Nine steps to choose the screen during printing process (a)

Selecting silkscreen is the next important decisive step. A high-quality screen, with a parameter indicator from the manufacturer, should have a similar uniform number of latitude and longitude lines, and also have comparable or identical pressure curves in both directions.

The warp and weft pressure curves with inconsistent number of latitude and longitude lines or inconsistent lines are called unbalanced screens and can cause moire and overprinting. A good screen must have enough area to support the necessary grayscale and clean ink delivery.

Your screen parameters should include data on the range of screen diameter changes, number of warp and weft screen lines and pressure curves, and fabric thickness. Most manufacturers provide a range of data in the description. If not, then you should ask him why he did not. The ideal screen is to have as thin a wire diameter as possible and a sufficiently high number of wires to meet the need of pulling force (if you want to check the screen wire number, you can use a screen wire counter). The mesh opening should be large enough to cover the entire dot pattern in a wide range of tones. The screen should also be relatively flat and dyed to reduce exposure to light.

The screen line meter allows you to screen the number of lines in the warp and weft directions. Using this tool, you can view the mesh you are using and make sure it provides the features you need. What's more, you can use it to determine the final warp and weft properties of the machine screen.

Step 1: Determine the image size

The physical size of the image determines all other on-machine printing issues such as the frame size, doctor blade length, stroke length, and ink pool size. Of course, this parameter is given by the customer.

Step 2: Set the Standard for Stroke Length

The first printing setup was the length of the squeegee stroke. It should be set to the minimum range that can just cover the entire image area. The shorter stroke length increases the number of ink fountains and allows for the printing of narrow latitude images. It also reduces discontinuous ink instabilities and prints clean dots. As the stroke length decreases, the time for the ink to remain on the screen is reduced, so the viscosity of the ink can be maintained at a higher level.

Step 3: Select the length of the doctor blade

The length of the squeegee is selected to be the shortest length of the image to be reproduced. You should leave enough length to bypass the end of the blade to ensure that no image is missing.

Step 4: Maximize the ink pool

The ink pool is the largest area of ​​the screen minus the print area. The print area is the area covered by the squeegee, which is slightly larger than the image area. The distance between the frame and the moving squeegee and the top of the squeegee is an important factor in setting the clearance. If the ink pool is too small, the dynamic tension of the screen will be too different at both ends and in the middle of the squeegee, resulting in inconsistent ink transfer at both ends of the image. As the ink pool decreases, the off-plan gap decreases and the ink transfer becomes less safe.

Step 5: Select the frame

The last parameter related to the image size is the size of the frame. The ideal frame is the largest frame that is suitable for printing. However, if the frame is larger than twice the size of the image, there is no advantage. On the contrary, a large image does not allow the ratio of the image/frame to be 1:2.

Also, don't let the print size be the only deciding factor in determining the frame size. The frame must be suitable for printing, but the frame must also provide a usable size ink pool. If the size of the frame is too large for you, the image is too large for your workshop.

The manufacture of the frame is also an aspect to be considered. The frame should be as hard as possible and have good resistance to bending and twisting.

Step 6: Determine the off-gaps

The purpose of the off-grid gap is to facilitate the separation of the screen and the substrate in the printing. Unless the off-set gap is set correctly, the size and accuracy of the image may change.

No matter what the tension is, excessive off-gauge gap will cause the image to expand. At higher tensions, it can cause negative screen lag, meaning that the screen and the substrate are separated at a faster speed than the doctor blade. This will result in blade noise and excessive blade distortion.

Insufficient off-grid gaps will cause the screen/substrate to be difficult to separate. This extreme leads to a positive screen lag, which means that the separation of the screen from the substrate is slower than the squeegee and it leaves a net mark. The correct off-gaps will show zero lag, or just a little lag, that is, if the squeegee passes a certain point, the point is immediately separated from the substrate.

Step 7: Correct the printing press

Parallelism is the first thing you need to consider when doing color overprinting. The squeegee blade edge, aisle, mesh and printing platform must be parallel to each other at all points. This ensures that the off-gaps gap is always consistent, and consistency is very important for every part of multi-color printing.

The automatic detachment function of the initial printing press should not be used. If this is the case, the off-page gap must be adjusted accordingly. The use of the automatic disengagement function compensates for deficiencies caused by improper geometry and excess ink, but it is performed under conditions that impair screen stability and image accuracy.