![]() ![]() ![]() The exposure is started from under the glass table using a mercury vapor lamp or fluorescent tube lights with a uniform intensity of light all over the screen. The positive of the design is placed on a glass-topped table and the dried photosensitive screen is placed over it. Solution A and Solution B are mixed in the darkroom.ġ20 ml ammonium dichromate (33% solution)Īfter applying the solution to the screen cloth, it is dried in the darkroom at room temperature. The sensitizing solution may be prepared as follows: The photosensitive coating may be given to the bolting cloth, fixed to the screen frame, dried, and exposed to light after keeping in contact with a positive film, and after insolubilisation of the exposed portion, the unexposed photosensitive coating may be given to the bolting cloth, fixed to the screen frame, dried and exposed to light after keeping in contact with a positive film and after insolubilisation of exposed portion, the unexposed photosensitive coating is washed out leading the blocking of the interstices of the cloth at the exposed portions and keeping them open (for forcing of the print paste later while printing) at the unexposed portion. ![]() This is based on the principle that when a coating of solution ammonium dichromate – gelatine or ammonium dichromate – polyvinyl alcohol is dried and exposed to light, insolubilisation takes place. Photochemical method is the most widely used method for preparing screen. When the metal frame is used for making the screen, the bolting cloth may be fixed to the frame by using a solution of polyvinyl acetate in a suitable solvent. The frames are usually 26” x 55” (measured externally) and 23” x 52” (measured internally) for printing 45” wide cloth. Screen PreparationĪ piece of nylon bolting cloth or metal gauge (phosphobraze) is stretched and nailed to a strong wooden frame, strengthened by metal brackets at the corner. Before we go into the details of the printing machinery, let us discuss the preparation of the screens used for flatbed and rotary screen printing. Today’s most important development in printing machinery lies in rotary screen printing machines. More perfection and production can be achieved using a modern automatic flatbed screen printing machine. Machines used for printing the fabrics are explained in the forthcoming section Fabric are printed conventionally using the table screen printing machines manually. ![]()
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