Offset Overprint Accuracy Related Questions (10-14)

10. Overprint Accuracy - How Does the Plate Image Radially Elongate?

In order to make the plate image size radially stretchable, the following process methods can be used:

(1) Reduce the thickness of the plate cylinder liner;

(2) While reducing the thickness of the printing plate, the thickness of the pad of the rubber roller is increased by the same amount, and the increase and decrease amount of the pad is kept equal.

The above two methods can even increase the size of the printing plate graphic, but these several increasing methods have the effect of simple and complex and different pressure in the process operation. Since the second method is more complicated in operation, the pressures of the printing plate and the blanket cylinder are not changed, the pressure of the rubber and the impression cylinder is increased, and the extrusion deformation of the blanket is increased to produce the kyphosis package, and the increase amount is more significant than the first type.

Operation must pay attention to:

(1) The allowable value of liner thickness increase and decrease can only be controlled in the range of ± 0.10mm, not too much;

(2) The registration error of the image size change shall not exceed ±0.10mm, otherwise there will be a hue shift and level confusion.

11. What is the relationship between overlay accuracy and paper distortion?

In multi-color printing, the image registration error caused by paper deformation is the main factor affecting the accuracy of overprinting. Paper deformation is varied, but it can be divided into: natural deformation and pressure deformation. The natural deformation is the change of the water content of the paper under the condition that the paper does not have the force of F, the elongation and shortening of the size caused by water absorption or dehydration.

Deformation. Moreover, this deformation has a close relationship with the ambient temperature and humidity.

The pressure deformation is the effect of the pressing force of the paper in the simple pressing, and the plastic deformation of the straight line size and area caused by the dislocation of the fibers.

The overlay error caused by these two deformations of paper is almost insurmountable. However, the three factors that control the deformation of the paper, namely, the water content, the ambient temperature and humidity, and the roller pressure, are important conditions for ensuring the direct size and area stability of the paper and reducing the deformation registration error.

The moisture content of paper has the following relationship with paper deformation:

(1) The linear size of the paper shall increase or decrease with the increase or decrease of the amount of water within the limits;

(2) The same kind of paper, if the water content is different, will produce different deformation; the higher the water content, the greater the natural deformation and pressure deformation;

(3) The higher the humidity of the paper, the lower the fiber binding force, and the more easily the position of the fiber when imprinting is moved and distorted;

(4) The water content is not uniform, and shellfish produces uneven deformation.

(5) The arrangement of paper fibers has a stretching rate greater than that of straight wires. The greater the water content, the greater the fiber misalignment of the cross-thread under pressure, and the elongation and deformation of the paper also from the B5lE.

Different fiber absorption and expansion conditions are different. Under normal circumstances, if the fiber diameter increases by 30% when expanded, its length increases by approximately 1%.

12. What is the relationship between the exact registration and the elasticity of the blanket?

The registration error caused by the change of the graphic size due to the deformation characteristics of the blanket is mainly due to the effect of the roller pressure and tension and the weight of the blanket itself.

The registration error of the blanket tightness is that the blanket is tight on the drum. The degree of tightening not only produces relative friction to the drum surface, but also causes dimensional changes of the graphics due to the deformation and elongation of the blanket. The resulting registration error has a close relationship. From the law of deformation of the blanket, we know that its push deformation depends on two points:

(1) The direction and size of friction;

(2) The elongation of the blanket.

That is to say, under the same direction and the frictional force of the stroke, the degree of deformation will be different if the elongation of the blanket itself is different. It is also determined by the degree of tightness of the blanket on the roller, that is: the tighter the tension: the smaller the elongation in the printing process, the smaller the change in the size of the graphic, but the number of friction on the plate has increased; on the contrary, the elongation The rate is large, but the amount of friction on the layout is reduced, and the elongation is too large, which is prone to ghosting.

According to the reason for the above-mentioned registration error caused by the above-mentioned blanket tightness, it is necessary to pay attention to:

(1) Blanket-printed blankets should be used;

(2) The tightness of the blanket should be maintained, not too loose or too tight. To make it constant;

(3) The registration error caused by the dimensional change of the text due to the tightness of the blanket must not exceed o. 10mm, otherwise the tone shift due to dot misalignment.

13. What is the relationship between the accuracy of overprinting and the elasticity of the rubber layout?

The blanket is tight on the cylinder. Due to the uneven distribution of surface tension, the stress in some areas is stretched tightly and the stress is stretched loosely in some areas. In the printing process, the elongation rate in the tensioned area is small, and the graphic size changes. Small; stretched area, large elongation, graphic size changes. Therefore, if the rubber layout is uneven, local registration error can occur.

The factors causing the elasticity of the rubber layout are:

(1) The rubber is cut and skewed, the punching eye is not rectangular after being clamped or clamped, so the surface is not evenly stressed;

(2) The strength of the splint screws varies;

(3) splint bending (for a few types of machines);

(4) The length of the trailing pad is not uniform.

The maximum allowable error of local registration must not exceed 0.10mm. When the width of the graphic text is partially inaccurate, the local tightening degree can also be changed. For example, a different thickness of paper may be locally clamped on the blanket tightening shaft, that is, the diameter of the bar may be locally increased.

14. What is the relationship between the exact registration and the torsion deformation of the blanket?

The intersection of the axes of the two rollers is not parallel, so that the blanket is subjected to both radial frictional force and axial frictional force, so that the blanket produces torsional deformation. The registration error of the torsional deformation of the blanket is under the effect of torsional forces. The imprints obtained on printed sheets are not the original rectangles, but instead are corresponding parallelograms. This kind of deformation error has no obvious hindrance to the general-purpose single-side printing products, but it will have an impact on the products with finer, higher registration accuracy, especially on both sides, and the positive and negative requirements for overprinting the precise products are harmful. For example, two types of registration errors can occur when registration is required on the front and back sides. One is that the upper and lower standards are registered and the rules are not allowed to be set; the other is based on the rules of registration and betting.

The torsional deformation of the blanket is due to the fact that the rollers are not parallel and generally have the following causes:

(1) The drum level is not the same;

(2) single-side wear of roller gear or bearing;

(3) The middle of the gap between the cylinders is smaller than the two ends;

(4) There is obvious plastic deformation in the corner of the corner of the rubber cloth and the corner of the opposite corner.