Maybe you have also experienced such a frustrating thing: you have printed a job a thousand times before without problems, but this time the ink will not stick to the paper. The efforts made to solve this problem ended in invalidity. What caused this problem? Is it paper? Or ink? Or many other reasons?
Mr. Frank Gualtieri, Senior Technical Consultant of GATF in Pittsburgh, said: "When investigating a printing failure, you have to determine all the factors that may cause the failure." He divided the possible causes of the failure into three categories: printing machinery Failures, human errors and raw material problems. "Find out what conditions (factors) have changed since the preparation of the quasi-machine or the last printing of the job, summarize the relevant data organization, and then confirm the potential cause of the failure." Mr. Gualtieri suggested that .
It is impossible to find a solution before deciding what the cause is; therefore it is critical to find the root cause as accurately and quickly as possible. "Once we find the cause, we can decide which solution to use," Mr. Gualtieri continued. He suggested confirming the only solution. "This solution must fundamentally solve the problem. Some quick fixes only It can temporarily cover up the problem and has not been solved at all. So avoid these quick methods. "
Four major problems
At a seminar on offset printing workshops called "Resolution of Printing Workshops", Mr. Gualtieri spoke at the meeting and focused on the four most common failures that occur in offset printing: white shift, blur, dirty version, and ghosting. He gave examples of each question one by one. Discussed in simple terms the various factors that may cause the problem:
White spot
Let's start with the distinction of the type of spots: Does the spot appear in the ink on the printing paper, on the blanket or on the printing plate? To determine the spot failure and spot location. Mr. Gualtieri pointed out several possible causes of this failure, including:
The printing machine or printing workshop is dirty;
Paper dust;
Ink viscosity is too high;
The paper has prominent small particles;
Ink grinding is not detailed enough;
Paper cutting debris;
The rubber roller is deteriorated or dirty;
Impurities from the ceiling or other sources.
Mr. Gualtieri believes that the first step in solving the problem is to thoroughly clean the printing press and printing shop. He also proposed to use the delta dampening device (delta dampening and A, I, R) automatic impurity removal device to help solve the problem.
Double shadow and blur
In the process of printing transfer, the printed sheet cannot pass through smoothly, and curling or wrinkling will cause ghosting and blurring problems. Mr. Gualtieri thinks, "First of all, you need to recognize the difference between ghosting and blurring. Two identical dots can be seen on the ghosting sheet, and when the dots are oval, that is blurring."
He suggested using quality control methods such as stars, expanded dots and ladders to quickly distinguish them. Common causes include:
Paper feeding is not correct;
Poor paper transfer from printing presses;
Blanket loosening;
Ink dot expansion rate is high;
The printing plate / rubber blanket is too tightly squeezed;
The dampening ability of the fountain solution is too weak;
Roller pressure is too high.
Dirty
Mr. Gualtieri divided this problem into two types: dirty when starting up and dirty when printing. The main reasons for the dirty start-up include: The printing plate is seriously fogged;
Poor roller adjustment;
The water feed is too low;
Insufficient exposure of genuine printing plates;
Ink viscosity is too low or too many additives;
The printing plate / blanket is squeezed and deformed.
The main causes of dirt in India include:
The printing plate is slightly fogged;
Wetting ability of fountain solution is insufficient;
Ink and pigment wear;
Ink breaks water;
Plate / blanket squeeze.
Adaptability of ink and water
GATF technical consultant Mr. Brue Tietz believes that the adaptability of ink and water is very important for the efficient production of printing workshops. At the 2000 Offset Workshop Technical Seminar with the theme "Capturing the Key to Ink / Water", Mr. Tietz discussed the problem of oil / water adaptability with many suppliers. He said: "Why should we control the ink-water balance? It is to control the process. The printing workers tend to let the process control them, and always solve it when it is out, rather than controlling the process to prevent problems. "
Factors affecting the water quality of printing houses
Mr. Tietz began to analyze step by step, breaking the assumption of "all water is the same" in the mind of the printing staff. He said: "Due to the different sources of water, the minerals contained in them are also different." He gave an example to illustrate that the minerals contained in well water and river water are not the same. Mr. Tietz also pointed out that the water from the faucets in the same printing plant is not always the same, although they come from the same source; "The water of the faucets will change with the seasons," he said: "In the snowy winter area , Coal slag and other substances that people sprinkle on the snow will also affect the composition of water. Therefore, the difference in water also affects the production work mode of the printing workshop throughout the year. "Other factors include:
The PH value of water is different, the ideal value should be 7.0;
Conductivity, which is based on the number of ions of minerals dissolved in water;
Chemical agents added by local water treatment companies, such as chlorine, fluorine, deodorant, etc.
Water and ink
Mr. Tietz said: "On the printing press, we use a water mixture made of water. Therefore, it is very important to understand the composition of the water." The water is usually composed of 98% water plus 2% of other The mixing agent is made of alcohol or alcohol, ink and wetting agent (active agent). If the amount of water in the bucket liquid is insufficient, it will not function properly.
Temperature is another factor that needs to be controlled. Mr. John Ritzic, Technical Service Manager of Braden Sutphn Ink Ink, said: "Temperature has little effect on process control. The higher the temperature, the lower the viscosity of the ink, and the amount of water and ink will increase. Ink After sticking to water, the viscosity will drop. "Other influencing factors are the type of substrate on which the live parts are printed and the date of delivery of the ink.
The balance and adaptability of water and ink play the most critical role in the high efficiency and high-efficiency production of the printing workshop. However, different jobs at different times have their own unique process requirements, which brings serious challenges to printing production. You can follow the following principles to help achieve and control the ink and wash balance:
Install a water treatment system;
Replace ink to ensure quality;
Clean the printing plate before the printing plate to avoid contaminating the bucket liquid;
Perform routine maintenance on the printing press.
In the end, Mr. Tietz concluded: "The better the control of the ink and water, the better the printing effect. You also get the superior and constant control of the process."
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