Printing plant-common techniques for dealing with failures

Offset printing is currently the main printing method of printing plants. The failure of lithographic offset printing due to the output system is the main reason for the inaccurate overprinting and uneven ink color, and even the printing factory cannot carry out, which delays the delivery time. This is one of the more difficult problems that printing plant workers often encounter.

1. Double or multiple faults in printing and feeding

1. The paper is uneven and the edges are upturned. When the air flow from the loose paper blowing nozzle touches the edge of the paper, the edge of the paper is raised to an arc angle, and the air flow is divided into two parts. One part of the airflow lifts the paper upward, while the other part of the airflow presses the paper downward, making the paper unable to separate, and the paper blocking brush is also useless, resulting in double or multiple sheets, or even a large stack of cardboard. The general processing method is to remove the paper and perform knock-back processing to make the paper flat and easy to separate.

2. The paper loading height exceeds the allowable height of the paper stopper. According to the printing experience of previous printing houses, the height of the general paper loading should be about 5mm lower than the paper teeth. If the adjustment is inappropriate and exceeds its allowable range, double or multiple sheets will be produced to enter the cardboard. The general processing method is to use a stopper wedge to control and keep the paper on the same plane. If there is a model with an adjuster, you can use the adjuster to reduce the paper height to solve.

3. The blower presser foot and paper blocking brush extend too little into the edge of the paper. According to the previous operation experience, the printing factory can generally reach about 8mm into the paper edge of the paper blocking brush, and about 10-15mm into the paper edge of the blower presser foot. Double or multiple sheets will appear if the adjustment is incorrect or the paper is not cut properly. Generally, the paper feeder is adjusted closer, the separation nozzle is about 5mm away from the edge of the paper, and the paper blocking brush and the air pressure foot are adjusted to solve.

4. When the paper is too thin, the air volume is not adjusted properly. When the printing factory uses 70g / m2 thin paper, if the air volume is not adjusted properly, it is also easy to produce double or multiple sheets. The general processing methods are as follows: (1) Adjust the blowing foot downward, increase the distance between the stack and the separation nozzle; (2) Adjust the air volume appropriately; (3) Reduce the separation nozzle Rubber band or transparent glue to reduce the wind force; (4) Press the paper brush down and increase its pressure to control.

5. The paper is not loose or sticky. Generally, when cutting paper, the cutting edge is stuck, or when the full version of the semi-finished product of the printing house is solid, water stains and ink stains cause sticking, thereby forming double or multiple sheets. Therefore, the printing house must shake up the paper before the paper is printed, that is, when the paper is loaded into the machine, the small semi-finished products should be loosened one by one, and the machine should be installed a little less to avoid heavy pressure. Cause bonding.

6. The presser foot of the printing house is worn out. When the blower presser foot is used for a period of time, it will wear out. When it presses down on the paper, the paper will make an oblique angle, the force will change the direction, the paper will move forward, and the paper blocking brush will be lost Function, when the paper separation nozzle sucks the paper down, it will suck on the edge of the paper and form double or multiple sheets. Generally, it is replaced by a new blower presser foot. If the wear is not too serious, it can be solved by welding copper sheets and then filing with a file.

2. The uneven ink color of printed products

The reasons for the uneven ink color of the printing plant products are: (1) The cylindricity wear of the rubber rollers of water transfer, ink transfer, ink distribution and plate-based ink, the wear of the shaft head of the bearing, the aging of the rubber roller skin, and the ink transfer ability Dropping, etc .; (2) Peeling of the roller layer, excessive wear of cylindricity, thin ink deposit on the surface, and ink deposits on the two ends, causing uneven roller sloshing; (3) support The locks of the water and ink rollers and the swinging bracket are seriously worn, which causes the rubber roller to jump when it is against the plate, which causes the pressure of the plate to be unstable, resulting in an imbalance of ink and ink, uneven ink color, dry plate, ink bar, old version The pressure of the rubber roller is too heavy), etc .; (4) The aging or poor quality of the water roller fleece causes the water transmission capacity to decrease; (5) The pressure of each ink roller, plate cylinder and ink roller against the plate is not regularly checked; (6) If the roller transmission gear wears out of tolerance, a regular "gear ink bar" with the same distance as the gear appears.

Three, printing overprint failure

1. The effect of printing house version distortion on overprinting. The metal sheet has a certain degree of extensibility. The printing factory will produce tensile deformation under the effect of tension, and the tensile deformation of the zinc plate is more obvious. When we found that the printing is not accurate, most of them pass the tensile printing. Version to adjust. The greater the tensile force, the greater the tensile deformation of the plate, and the uneven distribution of the tensile deformation. The printing plant receives the largest force at the gripping edge and the supporting edge of the plate, and its tensile deformation is also large, and the internal force is small. The deformation is also small. Therefore, printing companies should try to avoid the problem of inaccurate overprinting as much as possible.

2. The effect of the increase or decrease of the roller pad on the overprint. In the printing process, due to the expansion and contraction of the paper, the overprint is not accurate, and the method of increasing or decreasing the thickness of the roller pad can be used to solve the problem of inaccurate overprint between the diameters. The increase or decrease of the printing plate liner affects the printing plate deformation. The thicker the plate liner, the larger the graphic size extension. When the printing plate liner is reduced and the rubber cylinder liner is increased, it is revealed that the tensile deformation of the grey cloth increases and the radial deformation of the figure increases. The other is to reduce the thickness of the rubber cylinder and increase the thickness of the plate pad at the same time, then the amount of deformation of the rubber sheet is reduced, and the latter is generally used. 3. The effect of blanket elongation on graphic overprinting. The blanket is stretchable. The tighter the blanket is stretched on the roller, the smaller the elongation, and the smaller the graphic change. (1) Choose a rubber cloth with a small elongation. (2) During the process of overprinting, try to keep the rubber band tightness unchanged.

Overprinting is not allowed. In addition to the reasons mentioned above, printing plants should also pay attention to mechanical, adjustment, paper and other issues. In short, overprinting is usually generated instantaneously in high-speed printing plants. Accumulated, it is difficult to observe directly. Therefore, as long as we fully pay attention in the printing house, analyze the reasons, and take the most appropriate measures, we can avoid or reduce the occurrence of overprint errors.

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