In other words, the aluminum foil bag is very simple in appearance, so it is very easy to understand how the aluminum foil bag is silver coated. So it will last longer. Next, we will introduce the technological process of aluminum foil bag and some problems needing attention

The technological process of packaging aluminum foil is as follows: aluminum foil unwinding → gravure printing → drying → coating protective layer → drying → coating adhesive layer → drying → aluminum foil winding. In the whole production process, the surface quality of gravure printing text pattern, the heat sealing strength of adhesive layer, the adhesion of protective layer and its drying temperature, as well as the speed and tension control of coating machine operation should be strictly controlled. Therefore, in the national standard of "aluminum foil for pharmaceutical packaging", there are clear requirements for the surface quality of printed characters of medical aluminum foil, and the performance of protective layer and adhesive layer also have physical and chemical indexes, so as to protect the pharmaceutical PTP aluminum foil with good barrier, health safety, heat sealing and good physical and mechanical properties. In order to meet the above requirements in the PTP aluminum foil printing and coating production process, it is necessary to be familiar with the properties of the raw materials used, and pay attention to the following problems in the operation process:

1. Master the characteristics of aluminum foil and printing ink
The raw material used in the production of PTP aluminum foil is pure aluminum foil for industrial use. Generally, the thickness is 0.02mm, the tensile strength is 98kpa, and the rupture strength is 90kpa. The surface is clean and flat without wrinkles, indentation damage, sheet fluorescent material, and the surface wetting tension is not less than 32. The requirement for the pinhole size of medicinal aluminum foil is that the pinhole diameter of 0.1-0.3mm should not be more than 1 / m2. As the pinhole in aluminum foil is a penetrating defect, the drug efficacy will be reduced or deteriorated by the invasion of oxygen, water vapor and light, so the requirements for pinhole size are very strict; in addition, if the thickness of aluminum foil exceeds the required deviation (10%), the coating amount of adhesive layer and protective layer will be affected, which should be paid attention to by the operator.
At present, the printing ink for aluminum foil can be divided into two categories: one is polyamide ink. This kind of ink has good adhesion, dispersion, luster, wear resistance, solvent release, soft, and is mostly used in plastic film printing. When used in the printing of aluminum foil materials, the excellent performance of the ink can be shown, and its heat resistance can also meet the requirements of aluminum foil printing. The other is the special ink for aluminum foil, which is mainly composed of vinyl chloride vinyl acetate copolymer resin / acrylic resin. Its holding point is bright color, high concentration, strong adhesion with aluminum foil and good transparency. However, due to its high solvent volatility when used in gravure printing, it is easy to cause ink drying and deposition in the ink hole of gravure roller when used for medical PTP aluminum foil surface printing , resulting in paste. Therefore, it is necessary to carry out the necessary pretreatment for the deposition and condensation of ink. The method is to stir the deposited frozen ink or increase the temperature (water bath). If the storage time of the ink is too long, the ink will deposit, resulting in more resin solution on the upper layer, more pigment in the lower layer, light color in the upper layer and deep color in the lower layer. It should also be used after mixing evenly.
2. The amount of solvent added into the ink should be appropriate
When the viscosity of the ink needs to be diluted with a large number of diluents, the diluent should be added while stirring, so that the diluent evenly distributed in the entire ink. The measuring time is about 20-30s. Indoor temperature and humidity have an impact on the ink concentration. It is best to use the ink concentration detector to determine the amount of solvent added, and according to the change of temperature and humidity, determine the concentration of ink at regular intervals. When using gravure printing to print aluminum foil products, if the ink concentration is too low, the color of the printed text pattern will not be bright, and the stencil will be pasted; if the ink concentration is too high, the pattern will crack, which will not only waste ink, but also cause uneven and unsightly printing surface. In addition, the best ink should be selected according to the speed of the aluminum foil printing coater and the ink hole depth of the gravure roller.
3. The adhesive shall meet the requirements
The utility model has the function of firmly separating the inner side of the drug and the aluminum foil, which is used to seal the inner side of the drug with the aluminum foil. In the process of heat sealing, the adhesive layer is activated by hot pressing, so it is firmly bonded with PVC plastic sheet, which requires that the adhesive layer and PVC resin should have good thermal sensitivity and solubility with the substrate.
4. The drying temperature and time should be well controlled in the process of printing and coating
Printing graphics and text, adhesive layer and protective layer need to be dried in the coating process. The drying of aluminum foil surface coating needs a process, so it needs to stay in the equipment drying channel for a certain period of time, which depends on the winding speed of coating machine and the temperature selected in the drying channel. The two should keep corresponding relationship. Because the thickness of aluminum foil material is different, the physical and mechanical properties are different, and the thermal expansion, shrinkage and elongation of the material in the equipment are also different, so it should not stay at a high temperature for too long, otherwise the aluminum foil is prone to wrinkle and surface discoloration. Generally, the temperature of drying channel should be controlled at 170-210 ℃.
5. Analysis of coating speed, coating tension, coating thickness and bonding quality
In the process of printing and coating, the coating thickness of the adhesive layer has a great influence on the bonding strength of the rigid plastic PVC sheet. If the adhesive layer is too thin, the adhesion fastness will be reduced due to the lack of material during hot pressing; if the coating thickness of the adhesive layer is too thick, it will not only increase the cost, but also prolong the drying time, so it needs to be controlled within the appropriate thickness range. The coating thickness of adhesive layer is affected by the concentration of adhesive, coating tension, coating speed and the number of anilox rolls. When the shape, depth, number of lines per inch and the line pressure between the two rollers are set, the thicker the coating is, the higher the adhesive concentration, the smaller the coating tension and the faster the coating speed. Therefore, the thickness of the adhesive layer is generally adjusted by the concentration of the adhesive and the tension of the coater. Different kinds of aluminum foil have different requirements on the thickness of adhesive layer. Generally, the coating thickness should be controlled at 3.5-7.0 mm. In the process of aluminum foil printing and coating, machine speed, temperature and tension are not only related to each other, but also restrained each other. Their coordination is directly related to the printing and coating quality of aluminum foil.