Offset roller lining
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First, the classification of the lining
The surface of the offset printing plate cylinder and the blanket cylinder (adhesive roller) are lining, and the blanket roller lining can be divided into the following three categories.
1, rigid lining
Generally, a few sheets of paper under the blanket form a rigid lining. This kind of lining is relatively hard, and the elastic modulus of the lining is large, and a small amount of deformation can produce a large printing pressure. Therefore, the use of such a lining, the amount of compression of the lining is small, that is, the deformation of the lining is small, and the expansion and deformation of the skein are small. Therefore, the rigid lining has better transmission to the dots, which is beneficial to the reproduction of colors and layers, and is suitable for printing textured prints. However, it is important to note that the compression of the liner should be controlled within 0.2 mm, preferably around 0.1 mm. If the amount of compression of the liner is too large, it will not only be unfavorable to the machine, but also cause other failures, and it is not good for the transmission of the dots, and the advantage of using the rigid liner is lost. Therefore, the use of rigid lining requires high precision of the machine and accurate adjustment of the printing pressure. Otherwise, it not only can not reflect the advantages of the rigid lining, but will bring new disadvantages. That is to say, the rigid package has its unique use conditions and applications, and cannot be used everywhere. At present, it is unscientific for some printers to blindly use hard lining.
2, soft lining
The soft lining is usually a rag on the underside of the blanket plus a few sheets of tissue. The software package lining is exactly opposite to the hardware package lining. The elastic modulus is small, and the compression amount required for the same printing pressure is relatively large. Generally, the compression amount is controlled between 0.2 mm and 0.3 mm. The soft lining has a poorer transmission to the dot, but the width of the contact zone is larger when the soft lining is embossed, the contact is relatively good, and the ink color of the printed product is relatively full and full, and the advantage is better when the product is printed. Therefore, it is suitable for printing text, color blocks, and solid prints. In addition, the soft lining buffering ability is strong, the blanket is not easy to be crushed, and the precision of the machine precision and the printing pressure adjustment is relatively low, so the soft lining is suitable for use on a new machine or a new machine with low precision. .
3, neutral lining
Neutral lining is generally composed of rubber under the blanket. Its modulus of elasticity is centered, so its performance is also in the middle. Its use is also on the machine between the old and new machines. It can also be used on new and old machines. This kind of lining is more versatile and the performance is ok.
Second, the determination of the drum liner
The determination of the lining category can be determined according to the above, and the following principles should be considered in determining the total thickness of the lining:
1, determine the principle
1 The principle of relative sliding does not occur on the surface of the drum (synchronous rolling conditions)
There are three rollers in each color group of the offset printing machine. When printing, the three rollers are in contact with each other. In order to ensure the quality of the product, etc., it is required that the roller contact surface is a pure roller, and there is no relative sliding friction, but since the three rollers are through the gear For the transmission, the angular velocities are equal. To ensure that the surface does not slide, the rolling radius (R roll) of each roller is required to be equal. When the roller is a rigid body, the rolling radius of the roller is equal to the free radius of the roller (R from), and the blanket cylinder is provided with an elastic lining, which cannot be treated as a rigid body. The impression cylinder and the plate cylinder can be regarded as a rigid body, so the blanket The rolling radius of the drum is not equal to the free radius of the drum. Studies have shown that the rolling radius of the elastic roller is related to the compression of the lining on the elastic roller. The approximate relationship is as follows:
R roll = R from + λ, λ is the amount of compression of the elastic roller.
2 Roller gear pitch circle tangency principle (center distance condition)
The rollers on the offset printing machine transmit power through the gears. In order to ensure the smoothness of the transmission and reduce the wear of the gears, the gears are required to be tangentially meshed and driven in the pitch circle, that is, the center distance of the rollers is the two cylinder gears. with. However, in practical applications, some people tend to adjust the center distance of the drum too large, resulting in a large backlash of the gear teeth, a large reduction in the smoothness of the transmission, and an increase in the wear of the gear teeth, which not only reduces the product quality, but also Reducing the life of the machine is a problem that should be avoided.
3 pressure suitable principle
The contact pressure between the plate cylinder and the blanket cylinder is called the plate pressure, which is represented by λp. The contact pressure between the blanket cylinder and the impression cylinder is called the printing pressure, that is, the printing pressure, which is expressed by λi, and the general printing pressure is More than the plate pressure 0.05mm ~ 0.1mm. The appropriate pressure is the first principle to determine the drum liner. With regard to stress, special attention should be paid to preventing excessive pressure. Some people blindly increase pressure when they encounter problems, and the pressure is severely large. The press pressure is most sensitive to the expansion of the dot, and the overpressure of the plate causes the dot to expand, which affects the color and level of the print.
2, determine the method
The above principles cannot be satisfied at the same time. In practice, only some of the conditions can be met, or the above conditions can be met as much as possible, and the difference is not too great. The specific determination methods are as follows:
1 Method for determining the lining of synchronous rolling conditions
This method can meet the synchronous rolling condition under the fixed paper thickness, but does not meet the central distance condition, such as the paper thickness change, does not satisfy any conditions, so this method is only suitable for long-term printing of fixed paper thick printing products. Set the paper thickness to h, the plate pressure to λp, the printing pressure to λi, λp, λi according to the type of lining to set the specific data in advance, rigid lining: λp = 0.1mm, λi = 0.15mm, package lining: λp =0.2mm, λi=0.25mm, neutral lining: λp=0.15mm, λi=0.2mm, according to the synchronous rolling condition: RP rolling = RB rolling = Ri rolling, the following formula can be derived:
R P from =Ri+h
Plate cylinder lining is δp= R P from -Rp
R B from = R P from - λ λ can be calculated by λp instead of λ = λp
Rubber roller liner is δB=R B from -RB
Plate - rubber roller center distance A (P-B) = 2R B from + λ - λp = 2R B
Rubber-imprint roller center distance A(I-B)=2R BFrom +λ-λi≈2R BFrom
Plate - rubber roller gap H (P-B) pillow = A (P-B) - R P pillow - R B pillow
Rubber-embossed roller gap H(I-B) pillow = A(I-B)–R I pillow - R B pillow
From the above computer formula, it can be known that δP and δB are functions of paper thickness h, h changes, and the thickness of the lining is changed. In actual production, it is not convenient to change the lining when changing the paper thickness, so the package determined by this method is inconvenient. The lining data is suitable for long-term or in most cases where the fixed paper thickness or the paper thickness does not change much. In addition, it can be seen from the formula that the center distance of the drum is A (P-B), and A(I-B) is approximately 2R B self, which is very close to the sum of the two cylinder indexing circles, that is, the center distance condition is approximately satisfied.
2 Priority is given to the method of determining the printing plate-rubber roller
This method can meet the conditions of synchronous rolling and center distance between the printing plate and the rubber roller, and cannot change with the paper thickness, but the embossing-rubber roller does not satisfy any conditions. The advantage of this method is that when the thickness of the printed paper changes, the lining of the printing plate and the rubber roller does not need to be changed, and the center distance of the printing plate-adhesive roller does not need to be changed, and only the center distance of the embossing-adhesive roller can be changed. This operation is more convenient and trouble-free, so the application of this method is more common, but there are also disadvantages: when the paper thickness changes greatly, the synchronous rolling condition and the center distance condition between the embossing and the rubber roller are not satisfied. The friction of the surface of the two rollers is intensified, and the side gap of the gear teeth is increased, which is not suitable for long-term use in this state. According to the plate-rubber roller synchronous rolling condition R P roll = R B roll and center distance condition A (P-B) = R P from + R B from - λp = C can be obtained by the following formula:
R B from =(1/2)A(P-B)
δB = R B from -R B
R P from = R B from +λ λ=λp
δP = R P from -R P
A(I-B) = 2R B from +Ri+h-λi
A(P-B) = 2R B from =C C is a constant
H(P-B) pillow = A(P-B)–R P pillow - R B pillow
H(I-B) pillow = A(I-B)–R I pillow - R B pillow
It can be seen from the above formula that δP and δB are independent of h, A(P-B) is a known constant, and A(I-B) is a function of h, so H(I-B) should be adjusted with h.
According to the above method, the lining data, the roller pressure, the roller gap, and then the full version of the test print, test the pressure condition, generally speaking, there will be no problem, if the pressure is not enough, you can add a sheet of paper in the rubber lining Just fine. After the rubber bag lining is used for a long time, the lining will change the book, and the pressure may be insufficient. At this time, a piece of paper is added to the lining of the bag, but it should be noted that the original lining should still be given according to the original data.
Third, the relationship between the lining and overprinting
Roller lining has an important impact on product overprinting, mainly in the following aspects
1. The relationship between the drum liner and the length of the printed graphic
The three rollers of each offset group of the offset printing machine rotate at an equal angular velocity. The arc length of each roller surface is proportional to its free radius at the same corner. The length of the graphic on the printed sheet has the following relationship with the length of the graphic on the printing plate:
L print = (R print / Rp)? Lp
R is the free radius of the impression cylinder (R print = Ri + h), and Rp is the free radius of the plate cylinder.
It can be known from the formula that the free radius of the blanket cylinder has nothing to do with the length of the printed image, that is, the change of the blanket cylinder liner has no effect on the length of the printed sheet, and the length of the printed image is only related to the free radius of the plate cylinder and the impression cylinder.
The amount of change in the circumferential length of the printing plate or the impression cylinder radius can be directly increased by the above formula:
ΔL/ΔR=Lp/Rp
ΔL print image circumferential length change, ΔR is the drum radius change, that is, ΔR = R before -R. When ΔL is negative, the length of the graphic is reduced. When ΔL is positive, the length of the graphic is increased. That is to say, when the plate cylinder lining is increased or the radius of the impression cylinder is increased, the length of the printed graphic will be reduced, otherwise the opposite is true.
2. the relationship between multi-color overprint and pressure
According to the formula R roll = R from + λ, if the pressure changes, that is, λ changes, the rolling radius of the rubber roller changes. When the plate pressure and the printing pressure are simultaneously increased or decreased, it is equivalent to increasing or decreasing the rubber lining, and does not change the printed image. The length of the text, if only the plate pressure is increased without changing the printing pressure, which is equivalent to increasing the plate lining, the printed graphic will be shortened. If only the embossing is increased without changing the plate pressing, this is equivalent to increasing the embossing roller radius. The printed graphic will grow, otherwise the opposite. The amount of change can also be obtained from the previous formula, where ΔR is calculated by Δλ instead.
3. the relationship between the lining and overprinting when printing monochrome machine
It is assumed in advance that the paper has no dimensional change, and the offset printing machine is accurate in paper feeding and accurate in paper positioning. According to the above discussion, as long as the monochrome machine does not change the drum parameters (mainly the printing plate lining), the length of the graphic is always the same after each printing, so the overprinting will completely coincide. From this point of view, the monochrome machine is more than the multi-color machine. The accuracy is better.
4. the relationship between the lining and overprinting of multi-color machine printing
In the same way, it is assumed in advance that the paper has no dimensional deformation, and the offset printing machine is accurate in transferring paper. According to the analysis of the length of the lining and the text, it is known that the latter color must be completely coincident with the previous color, which inevitably requires that the impression cylinder, the plate cylinder and the lining of the latter color should be exactly the same as the previous color, that is, the rear color group. It is a replica of the front color group, but in fact it is impossible to make the color groups completely consistent in the machine manufacturing, there will always be a slight error, so the multicolor machine registration is not as good as the monochrome machine, but as long as the manufacturing precision reaches the given requirement Registration is not a problem. If the drum is corroded, worn, crushed or the processing precision of the drum itself is low, the drums have a large difference. It is no longer possible to register the colors, so the printing cylinders of the multi-color machine, the impression cylinder and the lining thereof are consistent. Sex is especially important, and special attention should be paid to the protection and maintenance of the impression cylinder.