1、 Dirt on the back of the product caused by improper thickness of printing ink layer

      At present, the judgment of whether the printing ink layer is moderate or not is generally based on visual inspection by experience, which is mainly based on the process of uniform compression of the printing layout, the uniform ink reception of the layout to achieve no bottom exposure, no false printing, and the color phase is consistent with the sample. Situation And Prevention Of Color Printing Products Sticking Dirty

      Due to uneven or insufficient printing pressure, poor glossiness of printing paper, deep hue of original print, weak hue of printing ink and other reasons, insufficient understanding is easy to lead to inaccurate determination of printing ink layer. In this case, if blindly increasing the amount of ink to meet the aesthetic feeling of ink color on the printing page, the back of the product will be sticky and dirty due to too thick ink layer.Situation And Prevention Of Color Printing Products Sticking Dirty

2、 We should correctly understand the relationship between printing pressure and ink layer thickness

      Both theory and process practice clearly show that appropriate pressure is an important condition to realize the uniform transfer of printing ink layer. When the printing pressure is insufficient or uneven, it will inevitably affect the uniform transfer of printing ink layer. The printing process practice can show that when the layout pressure is slightly insufficient or uneven, the ink color of the print layout appears to be blooming, and the thickness of the ink color of the whole layout is not consistent. After increasing the ink output, the ink color of the print appears thick, the phenomenon of layout blooming is eliminated, and the aesthetic feeling of the print layout is also improved. Situation And Prevention Of Color Printing Products Sticking Dirty

      It can be seen that a thicker printing ink layer can make up for the poor contact between the printing ink layer and the substrate caused by insufficient printing pressure and eliminate the printing blooming phenomenon, but it is easy to cause the printing to stick and dirty.

       On the contrary, if the printing pressure is adjusted enough and evenly, the ink distribution of the layout is appropriately thinned, the printed products will not flower, the ink layer will also appear strong and uniform, and the products will not be sticky and dirty. Therefore, the color printing products should first adjust the printing pressure, then adjust the ink delivery volume, printing effect is better.Situation And Prevention Of Color Printing Products Sticking Dirty

3、 We should deal with the relationship between paper printability and ink layer thickness

       In the process of embossing printing, if there is a lack of correct understanding of the printing suitability of all kinds of paper, the ink distribution is not properly controlled, and it is also very easy to produce printing sticking and dirty phenomenon. Add the paper with poor paper surface smoothness, the ink penetration is fast, and the ink absorption is large. When printing this kind of paper, if the layout pressure is insufficient or uneven, it is easy to expose the bottom and bloom after printing. When using the paper to increase the ink supply to make up for it, due to the thick ink layer of the layout and the slow drying speed of the imprint, it is easy to have the disadvantage of printing stickiness. Situation And Prevention Of Color Printing Products Sticking Dirty

      Therefore, for the paper with slightly poor smoothness such as offset paper, the printing pressure should be increased accordingly. The paper with good smoothness, such as coated paper and glass card, can achieve better imprint transfer as long as the appropriate printing pressure. Therefore, the printing ink layer should be as thin as possible to avoid the chance of over printing.Situation And Prevention Of Color Printing Products Sticking Dirty

        At the same time, from the perspective of anti sticking, the process principle of “deep ink thin printing” should be adopted for printing large-area plates, that is, the printing ink hue should be slightly darker to make the printing ink layer thinner, which not only meets the requirements of printing hue, but also achieves the purpose of better anti sticking.Situation And Prevention Of Color Printing Products Sticking Dirty

4、 We should master the relationship between plate properties and printing ink layer thickness

      The practice of letterpress printing process clearly shows that the plate quality has a great relationship with the ink layer printing thickness and printing pressure, that is, if the layout smoothness is poor, the ink layer and pressure required for printing will be large, otherwise it will be small. For example, due to the poor ink affinity and poor smoothness of the printed zinc plate, only by increasing the printing pressure and ink layer thickness can we make up for the defects in the characteristics of the plate and achieve the process effect of full printing ink layer. Situation And Prevention Of Color Printing Products Sticking Dirty

      However, we are very prone to printing dirt, so we should not use color printing products above the open format of the zinc plate printer. Due to the good surface gloss, soft texture, good flatness and ink affinity of resin plate, the printing ink layer can be thinned by one layer, which can achieve satisfactory printing effect and is not easy to get dirty. Therefore, resin plate printing is used for printing a large area, and the anti sticking effect is good.Situation And Prevention Of Color Printing Products Sticking Dirty

5、 Dirty printing caused by improper operation technology and process

1. Improper adjustment of inking roller device, excessive ink distribution and uneven printing

      The key influencing factors are whether the ink layer of the printing plate can be kept appropriate and uniform, the accuracy of the inking roller device and the quality of the rubber roller, and whether the ink roller position is adjusted correctly. When the ink roller shaft head and shaft hole have large gap or eccentric core due to wear, as well as the ink roller colloid is hard, out of roundness, lack of good elasticity and viscosity, Situation And Prevention Of Color Printing Products Sticking Dirty

      so that the ink roller is in uneven contact with the layout in the process of rolling ink brushing along the layout, it is easy to cause uneven local one-sided ink brushing and thin ink layer, which is one aspect. On the other hand, if the ink roller silk is too high or one end is too high, and there is uneven contact between the ink roller and the ink string iron roller, it is easy to make the ink layer coating of the layout insufficient or uneven. 

      Therefore, if we blindly increase the ink transmission to overcome the insufficient or uneven ink supply of the layout, the ink layer of the local layout will be too thick and the product will be sticky and dirty. Therefore, for printing large-area plate products, the inking roller device should have high precision, good round core of rubber roller, appropriate soft and hard gum, accurate height adjustment of inking roller and uniform contact with inking iron roller, so as to ensure normal ink transmission and ink distribution, so as to reduce the chance of sticking and dirt of printing products.Situation And Prevention Of Color Printing Products Sticking Dirty

2. Product sticking caused by improper paper receiving

      When the machine picks up and delivers the printed sheets to the paper receiving table, if the angle and height of paper placement (dropping) are not suitable, the upper and lower prints are easy to collide and cross the bottom. For example, in the paper receiving structure of dt400 four opening automatic platform printer, the paper dropping angle and height shall be accurately adjusted according to the print format and paper hardness. Otherwise, the paper edge at the mouth of the print sheet is easy to touch the imprint of the previous print sheet, resulting in damage to the ink on the print page. Situation And Prevention Of Color Printing Products Sticking Dirty

      Therefore, when the sheet of the machine is placed, it should be adjusted so that the paper edge at the mouth of the printing sheet is facing the paper, so as to prevent the printing from sticking and dirty. In addition, the method of taking paper and placing it in the air is also an important link of product anti sticking. The paper receiving should be handled with care to prevent sticking and dirt caused by the moving and friction of the lower printing sheet.Situation And Prevention Of Color Printing Products Sticking Dirty

       When lifting the paper, do not support the back with your fingers and hang the printing sheet along the plane to prevent the product from being pressed over the bottom by your fingers. The quantity of each stack of printing sheets shall be controlled according to the ink receiving condition of the printing plate, so as to prevent the product from being pressed too hard.

3. The product sticking caused by the virtual reality and uneven pressure of the bottom support of the printing plate

      If the color printing products use plywood as the bottom support of the printing plate, because the plywood material is not solid and the compression deformation coefficient is large, the defects in the characteristics of the bottom support can only be overcome by increasing the printing pressure and the thickness of the ink layer, which is bound to make the printing products sticky and dirty. 

      Therefore, magnetic plate table or other metal bottom support should be used for printing plate products with field, which can realize relatively flat and constant printing pressure, make the printing ink layer thin without flower, and is conducive to anti sticking.Situation And Prevention Of Color Printing Products Sticking Dirty

4. The paper is too acidic and humid, so that the printing is not easy to dry and cause sticky dirt

      For example, when printing plate products with offset paper or some domestic coated paper, due to the thick printing ink layer and the large acidity of the paper, it is not easy to dry the ink layer and imprint the bottom. In this case, pay attention to add drying oil properly in the ink to promote the oxidation of the ink layer and the drying of the conjunctiva in time, so as to prevent the printing from sticking and dirty.Situation And Prevention Of Color Printing Products Sticking Dirty

5. The printing caused by paper crease rubs too much at the bottom

       When printing coated paper, due to the good smoothness of the paper surface, if the crease mark of knocking paper is prominent, it is easy to rub with the imprint, resulting in over bottom. Therefore, depending on the layout structure and paper characteristics, the paper knocking method should be mastered as appropriate. For thicker coated paper with curl, try not to knock, but only use the method of kneading up or down to knead the paper straight and firm, so as to avoid over bottom imprinting.Situation And Prevention Of Color Printing Products Sticking Dirty