The absolute size of large-format screens is a major step in the production of large-format screens—mesh preparation, coating, exposure, and recycling—and is the main challenge. However, we are now simplifying the process of making screens with multiple solutions. For example, manual wire mesh production has been replaced by automation equipment in many factories, and screen coating is also replaced by automatic coating machines. Let's discuss each step and introduce some techniques and tools that can be used to simplify the production of large format screen printing plates.
Wire mesh preparation
Polyester mesh is a sophisticated design of synthetic fibers. This material has excellent barrier properties and moisture resistance, which is why it is used in soda bottles and film packaging. Specifically, it is an inert plastic product that is not easily bonded.
Direct-coated emulsions are somewhat like water-based coatings. These emulsions are not easily adhered to plastics and have poor adhesive properties. To produce high-quality screens with a long print life, the screen must be properly prepared so that the emulsion adheres well to the screen. Good adhesion is of great importance when using abrasive or aqueous inks, such as printing on glass or textiles. This area is partially covered by tape or blocked in an image, and it is also very important in the case of re-opening in the next stage of printing. It can avoid the damage of the screen.
The wire mesh must be cleaned to remove oil or contaminants. This prevents the emulsion from wetting the surface of the screen plate. The fibers also require wetting agents. This can increase the level of surface tension, or the energy of the surface of the polyester mesh, to an acceptable level so that the emulsion adheres to it. This principle is very familiar to printing houses that print on low-energy plastics, such as printing on polyethylene. These substrates require surface treatment to achieve a certain level of surface tension for optimal ink adhesion. A screen that has been well degreasing and pretreated will form a uniform, uniform film of water after rinsing. When the tackiness of the screen is improved, both the exposure latitude and the resolution can reach the highest value.
Glue
In order to achieve a stable effect, we strongly recommend that you use an automatic screen coater on a large-format screen printer. It is impossible to ensure a uniform coating thickness on this size of screen if using manual coating techniques. If your arm is not long enough and you can balance the weight of the entire wide application tank, hand-coating large-format screens is almost impossible.
When gluing, high solids emulsions should be used. This avoids shrinkage during drying and helps you to produce high-quality stencils using simple coating techniques. The current coating machine also has a built-in drying device, which can perform very well when using a large screen mesh with a large mesh. Webs with a medium to small number of meshes use a wetter emulsion to dry faster and more efficiently on the coater.
dry
Screen drying is usually performed in a non-contaminating environment within the isolation zone and is carried out in areas where there are safe light exposures. The warm and dry hot air around 100°F (40°C) can be freely cycled in the drying zone to remove moisture.
Photopolymer emulsions are not affected by residual moisture and high temperatures during drying and storage. They can be exposed without being completely dried. However, diazo- and dual-cure emulsions must be dried before exposure and exposed with a water content of less than 4%. You can use a contact gauge to accurately measure the amount of water remaining in the emulsion.
exposure
Technological advances in the field of stencil making have challenged traditional large format imagesetters and other similar methods in terms of cost and efficiency. The computer direct screen imaging system brings efficiency to the digital process of making screen printing plates, the film is eliminated, the exposure process and the screen processing process are also simplified, and the original large-format large-format vacuum printing machine is no longer needed. Finally, the time spent on repairing the pinhole on the plate is also greatly shortened because there is no more film or glass surface to attract dust.
Although large format inkjet printers differ from computer direct screen systems, their output quality is much better for printers who often have to wait for other corporate films. Many screen printers use large format inkjet printers to produce in-house printers. Oversized positive image film.
The projection exposure unit greatly reduces film costs. For a photograph used to make a large-format silk screen, if the magnification is 10 times, the size of the film is only 1% of the final product. A special emulsion controls the exposure time within one minute because no vacuum squeegee is required, so screen processing is again simplified.
You don't have to worry about how you expose your plate. The most important thing is to make the exposure time long enough to ensure that the emulsion cures completely, and to produce a durable, chemically resistant and scratch-resistant fabric with good adhesion. Printing plate. A color conversion exposure calculator was used to determine the correct exposure time for diazo, dual-cure emulsions. This method as the last point of the color conversion process shows the correct exposure time. For example, yellow diazos are bleached during exposure, which can change the color of the exposed stencil. Usually the color changes from green to blue or from brown to purple.
One tool for judging the exposure value is the use of a 21-step grayscale exposure calculator, which can be used in light-sensitive polymeric emulsions and diazo and dual-cure emulsions. The ideal exposure depends on the amount of time it takes to post-cure the 7 shades of gray in the screen.
Exposure is a major problem when you are exposing large format templates. In order to maximize the exposure latitude when exposing large-format screens, the most important thing is to choose a high-resolution emulsion, improve the coating process, reduce the uneven thickness of the coating layer, and pass through the screen properly. Ground pretreatment improves screen adhesion.
development
In order to achieve the best resolution, spray development must be performed on both sides of the screen with a high-pressure, uniformly-distributed developer. This is easy to do on small screen printing plates, but it is difficult on large format screen printing plates. Because it has certain requirements on the process and space. The effective solution is to use automatic, also capable of developing, cleaning equipment. This requires less space and does not require design. There is a spray head in the development tower. The best manual option is to use a pressure gun with a minimum speed of 1000 psi and a fan sprayer with a flow rate of 3-5 gallons per minute.
Recycling
Manually cleaning large-format screens requires workers to focus their attention particularly on the use of tools, so as to ensure work efficiency and safety. The tools used mainly consist of a brush with a long handle, which can reach the far corner of the screen, as well as protective clothing - glasses, gloves, boots and so on. Each step of cleaning requires the use of a separate brush to avoid cross-contamination between chemical containers. Please do not underestimate the importance of a good pressure gun. Buy one of the biggest and best washers you can afford. It won't disappoint you.
Automatic screen recycling equipment can do many difficult jobs and can reduce the possibility of workers being harmed by chemical agents. Combined and on-line equipment can systematically remove oil from screens, and the removal of ghosts is still a problem because the machine is not yet fully capable of doing so. So even if you are using an automated system, you still have many opportunities to clean it yourself.
On large screen printers
The appearance of large-format silk screens is closely related to people's pursuit of printing larger and better images on different substrates. Only by continuously innovating in materials and technology can it be possible to ensure the prosperity of the business and ensure that screen printing is always at the center of large-format imaging.
Source: Wuzhou Search
