumpling or otherwise preparing the FABRIC to inhibit the flow of the dye into the folds of the fabric. The pattern of the folds and where the colors are squirted determines the final design.

PrintingPrinting is that process in which fabrics are imparted colors in specific designs

Methods of printingBlock Printing: The blocks are usually made of wood and the design is hand carved, so that it stands out in relief against the background surface. The print paste is applied to the design surface on the block and the block then pressed against the fabric. The process is repeated with different designs and colours until the pattern is complete.Blockprinting is a slow, laborious process and is not suitable for high volume commercial use. It is a method still practised in the oriental countries where market exist for the types of printed fabrics produced.

Roller printing: roller printing has traditionally been preferred for long production runs because of the very high speeds possible. It is also a versatile technique since up to a dozen different colours can be printed simultaneously. The basic roller printing equipment, consists of a number of copper faced rollers in which the design is etched. There is a separate printing roller for each colour being printed. Each of the rollers rotates over the fabric under pressure against an iron pressure roller. A blanket and backing cloth rotate over the pressure roller under the fabric and provide a flexible support for the fabric being printed. A colour doctor blade removes paste or fibres adhering to the roller after contact with the fabric. After the impression stage the fabric passes to the drying and steaming stages.

Screen Printing : This Type Of Printing Has Increased Enormously In Its Use In Recent Years Because Of Its Versatility And The Development Of Rotary Screen Printing Machines Which Are Capable Of Very High Rates Of Production. An Additional Significant Advantage Is That Heavy Depths Of Shade Can Be Produced By Screen Printing, A Feature Which Has Always Been A Limitation Of Roller Printing Because Of The Restriction To The Amount Of Print Paste Which Can Be Held In The Shallow Depth Of The Engraving On The Print Roller. Worldwide, Some 61% Of All Printed Textile Fabric Is Produced By The Rotary Screen Method And 23% By Flat Screen Printing.

Stencil printingIt is just like screen printing .in this method the desired designs are made on stencil of a metal plate or wax paper.differnet stencils for different colours are made as per the colours used in the design.stencil is placed on the fabric and colors are sprayed with the help of a brush .thereafter stencils are removed and the desired design on the fabric is obtained.

Resist Printing: A printing method in which the design can be produced: (1) by applying a resist agent in the desired design, then dyeing the fabric, in which case, the design remains whitealthough the rest of the fabric is dyed; or (2) by including a resist agent and a dye in the pastewhich is applied for the design, in which case, the color of the design is not affected bysubsequent dyeing of the fabric background.

Duplex Printing: A method of printing a pattern on the face and the back of a fabric with equal clarity.Discharge Printing: In white discharge printing, the fabric is piece dyed, then printed with a paste containing a chemicalthat reduces the dye and hence removes the color where the white designs are desired. In colored discharge printing, a color is added to the discharge paste in order to replace the discharged color with another shade.