How much is the packaging offset? (229-238)

229. Why does the roller surface of the embossing zone slip?

During imprinting, the radius of each point on the plate cylinder is equal because the main compression is blanket and liner, and the absolute value of its linear velocity is the same. However, the circumference of the embossing zone of the blanket cylinder and the radius of each dot are not equal, and their line speeds are obviously different. In the circumferential direction of the embossing area, the surface of the blanket cylinder and the surface of the plate cylinder can have at most two line speeds equal to each other. The velocity of the other points must be different, there is a speed difference, and there is a slip in the speed difference. Sliding between the rollers is unavoidable. If the radius of the phase-rolling roller is not properly set, the slippage will be significantly increased. Therefore, in the offset printing production, it is necessary to minimize the slippage between the rollers.

230. What happens to the slip between the plate cylinder and the blanket cylinder?

1 Because the rollers are rolled under a relatively large pressure, if there is slippage in their embossed areas, there must also be friction, and the degree of friction is proportional to the speed difference and the size of the printing pressure. The friction on the printing plate will cause the alumina grains of the photosensitive layer and the blank portion of the plate on the plate to be worn, which will reduce the printing plate's resistance to printing.
2 The slippage between the rollers can cause circumferential deformation of the imprints or dots, making the imprints thicker in the circumferential direction, and the dots increase in an elliptical shape, which greatly affects the quality of printed products. Too much friction on the blanket can cause the blanket to slip excessively and cannot be instantly reset, causing ghosting problems. Slip and friction can also cause "falling" and "smoothing" phenomena.
(3) Excessive slippage will cause the liner and felt underneath the blanket to move and even wrinkle and crush the blanket.

231. What is the effect of slippage between the blanket cylinder and the impression cylinder?

Since the metal surface of the cylinder of the impression cylinder is much smoother than the surface of the blanket of the blanket cylinder, the friction coefficient between the front surface of the paper and the surface of the blanket at the time of imprinting is large, and the friction between the back surface of the paper and the surface of the cylinder surface of the impression cylinder is large. The coefficient is small, so the slippage between rollers during embossing mainly occurs between the back of the paper and the barrel of the impression cylinder.
When the radius of the blanket cylinder (including the rubber blanket lining) somewhere in the embossing zone is greater than the radius of the cylinder of the impression cylinder, the distance between the back of the page and the center of the blanket cylinder is greater than the radius of the cylinder of the impression cylinder. The surface of the cylinder of the impression cylinder slides forward, which has no obvious adverse effect on the deformation of the imprint and the dot gain. This forward slip usually occurs when printing thicker paper.
When the radius of the blanket cylinder (including the rubber blanket lining) is greater than the radius of the cylinder of the impression cylinder, the distance between the back surface of the blanket and the center of the blanket cylinder is smaller than the radius of the cylinder of the impression cylinder, and the back of the sheet is relatively Slide back on the cylinder surface of the impression cylinder. Because the paper in the imprint is pinched by the impression cylinder, the paper will stretch due to sliding. The paper that is sensitive to elastic deformation can be restored after the stamping is completed; and the paper that is plastically deformed will cause the paper to grow in the printing direction after being stretched.

232. What is "falling hair" and "smooth hair" and how did it happen?

When printing on the ground, lines, or text, improper operation can lead to burrs on the edges of the printed graphics. If the burrs are facing the direction of the gargle, it is called "pile down"; if the burr is toward the direction of the dragging, it is called "smooth".
When the radius of the plate cylinder is greater than the radius of the blanket cylinder, the linear velocity of the surface of the plate cylinder is greater than the linear velocity of the surface of the blanket cylinder. When the printing plate is pressed, the two produce sliding friction, so that the ink on the printing plate and the blanket is squeezed in the opposite direction. shop.
If the surface speed of the printing plate is fast, the ink on the surface of the printing plate is elongated toward the direction of the drawing, and the ink on the blanket is elongated toward the opening. The ink stretched on the printing plate is eliminated due to the degreasing action of the water roller and the ink collection effect of the ink roller, and does not produce inverted or smooth hair. The blanket on the blot is easier than the blank part of the adsorption of the paper off and pigment particles, resulting in contact with the blank part of the printing plate of the abrasive wear, and then by the ink erosion, gradually fat and lipophilic, resulting in burrs; The burrs have a longer "slip" phenomenon due to the longer sliding effect. On the other hand, if the linear speed of the surface of the plate cylinder is less than the linear velocity of the surface of the blanket cylinder, the phenomenon of "smoothing" occurs easily.
In short, the cause of inverted and smooth hair failure is due to the improper ratio of the radius of the drum, the poor surface strength of the paper and the insufficient wear resistance of the printing plate.

233. What is the specific content of the Shields liner lining theory?

The sizing theory of sizing reduces the pressure of the blanket, and therefore, the circumference of the blanket actually rolls over when the blanket is pressed is greater than the circumference of the blanket in the free state, and the greater the pressure, the greater the blanket. Thicker, the higher the convex bulge, the longer the circumference that the blanket turns. Based on the fact that the squeegee roller has an increased rolling radius after being pressed, the sitz reducer theory holds that the radius of the blanket cylinder must be smaller than the radii of the plate cylinder and the impression cylinder.

234. What is the synchronous rolling ratio?

The Seth reduction theory holds that if the circumference of the blanket cylinder when rolling is equal to the circumference of the rigid cylinder, it can be considered that the two cylinders are non-slip rolling. Therefore, the radius of rolling after the blanket cylinder is pressed must be equal to the radius of the rigid cylinder. The ratio of the rolling radius of the blanket cylinder to its free radius is called the rolling ratio, and the synchronous rolling ratio can only be determined experimentally at present. The distribution of the radii of the plate cylinder, impression cylinder and blanket cylinder of the offset printing press shall be determined experimentally and assigned with a certain ratio of the blanking ratio of the blanket in the case of a certain amount of compression and tension so that the roller can be The slippage is minimized.

235. What factors affect the synchronous rolling ratio?

The characteristics of a blanket. Different types, different characteristics of the blanket have different synchronous rolling ratio.
2 The amount of compression of the blanket. The same blanket has different synchronous rolling ratios under different compression amounts.
3 tightness of the blanket. The tighter the blanket is, the greater the synchronous rolling ratio. The tighter the stretch, the thinner the blanket, the smaller the free radius of the blanket cylinder, but because the synchronous rolling ratio is increased, the blanking radius of the blanket cylinder is larger.

236. What is the diameter of the pillow and the clearance of the pillow?

Rolling pillows are also called shoulder irons, that is, the two tables with the convex sides of the outer cylinder of the drum, the diameter of which is called the rolling pillow diameter, and the gap between two adjacent rolling pillows is called the roll bearing clearance.

237. What is a roll and no roll?

During the printing process, the rollers of the plate cylinder and the blanket cylinder are in contact with each other, and are not adjustable. However, the gap between the blanket cylinder and the impression cylinder can be adjusted. This form is known as walking. Walking the rollers helps to maintain a smooth rotation between the blanket cylinder and the plate cylinder and improve the quality of the printed matter, but the material properties and manufacturing process requirements of the cylinder parts are relatively high. The pressure between the blanket cylinder and the plate cylinder of the roll printing press can only be adjusted by adjusting the thickness of the cylinder liner.
During the printing process of the offset printing press, if there is a gap between the rollers of the three rollers, it is called a no-go roller. The offset printing machine that does not walk around the rollers tends to vibrate during the printing process, resulting in uneven pressure and causing ink bars.

238. What is the reduction of the roller?

Roller diameter reduction, that is, the difference between the radius of the roller cylinder when it is not covered with a pad and the radius of the roller. When the cylinder radius is less than the roller pad radius, it is a negative value; when the cylinder radius is greater than the roller pad radius, it is positive. value.

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