Analysis of the causes of color printing sticky dirt is a common fault in color printing. The occurrence of this kind of fault will affect the printing quality at least, and even cause a large number of scrapped products, which will bring great losses to enterprises. There are a lot of reasons for the dirty printing, such as printing ink layer is too thick, paper back is too smooth, improper ink mixing, printing pressure is not suitable. Sticky dirty ink characteristics of both the reasons, but also with the environment temperature and humidity. Only by carefully controlling the technology can we ensure the printing quality of the products.
1. A correct understanding of the relationship between printing pressure and ink layer thickness, appropriate printing pressure is an important condition to realize the uniform transfer of ink layer. Insufficient or uneven pressure will affect the uniform transfer of ink layer. In printing, when the pressure of the layout is insufficient or uneven, the ink color of the printed matter will bloom, and the ink thickness of the whole page is not consistent. Increasing the amount of ink can indeed make up for the lack of printing pressure caused by the poor contact between the ink layer and the substrate, but it is also easy to cause the printed matter to stick dirty. Therefore, it is necessary to adjust the printing pressure first, and then adjust the ink output of the page, so as to get a good printing effect.
2. Deal with the relationship between paper printability and ink layer thickness, the paper with poor surface smoothness can absorb ink quickly and absorb more ink. When printing this kind of paper, if the printing pressure is insufficient or uneven, it is easy to expose the bottom and make the printing flowery. If the ink amount is increased, the ink layer is thicker, and if the drying speed of the imprint is slow, it is easy to get sticky and dirty. For the paper with poor surface smoothness, the printing pressure should be increased correspondingly; for the paper with good surface smoothness, such as coated paper and glass cardboard, the ink layer should be as thin as possible to avoid sticky dirt. From the point of view of anti smudging, "deep ink thin printing" should be adopted for printing large area plates, that is, the color of the ink should be adjusted to a deeper level, and the ink layer should be thinner. In this way, the requirements of printing hue can be met and the sticky dirt can be avoided.
3. Master the relationship between the characteristics of plate and the thickness of printing ink layer. The quality of plate, the thickness of printing ink layer and printing pressure have a certain relationship. If the smoothness of the layout is poor, the ink layer and pressure required for printing will be large; otherwise, it will be small. If zinc plate printing is used, due to its poor ink affinity and poor surface gloss, only by increasing the printing pressure and ink layer thickness can the printing ink layer be full. However, it is easy to lead to dirt, so it is not suitable to use zinc plate to print color printing products with more than eight open format. Because of its good surface gloss, soft texture, good flatness and ink affinity, the printing ink layer of photosensitive resin plate is thinner, which can still achieve better printing effect and is not easy to get sticky dirt. Therefore, the printing of large areas of the image should use the photosensitive resin plate.
4. To avoid sticking dirt on the back caused by improper thickness of printing ink layer, the main basis for judging whether the printing ink layer is moderate is to press the printing plate evenly, the ink on the page is even, and the printing color is consistent with the sample. If the printing pressure is uneven or insufficient, the glossiness of the printing paper is poor, the color of the original manuscript is deep, and the color tone of the ink is too light, it is easy to determine the thickness of the printing ink layer. At this time, if you increase the amount of ink blindly, the back of the printed matter will be sticky and dirty due to the thickness of the ink layer.
5. Avoid improper operation caused by dirty printing. (1) improper adjustment of ink roller, excessive or uneven ink volume, when the roller shaft head and shaft hole appear large gap or eccentric due to wear; when the ink roller colloid elasticity becomes poor, the ink roller contacts with the layout unevenly in the process of rolling along the page, which is easy to cause uneven ink brushing of local layout and thin ink layer. In addition, if the ink roller is set too high or too high, it is easy to make the layout ink layer coating insufficient or uneven, at this time, if you blindly increase the amount of ink, it will make the local layout ink layer thicker, resulting in sticky dirt. Therefore, when printing large-area plate products, it is required that the ink roller device has high precision, the cot roundness is good, the cot colloid is appropriate, the ink roller and the ink roller contact evenly, and the height adjustment should be accurate, so as to reduce the chance of printing products sticking dirty.
(2) If the paper is not properly received, the paper drop angle and height should be adjusted according to the size of the printed matter and the soft and hard degree of the paper. Otherwise, the edge of the paper in the mouth of the printing sheet will easily touch the imprint of the previous sheet, which will damage the ink on the surface of the printed matter. In addition, the printed sheets should be handled with care to prevent the upper and lower sheets from moving and rubbing. The quantity of air dried paper should be controlled according to the ink condition of the printed page to prevent heavy pressure and dirt. (3) The printing plate backing is not solid, the pressure is uneven, the plywood material is not solid enough, and the compression deformation coefficient is large. If this material is used as the printing plate backing, the printing pressure and ink layer thickness must be increased, so the printed matter is easy to get dirty. Therefore, when printing on the spot, it is better not to use the plywood backing, but to use the magnetic plate or other metal backing, so that the ink layer is thin and not flowered, which is conducive to anti fouling. (4) In addition, it is not easy to dry the thick offset paper due to the acid. At this point, the ink should be properly added to dry oil, to prevent printing sticky dirty. (5) When printing coated paper, the surface of the paper is smoother. If the crease is protruding, it is easy to rub with the imprint and get dirty. Therefore, the paper tapping should be controlled according to the layout structure and paper characteristics. For thicker coated paper, try not to knock, only use the method of kneading up or down, and knead the paper flat and firm.
To sum up, there are many reasons that cause color printing to stick dirty in printing. As long as we have a good technical control, we can not only get a good anti staining effect, but also improve the printing quality and production efficiency.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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