PRINTING METHDOS AND PROCESS MODIFICATIONS

PRINTING PROCESS MODIFICATIONS 

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Heat Transfer Roller Printing 

Like traditional roller printing, heat transfer printing is done by passing the fabric around a central drum or cylinder where it contacts a roller for transferring the design. The roller is followed by a heating zone to effect the sublimation of the dye. Since all colors are applied to the fabric at the same time, 

however, the operation is simpler with lower processing costs and fewer personnel required. Production can change rapidly from one design to another simply by changing the design paper, whereas in roller or screen printing, each separate roller or screen moved from the machine and the machine set up for a new design with different rollers or screens. Short runs are feasible, fast deliveries are possible, given shorter time for processing, and companies need not keep costly inventories of fabric in stock. On the other hand, heat transfer printing is slower than is either roller or screen printing. 10 to 15 meters of printed fabric are produced per minute in transfer printing operations. 

Heat transfer printing has proved especially successful in printing knitted fabrics. Knitted goods are less dimensionally stable than are woven fabrics. Manufacturers using conventional screen and roller printing techniques on knit fabrics experienced difficulties in making multicolor prints in which the segments of the print must fit together accurately. In transfer printing, all parts of the design are applied at once, eliminating the problem of fabrics stretching as they move from one roller to another. 

Losses of fabric through faulty printing are substantially lower during heat transfer printing than are losses in conventional roller printing. Energy requirements are also lower. Garments and garment pieces can be printed, and precise placement of decorative motifs on a completed garment is possible 

Transfer Printing 

Literally moving a design from one surface to another is known as transfer printing. A typical well-known technique is that of iron-on prints of emblems and decorations, which are generally made of pigments in a paraffin or thermoplastic base that can be melted and bound by heat and pressure onto a fabric surface. These pigment transfers are not very satisfactory because they make the cloth stiff and are not fast to laundering or light. A more sophisticated and effective method of transfer printing is that of transferring a design intact by vaporizing it from the paper to a fabric. There have evolved two principal processes: dry heat transfer and wet heat transfer 

Heat Transfer Printing 

Heat transfer printing, or sublimation printing, is a system in which dyes are printed onto a paper base and then transferred from the paper to a fabric. The transfer of colors takes place as the color vaporizes or “sublimes.” Transfer printing is achieved by rolling or pressing the paper and the fabric together under pressure and at high temperatures (424°F or 200°e). Sublimation printing achieves a sharpness and clarity that other types of printing cannot match. One disadvantage of heat transfer printing, however, is off-grain printing. Some dyes used on nylons and acrylics have displayed variations in shade depth and, in some cases, problems with fastness to laundering. Heat transfer printing also consumes a large quantity or print paper that cannot be reused and may present a disposal problem. Transfer printing can also be used to apply designs to garments such as T-shirts and jackets. Often the design is comprised of pigment colors on a paper sheet. When this is placed on the textile item and a hot press is applied the pigments adhere to the fabric in the design pattern. The design area is usually somewhat stiffer than the rest of the fabric. 

Initially, heat transfer dyes were disperse dyes mostly effective on nylons and polyesters. Disperse dyes can also be used on acrylics, triacetates, and polyester and cotton blends where the proportion of polyester is relatively high. In the early 1990s development of several alternative processes have extended heat transfer printing to silk, cotton and other cellulosic fabrics, and wool.

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Textile Printing methods; Methods Of Direct Printing

Block Printing Methods
The oldest method of printing designs on fabric is block printing by hand. It is not commercially important today because it is too slow––printed fabric cannot be produced inexpensively in large enough quantities by the hand block method. To make blocked prints, the design must first be carved on a wooden or metal block. The dyestuff is applied in paste form to the design on the face of the block. The block is pressed down firmly by hand on selected portions of the surface of the fabric, imprinting the carved design as many times as desired on a specific length of cloth. To obtain variation of color in the same design, as many additional blocks must be carved as there will be additional colors. The portions of the design that will appear in different colors must be separately imprinted by hand before each design is complete. The more colors used, the more valuable and expensive the blocked print will be, because of the enhanced beauty of design as well as the labor involved in the hand printing.

Roller Printing Methods
Roller printing is the machine method of printing designs on cloth by engraved rollers. It turns out color-designed fabrics in vast quantities at the rate of 1000 to 4000 yards (914-3658 m) an hour. This method of producing attractive designs is relatively inexpensive when compared with any hand method. It is a machine counterpart of block printing. In roller printing, engraved copper cylinders or rollers take the place of the hand carved blocks. Just as there must be a separate block for each color in block printing, so must there be as many engraved rollers in machine printing, as there are colors in the design to be imprinted. With each revolution of the roller, a repeat of the design is printed. Engraving is frequently done by pantograph transfer. Separate photographs on individually sensitized copper plates are taken for each color of the design. An artist then paints the appropriate color of the pattern on each plate. The engraver traces the outline of the design on the plate with one arm of a pantograph, plate which simultaneously cuts the design (with a diamond needle on its other arm) into the curved surface of a copper roller. Next, a chemical resistant is coated over the areas of the roller that will print the color, and the roller is treated with acid. The acid etches the unprotected areas, which form the design pattern to be used for color printing.

Each roller is polished for uniform smoothness so that the dye will spread evenly on the raised areas. They are then locked into precise positions on the machine for proper registration (alignment). The number of rollers used depends upon the number of color in the design, and as many as sixteen rollers can be employed.

Each of the engraved rollers first comes in contact with a companion roller that has been submerged in the dye paste to be used for its part of the design. A sharp blade, called the doctor blade, scrapes the excess dye from the surface of the roller. As the fabric passes between the engraved rollers and smooth cylinder rollers, the dye from the shallow areas is passed on it.

Behind and along with the fabric being printed is another fabric, called the back gray, which absorbs the excess print paste and multi color roller printing prevents it from striking through and staining the smooth rollers


The printed cloth is immediately passed into a drying chamber and then into a steam chamber where the moisture and heat sets the dye. The back gray is eventually washed out and reused.

Duplex Roller Printing
Duplex printing is done with rollers on a special machine that imprints designs on both sides of the fabric at the same time. Most often, the same design is printed on opposite sides, although different designs can be printed on each side. The resulting fabric looks like fabric with a woven design. This process is seldom used now, as it is almost as expensive to create duplex prints as it is to weave designs.

Rotary Printing Method
A printing machine that utilizes seamless cylindrical screens made of metal foil was originally developed in Holland. This process is called rotary screen-printing. The machine employs a rotary screen for each color, as in flat screen-printing, and the design for each rotary screen is made in a manner similar to automatic flat screen-printing. As the fabric to be printed is fed under uniform tension into the printer section of the machine, its back is usually coated with an adhesive, which causes it to adhere to a conveyor-printing blanket. Some machines use other means of gripping the cloth firmly in place. The fabric passes under the rotating screens through which the printing paste is automatically pumped from pressure tanks. A squeegee in each rotary screen forces the paste through the screen onto the fabric as it moves along, at rates of up to 100 yards (91 m) per minute.

Rotary screen-printing combines the advantages of roller and flat screen-printing techniques. Rotary metal screens are lightweight in contrast to the heavy copper rolls, and they cost less. They give color depth that is similar to or as good as that of flat screens. Prints of various types and intricate designs with shades of up to twenty colors can be obtained with a high degree of accuracy and sharpness.

Stencil Printing
Stencil printing originated in Japan. Its high cost limits its use and importance in the United States. In stencil printing, the design must first be cut in cardboard, wood, or metal. The stencil may have a fine, delicate design, or there may be large spaces through which a great amount of color can be applied. A stencil design is usually limited to the application of only one color and is generally used for narrow widths of fabric.

Screen Printing Method
Originally, this technique was referred to as silk-screen printing because the screens were made of fine, strong silk threads. Today, they are also made of nylon, polyester and metal. Screenprinting is done with the use of either flat or cylindrical screens.

Flat bed screen printing
Flat bed screen-printing is done commercially on long tables 9 to 60 yards in length. The roll of fabric to be printed is spread smoothly onto the table, whose surface has first bee coated with a light tack adhesive. The print operators then move the screen frames by hand successively along the whole table. Printing one frame at a time, until the entire fabric is printed. Each frame contains one color of the print. The rate of production ranges from 50 to 90 yards per hour by this method. A substantial amount of commercial hand screen-printing is also done on cut garment parts. In printing cut garments, an apparel manufacturer arranges by contract with screen printers Greige Carpet Needle Belt Magnet Color 2 specializing in this service. Customized or unique patterns are printed on garment parts before the pieces are sewn together.

Such items as printed beach towels and novelty printed aprons, draperies, and shower curtains are also printed by hand screen methods because it is possible to make large screen frames for large design repeats.

Hand screen-printing is also used for printing limited-quantity, high-fashion couture as well as for printing small-quantity runs to market-test a design. Flat-bed Zimmer carpet printing machine lays down each color separately form printing paste applied by means of two magnetic roller squeegees. Pressure is controlled by the selection of heavy or light squeegees and by varying the current going to the electromagnet. Endless belts fitted with needles assure a positive drive for good register.

Printing Methods; Methods of textile printing

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Methods of Printing 

There are three basic approaches to printing a color on a fabric. Direct, Discharge and Resist. Transfer Printing is comparatively a new method which is also gaining popularity Direct Printing. The most common approach for applying a color pattern is direct printing. It may be done on a white fabric or over a previously dyed fabric, in which case it is called overprinting. The dye is imprinted on the fabric in paste form, and any desired pattern may be produced. The dyes are usually dissolved in a limited amount of water to which a thickening agent has been added to give the necessary viscosity to the print paste. 

Direct Printing Method

The principle of direct printing is creation of a colored design by applying a dye or pigment directly onto a textile substrate (yarn or fabric). Discharge Printing. Another approach for applying a color pattern is discharge printing. The fabric is dyed in the piece and then printed with a chemical that will destroy the color in designed areas. Sometimes the base color is removed and another color printed in its place, but usually a white area is desirable to brighten the overall design. When properly done, discharge printing gives very good results; however, the discharged areas may literally fall out of the fabric if the goods are not thoroughly washed after printing (a rare situation today). The usual method of producing discharge prints is to print the design, such as polka dots, with a paste containing a reducing agent. A steaming follows and then there is a good washing to remove the by-products of the reaction. Resist Printing A third approach to obtaining a color pattern is resist printing. Bleached goods are printed with a resist paste––a resinous substance that cannot be penetrated when the fabric is subsequently immersed in a dye. The dye will affect only the parts that are not covered by the resist paste. After the fabric has passed through a subsequent dyeing process, the resist paste is removed, leaving a pattern on a dark ground. Their are several other methods also for printing textiles. Two are of significant commercial importance: the screen print method and the roller print method. A third method, heattransfer printing is a comparatively new concept & less significant. Other printing methods rarely used in commercial production of textiles are block, batik, ikat, and resist printing. Many textile printers print fabrics in both screen and roller methods. Most heat-transfer printing is done by printers that specialize in this method. 

Batik 

Batik cloth is made by a wax-resist process. The name batik originates in the Indonesian Archipelago, where resist printing has become an important art form. Wax is applied to the areas that the printer does not want to dye. In Indonesia a small, spouted cup with a handle called a tjanting is used to apply the wax. Melted wax is poured from the tjanting onto the cloth. When it hardens, the wax coats the fabric so that the dye cannot reach the fibers. 

If several colors are to be used, the process becomes somewhat more complex. For example, if a fabric is to be colored white, red, and blue, the artisan begins with a creamywhite cotton cloth. Those areas that are to remain white and those that are to be red are coated with wax. The fabric is now subjected to a blue dyebath, and the exposed areas take on the blue tint. The wax is boiled off and reapplied to cover the blue and white areas. When the fabric is placed in the red dyebath, the color penetrates only the uncovered areas of the design. After dyeing is complete, the fabric is treated with a fixative (a mordant) to make the colors fast, and a final rinse in hot water removes all traces of wax. For faster production a technique was devised whereby the wax could be printed onto the surface of the fabric with a device called a tjap. The design is carved on a tjap block, the block is 

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