Ten factors affecting the dry speed of UV inks are worth exploring
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Known as the ink first, and exaggerated the "non-polluting, fast light, energy-saving" UV-curable ink - referred to as UV ink. The ink has been in existence for 30 years since its inception. When people talk about their characteristics, they always beautify their advantages and seldom blame their shortcomings (such as cleaning, removing ink, and not being able to reproduce and reuse). After focusing on this issue, the author visited several packaging and printing manufacturers in the north and south of the Yangtze River and summarized them as the top ten factors affecting the speed of UV ink drying. It is necessary for the packaging and printing industry colleagues to discuss and exchange again to make up for the printing process. The top ten flaws. Uncover the "red hijab" of light-curing packaging printing inks, let us analyze them one by one.
1 ink inhaled water
Naturally, the water is inhaled, mostly caused by the environmental humidity during storage and use, especially in the workshop and warehouse. It is also artificial, like the use of silk screen, offset ink, for a moment to forget to cover the cover or intentionally inject water to prevent dry skin and added. The intention is to isolate the oxygen in the air by water and prevent the crust from drying out. I don't know if the product is UV-free and will almost never cure and dry.
2 Ink imbalance
Ink and water balance is well known. But the specific point is that the PH value of water is equivalent to the pH of the ink, that is, the abbreviation: ink balance. Otherwise, it is not a water color oil, that is, oil color water (here referred to as offset printing) forms an ink emulsification phenomenon, which causes the UV ink ink film to be opaque, directly affecting the passing rate of ultraviolet radiation light energy. Thereby slowing down the film drying time, even though the light is solid, there is still water in the ink film. When the ink film is formed, once the film is rubbed or glued, the ink film is found to be pulled off. phenomenon.
3 lamp maintenance
We have long known that the general service life of UV lamps is about 1000 hours, which means that it is limited. This not only affects the light intensity but directly affects the drying and curing time of the UV ink. In addition, the impurities of the ink and the dust splash in the production process will weaken the light intensity in the ultraviolet region, thereby greatly reducing the light curing ink. The drying time, which is generally required to clean the dust frequently and cover the ink tank (bucket) is beneficial.
4 photosensitizer and initiator dosage
Participation in UV inks and catalytic drying (curing) are photosensitizers and initiating crosslinkers. Usually, people only pay attention to the wavelength of the pigment and ignore the printing inks of different viscosities and different degrees of purity to scientifically select different photoinitiators or cross-linking agents. For example, benzoin is different from benzophenone because it is both a photosensitizer and an initiator. The author recently used the 16IS ink of Zhejiang Songhua Ink Co., Ltd. in Qingdao Ideal Technology Printing Co., Ltd. in Shandong Province to cure and dry on the electrostatic PVC film. When 1% benzoin or 13% 907 photosensitizer was added, the dry speed was almost doubled.
5 Temperature and substrate tension
Around this issue, people seem to have little communication. It is often overlooked. The author verified this from the feedback from Mr. Ye Jianxing from Xiamen—low temperature, slow photocuring, high humidity and small tension of the substrate. The ink inhaled water molecules and caused the ink film to become mixed and imaginary, which greatly hindered the frequency of radiation energy. And will delay the exposure of the ink and affect the binding energy of the ink and the substrate.
6 color purity and dosage of ink system
With the fluctuation of the gray balance of the pigment, especially the decrease of the color purity and the increase of the amount and the fineness of the grinding dispersion, the method of color chemistry of the printing ink is not grasped, and after the pursuit of "color juxtaposition", it is not red. It tends to purple, that is, yellow tends to green; not yellow tends to orange, or green tends to blue... We artificially set a barrier to the drying of light-curing inks. Although the printing operator even designs and proofs only pursues "color juxtaposition", ignoring the juxtaposition of adjacent color (ring) phases hinders the enhancement or weakening of the effect of color matching on light curing, that is, although it can form a A new sense of color, but from the retinal nerves of people's eyes. We can only design the color juxtaposition just right when we understand the law of color grading. Otherwise, it is impossible to control the color purity and the thickness of the ink film to achieve uniform uniform drying of a multi-color.
7 Substrate and printing ink
Three types of substrates that absorb light or light that transmit or reflect light energy. Light-transmissive materials are superior to light-absorbing materials, while light-reflecting materials are secondary. In addition, there is also the transparency of the ink, especially by the viscosity, and sometimes the transparency of the substrate. The opaque or high-viscosity ink is weakened by the light energy, and sometimes the voltage is low and the light intensity is weakened. The speed of light curing.
8 mechanical or manual printing speed
Different mechanical printing or manual screen printing speeds have an optimal method of light curing. We have different printing runs at 2500 rpm, 3000 rpm, 3500 rpm to 8000 rpm and pass through the UV irradiation zone, but the drying speed is different at 800 °C on the same lamp surface. Although there is a distance between the lamp and the substrate, it also directly affects the formation of the ink film of the photocurable ink.
9 ink printing color sequence
Light-curing inks generally stipulate the order of printing, that is, the color sequence. The scientific color order is determined by the wavelength in the ink system. Printing inks such as lead printing and offset printing are arranged in accordance with the three primary colors, while photo-curing printing inks are strictly in accordance with their wavelengths. Otherwise, it is difficult to achieve uniform drying after light curing, especially the gray balance of the hue.
10 resin in the ink system
Whether we use a binary resin or a ternary or quaternary resin for unsaturated synthesis. Generally, an acrylic resin having a crosslinking monomer is used, and the epoxy resin has a short photocuring time under the same conditions. We will not explore why, we will often bring people an illusion - the same content, the same viscosity, the same printing method, the same number of UV lamps, the same light intensity, the same light energy, but should also face up to whether it is still With cross-linking ingredients? Is the transparency of the resin the same? Whether or not, etc., will harden the ink film at the same time. For example, different glycols, only neopentyl glycol as an unsaturated photocurable binder (resin), will greatly increase the photocuring speed by about three times. Also in this system, the addition of a tetrahydric alcohol (such as pentaerythritol) will improve the gloss of the UV-curable printing ink, the hardness of the ink film, and the like, and has already attracted people's attention.
In a device that normally passes through three ultraviolet tubes, electrical energy is converted into high-intensity ultraviolet rays, and the coating is irradiated to form a film by photocuring. In addition to the above ten factors, the ultraviolet wavelength and light intensity emitted by the UV lamp are also important factors affecting the speed and quality of curing. To this end, we have to know in practice, to transform in the understanding, and to further improve the curing speed of photocurable inks, which is the goal that the packaging and printing industry prays for.