Print ghosting is one of the common faults that affect quality and efficiency. Correctly analyzing and accurately judging the cause of ghosting and taking effective solutions in a timely manner is a problem worthy of attention by operators and managers. In the following, I will discuss several points of understanding with practical work experience.
First, equipment factors
1. Improper pressure on the impression cylinder
In the modern commercial printing with magazine as the main body, thin paper printing has gradually become mainstream, and it has been developed in the direction of 65g/m2, 70g/m2, 80g/m2 light coated paper or 80g/m2 coated paper. Because the thin paper has a high requirement on the pressure and uniformity of the pressure on the impression roller, once the pressure of the upper die of a certain group of impression rollers is not suitable, the color print will not be overlapped with other color prints. Ghost failure.
Fault features: (1) Each successive two prints are overprinted and bad alternately (3 times the diameter of the impression cylinder is alternating with every 3). (2) It is easy to occur when thin paper is printed. The judgment method is to draw out about 10 prints, and look at the sample table and shake it together. Observe whether there is such a rule with a magnifying glass.
Treatment methods: (1) cut off the first group of ink roller and printing pressure, close the second group, 3, 4 ink roller and printing pressure. If the ghost disappears, it means that the problem is in the first group and vice versa. (2) Open the tooth row of the unit in question, clean the dirt in the tooth pattern, and replace the worn tooth. (3) Use 105g/m2 coated paper strip to adjust the pressure of each row of teeth until the pressure is even and appropriate.
2. Damage to the open ball on the impression cylinder
Failure characteristics: (1) whether the paper is thick or thin will appear; (2) due to the open teeth do not turn, so when the printing is severely misaligned, two consecutive prints, there will be a serious ghost. (3) The time of occurrence should be not long after the caries have been overhauled or other factors that can eliminate caries.
Treatment method: Replace damaged open teeth, in the usual maintenance process, to ensure that the butter in the open ball is in place.
Second, the paper factor
1. The silk orientation of paper affects printability
Due to the characteristics of the direction of paper webs and the tendency of moisture to swell, some papers do not have printability in a certain direction. When the paper is affected by moisture and pressure in the printing process, a rectangular to trapezoidal deformation may occur. So that each color print is not the same.
Fault features: (1) Each print has a different degree of ghosting. (2) Ghosts do not appear on the same plate, the same thickness or different thickness.
Processing methods: (1) Reselect the color sequence and place the black ink in the last group. (2) Change the printing direction of the paper (for example, if the big side is changed to the big fourth side).
2. Uneven moisture absorption
The humidity of the workshop environment is not enough, causing the paper to be tight and deformed seriously, which can easily cause ghosting during the printing process.
Fault features: (1) The deformation of the paper can be clearly observed. (2) Paper with a basis weight of 128 g/m2 is most noticeable.
Processing methods: (1) Rapid heating, hold some boiling water under the paper table, and then cover the paper with a plastic cover to allow the paper to quickly absorb moisture in water vapor. (2) Rehanging the paper or spraying it around the paper.
Third, accidental factors
1. Loose plate or blanket
Loose plates or blankets, each time the plate is transferred to the blanket of the blot will be different, and ghosting failure occurs.
Fault features: (1) The printer is accompanied by a large abnormal sound. (2) Thick paper and thin paper will occur. (3) Each print has ghosting.
Treatment method: Tighten the printing blanket.
2. Unreasonable choices
The choice of gargle and trailing is irrational. If the layout with a small number of images and a lighter side of the ink is used as a gargle, both sides of the trail will have a ghost due to large local ink volume and paper deformation.
Treatment method: The gargle, drag slightly swap, then eliminate ghosting.
Although the cause of ghosting in the printing process is complicated, according to the characteristics of ghosting caused by various factors such as equipment, paper, environment, and process, the main causes can be quickly identified and then targetedly eliminated.
Source - "Printing Technology"