Screen printing 150 questions (65-70)

â–¼65. What is the main reason for silkscreen printing in the printing process and how can it be solved?

Closing the net in screen printing is also an aspect that cannot affect the quality of printing. There are many reasons for the screen printing screen during the printing process. The main reasons are as follows: 1 The particles in the printing ink are relatively large. 2 The ink is dried on the screen plate and conjunctiva. 3 The viscosity of the ink is too high to affect the missing print. 4 Low temperature The ink has poor fluidity.

All of the above four reasons can lead to the phenomenon of net closure. Problems encountered in daily production should be analyzed in specific situations and selected in the right way. Several solutions are now introduced as follows for reference when used. First of all, from the ink manufacturing and use methods to solve the closure method. For the reason that the particles of the ink are larger, the screen can be solved when the ink is manufactured. The main method is to strictly control the ink particle size should not be too large. From the point of view of modern manufacturing ink technology, solving the problem of large ink particles is not a difficult task.

In the printing process, the viscosity of the ink is increased due to the volatilization of the solvent, and instantaneous drying occurs at the mesh to block the mesh (drying the conjunctiva) and cause the netting phenomenon. This is especially true when using evaporation-drying inks. Evaporation-drying inks are dried by using solvents. Therefore, proper solvents must be used to control the drying speed during printing. In addition, attention must be paid to ventilation in the production room, temperature, and humidity conditions. In the selection of ink to take into account the impact of climate, the general use of fast-drying ink in winter, the use of late-drying ink in the summer, the use of dryness in the spring and autumn between the above two inks. Another point is that you can use the late drying agent for fine-line printing. If you use the late-drying agent, you must use other types of ink instead. Oxidation-drying inks are used, and the phenomenon of net-sealing does not appear much. However, if desiccants are used excessively in the summer, net-sealing occurs, and in the summer, desiccants need to be controlled.

When using two-fluid reactive inks, the drying speed of the ink itself is slow, so that the net-screening phenomenon hardly occurs, but the phenomenon of net-sealing occurs occasionally. The reason is that after the solvent evaporates, the viscosity of the ink increases, resulting in the closure of the net. Add an appropriate amount of the late drying agent to the ink for dilution to prevent the netting phenomenon from occurring.

In the printing process, the viscosity of the ink is increased, resulting in the main cause of the screen closure: the ink on the screen printing plate causes the viscosity of the ink to increase due to the evaporation of the solvent, and the phenomenon of net closing occurs. If the area of ​​printing graphics is relatively large, the ink on the screen printing plate will consume more, and the phenomenon of closing the screen will be small. If the picture area is small, the ink consumption on the screen printing plate is small, and the ink travels back and forth on the screen printing plate for a long time. As the ink moves on the screen plate several times, the viscosity gradually increases and it is easy to cause the screen closure. In this case, the new ink should be used frequently to prevent the occurrence of the screen-sealing phenomenon.
Poor flow of the ink will cause the ink to seal when not passing through the screen. This situation can be solved by reducing the viscosity of the ink to increase the fluidity of the ink.

In addition, the mesh number and the opening area of ​​the selected screen mesh are smaller than the grain size of the ink, so that it is also one of the reasons why the ink with the more extreme granules does not easily pass through the mesh holes.

â–¼66. What are the causes of screen printing and how can it be prevented?

Screen printing sometimes causes smearing after printing, which is mainly caused by insufficient ink drying. Generally, when the oxidatively drying ink is printed, the scumming phenomenon is relatively large, because the screen printing ink layer is relatively thick, while the oxidative drying ink surface is dried quickly and the inside is dried slowly, when the printed matter and print or print When other objects come in contact, dirt will be created. Cobalt desiccant or lead desiccant is generally added to the ink to increase the drying speed of the ink and prevent it from picking up. In addition, when the printed matter is stacked, it should not be stacked too much (because the overprinting of the printed matter, it is easy to produce dirt), and the printed matter must be fully dried before being stacked. The use of evaporative drying ink reduces blemishes. Strictly complying with the process requirements during printing and operating strictly according to the technical operating procedures are also an important measure to avoid smearing.

â–¼67. Why does the screen printing produce bubbles on the finished ink surface? How to avoid bubbles?

There are bubbles on the ink on the substrate after printing. The main reasons for bubbles are as follows.

1 The surface of the substrate is covered with dust and oil traces.

2 The ink itself has bubbles or uneven viscosity when printing.

3 The printing speed is too fast or the printing speed is not uniform.

The intrinsic factor of the generation of air bubbles is that due to the high ink viscosity, the surface tension of the ink is large, and the gas oil in the ink is difficult to escape from the ink film and stay in the ink layer. If the viscosity of the ink is low, the surface tension of the ink is small, and the air bubbles will disappear on their own. Therefore, the phenomenon that the ink of the printed matter will not appear as a bubble will occur.
The following measures are usually used to prevent air bubbles from forming in the ink layer.

1 Use hydrophobic solvents as much as possible.

2 When the ink itself generates bubbles, an appropriate amount of defoamer can be added to the ink. If the ink has poor fluidity, when the screen printing plate is lifted, the ink flow is relatively small and the screen marks cannot be filled, and a smooth and smooth ink layer cannot be obtained.

To prevent screen marks after printing. The following method can be used.

1 Use more fluid ink for printing.

2 can consider the use of slow drying ink printing, increase the ink flow time so that the ink gradually curing.

3 Use a single-diameter screen with a narrow wire diameter when making a plate.

â–¼68. Why do screen cracking occur on the surface of the finished ink layer? How to prevent cracks on the ink surface?

The main reason for the cracking of the ink layer on the surface of the substrate after screen printing is due to the effect of the solvent and the large temperature change. General styrene products use alcohol and petroleum solvent weak solvent can also crack. Some substrate materials can also cause cracking due to their own factors. In order to prevent the occurrence of cracks, the nature of the ink and the solvent resistance of the substrate should be taken into consideration when selecting the solvent. Solvent-resistant and oil-resistant materials can be used as substrates. Pay attention to keep the workshop temperature balanced. In multi-color overprinting, each color should be fully dried after printing, and the drying temperature should be strictly controlled. In general, paying attention to the above aspects, it is possible to effectively control the cracking phenomenon of the ink layer.

â–¼69. Screen printing can be processed as follows according to the actual situation.

1 After the first printing, if the screen printing plate is to be printed a second time, the remaining ink on the screen printing plate must be cleaned to ensure that the mesh part of the graphic is not blocked by the ink, and then is fully dried. Store it properly afterwards. Ready for the next use.

2 After the screen printing plate is printed, if it is no longer used, and it is intended to scrape the screen, the ink around the frame can be cleaned, the screen can be peeled off, or the screen can be directly peeled off, and then the frame can be cleaned. , frame for use in the next time stretching.

3 After the screen printing plate is printed, in the case of preparing for the secondary plate making, the residual ink can be cleaned first, and then the photosensitive film on the screen plate is removed with a release agent, washed with clean water, dried, and then stored well. Use when preparing for the next plate making.

â–¼70. Why is the stripping process when the screen printing plate is reused? What is the demoulding method?

Stripping refers to printing after the screen printing plate, the plate is no longer used, and plans to re-plate. In order to reduce the waste of the screen and reduce the cost, the cured photosensitive material on the screen plate can be peeled off from the screen, cleaned and dried, and then used again. The process of peeling off the screen plate using a photosensitive material is called film removal.

General release film release agent. The main components of the release agent are: bleaching powder, alkali hypochlorite, hydrogen peroxide, caustic alkali, ammonia, potassium permanganate, oxalic acid and so on.

The process of stripping process is: First, clean the ink on the screen plate when removing the film, then wipe the two sides of the screen plate with the stripper or soak in the stripper, and soak for about 5-10 minutes. When the film is whitened, it can be rinsed with water (or scrubbed with a sponge). After the film is removed, the screen is rinsed with water and dried, and it can be used again for coating.