Three common problems in the offset printing process
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Offset printing is currently the main printing method for printing companies. The lithographic offset printing is caused by the failure of the output system, the printing is not accurate, the ink color is uneven, and even the printing cannot be carried out, which is the main reason for delay in delivery. This is one of the more difficult problems most often encountered by printers.
First, double or multiple failures in paper feeding
1. The paper is uneven and the edges are upturned. When the airflow blown by the bulk paper blowing nozzle contacts the edge of the paper, the edge of the paper is curled at an arc angle, and the airflow is blown out into two parts. A part of the airflow lifts the paper up, and another part of the airflow pushes the paper down, so that the paper cannot be separated, and the paper stopper brush also loses its effect, causing two or more sheets, or even a large stack of paperboards. The general treatment method is to remove the paper for anti-tapping, so that the paper is flat and facilitate separation.
2. The paper loading height exceeds the allowable height of the paper. According to past printing experience, the height of general paper loading should be less than 5mm. If the adjustment is not appropriate and exceeds its allowable range, two or more sheets will be produced. The general treatment is to use a cork wedge to control the paper on the same plane. If you have a regulator model, you can use a regulator to reduce the height of the paper to solve.
3. The blower foot and the paper stop brush protrude too little into the paper. According to the previous operation experience, the general paper stopper brush protrudes into the paper edge by about 8 mm, and the blowing pressure foot reaches the paper edge of about 10-15 mm. If the adjustment is not correct or the paper is not cut properly, double or multiple sheets will appear. Generally, the paper feeder is adjusted closer to the whole, so that the paper separation nozzle is about 5 mm away from the edge of the paper, and the paper stopper brush and the blowing pressure foot are adjusted to solve the problem.
4. When the paper is too thin, the air volume is not adjusted properly. When 70 g/m2 of thin paper is printed, if the air volume is improperly adjusted, it is easy to produce double or multiple sheets. The general treatment method has the following points: (1) adjust the blowing foot downwards, increase the distance between the paper pile and the paper separation nozzle; (2) adjust the small air volume appropriately; (3) reduce the separation paper suction nozzle The rubber band or the transparent plastic to reduce the wind; (4) press the paper stopper brush down and increase its pressure to control.
5. The paper is not loose or sticky. Generally, when the paper is cut, when the cutting edge is bonded, or when the full version of the semi-finished product is printed on the ground, water stains and ink stains cause bonding, thereby forming two or more sheets. Therefore, before the paper is printed, that is, when the paper is loaded into the machine, it must be shaken and folded. For the semi-finished product, a small stack and a small stack should be loosened. When loading the machine, it should be installed less, avoiding heavy pressure and causing bonding. .
6. The blower foot is worn. When the presser foot is used for a period of time, it will wear out. When it presses down on the paper, the paper will be angled, the force will change direction, and the paper will move forward, causing the paper stop brush to be lost. The paper is sucked into the edge of the paper when it is sucked down, and forms two or more sheets. Generally, it is replaced by a new blowing presser foot. If the wear is not serious, it can be solved by welding the copper piece and then using a file to flatten it.
Second, the product color unevenness failure
The reasons for the uneven color of the product are: (1) the cylindricity wear of the rubber rollers of water transfer, ink transfer, uniform ink and offset ink, the wear of the shaft head of the bearing, the aging of the rubber roller, the decrease of the ink transfer capacity, etc. (2) Peeling of the water-separating roller layer, the cylindricity wear is super-poor, the surface has a thin ink layer, and the two end portions have an ink-collecting strip, which causes the rollers to sway and the ink is uneven; (3) Supporting the plate water The lock of the ink roller and the swing bracket are severely worn, causing the rubber roller to jump against the plate, resulting in unstable pressure on the plate, resulting in unbalanced ink, uneven ink, dry plate, ink bar, and old version (by the rubber roller) (4) the phenomenon that the water roller pile is aged or the quality is poor, resulting in a decrease in water transfer capacity; (5) the pressure of each ink roller and plate cylinder and the offset ink roller is not regularly checked; (6) if the roller The drive gear wears out of tolerance and there is a regular "gear ink bar" with the same gear spacing.
Third, overprint failure
1. The effect of printing plate deformation on overprinting. The metal sheet has a certain degree of elongation, and tensile deformation occurs under the action of the tensile force, and the tensile deformation of the zinc plate is more obvious. Under normal circumstances, we found that the overprinting was not accurate when printing, and most of them were adjusted by stretching the plates. The greater the pulling force, the greater the tensile deformation of the plate and the uneven distribution of the tensile deformation. The force on the edge of the mouth and the tip of the plate is the largest, the tensile deformation is also large, the force on the inside is small, and the tensile deformation is also small. Therefore, use the pull plate as much as possible to solve the problem of inaccurate overprinting.
2. The effect of the increase or decrease of the roller liner on the overprint. In the printing process, due to the expansion and contraction of the paper caused by the overprinting, the method of increasing or decreasing the thickness of the roller liner can be used to solve the problem of inaccurate overprinting between the gaps. The increase or decrease of the plate liner affects the tensile deformation of the plate. The thicker the plate liner, the greater the pattern size elongation. When the plate liner is reduced and the blanket cylinder liner is increased, the tensile deformation of the woven fabric is increased, and the radial deformation of the pattern is increased. The other is to reduce the thickness of the blanket cylinder and increase the thickness of the plate liner, so that the amount of deformation of the blanket is reduced, and the latter is generally used.
3. The effect of blanket elongation on graphic overprinting. The blanket is stretchable, and the tighter the blanket is stretched on the drum, the smaller the elongation, the smaller the pattern change. (1) Use a blanket with a small elongation. (2) In the process of overprinting, try to keep the degree of tension of the blanket unchanged.
In addition to the reasons mentioned above, it is also necessary to pay attention to the problems of machinery, adjustment, paper, etc. In short, the overprinting is usually generated at the moment of high-speed printing, and is accumulated by a small amount of change. It is difficult to observe directly. Therefore, as long as we pay full attention to the printing, analyze the reasons, and take the most appropriate measures, we can avoid or reduce the occurrence of overprinting errors.