1、 As we all know, when the ink in the ink hopper forms a layer of film due to the drying of the surface layer during the printing process, either place a stirring device or simply pour the ink out, otherwise, the film will adhere to the roller, resulting in uneven layout, resulting in random knife mark pollution. The reason is that the ink industry tends to: (1) the ink drying is too fast; (2) the ink liquidity is poor; (3) the ink precipitation has been dry. However, we don't know that this phenomenon is caused by the evaporation, evaporation or oxidation of the ink system. However, the printing industry thinks that the structure of the ink barrel or the ink hopper is not good, resulting in the stagnant part, and the air leaked from the dryer dries the surface of the ink or the hot air blows the ink into the ink hopper. Although there are different opinions about this phenomenon, printing operators generally adopt the following treatment methods: (1) do not use fast drying ink; (2) add medium and slow drying solvent; (3) replace the deteriorated ink (from poor liquidity to good liquidity); (4) keep stirring in the ink fountain; (5) set a closed top cover on the ink holder; (6) adjust the angle of hot air blowing. When the drying speed is too fast, or the ink concentration is too light, or the flow is poor, or the ink thixotropy is large, or the ink static electricity, people who have printing experience and common sense will adopt the method of adjusting the printing machine speed, which not only prevents the ink from drying on the printing plate in advance, but also overcomes the crust formed by the ink film formed in the packaging printing brush, and eliminates the mottling fault of the pictures and texts. 2、 Stabilizing the film quality of packaging printing ink can control the free radical polymerization, drying or solvent volatilization, as well as the oxidation activity of the ink film, so as to achieve the purpose of preventing skin formation. However, this kind of control function must be based on the needs, which does not affect the drying rate of printing image and text film, and does not affect the performance and quality of the ink products, which is the minimum standard for ink manufacturing. In order to achieve this goal, the author suggests the following three methods: Method 1: adding antioxidant and retarder. In the printing ink system, the function of adding antioxidant or retarder is to prevent the generation of free radicals in the film forming process of packaging printing graphics and texts, so as to stop the oxidation and volatilization polymerization of ink film. Once the solvent volatilizes in a very short period of time, the oxidation process of oil is also reduced, and the free radicals produced by the ink will continue to polymerize into film (such as Tianjin Li biochemical factory product series). Method 2: adding oxygen isolating agent. Liquid paraffin, known as oxygen barrier agent, is added to the packaging printing ink. The vapor generated is filled between the ink barrels, cans and boxes to form an oxygen barrier layer (film), which effectively prevents the solvent in the ink system from volatilizing due to vapor pressure. Method 3: adding complexing agent. Oximes (methyl ethyl ketone oxime, butyraldehyde oxime, hydroquinone and so on) were used to control the activity of drying agent in ink system, which could delay or prevent skin formation. For a long time, it has been more than 50 years since packaging printing inks were added with anti scaling agents (i.e. polymerization inhibitor). In the past 40 years, phenols were mostly used, while benzoic acid was used in ink. Compared with the first solvent with high boiling point, it was time-saving and labor-saving. Because phenols themselves are proton donors, they can produce peroxidized radicals in the process of oxidation reaction to generate ROOH, at the same time, they form a stable anti oxygen free radical, capture active free radicals, and terminate the oxidative polymerization reaction - prevent the coating of printing ink. With the development of science and technology, it has been found that butyraldehyde and methyl ethyl ketone oxime have the best effect on preventing ink crust after using oximes as anti scaling agents in recent years. Some ink manufacturers and packaging printing operators believe that the effect of oxime compounds has exceeded the traditional phenolic compounds. In the 1980s, methyl ethyl ketone oxime anti scaling agent was developed for the first time in China. After the appearance of butyraldehyde oxime, the application and effect in China have reached the advanced level in the world.Three, the application scope and precautions of anti skinning agents, such as the oxidation of packaging printing ink, especially the volatilization speed of solvents, the oil of modified resins, the amount of pigment used, fillers, driers, the storage temperature and humidity of the finished products of printing ink, and so on, have certain effects on the crust (gel) of the ink. Therefore, when using anti skinning agent (gel), we must take account of the above. At the same time, we should also pay attention to the basic situation of seven aspects, such as the amount of addition: 1. Generally, it is calculated according to the ink material (because the main component of the crust is the main raw material of the ink) or the total amount of the printing ink for packaging, and at the same time, the influence of other components should be considered. Generally, 0.1% ～ 0.3% is enough. Because of the difference of temperature and humidity in the four seasons of the year, the speed of crusting is different. Therefore, it is 0.1% in winter, 0.3% in summer and 0.2% in spring and autumn. Depending on the composition of the formula is scientific. 2. Dry rate of ink film. Although the production rate of methyl ethyl ketone in normal temperature or printing ink evaporation rate is less than 1% in normal temperature, it is still proved that the evaporation rate of methyl ethyl ketone is within the normal temperature range. This is because the complex formed by the auxiliary agent and drying agent makes the drying agent lose its activity temporarily. Therefore, it is different from the traditional method of using phenolic compounds to capture active free radicals to terminate the polymerization reaction, because oximes have little effect on the drying rate. If the dosage is too much, the evaporation time is prolonged, and the complex disintegrates too slowly, it often affects the film-forming and drying of packaging and printing ink Rate. 3. Yellowing. Once the anti scaling agent exceeds 0.3%, it will often lead to the yellowing of printing ink film, especially in white ink, which will cause yellowing after long storage. Therefore, strictly controlling the dosage or changing to butyraldehyde oxime can avoid yellowing. 4. Color. The color of packaging printing ink is often directly affected by the addition of anti scaling agent. Generally, the influence of blending oil is greater than that of color ink, and the influence of white or yellow ink is greater than that of dark color packaging printing ink. Generally, this phenomenon is difficult to observe by visual inspection, and has nothing to do with the addition amount. Although we have known that the color of the ink film will not be affected by the drying of the film, there will be a significant difference between the hues of the ink film of the packaging printing in the presence of some pigments (such as amphoteric pigments) and drying agents, which will cause trouble for color adjustment. In this case, the color difference test should be carried out before the continuous proofing of ink making. The purpose is to avoid the influence of color change on the appearance quality of ink film after printing. 5. Printing ink film status. Although the anti scaling agent does not have any effect on the state of the printing ink film, the packaging printing ink will crystallize when it is stored at low temperature for a long time, which will cause the haze of the packaging printing ink film and affect the gloss of the ink film. As a result of the above material and ink system in the binder, pigment, filler and drying agent design ratio is improper, there will be larger particles. Therefore, the test should be carried out before printing. 6. Gloss and weather resistance. The gloss of printing ink will not be affected by the addition of anti crust agent, but also has light retention. After adding additives, the weatherability of printing ink film is improved.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.