Offset Printing Failure - Sliver

Streak

Strokes are commonly called "bars", dark streak marks "ink streak marks," and light streak marks are called "water streak marks."

Streaks are a type of failure that is more difficult to solve in offset printing, especially when printing solid or spot colors. The appearance of streaks directly affects the print quality.

One trace of features, causes and exclusion

The occurrence of streak marks is caused by the instantaneous friction and sliding of the blanket, ink roller, water roller, etc. after contact with the surface of the printing plate, resulting in the destruction of the balance of the ink and ink relationship, and a straight line parallel to the axis line of the plate cylinder. Graphic and textual changes in the shape of the dots and the thickness of ink deposits have resulted in streaks.
According to the obvious features of the streak marks, ink marks and white streaks can be distinguished.

The dots in the ink streaks are irregularly enlarged, the dots are elongated, the text is heavy, and the ink becomes heavier, forming a pronounced deep streaks on the layout.

White streak marks, also called water streak marks, refer to the occurrence of irregular narrowing in the streak area, which constitutes an obvious shallow streak.

According to the category of the streak fault, it can be divided into a streak mark, a vibration streak mark, a roller streak mark and other factors.

The method of checking the striae is: using a half-dot mesh version, print on a coated paper with thin ink and observe whether or not streaks appear.

Streak failures often occur when the machine is in the stage of trial installation or the machine is in disrepair for a long time. Modern high-speed multi-color offset presses have few streaks in the printing process. Most streaks are caused by improper adjustment (see the table for details). 8-1).

Table 8-1 Characteristics and identification of striations, causes and solutions

Category characteristics and identification of the causes and solutions to the tooth bar marks 1, the entire layout appears streak, the shape of the stencil, the first streak from the mouth 10mm, fixed on each piece of paper.
(1) The pitch of the rack marks is the same as the pitch of the ink roller gear. (1) The pressure of the ink roller on the plate and the ink roller is too large.
(2) The accuracy of the uniform ink gear is poor, and the part that affects the vibration is detected. (2) The pitch of the rack marks is the same as the pitch of the roller gear. (3) Impression roller installation and excessive pressure.
(4) Roller gear accuracy is poor. Change gear position. (3) There are 5 to 8 rack marks with a fixed position. (5) The reciprocating motion of the ink-transmitting and ink-sinking mechanism and the printing time do not match properly or there is a gap at the shaft end. (4) There are 2 to 3 rack marks and the position is fixed. (6) Impact caused by cam mechanism or other problems. There are problems with individual teeth or inclusions. Roller mark 2, the roller off the ink after ink marks.
(1) Inconsistent ink color before and after printing. (1) The drum journal and bearing clearance are large.
(2) The roller is uneven and eccentric. (2) In the ink traces of the printed product, the left and right sides do not agree with the middle thickness. (3) The drum is not balanced. 3, there are still ink marks after the roller is pressed.
(1) Inconsistent ink color before and after printing. (1) There are problems with the arrangement of the roller and the diameter of the ink roller. (2) Heavier ink, wider striated lines, and small and uniform spacing between the ink slivers. The position is not fixed. (The paper is placed on the impression cylinder, and the position where the striated marks are generated corresponds to the occurrence of the occurrence on the machine. The cause of the mark). (3) Large ink roller shaft and bearing clearance.
(4) Ink roller accuracy: eccentricity, bending, deformation. The ink roller balance is not good. (3) Ink marks appear on the leading edge of the blanket. The width of the strip is equal to the circumference of the rubber roller. (4) Inking roller pressure is high. (4) The position of the streak is fixed, and the ink first weight gradually decreases. (5) The hardness of the rubber roller is large. 4. Problems with the wet system (1) The white streaks mostly appear on the image of the mouth and are relatively fixed in position.
(2) White streaks are generated in a certain area when printed (3) White streaks appear in the printing area and are fixed. (1) The contact pressure between the water roller and the printing plate is too large.
(2) The string water roller drive gear is seriously worn.
(3) Improper water transfer roller adjustment. Vibrating striations 5, the position of the streaks on each sheet is fixed, and the width of the streaks is the circumference of the rubber roll.
(1) Appears later in the middle of the page, that is, the latter half of the page. (1) There is an impact when the plate cylinder comes into contact with the blanket cylinder.
a pad is too hard.
b There is a raised plate at the roller contact, or a transitional ramp at neutral. (2) Appears in the front half of the paper. The distance from the tip of the streak to the gills corresponds to the distance from the impact of the blanket cylinder and the impression cylinder to the start of embossing. (2) Large drum journal and bearing clearance.
a Adjust the center distance between the rollers.
b Printed with a rolling pillow. (3) There are ink streaks in the local area of ​​the print, and the location rules are uncertain. (3) The impact of the mechanism that is prone to impact is transmitted to the impression cylinder, and vibration occurs in the printing part, so that the printing pressure changes directly. a Eliminate irregular vibrations in some institutions. b Printed with contact roll.

Two other causes of streak

(1) Rubber blankets with poor blanket quality are more prone to ink streaks than high quality, flat blankets. Air cushion blankets are better than ordinary blankets.
(2) Hard pad liner Although the printing effect is good, it is very sensitive to the accuracy of the machine, and it is prone to streaks. The blanket cylinder and plate cylinder have low printing pressure and are prone to ink streaks.
(3) The plate version of the printing plate has great friction and is not prone to ink bars. However, in the field version, the thin line version is easy to slide, especially for the large-area field version. The thin line version is most prone to ink streaks.
(4) Paper with high paper smoothness is prone to ink streaks. Example: Aluminum foil, advanced coated paper.
(5) thick thick ink ink viscosity, ink marks are not easy to appear, and thin, high transparency of ink ink marks are obvious, in addition, ink type has an impact on the production of ink bars. Black ink and blue ink are prone to dark bars, while yellow ink is similar to paper and ink marks are not obvious.

Three about ghosting:

Ghosting means that the same color blocks in the finished product have different dark shadows. The initial cause of ghosting is often due to improper imposition. The images that are not in one hue are combined on one layout. Because different hue requirements are not the same, calibrating the hue of a single image will destroy the hue of another image on the same surface, especially when horizontal and vertical cross-imposition occurs. One problem is particularly prominent. For example, when the dot density of CMYK is between 50% and 70%, printing adjustment is not in place, and ink bars similar to ghosts are prone to appear.

Source: Ke Yin Network