Screen Printing: Types, Development of Screen and the Printing Procedure
Screen printing is a way of printing images by forcing printing ink or paste with the aid of a squeegee through a specially prepared screen block to register a print on a substrate such as fabric, paper, leather, T-shirt etc. It is also referred to as Serigraphy or Mitography. This printing technique is widely used by several artists and most printing houses for the execution of their projects because it can be used in printing on virtually all surfaces such as papers, plastics, cloths, leather, glass, wood, rubber etc.
There are two main types of screens that are used for screen printing. Temporal Screens last for a shorter period of time. They are suitable for registering single or limited prints on clothes and papers. They are very easy to prepare and does not require a lot of money or effort. Examples of temporal screens are paper stencil screens and candle wax screens.
However, permanent Screens have a very long time span and if properly cared for, can last forever. They can be used in printing multiples, hundreds and even thousands of prints. Their preparation in comparison with the temporal screens demands considerable effort and money. Examples of permanent screens include photographic screens, lacquer screens and shellac screens.
There are various ways of developing screens for printing. Some of these have been detailed in the discussion below.
1. Paper Stencil Screen Preparation- This paper stencil screen is very similar to the stencil preparation though this is an extension of it. It involves the transfer of the finished design onto the paper to be used, while cutting out the positive areas (the image to be printed) of the paper. The prepared stencil is then attached to the stretched screen block with the aid of a masking tape. Enough allowances are left to serve as ink reservoirs. The screen is ready for printing.
2. Candle Wax screen/Shellac Screen /Lacquer screen preparation- The preparatory processes in these methods of screen preparation are the same. The only difference is the material used in coating the negative areas of the screen which may either be molten wax, shellac or lacquer. The finished design is transferred onto the stretched screen block. With the aid of a brush, apply the molten wax or thinned shellac or lacquer to block the negative areas of the design. Test screen for pinholes by doing a test print. Block pinholes if there are any. The prepared screen is ready for printing. Lacquered screens are very durable and more economical in terms of quality and quantity. They are very good for simple, bold designs.
3. Photographic Screen Preparation- The photographic screen preparation involves the use of light in developing or bringing out designs onto the screen. The sources of the light can be natural or artificial. Therefore, there are two main ways of making photographic screens thus the use of the solar energy (sun) during the day and the use of the strong fluorescent bulbs in the exposing or shooting box. In all these two ways, the screens have to be coated in the darkroom with a solution of photo emulsion mixed with a sensitizer. The screen is placed in the dark room to dry.
In the solar energy method, the inside or hollow part of the coated screen is filled with a sack of fine sand on a flat wooden board and turned upside down. The positive part of the paper (where the designs are) is placed on the frontal part of the screen and covered with a piece of cloth. The whole thing is exposed to the solar energy (sun) for some few minutes. The duration is dependent on the intensity of the sun. The screen is then removed and washed under running water. The design areas will be left open with the negative areas blocked.
In using the developing or shooting box in the dark room, after the screen is coated with the photo emulsion and sensitizer solution, it is left to dry. The design is then placed with face up on the glass of the shooting box. The frontal part of the dried coated screen is placed on the design with the inside or hollow part up. A sack filled with fine sand or heavy clothes hinged with stones are placed in the hollow part of the screen just to ensure firm contact between the glass plate, the paper with the design and the screen. The lights in the shooting box are switched on for about five minutes. The duration can be more or less depending on the number and watts of the fluorescent bulbs in the shooting box. The screen is removed and washed under running water. Afterwards, it is dried and ready for printing.
The following steps are followed when printing with prepared screens.
1. Prepare the printing table.
2. Place Substrate (t-shirt, hanky etc.) on the printing table.
3. Position the screen (hollow side up) on the substrate.
4. Fetch little printing paste into the non-image area (ink reservoir).
5. Draw pull paste across the image area of the screen with the squeegee tilted at a reasonable angle to register a print.
6. Go over the print if deeper print is required.
7. Gently remove, wash and dry screen for future use.
8. Allow print to dry and iron design to fix.
There are some important tips that should be noted when printing. These are:
-Correct placement of screens- The artist should pay close attention to how he/she positions the screen on the substrate or material to be printed. If screens are wrongly placed on the substrate it would result in wrong registration of designs at designated areas of the substrate. Also, if the prints are repeated on the cloth in a special pattern or arrangement, there will be gaps or disorderliness in the arrangement.
-Appropriate pressure on the squeegee- The pressure exerted on the squeegee should be moderate and well thought of. This is because if the pressure exerted is less, some areas of the screen will not be registered in print. On the other hand, if a lot of pressure is exerted on the screen, it will result in the blurring of designs on the substrate. This means that the printing ink or paste will extend beyond the boundaries or edges of the design. Therefore, the pressure exerted on the squeegee should not be too light neither should it be too much.
-Instant washing of screens- The screens used for printing should be washed immediately after printing to avoid the blockage of screens. This is due to the fact that when the printing ink residue is allowed to stay on the screen for sometime it ceases to be washed off from the screen resulting in its blockage. It is appropriate then to wash the screen right after the printing with soapy or warm water and foam to remove all ink residues. However, it should be washed gently otherwise it will result in the creation of pinholes which are small areas of the coated screen which are free from the coating solution or the tearing or reduction of tension in the taut stretched screen.
Developing printing screens manually or mechanically is the choice of the artist based on the resources at his disposal and the time s/he has to deliver. Each of the screen development processes and its printing procedure requires great patience and determination so as to produce accurate duplication of designs.