Common sense of the most popular printing fault di

Common sense of printing fault diagnosis

maybe you have also experienced such a frustrating thing: you have printed a living piece thousands of times before without any problem, but this time the ink can't stick to the paper. All efforts to solve this problem ended in failure. What causes this problem? Is it paper? Or ink? Or many other reasons

Mr. Frank gualtieri, senior technical adviser of GATF in Pittsburgh, said, "when investigating a printing fault with various temperature control indicators that can fully meet the rules of the national standard gb/t229 (2) 007, you should determine all factors that may lead to the fault." He divided the possible factors leading to the failure into three categories: mechanical failure of the printing press, human error and raw material problems. "Find out what conditions (factors) have changed since the preparation of the standard machine or compared with the last printing of the live piece, organize and summarize the relevant data, and then confirm the potential cause of the failure." Mr. gualtieri suggested

it is impossible to find a solution before deciding what the reason is; Therefore, it is crucial to find out the root cause as accurately and quickly as possible. "Once we find the reason, we can decide which solution to use to solve the problem," Mr. gualtieri continued, and he suggested to confirm the use of the only solution. "This solution must fundamentally solve the problem. Some quick fixes can only temporarily cover up the problem, but not fundamentally solve it. Therefore, we should avoid using these quick methods."

four major fault problems

at a symposium on offset printing workshop problems called "printing workshop fault resolution", Mr. gualtieri made a speech at the meeting and focused on the four most common fault problems in offset printing: day shift, blur, dirty version and ghosting. He gave examples of each problem one by one. The factors that may lead to the problem are discussed in simple terms:

white spots

start with the distinction of spot types: does the spot appear in the ink on the printing paper, on the blanket or on the printing plate? It is necessary to determine the spot fault and the location of the spot. Mr. gualtieri pointed out several possible reasons for this failure, including:

dirty printing machine or printing workshop

paper powder falling

ink viscosity is too high

paper has prominent small particles

ink grinding is not meticulous enough

paper cutting debris

the rubber roller is deteriorated or dirty

impurities from ceiling or other sources

double image and blur

in the process of printing and transmission, the printing sheet cannot pass smoothly, roll up or wrinkle, which will lead to double image and blur problems. Mr. gualtieri said, "first of all, you should recognize the difference between ghosting and blur. Ghosting is usually produced through additive manufacturing. You can see two identical points on the sheet, and when the points are oval, that is blur."

he suggested that quality control methods such as star markers, point expansion measuring strips and ladders should be used to quickly distinguish. The common causes include:

the paper feeding is not aligned properly

poor paper transmission of printing machine

loose application of rubber blanket

the dot enlargement rate of ink is high

the printing plate/blanket is extruded too tightly

the wetting ability of the fountain solution is too weak

drum pressure is too high

dirty

mr. gualtieri divides this problem into two types: dirty when starting up and dirty when printing. The main reasons for dirty start-up include: the printing plate is seriously fogged

poor adjustment of roller

the water feed is too low (the water feed is too low after the oil in the oil tank is sucked into the oil pump through the oil filter)

insufficient exposure of genuine plates

the viscosity of ink is too low or there are too many additives

plate/blanket extrusion deformation

the main reasons for dirty printing include:

the printing plate is slightly foggy

insufficient wetting ability of fountain solution

ink and pigment wear

ink water

plate/blanket extrusion

adaptability of ink and water

Mr. Brue Tietz, GATF technical consultant, believes that the adaptability of ink and water is crucial to the efficient production of the printing workshop. At the 2000 offset workshop technical seminar with the theme of "grasping the key of ink/water", Mr. Tietz and many suppliers discussed and solved the problem of oil/water adaptability. He said, "why should we control the ink balance? It is to control the process. The printing workers tend to let the process control them, and only solve them when it comes to them, rather than eliminate the problem by controlling the process."

Mr. Tietz began to analyze the factors affecting the water quality of the printing plant step by step, breaking the assumption in the minds of the printers that "all water is the same". He said: "due to different sources of water, the mineral composition contained in it is also different." For example, the mineral composition of well water and river water is different. Mr. Tietz also pointed out that the water from the faucet in the same printing plant is not always the same after adjusting the sample, although they come from the same water source; "The water in the faucet will change with the season," he said. "In areas where it snows in winter, substances such as cinders scattered on the snow will also affect the composition of water. Therefore, the difference in water also affects the production and work mode of the printing workshop in a year." Other factors include:

the pH value of water is different, and the ideal value should be 7.0

conductivity, which is based on the number of ions dissolved in water

chemical agents added by local water treatment companies, such as chlorine, fluorine, deodorizer, etc

bucket liquid and ink

tietz said, "in the printing press, we use bucket liquid mixed with water. Therefore, it is very important to understand the composition of bucket liquid." Bucket liquid is usually made of 98% water plus 2% other mixtures, which are basically made of alcohol or alcohol substances, ink and wetting agent (active agent). If the amount of water in the bucket liquid is insufficient, it will not work properly

temperature is another factor that needs to be controlled. Mr. John ritzic, technical service manager of Braden sutphn ink company, said, "temperature has little effect on process control. The higher the temperature is, the lower the viscosity of the ink will be. At the same time, the amount of water and ink will increase. The viscosity of the ink will decrease after it is adhered to water." Other influencing factors include the substrate on which the movable parts are printed and the date of manufacture of the ink, etc

the balance and adaptability of water and ink play the most critical role in the efficient and cost-effective production of the printing workshop. However, different living parts at different times have their own unique process requirements, which has brought severe challenges to the printing production. You can follow the following principles to help achieve and control ink balance:

install a water treatment system

change the ink to ensure the quality

clean the printing plate before the previous version to avoid polluting the bucket liquid

carry out routine maintenance on the printing machine

finally, Mr. Tietz concluded, "the better the adaptability of ink and water is controlled, the better the printing effect will be. You will also have superior and constant control over the process."

reprinted from: China packaging business