The matte printing is the imitation metal etching printing. Generally, the screen printing process is used to print the matte ink onto gold (silver) cardboard, stickers, or other paper-plastic composite materials with strong mirror effect. The ink layer is irradiated with ultraviolet light. After sandblasting, the printed material has a metallic matte effect and an etched three-dimensional effect. Frosted prints have a strong sand sensation, beautiful, generous, elegant and luxurious. In recent years, they have occupied a considerable proportion in the high-end packaging and printing fields such as cigarette labels, wine labels, and cosmetics packaging. However, because the etched ink layer is thicker, rougher, and less resistant to rubbing, the delicately printed product often causes problems such as bursting of the ink layer, fuzzing, and excessive dust after die cutting, which seriously affects the quality of the finished product. Among them, the ink burst problem is particularly troublesome. In some products, ink bursts occur after die cutting and embossing, and some occur during packaging, and some occur even after the printing has not yet been die cut after drying. Therefore, ink bursting is a problem that needs to be solved urgently.
Analysis of Causes of Ink Burst
1. Ink film thickness and brittle matte ink particles are coarse, in which the diameter of additive particles is approximately 15 to 30 Î¼m, and the thickness of the ink layer after screen printing can reach 100 to 150 Î¼m, and the surface of the ink film is rough and uneven. Absorbent materials and inks have poor adhesion, and therefore the ink film has the characteristics of being thick and brittle, and it is prone to burst when exposed to high pressure.
2. Improper drying after printing After the UV-curing device has passed through the UV-curing device after the printing of the matte ink, the temperature of the irradiated surface is too high, the polymerization reaction continues, and the ink layer automatically bursts after curing.
3. Improper die-cut indentation The die-cut indentation quality is the main factor affecting the appearance quality of the carton. Die cutters, irrational selection of indentation steel wire, improper use, etc. are the main causes of ink layer burst, such as die cutter dull and so on.
4. Improper paper handling The structure of paper, improper handling before printing and during printing are also factors that cannot be ignored. Poor paper or low moisture content of the paper will increase the paper's brittleness and toughness, and it will also cause the ink layer to burst. If the paper is not wetted or the semi-finished product is stored improperly, the water content of the paper is low, and the paper becomes brittle after being subjected to high temperature and calendering, and is easily cracked after being pressed.
Ink burst prevention measures
1. When the design of the matte pattern is properly designed, the matte pattern should be avoided as far as possible from the molding of the box, and the distance from the indentation and the cutting position should be at least 2 to 3 mm in order to avoid damage to the matte ink during die cutting, so as to facilitate the prominent three-dimensionality. As shown in Figure 1.
2. Choose a suitable matte ink, reasonably control the ink layer thickness and UV curing temperature
According to a drying method, the matte ink may be classified into two types: a non-UV curable ink and a UV curable ink. The non-UV curable ink is easily deformed due to its drying at a high temperature so that the metal mirror sheet is deformed and is almost eliminated. Currently, UV curable inks are generally used. The UV-curing ink is UV-cured and adheres to the paper. The curing time is only 3 to 5 seconds.
According to the size of the particle size, the matte ink is classified into three types: coarse sand, medium sand, and fine sand. Need to choose according to the fineness of the print and the customer's request. The first thing to do is to ensure that the number of screen meshes and the size of the screen are adapted to each other General coarse sand with 150 to 200 mesh, medium sand with 200 to 250 mesh, fine sand with 300 to 400 mesh screen. Secondly, the ink viscosity is properly selected according to the ink particle size in the printing process. The coarse sand is generally controlled at 2000Â±100CPS (measured at 25Â°C, the same below), the medium sand is controlled at 3000Â±100CPS, and the fine sand is controlled at 3500Â±100CPS. , and to add as little as possible ink additives, ensure that the printing speed is appropriate; choose the right UV lamp, so that the ink particles bond more closely, and attach more firmly on the paper.
It is worth noting that the UV lamp power is recommended to be around 10 kW. The UV curing equipment must be equipped with a cooling device. Generally, a large-diameter exhaust air duct is used and a water cooling device is installed on the lamp tube to avoid jams passing through the light-curing device. Heat distortion and paper brittleness occur.
3. Properly Design, Arrange Die-cut Process The perfect shape of the carton comes from the correct die-cut indentation. The nature of gold (silver) cardboard and matte inks determines the complexity of the die-cut indentation process.
(1) The correct choice of die cutter die cutter requires sharpness and high hardness. The aluminized film on the gold (silver) cardboard surface and the rough particles of the matte ink increase the difficulty of die cutting and accelerate the wear of the die cutter. According to statistics, the non-gold (silver) card frosted print has a print resistance of 800,000 times, while the gold (silver) card frosted print has a significantly lower print resistance.
Different die cutters should be selected for different thicknesses of paper. Austria Boland (BOHLER) and Qingdao Sandvik fish brand G12 die-cutting blades are better. The micro-thickness of the tip of the G12 die-cutting blade is controlled within 3Î¼m, and the sharpness and durability are very suitable for die-cut gold (silver) cardboard, PET and other difficult-to-cut materials. Its height is 23.80mm, and its thickness is 0.71mm, 1.07mm, 1.42mm and so on. Generally, 0.71mm can be used.
(2) Correct selection of indentation line and indentation steel wire The high-quality indentation steel wire should be of moderate hardness, strong stability, round head, circular axis symmetry, small height and thickness deviation, and complete specifications. The selection principle is: the thickness of the indentation steel wire is not less than the paper thickness, and the height is equal to the height of the die cutting blade minus the thickness of the die-cut material, and then the correction value is subtracted 0.05 to 0.10 mm. The selection principle of the indentation line is: the thickness of the indentation line is not less than the thickness of the paper, and the width is equal to 1.5 times the thickness of the paper plus the thickness of the indentation steel wire. For example: Die-cut 0.40mm thick paper, the height of the die cutter is 23.80mm, the thickness of the indentation steel wire is selected as 0.71mm, then:
The height of the indentation steel wire = 23.80-0.40-0.10 (0.05 to 0.10)
Indentation line thickness â‰¥ 0.40 (mm)
The width of the indentation line = 0.40 Ã— 1.5 + 0.71 = 1.31 (mm)
For the frosted product, the height of the indented steel wire needs to be slightly reduced on the basis of the above, ie, the indentation should be lighter, because the indentation is too deep to cause the problem of the explosion of the fold line. The amount of reduction is determined by the thickness of the paper, usually 0.10-0.20 mm. The amount of paper is reduced by 0.20 mm at 350 g/m2 or more and 0.10 mm at 350 g/m2 or less.
At the same time, when the distance between the indentation steel wire is too small, it is necessary to paste a sponge strip to play the role of back tension, press the paper tightly, and reduce the pressure.
In addition, the die-cutting plate is too thick, the die-cutting pressure is too large, the indentation die is too thick, and the indentation die is narrow and the like can easily cause bursting. In the case of die-cutting and frosted prints, corresponding adjustments are also made, and the accumulated paper dust, sundries, etc. in the indentation mold gaps are promptly removed during the die-cutting process.
(3) Reasonably controlling the opening and closing point of the open point is essentially creating a small width of a certain width at the edge of the die cutting knife, so that the cardboard box and the waste edge after die cutting do not spread out, and it is convenient for waste discharge. Even the point is usually hidden in the product after the molding is not easy to see, and to avoid the location of the glue line. If it has to be visible after molding, it should be as small as possible, otherwise it will not be easily separated at the point of waste, resulting in tearing of the paper and bursting of the ink layer nearby. Width = paper thickness +0.20mm.
(4) Properly arrange die-cutting time. The die-cutting of the matte-printed gold (silver) paperboard should be carried out as soon as possible after printing to prevent the ink film from drying out excessively to avoid ink bursting.
4. Maintain proper temperature and humidity Gold (silver) paper jams must be wetted before printing to stabilize the moisture content. During the storage period of the semi-finished products and during the die-cutting process, the temperature and humidity of the workshop should be kept constant to ensure that the paper has a suitable moisture content. The poorer the quality of the base paper, the drier the paperboard, the higher the chance of the prints exploding. In case of abnormal weather changes, the time for die cutting and the production of die cutter must be adjusted in a timely manner. Do not cut the paper and ink film in the case of brittleness.
The application of matte printing in our country is not long, the adaptability of printed materials is not ideal, and the printing process is not mature enough. It is necessary to fundamentally solve the problem of explosion of the ink layer in many aspects. At present, some improved matte inks have been successfully developed and put on the market. High adhesion scratch-resistant matte inks have excellent adhesion fastness and surface hardness to paper substrates, especially general-purpose gold (silver) cardboard, and print products have improved scratch resistance and scratch resistance. After the curing of the high-flexibility and impact-resistant matte ink, the ink film has excellent flexibility and can smoothly pass through post-processing processes such as die-cutting, embossing, and other impacts, eliminating the need for special evasion of die-cut indentations. The layout design also solves the problem of printing of die-cut indented parts that cannot be specially designed. The introduction of a new type of matte ink helps to solve the problem of bursting of the matte ink layer.
Source: Printing Talent Community
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