Offset printing is currently the most important printing method, which is characterized by the need to use dampening solution in the printing process, so offset printing inks require good water resistance. In the past, the binder of offset inks was mainly vegetable oils such as linseed oil. Most of them have been replaced by various resins with better performance. Common resins include rosin modified phenolic resin, alkyd resin and polyurethane alkyd resin.
An offset printing ink introduction
1 Classification of offset inks
According to the division of printing machinery, it can be divided into sheetfed offset printing ink and rotary offset printing ink;
According to different drying methods, it can be divided into osmotic offset printing ink, thermosetting offset printing ink, radiation curing (UV/EB) offset printing ink and printing iron offset printing ink.
2 environmentally friendly offset printing ink
At present, the printing industry in China faces great environmental pressure, because most of the inks used in printing contain organic solvents (compared with solvent-based inks, there are few organic solvents in offset inks), volatilization and emission of organic solvents. It will cause environmental pollution. In addition, the ink contains harmful heavy metal elements such as lead, chromium, cadmium, mercury, arsenic and antimony, which are extremely harmful to the human body and the environment. From the perspective of environmental protection and health, more and more users are taking low toxicity, environmental protection and pollution-free as an important condition when purchasing ink. In China, the development of environmentally friendly offset printing inks is still subject to many factors, but for the Chinese ink industry, the ultimate realization and promotion of green ink is the development goal and the ultimate pursuit.
3 waterless offset ink
Waterless offset ink. Waterless offset printing does not use fountain solution. It can be said that it has greatly contributed to environmental protection. It is expected that waterless offset printing in the past two years should have a good space for development in light paper printing. However, waterless offset inks are greatly affected by the ambient temperature during the actual printing process, which is easy to get dirty, and also requires special waterless offset printing equipment. In addition, due to the relatively expensive waterless offset printing plates, the application and promotion in China are limited, and the development is slow.
4 the composition of offset ink
Offset ink is a tree light bright and dry type ink, which is composed of color materials and connecting materials, fitness adjusters, drying adjusters, and printing effect modifiers.
Second, commonly used ink additives
Ink auxiliaries are auxiliary materials used to adjust the ink to suit different printing conditions. There are many kinds of ink additives. Generally used are detacking agents, spreading agents, desiccants, slow drying agents, thinners, anti-friction agents, varnishes, anti-smudge agents, varnishes, etc. The role of ink additives and their use.
1 spoiler
The debonding agent has a very low viscosity and is generally used in lithographic and offset printing inks to reduce its stickiness. In offset printing, due to changes in paper properties and printing conditions, such as large oil absorption, poor surface strength, and uneven coating on the front and back sides, when the desiccant is excessive or the room temperature in the printing room is too low, the paper may be pulled and printed. Stacking, paste, and other failures affect the quality of printed products. Therefore, when the above phenomenon occurs, an appropriate amount of the detacking agent can be added, thereby reducing and eliminating the above malfunction.
2 withdrawal agent
The lightening agent, also known as the thinner, is a relatively large amount of auxiliary agent used in offset printing. There are two common types of lightening agents: one is a transparent oil for bright light inks; the other is a resin type lightening agent for resin inks. If it is found in the printing that the ink color is too dark to restore the original, an appropriate amount of the light agent can be added to achieve the desired effect.
3 desiccant
Desiccant is one of the most important printing ink additives. The amount, type and method of use of the desiccant vary depending on the printing conditions and the printing paper. Commonly used desiccants are red dry oil and white dry oil. Drying of red dry oil is from outside to inside drying, while white bath oil is dried at the same time. When printing, I chose the type of dry oil according to the requirements of printing dryness and ink color. Generally, the amount of dry oil is 2%-3%, and too much will be suitable for the base, so that the drying speed is reduced.
4 slow drying agent
Anti-drying agents, also known as antioxidants, are an ink auxiliaries as opposed to desiccants. During the printing process, it often causes downtime for various reasons. When the downtime is long, the ink on the surface will dry and peel. In order to solve such problems, it is often necessary to add an appropriate amount of anti-drying agent to the ink on the machine, and run the machine a few times to make it dry too fast.
5 thinner
In printing, due to excessive viscosity of the ink or poor quality of the paper, problems such as paper pulling and missing plates may occur, which may affect the normal printing. In addition, in addition to adding an appropriate amount of debonding agent to reduce the viscosity of the ink, it may also be added. A small amount of thinner to reduce the viscosity of the ink allows the printing to proceed smoothly. There are many types of thinners, generally low viscosity No. 6 varnish.
6 anti-friction agent
Anti-friction agents are also called smoothing agents. Most of these substances are mainly waxy substances. When the printing ink particles are coarse, such as white ink, gold and silver ink, etc., add appropriate amount of anti-friction agent to increase the abrasion resistance of the printed matter. Smoothness.
7 varnish
High-grade printed products such as trademarks and albums, and printed surfaces must be covered with light to achieve high-light effect. When using varnish, the base can be added to the ink before printing, or after the printed product is printed. Print a varnish. However, the printed products that have been covered with light will be yellowed after a long period of time, and the light resistance is poor. Therefore, many new varnishes have been used to replace the varnish.
In addition to the above-mentioned commonly used ink auxiliaries, there are anti-smudge agents, anti-foaming agents, gold-plated oils, etc., which will not be described here, as long as they are used in strict accordance with the instructions.
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