Roller lining application

The so-called roller lining refers to various wrappings that are wrapped around the surface of the drum other than the drum shell. Offset printing plate roller and blanket roller surface are covered, in addition to printing plates and blankets, the commonly used lining materials are insulation paper, kraft paper, rubber mats, felt and other paper.

Roller lining generally refers to the lining of the squeegee. The lining of the lining determines the correct roll of the three rollers of the offset press. Multi-color printing, to improve the quality of printed matter, has a very important significance.

The purpose of spacers used in offset presses: The first is to use the elastic deformation of the liner material to produce the required printing pressure; The second is to compensate for machine manufacturing accuracy errors and defects existing between the printed surfaces; The third is to reduce the impact and load , To avoid the "hard touch" of the contact of each roller shell, to protect the mechanical equipment.

First, the classification of roller lining

According to the size of the reduction of the blanket cylinders (also called the cutting amount) of various types of offset printing machines, the cushion materials selected, the quality requirements of the products, and the performance differences of the offset printing machines, the cylinder liners can be divided into rigid packages. Lining, neutral lining, soft lining three categories.

l. Hard liner

Hard liner is composed of liner paper and blanket, that is, a few sheets of paper under the blanket will form a hard liner. The width of the roller pressure line is 4-6mm, and the reduction amount λ=0.04-0.08mm. Such linings are relatively rigid, and the elastic modulus of the lining is large, and a small amount of deformation can generate a large printing pressure. Most of the offset presses use contact rollers (ie shoulder irons) so that the rollers run smoothly.

The amount of shrinkage of the liner of the rigid drum liner is small, that is, the deformation of the liner is small, and the dot expansion and deformation are small. Under the condition of high precision of the printing machine, the use of hard lining ensures better transmission of dots, enables fine reproduction of small dots, facilitates the reproduction of colors and layers, and provides bright and realistic quality prints suitable for textured prints. . When using a hard lining, the friction on the surface of the printing plate is large, the wear of the printing plate is obvious, the printing plate has a low printing tolerance, and the manufacturing precision of the machine and the abrasion resistance of the material are required to be high. Otherwise, the printing pressure may be caused. The inequality appears with ink bars. Domestic JJl02A, JJ204, and JJ201 web offset presses, imported Miller, Heideberg, and Komori machines in Japan mostly use rigid liners.

2. Neutral liner

Neutral liners consist of thick paper, feathers, and blankets. The width of the roller pressure line is 8-10 mm, and the reduced diameter λ=0.1-0.2 mm.

The printing performance of the neutral lining lies between the hard and soft lining, the elastic modulus is centered, and the dot reproducibility is good. The wear of the printing plate is not large, the printability of the paper and the manufacturing precision of the offset printing machine Other requirements are not very demanding and the printing adaptability is strong. Most home-made sheetfed offset presses and partially imported mid-range offset presses mostly use neutral liners.

1 neutral soft liner

A domestically-made blanket with a thickness of 1.85 to 1.90 mm, plus a rubber or cork pad, can be found with a certain thickness of paper.

2 neutral soft liner

A Chinese-made blanket with a thickness of 1.85~1.90mm, plus a felt, can be found with a certain thickness of paper.

3. Soft liner

The soft lining is generally under the blanket and it is added with several thin papers. The width of the roller pressure line is 10-12mm, and the diameter reduction λ=0.2-0.4mm. The soft lining is the opposite of the hard lining. The elastic modulus is small, and the shrinkage of the lining required to produce the same printing pressure is relatively large. Therefore, the soft lining has poor transferability to the dot. When the soft liner lining is imprinted, the width of the contact area is relatively large, the contact is relatively good, and the ink of the printed product is relatively thick and plump. Especially when printed on the product, the advantages are better reflected. Therefore, it is suitable for printed text, color blocks, and field prints. .

The soft lining has strong cushioning ability, the blanket is not easy to crush, and the friction effect on the printing plate is small. Most of the sliding amount in the roller rolling can be eliminated by the displacement of the blanket, the printing plate has a long service life, and the printing rate is high. However, due to the deformation and displacement of the blanket, it is easily deformed, and the printed product dots are not smooth enough and are not suitable for printing fine products. The requirements for mechanical manufacturing accuracy and printing pressure adjustment accuracy are relatively low.

Domestic J1202 type, J2101 type, Germany PZO-5 type offset presses use soft lining.

Second, roller lining printing suitability

l. Hard and neutral hard liner

The outlets are clear, smooth, complete, and have good reproduction reproducibility, suitable for the printing of fine products and high-end packaging products;

The change of the geometric shape of the graphic and text is small, especially the increase of the width of the graphic and the printing plate is relatively small; the ink receiving amount of the paper surface is small, and it is not easy to produce the stencil printing phenomenon;

Plates are prone to wear and have low resistance to printing.

The amount of pad change is small, and when it is blanketed, it is easy to “hard”;

When it encounters paper folding angles, skew, and multiple sheets, it can easily bind the bad blanket;

The requirements for machine manufacturing accuracy are high, otherwise, there are prone to "black bars" or dirty plates, pastes and other ills.

2. Soft and neutral soft liner

Less plate friction, longer printing plate life, thicker ink layer, suitable for printing of medium-sized large-quantity lines, field products, etc.; Large displacement and deformation of the blanket, easily deformed and unsmooth dots; Increased width Larger; shimming blanket is not easy to play "hard mouth" but the liner changes a large amount; rubber blanket is not easily rolled bad.

Third, roller lining theory

l. Equal-diameter lining theory

Equal-diameter lining theory is based on the linear velocity theory, ie !=Rω. The theory is that when the rollers are rolling, they must keep the radii of the three rollers equal, so as to ensure uniform linear speeds on the surface of the three rollers, and no slippage will occur during the rolling so as to obtain ideal rolling, ink on the printing plate. After two transfers, it will be faithfully reproduced in print.

Because the blanket cylinder is not a rigid body but an elastic body, in the printing process, the embossed dots must be recessed to reduce the radius, that is, the radii of other points in the embossed area are not equal, so the equal diameter theory The radius of the lining three rollers is not exactly the same, but the radius of the blanket roller is slightly larger.

2. Reducing Lining Theory

1 geometry difference theory

When a rigid body comes into contact with an elastic body, they have only one or two points of equal radius, and the remaining points cannot have equal radii. Therefore, this theory holds that when the two cylinders are in contact with each other, only one or two linear speeds are uniform, and the rest of the points are not uniform, so that the surface slip of the plate cylinder and the blanket cylinder is generated.

2Sites (Sec) Reduction Path Theory

When the equal-diameter rigid body and the elastic body are rolled against each other, the stroke of the one-stroke movement of the elastic body is slightly longer than that of the rigid body due to the compression deformation of the elastic body. It is due to the fact that the radius of the elastic roller will increase after it is pressed, and it is proposed that the radius of the blanket roller must be smaller than the radius of the impression roller and the plate cylinder. That is, the plate cylinder is the largest, the embossing cylinder is centered, the blanket cylinder is the smallest, or the blanket cylinder is the smallest, and the other two rollers are equal.

Fourth, the roller liner lining

The so-called roller lining is determined in the shell of the plate cylinder and the blanket cylinder, covering a certain thickness of the cushion material as required to adjust the gap between the rollers and the printing pressure so that the gears are tangent to the pitch circle. Positionally engaged to meet the needs of the offset printing process.

l. Determination of principles

1 Roller surface does not produce relative sliding principle

The principle of synchronous rolling. The offset press has three rollers per color group. When printing, three rollers are in contact with each other. To ensure the product quality, there must be no relative sliding friction between the contact surfaces of the rollers. However, since the three rollers are driven by gears, their angular velocities (ω) are equal. To ensure that the surfaces do not slide, the rolling radii (R rolls) of the rollers are required to be equal. When the roller is a rigid body, the roller's rolling radius and free radius (Rself) are equal. Since the blanket cylinder is provided with an elastic wrapping, it is an elastic body whose rolling radius is not equal to its free radius. The plate cylinder and the impression cylinder may be like a rigid body.

The rolling radius of the elastic drum is related to the amount of reduction (λ) of the lining on the elastic drum.

That is: R roll = R from + λ
R Roll: Rolling radius R From: Free radius λ: Reduced amount of packing

2 roller gear circular circle tangent principle

The principle of center distance of the drum. All rollers on the offset press are powered by gears. In order to ensure the smoothness of the transmission and reduce gear wear, it is required that the gears mesh in tangential engagement with the pitch circle, that is, the center distance of the roller is equal to the index of the two roller gears. The sum of the circle radii. However, in practical applications, this is not the case. If the center distance of the rolling center is adjusted too large, the gear meshing clearance will be large, the transmission stability will be greatly reduced, the gear wear will also be intensified, and the product quality and the service life of the machine will be reduced to varying degrees. .

3 pressure suitable principle

The contact pressure between the plate cylinder (P) and the blanket cylinder (B) is called the platen pressure (λP-B), and the contact pressure between the blanket cylinder and the impression cylinder (I) is called the platen pressure ( λB- I), ie printing pressure. The general printing pressure is greater than the plate pressure 0.05-0.1mm, the appropriate pressure is the first principle to determine the roller lining. Should pay attention to prevent excessive pressure phenomenon, especially the edition pressure is most sensitive to dot gain, edition presses the conference to cause the network dot to enlarge seriously, thus affects the reduction of the color and the level of the printed product.

2. Determine the method

In practical applications, the above principles cannot be met at the same time, and only some of them can be satisfied. Therefore, we should adopt some technological measures to satisfy the above principles as much as possible so that the difference is not too great.

1 emphasizes the rolling ratio of synchronous rolling

According to the synchronous rolling conditions, the three rollers have the same radius while rolling. However, when the thickness of the printed material changes, the drum liner must also be properly adjusted. However, in actual production, it is inconvenient, so the lining data determined by this method is applicable to products with fixed thickness or slight variation in paper thickness in the long-term or most cases.

2 give priority to plate, blanket cylinder

In this way, the condition of simultaneous rolling and center distance between the printing plate and the blanket cylinder can be satisfied. It does not change with the change in the thickness of the print, but no conditions are satisfied between the impression cylinder and the blanket cylinder. The advantage is that when the thickness of the printed product changes, the lining of the printing plate and the blanket cylinder does not need to be changed, and the center distance between the plate cylinder and the blanket cylinder does not need to be changed. Only the center distance between the impression roller and the blanket cylinder can be changed. This is more convenient and saves you time.

Fifth, the inspection of the lining thickness

Blanket and liner materials are all elastomers. Both compressive and tensile deformations are relatively large. When measuring with a micrometric card, several points should be measured and the average value should be determined. Once the lining thickness and center distance of the drum have been determined, it is best not to change it often to achieve dataization and standardization of the printing process parameters, so as to ensure the quality of the printed matter is stable, save production time, and create conditions for the gradual realization of production automation.