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First, the composite flexible packaging adhesive should have the basic properties of a wide range of applications. The composite flexible packaging material must be made of a variety of plastic films, such as PE, PP, PET, OPA, PT, or paper or aluminum foil, which are adhesively bonded to form a unified functional material. Different substrates have different characteristics, and it is necessary to firmly bond different substrates with different properties, and it is not necessary to use any glue to meet the requirements. Of course, there are many types of adhesives, but not all of them can be firmly bonded to various plastics, metals, and papers at the same time. In addition, other conditions (mainly hygienic and safety conditions) limit the current world There are only two major types of adhesives that can be used to achieve this purpose: one is polypropylene modified with maleic anhydride or one copolymerized with acrylic acid or its ester and ethylene, which belongs to the plastics category. The other type is polyurethane adhesives, which belong to the class of resins, and many other adhesives are not licensed. This is clearly stipulated in the US FDA regulations and China's GB9683 "hygienic standards for composite food packaging bags" and GB9685 "hygiene standards for the use of additives for food containers and packaging materials". At present, almost 100% of the world uses polyurethane adhesive as a dry composite adhesive to manufacture food and pharmaceutical packaging materials.
2. The advantages of flexible composite flexible packaging materials are light, soft, high strength and easy to carry. Therefore, if the film is hard and brittle, it cannot be bent and it cannot be folded. It cannot. The film must be soft. Therefore, a hard and brittle adhesive such as epoxy is not useful in flexible packaging.
3, temperature resistance means that high temperature resistance and low temperature resistance should be good. Because as a food packaging material, when it packs the contents, some need to be pasteurized or 100°C boiled, or even higher temperature (121°C) cooking or ultra-high temperature (145°C) cooking is required. Adhesives must have high temperature resistance and cannot be melted or softened at high temperatures to cause debonding. In addition, some have to be chilled at 18°C ​​or chilled at 0°C to 5°C and deep frozen even at a lower temperature of 40°C. Similarly, adhesives cannot withstand high temperatures but not low temperatures. If they are hard and brittle at low temperatures (such as acrylics and rubbers), the packaging bag must break and the packaging fails. This is not allowed. Therefore, adhesives for flexible composite packaging materials must have excellent properties of high temperature resistance and low temperature resistance. Polyurethane adhesives have the highest temperature resistance, with temperatures as low as 190°C and high temperatures as high as 150°C.
4. Functionality refers to special properties other than adhesion. Because foods, medicines or cosmetics, daily necessities are varied, and the ingredients are complex, acids, alkalis, spicy, salty, oily, alcoholic, surfactant and aromatic substances are encountered. In recent years, pesticide packaging and chemical packaging have been developed. The more corrosive organic solvents (toluene, xylene, DMF, cyclohexanone, acetone, ethanol, isopropanol, methanol, and even glacial acetic acid, propionic acid, or hydrofluoric acid). Plastic films, especially PE and PP, are very resistant to media infiltration, and are not damaged in the face of strong acids, strong alkalis or strong polar organic solvents. However, if the adhesive cannot resist the erosion of these media, it will cause the packaging material to appear de-bonded after the contents are loaded, and the packaging will fail. Therefore, in addition to the 1, 2, and 3 point performances, truly excellent adhesives also need to be resistant to various media erosion functions.
5, the operation of the adhesive through the glue, glue, drying, compounding, curing these several operating procedures, to complete the process of manufacturing composite materials. There is a comprehensive operational performance issue here, in particular, it is easy to mix rubber, good glue stability, viscosity stability, good infiltration performance, uniform coating, good transferability, easy dry control of the amount of glue, quick drying, solvent High release capacity, low residual solvent, large initial tack, and less prone to wrinkle tunneling. Of course, in the appearance quality, the glue should be uniform, the color should be light, the glue should be freeze-resistant, and the liquidity should be good at low temperature without mechanical impurities. (To be continued)
Selection of Adhesives for Food and Drug Packaging (1)
According to incomplete statistics from industry associations, at present in China, there are more than 2,500 companies that only use plastic film as a base material to produce soft composite packaging materials. So many composite material manufacturing enterprises are faced with the problem of how to choose raw and auxiliary materials to achieve the high quality and low price of their products. To make composite flexible packaging materials, one of the essential raw materials is adhesives. At present, the main purpose of composite packaging materials is food, medicine packaging. This article focuses on the topic of food and drug packaging to talk about how to choose the adhesive.