Sunday, January 13, 2013

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.

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