Application of water-based flexographic printing i

Talking about the application of water-based flexographic printing in corrugated board

with the improvement of the requirements of corrugated boxes for promotional functions, corrugated boxes should have rich and colorful information that can attract the attention of consumers This poses a challenge to the printing of corrugated board

flexographic printing technology is the main printing method of corrugated board

has always been Corrugated board has become an indispensable material for manufacturing packaging containers because of its unique advantages, such as light weight, low price, high bending strength, high processing and structural adaptability, and good printability. So far, corrugated board has become one of the most widely used packaging materials in modern packaging, and its consumption is still rising steadily. It is estimated that the world demand for cartons and paperboards will increase at an annual rate of z.s% before 2010, and will reach 125 million tons by 2010. With the increasingly fierce competition, commodity packaging puts forward another functional requirement for corrugated boxes - promotion. Therefore, corrugated boxes must be able to carry rich text, images and other information and have bright colors Such as corrugated box packaging of alcohol, small appliances, shoes, hardware tools, microelectronic products, computer software, counter sales displays, fast food, etc. At present, flexographic printing, gravure printing and offset printing before laminating are commonly used in corrugated board printing. Among them, flexographic printing is the most commonly used

we know that corrugated board can be divided into "pre printing" and "post printing" according to the printing order. In short, "pre printing" refers to printing face paper (roll to roll) before corrugated board production, and then sending the printed face paper to the corrugated board machine for veneering and cardboard production; "Post printing" refers to printing on the finished corrugated board. However, whether it is "pre printing" or "post printing" The main printing method used is flexographic printing, in which satellite web printing machine is mostly used for pre printing (up to four or six colors or more due to the adoption of new design and the reduction of packaging wall thickness), and unit type sheet fed printing machine is mostly used for post printing (generally below four colors). According to relevant statistics, corrugated boxes using flexographic printing technology account for about 95% in the United States Western Europe accounts for 85%, old books account for more than 93%, and China accounts for more than 50%. The wide application of flexographic printing technology in the corrugated industry is inseparable from its many advantages

analysis of the advantages of flexographic printing applied to corrugated board

the advantages of corrugated board using flexographic printing technology are mainly shown in the following aspects:

1 The good softness of flexible printing plate makes it possible to achieve a good printing effect with only a small printing pressure. When printing on the surface of corrugated board, it can reduce the influence of uneven pressure caused by corrugated, make up for the defect of uneven thickness of corrugated base material, and reduce the "washboard" effect

2. The quality of flexo after light and chemical treatment is better than that of the previous rubber version Color separation is sometimes more obvious

3. The water-based ink used in flexographic printing is pollution-free, harmless to human body and meets the requirements of environmental protection. In addition Flexo printing machine adopts metal roller to transfer ink, and the printing plate only needs to touch the corrugated board gently, and the water-based ink will be fully absorbed

4. The flexographic press has a simple structure, and four rollers form a color deck It is convenient to install, adjust and clean the plate. The flexographic printing machine can also be linked with other processes, such as indentation, slotting die cutting, gluing, box making, counting, etc. to form a linkage production line, which greatly improves the production efficiency

5. The operation training of flexographic printing machine is also relatively easy, because when the roller is used for quantitative inking printing, the requirements of ink coloring can be achieved after the roller rotates 1-2 turns, and the color difference of the whole batch of prints is very small, which reduces the paper consumption

6. The large format printing function meets the requirements of large-scale carton production and just adapts to the development trend of corrugated board towards large format

several stages of corrugated board printing

1 Single text or depressed monochrome printing

this kind of printing machine has low printing accuracy. The ink needs several rubber rollers to beat it evenly. The drying time after printing is long. It is not suitable for high-speed printing. It plays a simple role of identification and cannot play a role of decoration

2. China with single text or line color blocks sent Chinese teacher volunteers to Mongolia and signed an agreement on color printing

this is mainly due to the use of three color water-based printing machine to overprint with high accuracy. The printing ink is water-based ink, which has fast drying speed Full color The printing effect is good However, due to the limitations of printing press and other factors, its application scope is not extensive

3. Direct printing of half tone patterns

at this time, the printing machine is already a three-color or four-color printing machine with high accuracy, and the number of lines of the roller is generally 25. Line/inch has a good reproduction effect on some half tone patterns. However, it is limited by the accuracy of the printing press and the number of printing colors The sense of hierarchy is not very strong

4. Color preprint

Color preprint is the direct printing of web paper. Through the multi-color group (4-8 colors) of satellite printer, it can produce exquisite patterns with high performance and high precision. Its ink is alcohol ink, which has fast drying speed, bright color and strong expressiveness

in order to improve the surface gloss, you can also add a layer of varnish to make the printed pattern bright and bright, not easy to wear. The printing plate is a thin resin plate, which can reproduce the level of the pattern more completely after fine color separation. The performance content of printed patterns is also more diversified and colorful Become a real sales package It has beautified f) experimental methods and experimental machines, and promoted sales

micro corrugated board will increasingly use offset printing

the commonly used micro corrugated board f (0.75mm), G (0.5mm), n (0.46mm), O (0.3mm) are composed of three layers, namely, face paper, corrugated core paper and bottom paper. At the same time, the micro corrugated board also has the following characteristics: ① high strength can enhance the protection function of the product, which is 40% higher than that of the thick board; ② light weight, which is 40% lighter than that of the thick board, and 20% lighter than that of the framed corrugated board; ③ smooth surface, exquisite patterns, bright colors, and strong visual effects

offset printing uses the principle of immiscibility of oil and water to make the graphic part only absorb ink and the blank part only absorb water on the printing plate almost on the same plane, and then transfer the graphic ink to the substrate through blanket. Offset printing has become the most widely used and technologically mature printing method at present with its high ability of image restoration and color reproduction. At present, it accounts for more than 50% of the total number of printing in China and is mainly paper printing. Direct offset printing of micro corrugated board is a new printing process, which has reached a high level in printing effect and printing quality Basically comparable to the printing quality of paper, it will become the preferred cardboard for high-end corrugated boxes and carton packaging It can bring huge economic benefits to packaging and printing enterprises, and is one of the main directions of offset printing development in the future. However, we should also recognize that there are still some problems in offset printing corrugated board:

① it has an impact on the strength of corrugated board

the huge pressure of offset printing will reduce the compressive strength of corrugated board; The use of fountain solution will reduce the surface strength and compressive strength of paperboard due to water absorption

② "washboard" phenomenon

washboard phenomenon is the most common quality problem in corrugated board printing. This phenomenon may occur if the pressure and ink volume cannot be well controlled in printing

③ ink imbalance

the biggest impact on the quality of offset printing is the ink balance, especially the large amount of water has a greater impact on the micro corrugated board

④ pH of fountain solution

too strong acidity will slow drying Corrosion plate; If the acidity is too weak, an effective hydrophilic protective layer cannot be formed on the blank part of the printing plate

⑤ performance of blanket

the performance of blanket includes surface performance and compression deformation performance. Surface performance is the guarantee of absorbing ink and transferring ink, and compression deformation performance is the basis of whether high-quality images can be obtained on corrugated board

flexographic printing is a technology that accumulates materials layer by layer to form a three-dimensional entity. Precautions when using water-based ink in flexographic printing

while understanding the characteristics of water-based ink, we should also pay attention to the following matters

I. because water-based ink is a pure water-based system, Therefore, do not mix water-based ink with alcohol based ink and solvent based ink or add organic solvents to water-based ink to avoid printing failures and affect printing quality

2. Before use, it should be fully stirred to maintain the uniformity of the ink composition. During use, it should be noted that the drill degree can be measured by mixing the water-based ink in the barrel with a stirring rod. After measuring its drill degree, it can be poured into the ink tank. If the drill degree is too high, an appropriate amount of diluent can be added If the viscosity is too low, it should be adjusted with thickener

3. Pay attention to the changes of brightness and pH value during printing. Trapped in the printing process, due to the volatilization of water, the drillability of water-based ink will increase and the pH value will decrease. The pH value should be controlled between 8.5 - 9.5. If it is beyond this range, pH stabilizer can be used to adjust and maintain the stability of drillability and pH value. In addition, if it is found that the drilling consistency of ink is slightly higher in use, an appropriate amount of water can be added to adjust

4 After opening and using, the stored ink should be sealed immediately to prevent dust from falling and crusting. After printing, the remaining water-based ink should be collected back to the corresponding original barrel or the cover of the ink tank should be tightly covered for next reuse. If the remaining ink contains impurities, it should be filtered first and then used together with new ink

5. Water based inks should be stored in a cool and ventilated place with room temperature s--so C to avoid high temperature or hot sun during storage. Generally speaking, water-based inks can be stored for 1 year without deterioration under normal conditions

6. The remaining ink left on the printing equipment after printing can be washed with clean water when it is not completely dry. If the ink cannot be washed with clean water, it can be cleaned with detergent

7. Use reasonable ink additives. The development trend of corrugated board flexographic printing

corrugated board flexographic printing presents the following development trends

① from monochrome to multicolor

② from low line to high line

③ from sheet fed printing to web printing

④ from low speed to high speed printing

⑤ from small format printing to large format printing

⑥ the sales packaging of micro corrugated board is increasing

conclusion

flexographic printing accounts for the main part of corrugated board printing, but with the expansion of market demand for micro corrugated board, direct offset printing will be more applied in micro corrugated board. The fact also proves that many printing machinery manufacturers are carrying out research and development in this field

reprinted from: Printed today