Screen printing pollution problem is solved comprehensively

Silk screen printing is a flexible printing method. It has the advantages of wide adaptability of substrates, short production cycle, and low equipment cost. Its products are very adaptable to the environment. Silk screens are printed using a leak-through screen. The non-image portion of this screen plate is blocked and does not penetrate ink. The type of material used for the screen depends on the appearance of the product. Before screen preparation, we must first stretch the screen, and ensure that the material frame is hard, so that the layout is smooth.

The image on the screen plate can be manually drawn onto the screen, but more often a direct photographic stencil is used, coated with a dichromate photographic emulsion, or a dichromate hexene polymer. , as a photosensitive material. Emulsion coating can be done using a scraper or an automated method. When the coating is hardened, the stencil can be exposed to ultraviolet light to produce a photochemical reaction to produce an insoluble image mask. The unexposed part will still dissolve in water. After the water is developed, the image is carried on the screen.

There are three steps to the recovery of the screen: In the first step, the residual ink is washed away with a solvent; the following cleaning solvents are used: terpene-based products, glycol ethers and dibasic ester mixtures, mineral alcohol, methyl ethyl Alcohol, acetone, etc. If the screen image is no longer to be used, the emulsion layer covering the screen should be removed. Emulsion cleaners are typically sprayed onto the screen and then brushed to remove the exposed holes. Typical emulsion scavengers include metaperiodate or periodate. After the inks and emulsions are removed, a "ghost image" remains on the screen. The scavengers of this "ghost" image include: potassium hydroxide, fatty ether ethanol. However, for workers and the environment, the use of screen recycling products will cause some harm.

Prepress

Screen version preparation

There are several emulsions or screens, such as direct or indirect photographic screens, that can be used to transfer images to screens. Most of the direct screen screens are water-soluble and therefore cannot be mixed with water-based inks. However, the chemical treatment of the water-soluble screen can increase its water repellency. Water-repellent screens must use solvent-based inks, and repellent screens must use water-based inks. If you want to replace solvent-based inks with water-based inks, you must use new solvent-repellent emulsions to compensate for water-based inks. Using a water-based ink will cause the emulsion layer to erode quickly and holes will appear in the screen plate.

print

The easiest way to reduce waste is to keep various wastes separated. Do not mix different wastes to save space. This will create problems and increase costs when dealing with waste.

Ink

Ink types include traditional solvent-based printing inks (including tantalum components), UV-drying inks, water-based inks, and plastic inks (for textile printing).

The most commonly used screen printing inks are solvent based. They dry by solvent evaporation. This dry version releases VOC (volatile organic compound) emissions.

Water-based inks include water, emulsion resins, other resins, pigment particles, and additives. Many think that these water-based inks can produce more vivid colors, and the printing effect is clearer than solvent-based ink prints. This may be because the use of water-based inks in the silk screen printing process allows the use of finer dot patterns for the addition. network. Water-based inks do not require organic solvents when the cleaning ear listens to the press, so no hazardous waste is created without heavy metals. Also, water-based inks are generally cheaper than solvent inks, but are essentially the same in quality, gloss, and adhesion as water-based inks. Water-based inks have a disadvantage in that they require the drying time of the prints to be longer. The ink remaining in the printing process can be recovered in the ink tank using a scraper, which not only reduces the amount of ink but also reduces the amount of cleaning emulsion.

Postpress

In order to recover the screen, as mentioned earlier, there are three basic steps. However, screen recycling generates a large amount of waste solvents and waste water. VOC volatiles can also occur when solvents are used to remove inks, which can have a negative impact on a person's health.

Many emulsion scavengers are dissolved in water and these waters are actually carriers of recovered chemicals. The main chemical in emulsion scavengers is metaperiodate, because periodate requires water as a carrier to achieve a certain chemical group in the emulsion, so for water-repellent emulsions, it is clearer than a solvent-repellent type. more difficult. Most commercial emulsion cleaners can remove water-repellent emulsions and solvent-repellent emulsions. With the high-pressure injection method, the emulsion can also be easily removed and the amount of cleaning agent used can be reduced. This flushing water should be considered for recycling because the main pollutants are suspended particles.

Ghost images are produced at the crossover portions of the cable and are particularly easy to generate in the use of solvent-based inks. When removing ghost images, the scavenger used will have a destructive effect on the mesh if it is used in excessive amounts. Therefore, the degree of cleaning should be changed according to the types of jobs used for recycling.

When selecting chemical substances for processing, considerations for chemical substances include: hazard, operability, utilization, quantity problems, cost issues, human acceptability, cleaning efficiency, impact on screen materials, and effects on printing. Impact and other aspects.

Improvement of equipment

There are several types of equipment that can be used to recover screens to prevent contamination. Many of these systems can save costs by reducing adjustment requirements, making operations easier, and reducing the amount of chemicals used. Each printer must determine the adaptability of these devices based on their particular process.

The current situation of the printer is to use a manual pump to apply screen-recovery chemicals to reduce the emission and exposure of chemicals in a more effective way. By allowing wire mesh recyclers to control the amount and direction of various chemicals, the use and waste of chemical substances can be raised.

In order to further reduce the amount of chemicals, a circulation system should be configured in the injection system.

The cleaning tank should be controlled in the designated area, and the used chemicals should be collected for recovery. The degree of exposure and amount of waste should also be controlled to a minimum.

A filtration system can be used to remove specific substances from the wastewater to make the chemicals reusable. Can work through different processes: If the filtration system is used independently, it may not provide special anti-pollution measures; but, if used with the circulatory system, the filtered solvent may reduce the amount of solvent used.

A circulatory system, through cooperation with several technologies, allows printers to reduce the use of solvents, with the result that contamination is minimized.

Distillation equipment can also be used to recover the system. These devices separate contaminants and provide a more efficient way for the solvent to circulate. Therefore, like solvent filtration and recycling systems, these solvent distillers also reduce the use of solvents, raw materials, and operating costs.

The entire packaged system is effective for the removal of inks, emulsions, and ghosts. These systems will reduce the amount of chemical components used in the cleaning process and the amount of cleaning labor.

Process improvement

Simple process improvements can also reduce the amount of solvent used, waste disposal costs, and staff working environment.

Whenever possible, try to avoid delays in cleaning and recycling the screen. The amount of chemical substances can be reduced when cleaned up.

A printer in Minnesota said that he said that during the removal of emulsions and ghosts, it was possible to use chemical jets that were not sprayed directly on the screen. This requires the staff to make a simple "limited box" to place the screen during chemical processing. This limited box can collect the spray solution for recycling and utilization.

A printing person in New York said that they kept the chemicals in a safe can or other packaging container to reduce the solvent loss due to evaporation. They used a pump and a spray head before, and used a high-pressure water washing method to perform the cleaning process. Only use ghost remover if absolutely necessary. The company is now beginning to manually remove the ink residue and emulsion layer scavenger, then use a low-pressure cleaning solution, and finally clean it with high pressure water. In such a process, no high-pressure water jet will be used to diffuse chemical substances into the air. According to the printer, this new method of applying chemical substances can reduce material use by 15%.

Another technique for removing ink is to use high pressure water jets. This high pressure water injection will loosen the emulsion and increase the removal efficiency. This method may reduce the use of 75% of the emulsion scavenger, but it will produce harmful noise to the staff.

The use of ghost removers will make the screen easier to break and will inject chemicals into the waste water. So using several simple techniques, you can reduce the situation above:

1. Use ghost remover only for "ghost" areas.

2. Avoid leaving the screen for a long time before recycling.

3. Use ink fading agent before recycling to prevent the formation of ghost images.

The reason why the screen is recycled is because the material is relatively expensive, and recycling the screen can save the time needed to stretch the net and adjust the pressure. Other staff members also believe that reusing the screen saves money and storage space compared to storing screen materials.

For screen printers who want to make long productions, they will directly discard the screen after the production process is completed. Because the net used in this way will not be long-lived, doing so can save on the chemicals used for recycling and the working time spent. However, because the chemicals used in the process of printing and imaging on screens may be harmful to the environment, it is not necessarily a good thing for environmental protection. Therefore, the printer must also do some necessary screen processing.