Summary
Because the printing production methods, inks, and technologies in the island are changing rapidly, and then considering the future trend of environmental protection, it is necessary to consider high speed, high quality and no pollution on the printing press. In addition to the discussion of ink, this article also includes the discussion of the relationship between the printing machine and the dryer, and finds the quality evaluation of the most suitable printing process.
I. Introduction
With the advancement of printing technology, printing quality is gradually becoming faster. However, during the rapid process, some problems occurred, such as drying. UV ink has better drying conditions than other traditional inks, so it has a wide range of printed materials and can be used in a variety of formats. From this point of view, in the future printing trend UV ink will occupy a large seat among various inks. Due to the wide range of application of UV inks, the two types of layouts are discussed for the fast speed and large production of rotary lithography, and the wide range of printed materials for screen printing. How to effectively get the best quality [Figure 1] must be analyzed with cost, quality and product value.
Figure 1
2. The origin of UV ink [ultraviolet ink]
1. Development History of UV Ink
The idea of ​​using ultraviolet rays to irradiate the ink to make it completely dry and hard in just a few seconds was proposed in 1994. It was not until 1960 that oil was successfully developed by a British company. At the beginning, UV inks were not taken seriously, because the characteristics emphasized by UV inks are quick-drying and solvent-free all-solid components. At the time, there were no better conditions compared to other inks. But UV ink is very popular in the screen version. Due to the screen printing, the printing speed is not faster than that of other format printing. Strictly speaking, there is a big difference, and the printed ink film is particularly thick, which naturally takes longer. The main reason is "solvent" This thing. And the shortcomings brought by the solvent in the screen, such as the ink can not be printed on the screen, only because the solvent evaporates in the mesh; the ink is too hard to print and the ink is too thin to print, all due to the solvent . In short, when the industry mentions the problems caused by "solvent", it will be very nerve-wracking. Therefore, the two major characteristics of UV inks solve the problems troubled by screen printers, and they also think that the development of UV inks is too slow.
Second, the characteristics of UV ink
[1] Convenience and low inventory: The new UV printing ink only needs to have four basic colors to mix into the desired color, and the thickness of the printing 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: You can add pigments or pigments in the extension base to achieve the brightness you want according to the standard ratio.
[3] Color Matching Ability: Adding the extension base of the pigment can obtain proper viscosity, hue and lightness, and it can be equipped with extremely rich colors. As long as two or more basic colors are mixed to obtain various desired colors.
[4] Ink saving: Because its ingredients do not contain solvents, it only takes between one-third and one-half of the traditional amount of ink to achieve the desired effect.
[5] The ink roller and printing plate are not blocked: unirradiated ink, even on the ink roller or printing plate, will not dry for at least 48 hours, so there is no need to worry about skinning or blocking .
[6] Ink saving: Only the traditional ink hot air stove electricity cost can be dried between three quarters and one fifth.
[7] Glossiness: The glossiness of UV printing ink is very pleasing, and can also be treated to achieve special effects.
3. Comparison between UV ink and traditional ink
The biggest difference between UV ink and traditional ink can be regarded as its constituent molecules. It is an all-solid tissue form and contains no solvents. And its agents, pigments, resins and other chemical agents are different from traditional inks. Traditional inks contain solvents [40% -60%], and the dry film of ink mixed with blending agents, pigments and additives will be left after the solvent is completely evaporated. The pigment and resin systems of UV inks are not as bright and opaque as traditional inks.
Fourth, the advantages and disadvantages of UV ink
UV is a type of electromagnetic wave, and UV ink uses the radiant energy of UV to achieve its drying effect. There are many kinds of UV dry-solid systems, but the principle is all about the chemical reaction caused by the sensitizer absorbing high-intensity ultraviolet [UV]. The sensitizer is a chemical product with a special reaction ability, which can convert light energy into chemical energy and instantaneously 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 immediately in the environment due to sunlight.
[1] Advantages
1. No volatile organic compounds: Most UV products contain little or no organic solvents.
2. Improve the quality of the finished product: the composition structure produced by the high-density cross-linking combination of polymers [Crosslinked] not only has a high degree of toughness [Toughness], but also obtains anti-fouling [Stainresistance] and abrasion [abrasionresistance] And the characteristics of anti-solvent [Solventresistance].
3. Low energy requirement: The energy consumed by a typical radiation dry solid production line is only 25% of that required for drying with thermal energy.
[2] Disadvantages
1. "Sight-seeking" type of solidification: UV products are usually only solidified under direct UV irradiation. 2. Difficulties with pigment systems containing dry solids: UV has difficulty penetrating thicker and pigment-containing coatings. Generally speaking, only EB has a good effect. Recent research and development in chemistry and light energy have improved the effect of UV on products.
3. The price of raw materials is too high: the current high price of raw materials is due to the small market, coupled with high research costs, resulting in unit prices higher than traditional products. It should be noted here that UV products are 100% solids, unlike traditional inks, coatings and adhesives that contain volatile solvents.
4. Drying equipment [curingunit]: The cost is too high and the investment price of basic equipment is high.
5. Possible dangers of UV products: Most UV products can be regarded as skin irritants before they are dried. However, due to the low volatility of these products, if you can maintain the habit of wearing skin care gloves and eye protection during operation, you will reduce such problems.
6. Poor adhesion: Generally speaking, compared with traditional products, some materials including steel sheet and aluminum sheet have poor adhesion, for chemical improvement and post-baking treatment [post-Baking] , It can eliminate some problems of poor adhesion, and can also reduce the pressure [stress] caused by shrinkage [shrinkage] during the drying process.
3. Discussion on the factors affecting the quality of UV printing
The first step to consider before printing is design. The design should first think of printing ink, because any printed matter is the effect of printing ink on the cured film of paper or other types of printing materials.
1. Ink
[1] The shelf life of UV ink is not long: At present, the shelf life of UV ink is not long, because the UV ink is more prone to gelatinization and deterioration.
[2] Ink film thickness and transparency of UV ink: If the thickness of the ink film is too thick, it will also affect the speed of UV light irradiation, resulting in difficult ink hardening. As for the transparency of the ink, transparent UV ink dries much faster than opaque UV ink. In the ink, the speed of UV light irradiation is not only faster, but also more uniform. For example: the color with the fastest curing speed is blue in color four-color printing, followed by magenta and yellow. The curing speed of black ink is very slow, and the most difficult to harden is opaque white. Not only that, opaque white also tends to yellow under UV light.
Second, the printing machine
In terms of the screen version, the layout differs according to the printed matter, and there are different printers. [Figure 2]
Figure II
This article mainly discusses the screen printing lithography. Separate pre-press and post-press to address the factors that may occur during printing.
[1] Scraper
1. The hardness unit of the hardness blade surface is generally measured with a JIS [Japanese Industrial Standard] hardness tester. If the hardness of the blade surface is greater, the contact between the blade surface and the plate surface is smaller, so it is suitable for printing high prints with sharper and finer tangents and thinner ink. Conversely, the softer the blade surface of the doctor blade, the larger the contact area, so it is suitable for thick, rough, monotonous printing patterns. The distinction is as follows: extra soft 45 degrees to 55 degrees, soft 55 degrees to 65 degrees, medium 65 degrees to 75 degrees, hard 75 degrees to 85 degrees.
2. In simple terms, the width of the scraper must be greater than the width of the print and less than the width of the screen 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 blade width still has its basis for decision. The positions of the print width and the screen frame width are discussed separately.
A. From the standpoint of the screen frame: Of course, the width of the scraper must be smaller than the screen frame before printing. In an ideal situation, the smaller the width of the scraper, the better, that is, the greater the distance between the left and right ends of the scraper and the frame, the better, because in this state, during the scraping process, the mesh can Soft contact with the object to be printed, the stretch of the mesh is also small. Conversely, if the distance between the scraper and the frame is too small, the mesh will be too stiff, and the angle of the mesh at both ends of the scraper will be too large, resulting in distortion of the shape. This is the main reason for the distortion of the print. Generally speaking, every 10 inch increase of the scraper has an error of 100 micron, and the width of the scraper is preferably not more than 50% of the size of the screen frame. If this requirement cannot be met, at least the ends of the scraper are at least The distance must be 5 cm to ensure the printing quality.
B. From the standpoint of the printing pattern: Generally, the scraper width must be 2 to 10 cm larger than the printing pattern width. For the reason that the smaller the scraper width is, the better it is. 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. Scraping speed and angle Scraping speed and angle mainly affect how much ink reaches the printed object through the mesh cloth. If the scraping speed is fast, the ink penetration is less and thin, and if the scraping speed is slow, the ink penetration is more and thick. However, if the printing speed is too fast, the thickness of the ink is not enough, and it is easy for the printing pattern to be unclear, and too slow may easily cause ink bleeding, making the printing pattern not sharp enough. The general printing scraping speed is about 60 to 200 cm per second, depending on the conditions at that time. The angle of the scraping also affects the amount of ink output. The smaller the angle, the larger the ink output, and the larger the angle, the smaller the ink output. The commonly used angle is between 45 degrees and 75 degrees. When scraping, you must pay attention to the uniform speed requirements and the angle must be consistent, so that the phenomenon of different ink density in the same printed product will not occur.
4. Squeegee pressure: First of all, it is necessary to understand a concept. Screen printing does not rely on the pressure of the squeegee to press the ink onto the object to be printed. Through the mesh, and by the adhesion between the printed matter and the ink, to achieve the purpose of printing. Therefore, the pressure should be as light as possible within the range as possible, and the scraper surface should be in line contact with the object to be printed, otherwise the pressure will be too large. When the printing pressure is not enough, it is bound to fail to print the printing pattern. When the printing pressure is too large, not only does the amount of ink squeeze increase, but also the blade tip is bent excessively, so that the plate surface is in surface contact with the printed object, causing printing It is not clear, and the scraper wears out and the printing film on the layout will peel off.
[2] Mesh
In screen printing, in terms of selectivity of the printed object, due to its slow speed, most of the objects are not easy to absorb ink, so the development of printing ink is in two directions. One is the ink containing solvent. After the printing is completed, the solvent evaporates and the ink is fixed on the object to be printed. However, because the solvent is harmful to human health and causes pollution problems, the ink will develop 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, so you need to use a thin mesh to get good results, but the price of the thin mesh is more expensive, so a method has been developed Pressed and calendered mesh fabrics are suitable for the drying of UV inks and are called UV mesh fabrics.
1. Advantages The general mesh UV fabric can be used to replace the high mesh fabric, which reduces the cost.
2. Disadvantages After the mesh is rolled flat, the mesh shape is slightly uneven, which affects the straightness of the printed edge and is not suitable for fine printing.
3. Drying
Because the UV drying equipment is expensive and its loss rate is fast, we analyze the equipment in the drying process.
[1] Advantages and disadvantages of UV drying
1. Reduce air pollution: Because UV-dryable materials do not contain solvents and have 100% solids, there is no disadvantage of pollution.
2. Space saving: The UV drying device is simple and safe, and can be dried in a short time and at normal temperature, so the manufacturing cost is lower than the traditional hot air furnace.
3. Save manpower: Because the process is simple, save manpower and increase productivity and save electricity costs, because drying only takes a few seconds, so save about 60% of electricity costs. 4. Improve quality: improve the quality and precision of the dried objects, and have material resistance, chemical resistance, non-toxicity, especially in food packaging and toy printing. A special effect called woven and matt is also obtained by UV drying.
[2] UV discharge tube
1. Emission intensity The relationship between the UV emission intensity and the type of lamp source, the range of the UV light emitted, the color and the number of lights on drying, and the ink adhesion and drying rate are closely related.
2. Lamp life such as type, wattage, usage frequency and time, instant start, cooling condition, installation location, correct use and maintenance.
[3] The radiator is composed of a reflector, a lamp holder, a cooling system and an exhaust system.
1. Reflector
A. Wide-beam shape [flat light shape and astigmatism shape]
B. Condensing shape: improve drying efficiency, avoid waste of light source and harm to human body.
2. The UV lamp of the lamp-end fixing base normally emits a temperature of more than 80 degrees, so it must be a high-temperature resistant and well-insulated ceramic fixing base.
3. The main function of the cooling system is to reduce the temperature. It is in a high temperature state under UV irradiation. Normal cooling is not given. The lamp tube, radiator, and circuit are overheated and short-circuited.
4. Exhaust system, shielding and safety device The exhaust system mainly makes the operating environment free of heat and odor, and a comfortable space. UV light may cause skin and eye damage, so add shielding to prevent UV light. In addition, for safety reasons, add a shutter device or a reflector to turn up the device.
4. Evaluation of differences in UV printing quality
In UV printing, which method of printing is the most appropriate quality performance, so the product evaluation price list is used. Analyze UV ​​screen printing and traditional thermosetting rotary printing. Since the cost and quality level can be seen from Table 1, the overall relationship between quality and cost is equal to each other, so 45% is used as the analysis ratio for evaluation in consideration.
[1] Quality
1. Resolution: The relationship between the mesh specifications of the screen version, so that the resolution of the screen printing is poor.
2. Ink color: UV ink performs worse than traditional ink [thermosetting].
3. Gloss: UV ink is better than thermosetting ink.
4. Abrasion resistance: The ink film formed by drying the UV ink is stronger than the thermosetting ink.
5. Hardness: UV ink is better than thermosetting ink.
6. Drying temperature: UV ink without thermosetting paper shrinks due to heat. The phenomenon of waves occurs.
[2] Cost
1. Space cost: Thermosetting ink takes up more space.
2. Equipment cost: The price of thermosetting is higher than that of UV.
3. Ink cost: UV price is greater than thermosetting ink.
4. Ink stock: UV needs less pigments to get rich colors.
5. Energy consumption: The energy used by UV is about half of that of thermosetting.
6. Maintenance and consumable costs: The materials used by UV have a high wear rate, which results in higher costs.
[3] Others
1. Production volume 2. Environmental protection issues 3. Operation and safety
[4] From the evaluation results in Table 1, it can be seen that UV printing is better, as long as the research and development are improved for its lack.
Table I
5. Future trends of printing
With the rapid development of science and technology, coupled with the rise of environmental awareness, UV printing is imperative. Therefore, the future UV printing needs to be improved and discussed.
[1] Ink price: The price of ink is about 3 times compared with traditional, and the ink depends on import. Island ink manufacturers should actively develop UV inks.
[2] Equipment price: The UV drying equipment itself is quite expensive, and vulnerable materials such as lamps, blankets, etc. Therefore, in addition to the development of new dryers, replacements for vulnerable materials are also found.
6. Conclusion
At present, the island uses UV inks only for the screen printing industry, while other printing businesses have less influence on the quality of their printed products due to differences in the differences, and invest in UV equipment, not only to purchase new equipment, UV printing There will be a lot of room for development.
references
1. Works by Luo Fulin and Li Xingcai [1995], Introduction to the Printing Industry [Part 2], p.369, Publishing Department of China Culture University, Taipei.
2. Institute of Printing Industry, Chinese Academy of Sciences, 1983, UV Dry Objects, Printing Collection, p.269-p.298.
3. Institute of Printing Industry, Chinese Academy of Sciences, 1983, Plastic Materials and Screen Printing Inks, Printing Collection, p.151-p.164.
4. Wu Guangwen, 1994, Evaluation of the adoption of drying methods for rotary lithographic printing inks, Huagang Printing Communication Technology, p.87-p.97.
5. Li Zhiming, 1994, Discussion on Screen Printing Inks, Huagang Printing Communication Technology, p.150-p.159.
6. Wu Zhengzhang, 1992, Discussion on the Printing Process Variables of Screen Printing, Screen Printing Industry Information Phase II, p.50-p.51, Industry Intelligence Magazine.
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