Adhesives are also called adhesives. There are many kinds of adhesives on the market. The adhesives described in this paper are mainly used in the field of medicines or food packaging, such as the compounding of medicinal plastic film and metal aluminum, compounding with plastics, and hot pressing of pharmaceutical aluminum foil and polyvinyl chloride. The adhesive used.
(a) Basic requirements for adhesives for pharmaceutical packaging
Good safety and health performance. There should be no odor and no toxicity. If the drug is in direct contact with the adhesive, it should also be non-corrosive to the packaged drug. Since the product protected or packaged by the medicine packaging material is directly imported, not only the base material should be odorless, odorless, non-toxic, but also the adhesive used must have the same performance. Therefore, the raw materials, auxiliary materials and solvents for producing the adhesive should be safe. Sex and hygiene.
Adhesion performance is excellent. Because of the different materials of the packaging materials, adhesives are used to bond them. The adhesive must have excellent adhesion to different materials. Substrates used in pharmaceutical packaging composites have a wide variety of materials and properties, such as paper, fabrics, aluminum foil, plastics, etc., and plastics have a variety of brands. Their surface properties are different in molecular structure and face so many For a complex material, the adhesive must have the ability to adhere to more than two different materials at the same time.
Good heat resistance. Some pharmaceutical packaging materials are subjected to high temperatures during the packaging process. For example, when aluminum foil blister packs medicines, aluminum foil and polyvinyl chloride can be hot-pressed under high temperature conditions of 150°C-220°C; some packaged cooking foods need to be packaged together Together with high-temperature cooking sterilization, which requires the adhesive to withstand the test of high temperatures.
Excellent chemical resistance and medium resistance. The chemical composition of the drug itself is very complex. After packaging, it is subjected to high temperature treatment and long-term storage. It is necessary to maintain the perfect packaging material. In addition to the substrate itself should have excellent chemical resistance, resistance to media erosion, the stability of the adhesive is also very important. , To be able to resist the erosion of various media and chemical components, otherwise it will cause the composite layer peeling and lose its effect.
Soft performance is good. When packaging medicines with flexible packaging composites, the packaging is soft and easy to carry. It is important that it should be foldable. Adhesives should also possess this property. If the adhesive film is hard, brittle, and unfoldable, and it does not match the substrate, it will lose its performance.
(II) Types and Properties of Adhesives for Pharmaceutical Packaging
Pressure-sensitive adhesive
Suitable substrates for pressure sensitive adhesives are paper and plastic films such as polyvinyl chloride, polyethylene, polypropylene, polyester, polytetrafluoroethylene, polyimide, cellulose acetate, and the like. 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 rubbers, celluloses, polyacrylates), tackifiers (rosin, rosin esters, various petroleum resins, epoxy resins or phenolic resins), Plasticizers (chlorinated paraffins, phthalates), antioxidants, stabilizers, crosslinkers, colorants, and fillers.
The earliest pressure-sensitive adhesives were based on natural rubber. The formula was 100 parts of natural rubber that had undergone plastication, 75 parts of polyterpene resin (melting point 70°C), 5 parts of petroleum resin, and partially polymerized trimethyl 2 Chloroquinoline 2 parts mixed. The other formulation was made up of 100 parts of smoked rubber tablet, 50 parts of zinc oxide, 75 parts of hydrogenated rosin and a small amount of tackifier and plasticizer. Later, synthetic rubbers and synthetic resins were used instead of natural rubber. Among them, acrylates and their copolymers were most commonly used, such as acrylic copolymer emulsion-type high-strength pressure-sensitive adhesives. The proportioning method was to prepare 100 parts of 43% solids. Butyl acrylate - 2-ethylhexyl acrylate-vinyl acetate copolymer emulsion (composition ratio of 50:17:33) and 30 parts of 50% solids ethylene-vinyl acetate-vinyl chloride copolymer emulsion (composition ratio The mixture was 19:36:45 and coated on a polypropylene film treated with corona discharge and dried at 110°C for 1 minute to form a pressure-sensitive adhesive tape. This tape has a peel strength of stainless steel of 600 g/25 mm.
With the continuous improvement of the hygienic performance requirements of pharmaceutical packaging materials, natural rubber additives added odor, and some toxic, have not been used in pharmaceutical and food composite packaging. However, acrylic pressure-sensitive adhesives still have certain advantages, such as being mono-component, not cross-linked and cured, not having to be glued, and being easy to use. Unfinished adhesives will not ring overnight or longer. Sealed without leakage can be saved. In addition, the surface state of the adherend is excellent, and many non-polar materials such as plastics, metal materials, and small surface tension can also be adhered. However, due to the wide variety of materials in the packaging of compound drugs, companies have turned to two-component polyurethane adhesives for the compounding of polar plastic materials and non-polar materials.
Polyurethane adhesive
Polyurethane adhesives are highly elastic and have better heat resistance, solvent resistance, cold resistance, chemical resistance, oxidation resistance, and ozone resistance than other flexible adhesives. It has very good affinity for metals, plastics, wood, rubber, and fabrics, so it is widely used, and it is widely used in the fields of medicines and food packaging. The most widely used is the combination of plastics and plastics, metal and plastics, and blister packaging.
The earliest application of polyurethane adhesives was in the 60s, when food composite packaging was just introduced. When used as adhesives, it was mainly divided into three categories: polyisocyanate, urethane prepolymer, and isocyanate-modified polymer, depending on its composition.
Polyisocyanate
Usually triphenylmethane P-triisocyanate, hexamethylene diisocyanate, diphenylmethane-4, 4-diisocyanate or toluene diisocyanate, etc., these polyisocyanates used less alone, mainly as a cross-linking of rubber adhesives Agent, or as a curing agent for polyester and polyether polyhydroxy compounds. The polymers used with it are polyacrylates, epoxy resins, xylene resins, polyphenol amine resins, and the like.
Urethane prepolymer
It is a partial reaction product of a polyisocyanate and a polyhydroxy compound. Since the terminal group of this polymer has an NCO group, it can be cured in the presence of an appropriate curing agent, or it can be cured by air moisture to form a single group. Parts of adhesive.
Isocyanate modified polymer
It is a linear polymer having a hydroxyl group at the terminal group, also called a thermoplastic polymer, reacted with a diisocyanate and a difunctional or higher polyester or polyether. According to the dosage form, polyurethane adhesives can be divided into two categories, one-component and two-component, and 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 component B is also the urethane prepolymer that has been described. The polyols are mainly castor oil or polyethylene glycol. One-component can be divided into two categories. One is to directly use the component A in the two-component, ie isocyanate-modified polymer; the other is the carbamic acid produced by the reaction of diisocyanate and ethylene glycol. Ester, which has the inherently good adhesive properties of ethylene glycol, a short chain compound.
Development trend of adhesives for pharmaceutical packaging
At present, the pharmaceutical composite packaging material pressure-sensitive adhesives have been replaced by polyurethane adhesives, and ester-soluble polyurethane adhesives are mainly used. These adhesives are two-component ester-soluble polyurethane adhesives whose main agent is polyether or polyester polyols modified by aromatic isocyanates. After that, the hydroxyl group-containing polyurethane polyol and the curing agent are a combination of aromatic isocyanate and trimethylolpropane. These adhesives have excellent performance, mature technology, and many varieties, but they are toxic, costly, and emit large amounts of solvents that pollute the environment. Long time of the composite material may cause hydrolysis and release of a carcinogenic substance TDA (aminoethane sulfonic acid diacetic acid), which seriously jeopardizes the operator's health. With the increasing awareness of environmental protection, the use of such adhesives continues to decline. The packaging of such adhesives in developed countries in Europe and America is now reduced from 80% 10 years ago to 30% today. Alcohol-soluble polyurethane adhesive has the advantages of using industrial alcohol as a solvent, low production cost, good hygienic performance, harmless to workers, and no pollution to the environment. The disadvantage is that it is not resistant to high temperatures of 100°C, and it cannot package strong corrosive products. During the production process, a good glue solution can only be used up on the same day. If it can only be diluted and stored, the next day of production, it will be used as a thinner. . Do not use if glue has whitened or thickened.
Adhesives based on water-soluble or water-dispersible solvents, called waterborne polyurethane adhesives, have the advantage of replacing organic solvents with water. There is no potential risk of combustion explosion, and the cost is low. However, the performance of the adhesive is poor, and the adhesive has poor wettability to the substrate to which the adhesive is adhered, because the surface tension of water is 72 mN/m, and the surface tension of the substrate is only 40 mNîž„m, and the difference is large and incompatibility. , The adhesion is not high. In addition, the heat capacity of water is large and needs to be dried, thereby consuming more energy, the cost is increased, the production speed is low, and some properties are still inferior to those of solvent type adhesives.
The adhesives for pharmaceutical composites develop in the direction of solvent-free adhesives. The solvent-free adhesives are also basically composed of two-component polyurethane adhesives. The main agent and curing agent have high viscosity at room temperature and fluidity, and the main agent and curing agent during compounding. Mix according to the ratio, roll on the substrate after heating up. Since no organic solvent is used, the cost is reduced, there is no pollution to the environment caused by the volatilization of the organic solvent, and the huge drying, heating blast, and exhaust emission devices of the device are omitted, thereby reducing energy consumption. The product has no residual solvent damage, the production speed is increased, the maintenance cost is low, and the benefit is significant. The application prospect in the pharmaceutical packaging field is promising.