1. Pressure sensitive adhesive
Suitable substrates for pressure-sensitive adhesives include paper and plastic films, such as polyvinyl chloride, polyethylene, polypropylene, polyester, polytetrafluoroethylene, polyimide, and cellulose acetate. Metals such as aluminum foil, copper foil, lead foil, etc.
The main components of pressure-sensitive adhesives include synthetic resin adhesives (including natural rubber, synthetic rubber, cellulose, polyacrylate), tackifiers (rosin, rosin ester, various petroleum resins, epoxy resins or phenolic resins), Plasticizers (chlorinated paraffins, phthalic acids), antioxidants, stabilizers, crosslinking agents, coloring agents and fillers, etc.
Early pressure-sensitive adhesives used in pharmaceutical packaging were mainly composed of natural rubber, and its formula was 100 parts of plasticized natural rubber, 75 parts of polypinene resin (melting point 70℃), 5 parts of petroleum resin and partially polymerized trimethyl Mix 2 parts of dichloroquinoline. The other formula is made up of 100 parts of plasticized smoke sheet rubber, 50 parts of zinc oxide, 75 parts of hydrogenated rosin, and a small amount of tackifier and plasticizer. Later, synthetic rubber and synthetic resin were used instead of natural rubber. Among them, acrylic esters and their copolymers are the most commonly used, such as acrylic copolymer emulsion high-strength pressure-sensitive adhesive. Butyl acrylate-2-ethylhexyl acrylate-vinyl acetate copolymer emulsion (composition ratio of 50:17:33) and 30 parts of 50% solid content ethylene-vinyl acetate-vinyl chloride copolymer emulsion (composition ratio (19:36:45) mixed, coated on the polypropylene film treated with corona discharge, and dried at 110°C for 1 minute to make a pressure-sensitive tape. The peel strength of this tape to stainless steel is 600 g/25 mm.
As the requirements for the hygienic performance of pharmaceutical packaging materials continue to increase, the adjuvants added to the natural rubber-proportioned adhesive have peculiar smell and some are toxic, and have not been used in the composite packaging of pharmaceuticals and food. However, acrylic pressure-sensitive adhesives still have certain advantages, such as one-component, no cross-linking and curing, no need to dispense glue, simple use, and unused glue will not be broken overnight or longer, as long as Keep it airtight and airtight. In addition, the surface of the adherend is excellent, and many non-polar materials such as plastics and metal materials can be adhered firmly with low surface tension. However, due to the wide variety of materials in composite pharmaceutical packaging, companies have turned to two-component polyurethane adhesives for the composite of polar plastic materials and non-polar materials.
2, polyurethane adhesive
Polyurethane adhesives have a high degree of elasticity. Compared with other flexible adhesives, they have better heat resistance, solvent resistance, cold resistance, chemical resistance, oxidation resistance and ozone resistance. It has a good affinity for metals, plastics, wood, rubber, and fabrics, so it is widely used, especially in the fields of medicine and food packaging. The most applications are plastic and plastic compounding, metal and plastic compounding, and blister packaging hot pressing.
The earliest application of polyurethane adhesive was in the 1960s, when food composite packaging was just on the market. When used as an adhesive, it was mainly divided into polyisocyanate, urethane prepolymer, and isocyanate modified polymer according to its composition. kind.
Usually triphenylmethane P-triisocyanate, hexamethylene diisocyanate, diphenylmethane-4, 4-diisocyanate or toluene diisocyanate, etc., these polyisocyanates are used seldom individually, mainly as cross-linking of rubber adhesives Agent, or as a curing agent for polyester and polyether polyhydroxy compounds. The polymers used in conjunction with it include polyacrylate, epoxy resin, xylene resin, polyphenol amine resin and so on.
It is a partial reaction product of polyisocyanate and polyhydroxy compound. Because the end group of this polymer has NCO group, it can be cured in the presence of a suitable curing agent, or it can be cured by air moisture to form a single group Parts of adhesive.
③Isocyanate modified polymer
It is a linear polymer that has a hydroxyl group at its end by reacting a diisocyanate with a polyester or polyether that is more than difunctional. It is also called a thermoplastic polymer. According to the dosage form, polyurethane adhesives can be divided into two categories: one-component and two-component. The latter is better than the former in terms of adhesive strength. The two-component A component is mainly an isocyanate modified polymer, and the B component is also the urethane prepolymer that has been introduced. The polyol is mainly castor oil or polyethylene glycol. One-component can be divided into two categories, one is the direct use of the A component of the two-component, that is, the isocyanate modified polymer; the other is the carbamic acid formed by the reaction of diisocyanate and ethylene glycol Ester, which has the inherent good adhesion properties of short-chain compounds such as ethylene glycol.