In recent years, due to the development of China's printing industry, offset printing has not only achieved great development in the field of book printing, but also has significantly improved the application in the field of packaging and printing. The development of laser platemaking, PS plate, ink, paper, and printing machinery can make the speed, quality, and variety of offset printing processes significantly improved. Many experts are engaged in the research of this work. The printing press manufacturer not only manufactured a sheet-fed high-speed printing press, but also improved the ink transfer system, improved the dusting equipment, and improved the lining process materials. Efficiency and product quality. The paper manufacturer also improved the selection of materials and processes for the paper surface coating, improved the initial absorption of the paper and the solidification rate of the ink, in order to meet the requirements of the sheet-fed printing process and the rotary thermosetting offset printing process. In terms of media, there has been direct plate (CTP) media technology. These advances in offset printing materials also place higher demands on offset inks and can focus on the following characteristics of inks.
Fixation of sheetfed offset printing ink
Whether it is general offset ink or bright fast-drying ink, it has the problem of increasing the dryness. Dryness of ink refers to the property of ink sticking to the surface of the paper after the ink is printed on the paper, due to the absorption of the paper and the volatility of the solvent in the ink, which will not stick to the back of the paper without strong embossing or rubbing. The dryness of the ink is related to the ink manufacturing process technology and formulation, and is also related to the printing equipment and the printing process. More than ten years ago, most Chinese offset printing inks used rosin-modified phenolic resin as the main link material, commonly used is the bisphenol A and p-tert-butyl phenol process technology route. In recent years, the process technology of octylphenol or phenylphenol has been used to increase the release of mineral oil, thereby improving the fixation of the ink. More than a decade ago, the ink generally took about 15 minutes to dry, and now it takes only 10 minutes or less to dry. This indicator has reached the best level of similar foreign products. Since the initial solidification and drying time of the ink becomes shorter, the drying time of the oxidized conjunctiva at the later period is also shortened. In addition, in terms of environmental protection, non-aromatic or less aromatic solvents are used to reduce the harm to the human body, and this solvent has a marked acceleration effect on the fixation and drying of the ink.
The printing factory often uses viscosity-reducing anti-dirty agents when using inks, which can play a good role in preventing stickiness, but it is better to add less.
Many auxiliaries are used in the ink manufacturing process. These auxiliaries can not only improve the fixing speed of the ink, but also promote the later oxidation and cross-linking, and are beneficial to improve the gloss and fastness of the ink film. Currently, a small amount of cross-linking agents and accelerators have been used to improve the effectiveness of a single oxidized conjunctiva in the past. Many ink factories have introduced foreign advanced additives.
Another product of offset printing ink—non-film-forming ink, can guarantee within 48 hours (individual manufacturers can not reach) in the process of using the ink roller without skinning, the middle shutdown will not affect the printing quality, and will not affect the ink fixation and drying. The time does not affect the post-oxidation conjunctiva drying effect, reduces the waste of cleaning ink, and saves ink. Now it is a very mature technology.
Drying of Rotary Thermosetting Offset Printing Inks
The thermosetting type color rotary offset printing machine has high printing speed, high printing quality, and can print on both sides. The ink used requires pure color, high concentration, good fluidity, and fast heat fixation. The temperature of the heating should not be too high, should be based on the absorption of the paper to determine, the color rotary offset press which has risen in recent years also brought many problems such as gas heating control, thermal process temperature control, safety management and so on. This printing process can print a thin web of coated paper, ie, printed, ready-to-fold, ready-to-install, short time for publication and good quality. It should be pointed out that the ink used in this process is not instantaneously dry, nor is it completely cross-linked and conjunctiva type, but the low-boiling solvent in the ink is volatilized and solidified and dried. After this fixing and drying process, the ink can be considered to be substantially dry. Finally, the entire drying process must be completed by means of oxidative conjunctiva action and cross-linking.
For good color inkjet offset printing inks, the ink is mainly dry due to the absorbency of the paper, and its gloss and firmness are not good, which is suitable for newsprint printing. The main material of this type of ink is petroleum resin and solvent. Because the structure of petroleum resin is relatively single, the appearance strength is poor, and the dissolving power is limited, the ink luster produced is not very good, and the firmness is also general, but it has good permeability. And water resistance, can guarantee the smooth progress of the offset printing process.
Ink transferability during printing
The transferability of offset ink refers to the smoothness of the ink transferred to the roller, the PS plate, and the blanket, and finally printed on the paper. This property of the ink is closely related to the viscosity, viscosity, flowability, thixotropy, and water resistance of the ink. At present, no matter which ink factory ink production than the original have greatly improved, that is, the first few indicators strict control, stickiness indicators, for example, the past control is relatively loose, and now the control is more stringent, that is, The narrow range of indicators is conducive to the operation of printing workers. Since printing is affected by temperature and humidity, the inks used in summer and winter should have some differences. The ink should be thicker in summer and softer in winter, which is the control problem of the upper and lower limits of the above indicators. Such as the summer is easy to produce ink rejection phenomenon, which is caused by poor ink transfer, and in the winter there may be a phenomenon that the ink is relatively hard, need to adjust the ink viscosity adjustment.
Another indicator of good ink transferability is thixotropy. The thixotropy of the ink should not be too large, otherwise it will produce printing, especially in the winter should pay attention to the control of this index. The transferability of web offset printing ink is better, the coloring power is stronger, and the fluidity is better, so that the printing job can be successfully completed, otherwise it is difficult to complete the printing on the high-speed printing machine.
Offset problem of offset printing ink
Some packaging and printing companies often have inconsistencies in the hue before and after the printed product. The probability of problems in the yellow, magenta, and blue primary inks is relatively small, and the problem often arises from some spot color inks that the user requires, such as complex colors. , Including light gray, light brown or dark tea, dark green, dark brown and other colors, some colors are the same when printed, so after a few days the ink will change, appear color cast, different shades, Problems such as lack of coverage. The main reason for this situation is that the ink brands used in printing plants are more complex, and some printing factories do not have colorimeters or reflective densitometers. They use three basic color tones, such as magenta, sky blue and medium yellow, and the ratio is inaccurate. . Moreover, the production conditions of the plants are different, the raw materials are not the same, there will be errors in the hue, such as magenta, some purple, and some red; another example is sky blue, some reddish, some greenish Medium yellow, some reddish, some greenish.
Dilution of the diluting agent used by the ink and the brightening effect of the bright paste are inconsistent. Diluting with the white ink improves the hiding power and makes the color shift more likely to occur.
Should pay attention to the use of ink orientation management and calibration, it may reduce the occurrence of the above situation.
Offset printing ink in other printing methods
The development of the printing industry in China is uneven, and some places have developed rapidly. Many advanced equipment and technologies have been introduced, and high-level products have been printed, but some areas are relatively backward. Some regions have unique features in certain printing processes. In some places, there are certain markets (printed with resin or copper-zinc printing). However, there are many drawbacks in the use of offset printing inks, mainly due to lack of understanding of inks. If you do not know enough, you should use special ink for letterpress. Some screen printing companies also use offset printing inks, and need to adjust the ink's viscosity, dryness and other properties.
Offset printing ink environmental issues
Our country is more and more strict with environmental protection requirements. Whether it is an ink factory or a printing factory, we all pay great attention to environmental protection issues. Modern ink manufacturers use squeeze water technology, that is, in the pigment manufacturing process, without the dehydration process, in the case of water, kneading with the linking material, extruding the water, tightly bonding with the linking material in the case of soft, and then grinding One or two passes can reach the fineness requirement. This process reduces the flying of pigment dust and avoids environmental pollution. It can be said that the ink factory has taken a big step toward environmental protection and is conducive to environmental improvement and human health.
Another environmental protection is soybean oil offset printing ink. The linseed oil, tung oil, and eucalyptus oil in the original ink composition are all dry oils, while soybean oil is a semi-dry oil, and the oxidative conjunctiva ability is weak and cannot be directly applied. It is necessary to use modified technology to turn soybean oil into a standard for dry oils. . Another is the use of aromatics-free or less aromatic solvent manufacturing ink, this ink has reached the environmental requirements, at present China has been trial production, and achieved the American Soybean Association certification. It is suggested that printing houses should pay more attention to the health of printing workers and apply environmentally friendly ink.
In short, in the past 10 years, most of China's ink manufacturing companies have become joint ventures. They have introduced foreign companies' advanced technologies, advanced production management experience, and quality management systems; they have merged into the world sales network system to improve the quality of ink in China. Steps basically catch up with advanced countries (except for individual species). At the same time as the development of the offset printing process, attention should be paid to the development of gravure printing processes and flexographic printing processes, such as the application of benzene-free gravure printing inks and water-based inks.
Reprinted from: Ke Yin Network