The phrase "water is rising and ships are high" should be appropriate to the technical people in the printing industry. A good horse with a good saddle, advanced equipment and advanced process technology can achieve the desired effect, save time, labor, and cost, and produce a more representative packaging and printed matter, which is beautiful, generous, bright, elegant, representing Advanced equipment, advanced technology and advanced design and corporate image.
The pre-press process production requirements of ordinary gravure printing machines are relatively strict, but the pre-press process production of compound and transfer connection gravures needs to be cautious. The pre-press process is formulated to provide a clear path for print production guidelines, and everything is interlinked. Every detail of each process is not allowed to have human errors or predictable errors. Once an error occurs, it will cause irreparable losses.
1. Formulation of process raw and auxiliary materials
â‘ Transfer film: PET-based film is generally selected. In contrast, PET-based film has a smaller tensile stretch range than OPP-based film and has good stability.
â‘¡Backing paper: The selection of backing paper should refer to the sample sheet or customer requirements. The surface of the paper is smooth and smooth, and the softness is good (the paper fiber cannot be too hard). After the die cutting in the subsequent process, the indentation is full, and the box type has no burrs.
â‘¢Composite adhesive: At present, the compound adhesives used in domestic composite products are solvent-based, water-based, and UV adhesives. Its characteristics vary.
Solvent-based compound adhesive: fast drying, good release performance, odor, not conducive to environmental protection, the compound product is curled and placed for a long time, the color becomes yellow, and the cloudiness is observed under bright light (rosin content in various similar solvent adhesives) Cause).
Water-based compound adhesive: No solvent volatilization, non-toxic, environmental protection, especially when the base film is glued and laminated with paper, the glue liquid is a natural flowing liquid, which can quickly and fully fill the concave part of the paper surface, smoothness Good, good compound fastness, no warpage, flat and beautiful appearance, excellent comprehensive performance.
UV adhesive: fast drying speed, soft colloid, good adhesion performance, high bonding strength, high temperature and bonding effect unchanged after freezing, no color burst, no brittleness.
According to different equipment performance, drying method, gluing method, product requirements, etc., different compound adhesives can be selected to achieve the desired effect.
â‘£Varnish: Referred to as resin oil, it is used to coat gold, silver, and laser paper after compounding or transfer, so that the surface has better adsorption for ink when printing.
There are two commonly used varnishes, the first one: oily varnish (volatile drying type). Main ingredients: synthetic resin, nitrocellulose, acrylic resin and additives. Coating advantages: thick coating layer and fast drying speed. Disadvantages: resin inks of the same system are easily soluble in the printing process; the second: water-based varnish. Main ingredients: acrylic emulsion, defoamer and additives. Coating advantages: less coating volume, thin varnish layer, cost saving, and it is not easy to dissolve with ink during the printing process. Disadvantages: Non-volatile resin, slow drying speed.
⑤Printing ink: At present, volatile dry oily ink is used for paper gravure ink. The solvent is ethanol acetate, ethanol (isopropanol), butyl acetate or even toluene, which is harmful to the human body and is not conducive to environmental protection. The water-based gravure ink is immature and the technology is still in the process of development. In the selection process, it should be noted that the ink system is benzene-free ink, the volatile drying speed is neutral, the ink pigment particle fineness is 3-5 μm, the color density, color saturation, high temperature resistance, good adhesion, easy bronzing, printing surface Not easy to scratch. Thinner: ethyl acetate, ethanol (over 98.5% anhydrous) or isopropyl alcohol. Slow drying agent: butyl ether (less toxic).
2. Pre-production process analysis
â‘ Introduction of composite and transfer paper process
The transfer film and the backing paper are bonded together with an adhesive. Since the paper is breathable, the wet compound method is generally used. The film is first coated with glue, then pasted by the impression roller, and finally dried. The glue application method can be three-roll glue application or anilox roller glue application; the oven temperature and printing speed determine the drying condition of the product. The quality indicators that need to be controlled are: compound fastness, surface flatness, peeling integrity.
Separate the base film from the paper so that there is only one layer of adhesive, aluminum layer and coating layer on the surface of the paper. The quality of the peeling process is largely determined by the preparation of the base film coating, coating layer and composite effect. In the process, the peeling itself needs to be controlled mainly by the tightness, uniformity of the film collection and no scratches on the surface. The stripped PET and film can be re-coated and transferred again, greatly reducing production costs.
â‘¡Composite and transfer line gravure printing process
Generally, the composite paper needs a 24-hour curing period, and the PET-based film is transferred to the paper after the aluminum layer and the coating layer are peeled off. However, if the length of the drying tunnel is 16m and the maximum temperature is 200 ° C, after passing through the double cooling roller, the ideal compound and transfer to the paper can be achieved.
â‘¢Coating roller
The use of the glue roller depends on the product being produced, and the size of the sizing amount directly affects the product quality, compound fastness, and peeling integrity.
â‘£Printing plate
The 960CERUTTI3288 uses a hollow plate (a plate without an axis in the base-making process of the plate-making factory), but has been changed to a plate with an axis (the axis and the plate are welded together during the base processing). At present, there are many printing companies in China that do not have a good solution to the problems that occur in the printing process of hollow plates. Its main disadvantages are: the plate-making time is correspondingly longer, the machining is more difficult, the axis used by the plate-making factory and the axis of the printing factory cannot be completely matched, or the dynamic balance of the printing plate due to long-term use and wear The swing beyond the specified range is greater than (0.3mm), so during the printing process, there are obvious overprint fluctuations and other running rules. However, from the standpoint of product quality and craftsmanship, we do not use hollow version as much as possible, which brings us many inconvenience factors in printing production; although the price of the shaft version is slightly higher, from the production of finished products Considering the output rate, it is still beneficial.
The gravure-to-machine UV glazing process is already very mature in China, but if we want to achieve post-press processing without defects, we must consider the pre-press process. Since the paper must undergo high-temperature baking in the UV lamp tube during UV printing, deformation of the paper often occurs, which causes difficulties in registration for post-printing processing. Therefore, in the prepress process typesetting, we should focus on the factors affecting the post-processing of the precision of the die cutting card position and the deformation rate of the paper.
The following is a brief introduction to the fine cigarette packaging clamshell products:
960CERUTTI3288 type gravure printing machine, the maximum width of printing is 820mm, the precision of hot stamping, concave and convex, die-cut registration of the flip product of the dry cigarette pack is high, most of them use 18 fights (3 × 6), two horizontal rows 4mm double knives are added to the joints of the single-pole connection, and 6 of the three joints are arranged in a vertical row, which greatly solves the problem of inability to register after printing due to paper deformation.
New equipment, new technology, new technology and re-innovation are the goals we strive for together. Only by having advanced and advanced process technology can China's printing technology be advanced to the international leading level, and can it be the leader in the world's high-tech printing technology.
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