Quality Control of Screen Printing for CD-ROM Copying Four Elements (2)

Variables that need to be controlled on the press are the distance between the overlay, the screen plate and the substrate, and the squeegee.

The inked plate affects the amount of ink that is printed. If your printer does not have a fixed ink reflow angle (mostly available), a standard angle should be used for all jobs. In addition, the overlay should also be adjusted so that it is close to the screen plate. You will need to do another test until it is set to the height that suits your application. The ink-coating stroke should be very smooth. A thin layer of ink is applied to the entire screen printing plate so that the amount of ink adhered to the entire printing is uniform. The decorator of a CD disc usually adjusts the distance between the screen printing plate and the surface of the printing material to the thickness of one or two discs (about 1 to 4 mm). You should experiment to find the best distance for your application within this range. If you determine the optimal distance, you should stay the same.

Some people try to offset the lower tension of the screen by increasing the distance between the screen and the printing material. This should not be advocated because if the screen distance is too large, the screen printing plate is larger in the squeegee. The pressure will be further stretched when contacted with the printing material. The results will lead to inaccurate overprinting of prints and shortened service life of screen printing plates. To meet the requirements of both full-surface printing and high-resolution printing, the squeegee is a variable factor on the printing press. The amount of ink adhered can be influenced by changing some of the variables of the squeegee, such as hardness, angle, pressure, and edge shape.

In these variables, the squeegee pressure and angle should be kept constant, so as to ensure effective conversion between different types of jobs. In order to make these variables easier to standardize, most printers on the market offer a fixed gauge and a manometer that measures the squeegee pressure.

The shape of the edge of the squeegee (sharp, rounded, etc.) and hardness are the main variables used to compensate for different printing requirements. In general, the use of a squeegee with a straight edge ensures uniform and consistent ink color. A blunt or uneven squeegee can cause color shifts during the printing process, and scratches can sometimes appear on prints. The use of different squeegee blades and hardness can effectively control the amount of ink deposited. For example, a 80 Shore hardness squeegee may be suitable for printing solid images, but the amount of ink missing is too high to print high resolution half tone images. If other variables remain the same, switching to a 90 Shore hardness squeegee may be a quick solution.

Another option is to vary the shape of the squeegee blade depending on the type of job being printed. When printing solid images, edged round squeegees can be used because the edge of the squeegee ink layer is thicker and the edged squeegee is more suitable for gradation printing. The best option is to use a combination, that is, use a softer, round edge squeegee to print in the field, and use a harder edge sharp squeegee to print fine prints.

3, ink

Most CD disks use UV inks to hold the sulphate. In order to obtain ideal prints that have both on-site and high-resolution images, the correction of the ink is usually unnecessary if you control the variables of the platemaking and printing presses. In most cases, the adjustment of the press determines the use of the ink. However, in order to increase flexibility, inks can also be corrected for special situations.

Tricolor inks are mainly used for printing halftone images. They have a higher viscosity than inks in the field and help dry and print clear, high-resolution images. Field inks have low viscosity, good fluidity and good coverage, making them suitable for printing large areas of the field. When a job requires both printed dots and printed on the ground, the use of three primary colors of ink, the opacity is no problem, the ink can be diluted to improve its fluidity. If you need to use an opaque, solid ink to print a halftone image, add some thickener to the ink so that the ink can support fine dots.

4, combined printing

In combination printing, there is no need to change some variables, and both solid images and halftone images can be successfully printed on the same plate. There are two methods.

For example, suppose you use a 390-mesh, 34-gauge wire screen to print solid images. The standard stencil is prepared by applying two direct emulsions on both sides of the screen.

To produce screen printing plates suitable for printing these two images, we must first select screens suitable for printing in the field (wire diameter 31u). Then, in terms of printing presses, we can use standard settings for high-resolution prints defined by å·³ ( With 90 Shore hardness, sharp edged squeegee). Due to the large mesh openings, the solid area will be successfully printed. At the same time, the parameters of the squeegee will limit and control the adhesion of the ink, resulting in a clear gradation dot.

Conversely, you can also standardize the screens you use (all live jobs use 390 mesh, 34u wire mesh) to change the method of plate-making glue of this combination print to produce a thicker template. In this case, the thicker stencil prints a thicker layer of ink that is suitable for printing in the field, while the smaller stencil aperture contributes to the finer levels of the printed tonal area.

In order to print successfully, the variables that need to be adjusted should be reduced as much as possible, which can simplify job conversion, reduce downtime, increase the efficiency of the production line and the consistency of printing, and produce high quality prints.

Source: Disc Manufacturing Expert