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Tuesday, April 7, 2015

Basic Ingredients of Printing

The Basic Ingredients of Printing

The Basic Ingredients of Printing are as follows:
  • Dyestuffs and Pigments
  • Thickener
  • Acid or alkali or acid liberating agents
  • Carrier or swelling agents
  • Solvents or solution acids or dispersing agents or humectants
  • Antifoaming agents or de-foaming agents
  • Wetting agents
  • Catalyst or oxygen carrier
  • Oxidizing and reducing agents
Printing Ingredients
 
Dyestuff and Pigments
Dyes or dyestuff may be defined as colorants in which the coloring substance is dissolved in liquid, are absorbed into the material to which they are put in an application for.
Pigments consist of extremely fine particles of ground coloring matter suspended in liquid which forms a paint film that actually bonds to the surface it is applied to.

Thickener
Thickener is a thick mass which imparts stickiness and plasticity to the print paste so that it may be applied on the fabric surface without bleeding or spreading and be capable of maintaining the design out lines.
Thickener gives the required viscosity to the printing paste; prevent premature reactions between the chemicals contained in the print paste.

Acid and alkalis
Acid: Organic acid
Alkali: Sodium and potassium hydroxide, sodium carbonate, potassium carbonate etc.
These control PH and fix dye on the fabric.

Carriers and swelling agents
These accelerate the rate of dye penetration by fibre polymer, swell the fibre and reduce crystallinity.
Swelling agents: Resorcinol, phenol, polyethylene glycol etc.
Carrier: Diphenyl

Solvents or solution acids or dispersing agents
This prevent aggregation of the dye stuff molecules in the highly concentrated paste of the dye, solution aids increase the solubility of insoluble dyestuff, solvents increase the color value of the prints, assist dye penetration and helps to get bright design. Ex: Diethylene glycol, acetin, urea, gycerine etc.

De-foaming agents
De-foaming agents prevent the formation of foam during printing. E.g. silicone defoamers, sulphated oil etc.

Wetting agents
Substances which reduce the surface tension of water, thereby allowing it to wet a surface easily, which are otherwise non wettable are known as wetting agents or surface active agents, e.g. TRO, olive oil, castor oil etc.

Catalyst or oxygen carrier
These prevent fibre damage, during steaming; accelerate the final color development by oxidation. E.g. Potassium ferrocyanide, copper, sulphide etc.

Oxidizing and reducing agents
Oxidizing agents develop final color in steaming or in the subsequent after treatment, assist in color fixation etc. e.g. sodium chlorate, potassium chlorate, sodium nitrite etc.
Reducing agents destroy color of the fabric. E.g. sodium hydro-sulfite, stanus chloride etc.

Difference between Dyeing and Printing

Dyeing is the process by which a textile material is changed physically and chemically and finally looks like colored materials.
Printing means partial or localized dyeing. It can be described as the controlled placing of defined areas of color onto a substrate.

Difference between Dyeing and Printing method

Dyeing
Printing
It means full dyeing of fabric.
It means partial dyeing of the fabric.
Fabrics, yarns and fibres are generally dyed.
Only fabric is printed.
Dyed both side of the fabric.
One side is printed.
Here, any specific design is not necessary.
Here, specific design is necessary.
Generally one color is used.
One or more color is used.
Color is applied in solution form.
Color is applied in thick paste form.
Thickener is not used.
Thickener is used.
Large amount of water is used.
Less amount of water is used.
Steaming or curing is not necessary.
Steaming or curing is necessary for fixation.
Not expensive.
Expensive.
Dyed fabric is relatively soft.
Printed fabric is relatively harsh.
Liquor ratio is high.
Liquor ratio is less.
Dye solution concentration is less in dye bath.
Printing paste concentration is higher in printing.

Friday, February 27, 2015

Textile Printing Techniques

Color always provides interest and impact. Printed textiles can attract consumers and convey new fashion trends easily and comparatively quickly. They help to balance collections or ranges and add variety. Some of the most common printing techniques are discussed here:

Printed fabric

Block printing

This uses wooden blocks which are engraved with the design or the design is hammered into metal strips.

Burn-out printing

This is a technique whereby a chemical is printed on to a fabric constructed from two fibres. The chemical destroys one fibre creating sheer areas.

Discharge printing

A light pattern on a dark background is created by printing a paste on to the fabric. The paste removes the background color.

Engraved roller printing

This uses images that are engraved on to a metal roller. The roller is inked and is transferred to the cloth under pressure.

Screen printing

Screen printing is based on the stenciling process. A fine mesh screen is created and the areas not to be printed are chemically blocked out by a photographic process. A different screen is needed for each color required. A squeegee is used to push the printing ink through on to the cloth. This may be done by hand or by a machine, depending on whether the fabric is a sample length, a ‘one-off’ or for mass production. The textile may be printed before the garment is constructed or after depending on whether the print is a place print, a motif or a graphic print on cut pattern pieces.

Heat transfer printing

This works by passing a paper with the printed design through heated rollers, with the cloth, consequently transferring the print. Dye transfers from paper to cloth can be done by hand using colored paper and a small heat press.

Printing inks

Glitter may be added to flat color or hand-rendered paint effects. Flocking provides a velvety texture which depends upon the fibre used to flock. Expanding inks also provide texture and begin to expand after being applied to the cloth.

Photocopy transfer paper

This is a sampling or ‘one-off’ technique where a design may be photocopied on to a coated paper – the scale is limited to the scale of copies produced from the copier; a large print could be created by patching pieces together. The printed paper is then transferred to the cloth by heat, usually a heat press, sometimes an iron, depending upon the size of the print. The backing paper is then removed. This technique is useful for reproducing photographic quality imagery. If a design includes any text it is essential that this is reversed (as a mirror image) on the photocopier so that it will print the correct way round on the cloth.

Thursday, February 26, 2015

Different types of Prints

Prints are the impression of any creative design made over the fabric or garments using paints or dyes during manufacturing process or at any finished stage. Printing signifies the application of color to the finished fabric to produce the desired patterns which may be floral (natural) to hide some manufacturing defects.

Floral printed fabric
Floral Printed fabric
The different types of prints are as follows:

Classical

This is also known as ethnic or traditional print. In this print, classical motifs or traditional art work or traditional collections are used such as mango, elephant with the chariots, old musical instruments etc. The culture of any particular place can also be considered such as tie and dye, batik, block of Rajasthan etc.

Floral

It has the print of varieties of flowers either in bunch or single spotted huge or small, combination of leaves and other addings. Here color combination is very important.

Stripes

One would have been different types on the garment but would not have noticed its classifications. We have many types of stripes for instance pin, zigzag, spiral, zebra, diagonal, horizontal, vertical, curved, lamp post stripes etc.

Check

Checks are the prints which are got by interesting horizontal and vertical lines at ninety degree angles. There are basically four types of checks such as plaids, Madras, Bombay and Oxford check.

Dots

The dots are the spots either designed or plain and come in all colors of choice. The dots are basically divided into three types as big dots, small dots and polka dots.

Geometric

This is the print where all the geometrical instrument designs are created and the mathematical signs are used such as plus, minus, multiplication, division etc. There is no prescribed color combination.

Directional

Any print which is designed directionally horizontal, vertical or diagonal is called the directional print. Its feature is to follow the direction of the first one. This type of print is used in Egyptian dresses.

Self

Any design which has to be printed should be of the same shades of the background color. As for example rubber prints.

Computerized

The design of this print is taken from computer graphic designs and videogames. Can be used for children and teenagers.

Wild

The effect of the forest with or without animal, nature are used in this types of print. Mostly dull colors are used.
Example: Camouflage fabric which is used in the uniform of the military men at war.

Animal

In a wild print, the nature such as forest with the pictures of animals are used but in animal print, no wild effect is shown but the importance is given only to the skin texture of the animals and their foot prints such as Zebra, Tiger, Deer, Snake etc.

Abstract

This print is made using the irregular shapes with matching color scheme.

Numerical

Here the numbers from 0-9 are used. Sometimes with or without mathematical signs.

Alphabetical

This print is made using alphabets, wording etc. but cartoons are mostly not used as combination with this. Example: Newspaper print.

Children’s

It consists of designs which can emphasize the children’s mood such as cartoon characters, chocolates, fruits, ice creams, toys etc.

Photo-print

The photos of the famous stars, pop singers, old cars etc. are printed on T-shirts which are called photo-print.

Marble

This look like a marble finish. This can be made by hand in manual process also. For this we require a wide opened pan of water, oil paints/enamels and paper.

Wednesday, February 4, 2015

Printing on Denim fabric

     Printing on denim is another issue we should be careful about, otherwise, you may have a latent problem that you are unaware of until it is too late.

Printed denim fabric
     Denim is made from “Bean dye” with the warp threads heavily covered by starch mixed with indigo or sulphur dye. If you want to print on it the only method you can use, is to use pigment print to cover the dark color of denim. However, when you do that the pigment dye applied is on the surface of the fabric; to make it clearer, it is on the starch mixed with indigo or sulphur dye but not on the cotton fibre. When the printing is done, the printed design may look acceptable without giving you a clue that there is a hidden problem. However, when garments are made from this fabric and washed, you will notice that the printing has disappeared leaving only faint marks where the printing used to be. This is used because during washing the starch is washed away and the printing which was attached only to the starch went with it.
     When you order printed denim you must tell the printing how much you want the printing to stay on the fabric after wash. The following are examples:
  • 100% of the printing to stay
  • 70% of the printing to stay
  • 40% of the printing to stay
  • 5% of the printing to stay
     If you want 100% of the printing color to stay on the fabric after wash, you must do the following:
  • Before printing you must desize the fabric very thoroughly. Desize means to away the starch on the fabric.
  • The pigment dye must contain sufficient “binder” to make the dye stay.
  • After printing you must get the fabric through the “baking process” for sufficient time and temperature.
     If you do the above 3 steps thoroughly, the printing will be color fast and remain bright and fresh after washing. However, I’m not sure this is what you need because; usually garment buyers or consumers would not like the printing on denim to be color fast to stay bright and fresh like new. They probably would like 30% or 40% of the printing to go away after washing with 60% or 70% of the color to stay. In such case, the 3 steps as described above must be done to a different extent:
  • You still desize the denim thoroughly before printing.
  • You still use “binder” in your pigment dyed, but use less amount.
  • You still get the printed denim through the baking process but at lower temperature and for shorter time.
     For the above adjusted process, a certain amount of the dye will be washed away when the garment goes through the washing process, to achieve the slightly faded look desired.

Tuesday, February 3, 2015

Batik-printing method

     Unusual color effect can be produced employing various batik styles.  Ties are often dyed by batik techniques. Parts of each cloth are knotted or tied with a string and then dyed, usually by dipping. In the knotted or tied places the dye solution cannot penetrate; this produces unique effects.
     Another batik method is the use of wax resist. This can be applied in the form of melted wax or an oil soluble resin solution. The treated areas resist subsequent printing or dyeing. After dyeing, the resist is removed.
     A more popular form of batik is the application of hot wax with a thin brush on the outlines of a design. Within the outlines, a dyestuff solution is applied. It spreads evenly over the surface; after drying the silk is steamed and finished in the usual manner. Before steaming the painted cloth is wrapped in absorbent paper. During the steaming, the softened wax is absorbed by this paper.

Batik Printing
Batik Printed Fabric
     An improvement over this purely manual method is the use of a screen to print the outlines. Glue and British gum are used as mechanical resists, preventing the spread of dye solutions. These resists lines can also be colored.
     A multi step hand printing technique that includes the application of a substance to protect of limit desired areas of the base fabric from coloring by resisting dyestuff. When fabric is submerged in the dye bath, the chemical or wax-protected areas resist the dyestuff; dyestuff adheres to or penetrates untreated areas. The waxing dyeing and wax removal processes are repeated until design or desired effect is completed. White areas may be left white, dyed or over printed.

Monday, February 2, 2015

Block-printing method

     Similarly to the art of screen printing, block printing originated in the Far East. India and China are the probable birthplace of block printing as, according to historians, their people used hand carved wood blocks for the production of ornaments on textiles. The principle of this method remains the same; the blocks are made by more modern methods.
     The blocks are generally about 3 inches thick and are preferably made of sturdy plywood. When design is to be carved by hand, a hardwood surface is used. When a 40 inch cloth is to be printed, the weight of the block would be too great to provide only a lengthwise repeats; the block therefore, is made smaller and carries side repeats of the pattern as well. In the preparation of blocks, therefore, not only the continuity of the pattern is taken into consideration, but also the width of the cloth, which determines the size of the blocks.
     Formerly, after tracing the pattern on the surface of the block, it was carved out by hand. Now, this technique is partly replaced by use of a metal plate, on which the design appears in relief. For teaching the art of block printing some textile and art schools use a wooden block, to which a heavy piece of linoleum is attached. The students then carve the desired design into the linoleum layer.
     The table on which block printing is done is similar to a screen printing table, but its surface is preferably harder.
     The supply of print paste is carried on a specially constructed table on wheels. The print paste, which is kept considerably thinner (or softer) than for screen printing is in a container covered with thick felt. This felt is saturated with the paste and from the felt the color is transferred to the block surface by laying the block on the felt. The block, when picked up, must show an even coverage of color paste on the surface, this is then transferred to the cloth to be printed.

Screen printing

     The preparation of print paste and all methods of finishing are the same as for machine printing.
     Block printing, representing purely manual productions is used very little, if at all, for commercial purpose. It has been practically completely replaced by the much more efficient screen printing.
     Design is engraved on wooden, linoleum or copper blocks; dye is applied to the raised areas of the designed blocks, block is pressed on the fabric, desired color and design is transferred to base fabric. Procedure is repeated design as many times as design is desired. Multicolored patterns require separate blocks for each color.

Flat-screen Printing method

     Penetration of the pile is important in carpet printing and there are two principles upon which flat bed machines have been constructed. The BDA machine, which is no longer widely used, employed an ingenious arrangement in which the reservoir of dye was trapped between the blades of a double squeegee passing over the screen, penetration of the pile being assisted by the application of a vacuum from beneath (Fig: a). In the Zimmer machine the print paste is trapped between the electromagnetic roller squeegee (Fig: b). Penetration in this case is encouraged by the pressure created by the second roller running over the wedge of paste, which is traps as it moves forward over the screen. Shorter pile lengths are preferred for this machine. There are also other versions of the rotary-screen printing machines with heavier gauge screen and rollers.

Flat-screen printing

     A more novel method for applying color to carpet substrates is through the use of a bank of miniature jets of dye. This principle was first used in the Millitron machine of Milliken & Co., although other similar machines are now available. The jets are controlled by computer operated electromagnetic valves, and the mechanism has eliminated the need for screens. Since there is no distortion of the pile, optimum surface appearance is maintained and the pattern can be changed simply by the use of different computer software.

Resist and Carpet Printing

Resist printing

     Resist printing offers a way of producing an effect similar to that of discharge printing. It also uses dyes that can withstand discharge process, so that high fastness standards are possible.
     The principle of resist printing depends on preventing dye from reaching, or becoming fixed on, defined areas of fabric. Both mechanical and chemical techniques are adopted to provide the resist. Inert compounds such as waxes, resins, fats, china clay, zinc and titanium oxides, and salt of lead and barium all act as mechanical resist for dye.
     Chemical resists, on the other hand, act to prevent the fixation mechanism from operating. Consequently their use requires an awareness of the chemical reactions involved in dyeing the ground shade. A nonvolatile acid, for example, will prevent the alkaline fixation of reactive dyes on cellulosic fibres, an oxidizing agent will prevent the reduction of vat dyes, and so on.
     “Burnt-out” printing techniques have also been developed in which part of the fibres themselves is chemically removed to produce a clear-cut, shaped space in the fabric. Effective results are obtained in this way with polyester/cotton blends, with areas in which the cotton fibres have been “burned away” leaving the colored polyester threads behind. The effects produced depend on the original colors of the two types of fibre and they are achieved without undue loss of fabric strength.
     There are many other possible printing styles are available, notably those producing African prints, some of which have evolved from tie dyeing or the mechanical wax-resist ‘batik’ style.

Carpet printing

     The introduction of carpet printing was stimulated by the desire to expand the possibilities for producing patterned tufted carpets. Various machines have been designed, similar in principle to those used for printing fabric.

Carpet printing
    
     The above figure shows one type of roller, in which a sponge rubber or nylon flock fibre design caps the cut-out pattern in the rubber surface of the roller. The face of the carpet is pressed successively on to the upper surface of each of four rollers arranged one above the other in a line at 450 to the horizontal. The principle has proved popular but its application is restricted by the relatively poor resolution of detail that it can achieve.

Sunday, February 1, 2015

What is Discharge Printing?

     In addition to the straightforward application of dye, textile printing offers the designer certain styles that can be used to obtain aesthetic effects. Discharge-printing, for example, can provide intricate printed patterns on a colored background (the ground color). The new pattern may be white or it may be a different color from the original fabric, in which case it is referred to as an ‘illuminated’ style. Effective discharge methods have been developed for both natural and synthetic fibres.
     Discharge printing is carried out where small areas of pattern are required on a large area of ground color, too large to be produced efficiently by printing methods. It enables finely detailed patterns of good definition to be introduced on to the fabric, which adds significant value to the end product. The technique depends on the fact that some dyes may be chemically removed from the dyed fabric using a discharge agent, to leave a corresponding white area. The necessary discharge agent is mixed with a color-free printing paste and the pattern printed on to the previously dyed fabric as usual. Drying or streaming and then washing follow. For illuminated styles a discharge resistant dye is incorporated into the paste so that discharge and coloration with the illuminating color occur simultaneously.
     The efficiency of the discharge reactions is critically dependent upon the selection of suitable dyes. Easily discharged dyes are required for the ground shade, while discharge-resistant dyes are needed for the illuminating discharge. The method can be used on fabric dyed with indigo vat dye either by destroying the color with an oxidizing agent, or more commonly by converting it to a leuco compound using a reducing agent, which then combines with the leuco compound and prevents its re-oxidation.
     Selection of the thickening agent for the print paste is also more critical than for direct printing because it must remain chemically resistant to the reducing action and retain its viscosity throughout. If the latter proves unsatisfactorily, migration of the print paste beyond the required area carries the reducing agent with it, blurring the definition and fine detail of the pattern. This effect is called ‘flushing’. In illuminated discharges it appears as a white surround to the printed pattern, in which case it is referred to as ‘haloing’. It can be controlled, however, with proper attention to preparation of the print paste.

Saturday, January 31, 2015

Transfer printing method

     The ability of disperse dyes to sublime on heating has led to a very different approach to textile printing. In this the design is first printed on paper using disperse dyes. The paper can then be inspected for faults; if any exist, that area of paper can be discarded to avoid wastage of fabric. The fabric is placed face down on the printed surface of the transfer paper, and the two are squeezed together in a heated press at a temperature high enough to vaporize the dye, which transfers in the vapor phase to the fabric. Transfer printing has the advantage that no printing paste is applied to the fabric and so no washing-off is necessary.
     The production of transfer printing paper for textile purposes began to grow rapidly in the early 1970s but so far its use is restricted to the application of disperse dyes, and hence to the printing of synthetic fibres. The paper can be prepared by gravure printing, in a manner similar to the engraved roller printing of textiles. An alternative is flexographic printing, in which the image is formed in relief on a composite rubber molding using sophisticated methods for cutting the pattern; this method has the advantage that wide paper may be printed satisfactorily. Another method is lithographic printing, which involves the preparation of a discontinuous design on a plate by photographic techniques.

Transfer Printing

     The fabric and paper are brought into close contact using a continuous calender type of processor (above figure). The fabric and paper are placed face to face and held close to a heated cylinder under light pressure from an endless blanket, often made of the heat-resistant material Nomex. Fast rates of production are possible with this system.

Rotary-screen printing method

     Fully-automatic flat screen printing is not continuous yet. Rotary-screen printing on the other hand is continuous. Rotating screens are used which are automatically fed (by means of pumps) with paste from inside. Driving the screens can be done at either side.
     The value of continuous rotary-screen printing first became apparent in the 1960s. The hollow screens, each applying the appropriate motif, are arranged sequentially as in roller printing, but they are aligned over a moving horizontal blanket that carries the fabric between the two. As the fabric moves forward the screens rotate and apply the color. One arrangement for the delivery of print paste is shown in cross-section in the following figure:

Rotary screen printing

     The squeegee blade is flexible to accommodate any variations in pressure required to force the paste evenly through the mesh of the screen across the width of the fabric. In some models the squeegee is replaced by a metal rod held in position by a magnetic field. This is more suited to heavier fabrics, since the mechanism imposes a higher limit on the minimum amount of paste that can be delivered. In general the rotary-screen printing machine requires a lower pressure between roller and fabric than is used with engraved rollers.
     As with all screen printing, some control of delivery can be obtained through variation in the mesh size, a large mesh being appropriate for fabrics made from coarser fibres or areas of solid color, whilst a finer mesh is better for producing fine detail or for fabrics made from fine fibres.
     The advantages of rotary-screen printing machines over engraved-roller machines include faster production rates, greater ease of setting up and a lower dependence on experience for successful operation. Computer aided design techniques for printing screens are now increasingly widely used.

Thursday, January 29, 2015

Advantages and Limitations of Screen printing

The screen printing process consists of forcing of a viscous print paste through open areas of the screen with a squeeze. There are mainly three types of screen printing methods:
  • Hand screen printing.
  • Semi-automatic screen printing.
  • Fully automatic screen printing → a. Flat, and b. Rotary
At present in great demand being the most logical development of the stenciling process.
Advantages
Compared with other processes screen printing has the following advantages:
  • It requires relatively cheap equipment.
  • Very few preliminaries.
  • It is very economical for short runs of suitable subjects and so widely used for show cards, posters etc.
  • It permits printing on almost any surface.
  • Inks used can be oil colors, water paints or lacquers etc. This permits the process to be used for producing any effect most delicate of pastel shades or glossy weather proof colors, so heavy that they stand out in visible relief.
  • Areas of far greater size can be stenciled. Frames 1.27m X 1.52m (50” X 60”) are frequently used for textile printing.
  • Surface to be printed need not be flat.
Limitations
Limitations of the processes are:
  • It is not suitable for fine detailed reproductions.
  • Delicate gradations (half-tones) are rather difficult.
  • It is unsuitable for very long runs.
  • Stencils have a limited durability.
  • It is a relatively slow printing process.