Analysis of Factors Affecting the Quality of Stretch Net in Screen Printing

In the screen printing industry, you may find countless theories and techniques, even in seemingly simple places such as opening an ink lid or straining a screen. There may be countless experienced people who show you how good a method is, but they cannot give scientific proof of why this method is the best.

In terms of stretch nets, many experts have put forward their own theories, many of which are confusing. Based on this, here is a personal point of view on the stretch net.

An important issue to pay attention to when stretching a net is to tighten it. A looser screen is only needed in one case, ie for circular or irregularly shaped substrates, in order to make the screen fully in contact with the various parts of the substrate. But in flat screen printing, high tension can not only improve production quality, but also achieve higher production speed. An article said that if the tension is too great, it will cause damage to the screen. In actual fact, the reason why the tension may be caused by the screen may be caused by the printing process is not mastered, if you can maintain a relatively low clearance clearance, reduce the pressure of the squeegee, control the printing station, you will see What kind of gratification is the quality of printing brought to high tension.

The factors affecting the screen tension mainly include the number of screens, the screen size, the stretching method, the stretching equipment, and the experience of the stretching net. The number of meshes is an obvious factor, but it does not refer to the specific number of lines per inch, but refers to the decrease in the diameter of the line as the number of lines increases. For example, can a 330 line/inch screen support a greater tension than a 380 line/inch or 420 line/inch screen? The answer is yes. But is a 380-thread/inch, 34-micron-diameter screen cable capable of supporting greater tension than a 31-micron diameter screen cable? Actually not, it is 3-4 Newtons. Therefore, the number of meshes is only an inexact parameter of the size of a wire support tension. The screen diameter is the most important core.

Screen size (or frame size) is another factor. Mesh number of 380 threads/inch The 34 micron diameter wire mesh is different from the tension supported on a 24 x 24 inch mesh frame on a 71 x 81 inch mesh frame. The smaller the frame size, the greater the tension that can be achieved. But how much tension can you get in a large format frame? According to the article, the tension of a screen with a mesh number of 380 lines/inch can be no more than 20 newtons on a 48 x 48-inch frame. We experimented with screens with a mesh count of 380 lines per inch. Using the pneumatic stretching system, we could reach 35 Newtons on a 41×51 inch frame and 25 Newtons on a 41×88 inch frame.

In the stretch method, the biggest problem is how to deal with the relaxation of the screen after stretching. After a stretch, the screen plate that reaches 20 Newtons will have tension less than 20 Newtons overnight and may drop to 17-18 Newtons. Then cleaning, degreasing and coating will reduce 1-2 newtons. The tension will drop after printing 100 copies on the machine. It may be two or three newtons or more. Recycled and used again, the tension has to be reduced by 1-2 newtons. After two printings, the original 20 Newtons fell to 12-13 Newtons.

Experienced teachers often use rubber bands as an example when talking about this issue. Cut a piece of rubber band, nail it to the wall at one end, put the object on the other end into the water, measure the length of the original rubber band, measure the length again after one day, and you will find that the length increases. After another day or two, the length has increased. Until it reaches a stable length, it does not increase with time. The same applies to screen tension changes. Therefore, it is best to use a new stretched screen version when performing color overprinting, or to use a tightly stretched screen version before it is stable.

In fact, unless you use a screen printing machine, there is no way to make it completely stable. The refastenable frame is designed for this purpose. It can tension the screen after each use until it is stable. Note that the term "retensionable" here does not mean that the frame itself will be tensioned, nor does it have a self-tensioning function.

It is a key point for the stretch net to ensure that the tension of all parts of the screen plate is consistent. If you want to produce a screen size of more than 48 inches, it is recommended to check the tension of the screen at 9 locations, namely the center of the screen, the four corners, and the midpoint of each side. Regardless of the tension of the center point, the tension difference between the other 8 points and the center point should be within ±1.5.

Why do you need to maintain the same tension across the screen plate? This is because the squeegee and the floating bar are not very flexible. If the tension on the center point and the right side of the screen is 20 Newton and the tension on the left is 17 Newton, the pressure of the squeegee must be adjusted to ensure the ink supply. The amount is consistent. As a result of this, dot gain and color drift may occur.

The tools used by the net can also limit or increase the tension of the net. In the past, hand-stitched nets certainly could not reach the required tension.

If the above conditions are met, a better screen version should be able to be produced, but if the quality of the production staff is low and the work is not serious, a good screen version cannot be produced. Therefore, it is imperative to strengthen the training of producers' ability. The level of production personnel is related to the types of training they receive, related to the trainers, and related to the training standards.

As a printer, you must be strict with yourself and try your best. Success comes from the continuous improvement of the ability, not the backwardness or cessation of ability, we must take the initiative to improve. Only in this way, product quality will gradually increase, and work efficiency will gradually increase.

Source: Ke Yin Network