The use of servo drives on pad printers is increasing at the high end of the pad printer market. This is especially true when you have a series of print jobs. Recalling past assignments is a simple matter of typing in code to make the appropriate settings. Today, the feed mechanism is very precise, and the user of the pneumatic transmission system sees the position tolerance actually disappearing when he starts using the servo drive system. If your factory cannot afford a servo-driven press, consider the servo-driven feed system, especially the shuttle feed system.
Another area of ​​growing interest is the use of UV-curable inks in pad printing. UV-cured screen printing inks do not contain solvents, and UV-curable inks used in pad printing must contain solvents. Conventional solvent-based pad inks contain about 60% solvent, while UV-cured pad inks contain 30% solvent. The manufacturer cannot remove the solvent from the ink yet because the volatilization of the solvent makes the surface of the ink tacky enough that the ink can be adhered by the printing silicone rubber head from the etching site of the printing plate and the substrate can be used by the substrate during the pad printing process. Pull down from the print head.
Solventless printing UV
The study of ink depends on the difference in surface energy between the print head and the surface tension of the ink, followed by the difference between the surface tension of the ink and the surface energy of the substrate. Correct and consistent balance between these elements has proved to be very difficult. Air conditioning must be installed in the workshop to control the surface temperature very accurately. The viscosity of the ink and its shear properties also play an important role. In addition, the ink must be cured between the two inks. The use of inks in pad printing is too small to make ink manufacturers feel that investing in research and development of UV pad printing inks is also not feasible.
UV printing inks have a large target market. In general, pad printing applications require the parts to be transported soon after printing, and the ink has excellent chemical and mechanical resistance. This kind of operation belongs to the category of commonly used two-component solvent-based inks.
Pad printing inks are also suitable for four-color printing. Unfortunately, for the CD market, they came too late, and the CD market has turned to rely on screen printing and no horizontal printing. This does not mean that the CD market does not provide future opportunities for printing, but that the printing method also has to cope with competition from digital printing. Digital printing is cutting into the low-intensity CD market.
UV inks must be cured with a high-intensity UV light source. This curing system is generally installed above the conveyor belt. UV light sources, on the other hand, can be installed in fully automated feed systems. The print must be irradiated with UV light of a specific intensity for a certain period of time to properly cure the ink. In addition to many professional equipment manufacturers who have served the printing industry for many years, ink suppliers often supply cured parts.
If you print UV inks on different parts, you must be able to change the height of the UV light source to focus the UV output energy on the ink layer. Of course, if the reflector beam is a wide beam, this is not necessary. However, the duration of the exposure needs to be changed to ensure that the ink layer receives the proper amount of UV energy to achieve full cure.
Depending on the application, it may be more expensive to use an infra-red element before the UV curing stage to fully drive a servo motor. If you have not budgeted, consider choosing a pneumatic pad printer and combining it with the servo drive part movement system to achieve accurate positioning line warm-up (Figure 3). This can often drive off the residual solvent and help the ink smooth the surface before curing. Otherwise, the UV curing process is so fast that when the dots are printed, the surface of the ink layer may be rough.
Although some trials are required before using UV-curable inks, they also bring several benefits to printing, including the following:
1. Reduce the solvent content;
2. When the ink is exposed to high UV energy, the ink layer is actually cured or polymerized instantaneously (in fact the pad printing produces a thin layer of ink that helps to speed up the curing process);
3. Less energy consumption than infrared or hot air drying;
4. The cured ink layer has good chemical resistance and mechanical resistance;
5. Printed parts can be transported almost immediately after printing.
As with any ink, it must be tested before production. UV-curing inks require a surface energy of the substrate of at least 48 dynes/cm (1 dyne = 10-5N) for good adhesion. You must also follow the health and safety instructions on the material safety data sheet and product label.
UV curing inks have been used in the screen printing industry for many years. One problem that has gradually emerged is that screen printers who are exposed to these inks for a long period of time will become hypersensitive to such inks. The result is that they experience adverse reactions when exposed to UV inks, much like severe allergies. So they can no longer use UV curing ink.
Wearing suitable personal protective equipment is a must for UV ink users. Nitrile rubber gloves are very suitable for hand protection. In addition to the solvent added for ease of pad printing, UV inks do not run out of steam. Except for high UV energy, the ink does not dry out, and if it splashes on clothes, it is still not dry. In this case, you should change clothes.
Also keep in mind that UV-curing inks usually produce ozone, which is a toxic gas that must exit the pressroom. Oxygen rapidly decomposes in the discharged airstream. Before the closed oil boom became popular, the author used UV-cured ink for pad printing for the first time many years ago. Since then, ink technology has advanced, the curing system has become more reliable, and the ink has become more stable in the oil. If UV pad printing inks are used in open pan systems, a small amount of solvent must be added to achieve the correct balance of solvents in the ink.
Technical data sheets for UV inks can be obtained from ink manufacturers and their recommendations must be followed. When it comes to solvent-based inks, they have a wide latitude when they become dry. There are few UV curing ink variables and good process control is critical, otherwise the ink performance will not be good.
Another point to note is that the surface energy of the substrate should be 48 dyne/cm (1 dyne = 10-5N) or more. If one layer of UV-cured ink is printed on the other layer, or the first layer of ink is completely cured before the second layer is printed, the adhesion between the ink layers will not be good. This is because the surface energy of the fully cured UV ink layer is low, which prevents the second layer of ink from adhering well. Some additives can be added to the ink to improve adhesion, but my advice is to print the second layer of ink within 4 hours after printing the first layer of ink. Although the UV-cured ink immediately changes from liquid to solid upon exposure to a UV light source, polymerization within the ink layer persists for 24 hours.
Today's UV-curable printing inks are a vibrant commodity that is available from most major pad printing inks and machinery suppliers. You must understand the required operating procedures. If you adhere to these requirements, when printing with UV inks, different sizes and shapes of parts need to adjust the height of the UV lamp when the curing system collects UV energy, using a reflective device with a wide energy distribution (parabolic or For a polyhedral system, by adjusting the exposure time instead of the height of the lamp, an appropriate curing effect can be achieved and good results can be achieved.
Combination of pad printing and laser marking
Many pad printer suppliers are now focused on selling laser marking systems. There is a very clear coordination between these two technologies. Product markings that do not use ink have a sharp edge on the laser marking compared to conventional impact marking and chemical etching. The latter two technologies are common in the market for tools (blade, saw blade, etc.). Laser marking is fast and accurate. It can process many different materials. It involves certain plastics, including materials that change color when exposed to laser light. This system can be used to remove lacquer on parts such as automotive gauges and displays.
The most obvious combination of pad printing and laser marking is the production of printing plates for pad printing. Lasers are commonly used to etch steel printing plates and less durable metal foil plates. The laser is mounted directly next to the pad printer and images the foil plate that enters the pad printer.
After the pad printer prints the desired number of impressions using the plate, the plate is angled by the platen, and a new plate is then sent to the pad printer. This excellent system produces short-lived, high-quality pad printing images with lot numbers and date codes for circuit breakers.
This system may use continuous encoding or generate discontinuous images. However, these applications require the use of a large number of plates, the cost of which must be justified by the final print price.
Another application of laser marking and pad printing is when you want to decorate metal surfaces with permanent markers and fill them with pigments. In this case, the laser generates ablation marks on the metal surface, and pad printing fills the ink with this trace. This method has long been used in some modern faucets and washing room components, where the "hot" and "cold" logos are painted in red and blue, respectively.
Consideration for the future
Where will the printing industry go next? My guess is that some high-end pad printing applications will be combined with Cartesian robots (moving spindles with their linearized robots) and inkjet printheads. These robots move a digital print head over a tangible object, moving as the outline of the object moves and printing the desired strip image. The quality of the printed image depends on many parameters, but the main one is the size and resolution of the software and inkjet printheads. The positioning accuracy of this automatic device can reach ±0.001mm. These devices can even be equipped with video systems and programmed on the Internet. Users often discuss with me information about direct digital printing systems for irregular objects and containers. Although I do not currently have such systematic information, I know that they are being developed.
The effect of inkjet printing on pad printing and any other analog printing method can easily become fantasies. However, in addition to the low-cost semi-automatic machines that are currently available, there is still a full manual pad printer market.
Why does inkjet digital printing replace pad printing?
No, at least not completely. The reason for not including the fact that only a limited range of ink chemicals can be ejected through the nozzles of inkjet print heads, in contrast, the pad printer can use a variety of different ink systems to suit the many prints it can print The object is suitable for the use environment of the print.
At this moment, any kind of print job involving irregular parts is best suited for pad printing or other simulation methods such as screen printing, hot embossing, thermal transfer printing and in-mold molding. Digital printing of complex three-dimensional objects will eventually have a proper place in the market, but only time will tell how much it will occupy.
The fact is that as the demand for color printing in this area continues to increase, the opportunities for printing technology will continue to increase. The real question is whether those opportunities will occur in mature economies or in developing countries. We hope that Both are.
Reprinted from: China Printing and Packaging Network