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1, aluminum foil adhesive type and performance At present, aluminum foil adhesives are divided into two categories: one is made of natural rubber or synthetic rubber and acrylates made of a single-component rubber or rubber A resin type adhesive. Its main agent is an elastomer, which is formulated with tackifiers and organic solvents to form an emulsion. The organic solvent in the adhesive mechanically coated on the substrate is volatilized by a strong hot gas flow to form a coating. This adhesive has adhesive properties to a wide variety of materials and can be used as long as the desired temperature is achieved. It is characterized by a low requirement for the surface state of adherends. Because it is a single component, it does not produce cross-linking. It is simple to use, and the unused glue liquid will not deteriorate even if it is stored for a long time even if it is stored overnight, as long as it is sealed and stored. can. The second type of adhesive is a two-component polyurethane adhesive. The adhesive is composed of two components: a main agent and a curing agent. The main agent and the curing agent are usually packaged and stored separately. When used, they are mixed in a certain proportion. Mechanical coating is performed after dilution with a solvent (eg, ethyl acetate) to a certain concentration (eg, 20%, 30%, or 40%). The main agent of this adhesive is composed of many active hydrogens, such as hydroxyl, amino, etc., and the curing agent is composed of polyisocyanate compounds. When the isocyanate group in the curing agent is in contact with the active hydrogen in the main agent molecule, an addition reaction is automatically performed to generate a urethane structure, so that the main agent and the curing agent are combined with each other, and the molecular weight is multiplied and even generated. The cross-linked product with a three-dimensional conformation with a branched chain structure has the characteristics of high and low temperature resistance, resistance to media erosion, and high adhesive force. Because the polyurethane molecule contains a large number of polar groups, the dipole moment is large, and it has a great affinity for the adherent material, so at the same time it plays a role in bonding a variety of materials. In addition, the isocyanate group in the curing agent is a very reactive group, and in addition to reacting with the active hydrogen in the main agent molecule, it can also react with the active hydrogen in the surface material molecule of the adherent material to form a chemical bond. This allows the adhesive molecules to bridge the two materials being adhered at the same time, resulting in stronger adhesion, which is why the polyurethane adhesive has good adhesion to a variety of materials. The polyurethane adhesive has a high cohesive force after being cross-linked and cured. The appearance of the polyurethane adhesive is strong and flexible, and has good heat resistance and resistance to media erosion. It still has extremely high adhesion at a temperature of -170°C. This is not comparable to other adhesives. The use of this type of adhesive allows the aluminum foil and the blister PVC hard sheet to be firmly bonded by heat and pressure to seal the drug. During the heat-sealing process, the adhesive layer is activated by heat, so that the aluminum foil and the PVC hard sheet are firmly bonded together.
2. Factors to be Controlled by the Adhesive Layer Coating 2.1 The adhesive layer shall be coated and dried to control a certain temperature and time. The adhesive layer needs to be dried during the mechanical coating process. Drying requires three processes, namely, low-temperature blowing, solvent volatilization process, medium temperature drying process, and high-temperature drying process. Because the drying oven of the equipment is longer, the time that the aluminum foil needs to stay in the drying tunnel of the drying oven should be controlled. The degree of drying is related to the winding speed of the coater and the temperature inside the oven. The winding speed is fast and the temperature is high. The winding speed is slow and the temperature is low. Since the aluminum foil material has different thermal expansion properties and extensibility, it cannot be held at an excessively high temperature for a long time. Otherwise, the aluminum foil is prone to wrinkle and surface discoloration. Speed ​​and temperature control. In principle, it is preferable that the binder solvent is volatilized and that no odor is left.
2.2 The thickness of the adhesive layer should be controlled within a certain range. The thickness of the adhesive layer has an effect on the firmness of the adhesive. If the adhesive layer is too thin, the adhesiveness of the PVC hard film may decrease the adhesiveness of the hard PVC film; if the coating is too thick, the production cost will increase. As a result of waste, the thickness of the adhesive needs to be controlled within an appropriate range. In the production process, the thickness of the adhesive depends on the number of screens of the coated wire roller, the pressure of the rubber roller, and the angle of the blade. We call these three factors fixed factors. Because the number of roller lines in the production process is fixed, the pressure and force angle of the roller can also be set by a certain instrument. The factors that can be changed are: the mechanical tension, the concentration of the adhesive, the coating speed, and the thickness of the coating in the coating process. The relationship between the changeable factors is: the greater the adhesive concentration during coating, the coating tension. The smaller the coating speed is, the thicker the coating is. The smaller the concentration is, the greater the tension is, the slower the speed is, and the coating is thin. Therefore, the thickness of the adhesive layer is adjusted by the concentration of the adhesive and the tension of the coater. Different thicknesses of aluminum foils require slightly different thicknesses of the adhesive layer. In general, the thickness should be controlled to 1.5-3 microns. .
3, aluminum foil gravure quality control 3.1 to master the ink and solvent mixture concentration. According to the speed of the printing coater and the depth of the ink in the gravure roll, the best printable ink concentration. The factors affecting the ink concentration are temperature and humidity. It is best to use an ink concentration detector to determine the amount of solvent to be added, and to measure the concentration of the ink every 30 minutes according to changes in temperature and humidity. Adjust the data according to the data to ensure that Printing quality. If the concentration of the gravure ink used is too low, it is easy to cause the print text pattern color is not bright, and the graffiti phenomenon occurs; the higher the ink concentration, the easier it is to cause the forward direction of the squeegee; Very high, the pattern will produce cracks. The ink on the surface of the aluminum foil and the ink sticks are in pieces and the surface quality is poor.
3.2 Correct application of thinner. When a large viscosity ink needs to use a large amount of diluent, it should be stirred while adding a diluent in order to achieve uniformity, and strive to evenly distribute the diluent throughout the ink. If the thinner is added, it is fixed in the local flush and does not mix evenly. It is easy to wrap the partial ink around the pigment and the resin peels off to cause the pigment to precipitate, especially the relative density of the pigment is more obvious, due to the viscosity of the ink. Different pigments have different relative densities, so the ink thickness of each color can not be treated the same. Generally, it is adjusted to graphic and needleless ink dots. The strokes of writing lines have no broken pens. It is advisable to draw the word line clearly. It is determined by the viscometer 4# cup. Between 20-30 seconds.
3.3 Ink condensation precipitation treatment. Since the ink binder (polyamide) may be affected by temperature or the solvent is too small due to the excess of the diluent used in the ink, the solubility of the resin is reduced. Therefore, the condensed and precipitated ink must be stirred or increased in temperature. deal with. If the ink storage time is too long, or for other reasons, the ink will appear to precipitate, there are many ink upper resin solution, the lower pigment; the upper color is light, the lower color phenomenon, and caused by poor fastness, so when in use should Stir it.
4, the quality of the aluminum foil printing problems and solutions 4.1 The color difference of aluminum foil gravure printing. The consistency of printing colors can only be relative. Strict control of the color difference of the same batch of products is more difficult, and the strict control of the color difference between large batches or different batches of products is even more difficult. Cause 1 Ink: Ink is the main factor that determines the color consistency of the printed product. The ink itself also has the problem of color difference between the same batch and the color difference between different batches. This is an important indicator reflecting the quality of the ink. To solve the problem of gravure color difference of aluminum foil, we must first choose the ink with stable quality and no deviation in hue. It is best to use the same batch of ink for a batch of printing inks, because different batches of ink cannot guarantee the hue of inks between batches is not different. The second requirement is that the amount of ink added to the ink tray each time during the printing process is less, so as to keep adding new ink frequently. In particular, for some patterns with less ink, if the amount of ink is too large at one time, the ink will oxidize when exposed to the air for a long time, causing the ink to become old. For example, with a long black ink, there will be no black ink; with a long red ink, it will turn dark red, and there will be no new ink. In the printing process, the volatilization speed of the mixed solvent used in the ink should also be strictly controlled. When the volatilization rate is too fast, the ink transfer rate may be reduced, thereby affecting the color of the printed product.
4.2 Odor problems. When the printed product is used as a package, no odor is allowed. The main reason for the occurrence of odor is that the adhesive protector itself is incomplete and has a monomer odor. In addition to the ethyl ester, the good quality adhesive has no other odor, while the incompletely reacting adhesive does not, and can smell the monomer. Another reason is the odor of the ink. This is because the ink has too many high-boiling solvents and does not volatilize during the printing process. Although it has passed the compound drying tunnel, it still does not completely escape, especially the odor containing toluene solvent is the largest. It can be smelled when you open the roll and in the print. The solution can be prescribe the right medicine, is the reason for the adhesive can be considered for replacement, the use of good quality adhesive; ink is the reason, in addition to using other inks, but also can be stored for a long period of time. When using solvents, do not use benzene solvents as much as possible.
4.3 Knife wire problem. Knife wire refers to the fact that some ink with no pattern lines on the plate surface is not scraped and transferred to the top of the object to be printed, and line-like contamination occurs where ink is not allowed. Generally, it takes a period of time for printing to take place, and after printing a certain number of impressions, such problems occur. Printing inks, printing plate rollers, and doctor blades are the main factors for the appearance of knife threads. Cause 1 is related to the quality of the ink. This phenomenon is less when high-grade ink is used, and low-grade ink is more. In addition, impurities such as impure substances, coarse particles, and foreign matter in the ink can be formed by raising the scraper or the damage scraper. 2 ink viscosity is too large, the layout of the ink is too dry, the friction between the platter and the blade is relatively increased, the scraper is difficult to scrape off the layout of the ink. The poor quality of the 3 cylinder light and chrome plating or adhesion of hard objects on the plate will directly damage the blade. Solution: Reduce the viscosity of the ink as much as possible so that the scraper can easily scrape the ink off the non-screen part; try to increase the proportion of fresh ink; adjust the scraper (grinding, pressing, hardness, thickness, angle, position, etc.) and check the scraper installation Is it balanced and use slow-drying solvents as much as possible?
4.4 Ink drying is too fast. Reasons: 1 improper use of solvents. 2 The hot air around the plate is large. Solution: Select the appropriate solvent, cover with an ink tray, and check for airflow from the dryer.
4.5 Insufficient drying of the ink. Cause 1 The solvent is not suitable. 2 ink viscosity is too high. 3 ink is not suitable. Solution: Select the appropriate solvent, use a low viscosity ink, check the viscosity of the ink frequently, and change to the ink that is suitable for the speed of the machine. (White Ice) (From "China Packaging News")
Blister packaging printing coating quality monitoring
The blister package for medicines is to place the medicines in the recesses of a plastic hard-plastic sheet formed by plastic injection, and then use a printed and coated aluminum foil to adhere and seal the plastic hard sheets so that the medicines are protected and facilitated. Consumer identification access. The quality monitoring points for the production of pharmaceutical blister packaging are: adhesive quality, adhesive quality of plastic hard sheets and aluminum foil, and quality of aluminum foil printed text patterns. In the production process of blister packaging, the quality of the aluminum foil gravure printing and the heat-sealing strength of the coating adhesive layer are strictly controlled in the production. Therefore, in the national standard “Aluminum Foil for Pharmaceutical Packagingâ€, the appearance quality of aluminum foil after printing is Definite requirements, but also on the quality of the adhesive layer has physical and chemical indicators, so as to ensure that medicinal blister packaging has good barrier properties, health security and heat sealing properties and good physical and chemical properties.