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People have been arguing about the connection between printing and processing equipment, and the problem of off-line printing and reprocessing. In most cases, connection printing is used for one-, two-, three-, and four-color printing - because the set-up time of the processing unit and the flexo unit match. However, before deciding on connection or off-line printing, the printing combination must first be analyzed. The content of the analysis includes the percentage of printed colors, full-print/line printing/screen printing, corrugated cardboard (N/F/E/B), whiteboard/coated whiteboard, network cable, and/or varnish. . Because of the different requirements of each carton company, the machinery supplier should provide corresponding solutions for the current status of customers and future development trends. Regardless of the mode of the printing production line, if many of its parameters are not set correctly, the die cutting machine will seriously affect the quality of flexographic printing. These parameters mainly include: substrates, anilox rollers, inks and their delivery.
Substrate
In the post-printing process, it is crucial to maintain the smoothness of the printed surface of the corrugated board. In order to reduce the washboard phenomenon, rather than increasing the strength of the board, a higher weight of face paper is generally used. Studies have shown that the compression of the board and its hardness are the main causes of laundry board printing problems. Therefore, the use of high-pressure and high-hardness paperboard can reduce such problems.
Regardless of flexographic preprinting or postprinting, the transfer of ink sometimes means the ability of the substrate to absorb ink. However, it is not always necessary because paper absorbs a large amount of ink, causing excessive consumption of ink. We usually use the word "storage", which sounds more visual. Due to certain factors, ink can cause ink bleeding. These factors include: pressure, ink type, paper smoothness, and pore size. The ink enters the cardboard surface by capillary action. Some papers are acidic and the ink is dried by neutralizing the amine solution in the ink. The drying mechanism relies on the liquid phase of the ink penetrating the pores of the paper, and the die cutter so that the resin component can overprint the pigment and print it onto the paperboard surface.
The ideal state is to use a minimum amount of ink to achieve a given color density and quality, and firmly print on the surface of the board. Paper with a smooth surface (coated or semicoated paper) requires less ink, and coarse paper (lower hiding power) requires more ink because more ink is required to cover the surface of the paper. Convex groove. At the same time, no matter what type of substrate is used and what adjustments are made by the ink, the printing on rough cardboard will increase the dot. The dot gain rate depends on the paper size, the surface properties of the paper, and the size of the pores.
When using modern machinery to print high quality stencils and fine lines on semi-coated, coated or decorative cardboard, the relief depth should be between 1 mm and 1.2 mm. More on-site and thick-line printing on the basic equipment (all waste paper linerboard and Kraft paperboard) does not require a specific bas-relief version. In this case, the relief depth can be adjusted to between 1.5 mm and 1.8 mm; if it is post-print, the thin and light flexographic platesetter (2.84 mm/0.112 inch or 3.18 mm/0.125 inch) is more suitable for corrugated board printing. machine. The device can be used for high-quality screen printing and bar code printing, especially cardboard printing at the time of switching from offset printing press to post printing.
Anilox roller
The anilox roller has a major influence on the printing process and is hailed as the "heart of the press". Therefore, it must not be ignored. From the advent of chrome roll in the 1960s to the birth of ceramic rolls (un-engraved) in the 1970s and the development of laser-engraved ceramic rolls in the 1980s, the anilox roll technology has undergone a breakthrough. In the early stages of its development, the number of screen lines, the shape of the cells, the angle of arrangement, and the depth of their choice are limited. This limitation comes from the limited number of engraving tools in the engraving machine. In addition, most of the limitations are due to the fact that the engraving tool must exist in the shape of a cell, ie, "processed state," so that the engraving tool is removed from the surface of the roller. For this reason, the ink's grinding alignment angle should be maintained at 45°. Perhaps because of this limitation, the number and depth of screen lines are usually determined by the engraving machine. In some carton companies, the number and depth of screens have not been replaced or improved over the long term, even when processing different paperboards. The operator of the press is simply involved in the choice of anilox rollers.
Computerized measurements of cell volume, structure, and alignment angles ensure that anilox roll suppliers can more accurately predict the printing capabilities of the device. For high-quality printing presses, a laser engraved roll with a defined number of screens and a large area of ​​smooth ink film is the best choice.
However, the final choice of anilox roller must be based on actual needs. In the most basic form of roller, there are four types of screen lines available: full-frame field, field and line, thin line and font, and four-color printing. Obviously, the final printed product is a combination of the above types. When subdividing it into individual colors, they can be classified into the above categories, and their printing effects may have some differences.
The number of screen lines can be roughly divided into the following types according to the type of printing: 100 lines/inch, 250 lines/inch or less (full-size field), 200 lines/inch to 300 lines/inch (ground and lines), 250 lines/ Inches ~400 lines/inch (thin lines and fonts), 400 lines/inch ~1000 lines/inch (including above) (four-color printing). Plates can use a variety of screens, so there are a variety of network cable options for the four-color printing process. The simplest reason is that the finer the printing plate lines, the smaller the number of roller screens. Also, the amount of ink or coating used is usually based on the following criteria: To a large extent, the depth of the cable is determined first, ie, the theoretical volume of the specific cell shape is calculated. Anilox roller suppliers must understand the wet and dry weight of the ink, as well as its solids content, so as to provide customers with better usage advice.
Since the "single beam" laser is a non-contact engraving process, the shape of the cell is similar to that of a disk or hemisphere. The application of traditional computer technology means that lasers can fire more than once on a single cell. This process is accomplished by using "dual beam" or "double-click" methods. This method is a great advancement for the engraving process. The ratio of the screen to the plate has increased from 3:1 to 4:5 or even more. This allows for more open and useful cell counts, especially when the number of meshes is large (usually when using high-pigment "enhanced inks").
The final factor that affects print quality, ink loss, and overall quality lies in the proper management and maintenance of the press. Suppose you have a clean and tidy factory. Of course, this is very important for production safety, employees' work attitude and customers. However, if the anilox roller cannot be monitored and cleaned as needed, then the benefit of the ceramic anilox roller is There will be discounts. Ceramic anilox rollers can be used for a long period of time, whereas conventional anilox rollers require periodic replacement. Therefore, the ceramic anilox roll should be inspected to see if it is missing due to the ink drying in the cells for too long. The anilox roller can be cleaned with a damp cloth saturated with a saturated solvent or other cleaning method, but this only serves as a surface cleaning effect.
If the gravure is encountered during the cleaning process, the hand-washed anilox roll exposes the deficiencies of the above cleaning methods. Hand-washed anilox rollers have become popular with the widespread use of aqueous inks. Therefore, the state of the roller was checked by measuring the cell volume of the roller. The lack of the volume of the cell site will affect the printing effect. At the same time, if the cell volume is increased by increasing the color number of the ink, the ink consumption and the production cost will be further affected.
Although an automatic cleaning system can be installed and installed on today's presses, this is not enough for thorough cleaning of the cells. More effective cleaning systems include ultrasonic cleaning, high-pressure carbonate cleaning, and “low temperature†freezing and cleaning systems. If used properly, moving companies can do a good job of cleaning. There are many private cleaning companies in the industry. Most of them provide manual cleaning services. The cleaning results are also good.
Ink and ink delivery
Water-based inks are suitable for the printing of paper and cardboard in terms of their frictional resistance, printability, printing density, dot gain, and their lack of VOCs (unstable organic compounds). Ink suppliers formulate printing inks, varnish, and coatings of different properties and characteristics for use in different production applications. Depending on the process requirements, the type of substrate, and the speed of printing, the ink will vary in color, formation, and composition. Most printing processes use inks that consist of pigments and a color developing agent. The color of the ink is derived from the pigment, which is then dissolved in the developer or varnish, which transports the pigment during the printing process and bonds the pigment to the substrate. The original color pigments were extracted from animals, plants and minerals. Today's color pigments are usually petrochemicals. The quality of the pigment and its solubility determine the quality of the ink and its effect on the finished product.
In addition to the pigments and the developer, ink additives (such as thinners, desiccants, defoamers, etc.) are used in the process of disposing the ink so that the ink reaches a prescribed standard. A higher-quality ink has a higher concentration, and its ability to cover a printing surface is higher than that of a cheap ink. The color development agent is the main liquid component of the ink, 9tUv ZD2F20 fingerprint attendance access control machine, color pigment suspended in the color development agent. The color developing agent can dry the pigment or adhere the pigment to the cardboard, and is also divided into various types according to the required concentration and drying properties of the ink. The ink should be fluid at the time of printing so that it can be fed into the printer and transferred to the substrate after measurement. But once the film is on the substrate, it must be able to withstand the friction and pressure from other surfaces—in short, taking into account many factors, the film must have dried or hardened at this time.
The quality of the ink is very important for the smoothness of the surface of the paper, so the pigment and the color developing agent in the ink cannot be separated, otherwise the anti-friction effect of the ink will be poor, and the ink will appear on the surface paper.
The control of the drying temperature is very important, and the transfer of the ink depends to a large extent on the control of the drying temperature. This must be carefully controlled to maintain a constant temperature. If you increase the temperature, the viscosity of the ink will decrease. For example, after the temperature of the ink is raised by several degrees Celsius, the syrup in the form of a stable solution will be converted into a flowable water. Keeping this in mind, low-temperature inks do not print as well as high-temperature inks, especially when using a squeegee system and the need to maintain a certain amount of ink delivery. This problem is more common in North America and northern Europe, because the ink temperature will fluctuate significantly with the change of seasons, thus affecting the control of printing temperature. At the same time, in order to maintain a consistent viscosity, the amount of diluent must also be controlled. In general, the higher the ink temperature, the less diluent is needed. The dilution of the ink will largely affect the printing density. The aqueous ink diluent can be water or a viscosity reducing medium.
If water-based inks are used on paperboard surfaces with absorbent properties, the drying effect depends on a variety of factors, including ink evaporation rate, penetration rate, and sedimentation rate. The ink will evaporate and dry under airflow and heat. The heated gas passes over the printing surface and removes the volatile substances in the ink. Penetration drying is when the ink enters the surface of the paper under capillary action. When the ink is completely absorbed, it is neither contaminated nor transferred to other printed surfaces. The liquid ink is divided into two stages in the sedimentation process: the solid phase and the liquid phase. The liquid part is absorbed by the paper fibers, leaving the ink resin and pigment on the surface of the paper. Water-based ink systems dry quickly by evaporation on the press. In order to reduce the amount of water evaporation from the fountain roller or squeegee blade system, modern corrugated posterior printing presses are equipped with closed inking units.
Water-based inks are sensitive to the addition of thinners, so adjust the viscosity of the ink from time to time. When water is added to the ink, care must be taken not to overdilute it, and fresh ink should not be added to the ink in order to increase the viscosity of the ink. In practice, an excessive amount of fresh ink is usually added. Therefore, the correct approach is to slowly pour the diluted ink into fresh ink. The control of stickiness is very important for maintaining ink performance and controlling printing color.
The advantage of water-based inks is that the solution loses less when evaporating, so its adjustment requirements for ink are less than solvent-based inks. Since water-based inks for paper and board printing are mainly dried by sinking into the light-sensitive underlayer, only a small portion is dried by evaporation. Therefore, special attention must be paid to the surface quality of the light-sensitive substrate. The drying speed of the ink in the photosensitive base layer depends on the water absorption rate of the surface of the photosensitive base layer and the specific gravity of the resin/water used in disposing the ink. Here, some optimal effect should be found between the ink drying speed and printability. Fast-drying inks used in high-speed printing presses are easier to dry on plates and anilox rolls, so close inspection of the printing press is required.
The addition of additives to the ink improves the performance of the ink and plays a special role. The actual added ratio is very small, but the amount is relatively large. If you want to make the best use of additives, you need to understand its features, defects, and any side effects that may occur. Water-based ink additives include the following types: defoamers, antiseptics, wax auxiliaries, surfactants, wetting agents, transmission agents, binders, anti-blocking substances, etc. Each type has a different role. .
The use of surfactants helps disperse the pigments, which improves the quality of the gloss and color of the print, and reduces the possibility of pigment flocculation when the ink is diluted. The foam can cause troubles in the preparation of the ink and the printing process, especially when stirring at a high speed, so an antifoaming agent is required. Elimination of foam is more difficult and additional defoamers may be needed, which may result in print notches and even print unevenness. In addition, some defoamers contain hydrocarbons, which can damage the photosensitive resin plate (for printing plates). The foam effect differs depending on the hardness of the water used. The silicon antifoaming agent is diluted with water and added to the ink at a constant stirring speed. If undiluted silicone defoamers are used, they can cause small holes in the printed surface and missing dots in the ink. Special precautions should be taken when adding defoamers. The maximum amount added is 1% of the ink volume.
Changes in the pH of water-based inks can also affect ink and print quality. If the pH is too high, the amine in the ink causes the ink to dry more slowly; conversely, if the pH is too low, the viscosity of the ink will change significantly and the resin will even precipitate out of solution. The pH of the finished ink can be easily checked using a standard pH meter. Traditional aqueous inks are alkaline and have a pH of more than 7. Generally suitable Ph values ​​range from 8 to 9. However, the formula type of the ink affects the adjustment of the pH value.
7tGf Several Factors Affecting Printing Quality
Die-cutting machine The current flexo printing process in carton enterprises is mainly through preprinting machine, printing slotting machine, flexible automatic folding and sticking box linkage line, round press die cutting and printing linkage line, connection/offline printing machine and flattening. / Round press die cutting machine to complete these devices. In order to further improve the printing quality, carton enterprises need to improve in all aspects. For example, they must scientifically estimate the paperboard specifications of the printing press according to the printing task; at the same time, the choice of printing color is equally important because the general user requires five colors. Printing presses and glazing (or six-color printing presses for printing, packaging colors, and glossing). In addition to this, the set-up time and operating environment of the equipment are also very important for optimizing equipment investment. Peripheral equipment can also be considered as part of this optimized investment, including anilox rollers with a variety of network cable counts and ink storage, and fast switching Anvil, stick and pH control equipment and paper and plate cleaning equipment.