Exploring the difference analysis of UV printing quality（part1）
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In addition to discussing inks, this paper also discusses the relationship between printing presses and dryers to find out the best quality evaluation of the printing process.
First, introduction
With the advancement of printing technology, the printing quality is gradually becoming faster. However, in the process of rapidization, some problems occur, such as drying. UV inks have better drying conditions than other conventional inks, so UV inks can be used in a wide range of printed materials and in various layouts. From this point of view, in the future printing trend, UV ink will occupy one of the various seats in various inks. Due to the wide range of applications of UV inks, the speed of the rotary lithography, the large amount of production, and the wide range of printed materials on the screen are discussed. How to effectively obtain the best quality must be analyzed with cost, quality and product value.
Second, the source of UV ink [UV ink]
1, the history of UV ink development
The idea of using ultraviolet light to illuminate the ink to completely dry and harden in just a few seconds has been proposed in 1994. It was not developed until 1960 by a British company. UV inks were initially unrecognized because the UV inks emphasize the fast-drying and solvent-free all-solid components. At the time, there were no better conditions at all compared to other inks. But UV inks are very popular in the screen. Due to screen printing, the printing speed is not faster than other types of printing. Strictly speaking, the printing ink film is particularly thick and naturally takes a long time. The main reason is "solvent". This one thing. And the shortcomings caused by the solvent in the screen, such as the ink plug net can not be printed, only because the solvent evaporates in the mesh to dry out; the ink is too hard to print and the ink is too thin and can not be printed, all caused by solvent . In short, the problems brought about by the "solvent" of the industry will be very troublesome. Therefore, the two characteristics of UV ink solve the problems plagued by the screen printing industry, and the industry is still too slow to develop UV ink.
2, the characteristics of UV ink
[1] Convenient and low inventory: The new UV ink can be mixed with only four basic colors, and the thickness of the printed ink film is thin, and the required ink volume is reduced, so it is very simple and the inventory can be reduced.
[2] Opacity is easy to control: pigments or pigments can be added to the extended base to achieve the desired brightness.
[3] Color matching ability: When the pigment is added to the extended group to obtain appropriate viscosity, hue and lightness, it can be blended with extremely rich colors. As long as two or more kinds of basic colors are mixed, various desired colors can be obtained.
[4] Ink province: Since the composition does not contain solvent, it only needs to be between one-third and one-half of the traditional one. The amount of ink can be used to obtain the desired effect.
[5] The inking roller and the printing plate are not blocked: the unexposed ink can be dried for at least 48 hours even on the ink roller or printing plate, so there is no need to worry about the crust or plate blocking on the roller. .
[6] Ink: Only three-quarters to one-fifth of the electricity cost of traditional ink stoves can be dried.
[7] Gloss: The gloss of UV ink is very good, and special treatment can be achieved to achieve special effects.
3, UV ink compared with traditional ink
The biggest difference between UV ink and traditional ink is its constituent molecules. It is an all-solid tissue form that is solvent free. And its media, pigments, resins and other chemicals are different from traditional inks. Conventional inks contain solvents [40%-60%], and the ink dry film blended with the blending agent, pigment and additives is left after the solvent is completely evaporated. The pigment and resin systems of UV inks do not have the same high brightness and opacity as traditional inks.
4, the advantages and disadvantages of UV ink
UV is a type of electromagnetic wave, and UV ink uses UV radiation energy to achieve its drying effect. There are many kinds of UV dry solid systems, but the principle is based on the chemical reaction caused by the sensitizer absorbing high-intensity ultraviolet [UV]. The sensitizer is a chemical product with special reaction ability, which can convert light energy into chemical energy and instantly solidify different mixtures. But the most important point is that the energy of the UV light used is six hundred times that of the domestic fluorescent lamp, so it will not dry out immediately due to the sunlight in the environment.
[1] Advantages
1. Volatile organics: Most UV products contain little or no organic solvents.
2, improve the quality of the finished product: through the polymer high-density cross-linking combined with [Crosslinked] the resulting structure, not only has a high degree of toughness [Toughness], and thus get stain resistance [Stainresistance], anti-wear [abrasionresistance] And the characteristics of the antisolvent [Solventresistance].
3, low energy demand: a typical radiation dry solid production line consumes energy, only 25% required to use thermal energy to dry.
[2] disadvantages
1, "line of sight" type of dry solid: UV products usually only dry under UV direct sunlight. 2. Difficulties in drying solids containing pigment systems: UV has difficulty penetrating thicker pigmented coatings. In general, only EB has a good effect, and recent research and development in chemistry and light energy has improved the effect of UV on products.
3. The raw material price is too high: the current high raw material price is due to the small market, coupled with the high amount of research costs, resulting in higher product unit prices than traditional products. It should be noted here that UV products are 100% solid, unlike traditional inks, coatings and adhesives containing volatile solvents.
4, dry solid equipment [curingunit]: the cost is too high, the basic equipment investment price is high.
5. Possible dangers of UV products: Most UV products can be considered skin irritation before they are dried. However, these products, because of the low volatility, can maintain the habit of wearing skin care gloves and eye protection during operation, which will reduce such problems.
6. Poor adhesion: Generally speaking, compared with traditional products, some materials, including steel sheets and aluminum sheets, have poor adhesion, chemical improvement and post-baking treatment [post-Baking] Can eliminate some of the problems of poor adhesion, but also reduce the stress [stress] caused by shrinkage during the dry process.
Third, the factors affecting the quality of UV printing
The first step to consider before printing is the design. The design should first think of ink, because any printed matter is the effect of the ink on the cured film of paper or other kinds of printing materials.
1, the ink aspect
[1] UV ink storage period is not long: the current UV ink storage period is not long, because UV ink is more likely to produce gelation and deterioration.
[2] Ink film thickness and transparency of UV ink: The thickness of the ink film is too thick, which also affects the speed of UV light irradiation, resulting in hardening of the ink. As for the transparency of the ink, the transparent UV ink is much faster to dry than the opaque UV ink. In the ink, the speed of UV light irradiation is not only faster, but also a more uniform relationship. For example, the color with the fastest hardening speed is blue in color four-color printing, followed by magenta and yellow. The black ink hardens at a very slow rate, and the hardest to harden is opaque white. Not only that, opaque white will have a yellowing tendency under the illumination of UV light.
2, the printing machine
In terms of screen printing, the layout depends on the printed matter, and there are different printers.
The main topic discussed in this paper is the screen printing lithography. Separate pre-press and post-press, for factors that may occur during printing.
[1] scraper
1. The hardness unit of the hardness scraper blade surface is generally measured by a hardness tester of JIS [Japanese Industrial Standard]. If the hardness of the blade surface is larger, the contact between the blade surface and the plate surface is smaller, so it is suitable for the printing high, the tangential line is sharper and smaller, and the ink is printed thinner. On the contrary, the softer the blade surface, the larger the contact area, and it is suitable for a thick and rough, monotonous print pattern. The distinction is as follows: special soft 45 degrees to 55 degrees, soft 55 degrees to 65 degrees, medium 65 degrees to 75 degrees, rigid 75 degrees to 85 degrees.
2. In terms of width, the width of the blade must be larger than the width of the print and smaller than the width of the frame, so as to meet the printing requirements. However, in order to require quality and reduce the occurrence of print distortion, the consideration of the width of the blade is still based on the basis of the width of the print and the width of the frame.
A. In terms of frame position: Of course, the width of the scraper must be smaller than the frame to be printed. In the ideal situation, the smaller the width of the blade, the better the distance between the left and right ends of the blade and the frame, because in this state, the mesh can be printed. The softness is in contact with the printed matter, and the stretch of the mesh is also small. On the contrary, if the distance between the scraper and the frame is too small, the mesh is too stiff, causing the angle of the mesh at both ends of the scraper to be too large, causing the shape to be distorted, which is the main cause of the distortion of the print. Generally speaking, for every 10 inch increase of the scraper, there is a 100 micron error, and the width of the scraper is preferably not more than 50% of the size of the frame. If this requirement is not met, at least the ends of the scraper are separated from the frame. The distance must be 5 cm to guarantee the printing quality.
B. In terms of print position: Generally, the width of the blade must be 2 to 10 cm larger than the width of the print. The reason why the width of the blade is smaller is better, and the size of the print must be selected. If the ink return knife is used, the width of the ink return knife should be wider than the width of the printing blade, so that the ink overflowed at both ends of the printing blade can be completely transported back.
3. the speed of the printing and the angle of the printing speed and angle, mainly affect the amount of ink through the mesh to reach the printed matter. When the printing speed is fast, the ink is less and thin, and the slow printing speed is more transparent and thicker. However, if the printing speed is too fast, the thickness of the ink is insufficient, and the printing is unclear, and if it is too slow, the ink is easily bleed, so that the printing is not sharp enough. Generally, the printing speed is about 60 to 200 cm per second, depending on the conditions at that time. The angle of the squeegee also affects the amount of ink discharged. When the angle is small, the amount of ink is large. When the angle is large, the amount of ink is small. Generally, the angle is between 45 and 75 degrees. When scratching, you must pay attention to the uniform speed requirement, and the angle must be consistent, so that the ink will not be different in the same printed matter.
4. [1]Scratch pressure: First of all, we must understand the concept that screen printing does not rely on the pressure of the scraper to press the ink onto the printed matter, but pushes the ink by the scraper to generate hydraulic pressure inside the ink. Through the mesh, and the adhesion between the printed matter and the ink, the purpose of printing is achieved. Therefore, the printing pressure should be as light as possible within the range as far as possible, and the blade surface can be in line contact with the printed object, otherwise the printing pressure is too large. When the printing pressure is not enough, the printing is inevitably impossible. When the printing pressure is too large, not only the extrusion amount of the ink does not increase, but the tip of the blade is excessively bent, so that the printing surface is in surface contact with the printed matter, resulting in printing. It is not clear, and the blade is worn out and the printing film on the layout will be peeled off.
[2] mesh
In terms of the selectivity of the screen printing, most of the objects that are not easy to absorb the ink are mostly due to the slow speed of the printing. Therefore, the development of the ink is going in two directions. One is a solvent containing ink. After printing, the solvent evaporates to fix the ink on the printed body. However, because the solvent is harmful to human health and causes pollution problems, the ink develops in the other direction. Or heat to fix the ink to reduce the occurrence of pollution. However, the ink is fixed by light or heat, so the thickness of the ink film must be very thin. Therefore, a thin mesh cloth is required to obtain a good effect, but the price of the thin mesh is relatively expensive, so that a kind of development is developed. Pressurized calendered mesh, suitable for drying UV inks, is called UV mesh.
1. Advantages The UV mesh of the general mesh can be used to replace the mesh of high mesh, which reduces the cost.
2. Disadvantages After the mesh is flattened, the shape of the mesh is slightly uneven, which affects the linearity of the edge of the print, and is not suitable for fine printing.