How to replace flexographic UV ink with flexo ink
Water-based ink as an environmentally friendly ink, in addition to containing a small amount of additives, rarely containing organic solvents, no VOC emissions. However, in order to high-end labels, especially film stickers on the label, with flexo water-based ink to replace the flexo UV ink, industry colleagues doubts is not small. So, flexo water-based ink in order to replace the flexo UV ink, its printing performance must meet what market demand? Here, the label Jun for you finishing a lot of flexo ink recipe, and thin look ~ ~
The pH of the water-based ink is as unstable as the sawtooth wave curve. To stabilize, it is necessary to shorten the time to measure the pH and the addition of the stabilizer, that is, to increase the pH and the addition of the stabilizer. Therefore, foreign label printing enterprises in water-based ink applications often use pH real-time control device, at any time to determine the pH value, at any time to add stabilizers to maintain the stability of water-based ink performance.
PH stable water-based ink, the pH value between 8.25 ~ 8.5, very small fluctuations. This kind of water-based ink transfer stability, viscosity stability (due to the evaporation of water latent heat, water-based ink because of water evaporation caused by the high viscosity of the ink viscosity is very low, water-based ink viscosity is often the loss of ammonia to pH So that the color density is stable.
In order to ensure that the ink stored in the anilox roll hole in the smooth transfer to the plate, you must use similar to gravure printing process of low viscosity ink, otherwise it is difficult to suck out the ink in the hole. However, due to the characteristics of flexo anilox grooved hole with the electric carved gravure of the inverted pyramid mesh features are very different, so flexo UV ink viscosity and no need to be as low as gravure ink.
Foreign in the development of flexographic UV ink, then it is the choice of a lower viscosity of the monomer resin, so that flexo UV ink reached today's realm. Similarly, the reasonable viscosity of flexographic water can be similar to UV ink, without having to deliberately pursue low viscosity. Imagine that the flexo printer's ink transfer mechanism is the same, only the drying mechanism is different, and if so, what are we necessary to reduce the viscosity of the flexo water-based ink?
Properly improve the color density of water-based ink
The quality of the flexographic prints is subject to the anilox roll technology. In order to achieve the high number of plates, the anilox rolls must also be of high number, and the optimum ratio of the depth of the mesh and the opening , When the anilox roller is a high number of lines, the amount of ink storage will be a corresponding decline, BCM value will be relatively low. At this point, if the same plate on both the pursuit of high numbers, but also the pursuit of high color density, it is necessary to improve the color density of ink, in short, to improve the proportion of ink pigment.
Now already know, flexo UV ink pigment ratio is generally 25%, flexo water-based ink pigment ratio is generally 20%, flexo solvent-based ink pigment ratio is also about 20%. As the flexographic solvent-based ink surface tension is generally lower than the flexo water-based ink, the transfer rate from the plate to be slightly worse, the same pigment ratio of solvent-based ink after printing the color density slightly lower than the water-based ink The Therefore, compared with flexo UV ink, the flexographic water-based ink in the color density requirements, but the proportion of the pigment and then increase.
Change the surface tension of the ink according to the plate characteristics
According to the data we now have, the surface tension of the flexographic ink is required to be as close as possible to the surface energy of the plate (also known as the surface tension of the plate), that is, the difference should be as small as possible. There are two general practice: one is to adjust the plate, the other is to adjust the ink, because the plate is basically controlled by foreign manufacturers, so the first approach to achieve the possibility of minimal What we can do now is to ask the surface of the plate to be stable, and then by adjusting the surface tension of the ink to match.
The surface tension of the aqueous ink is related to the following materials: aqueous solutions, aqueous emulsions, cosolvents, additives and the like. Unlike solvent-based inks, the surface tension of water-based inks is more difficult than solvent-based inks, and requires extensive laboratory and experimental work. Conventional market applications are often based on a large number of experiments and Trial on the basis of. I advocate in the trial before the need to do some data measurement and analysis work to avoid blind trial caused a lot of material loss.
Adhesion to non-absorbent materials such as films
Ink should be attached to the surface of the film, requiring the film surface tension above 38mN / m, if the film surface tension is not compliance, must be in advance of the film corona treatment or primer coating the appropriate coating to change the surface properties of the film. When printing water-based inks on the surface of the treated film, it is necessary to have the following prerequisites for the high adhesion of the water-based ink on its surface:
(1) the characteristics of water-based ink must be similar to the characteristics of the film, water-based ink in the transfer to the film on the moment, the film should have a slightly soluble stage. The micro-soluble phase is the ink in the film surface to establish the anchor point, the establishment of the ink film can be attached to the surface of the foundation.
(2) ink in the film surface wetting, the stronger the wetting capacity, the more the formation of anchor points.
(3) the formation of fine and strong ink film, the anchor points are effectively connected.
Pay attention to the drying speed of water-based ink
Water-based ink composition, the water is about 50% or more, while the ordinary water 25 ℃ when the latent heat of up to 1043 kcal / lb, is more than 400 kcal / pound 4 times, so the industry consensus is: water-based ink Drying requires more energy.
Water-based ink in the flexo machine generally use infrared or hot air drying, and does not require special equipment. As long as the flexo machine can use solvent-based ink, you can also use water-based ink. I saw in the foreign use of water-based ink flexo machine, the drying device did not do special treatment.
Check the initial length of the flexo water-based ink can be double-slot scraper fineness meter, and with the mature flexographic solvent-based ink to do the same, to achieve the same initial length can be. Because as long as both the initial length of the same dry, under the same drying device under the dry performance is basically the same.
Note the surface tension of the ink after drying
Compared with the resistance of the ink film, water-based ink with UV ink or a gap, so the water-based ink printing cover a layer of UV varnish is a wise move. UV varnish price is not high, but good physical properties, the cover in the water-based ink film on the premise that: its water-based ink film must have a good wetting, can not shrink. Therefore, the surface tension of the aqueous ink film must be greater than 38 mN / m.
Detection of water-based ink film surface tension method is relatively simple, a corona pen can be. But to improve the surface tension of water-based ink film also need to start from the water-based ink formulations, which is not intended. After the order is completed, it is necessary to clean the ink road, otherwise it is necessary to cut the skin, dirty printing materials or machines. To save this part of the ink loss is recommended: in the ink tank coated Teflon, the excess water-based ink can be put back to the ink tank, the machine can leave the water-based ink wipe, wipe with water. Do not underestimate this measure, or the advantages of UV ink is always there.
Prevention of ghosting failure
When the roll speed is not synchronized with the anilox roll speed, especially when the anilox roll speed is lower than the roll speed, the flexo is likely to be ghosted due to the drying problem of the ink and the replenishment of the new ink. This problem does not exist when using UV inks, but it must be taken when using water-based inks