Second, a large area of ​​the pinhole on the ground
There are two types of pinholes in a large area on the ground. One is pinholes used in thin film printing, such as plastic film, aluminum spray paper, and paper coated with PE resin on the surface. The pinholes on these materials are the pressure applied to the plate, and the air gap created by the extrusion of the double-sided tape. In addition, the anilox roller has a small amount of ink, poor coverage, high ink viscosity, and poor leveling of the ink. The ink in the cell site can be easily transferred to the printing substrate in a bit by bit, leaving white on the ground. Huge piece, called the pinhole. Another type of pinhole appears on the paper, especially on paper with rough surface and good water absorbency. Observe with a magnifying glass to clearly see the fibers of the paper. The place where the fiber protrudes is dark in color, where it is recessed. The color is light, and the thick one looks like a white one. It is also called a pinhole. However, if a batch of coated paper with good smoothness is changed, such pinholes will be greatly improved. Obviously, this is a special phenomenon that is different from pinholes in films.
The solution to pinholes is:
1. As far as possible the use of high-density double-sided adhesive, its poor flexibility, air gap is small, often used in the field printing. However, if there are small anti-white characters on the large field surface, the use of this double-sided adhesive should prevent excessive pressure and paste. High-density double-sided adhesive has a distinct side effect, that is, the pattern border is prone to print marks, which is a characteristic defect of excessive flexographic printing pressure. In order to solve this problem, it is necessary to carefully control the printing pressure, that is, the pressure of the plate roller on the embossing roller.
2. The anilox roller with a larger amount of ink storage, ie, an anilox roller with a lower number of lines, makes the amount of ink larger and the saturation of the color higher.
3. Adjust the appropriate ink viscosity, not too high, we must make full use of the role of ink leveling in the anilox roller surface, add some slow drying agent in the ink, which will effectively solve the pinhole problem.
4. Control the printing speed. The speed of printing is also indirectly related to the amount of ink on the anilox roller. On a single-squeegee flexo press, the higher the speed, the darker the ink; conversely, the higher the speed on a double-squeegee flexo, the lighter the ink. When the same anilox roller is at a high or low speed, the ink loading is not absolutely constant. When solving the pinhole problem, in order to obtain a relatively large amount of ink, the speed of the single-squeegee flexo press can be increased. Squeegee flexo presses can slow down.
5. Stacked colors. Offset printing and embossing have a tradition in that when the color saturation does not reach the specified value, a double color printing is used, that is, printing two printing. This method can also be used on flexo printing. There are two Indian seals, and even India and India. In the case of a stacked-color process, pinholes are basically not found because the pinholes are overlapped during the overlapping process and masked.
6. For the other types of pinholes that appear on the previously mentioned paper, there are two possible solutions:
a. It is well known that inks are used on absorbent substrates, such as relatively rough paper, primarily by osmotic absorption drying. Therefore, after the ink is transferred to the paper, it penetrates into the interior of the paper until the toner particles in the ink become sufficiently tight and the gap between the particles is continuously reduced. When the capillary pull force between the pigment particles is equal to the absorption connecting force in the paper, Complete the absorption and infiltration process. The degree of penetration of the ink into the interior of the paper is directly proportional to the capillary pull in the paper. d:=(PX r2 X t/2 n) 1/2 where: d-ink presses the depth of paper, P-printing pressure, r-paper capillary radius, t-time, n-ink viscosity. Since the printing pressure is far greater than the capillary attraction, the latter is ignored in this formula. From the formula, it can be seen that the depth of the ink pressing paper, that is, its hiding power, mainly depends on the printing pressure. Excessive printing pressure will result in flexographic imprints on the film, that is, around the frame. However, in the printing of paper, even if the pressure hits a lot, we rarely find the phenomenon of boxing around. The main reason for this difference is that the drying mechanism of the ink on these two different materials is different. On the film, it is volatilized to form a film and is absorbed on the paper. In addition, from the analysis of the surface density of the material, the surface density of the film is also higher than the surface density of the paper, and the printing plate is pressed and deformed on the surface of the film so that the force that causes the surrounding frame to be scattered is transferred by the loosened paper surface. Rest assured to increase some of the pressure without worrying about causing a border effect.
b. Replace the flexible media with good ink transfer properties. The commonly used DuPont Selimi plate has general-purpose EXL, NOW, UVP, etc., and can be used when printing paper and film. However, if the surface of the paper is too rough, such as kraft paper, try PLS with a lower surface hardness. The author used this type of material in kraft paper printing before.
There are two types of pinholes in a large area on the ground. One is pinholes used in thin film printing, such as plastic film, aluminum spray paper, and paper coated with PE resin on the surface. The pinholes on these materials are the pressure applied to the plate, and the air gap created by the extrusion of the double-sided tape. In addition, the anilox roller has a small amount of ink, poor coverage, high ink viscosity, and poor leveling of the ink. The ink in the cell site can be easily transferred to the printing substrate in a bit by bit, leaving white on the ground. Huge piece, called the pinhole. Another type of pinhole appears on the paper, especially on paper with rough surface and good water absorbency. Observe with a magnifying glass to clearly see the fibers of the paper. The place where the fiber protrudes is dark in color, where it is recessed. The color is light, and the thick one looks like a white one. It is also called a pinhole. However, if a batch of coated paper with good smoothness is changed, such pinholes will be greatly improved. Obviously, this is a special phenomenon that is different from pinholes in films.
The solution to pinholes is:
1. As far as possible the use of high-density double-sided adhesive, its poor flexibility, air gap is small, often used in the field printing. However, if there are small anti-white characters on the large field surface, the use of this double-sided adhesive should prevent excessive pressure and paste. High-density double-sided adhesive has a distinct side effect, that is, the pattern border is prone to print marks, which is a characteristic defect of excessive flexographic printing pressure. In order to solve this problem, it is necessary to carefully control the printing pressure, that is, the pressure of the plate roller on the embossing roller.
2. The anilox roller with a larger amount of ink storage, ie, an anilox roller with a lower number of lines, makes the amount of ink larger and the saturation of the color higher.
3. Adjust the appropriate ink viscosity, not too high, we must make full use of the role of ink leveling in the anilox roller surface, add some slow drying agent in the ink, which will effectively solve the pinhole problem.
4. Control the printing speed. The speed of printing is also indirectly related to the amount of ink on the anilox roller. On a single-squeegee flexo press, the higher the speed, the darker the ink; conversely, the higher the speed on a double-squeegee flexo, the lighter the ink. When the same anilox roller is at a high or low speed, the ink loading is not absolutely constant. When solving the pinhole problem, in order to obtain a relatively large amount of ink, the speed of the single-squeegee flexo press can be increased. Squeegee flexo presses can slow down.
5. Stacked colors. Offset printing and embossing have a tradition in that when the color saturation does not reach the specified value, a double color printing is used, that is, printing two printing. This method can also be used on flexo printing. There are two Indian seals, and even India and India. In the case of a stacked-color process, pinholes are basically not found because the pinholes are overlapped during the overlapping process and masked.
6. For the other types of pinholes that appear on the previously mentioned paper, there are two possible solutions:
a. It is well known that inks are used on absorbent substrates, such as relatively rough paper, primarily by osmotic absorption drying. Therefore, after the ink is transferred to the paper, it penetrates into the interior of the paper until the toner particles in the ink become sufficiently tight and the gap between the particles is continuously reduced. When the capillary pull force between the pigment particles is equal to the absorption connecting force in the paper, Complete the absorption and infiltration process. The degree of penetration of the ink into the interior of the paper is directly proportional to the capillary pull in the paper. d:=(PX r2 X t/2 n) 1/2 where: d-ink presses the depth of paper, P-printing pressure, r-paper capillary radius, t-time, n-ink viscosity. Since the printing pressure is far greater than the capillary attraction, the latter is ignored in this formula. From the formula, it can be seen that the depth of the ink pressing paper, that is, its hiding power, mainly depends on the printing pressure. Excessive printing pressure will result in flexographic imprints on the film, that is, around the frame. However, in the printing of paper, even if the pressure hits a lot, we rarely find the phenomenon of boxing around. The main reason for this difference is that the drying mechanism of the ink on these two different materials is different. On the film, it is volatilized to form a film and is absorbed on the paper. In addition, from the analysis of the surface density of the material, the surface density of the film is also higher than the surface density of the paper, and the printing plate is pressed and deformed on the surface of the film so that the force that causes the surrounding frame to be scattered is transferred by the loosened paper surface. Rest assured to increase some of the pressure without worrying about causing a border effect.
b. Replace the flexible media with good ink transfer properties. The commonly used DuPont Selimi plate has general-purpose EXL, NOW, UVP, etc., and can be used when printing paper and film. However, if the surface of the paper is too rough, such as kraft paper, try PLS with a lower surface hardness. The author used this type of material in kraft paper printing before.
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