Some Problems of High-efficiency Offset Printing Ink Cleaning Agents

In the 1970s, air-cushion blankets and PS plates were placed in the printing market one after another, which enabled the rapid development of offset printing technology. By the 1990s, offset printing had become a multicolor, high-speed, best-quality printing method. According to statistics, among the world's total printing output, offset printing ranks first, so it has the reputation of “emulated printing queen”.

There are many types of offset presses, some of which are small and exquisite. They can be printed on a desk, such as offset business cards. Others are like giants. They have a two-story building, such as a color newspaper offset press. No matter which type of offset press, the inking system delivers high-viscosity, high-thixotropy inks. There are as few as two or three ink rollers in one color group, and as many as 20 roots. The ink can be spread into a uniform ink film and transported to the surface of the printing plate under the shearing action of many ink rollers. The inherent properties and ink transfer performance of the ink roller directly affect the print quality of the offset printing product. Therefore, the cleaning and maintenance of the ink roller has always been a concern for offset printing professionals.

Ink roller cleaning is divided into three types, one is to change the color before the color wash, the second is the daily cleaning after the end of printing, the third is regular maintenance cleaning. Although cleaning agents are auxiliary materials for printing, their economic benefits and social benefits cannot be ignored due to their large usage.

I. What is a high-efficiency offset printing ink cleaner?

The so-called high-efficiency offset ink cleaner (also called car wash water) is relative to the long-term use of gasoline as an offset roller cleaning agent.

Prior to the 1980s, the composition of cleaning agents that replaced gasoline was relatively complex, resulting in poor cleaning performance and even less than the ability of gasoline to clean ink. However, after the 1990s, especially in recent years, offset printing ink cleaners with simple composition and excellent cleaning effect have emerged in foreign countries. They mainly consist of organic solvents that do not chemically damage the offset roller and blanket, and can generate relatively stable oils. Water-in-oil emulsion surfactant composition. In order to prolong the service life of the ink roller and blanket, it is also necessary to add an additive for preventing the aging of the rubber, and a small amount of water can be added during use. This cleaning agent was developed based on the chemical laws of “similar chemical structure and mutual solubility”. When the cleaning agent contacts the emulsified ink remaining on the ink roller and the blanket, the organic solvent dissolves the binder and other organic resins in the ink. Water can bring hydrophilic pigment particles and hydrophilic paper powder and paper mixed into the ink, and can dissolve inorganic and colloidal compounds that remove residual wetting fluid from the offset ink. Therefore, the washed ink roller and blanket have a clean surface with no traces of pigment and will not produce "crystal" and "white scale".

Gasoline is a single solvent that only cleans the binder in offset inks. The proportion of gasoline is small and the volatilization rate is very fast. Therefore, the ink rollers and blankets that have been cleaned with gasoline often need kerosene for auxiliary cleaning. Scrub with water to remove pigment marks. In view of this, compared with gasoline, it is appropriate to call such a cleaning agent a "high-efficiency offset ink cleaner".

Gasoline contains volatile substances that stimulate the body's central nervous system and damage blood components. If it is leaded gasoline, the harm to human health becomes even more serious. Gasoline has a low flash point of about 22°C and is a highly volatile flammable liquid. In our country's southern and northern regions, there were once offset printing workshops using gasoline to clean the ink rollers. A lot of gasoline gas filled the workshop and a fire broke out, causing painful lessons for casualties.

High-efficiency offset ink cleaning agent does not contain any substances harmful to the human body. Its flash point is about 44-60°C, which is 2-3 times of the flash point of gasoline. It is a pollution-free, environment-friendly and fire-fighting printing material. Countries with advanced printing and environmental protection, such as Germany and the United States, have forbidden the use of gasoline to clean the ink roller, and use high-quality offset ink cleaners instead of gasoline. This completely eliminates the harm of gasoline to human health and environmental pollution. Eliminate the hidden dangers of gasoline fire.

Second, the use of efficient ink cleaning agent

The ink roller and blanket of the offset press pass a slight water-in-oil emulsion ink. This emulsified ink is formed due to the high speed shearing action of the wetting liquid and the ink on the ink roller. From the laws of similar chemical structure, the cleaning solution must be a water-in-oil emulsion to clean the ink on the ink roller and blanket.

The original liquid of high-efficiency offset printing ink cleaner is generally a colorless, transparent, slightly odorous liquid. Add a small amount of water and gently shake it to become a milky white emulsion. The phase volume theory of emulsion formation in colloidal chemistry indicates that if the volume of the aqueous phase is between 26% and 74% of the total volume, the resulting emulsion may be of the oil-in-water type (O/W) or water-in-oil type. (W/O); if the proportion of the aqueous phase volume to the total volume is less than 26%, the resulting emulsion can only be W/O type; if it is more than 74%, the resulting emulsion can only be O/W type. According to the above theory, to form a W/O emulsified cleaning liquid, the proportion of water in the total volume of the cleaning agent emulsion should be below 26%. Production practice proves that the cleaning agent is arranged in the ratio of water: cleaning agent stock solution = 25:75, and the cleaning effect is the best. The ink roller is not only clean and clean, but also it takes less time to clean the ink roller. It is understood that, at present, some domestic manufacturers feel that the detergent liquid is more expensive, they add more water to the detergent liquid, to reduce costs, there are 1:1 ratio, and even some make up the total volume of cleaning agent 2 /3. According to the phase volume theory, the cleaning agent thus configured is not a complete W/O type emulsion, but an O/W emulsion has been formed. The organic solvent is too small, the effect of cleaning ink is significantly reduced, and the cleaning time is prolonged. The use of a large amount of rust may cause the axial center of the ink roller to be rusted, which is unfavorable to the maintenance of the ink roller.

The use of efficient offset printing ink cleaners is extremely simple. If it is manual cleaning, pour the emulsified cleaning liquid into the cleaning bottle and use the same method to clean the ink roller while turning the machine. If the offset printing machine is equipped with a device for automatically cleaning the ink roller and blanket, as long as the water and detergent liquid is injected into the cleaning tank at a ratio of 25:75, the cleaning button can be pressed to automatically clean.

Third, the price of efficient ink cleaner

"Getting high profits and investing in low costs" is the goal of all businesses, and printing companies are no exception. High-efficiency offset printing ink cleaners have such advantages compared to gasoline. However, when it comes to prices, printers seem to feel uncomfortable. Fortunately, recently, our country has produced a high-efficiency ink cleaning agent. Its quality is the same as that of imported cleaning agents. The cleaning effect is even more than that of imported cleaning agents, but the price is only half that of imported cleaning agents. In this way, the use of domestic high-quality offset ink cleaners is cheaper than using gasoline. For example, in Beijing, there is an offset printing plant that cleans a set of ink rollers for four-color offset printing presses. The domestic cleaning agent consumes 1.5 liters and takes 20 minutes; for petrol it consumes 3 liters, but also uses 1 Raising kerosene for auxiliary cleaning takes 30 minutes. The domestic cleaning agent was 17.6 yuan per liter, gasoline was 3.10 yuan per liter, kerosene was 2.20 yuan per liter, and the offset press had a printing speed of 9,000 per hour. On the surface, the price of domestic cleaners is about 6 times that of gasoline, but it takes 1/3 less time to clean them with cleaners than with gasoline, and does not require kerosene for auxiliary cleaning. The calculations show that cleaning agents are used. It costs about 30 yuan more than using gasoline. Nowadays, more and more short-run offset printing jobs are needed. Frequent plate change, ink change, and ink roller cleaning are required each time. The less time it takes to stop the cleaning, the longer the machine runs, and the more the production value becomes. high. Therefore, compared with gasoline cleaning, cleaning the ink roller with a high-quality offset ink cleaning agent greatly improves the production efficiency. Without doubt, the output value and profit will also increase substantially.

In addition, the ink roller cleaned with the high-efficiency ink cleaner was cleaner than gasoline, and the start-up printing saved about 30% more paper than gasoline. An ink roller that is cleaned with a cleaning agent can generally extend its service life by more than one year compared to an ink roller that is cleaned with gasoline. The cleaning agent is not flammable and does not need to be stored in a warehouse with extremely strict fire prevention facilities, which saves money and space. It is not difficult to see that comprehensive accounting and the use of high-quality offset printing ink cleaners instead of petrol cleaning ink rollers saves a considerable sum of money.

Most of the printing companies in China are located in politically, culturally, and economically developed cities. Therefore, the environmental governance and safety and fire prevention of printing companies are of special significance. The relevant government departments have also intensified their efforts in this regard. Recently, with the international market price of gasoline in Shanghai, the leaders of printing companies have clearly realized that the process of using gasoline to clean the offset roller will be eliminated, while the use of high-quality offset ink cleaners is increasing. Domestic production of high-quality offset printing ink cleaners and their placement in the printing market will certainly bring greater economic benefits to printing companies, providing press operators with a safe working environment and thus achieving good social benefits.

Author: FENG Rui dry Source: printing technology

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