The major technical problems in packaging and printing have long plagued people. The problems are mainly concentrated on the following points: 1 ink migration; 2 yellowing of ink film; 2 white dots on printed products; 4 sticking and adhesion; 5 discoloration and fading; 6 ink film Floating white; 7 pin holes and shrink holes; 8 transfer without ink; 9 bite color (commonly known as string color) and fade; 10 gloss difference (white). These printing technology problems have become a commonly agreed production failure. In order to sum up the above-mentioned failures, the author of this article has been simplistic in terms of "familiar issues and simplification of profound issues." He has worked with nearly 30 packaging and printing companies, ink manufacturing companies, and material manufacturers, especially for the production line operators. Into a fruitful exchange, and through observation and analysis in the process of cooperation, we believe that the “Top Ten” printing technology problems such as “ink migration” have been or are directly hampering the normal progress of China’s packaging and printing production, and have seriously reduced the number of packaging and printing products. quality.

Preventing and resolving the above failures is conducive to technological progress and product updates. In order to solve the ten difficult problems to find a more convenient method, the author put forward some superficial causes and preventive measures, in order to pack the printing industry readers, and provide reference for ink production peers.

1. Ink migration. Migration - The pigment in the ink penetrates or passes through the film and contacts another class of material (sometimes also stuck to the product in the package) causing contamination. The reason for this is that packaging printing inks and substrates (such as plastic films) contain excessive plasticizers. Excessive amounts of other additives in the ink system sometimes cause some of the ink's pigment to dissolve due to the solvent in the printing ink composition. Moving substrates (such as film), but also when the stored packaging prints are used in summer, the pattern ink film on the printing accessories tends to soften due to the increase in temperature, which accelerates the speed of migration. The countermeasures are: to minimize the use of plasticizers or hydrophilic substrates in substrates, especially packaging printing inks, and to avoid the use of inks containing pigment dyes dissolved in plasticizers and water. The change of color dye is easy to judge from the appearance. Therefore, in the formula design and production of inks, the two, three, four times...overprint processing and the best conditions for the end use and purpose should be considered.

2. Ink film yellowed. Printing Ink Film In the white ink system, titanium dioxide is usually used as the colorant for inks with high coloring power, high hiding power, good whiteness, and high light scattering capability. Do you not know that the material has obvious "photochemical activity", that is, there are often problems such as loss of light, discoloration, powdering, and peeling after printing. Yellowing is one of the biggest headaches for people in recent years. To overcome this shortcoming, the X24 can only overcome the drawbacks and make up for its shortcomings. If yellowing is found during printing, the operator only needs to temporarily add it to the ink hopper, which not only greatly improves the whiteness and hiding power of the original white ink, but also greatly reduces the cost of printing ink materials by up to 10%. As much as 30%.

Furthermore, the yellowing of color ink is the same as that of white ink. It is only necessary to add X24 and 0.5% to 2% to avoid yellowing. In the same way, the pH and environment of the substrate can also lead to yellowing of its graphics and ink film. In a large number of practices, we have clearly felt that the pH value tends to increase the oil absorption of pigment fillers in the ink system, resulting in “false thick” or dry knots of the ink; in severe cases, the ink is not transferred or the color concentration becomes light after transfer. and many more. Usually to eliminate yellowing, the addition of 1010 antioxidants and anti-ultraviolet absorbers is also a temporary treatment.

In addition, the yellowing of the compound material after it comes into close contact with the ink film will also occur from time to time, and controlling the pH value becomes crucial.

3. Print white spots. The printing technology issue reminds people: The stability of the printing ink during storage and use is the result of the interaction between the components of the product system. We all know that the polarity of the solvent is different, and the active ink additives also have different effects on the absorption of pigments on the surface of the pigment. The binder and the coagent will produce competitive adsorption on the pigment surface, depending on the binder, The affinity of the coagent with the pigment surface. The physisorption of the surface active agent of the ink particles does not affect the chemisorption of the polymer, because the physical adsorption of the surface active substance on the surface of the pigment is not strong. From this point, it has been known that the excessive addition of reactive dispersants, abrasion-resistant wiping wax, and even amide-based resin binders in the printing ink system can affect the attachment of the printing ink film to the printing ink while performing the grinding process. Among them, due to too few dispersing aids, especially the improper order of addition, and in particular the time of dispersion is too short, a large number of pinhole white spots on the surface after printing on the machine and complex white defects after printing will occur.

In order to prevent the above failures, we should reasonably select the ink's co-agent, or extend the time to grind and disperse the ink in an appropriate amount, or stir the ink after printing and then print it.

4. Stick back and stick together. In recent years, in the area south of Jiangsu Province and even in the Qilu region, the back-adhesion or adhesion of India-Indian compound inks is even worse than the gravure and surface printing inks in the past. Most of the time is concentrated in July-October. Often after the packaging and printing, the ink does not return to stick or the phenomenon of adhesion of the printing ink within a short period of time after the ink is dried and filmed. However, the ink film does not feel handed after printing or after the printing has been delivered to the user for a period of time. Slippery, sticky or sticky, or severely sticking when dispensing. The appearance of this phenomenon is actually caused by the low softening point of the ink binder of the packaging and printing products. Of course, there are also inks that, during dilution printing, mistakenly add too much slow-drying solvent or inhale moisture and appear dry inside. Commonly called skin coke bone raw) caused.

In order to prevent the recurrence of the failure, one is to strictly select the type of ink produced by the regular manufacturer and with the technical parameters; the second is to use the mixed solvent (not containing water) in strict accordance with the volatilization rate or evaporation rate of the solvent. Third, in the packaging and printing, should be stained with oil and wax and other substrates for surface treatment; fourth is to be printed on the next dry ink film after the second overprint; five is the use of ink system in the link material softening point Higher ink (or ink after first performing its softening point test).

5. Discoloration of printed products. Discoloration of ink film in packaging and printing is a failure in the printing process or in the outdoor aging stage of finished products. The printing ink film undergoes aging in the atmosphere. Under very severe conditions, premature discoloration or even discoloration occurs. The ink film is exposed in the atmosphere. Due to the effect of ultraviolet rays, the degree of color change depends on the temperature, temperature, and sunlight of the atmosphere. The light intensity and the properties of the printing ink film, the saturation of the color and the tinting power of the color printing and the pH of the ink film, the impurities in the atmosphere, or the length of the continuous or indirect exposure time in the atmosphere are different. Therefore, before printing, we should try not to use fading lake ink, but try to use rutile titanium dioxide production of white ink, can also be added to the packaging printing ink X24 to improve its anti-tarnish. Another method of adding brighteners is one of the commonly used methods.

6. Ink film floating white. After the white ink and blue ink system is printed, the surface of the wet ink film exhibits irregular white pigment white spots (also known as floating colors, which are different from black and blue floating white spots), especially when compounded or More noticeable after the aluminum plating. The blue ink, after printing, tends to have different sizes of pinhole-like blank spots, which seriously affect the appearance quality of the packaged printing products. The main reason for this failure is related to the type of pigment used in the ink system, and the flocculation or separation of the pigment due to mixing with another ink, resulting in floating of the pigment in the ink system.

The countermeasures are: It is better to use the same ink with the same particle size and the same specific gravity as the raw material to produce the ink. The second is to extend the dispersion time or subtract the auxiliary agent containing the activity.

7. Pinholes and shrinkage holes. In the packaging printing process, due to the mechanical operation, especially the rotation of the printing plate and the printing roller, the ink film often forms pinholes, small and large holes (often referred to as chemical pinholes) of different sizes and sizes. The same part, the same size of the hole is often divided into mechanical pinholes, but occasionally there will be point-blank pinholes are often due to impurities or ink system in the tiny resin particles in India after the drying shrinkage.

Chemical pinhole failures are due to too rapid solvent volatilization in the wet ink film, and the inability of the wet film to level out due to the overflow of air bubbles in the printing ink film, resulting in needle-like small holes left after the packaging printing ink film is dried. Of course, there are also ink holes produced when the ink is produced and blended with color ink, or ink is excessively diluted to produce bubbles that do not disappear. When the bubbles overflow during printing and drying, the ink film has lost its fluidity. Also when the ink contains trace amounts of water or high temperature, especially under high temperature environment, the pinhole phenomenon mentioned above is more likely to occur. That is what people call: The horsehair effect and the stable foam is called wet foam or dynamic foam. The foam is brittle. Easily eliminated by chemical defoamers.

Strict selection of ink, more important to narrow the choice of materials, and control the viscosity of the ink, or moderate use of solvents with slow evaporation rate, in order to improve the leveling of its printing ink film, to prevent the incorporation of moisture, impurities, check the vacuum pump air cleanliness and The level of contamination on the surface of the substrate is also very important. For two-component inks and two-component adhesives, they should be used for a period of time. Printing inks that have generated surface or inherent flocculation should be prohibited.

8. Transfer does not ink. In the normal printing process, the ink occasionally does not rotate with the ink fountain roller, and even the ink accumulates on the printing press. In particular, after the printing speed is increased, the color tone of the printing ink is relatively light or shaded.

This failure was mostly caused by too high a pigment content, a too thick ink, a too high yield value, or a too short ink head. In recent years, these phenomena have been caused by excessive acid values ​​in the ink system or the linking materials or pigments, or excessive ingestion of acidic water or the addition of a single solvent. There is no problem at the beginning of printing, and often when the ink is diluted. The ink is from thin to thick, and even like a block of tofu, it is forced to shut down and change ink.

Once this failure occurs, appropriate amount of TM-27 coupling agent shall be added to the national inspection-free product, and TM-3 coupling agent (Tianyang Chemical Factory) shall be seriously added, or alkali solvent shall be added for dilution, or wetting aid or gold transfer oil shall be added. Or increase the printing pressure. If the roller is bad, the roller should be replaced. An agitator can also be installed in the ink fountain.

9. Biting color (commonly known as string color). In the packaging printing process, when the first pass or the second pass of color printing, the previous printing ink film surface will be found to make the printing ink film too soft, even wrinkling phenomenon, this phenomenon is called bite color Prelude. However, when printing (overprinting) later, the ink system contains a strong solvent, which may completely penetrate the ink film and be bitten, so as to be miscible in the ink film of the next color. The packaging printing ink film is mixed with noise (dyeing). The main reason is that the printing ink contains soluble components (resin or solvent).

When printing on such inks, dilution solvents must be used. Do not use strong solvents (true solvents) to adjust the viscosity of inks or speed up the printing process to shorten the time for two or three times of overprinting. Mixing can be used before printing. The solvent adjusts the redissolved (redissolved) effect of the ink to determine the proportion of the diluted solvent.

10. Bad gloss (whitening). Most of these failures occur during the printing process of volatile drying type printing inks, and an opaque white ink film layer appears during the process of rapid volatilization of solvents after high-speed printing. This phenomenon is sometimes temporary, but most of it may be long-lasting. This is due to the fact that the cooling (device) blowing or the air in the vicinity of the drying printing ink film freezes to the dew point, that is, absorbs the weight of water (vapor) and returns to the ink film to be condensed. In addition, solvents such as inks or pigments in aqueous systems can also cause a poor gloss of printed ink film. In other words, the higher the volatility of the solvent, the graphic ink film (whitening) gloss of the packaging printing ink