Blanket and Liner Application Questions in Offset Printing (1-9)

During the entire printing process, blankets are always involved. This is the difference between offset printing and other printing.

In the offset printing process, the image on the plate must be transferred to the rubber roller and then transferred to the paper. This or that problem with this transfer will affect the print quality.

The transfer effect of the blanket, in addition to the performance of the blanket itself, there are other factors. However, the structure, performance, and amine-printing expertise of the blanket as well as the actual level of process technology are also critical.

1 What is offset press pressure?

The offset printing press is based on the principle of three rollers. Between the plate cylinder and the blanket cylinder, there must be pressure between the squeegee and the impression cylinder in order to achieve the correct transfer of the graphic point. To make it stressful, sweetness leads to a push between them. This mutual pushing force is called pressing pressure.

2 What is the relationship between the forces between the rollers?

(1) Between the three Rollings, the paired forces and counteractions always exist and disappear at the same time;

(2) The force and reaction force of the adjacent two rollings are equal in magnitude and opposite in direction.

(3) The generated force (ie pressure) points to the center of the scroll and is perpendicular to the contact surface;

(4) Analyze each roll-to-run, between the bearings and journals passing over the centerline, and the size of the bearing force, in the opposite direction.

3 What is the condition for producing roller pressure?

The pressure between the three rollers is determined on the premise that the distance between two adjacent rollers is determined, and then the rollers are filled with printing plates, blankets, and backing materials to produce pushing force. The center of the roller is separated from the plate; the thickness of the blanket and pad has the following relationship:

(1) After the plate cylinder and the blanket cylinder are lining, the sum of their radii must be greater than the center distance between them.

(2) The sum of the original radius of the printing paper after the blanket cylinder liner and the embossing roll plus one must be greater than the center distance between them.

(3) Three rolling pressure requirements, the three roller contact pressure, the center must be equal to the same, and is equal to the sum of the circle radius of the two rolling simple gear.

4 What is the physical meaning of stress?

When the plate cylinder and the blanket cylinder, the blanket cylinder and the impression cylinder are pressurized, the elastic rubber and the tree mat are changed in shape and volume, and elastic deformation occurs. The roller pressure is generated on the basis that the blanket forms an extrusion deformation. Extrusion deformation is the direct cause and source of stress. In the physical sense, when an object deforms, it exerts a force on the object that deforms it. This force is called the physical force of the elastic roller pressure. It is essentially the force generated by the elastic deformation of the blanket. That is, the elasticity of the blanket.

Extrusion deformation value is determined according to the nature of the cushion and the elasticity of the blanket and the radius of the drum. Different types of tree cushions and radii will have different extrusion deformation values.

5 What is the role of stress?

The purpose of the pressure between the rollers is to make the printing ink of the printing plate keep a good transfer under the pressure of the roller, so that the ink layer is transferred to the blanket and transferred to the paper, and the evenness is not empty; In the above-mentioned two transfer processes, the ink traces are maintained within the permissible deformation value range of the image and text points, and the color reproduction of the halftone dots is achieved, which conforms to the original tone level.

The role of pressure: can make the rough printing surface completely contact, so that the ink mark is printed and the dot is printed. The surface of paper, blankets, and printing plates is relatively flat to the naked eye, and the hand feels relatively flat. The actual shape is rough holes. For these rough surfaces, under certain pressure, the adjacent printing surfaces should be deformed by pressure on the flexible printed surface to achieve reliable air contact and overcome various printing contact surfaces. The group's roughness and unevenness, so that the ink, moisture and the solid surface can suck each other, to achieve the purpose of effective transfer. The role of pressure can also overcome the molecular attraction and enhance the role of adsorption. The ink molecules belong to the adsorption transfer between each printing transfer surface. That is, the adsorption force of the ink on each transfer surface exceeds the attraction force between the ink molecules, and the ink begins to break in the middle, resulting in a good transfer. However, the ink must be in close proximity to generate adsorption, and only under a certain pressure can it have good adsorption and transfer.

Pressure infiltration. The ink is printed on the paper, in which the binder material penetrates the paper; the ink penetration on the paper can be divided into: free penetration and pressure

6 What are the characteristics of offset roller pressure?

Offset printing is an indirect printing method for flexible rubber blankets. In the three-roller rolling process, the pressure change brings with it a complicated transfer problem of the graphic ink.

(1) According to the principle of three rollers, all the printing transfer surfaces need to press with pushing force, always press the hard rigid body and the soft rigid body (the printing plate and the embossing roll are simply rigid rigid bodies, the rubber is the simple surface. This is a soft rigid body, which allows the printing transfer surface to remain in full contact during extrusion deformation, resulting in a good transfer of printing plate dots.

(2) The cushioning effect of the elastic body on the pressure, with a flexible blanket as the graphic transfer medium. When the elastic blanket is subjected to a pushing action, deformation occurs, and when the force is removed, the original shape is quickly restored. In this way, when excessive pressure acts on the deformation of the blanket, the pressure is buffered so that a certain amount of pressure disappears in the elasticity, so that the contact pressure on the surface of the elastic body is relatively gentle. The printing pressure of the elastomer does not require excessive printing pressure.

(3) Offset pressure is round and round, and its pressure rolling characteristics are:

The roller is pressed in the round press motion, not only makes the pressure of the stamping light very light, but also has a good printing contact surface, so that the printed images are all printed and the ideal printing effect is achieved.

(4) Transfer of graphics and text The characteristics of the two embossing belts are: the transfer of the printing plate graphic and text is completed by two imprinting belts, which is an important feature of offset lithographic pressure transfer, not only the minimum pressure available but also reduced The amount of friction, therefore, the printing effect is very good, the graphic transfer is clear, complete, real, and at the same time creates an important condition for prolonging the life of the printing plate.

7 What does the relationship between graph and trace transfer and stress?

Graphic ink transfer is achieved under pressure to achieve good contact between the ink and the printing transfer surface. However, if the printing pressure is too large or too small, it will bring great harm to the correct transfer of the ink.

Because it is a round pressure circle, it can be divided into several pressure conditions in the entire rolling pressure:

(1) When the two rollers are just in contact with each other and the pressure is at zero, the pressing deformation of the blanket gradually increases to the maximum pressure, which is also the best point for the imprint transfer. Then the pressure gradually decreases until it disappears, and the blanket recovers. status.

(2) Proportional transfer of ink. The ink transfer amount increases significantly with the increase of the pressure, and the ink can be printed more completely. However, the unevenness and the roughness of the paper often change, so it is difficult for the transferred ink to maintain a constant and the same thickness, and part of the print sometimes has an emptiness and does not achieve the image.

(3) ink transfer saturation section. There is a critical pressure point. In this period, the pressure is increased, the ink transfer is approximately constant, the imprinting level is enhanced, and the imprinting can be printed under the objective conditions, and the same amount of ink transfer can be maintained between the printed sheets. Keep the ink color consistent and get the best ink transfer.

(4) The pressure is too large for the ink spreading section. Under the effect of excessive pressure, the ink transfer position tends to decrease as the pressure increases. The main reason is that the ink is under pressure and spread, the dot is deformed, the middle ink layer on the imprinting surface is thinner, and the ink layer on the edge is thicker. At this time, the effect of copying and copying is poor.

(5) Overpressure limit. The amount of ink transferred increased with the increase of pressure, mainly due to the effect of excessive pressure, so that the ink spreading was fully reflected. However, the imprinting of the blots and the spread of the outlets were serious and greatly reduced the copying effect.

8 What is the best printing pressure?

Offset press is a round press, rolling pressure from small to large, from large to small changes in the process. In the whole process of continuous change, we must ensure the full transfer of graphic inks and imprints on the one hand; on the other hand, we can print in the transfer process without aliasing, the dots do not spread, the friction is small, and the rolling pressure is small. This is called the optimal pressure, or ideal pressure.

9 How to get the ideal pressure?

To achieve the desired pressure, the following points must be made in the process of correcting the rolling pressure process:

(1) Accurately measure and correct the distance between the center of the drum and the gap of the leveling drum,

12) Correctly calculate the value of the cylinder liner, accurately measure the thickness of the liner, and keep the radius of the cylinder constant.

(3) The roller carefully examines the unevenness of the printing plate and the blanket in the case of three-fold or one-half of the total pressure;

(4) Effectively fill the unevenness of the blanket so that it is even and uniform;

(5) Increase the minimum liner thickness within the limit so that the contact condition is satisfactory;

(6) Choose the ideal tree mat to reduce the extrusion deformation value of the blanket and the imprinting width of the roll-combination.