1. Pressure sensitive adhesive

The substrates suitable for pressure sensitive adhesive are paper and plastic film, such as PVC, polyethylene, polypropylene, polyester, polytetrafluoroethylene, polyimide, cellulose acetate, etc. Metals such as aluminum foil, copper foil, lead foil, etc.

The main components of pressure sensitive adhesive include synthetic resin adhesives (including natural rubber, synthetic rubber, cellulose, polyacrylate), adhesives (rosin, rosin esters, various petroleum resins, epoxy resins or phenolic resins), plasticizers (chlorinated paraffins, phthalic acids), antioxidants, stabilizers, crosslinking agents, colorants, and fillers.

The pressure sensitive adhesive used in early drug packaging was mainly composed of natural rubber, with a formula of 100 parts of plasticized natural rubber, 75 parts of polypinene resin (melting point 70 ℃), 5 parts of petroleum resin, and 2 parts of partially polymerized trimethyldichloroquinoline. The other formula is composed of 100 parts of plasticized tobacco rubber, 50 parts of zinc oxide, 75 parts of hydrogenated rosin, and a small amount of tackifier and plasticizer. Later, natural rubber was replaced by synthetic rubber and synthetic resin, among which acrylate and its copolymer were most commonly used, such as acrylic acid copolymerized lotion based high strength pressure sensitive adhesive, The proportioning method is to mix 100 parts of butyl acrylate 2-ethylhexyl acrylate vinyl acetate copolymer lotion (composition ratio: 50:17:33) with 43% solid content and 30 parts of ethylene vinyl acetate vinyl chloride copolymer lotion (composition ratio: 19:36:45) with 50% solid content, apply it on the polypropylene film treated by corona discharge, dry it for 1 minute at 110 ℃, and then make pressure sensitive tape. The peel strength of this tape on stainless steel is 600 grams/25 millimeters.

With the increasing requirements for the hygiene performance of pharmaceutical packaging materials, the additives added to the adhesive with natural rubber ratio have peculiar odors and some are also toxic, and are no longer used in pharmaceutical and food composite packaging. However, acrylic pressure-sensitive adhesives still have certain advantages, such as being single component, non cross-linking and curing, no need for adhesive preparation, simple use, and the unused adhesive solution will not damage overnight or for longer. As long as it is sealed and stored without leakage, it can be used. Furthermore, the surface state of the adhesive is excellent, and many non-polar materials such as plastic and metal can adhere even with low surface tension. However, due to the wide variety of materials used in composite drug 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 and have better heat resistance, solvent resistance, cold resistance, chemical resistance, oxidation resistance, and ozone resistance compared to other flexible adhesives. It has good affinity for metals, plastics, wood, rubber, and fabrics, making it widely used, especially in the fields of pharmaceutical and food packaging. The most commonly used methods include plastic to plastic composite, metal to plastic composite, and hot pressing for blister packaging.

The earliest application of polyurethane adhesive was in the 1960s, when the food composite packaging was just on the market. When it was used as adhesive, it was mainly divided into three categories according to its composition: polyisocyanate, carbamate prepolymer, and isocyanate modified polymer.

① Polyisocyanates

Usually, triphenylmethane P-triisocyanate, hexamethylene diisocyanate, diphenylmethane 4, 4-diisocyanate, or toluene diisocyanate are used. These polyisocyanates are rarely used alone and are mainly used as crosslinking agents for rubber adhesives or as curing agents for polyhydroxy compounds such as polyester and polyethers. The polymers used in conjunction with it include polyacrylate, epoxy resin, xylene resin, and polyphenylamine resin.

② Carbamate prepolymer

It is a partial reaction product of polyisocyanates and polyhydroxy compounds. Due to the NCO group at the end group of this polymer, it can be cured in the presence of appropriate curing agents or cured by air moisture to produce a single component adhesive.

③ Isocyanate modified polymer

It is a linear polymer with hydroxyl groups at the end group, also known as a thermoplastic polymer, formed by the reaction of diisocyanate with polyester or polyether with more than two functional groups. According to the dosage form, polyurethane adhesives can be divided into two categories: single component and dual component. From the perspective of adhesive strength, the latter is better than the former. The two-component component A is mainly isocyanate modified polymer, and component B is also the introduced carbamate prepolymer. The polyalcohol is mainly castor oil or polyethylene glycol. Single component can be divided into two types. One type directly uses component A of the two components, namely isocyanate modified polymers; The other is the carbamate produced by the reaction of diisocyanate and ethylene glycol, which has the inherent good adhesion properties of ethylene glycol, a short chain compound.