The benefits of high pressure cleaning and high pressure wire mesh

Every screen printing factory that I have visited will use different types of high-pressure cleaners in the production and recycling of screens. These machines can have a variety of configurations as needed, and as more and more manufacturers transfer their production bases to lower cost regions, the prices of these machines have also dropped significantly in recent years. Everyone can go to a local supermarket to buy such equipment, but does it really help? What's more, what do you want industrial high-pressure cleaners to do for you?

High-pressure cleaners have different roles when they are used at different stages. Now, I will introduce several principles for the successful selection and use of high-pressure cleaners and the proper handling of screens.

Some seemingly simple measures can actually help you save a lot of plate-making time and screen cleaners. But before choosing the silk screen process, you need to know exactly what high pressure cleaning is.

Line water pressure in the United States is usually 75 psi. Concentrating this water in a nozzle can increase its pressure, but it is also as high as 200 psi, so it cannot be said to be high pressure water.

The line pressure is usually used to clean the image area on the exposure plate. Many screen printing plate manufacturers believe that the use of low pressure water can protect the details of the image on the plate to prevent damage to it. But this is an illusion. If the screen can be properly dried, imaged and rehydrated, it will not be damaged by the high pressure water during the final cleaning process. This we will say later.

General hardware and pressure washers sold in gardeners are relatively inexpensive, between $100 and $300, and their operating pressure is between 500-1750 psi. This is certainly better than a little pressure, but in actual work, their pressure is still lacking and the scope of use is limited. In addition, these devices are designed for temporary use, and their rated workload is relatively low. If only for image cleaning, it can meet the requirements, but it is difficult to use it to prepare and reclaim the net.

You need to use a washer with a pressure above 1000 psi to handle the job. I think the most suitable pressure range is 2400-3000psi. Such high pressure needs to be driven with 5 to 10 horsepower engines. These industrial cleaners are designed for continuous operation over 4 hours. Their cost is between $400 and $4000, depending on the operating pressure, the duty cycle (how long the unit can run without stopping before having to rest), and the specifications of the motor used.

Mesh preparation

We must start by tightening the mesh on the screen plate. During the first round of preparation, imaging, and recycling, the original mesh is very unstable and its tension often changes. In addition, different oils and silicones used in the weaving process may also remain on the mesh. The correct method is to remove these contaminants before treating and coating the screen plate with emulsifiers. The way you handle screen printing plates directly affects the service life of the screen and the tension of the screen.

For screen printing plates using stretch-and-glue racks, the stability of the mesh tension will be directly affected by the high pressure cleaner. Mesh tension can only decrease when gluing. When people first studied mesh tension in the 1980s, researchers thought that the tension of the mesh after tension was caused by a phenomenon called "cold flow." This is a process in which polymer molecules are aligned along the direction of the tension vector. During the alignment, they slide past each other, reducing the overall tension. This phenomenon is the greatest difficulty faced by people in the use of reservable racks. People can only maintain a stable target value by continuously adjusting the mesh tension.
The development of high density low modulus polyester polymers can significantly improve the problem of tension drop, but it cannot completely solve this problem. A study done by the University of Wales in the 1990s showed that mesh tension cannot be evenly transferred to the screen. In fact, the researchers found steering friction at the intersections of the cables, which showed the transfer of pressure to the screen. Only with the help of time or extra mechanical force, the mesh tension can remain stable.

When you wash the screen plate with a high pressure cleaner for the first time, its tension may drop by 10 to 15 N/cm. Water pressures above 2400 psi will open the nodes of the cable and lubricate the cable, causing the cable to slip and drop in tension. You can find the same problem in the first 150 prints of the new stencil printing. Continuous non-contact fatigue cycles can also cause the same node looseness, causing a significant drop in tension.

After high-pressure cleaning and anti-wear treatment, you should adjust the final screen tension. Our company has greatly improved the production performance of the original network through this method. You can reduce the tension drop in the printing process by more than 80% by high-pressure flushing, adjusting the mesh pressure to the target value, and lubrication. If you use a static rack, you can't correct it. You can only watch the tension drop.

Template production

Our company recently changed the way of screen cleaning, significantly improved the quality of high-density stencils, and reduced the moiré on the halftone pattern. Like many screen printers, we also live under high pressure because we have to be extra careful when cleaning exposed images - our preparation of screens, the environment of the screen printing shop and the exposure systems used There are very strict requirements.

Now, we first soak the exposed silk screen in water for two minutes or longer so that a better rehydration reaction occurs in the unexposed areas. We also use spray to clean the screen and further remove unexposed resin from the stencil. When cleaning the printing surface, we use 500 psi pressure.
Our changes to the stencil making process have greatly improved the sharpness of the edges of the image, the connection of the stencil, and the sharpness of the image. The line water pressure does not have enough force to enter the edge area of ​​a fine mesh node or a circular mesh point. We are now working hard to solve these problems and improve the quality of print.

The decrease in moire is the most obvious improvement. Proper cleaning can help us get the ideal halftone dot and easily remove the unexposed emulsifier coating.

Recycling

High pressure cleaning plays an important role in screen recovery and ghost removal. Some printers believe that the use of 3000 psi pressure in the screen recycling process is somewhat too high to cause damage to the screen. They point out that oil cleaners and stencil removers soften or damage the emulsion layer. Their ideas are correct, but these products are the foundation of the entire production process, and not just part of the workflow.

The use of high-pressure water during the recovery process removes ink and emulsifiers from the mesh nodes. This can make the mesh more emotional, the greater the original printing tension, the better the printing effect. Another problem I often hear is that high pressure can tear the mesh. The screen may break during recycling, but high pressure cleaning is not the main reason for it to break. As mesh tension decreases, the possibility of wire mesh breakage increases. The low-tension screen is more elastic, like a net on a trampoline. When you wash the low-tension screen with high-pressure water, the screen will quickly rebound after being exposed to water pressure. This will cause the mesh to vibrate and cause the screen to break. On the other hand, high-tension mesh (25 N/cm or more) is less elastic, so high-pressure washing can effectively remove ghosts on this type of template.

In order to reduce the chance of breakage of the wire mesh during recycling, it is best to start with the bottom of the wire mesh and at least 12 inches from the mesh. As far as the top of the washer is 1 to 2 inches away from the surface of the screen, the cleaning roller can only be removed. Finally, keep clearing the screen until all the patterns are removed. The combination of higher mesh tension and high water pressure can extend the life of the screen, improve image quality, and reduce the appearance of moire. In this way, you can also get more benefits from stable printing pressure and fewer ghosting failures!

Reprinted from: ISP "International Screen Printing"