The relationship between packaging and adhesive materials is very close. The development of bonding technology has enabled many new materials and technologies to be used in the packaging industry, creating conditions for packaging. It can be said that without adhesives, there are no bright and colorful modern commodity packaging. Packaging is also an important consumer sector for adhesive materials. According to statistics, in 1989, the world's total production value of adhesive materials was approximately US$13 billion, of which packaging consumption accounted for US$3.5 billion. In the United States, developed countries such as the United States accounted for more than 20% of total consumption of packaging adhesive materials in 1990, and their sales growth rate is estimated. It will remain at about 9%, exceeding its growth rate in the construction and automotive industries.
The main uses of adhesives in the packaging industry include: preparation, forming and sealing of corrugated paperboard, cartons and cartons; roll-tube bonding and capping of mandrels, paper cans, paper tubes, and sticking of bottles, cans and cans Standards and seals, composites of paper and paperboard, polymer films, metal foils; laminating and sealing of flexible packaging plastic bags, peelable protective films; pressure-sensitive packaging and merchandising strapping. Even for adhesives of the same type, the types thereof are numerous. Which type of adhesive is selected in actual production depends on the production conditions, the production cost, the use of the substrate, and the end use. In view of space limitations, this article is divided into three parts according to the use of paper packaging, plastic flexible packaging, label nameplate glue, etc. to give a brief introduction:
First, paper packaging
There are two types of paper packaging, one is pure paper packaging, such as corrugated paper boxes, paper drums, paper boxes, paper bags, it is the most use of the most widely used packaging. The other category is paper-based composite packaging, such as paper/plastic composite bags (bags), paper/aluminum foil composite boxes (bags), and paper/wood composite material boxes (boxes).
The first type of adhesive used for pure paper packaging is based on natural starch glue. Starch adhesives, as universal adhesives, have unique advantages in terms of raw material source, manufacturing process, cost, environmental hygiene and use. Compared with silicate (also known as water glass), starch glue has the characteristics of high adhesive strength, light weight, no corrosion, no pollution, high strength, and good toughness. In foreign countries in the early 1950s, starch glue was used instead of babbitine, which was used in the manufacture of cartons and cardboard. China has also banned the use of water glass in the preparation of cartons. However, starch glue has one disadvantage: its made of starch glue has a water content of more than 70%, and it is slow to dry. At the same time, the water in the adhesive penetrates into the paper during the drying process, which reduces the initial tack force and prolongs the production cycle. If it cannot be dried in time, it will cause running edge, squeaking, slitting, and the like. The phenomenon has limited its application.
Starch gum production methods can be divided into three categories: Stein-Hall method, oxidation method and biological fermentation method. The Stein-Hall method is a thermal gelatinization method. It heats at the bonding site and gelatinizes the starch to form a bond. The bonding speed is fast and the energy consumption is high, and it needs to be used on special equipment. Oxidation is divided into thermal oxidation and chemical oxidation. It breaks starch molecules into fragments through oxidizing agent or heating, then pastes with caustic soda and then is complexed with borax. This method is simple in production process, low in cost, and is now commonly used. The bio-fermentation method utilizes enzymatic hydrolysis of starch by enzymes to produce high-solid-content starch glue with a neutral pH, making the starch glue significantly improved in initial tack, tack retention, drying speed, and shelf life. This technology is also improving the grade of starch glue.
In addition to starch gums, synthetic polymer emulsions are also used in many applications such as corrugated paper, enamel tile, and matt. The synthetic properties of synthetic polymer emulsions are ideal, especially the weather resistance, water resistance, and cold resistance. , Toughness, and initial tack are all unmatched by starch glue. Although the cost of synthetic polymer emulsions is high, its usage still shows an encouraging trend. Synthetic polymer emulsions used in this category include polyvinyl acetate emulsion (PVAC) and its modified products.
The second type of paper-based composite packaging is a relatively high-end packaging form developed on the basis of the first type. Compared with pure paper packaging, the composite packaging is not only luxurious in appearance but also full of magnificent styles. New packaging features such as moisture and stain resistance, tear strength and crush resistance have all been greatly improved. Because of this, the scope of application and the amount of use of such packaging are developing at an alarming rate. Composite rubber is a key material for composite packaging processes. The traditional compound rubber is a solvent type. It dissolves SBS, rosin, terpene and other high-molecular substances and additives in toluene and other organic toxic solvents to make a solution of about 40%. It is diluted with solvent before use and becomes low. The solid content was coated on a biaxially oriented polypropylene (BOPP) and oven-dried. Then the film and paper were pressed together by hot rollers. This process discharges a large amount of toxic flammable and explosive solvents into the air, which seriously pollutes the environment, impairs the health of the operating workers, and causes serious fire hazards. In addition, the use of a large number of auxiliaries such as rosin, composite rubber aging resistance is also very poor, the composite product is easy to yellowing, short life, energy consumption, high cost, although this process is still dominant in the market, but Its tendency to be replaced by environmentally friendly adhesives has been widely accepted and respected.
The domestic environment-friendly compound adhesive has entered the mature stage of technology and is in the stage of promotion and application. In the market, the main types of environmental protection compound glues are divided into two categories. One is compound adhesives modified with ethylene-vinyl acetate emulsion (VAE emulsion) as the basic material. This kind of product has the advantages of good cover powder capability and good processability, but it also has the disadvantages of small composite strength, difficult use in winter, large amount of glue consumption, and high cost, and thus it is gradually withdrawing from the compound rubber market. The second category is acrylate-based emulsion-modified adhesives. As long as the molecular structure is well-designed, these products can overcome all of their shortcomings while having the advantages of VAE emulsion-modified adhesives. Among them, Sichuan Vision Industrial Co., Ltd. is a representative of the Fasette series rubber. The emulsion has similar flowability and solid content as the VAE emulsion, so that the powder coating ability and process adaptability are excellent, and the weather resistance, temperature adaptability, and peeling fastness are all excellent and the cost is greatly reduced. Not only composite paper / BOPP, but also composite paper / PET, paper / PVC, paper / aluminum foil, paper / paper, and has formed a large-scale production and sales. It can be predicted that through the joint efforts of people in the industry, the environmental protection of rubber compound fully replaces solvent glue is just around the corner.
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
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