Technical essentials of the hottest aluminum foil

Technical points of aluminum foil lithography (II)

6 Prevent the printing matter from sticking dirty

printing matter sticking dirty and poor dryness are the two main disadvantages in aluminum foil printing at present, and they are the surface phenomenon of the internal factors of ink. Because the aluminum foil paper can't or basically can't absorb the solvent in the ink, the solvent such as dry vegetable oil and high boiling point kerosene in the ink binder can't penetrate into the interior of the paper and have to stay in the ink layer on the surface of the paper, so that the ink layer can't thicken and fix quickly. Therefore, the ink layer loses the opportunity of initial drying. That is to say. The ink layer slowly polymerizes at constant temperature for 30min, and the drying process of oxidized conjunctiva becomes the main drying form of the ink layer of aluminum foil paper. The solvent retained in the ink layer not only fails to thicken the ink rapidly, but also hinders the polymerization and oxidation of the ink layer, which makes its drying speed slower. The nature of aluminum foil determines that its printing ink layer cannot be dried quickly. In addition, due to the high smoothness and poor adsorption of aluminum foil paper, the printed matter is very easy to get sticky and dirty after printing. Once this happens, the relatively smooth and smooth ink layer will become fragmented or incomplete instantly when printed, which will seriously affect the visual effect of the product and even become waste products. The phenomenon of slow drying of printing ink makes the phenomenon of sticking dirty more prominent. Therefore, it can be said that the phenomenon of slow drying and dirt is interactive and interrelated, and has become an important content that we need to pay great attention to and care about throughout the aluminum foil printing process. Around these two problems, corresponding technological measures and requirements should be adopted. In order to prevent the printing matter from sticking and dirty, the following measures should be taken:

(1) add an appropriate amount of desiccant (dry oil)

in aluminum foil printing ink, adding an appropriate amount of desiccant can have a certain effect. Adding desiccant appropriately to the ink can accelerate the oxidation and polymerization of the ink layer, promote the drying and solidification of the ink layer, and prevent the occurrence of sticking and dirty faults by using its drying effect on the core technology of the ink, which is in the hands of Switzerland, Japan and other countries. However, do not add too much desiccant, otherwise things will turn against each other when they reach the extreme, which will not only fail to achieve the purpose of improving the fixing speed and timely dryness, but also lead to excessive dryness of ink, dry glue, dry plate, and even inability to print in the printing process

in addition, the viscosity of the ink may increase during the printing machine journey, that is, the aluminum foil can pull with the maximum viscosity due to the increased viscosity and dirt. Therefore, some people think it is wrong to add more desiccants (dry oil) to solve the problems of dirt and dryness. The application requirements of desiccant are relatively complex, including not only the factors of quantity, variety and application technology, but also the conditions of temperature and humidity, machine speed, potion, ink, substrate and printing products in the workshop. It is not only the factors of variety and dosage, application technology, but also the factors of temperature and humidity, machine speed, potion, ink, substrate and printing products in the workshop. In addition, the main object and function of desiccant in the ink system is dry vegetable oil, which is useless for ink oil. Because dry vegetable oil has the function of absorbing oxygen, it and resin can change from liquid state to solid state in the process of absorbing oxygen. The function of desiccant is to shorten this process. The ink oil has no such function, so the desiccant has no effect on printing, especially for aluminum foil printing

(2) master the stacking volume of prints

because aluminum foil prints are very easy to be sticky and dirty, the ink layer wetted by prints is more prone to such failures under the action of the gravity of the paper itself, so mastering the stacking volume of prints is a very important link. Generally speaking, measures should be taken to dry the plywood to minimize the pressure on the ink layer caused by the gravity of each blade of paper, so as to prevent the surface and back of the paper from sticking dirty. Under normal circumstances, the stacking amount of a knife of paper each time is generally about 30 sheets

(3) keep the minimum amount of water in the layout

the absorption of water by paper is the main way of water consumption on offset printing plates. Aluminum foil paper does not absorb ink, but also does not absorb water. Therefore, when printing aluminum foil paper, the amount of water consumed in the bucket is very small. You can keep the minimum amount of water in the layout on the premise that the layout is not dirty, so as to avoid the disadvantages of diluting the ink color and sticking dirty when the printed ink layer is not dry. At the same time, less moisture in the layout is also very beneficial to maintain bright ink and improve product quality. Due to the special smoothness and non absorbability of aluminum foil paper, it loses the initial fixation and drying process of the ink layer, and the ink layer can only adhere to the surface of the paper, expecting to oxidize the film slowly, which determines that the ink layer will not be fixed and dry for a considerable period of time after it is just printed on the paper. Therefore, during this period of time, you cannot move or rub the newly printed paper, otherwise it is very easy to cause the surface and back of the paper to be sticky and dirty. Moreover, even if the ink layer has been fixed on the paper for a period of time, because it has not completely oxidized the conjunctiva, it is also necessary to avoid rubbing between the sheets. If you rub the paper during this period of time, the ink layer will not be dirty, but then there will be rubbing scratches, which will also damage the ink layer. Only after the ink layer is basically fixed and the conjunctiva is dry, this kind of condition will be eliminated

7. Improve the operation technology of the printing machine

in the printing process, in order to prevent the phenomenon of sticking back, it is necessary to spray powder on the printed matter, but the best printing machine speed when printing multicolor pattern aluminum foil paper printed matter with a monochrome or two-color printing machine is 5000 pieces/hour ~ 8000 pieces/hour. Because the paper surface of the aluminum foil paper is relatively smooth, when the ink water resistance is poor, too fast machine speed will cause poor ink transfer, and it will also make it difficult for the operator to change the drying rack. The printing pressure must match the paper strength. Because the aluminum foil paper is strong and tough, it is best to use a flat pressing square box machine and a four opening flat press to increase the printing pressure, promote the ink adhesion, and make the printed matter obtain a uniform ink layer. Aluminum foil paper should prevent excessive crystallization of the underlying ink when printing and stacking colors. When the background ink is dry to 90%, it is necessary to overprint the second color. In conditional units, it is best to adopt multi machine overprint, so as to ensure the quality of printed products

during the printing process, the padding should be flat to make the pressure uniform, so as to make the imprint bright and flat. To sum up, in offset printing, we should pay attention to the following aspects:

(1) aluminum foil offset printing must use high-quality ink, which requires high color, good transferability, fast drying and good imprinting fastness. It is best to use special ink (such as pop ink)

(2) strictly control the acidity of the fountain solution and the moisture of the printing plate. The fountain solution plays a very important role in the drying of aluminum foil offset printing. Therefore, in printing, the pH value and conductivity of fountain solution must be strictly controlled. To measure, speak with data, and the moisture of the printing plate should be controlled to the minimum. This can minimize the emulsification value of the ink

(3) the ink layer should be uniform, and the amount of ink should not be too large to avoid sticking and rubbing. In the allocation of spot color ink, the method of dark light printing should be adopted

(4) the speed should not be too fast and should be maintained at an appropriate speed

(5) prints should not be stacked too high. Too high a stack of papers is likely to cause dirt on the back of prints. In printing, you can spray an appropriate amount of powder or dry it with infrared

(6) strictly control the printing pressure

(7) control the paper receiving thickness. Due to the slow fixing speed of synthetic paper ink, too much paper will cause the printing product to stick back during the printing process. Therefore, the paper must be received with an air rack, and the thickness of the paper is generally 8cm ~ 20cm. The printing manufacturer can decide the thickness of the paper according to the size of the printing pattern and the printing environment at that time

(8) pay attention to the ambient temperature and humidity. Aluminum foil printing has certain requirements for temperature to ensure the drying effect of the ink layer. The ideal ambient temperature is above 25 ℃. Printing under such temperature conditions is conducive to the drying of the ink layer, which is more convenient to operate. Because higher ambient temperature can speed up the movement of material molecules in the ink layer, which is conducive to the contact between vegetable oil and oxygen in the ink layer to produce a film layer, so as to speed up the oxidation and polymerization reaction and meet the requirements of accelerating the drying of the ink layer

on the other hand, because the drying process of the ink layer is also an exothermic reaction process, the heat generated by the reaction further promotes the drying of the ink layer, thus forming a virtuous cycle of the ink layer accelerating the conjunctiva. This is greatly beneficial to the drying of imprinting and the complete transfer of ink layer. Aluminum foil paper is best printed in a relatively dry environment, which is good for the drying of prints and the prevention of dirt. However, it should be noted that aluminum foil is easy to curl in high temperature, so it is necessary to control the temperature of the printing workshop

in addition, pressing a little other paper on the paper when not printing can also solve the phenomenon of some curls. Because the drying of the ink layer first needs to evaporate the internal water, only after the water evaporates, the ink layer can effectively carry out oxidation and polymerization reactions until it is finally dried into a film. The speed of water evaporation in the ink layer is directly related to the ambient humidity. When the environmental humidity increases, that is, the air is relatively humid, the speed of water evaporation in the ink layer appears slow, and the drying time of the ink layer increases. On the contrary, when the environmental humidity is reduced, that is, the air is relatively dry, the evaporation rate of water in the ink layer is correspondingly accelerated, and the drying time of the ink layer is correspondingly shortened. In addition, if the sample is made into a rectangle in a humid environment (as shown in Figure 1) and cut into a cut printing with a length of 1/2 of the sample length in the long axis direction of the sample, the activity of oxygen in the air will be less active, which will directly affect the parameters of ink on high-end models. We will always inform customers of the oxygen inhalation of the instruction layer, resulting in the slow oxidation and conjunctive process, that is, the drying process, This is another reason why the ambient temperature affects the drying of the ink layer

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technical points of aluminum foil lithography (I)

reprinted from: China Packaging News