Tips for using flexo water-based ink

The special ink used in the flexographic printing machine is water-based ink, which has the advantages of no pollution to the environment, no impact on human health, not easy to burn, good safety, stable ink performance, bright colors, no corrosion of the plate, simple operation and price Cheap, good adhesion after printing, strong water resistance, rapid drying, printing speed can reach 150-200m per minute. Because of the above-mentioned characteristics, flexographic water-based ink is particularly suitable for the printing and use of packaging and decoration printing products such as food, medicine, cosmetics, etc., which have strict requirements on hygienic conditions. So what problems should be paid attention to in its use?

Main indexes of flexo water-based ink
1. Fineness
Fineness is a physical indicator that measures the particle size of pigments, fillers, etc. in the ink, and is directly controlled by the ink manufacturer. The user generally understands it and cannot change its size during use. The fineness of flexographic water-based ink is generally below 20μm, and the instrument for measuring fineness is the fineness scraper.

2. Viscosity
Viscosity is one of the main indicators of water-based ink. The viscosity value will directly affect the quality of printed matter, so the viscosity of water-based ink should be strictly controlled in flexographic printing. The viscosity of the water-based ink is generally controlled in the range of 30-60 seconds / 25 ° C (with paint No. 4 cup), and the viscosity is generally controlled between 40-50 seconds. If the viscosity is too high, the leveling property will be poor, which will affect the printing suitability of the water-based ink, and it is easy to cause dirty plates, paste plates, etc .; if the viscosity is too low, it will affect the ability of the carrier to drive the colorant.

If the water-based ink is left for a long time, some inks with poor stability are easy to settle and delaminate, and others will appear to be thick. At this time, sufficient stirring can be carried out, and the above problems will disappear naturally. When using fresh water-based ink, be sure to stir in advance before making dilution adjustments. During normal printing, the ink fountain should also be stirred regularly.

Water-based inks easily freeze below 0 ° C. If the water-based ink freezes, it can be placed in a room with a high temperature to allow it to dissolve naturally. After stirring evenly, you can continue to use it. When the temperature difference between winter and summer is large, the viscosity is the most sensitive. When the temperature is high, the moisture evaporates quickly and the drying is fast. When operating, it is necessary to reduce the drying time or increase the speed of the machine; when the temperature is low, the moisture evaporates slowly and the water-based ink drying is also slow. Speed ​​or add drying device. When using in winter, it is best to put the water-based ink stored in the warehouse in advance in the workshop to balance the viscosity.

3. Dry
Drying is one of the most important indicators in water-based inks, because the drying speed is the same as the viscosity, which can be directly expressed in the quality of the printed matter. The operator must understand the drying principle in detail, so that the drying time of the water-based ink can be reasonably adjusted according to the different products or substrates. While ensuring that the water-based ink dries well, one must also consider that the viscosity is moderate or the pH value is stable.

The drying of water-based ink includes three methods: volatilization, absorption and reactive solidification. After the water-based ink print is completely dried, it has strong water resistance and abrasion resistance. If it dries too fast, the surface of the ink layer is easy to skin, and the water-based ink is easy to dry onto the printing plate, resulting in dirty plates, unclear surroundings of the pattern, and the internal moisture cannot be eliminated, resulting in inaccurate overprinting, which can be adjusted with a blocking agent. It can be solved by increasing the speed of the printer or turning off the drying system. During shutdown, it is best to clean the anilox roller or ink fountain. When shutting down for a short time, the ink fountain should also be stirred frequently to prevent surface skinning; if the drying is too slow, the paper will stretch and reduce gloss, which will affect the multi-color printing and may cause adhesion. , Which brings a lot of trouble to machine operators. At this time, you should first check whether the pH value is correct, according to the level of the pH value, add an appropriate amount of stabilizer or ethanol to adjust to make the water-based ink dry faster.

4. pH value
The water-based ink contains a certain amount of ammonium solution to improve its stability or enhance the water resistance after printing. Therefore, the pH value is one of the important indicators. The pH value of the water-based ink at the factory is generally controlled at about 9. The pH value of the machine can be adjusted or controlled between 7.8 and 9.3. It should be flexibly controlled according to the substrate and temperature. At the same time, it is necessary to take into account the relationship between drying and viscosity, and add various additives to adjust. The pH value of the gold ink should not be too high and can be controlled between 8 and 8.5 to make it slightly alkaline. Generally, it is tested once every 2 to 3 hours and adjusted with the test, and the pH value should be controlled within the best printability range. [next]

Types, uses and dosage of main additives for water-based ink
The main additives for water-based ink are diluent, stabilizer, retarder, cleaning agent, defoamer, gold ink thinner, UV gold ink curing accelerator, etc.

1. Dilution agent
Dilution agent is a milky white slurry liquid with certain viscosity and high pH value. It can be adjusted with various colors and dilute four-color ink without reducing viscosity and pH value. It can be used directly on the machine to enhance the brightness of the printed product. The dosage can be based on the user's color draft and the color depth.

2. Stabilizer
The stabilizer is a colorless transparent liquid, and its pH value can reach 11. It can increase the pH value of the water-based ink and enhance the curing and drying time of the water-based ink. If the printing is normal, the pH value is relatively stable, and the viscosity is too large, it can be diluted with 1 to 1 water to adjust the viscosity of the water-based ink, and the usage is generally controlled at 4% to 6%.

3. Blocker
The retarder (slow-drying agent) is a slightly yellowish liquid with a pH value of about 5.5. It can inhibit and reduce the curing and drying time of the water-based ink, prevent the skin from forming on the surface. Dirty plates and paste plates caused by drying too quickly have a certain inhibitory effect. When the viscosity of the water-based ink is too high, and does not require the use of excessive retarder, it can be used after dilution with water, the general dosage is controlled at 3% to 5%.

4. Defoamer
The main performance of the defoamer is to eliminate bubbles in the water-based ink, and to prevent problems such as white spots, trachoma, and water marks caused by the appearance of bubbles during printing. The dosage is generally 0.5% to 1%. Too much dosage will affect the quality of the product. It is best to use it from the sprayer
5. Gold and silver ink thinner
The gold and silver ink thinner is a milky white turbid liquid, which has a certain viscosity, and the pH value is slightly alkaline. The main performance is to adjust the viscosity of the gold ink and improve the printability without oxidizing or darkening the gold and silver ink. , Maintain the original luster of gold and silver ink. The dosage is generally controlled between 2% and 8%, and should be used flexibly according to the temperature, substrate and speed.

6. UV gold ink curing accelerator
When deploying UV gold ink on site, UV gold ink curing accelerators are mainly used to help increase the speed of light curing and drying, increase vehicle speed, and increase production. The general dosage can be controlled at 5% ~ 10%.

7. Cleaning agent
The cleaning agent is mainly used in the machine to clean the printing plate and anilox roller and to deal with the dry and skinned water-based ink.

Recovery and utilization of residual ink
Because the ink fountain must maintain a certain amount of ink to ensure that each printing machine can print normally, it is impossible for each machine to run out of ink every time. At the end of each batch of product printing, there is generally a certain amount of remaining ink. For multi-variety and multi-color printing, each product will have a certain amount of ink remaining for processing. If it is not adjusted in time, continued use will cause waste and increase costs. This requires that the remaining ink should be kept at the lowest point as far as possible during the deployment. The remaining ink must be stored separately and sealed well, and no ink skin or debris should be mixed in. If it is not clean, use a filter to filter it well. The next time you use it, use the remaining ink first. The light color can be adjusted to the dark color. The paper with rough paper or medium and low grade products can be used first.

Water-based ink preservation
The shelf life of flexographic water-based ink is generally one year, exceeding the shelf life or longer, as long as there is no solidification colloid, but the surface is layered or precipitated, as long as it is fully stirred evenly, it can be used continuously. The storage temperature should be in the range of 5 ℃ -30 ℃. It is best to store in the warehouse, not in the open air, not in the sun, and not in the warehouse below 0 ℃. The retention period of gold ink is half a year or less.

FISHING RODS

WEIHAI WEFISH OUTDOOR PRODUCTS CO.,LTD , https://www.wefishtackle.com