The Screen Printing Process
Each printing technique has its own cost factors. To understand the cost of Screen Printing the following explanation should provide insight into the factors involved:
1. Step one is to convert the finished artwork into a positive (a transparent film with dark areas in the form of the artwork on it) or more than one positive depending on the number of colours involved. A positive is required for each colour and when printing full colour, the artwork is separated into the four CMYK (Cyan, Magenta, Yellow and Black) process colours . Producing positives can be done essentially in three different ways depending on the type of positive that is required. Hand-cut film, Plotter-cut film and photgraphic film, produced with an imagesetter or digital printer. Positives for full colour work and for artwork with fine detail can only be done with the last process.
2. The second step is to prepare a screen with stencil for each colour to be printed. The stencil may be applied to the screen either by using photo sensitive emulsion or by using a special film that can be applied directly to the screen.
Referring to a screen in this instance I mean the actual mesh that has been tightly stretched over a frame and ready to be used for printing. When using emulsion as a method to get the stencil onto the screen, quite a bit of time is required to prepare the screen. After the emulsion has dried (in a dark room for approximately one to two hours) the positive is placed on top of the screen and illuminated for a set time (approximately 4 minutes). The light causes the exposed areas of the screen to become hard and the areas under the positive remains soft. The soft emulsion is then washed out with water, leaving the artwork on the screen with no emulsion in the areas of the artwork. The screen is then left to dry for at least 30 minutes depending on the climate.
3. The third step is to set up for printing by registering the screen and stencil to the material or substrate that has to be printed. Only one colour can be printed at a time and the registration process is repeated for each subsequent colour that forms part of the artwork.
4. The fourth step is to print the actual material and to place it in a position where it can be undisturbed until it is dry, or pass it through a drying tunnel with heated elements to spead up the drying.
5. Drying printed items are done differently for flat substrates printed with solvent inks than for textile fabric that is printed with water based inks.
Items that are printed with solvent inks are normally placed onto a drying rack so that the ink can air dry before printing subsequent colours or until the image is complete. Drying times vary depending on the type of ink and the size of the printed area as well as on the circulation of air in the room. Electric fans are often used to increase the air circulation and extract the chemical gasses. Normally a minimum of thirty minutes is allowed for the printing to dry in this method.
Printing t-shirts is slightly different in that the shirt cannot be moved before having printed all colours and in this instance a method is used to keep the shirts fixed in the same position while the different colour screens are moved over the shirt and printed until the image is complete. After the image has been printed onto the shirt, it is dried either by using a heat press or a drying tunnel.
6. After all the items were printed with a specific colour the screen has to be cleaned of excessive ink and removed from the printing table. The process of registration, setup, printing and cleaning is repeated for each colour in the artwork. (T-shirt printing is slightly different) The preparation part of the job before printing can start is the most time consuming and takes at least four to five hours.
7. Once the job is complete, the emulsion is cleaned off the screen by using a variety of chemicals and a high pressure water hose, leaving the screen available for the next job. Screens (a fine woven mesh normally made from synthetic threads) have a limited life and once it gets damaged after a number of uses, it needs to be removed from the frame and replaced with a fresh new screen
Screen printing is largely a manual process and labour forms a considerable part of the overall cost. Screen printing is not an instant process and the more colours that are involved, the more time consuming it becomes.
The preparation and setup part of each job is more or less the same for each colour and the cost involved in getting to the point of printing every colour is a relatively large overhead. The total cost of the job is amortized over the print quantity and this results in a relatively inexpensive unit price for large quantities, but an exponentially increasing unit price as the quantity is reduced.
See our Screen Printing Prices for printing Correx posters and t-shirts