Analysis of ten technical problems in the applicat

2022-07-27
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Analysis of ten technical problems in the application of ink in the printing process; ② Yellowing of ink film; ② Printing white dot; ④ Back adhesion and adhesion; ⑤ Discoloration and discoloration; ⑥ White ink film; ⑦ Pinhole and shrinkage; ⑧ Transfer without inking; ⑨ Biting color (commonly known as cross color) and fading; ⑩ Poor gloss (whitening). These printing technical problems have become a common consensus of production failures. In order to sum up the above failures, the author, in the spirit of "popularization of profound problems and simplification of complex problems", has had fruitful exchanges with experts and scholars from nearly 30 packaging and printing enterprises, ink manufacturing enterprises and material production enterprises, especially the operators in the production line, Through observation and analysis in the process of cooperation, it is believed that the ten printing technical problems such as "ink migration" have directly hindered the normal progress of China's packaging and printing production, and seriously reduced the quality of packaging and printing products

preventing and solving the above faults is conducive to the progress of technology and the renewal of products. In order to find a more convenient method to solve the ten difficult problems, the author puts forward some superficial causes and preventive measures for the readers in the packaging and printing industry and for the reference of the ink production peers

1. ink migration. Migration - the pigment in the ink contacts another kind of substance through or through the film (sometimes it will stick to the goods in the package) and cause pollution. The reason is that the packaging printing ink and substrate (such as plastic film) contain excessive plasticizers. Sometimes, excessive other additives in the ink system will move in the substrate (such as film) due to the solvent in the printing ink component dissolving part of the ink pigment. Also, when the stored packaging printing materials are used in summer, the image ink film on the printing accessories will become soft due to the rise of temperature, Accelerates migration. The countermeasures are as follows: in the substrate, especially the packaging printing ink, the plasticizer or hydrophilic substrate shall be used as little as possible, and the ink containing pigments and dyes dissolved in plasticizer and water shall be avoided. It is easy to judge the change of color and dye from the appearance. Therefore, in the formulation design and production of the ink, the best conditions for the overprint processing of the second, third, Fourth... And the end use and purpose should be considered

2. the ink film turns yellow. In the white ink system, titanium dioxide with high tinting power, large hiding power, good whiteness and high light scattering ability is generally used as the ink colorant. It is unknown that this material has obvious "photochemical activity", that is, problems such as loss of light, discoloration, chalking and peeling often occur after printing. Yellowing is one of the most troublesome faults in recent years. To overcome this defect, the x24 sold on the market can overcome this defect and make up for its deficiency only by proper processing. If yellowing is found during printing, the operator only needs to temporarily add it to the ink bucket, which can not only greatly improve the whiteness and hiding power of the original white ink, but also greatly reduce the cost of printing ink materials by as much as 10% ~ 30%

in addition, the yellowing of color ink is the same as that of white ink. Only adding x24, 0.5% ~ 2%, can also avoid yellowing. Similarly, the pH value and environment of the substrate will also lead to the yellowing of its graphics and ink film. In a large number of practices, we have obviously felt that pH value often makes yannike's "vibrant campus" project in the ink system dedicated to cultivating sports culture in schools, which increases the oil absorption of fillers, resulting in "false thickening" or drying of the ink. In serious cases, the ink cannot be transferred or the color concentration becomes lighter after transfer. In order to eliminate yellowing, adding 1010 antioxidant and anti ultraviolet absorbent is also a temporary treatment method

in addition, it is very important to control the pH value because the yellowing of the composite compound after close contact with the ink film also occurs from time to time

3. white dot of printed matter. The printing technology problem reminds people that the stability of printing ink during storage and use is the result of the interaction between the components of the product system. We all know that different polar strengths of solvents have different effects on the adsorption of active ink additives on the pigment surface, and the competitive adsorption of binders and active additives on the pigment surface mainly depends on the affinity between binders, active additives and the pigment surface. Because the physical adsorption of the ink particle surfactant does not affect the chemical adsorption of the polymer, this is because the physical adsorption of the surfactant on the pigment surface is not firm. From this point, it has been known that the excessive addition of active dispersants, wear-resistant waxes and even amide resin binders in the printing ink system will affect the attachment of the packaging printing ink film. At the same time, during the grinding process, there are too few dispersants, especially the improper addition sequence, especially the short dispersion time, When there are a large number of pinhole white spots on the surface after printing on the machine and the white fault after printing will occur

in order to prevent the above failures, the active additives of the ink should be reasonably selected, or the time for grinding and dispersing the ink should be appropriately extended, or the ink should be fully stirred before printing

4. back adhesion and adhesion. In recent years, in southern Jiangsu, even in Qilu, the back adhesion or adhesion of compound printing ink for internal printing is more serious than that of gravure and surface printing ink in the past. Most of the time is from July to October. Often, after packaging and printing, there is no back adhesion or print adhesion within a short time after the ink is dried and formed into a film. However, when the ink is released for processing after printing or after the printing is delivered to the user for a period of time, there will be a serious phenomenon that the ink film does not feel smooth, the fingers are sticky, or the ink sticks together during slitting or packaging. This phenomenon is actually caused by the low softening point of the ink binder of the packaging and printing products. Of course, it is also caused by the surface dryness and internal wetness (commonly known as skin scorched bones) caused by the mistakenly adding too much slow drying solvent or inhaling moisture when the ink is diluted for printing

in order to prevent the recurrence of this fault, first, strictly select the ink varieties produced by regular manufacturers with technical parameters; Second, when printing, the mixed solvent (not containing water) shall be selected in strict accordance with the volatilization rate or evaporation rate of the solvent; Third, in the packaging and printing, the surface treatment should be carried out on the substrate stained with oil and wax; Fourth, the second overprint shall be carried out after the last printing ink film is dry; Fifth, select the ink with high softening point of binder in the ink system (or conduct the softening point test before determining the ink)

5. printing discoloration. The green manufacturing level of enterprises related to graphic and ink film of packaging and printing has been greatly improved. Discoloration is the fault of the printing process or finished products in the outdoor aging stage. After aging in the atmosphere, the printing ink film will fade or even change color prematurely under very harsh conditions. The ink film is exposed in the atmosphere. Due to the action of ultraviolet light, the degree of color change will vary with the temperature of the atmosphere, the light intensity of sunlight, the nature of the printing ink film, the color saturation, the color printing coloring power, the pH value of the ink film, the impurities in the atmosphere Or the length of continuous or indirect exposure in the atmosphere. Therefore, before printing, we should try not to use the lake ink that is easy to fade according to the oil supply plastic hose, but try to use the white ink produced by rutile titanium dioxide. X24 can also be added to the packaging printing ink to improve its anti discoloration. Another kind of adding brightener is one of the common methods

6. the ink film is white. After printing of white ink and blue ink system, the surface of wet ink film shows irregular white pigment white spots (also known as floating color, which is different from black and blue floating color white spots), especially when it is exposed after compounding or aluminizing. However, blue ink often has blank spots of different sizes similar to pinholes after printing, which seriously affects the appearance quality of packaging and printing products. The main reason for the failure is related to the pigment type selected in the ink system. It also causes the flocculation or separation of the pigment due to the mixing of another ink, resulting in the floating of the pigment in the ink system

the countermeasures are as follows: it is better to use pigments with the same particle size and specific gravity as raw materials to produce inks. Secondly, it is better to extend the dispersion time or subtract the active additives

7. pinhole and shrinkage. In the process of packaging and printing, due to the operation of machinery, especially the rotation of printing plate and printing roller, the ink film often forms pinholes, which are different in size and number (often referred to as chemical pinholes). In the same part, the pinholes of the same size are often divided into mechanical pinholes, but occasionally there are pinholes of dot blank circle, which are often caused by impurities or small resin particles in the ink system after drying

the chemical pinhole fault is caused by the fast volatilization of solvent in the wet ink film and the overflow of air foam in the printing ink film, resulting in the pinhole left after the packaging printing ink film is dried. Of course, there are also pinholes caused by the loss of fluidity of the ink film after the bubbles overflow during the printing drying process. In addition, when the ink contains a small amount of water or at high temperature, especially at high temperature, the above pinhole phenomenon is more likely to occur, that is, people call it: the stable foam with malawang effect is called wet foam or dynamic foam, and its foam is brittle and easy to be eliminated by chemical defoamers

strictly select the ink, more importantly, select the thinner, control the ink viscosity, or appropriately select the solvent with slow volatilization speed, so as to improve the smoothness of the printing ink film, prevent the mixing of moisture and impurities, and it is also very important to check the cleanliness of the vacuum pump air and the pollution of the substrate surface. For two-component inks and two-component composite adhesives, they should be placed for a period of time. Printing inks that have produced surface or internal flocculation should be prohibited

8. transfer without inking. In the normal printing process, the ink does not rotate with the ink bucket roller occasionally, and even the ink accumulates on the printing machine. Especially after the printing speed is accelerated, the color tone of the printing ink is shallow or different

in the past, this fault was mostly caused by too high pigment content, too thick ink, too large yield value or too short ink head. In recent years, the above phenomena are caused by too high acid value of binders or pigments in the ink system, or excessive absorption of acidic water or the addition of a single solvent. There is no problem in printing. Often, when the ink is diluted, the ink changes from thin to thick, or even like tofu blocks, and is forced to stop for ink change

once this fault occurs, add a proper amount of tm-27 coupling agent, a national inspection free product. In severe cases, add TM-3 coupling agent (Tianyang chemical plant) or add alkaline solvent for dilution, or add wetting agent or gold transfer oil, or increase the printing pressure. If the roller is defective, replace the roller, or install an agitator in the ink bucket

9. biting color (commonly known as cross color). In the process of packaging printing, when the first or second pass of chromatic printing is carried out, the surface of the previous printing ink film will be found to make the printing ink film too soft and even wrinkle. This phenomenon is called the prelude to color biting. When the ink system contains strong solvent in the next printing (overprint), it may completely

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