SERIGRAPHY
The serigraphy is a permeographic printing technique that uses as a matrix a polyester fabric stretched on a metal frame defined as a serigraphy frame. The fabric used is also called silkscreen fabric.
The serigraphy as a printing technology includes several steps that are divided into:
- PREPRINT
The preprint refers to the whole process that starts from the graphic sketch preparation to the production of films using graphic files suitable for the production of films (vector files) provided by the customer, up to the preparation of the frames and recording them in the printer.
- FILM DEVELOPMENT:
Once the customer provides the logos, the production of the films starts. Silkscreen films are created with computers and graphic programs that are using colour separation software. At this stage, also the number of colours, that have to be printed, will be evaluated. In serigraphy, each colour matches one film. Therefore, the final print is printed sequentially in various colours by drying them after printing on the surface.
- ENGRAVING THE PICTURE IN THE SILK-SCREEN FRAME:
Once the number of colours and any desired effects are decided, the films are printed and afterwards the production of the silk-screen frames starts. Special equipment tenses the silk-screen fabrics on metal frames and sequentially glues them solidly on the frames.
The preparation of silk-screen frames is based on the photoengraving process. In practice, a water-soluble photo emulsion on an aqueous basis is applied on both sides of the silk-screened tissue on the frame. Afterwards this photo emulsion is dried away from light in warm air at 35-40 ° C for about 20 minutes.
The silk-screen film is placed in close contact with the photo emulsion on the side in order to get in contact with the surface to be printed and exposed to ultraviolet light.
The part where the film is transparent and allows the light to pass, the underlying photo emulsion hardens. The part where the film has a high-density black, the light cannot pass and therefore the underlying photo emulsion is prevented from hardening and remains water-soluble.
Once exposed to light, a water wash dissolves the non-hardened photo emulsion by clearly revealing the open areas of the serigraphic tissue. At this point, the frame is dried again in hot air at 35-40° C and is then ready to use in printing.
FRAME REGISTRATION:
The print quality of the various colours on the final print is determined by the quality of the printing machine (reduced play in mechanical movements and good fixing of the frame) and the quality of the silk screen fabrics used, as well as the accuracy of their tension. A film with crosses is placed on the object to be printed. All the frames ready for printing are afterwards placed on these crosses of reference.
PRINTING PROCESS:
Once the frames are placed on the printing machine, the printing process consists of four steps:
- Lower the frame toward the surface of the object to be printed.
- The passage of the squeegee, which passes with a moderate pressure on the frame, transfers the ink from the top to the underlying surface through the free tissue from the photoemulsion.
- Raise the frame to its starting position.
- Passage of the product printing in the oven to dry the ink.