The hottest liquid flexo and corrugated box printi

Liquid flexographic printing and corrugated box printing I. Introduction in the past 20 years, the development of flexographic printing in packaging and printing is obvious to all, especially in the printing of corrugated boxes, in addition to flexographic printing, we do not want to be a second person. Its convenient and exquisite printing is of great help to the promotion of products. The current success of flexo printing is closely related to the improvement of preprint, ink, flexo printing machine and printing materials, but the progress and development of photosensitive flexible plates in the past 20 years can not be ignored

at present, the printing of corrugated boxes in China has gradually shifted from the traditional hand carved rubber plate to the photosensitive flexible plate, but the vast majority of them use solid photosensitive flexible plates, and only a few use liquid photosensitive resin plates. However, in Europe, the United States, Japan and Australia, liquid photosensitive resin plates account for more than 50% of the corrugated box printing market, and there is a trend of continuous growth

today, I want to borrow a little space to make a report on the characteristics and recent development of liquid photosensitive resin version for your reference

II. Development process and performance of liquid photosensitive resin plate

both liquid photosensitive resin plate and solid photosensitive plate began to develop around 1970. At that time, high-speed UV sensitizer (u.v light sensitizer and initiator) and photopolymerizer (monomer) had just appeared on the market. DuPont, grace, Uniroyal and Hercules in the United States, Asahi (Asahi) in Japan and BASF in Germany and other advanced chemical companies immediately adopted this new product to develop printing plates. (at present, the printing departments of grace, Uniroyal and Hercules in the United States have merged into MacDermid graphic arts)

by 1975, according to the chemical properties and market demand, two different types of plates were developed, namely the so-called liquid resin plate and solid plate, The imaging principle of these two types of plates is the same:

1. Ultraviolet light is absorbed by the photosensitizer and immediately produces activated free radicals

2. Free radicals react with monomers, and then produce chain reaction

3. Chain reaction connects monomers and high molecular rubber or resin into permanently solidified fonts or images, The difference between solid plate and liquid plate is in their physical properties and plate making process:

1. Solid plate is mainly made of thermal plastic block copolymer, which is normally wet as solid, but has not yet been cured, while liquid plate is mainly made of high viscosity photo sensitive resin

2. Solid plate manufacturers rely on customer specifications to make plates of various sizes and thicknesses and send them to plate manufacturers. As long as the plate maker puts the plate on the plate printer and uses the negative to expose and image. The liquid plate supplier sends the barreled photosensitive resin to each plate making manufacturer. The plate maker should use a specific machine to make the liquid resin into plates of the required size and thickness, and then expose and image on the negatives of the plate printer

3. The main component of solid plates is rubber, and most of them need to be washed with organic solvents. (it can be divided into digital display horizontal tensile testing machine, microcomputer screen display horizontal tensile testing machine and microcomputer controlled horizontal tensile testing machine according to the display mode. Recently, water washed solid plates have been published in maidemei and DuPont. At present, due to high hardness, they are not suitable for corrugated box printing). The uncured part of the liquid version is a water-soluble resin with high viscosity. It is easy to remove the resin by physical methods (extrusion and air blowing) at high temperature, and then rinse it with water

4. The solid version is mainly made of rubber, so it has good ink resistance to alcohol ink and water-based ink. Liquid version is based on polarized polyurethane, so it is not suitable for alcohol inks, but only for water-based inks. (if the printing factory still uses oil-based ink or "water washable ink", the liquid version is more dominant than the solid version)

III. the advantages of liquid version in corrugated box printing

from the perspective of plate making process and ink resistance, the solid version seems to have a slight advantage, but why is the liquid photosensitive resin version widely used by corrugated box manufacturers at home and abroad? The main reasons are as follows: 1. Solid printing ink has excellent transmission. In recent ten years, water-based ink has made great breakthroughs in flexographic printing. In addition to bright colors and uniform gloss, physical properties such as wear resistance, water immersion and adhesion to corrugated paper have been significantly improved. Although the ink has made progress, the thickness of the corrugated surface paper and the uneven height of the corrugated are still quite difficult to cover when printing. Liquid plate has unexpected advantages in this regard, mainly related to the properties of the plate

the resins of liquid plates are acrylatc polyurethanes with high polarization. The surface tension of the plate is higher than that of the solid plate by dynes/cm (liquid plate: dynes/cm; solid plate: dynes/cm), so using an LOX with the same ink volume, the ink volume of the liquid plate is% higher than that of the solid plate. At the same time, the stress of the liquid plate is low, the strain capacity is large during printing, and it also has good surface contact with the thicker surface paper or corrugated paper, Therefore, the coverage effect of the solid base is better

it is more economical to make a plate: the raw material cost of the liquid plate is almost the same as that of the solid plate, but the liquid plate saves money and time in the process of plate making. As we said earlier, the main component of the solid version is non fluid (physically cured) rubber. When printing through the negative, the exposed part produces a chemical chain reaction to become permanently cured rubber. The non exposed part needs to be dissolved in organic solvent, and the solidified font is highlighted on the plate for printing. Generally speaking, the washing solvent can only dissolve% of the rubber at most, so it needs to be replaced, otherwise the developing ability of the solvent will be weakened. Therefore, a gallon of tetrachloroethylene/butanol solvent can only dissolve 200g of rubber at most. By analogy, a solid version with a thickness of 6.50 mm (mm) of 1 square meter and a font height of 3.2mm requires gallons of solvent. Although the solvent can be recovered, there is a lot of loss in the volatilization in the plate washer, the residue in the solvent recovery, or being taken away by the plate (plate absorption) when washing the plate. If we can have a solvent recovery rate of 60%, we still need to consume more than 3 gallons of tetrachloroethylene/butanol solvent per square meter. At the same time, the plate absorbs a large amount of solvent when washing the plate. Generally, it needs to be dried in a dryer at 65 ℃ for hours before the plate can be restored to its original thickness. The thicker the plate, the longer the drying time

but the liquid plate is not. When the photosensitive resin is exposed by the negative film and the font is cured by the Guanghua bonding reaction, the non exposed part is still the flowing resin. With physical methods (extrusion, or high-pressure air blowing away), 80% of the non curing flowing resin on the tensile strength (maximum tensile stress) of 1) can be recycled, and a small amount of resin remaining on the plate can be washed with water solvent, so the liquid plate is much more economical in plate making materials and process than the solid plate. In the process of plate washing, the plate only absorbs a very small amount of water solvent, and the thickness can be said to have not increased, so it generally takes only minutes to dry, so the time of the whole plate making process from exposure, washing, drying to post exposure is reduced by more than 50%

the flexographic industry in Japan has developed an "island plate making method" to use the characteristics of liquid plates as thick plates for corrugated boxes. Generally, flexo back exposure is full back exposure, which solidifies to form a certain thickness of subbase. However, the island plate making method uses local back exposure, that is, only in the areas with fonts and graphics. This part of the subbase and font graphics form blocks on the underlying polyester film, like isolated islands distributed on the plate, and all the resin without curing is recycled. The advantage of this version is not only to increase the proportion of photosensitive resin recovery, but also to make the whole plate lighter and more comfortable, which makes it easier to install the version, rather than easy to warp the version

solid plates should not be made by "island plate making method" on corrugated box printing. Because you want to wash the solid version to the bottom polyester film, you need to add a green button to indicate that the oil cylinder increases the washing time, consumes more solvents, and the plate expands more. What's more, the washed plates can't be recycled, so why waste solvents? So this method is only applicable to liquid plates

based on the above advantages, liquid plates are popular in corrugated box printing in Europe, the United States, Japan and Australia. Especially in countries that pay attention to conservation and environmental protection, such as Japan, the liquid version with plate recycling and solvent washing has monopolized the corrugated box printing market

IV. the development of liquid plates in recent years

the early liquid plates had several obvious shortcomings when they were just launched, but they have been improved step by step recently

1. the surface of the plate is too sticky

because the raw material of the liquid plate is polyimide with strong adhesion, it is inevitable that the surface will still have adhesion after curing. In order to solve this problem, in the early stage, both Medusa and Asahi used low solubility fatty acids to dissolve in the resin, using the principle of solubility change after curing to cause the separation of fatty acids, and a thin layer of fatty acid cream rice was formed on the surface of the plate to reduce the viscosity. However, this method is only a palliative. When printing, the ink will gradually take away this layer of fatty acid cream, and then the surface of the plate becomes sticky again

in recent years, u.v.c (short ultraviolet) tubes have gradually become popular, and various new photosensitizers and polymeric monomers have been introduced. If there is a suitable formula, using short UV exposure can achieve a very good debonding effect. The TF2 photosensitive resin plate recently launched by Medusa is exposed after short UV debonding. The surface of the plate is smoother than that of the general solid plate, which is very suitable for the printing of corrugated boxes

2. Line enlargement

the plates used in the early corrugated box printing were mostly hand carved rubber plates or laminated rubber plates, which were difficult to print fine fonts and accurate points. When the photosensitive resin plate or photosensitive solid plate comes out, the requirements of corrugated box printing are getting higher and higher. Foreign corrugated box manufacturers gradually found that the font of the liquid version looks very fine and the anti white is deep, but the printing effect is not as good as that of the solid version. Because the expansion ratio of dots and lines is higher than that of solid version. After our detailed study, we found that this phenomenon is related to the physical properties of the plate. When the plate is cured by UV irradiation, the thin line and point curing degree of liquid plate is lower than that of solid plate. After plate washing and post exposure, the shore a hardness of thin lines and dots of liquid plates is lower than that of wide solid parts. Therefore, when printing corrugated boxes with high pressure, the expansion rate of thin lines and dots is relatively high. Based on this understanding, McDermott first proposed the plate making method of composite liquid plate. Before applying ordinary photosensitive resin for plate making, first apply a layer (0..20mm) of photosensitive resin with higher hardness than the bottom layer on the negative range of thin lines and dots, and then apply ordinary liquid plate. In this way, the hardness of the surface layer of thin lines and dots of composite plate is higher than that of the rest, which reduces his dot expansion when printing

such liquid composite materials can enjoy high ink transmission without excessive dot expansion, which is the most suitable for chromatic printing of corrugated boxes

3. the plate is not strong enough

the development of early liquid plates paid more attention to the photosensitivity of plates