Drawing is one of the most frequently encountered problems in gravure printing. It involves many factors such as gravure printing machine, plate cylinder, doctor blade, printing environment, ink, etc. Improper handling will affect production and quality.
Drawing, also known as drawing, starting line, when the ink performance and ink color is different, its performance is also different, the general black, blue, magenta drawing phenomenon is more obvious, and generally appear in a large area of ​​the shallow network.
The common wire drawing is mainly divided into three types: drawing in the shallow position, drawing in the squeegee in the solid color, and drawing in the blank in the printing blank.
Shallow wire position drawing
1. From the origin of the design plate to prevent wire drawing
Take full account of printability in manuscript design and plate making. Must take into account the printing direction, try to avoid printing from light to dark; black, magenta version of the most likely to appear shallow online drawing, especially the black version, due to the coarse carbon particles in the ink, when the black network is very shallow, a network of points Almost no carbon particles can be loaded, so drawing is more likely to occur. Therefore, a large area of ​​black shallow net should be set as a special gray version, reducing the difficulty of printing and reject rate.
2. Correct use of squeegee to avoid drawing
(1) The selection of the squeegee. The surface hardness of the chrome plated roller is HV850～1100. The hardness of the squeegee should be lower than the hardness of the plate. About HV600, the hardness is too low. The ink scraping is not clean. If the hardness is too high, the plate wear will be accelerated and a tool mark will be generated. Affect the quality of printed products.
(2) The flatness of the squeegee. When the squeegee is installed, the blade should be flattened first, and then the screws should be tightened from the middle to the two sides in order. It cannot be reached in one step. It needs to be repeated two or three times to ensure that the blade is evenly loaded.
(3) The sharpness of the squeegee. The 600# water sandpaper or 2# metallographic sandpaper can be used to grind the squeegee, or use a special grinder to grind the back of the squeegee into a bevel of about 25°, even if a new knife is used.
(4) Squeegee angle. The squeegee angle is smaller than normal when printing, and at the same time, the distance between the squeegee and the plate contact point and the imprinting point is shortened.
3. Reasonable matching ink to prevent wire drawing
(1) When the screen has a large area of ​​shallow net or level transition, good quality ink should be used to prevent the ink pigment particles from being too thick to cause wire drawing. Usually the fineness of the ink is 15μm, too coarse ink particles to the squeegee The printing plate has a lot of damage.
(2) When dispensing ink, under the premise of no influence on other patterns on the same plate, slow-drying solvents should be considered. Do not add too much auxiliary solvents such as ethyl acetate to prevent the ink from changing. print.
(3) Ensure that the ink viscosity is moderate and stable. The generation of drawing has a direct relationship with the viscosity of the ink. In general, the higher the viscosity of the ink, the easier it is to produce a knife line during printing. In addition, due to the different performance of each brand of ink, the amount of solvent added is not the same, the ink can be mixed with reference to the specific data provided by the manufacturer, and combined with their own printing conditions and the printed product for specific operations.
Field block color drawing
The drawing performance of the real-color color block is represented by the fact that the edge of the solid color block is raised by the squeegee and the edge of the printing color block is dotted. Generally, the short line is several millimeters. The main reason is that the ink viscosity is too high and the ink There is excessive crystallization of pigment particles. The solution is as follows.
1. Filter the ink and add a certain amount of new ink during use.
2. Adjust the squeegee angle slightly, and shorten the distance between the squeegee blade's point of contact with the plate and the embossed point.
Drawing, also known as drawing, starting line, when the ink performance and ink color is different, its performance is also different, the general black, blue, magenta drawing phenomenon is more obvious, and generally appear in a large area of ​​the shallow network.
The common wire drawing is mainly divided into three types: drawing in the shallow position, drawing in the squeegee in the solid color, and drawing in the blank in the printing blank.
Shallow wire position drawing
1. From the origin of the design plate to prevent wire drawing
Take full account of printability in manuscript design and plate making. Must take into account the printing direction, try to avoid printing from light to dark; black, magenta version of the most likely to appear shallow online drawing, especially the black version, due to the coarse carbon particles in the ink, when the black network is very shallow, a network of points Almost no carbon particles can be loaded, so drawing is more likely to occur. Therefore, a large area of ​​black shallow net should be set as a special gray version, reducing the difficulty of printing and reject rate.
2. Correct use of squeegee to avoid drawing
(1) The selection of the squeegee. The surface hardness of the chrome plated roller is HV850～1100. The hardness of the squeegee should be lower than the hardness of the plate. About HV600, the hardness is too low. The ink scraping is not clean. If the hardness is too high, the plate wear will be accelerated and a tool mark will be generated. Affect the quality of printed products.
(2) The flatness of the squeegee. When the squeegee is installed, the blade should be flattened first, and then the screws should be tightened from the middle to the two sides in order. It cannot be reached in one step. It needs to be repeated two or three times to ensure that the blade is evenly loaded.
(3) The sharpness of the squeegee. The 600# water sandpaper or 2# metallographic sandpaper can be used to grind the squeegee, or use a special grinder to grind the back of the squeegee into a bevel of about 25°, even if a new knife is used.
(4) Squeegee angle. The squeegee angle is smaller than normal when printing, and at the same time, the distance between the squeegee and the plate contact point and the imprinting point is shortened.
3. Reasonable matching ink to prevent wire drawing
(1) When the screen has a large area of ​​shallow net or level transition, good quality ink should be used to prevent the ink pigment particles from being too thick to cause wire drawing. Usually the fineness of the ink is 15μm, too coarse ink particles to the squeegee The printing plate has a lot of damage.
(2) When dispensing ink, under the premise of no influence on other patterns on the same plate, slow-drying solvents should be considered. Do not add too much auxiliary solvents such as ethyl acetate to prevent the ink from changing. print.
(3) Ensure that the ink viscosity is moderate and stable. The generation of drawing has a direct relationship with the viscosity of the ink. In general, the higher the viscosity of the ink, the easier it is to produce a knife line during printing. In addition, due to the different performance of each brand of ink, the amount of solvent added is not the same, the ink can be mixed with reference to the specific data provided by the manufacturer, and combined with their own printing conditions and the printed product for specific operations.
Field block color drawing
The drawing performance of the real-color color block is represented by the fact that the edge of the solid color block is raised by the squeegee and the edge of the printing color block is dotted. Generally, the short line is several millimeters. The main reason is that the ink viscosity is too high and the ink There is excessive crystallization of pigment particles. The solution is as follows.
1. Filter the ink and add a certain amount of new ink during use.
2. Adjust the squeegee angle slightly, and shorten the distance between the squeegee blade's point of contact with the plate and the embossed point.
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