The hottest pad printing ink and printing quality

Pad printing ink and printing quality

in pad printing process, ink is often considered to be the most critical factor affecting printing quality. However, the control of other factors is also very important. Printers often attribute printing problems caused by other factors to ink. Sometimes they can't solve the problem in a few hours, mainly because they ignore other variables such as mechanical settings, environmental conditions and so on. Therefore, the printing staff should thoroughly understand the pad printing process and the role of ink. When problems occur, all factors affecting the quality should be taken into account, rather than blindly looking for ink problems

1 type of pad printing ink

the ink specially used for pad printing is different from general solvent based ink, water-based ink and UV curing silk printing ink. Although pad printing ink and screen printing ink have some similar characteristics, they still have great differences. Different from silk screen printing ink "I believe that the drying speed of pad printing inks is faster, which is also the most prominent feature of pad printing inks. At the same time, pad printing inks are often printed on thin films, which makes pad printing inks vulnerable to some factors such as temperature, humidity and static electricity. Inks specially prepared for pad printing include single component inks, two-component inks, drying inks, oxidation inks and sublimation inks.

1) single component inks

One component ink (also known as solvent. Dr. Timothy Weber, vice president and general manager of HP 3D materials and advanced utilization, said, "the total market for 3D printing is about $5billion to $6billion volatile ink) Drying depends on solvent volatilization. This kind of ink does not have to add catalyst. There are two kinds of one component inks, gloss and non gloss, which are mainly used for the printing of plastic substrates

2) two component ink

two component ink is also called chemical reaction ink. Before printing, catalyst must be added, and the catalyst reacts with the resin in the ink to achieve the purpose of ink drying through polymerization

when using two-component ink in pad printing, it is necessary to add a certain ratio of catalyst, usually measured by weight. The addition rate of catalyst must be strictly controlled. Adding too much will greatly shorten the "adaptation period" of the ink. Adding too little may lead to the ink not reaching the best drying performance during drying. Generally speaking, if the proportion of ink and catalyst is improper, it will lead to printing defects such as uneven ink adhesion and insufficient durability of printed images

3) drying ink

drying ink is divided into two types: one is to add another catalyst on the basis of standard two-component ink; The other is the ink specially prepared for substrates such as glass, ceramics and metals. Just like its name, baking ink must be heated and dried at a certain temperature. When using this kind of ink, we should calculate the drying time. The higher the temperature is, the shorter the drying time is. But too high the drying temperature will make the ink film brittle, so we should dry the ink at a temperature that can maintain the flexibility of the ink

4) oxidized ink

oxidized ink absorbs oxygen in the surrounding environment for polymerization to form an ink film, without adding a catalyst. Typical applications of oxidized inks are flexible packaging substrates and synthetic material substrates, such as rubber products or keyboards. Due to the slow drying speed and long time of oxidation ink, the amount of use is limited

5) sublimation ink

sublimation ink requires special processing in the process of use, that is, it needs to be heated after printing to make the substrate appear porous. In this way, when the dye contacts the heated substrate surface, the dye in the ink becomes gaseous, and then enters the surface of the substrate, which actually changes the surface color of the substrate. Once the substrate cools, the ink sticks to the surface of the substrate

the most common applications of sublimation inks are computer keyboard printing and those prints that require high oil resistance and wear resistance, which cannot be achieved by using two-component inks. Especially noteworthy is that sublimation ink actually changes the surface color of the substrate, so it is difficult to match the color of the substrate and the ink. Therefore, the color of the substrate must be lighter than that needed for the final printing, because the color change of sublimation ink on the surface of the substrate with darker color is often not obvious

6) special inks and additives

pad printing special inks include edible inks, silicone resin inks, lubricating inks, corrosion-resistant inks, conductive inks and UV curing inks. The ability of these inks to quickly become sticky will determine whether they can effectively transfer the ink to the substrate surface. At the same time, in order to adjust the printability and performance of ink, in addition to adding solvents and catalysts, many additives may be used, such as viscosity inking agents, antistatic agents, rheology agents, etc. However, the use of additives will have a great impact on the printing performance of ink, so we must be careful when using

2 the first step in the pad printing process is to add ink to the etched concave area of the printing plate, which marks the beginning of the printing cycle (as shown in Figure 1). Some pad printing machines use open inking holes, while others use closed inking holes (such inking holes can prevent the solvent from volatilizing in the inking holes). At this time, the viscosity of the ink must be low enough so that the ink can spread smoothly on the surface of the transfer plate and enter the etched image area of the concave base extension copper industry chain

step 2: scrape the ink on the raised part (blank part) of the pad printing plate with an ink scraper, and only let the ink enter the etched concave image area. Because the solvent volatilizes rapidly, the ink on the surface of the image depression will be more sticky than the ink below

in the third step, according to the prompt of the system, the pad printing head evenly applies pressure to the rolling gravure and squeezes out the air on the gravure at the same time. At this time, because the viscosity of the surface ink in the image depression area is large, the ink can leave the etching depression area and adhere to the pad printing head

step 4: after the pad printing head leaves the pad printing gravure, the solvent in the surface ink of the pad printing head volatilizes, which makes the ink layer on the surface of the pad printing head become more sticky

step 5: when the surface of the pad printing head contacts the surface of the substrate, due to the high viscosity of the ink on the surface of the pad printing head, the ink leaves the pad printing head and adheres to the surface of the substrate. In this step, although the pad printing head may exert great pressure, the pad printing head is designed to be curved and elastic, so that the image can contact the substrate in a curved way rather than a flat way. In fact, the contact between a properly designed pad printing head and the substrate will not form 0. This can prevent air from remaining between the pad printing head and the substrate. If air remains in the image part, it will cause incomplete image transfer

step 6: the pad printing head leaves the surface of the substrate and returns to its original state. If the change factors involved in these six steps can be properly controlled, the pad printing head will leave the substrate cleanly. At this time, a complete pad printing cycle is over, and the pad printing head is ready for the next pad printing cycle

from the above six steps, it can be seen that a remarkable feature inherent in pad printing ink is that this ink has a prominent ability to become sticky, and the particle size and proportion of pigment are very different from other types of inks. In many pad printing, the depth of gravure etched images is 25 u TN, or even smaller. In this case, the pigment particles contained in pad printing ink must be smaller than most silk printing inks. In addition, because the ink film thickness of pad printing is about 20% of that of silk printing, the pigment concentration in pad printing ink must be high enough to obtain sufficient hiding power

since pad printing inks have very high requirements for viscosity changes, the volatilization rate of the solvent used in pad printing inks is much faster than that used in ordinary silk printing inks, otherwise it is difficult to obtain ideal printing effects

3 allocation of pad printing ink

generally, the ink manufacturer will give guidance on which substrate the ink is suitable for, but this opinion is only for reference. To choose a suitable ink, you need to understand several things: what kind of substrate to use; Whether the substrate needs pretreatment before printing; What color needs to be printed; Printing requirements such as abrasion resistance, chemical resistance and weather resistance of ink; And the recommended drying or curing method of ink

once the ink suitable for the substrate is selected, remember to mix the ink according to the method recommended by the ink manufacturer. Many ink manufacturers have provided a manual of technical data, which contains the catalysts, additives and solvents that the ink can be compatible with, as well as the correct ratio of ink blending. Many inks are blended by weight rather than volume, so it is best to weigh accurately with a digital instrument with a weighing accuracy of at least 0.1 G. If color matching is to be carried out, an instrument accurate to o.o1g should be used to weigh, so as to avoid the waste of ink in color matching test

the best time to dilute the ink consistency is to mix the ink and additives correctly. You can dilute it with a suitable solvent or a mixture of several solvents. Standard pad printing inks usually have many suitable diluents to choose from, including three diluents with fast, medium and slow volatilization speed. Ink manufacturers generally have a range value for adding diluents, generally adding diluents according to the proportion of% ink

deciding which diluent to use and how much to add is a guess for most people, which is actually incorrect. Before printing a batch of live parts, the diluent should be tested. First, adjust the printing speed of the printing machine to the required speed, and adjust the pressure of the pad printing head to look at the best state. Then it can be tested. First, add a diluent with medium volatilization rate, and take the middle value of the recommended range as the addition proportion. For example, if the recommended range value is%, add 15% diluent. Try printing several times to fully wet the etched gravure and properly expand the pad printing head. Try printing on the substrate at least 12 times, and adjust the pressure of the pad printing head if necessary. If the printed image has quality problems, the following two steps can be used to test

step 1: take an image printed at normal printing speed and turn off the printer. Check the image on the pad printing head and use a small mirror to observe the image under the pad printing head. Check whether the image on the pad printing head is complete and whether the image position is correct. If the image on the pad printing head is OK, continue with the second step. (Note: if the image part on the pad printing head is lost, or the image edge looks jagged, generally speaking, it is because the ink is too thick. Add a certain amount of diluent, and repeat this work until an acceptable image can be obtained on the pad printing head: if the image position on the pad printing head is found not at the position it should be,

adjust the position of the pad printing head.) Step 2: if there is no problem with the image on the pad printing head