This time, I pondered the use of the word "Coater", which is not very appropriate. "Coater" is not an official usage, but it is better understood as "coating a mechanical device." The so-called "Coater" seems to be an industry term.
"Coating" on offset printing generally refers to the process of applying a transparent or translucent liquid to a printed product.
2 Varnish
Varnish can be roughly divided into 4 types:
1) Oily OP (Overprint) Varnish;
2) UV (Vltea Violet) OP Varnish;
3) waterborne varnish;
4) UV Varnish.
The so-called OP Varnish refers to the Varnish used in the printing unit ink fountain. Of course, the coating thickness of the varnish is approximately the same as the thickness of the ink (about 1 μm). According to its base inks are oily inks and UV inks with the corresponding oil OP Varnish and UVOP Varnish. Occasionally, the combination of oil ink and UVOP varnish is used. In many cases, the purpose of protecting printed materials is for their use.
Waterborne varnish and UV varnish are varnish used on Coaters. The film thickness of the varnish (before drying) can be more than 3 times (3 μm or more) than the OP varnish. Therefore, it is easier to obtain gloss than OP polish, and it is mostly used for the purpose of high gloss. After the final drying process, the film thickness and gloss change. This article will talk about the varnish used on the coater coater (waterborne varnish and UV varnish).
3 Purpose of Coating Varnish
As mentioned earlier, there are roughly two purposes for coating varnish, namely, “protecting printed matter†and “adding gloss to printed matterâ€.
4 Waterborne Varnish
In literal terms, because it is a water-based gloss oil, it contains more water. After printing with oil-based ink, varnish is coated on the substrate in-line and evaporated by evaporation with heat energy from an IR (Infra Rad) dryer. After the printed product comes out of the delivery section, the varnish and the underlying oily ink are not completely dried. Finally, they are left for several hours and completely dried by oxidative polymerization.
As the word “evaporation†is used in the drying process, most of the waterborne varnish is vaporized without leaving it on the paper, so the final product's light film layer becomes thinner and does not hold too much of its luster effect. hope.
5 UV Varnish
The UV varnish is generally printed on a UV ink layer, and is cured by a UV-curing device emitting ultraviolet rays and a photopolymerization initiator contained in the UV varnish chemically. The difference between the UV varnish and the varnish is that "instant cure" and "the varnish volume is basically unchanged." Regarding the volume problem, although the chemical reaction will have a volume shrinkage of 1% to 5%, compared to the waterborne varnish, the final product has a thick gloss layer and can be expected to have a better gloss effect.
6 Application and Flexible Application of Waterborne Varnish and UV Varnish
Did the above say: "Because UV Varnish is better, so the work is done with UV Varnish, OK" What is the reality? The reality is that in terms of penetration rate, Varnish is higher than UV Varnish. Why is this?
1) Cost
It can be imagined that this factor accounts for the largest proportion. Compared with the general price of waterborne varnish of 600 yen/kg/40 RMB/kg, UV varnish is 1800 yen/kg; it is 3 times the price. Because the price varies due to factors such as the amount of light oil purchased by the manufacturer, it is hoped that this will serve as a reference.
2) Glossiness
Although the gloss of coating products varies significantly depending on the type of paper and varnish used, the coating speed of the varnish, etc., but generally, the gloss of the varnish is less than 60, while UV Varnish gloss is about 80, when the product is mainly used gloss gloss UV light oil. However, in the case of waterborne gloss oils, glossiness of about 80 can be obtained if light is connected after printing.
3) Post-printing wear resistance
Since UV varnish cures instantaneously, it has the advantage of increasing surface strength. Conversely, products using UV coating produce so-called lacquer cracks during the bending process. Therefore, UV varnishes need to be fully verified before they are commercialized. Waterborne varnish is often used where there are concerns about varnish cracking and the prevention of post-printing process flaws.
4) Spray-free powder
For printing products related to foods, pharmaceuticals, etc., there is a case where dusting is not suitable from a hygienic point of view. If you use UV Varnish, you don't have this problem, and sometimes use Varnish based on specific conditions.
7 Varnish coating method
The varnish coating method is a flexographic printing method that does not use a printing plate. Therefore, it is basically a full-page printing method. However, in the case where only the image portion is glazing or the paste portion and the date portion are not polished, it is necessary. Cut the blanket or use a solid resin plate.
As a way to provide lacquer to blankets, nearly all manufacturers have recently adopted sealed ink chambers. The chamber is literally translated as a “small houseâ€, in which the varnish can be recycled and the varnish injected into the cells of the anilox roller surface. Varnish on it is transferred to the blanket and finally printed on the substrate.
8 Factors for determining the quality of glazing
According to the purpose of application of glazing, although there are many factors that restrict its quality, what we hear most often in the ear is "gloss." Here we will focus on UV glazing with a gloss of about 80.
1) The thickness of light oil accumulation
In the foregoing, an ink-type glazing device was introduced. In this type of device, an anilox roller needs to be replaced in order to change the thickness of the varnish. The accumulated thickness of the varnish is determined by the number of lines of the anilox roller (line/inch, ie, the number of cells per inch). According to the company's experience, 80 to 300 lines/inch anilox can be selected for the line of the offset press, 80 lines/inch screen is used for the upper layer of lacquer, and 300 lines/inch screen roller is used for the upper layer. Varnish. Of course, a "sawtooth" sensation occurs when the thick lacquer is applied. This is because at this time, the openings of the cavities are enlarged, so the smoothness is reduced.
2) Smoothness
As described above, an anilox roller with a small number of screen lines can accumulate a large amount of lacquer, but the smoothness is reduced. In order to increase the smoothness, it is a method to grasp the gloss oil from the time after coating to curing.
First, consider the method of lengthening the distance between the glazing unit and the UV lamp. However, this method is limited by the installation space, and each printing machinery manufacturer is similar in this respect. Followed by the method to reduce the printing speed. In this case, the efficiency of production must be ignored. A further method is to use a lower viscosity varnish or to warm the varnish to reduce its viscosity.
9 Varnish Design
In recent years, not only lusterless varnish but also embossed varnish with a matte tone has been used. The varnishes used include UV embossed UV OP varnishes and embossing embossed glazing UV glazing varnishes, which are mutually exclusive properties. The part where the OP varnish and the transparent varnish are overlapped has an embossing emboss effect (viewed with a magnifier and has a similar state in which the water droplets are solidified), and other parts that are only transparent varnish are processed with the usual gloss effect.
The business benefit of this process is that, due to the contrast between the transparent varnish part and the frosted part, the varnish part can be clearly seen. Advantages in production: Since the image portion is determined by the OP optical oil, the resin plate can be used without the use of a resin plate, and it can be realized by partial polishing.
10 Market expansion
The technical foundation of glazing has been built more than 20 years ago. It is not the most mainstream technological innovation project in recent years. Why did the coating become today's topic? The biggest reason is the change of the market. Japan's printing companies are extremely confused by the drop in wages (extremely the collapse of the price system). Therefore, in order to be able to avoid price competition, we are always devoted to the glazing process as a "separate technology" for our own company. In particular, glazing can design solutions that cannot be printed with oil inks. As a result, the shinning market is likely to continue in the future? The author looks forward to this.
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