Diagnose printing faults
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Perhaps you have experienced such a frustrating thing: a job you have printed thousands of times before has no problem, but this time the ink does not stick to the paper. The country that has done this to solve this problem has ended in invalidity. What caused this problem? Is it paper? Or ink? Or for a variety of other reasons?
The possible factors that lead to failure are divided into three categories: printing machine mechanical failure, human error and raw material problems. “Find out what conditions (factors) have changed from the start of the schedule, or compare the last print of the job, and summarize the relevant data to confirm the potential cause of the failure.”
It is impossible to find a solution before deciding what the cause is; therefore it is critical to find the underlying cause as accurately and quickly as possible. “Once we find the reason, we can decide which solution to solve the problem.” It is recommended to confirm the only solution. “This solution must solve the problem fundamentally. Some quick fixes can only temporarily cover up the problem, and Not solved at all. So avoid using these quick methods."
Four major problems
The four most common fault problems that occur in offset printing: white shift, blur, dirty version, and ghosting. He gave examples of each question one by one. In-depth discussion of the various factors that may cause this problem:
White spot
Start with the distinction of spot type: Does the spot appear on the ink on the paper, on the blanket or on the plate? Be sure the spot is faulty and where the spot is. Several reasons that can cause this failure include:
Dirty in the printing press or printing shop;
Paper off powder;
The viscosity of the ink is too high;
Paper has prominent small particles;
Ink grinding is not detailed enough;
Paper cutting debris;
The rubber roller is deteriorated or dirty;
Impurities on the ceiling or other sources.
The first step in solving the problem is to thoroughly clean the press and the pressroom. It is proposed to use a delta dampening device (delta dampening and A, I, R) automatic impurity removal device to help solve the problem.
Double shadow and blur
During the printing process, the sheets cannot pass smoothly, roll up or wrinkle, which can cause ghosting and blurring problems. First you have to recognize the difference between ghosting and blurring. Two identical dots can be seen on the ghost print, and when the dots are oval, it is blurry.
It is recommended to use star marks, network points to expand the quality control methods such as measuring bars and ladders to quickly distinguish them. Common causes include:
Paper feeding is not allowed;
Poor paper transfer from the press;
Blanket
The ink dot enlargement rate is high;
Plate/blank extrusion too tight;
Wetting solution wetting ability is too weak;
The roller pressure is too large.
Dirty
There are two types of problems: dirty start-ups and dirty prints. The main reasons for starting the dirty are: The printing plate is heavily foggy;
Roller adjustment is not good;
The water feed is too low;
The amount of genuine plate exposure is insufficient;
Ink viscosity is too low or too much additive;
Plate/blanket extrusion deformation.
The main reasons for the dirty in the printing include:
The printing plate is slightly foggy;
Insufficient wetting ability of dampening solution;
Ink pigment wear;
Ink is guilty of water;
Plate/blanket extrusion.
Ink and water adaptability
The adaptability of inks and water is critical to efficient production in the print shop.
Factors affecting the water quality of the printing plant
Mr. Tietz began a step-by-step analysis that broke the vision of the printer's mind that "all water is the same." He said: "Because of the different sources of water, the mineral composition is different." He exemplified that the mineral content of well water and river water is different. Mr. Tietz also pointed out that the water flowing from the faucets in the same printing plant is not always the same, although they come from the same water source; “the water in the faucet changes with the seasons”, he said: “The snowy area in winter The substances such as cinders that are scattered on snow also affect the composition of the water. Therefore, the difference in water also affects the production mode of the printing shop during the year. Other factors include:
The pH of the water is different, the ideal value should be 7.0;
Conductivity, which is based on the number of ions dissolved by minerals in water;
Chemical agents added by local water treatment companies, such as chlorine, fluorine, deodorants, etc.
Water fountain and ink
Mr. Tietz said: “On the press, we use a water-filled liquid with water. Therefore, it is very important to understand the composition of the water.” The water is usually made up of 98% water plus 2% other. Made of a mixture, the mixture is basically made up of a mixture of alcohol or alcohol, ink and wetting agent (active agent). If the amount of water in the water hopper is insufficient, it will not function properly.
Temperature is another factor that needs to be controlled. Mr. John Ritzic said: “The temperature has little effect on the process control. The higher the temperature, the lower the viscosity of the ink, and the amount of water and ink will increase. The viscosity will drop after the ink sticks to the water. "The other influencing factors are the type of substrate on which the job is printed and the date the ink was shipped.
The balance and adaptability of water and ink play a key role in the efficient and productive production of the printing shop. However, different jobs at different times have their own unique process requirements, which brings severe challenges to printing production. You can follow these guidelines to help achieve and control ink and water balance:
Install a treatment water system;
Replace the ink to ensure quality;
Clean the plate before the previous version to avoid contaminating the water bucket;
Regular maintenance of the press.
Finally, Mr. Tietz concluded: “The better the control of the ink and water is, the better the printing will be. You will get a superior and constant control over the process.”