Study On Textile Printing Process

Introduction of Textile Printing

The word “printing” derives from the?Latin word?“pressing?“. It implies a process that uses pressure.?Textile printing?is one kind of?localized dyeing?where dyes or?pigments & chemicals are applied?by any method which can produce a particular effect of colour on fabric according to design. In a word, Applying coloured patterns and designs to decorate a finished fabric is called?‘Printing’.?In an adequately printed fabric, the colour is affixed to the fibre or fibre surface (pigment) so that it may not be affected by washing, friction, or any other means. It’s a?combination of art, engineering &?dyeing.Printing is a process of decorating textile fabrics by application of pigments, dyes, or other related materials in the form of patterns. Although apparently developed?from the hand painting of fabrics, such methods are also of great antiquity. There is evidence of printing being carried out in India during the 4th century?BCE, and a printing block dated at about 300?CE?has been unearthed in the burial grounds of Akhmīn in?Upper Egypt. Pre-Columbian printed textiles have been found in?Peru?and Mexico. Textile printing has become highly sophisticated and has involved the skills of many artists and designers.

Textile printing?is related to dyeing, whereas in dyeing, the whole fabric is uniformly covered with one color. In printing, one or more colors are applied to the fabric in certain parts only, and in sharply defined patterns. Printing is therefore called as localized dyeing. The dyes and pigments are applied locally or discontinuously. In this article I will concentrate of the types of printing methods in terms of the machinery used to deliver the print paste and the mode?by which paste is delivered to the substrate, be it flat screen, rotary screen, copper roller, ink jet printing or another mechanism.

Feature of Printing

ü Printing is applied in form of design or pattern. Single or?multi color?can be applied.

ü A special type of viscous liquid is used to hold the dye/pigment & chemical which is called?‘Print paste’.

ü High viscosity of print paste helps dye to adhere to surface of fibre. But the fixation is done by applying steam which is called ‘curing’

ü For dyeing low viscous or aqueous medium is used but printing is done in wet viscous medium.

ü The Dyes used for printing mostly include vat, reactive, naphthol (azoic) and disperse dyes which have good fastness properties.

ü The pigments, which are not truly dyes, are also used extensively for printing. About 96% is done by pigment. These colors are fixed to the fiber through?binder.

ü Steaming is essential in printing material.

ü The material are spot dyed and ma not be required to complete wet.

ü Liquor ratio is less hence the material can be easily dried.

I can say that textile printing?is the process of applying?color?to?fabric?in definite?patterns?or designs. In properly?printed?fabrics the colour is bonded with the?fibre, so as to resist?washing?and?friction. Textile printing is related to?dyeing?but in dyeing properly the whole fabric is uniformly covered with one colour, whereas in printing one or more colours are applied to it in certain parts only, and in sharply defined patterns.?

Process Flowchart Of Textile Printing

Fabric preparation

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Preparation of printing device (block/flat or rotary screen, roller)

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Printing paste preparation

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Impress on fabric

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Drying the printed fabric

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Fixation by curing

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Washing & soaping

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Finally dry

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Delivery

Preparation Of Cloth For Printing

Cloth is prepared by washing and bleaching. For a colored ground it is then dyed. The cloth has always to be brushed, to free it from loose nap, flocks and dust that it picks up whilst stored.?

Frequently, too, it has to be sheared by being passed over rapidly revolving knives arranged spirally round an axle, which rapidly and effectually cuts off all filaments and knots, leaving the cloth perfectly smooth and clean and in a condition fit to receive impressions of the most delicate engraving. Some fabrics require very careful stretching and straightening on a?stenter?before they are wound around hollow wooden or iron centers into rolls of convenient size for mounting on the printing machines. Gray cotton fabrics obtained from loom or knitting have to go through several steps to make printing useful.?

Preparation Of Colours

The art of making colors for textile printing demands both chemical knowledge and extensive technical experience, for their ingredients must not only be in proper proportion to each other, but also specially chosen and compounded for the particular style of work in hand. A color must comply to conditions such as shade, quality and fastness; where more colors are associated in the same design each must be capable of withstanding the various operations necessary for the development and fixation of the others. All printing pastes whether containing colouring matter or not are known technically as colours.

Colors vary considerably in composition. Most of them contain all the elements necessary for direct production and fixation. Some, however, contain the colouring matter alone and require various after-treatments; and others again are simply thickened mordants. A mordant is a metallic salt or other substance that combines with the dye to form an insoluble colour, either directly by steaming, or indirectly by?dyeing. All printing colours require thickening to enable them to be transferred from colour-box to cloth without running or spreading beyond the limits of the pattern.

Starch Paste

Starch paste is made from?wheat starch, cold water, and?olive oil, then thickened by boiling. Non-modified?starch?is applicable to all but strongly alkaline or strongly acid colours. With the former it thickens up to a stiff unworkable jelly. In the case of the latter, while mineral acids or acid salts convert it into dextrine, thus diminishing its?viscosity?or thickening power, organic acids do not have that effect.?

Today,?modified carboxymethylated cold soluble starches?are mainly used. These have a stable viscosity and are easy to rinse out of the fabric and give reproducible "short" paste?rheology.Flour paste is made in a similar way to starch paste; it is sometimes used to thicken aluminum and iron mordants.?Starch paste resists of rice flour have been used for several centuries in Japan.

Gums

Gum arabic?and?gum Senegal?are both traditional thickenings, but expense prevents them from being used for any but pale, delicate tints. They are especially useful thickenings for the light ground colours of soft muslins and 9 penetrate as well into the fibre of the cloth or as deeply as pure starch or flour and is unsuitable for very dark, strong colours.Gum tragacanth, or Dragon, which may be mixed in any proportion with starch or flour, is equally useful for pigment colours and mordant colours. When added to a starch paste it increases its penetrative power and adds to its softness without diminishing its thickness, making it easier to wash out of the fabric.?

It produces much more even colours than does starch paste alone. Used by itself it is suitable for printing all kinds of dark grounds on goods that are required to retain their soft "clothy" feel.Starch always leaves the printed cloth somewhat harsh in feeling (unless modified carboxymethylated starches are used), but very dark colours can be obtained. Gum Senegal, gum arabic or modified guar gum thickening yield clearer and more even tints than does starch, suitable for lighter colours but less suited for very dark colours. (The gums apparently prevent the colours from combining fully with the fibers.) A printing stock solution is mostly a combination of modified starch and gum stock solutions.?

Styles of Printing

1.Direct

In direct printing, a color pattern is printed directly from a dye or pigment paste onto a textile substrate without any prior mordanting step or a follow-up step of dyeing, etc. In this style of printing in one or several colors where the dyes are applied and then fixed by ageing or other appropriate means. The fabric is usually initially white but may sometimes have previously dyed.

2.Overprinting

In the direct printing, a common approach is to apply a color pattern onto a grey or bleached fabric. If done on colored fabric, it is known as overprinting. The desired pattern is produced by pressing dye on the fabric in a paste form. To prepare the print paste, a thickening agent is added to a limited amount of water and dye is dissolved in it. Earlier starch was preferred as a thickening agent for printing. Nowadays, gums or alginates derived from seaweed are preferred as they allow better penetration of color and are easier to wash out.

3.Mordant

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

4. Flock

A method of fabric ornamentation in which adhesive is printed on and then finely chopped fibers are applied all over by means of dusting-on, an air-blast, or electrostatic attraction. The fibers adhere only to the printed areas and are removed from the unprinted areas by mechanical action.

5.Discharge

This process is used to remove color from a dyed fabric in a desired pattern. A paste containing a chemical with a bleaching effect is applied through a printing process. The fabric is then placed in a steam unit for a specified time. The steam has the effect of removing the color from the fabric, leaving a lighter pattern in the printed areas. If desired, a non-dischargeable dye can be incorporated into the?printing process?to achieve a multicolored design.Simply we can explain, in?discharge printing, a textile fabric is first dyed with a suitable dye and then the dye is selectively destroyed from certain areas of the fabric to give the look of a printed pattern.

6.Dyed

This style consists of two steps: printing with a mordant and dyeing. After dyeing color only fixes in places where mordant was applied as a result a design is produced on the fabric.

7.Transfer

In transfer printing, a design is printed first on a flexible non-textile substrate (e. g. paper) and later transferred from the paper to a textile substrate.

8.Resist/Reverse

In this case fabric is first printed with a white or colored resist agent and then dyed. A design is thus produced, as the dyestuff does not get fixed in places where the resist agent was applied.

9. Resist

In resist dyeing, a wax or other substance is printed onto fabric which is subsequently dyed. The waxed areas do not accept the dye, leaving uncolored patterns on a colored ground.

10.Azoic

Fabric is printed with coupling compound of?azoic dye?and then padded with a diazo compound. Color show up in printed areas as only there the reaction between two compounds occur.

11.Metal

In the metal style of printing fabric is printed with silver or gold solution or non-removable resins.

12.Crimp/Crepon

Fabric is printed with thickened sodium hydroxide solution and then immersed in water. Thus only the printed areas shrink and an effect is produced.

13.Pigment

Printing is done by the use of pigments instead of dyes. The?pigments?do not penetrate the fiber but are affixed to the surface of the fabric by means of synthetic resins which are cured after application to make them insoluble. The pigments are insoluble, and application is in the form of water-in-oil or oil-in-water emulsions of pigment pastes and resins. The colors produced are bright and generally fat except for crocking. Most pigment printing is done without thickeners because the mixing up of resins, solvents and water produces thickening anyway.

Block printing

Description :

Block printing is a method where the pattern was cut into wooden blocks, or was built through an assembly of metal stripes, nails and so on. 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 colors until the pattern is complete.?

Application :

The block printing is used from time immemorial and is still being practiced in all Asian countries as it can be done even at homes by the people in their free time.?Block printing?is a slow and laborious process and is not suitable for high volume commercial use. This printing method is used only at small scale or in cottage industry and is not used at industrial scale because of less flexibility and productivity.