PP Woven bags are mainly divided into non-laminated woven bags and laminated woven sacks. The corresponding two main printing methods are flexographic printing and gravure printing. In this article, we will discuss how to choose printing ink for non-laminated pp woven bags with flexo printing, which is most commonly used in non-laminated woven bags.
In flexo printing, firstly, the pattern should be engraved into a plate with resin material, and then the plate should be bonded to the round roller of the printing machine. The operation of the round roller and the transportation of the PP WOVEN FABRIC ROLLS are carried out at the same time. The resin plate stained with ink contacts the woven bag with the rotation of the round roller, and the ink on the pattern should be pressed on the woven cloth to form a single color pattern. For multi-color patterns, multiple resin plates need to operate in sequence.
The existing flexo printing inks include alcohol soluble solvent ink and water-based ink. Among them, water-based ink accounts for the vast majority. Its advantages are no pollution to the environment, no impact on human health, not easy to burn, good safety, stable ink performance, bright color, no corrosion of plates, simple operation, low price, and good adhesion after reflection, strong water resistance and rapid drying. It is precisely because of the above characteristics, Woven bag water-based ink is especially suitable for the printing and use of food, medicine, cosmetics and other packaging and decoration printing products with strict sanitary conditions.
What problems should it pay attention to in use water-based ink?
Fineness is a physical index to measure the particle size of pigment filler in ink. It is directly controlled by the ink manufacturer. Users can generally understand it. Its size cannot be changed in use. The fineness of woven bag water-based ink is generally below 20 um. The instrument for measuring fineness is fineness scraper.
Viscosity is one of the main indexes of water-based ink. 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 water-based ink is generally controlled within the range of 30 ~ 60 seconds / 25 ℃. If the viscosity is too high and the leveling performance is poor, it will affect the printing applicability of water-based ink, which is easy to lead to dirty plate, paste plate and other phenomena. If the viscosity is too low, it will affect the ability of the carrier to drive the pigment. The adhesion of water-based ink comes from the connecting material. The adhesion of water-based ink with acrylic resin and water as the formula will be relatively high. This is because the water-based ink with acrylic resin has fast drying, good flexibility, good water resistance and adhesion of more than 90%. The pH value of acrylic water-based ink needs to be adjusted during use, so it will have the smell of ammonia. Of course, after a period of time, with the volatilization of ammonia, there will be no odor.
Drying is one of the most important indicators of water-based ink, because the speed of drying and viscosity can be directly reflected in the quality of printed matter. The operator must understand the drying principle in detail in order to reasonably allocate the drying time of water-based ink according to the different products or substrates. While ensuring the good drying of water-based ink, we must also consider the moderate viscosity or stable pH value.
The drying of water-based ink includes volatilization, absorption and reactive solidification. After the water-based ink print is completely dried, it has strong water resistance and friction resistance. Drying is too fast, the surface of the ink layer is easy to peel, and the water-based ink is easy to dry up on the printing plate, resulting in dirty plate and unclear pattern outline. It is best to clean the anilox roller or ink bucket during shutdown, and often stir the ink bucket during short-term shutdown to prevent surface scaling. If the drying is too slow, the printed matter is easy to adhere. At this time, check whether the pH value is correct, and adjust it by adding stabilizer or ethanol according to the pH value to make the water-based ink dry faster.