Packaging adhesives (below)

Second, plastic flexible packaging adhesive

Plastics have shown some of their outstanding properties since the early 1970s as new materials entered the food packaging field. Such as 1 has a wide range of physical and chemical properties; 2 applies to automatic packaging production line; 3 has a reliable source of raw materials; 4 small permeability, good oxygen barrier, adapted to preservation and storage; 5 safety and health non-toxic; 6 light weight , Good air permeability; 7 Low energy consumption, low cost; 8 Packaged waste is easy to handle, less environmental pollution; 9 Suitable for gravure printing and screen printing, packaging more beautiful and beautiful.

In particular, different polymers are compounded into packaging bags to overcome each other's deficiencies and combine their superior properties together. They not only have high strength and low oxygen transmission rate, but also are resistant to freezing storage or resistant to high temperature cooking temperatures above 120°C. Therefore, the development is very fast.

The history of plastic packaging is very long. The earliest real industrialized composite material was low-density polyethylene (LDPE). Until 1957, it began to use aluminum foil and polyester film (PET) to make composite bags. The adhesives used at that time were mainly natural adhesives and thermoplastic resins or rubber solutions. Due to poor heat resistance, only dry foods and fast foods could be packaged and applications were limited. In order to meet the requirements of higher temperature use, an adhesive capable of being cross-linked is required, so epoxy resin and polyurethane are used in the composite film packaging industry. Since then, the cross-linked acrylate adhesive has been successfully researched and applied to the manufacture of composite films. It has better usability, adhesive fastness and weather resistance. This has further expanded the range of choices and uses of packaging materials.

In the development of composite adhesive films for food packaging, adhesives for thermoplastic resins have also been developed. There are many varieties nowadays. Compared with polyurethane two-component adhesives, thermoplastic adhesives have low costs. One-component, only need to be diluted before and after use, without weighing, product quality and other characteristics, after the composite without curing, interlayer peel strength up to 3.2 ∽ 5.9N/25mm, can fully meet the requirements of the composite process.

With the development of the economy and the improvement of living standards, people are increasingly demanding packaging. There are more and more new types of adhesives used in food flexible packaging, and old ones are being eliminated or improved. In solvent-based adhesives, the solvent accounts for most of the weight (>70%). In the process of use, it enters the air in the form of steam because the solvents are generally poisonous, they are easy to catch fire, and they pollute the environment. slowing shrieking. In response to this trend, the development and application of water-based adhesives and solvent-free adhesives have received widespread attention, and some varieties have been available.

Hot-melt composite adhesive is one of the more advanced varieties currently used. It has low cost, can bond a variety of materials, is hygienic and non-toxic, and is safe and reliable. The composite material produced has a certain adhesive strength. The varieties used are mainly polyethylene-vinyl acetate (EVA) types, such as glues.

Solvent-free glue in the compounding process, no drying equipment, no organic harmful substances excluded, low energy consumption, no pollution, easy to use. This kind of glue is composed of high polymer prepolymer, 100% active ingredient, low viscosity, and after application, it is cured under certain conditions.

In general, as a composite adhesive for food flexible packaging, the following conditions should be met:

1 No odor, no poison; 2 No harmful substances are extracted when packaging oily foods; 3 Adapt to storage requirements; 4 Good weatherability, no yellowing, no foaming, no chalking and delamination; 5 Resistant to vegetable oil, essence, vinegar and Alcohol; 6 does not erode and destroy the ink, and has a good wetting ability of the ink; 7 meet the production process requirements.

Third, the label adhesive

Product performance introductions, instructions for use, and trademarks are printed on the packaging, in addition to being printed directly on the packaging. The reason why the direct printing method is limited is because other flexible packaging materials, such as paper and plastics, are easier to print during the manufacturing process. Other packaging forms, such as wooden boxes, glass, and metal, are used less because of process and cost issues. Once adopted, recycling will also encounter difficulties. Stickers in this area have irreplaceable advantages.

The initial labeling is done by hand, so the requirements for adhesives are not high, generally based on natural rubber, animal glue and its modified varieties, such as starch glue, casein glue, natural rubber, fish glue , bone glue and so on. The disadvantages are slow drying, poor initial adhesion, low water resistance, and easy to fall off during transportation and storage. With the development of science, the packaging of many products is done on the automatic line, and label sticking is also part of automation: therefore higher requirements are placed on the label glue. These requirements include:

1 The initial tack is good, the tag does not fall off after the instant pressure, does not slip, does not warp.

2 Drying speed. Suitable for high-speed automation labels.

3 Fastness after curing, good toughness, adhesive layer is not brittle, does not fall off.

4 non-toxic, no pollution.

5 is conducive to the recycling of packaging.

At present, the adhesives used for labeling can be divided into pressure-sensitive adhesives, hydrosols and water-remoistive adhesives.

General pressure-sensitive adhesives have a high initial tack, hold tack, and have good adhesion properties to most of the packaging materials, and are also convenient to use. Therefore, in the label adhesive, the amount thereof is the largest. Label adhesive pressure sensitive adhesives generally have acrylate emulsions, rubber emulsions and other modified products.

The water-based label adhesive uses water as a solvent, and is mainly used for coating when it is used, and is more suitable for high-speed automatic production line labels. The glues used in this application mainly include polyvinyl alcohol modified rubber, casein modified rubber, and some polymer emulsions such as ethylene vinyl acetate (VAE emulsion).

Water re-label adhesives are mainly used for stamps, envelopes and other small packaging labels or adhesives, some polymer solutions coated on the substrate are not sticky after drying, but when the water is re-adhesive, this Gel is a water remoistening adhesive. The main adhesives for this application are polyvinylpyrrolidone, polyvinyl alcohol, and starch.

Since packaging is an extremely large field, the types of adhesives involved are extremely numerous. The adhesives involved in this paper are only a small part of them, and with the development of packaging technology, more will be born. The variety of adhesives, I believe that the packaging industry will inject new impetus into the development of adhesives, adhesive technology development will also give packaging technology to win more space.