Advantages and disadvantages of waterborne polyurethane in food and drug packaging
Food packaging is divided into ordinary packaging and high-performance packaging, the corresponding waterborne polyurethane adhesive can be divided into four categories: general use, steaming boiling, transparent cooking, aluminum foil cooking.Usually such adhesives are two-component solvent-based polyurethane adhesives, the main agent is polyether or polyester polyol After the aromatic isocyanate modified with hydroxyl polyurethane polyol (called a component), curing agent is aromatic isocyanate and three hydroxymethyl propane admixtures (called b component), when used, the a component and b component are mixed in a certain proportion, and then diluted with ethyl acetate to a certain concentration after sizing coating.At present, such glue has been produced in China, mainly with poly adipic acid polyester polyol as raw material, and most of the foreign use epoxy propane polyether as raw material, the cost is low.Transparent cooking bag and aluminum foil cooking bag with composite film polyurethane adhesive generally includes 121 cooking sterilization with composite film adhesive, and 135 high temperature cooking sterilization with composite film adhesive, the so-called high temperature cooking refers to 121~145 high temperature and 0.18~0.40MPa steam pressure for food sterilization processing technology.This not only requires a variety of base material can withstand high temperature test, the adhesive used also should be able to withstand high temperature.The polyurethane adhesive used in ordinary packaging is easy to hydrolyze at this high temperature, the adhesive strength is reduced, and the film is easy to fall off.In order to improve the cooking resistance of polyurethane adhesives, the molecular structure of soft polyester and hard segment is usually changed, the chain segment resistant to humidity, heat and high temperature is introduced, the variety of crosslinking agent is changed, the density of crosslinking agent is adjusted, and even the blending of high polymer and the formation of interpenetrating polymer network (IPN) is adopted to solve the problem. The pressure sensitive adhesive drug compound packing materials, mainly use ester soluble polyurethane adhesive, the adhesive is a two-component resin soluble polyurethane adhesives, its main agent polyether or polyester polyol after aromatic isocyanate modified polyurethane polyol containing hydroxyl, curing agent is aromatic isocyanate with trimethylolpropane composite. This kind of adhesive has excellent performance, mature process and many varieties, but the toxicity is large and the cost is high, and a large number of solvents are discharged to pollute the environment.Composite materials for a long time, may hydrolyze, release a carcinogenic substance TDA(diacetic acid), serious harm to the health of operators with the enhancement of environmental awareness, the use of this kind of adhesive is declining.Now developed countries in Europe and the United States using this kind of ad...
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