Foreword
In the new century, environmental protection has become a problem that involves the survival and development of each enterprise and individual. With the continuous emergence of new environmentally friendly materials and technologies, green packaging has gradually become a realistic choice. Nowadays, more and more people are realizing that establishing environmental awareness and keeping up with the trend of international green packaging are the only way that China's packaging industry can shorten the gap with the developed countries' counterparties and meet the development needs of domestic and foreign trade.
According to related data, the packaging industry is one of the major industries in China's national economy and has been continuously and rapidly developed over the past decade or so. In the past, the phenomena of "first-class products, second-class prices, and third-class packaging" in the packaging industry are gone forever. China's packaging industry currently has more than 25,000 companies. Its annual production value has increased from 7.2 billion yuan in 1980 to 220 billion yuan in 2000, which is increasing by nearly 20% every year. However, the development of the packaging industry also consumes a lot of resources. In China, the industrialization level of the packaging industry is still low, the use of packaging products and the recovery and processing systems are not perfect, and the management methods are scarce, resulting in a large number of packaging wastes that damage our living environment. Therefore, it is inevitable that China's packaging industry will fully promote "green packaging."
The development of "green packaging" is also an inevitable choice for China's packaging industry to join the WTO and meet the global economic globalization. In 1987, the UN Environmental Protection Agency held its first meeting on the protection of the ozone layer in Montreal, Canada. Representatives of 56 countries and regions signed the protocol and for the first time set forth clear requirements and directions for the coordinated development of the packaging industry and the environment. Some countries have successively promulgated relevant laws and regulations concerning packaging and packaging waste, and more and more environmental protection clauses have appeared in national trade agreements. Green packaging has become a barrier for western developed countries to hinder the entry of developing country goods into the international market, forming a "green trade barrier." If there is no green label product, some developed countries will refuse to import, and may not offer preferential prices and tariffs. After China's accession to the WTO, although China will have an all-round multilateral trade environment, if packaging fails to keep up, it will restrict the development of foreign trade exports and make it more difficult for China's products to reach the international market.
Packaging materials for export goods can only be allowed to enter the importing country if they meet the requirements of the importing country, otherwise the customs of the importing country will not release. Many countries restrict or impose mandatory supervision and management on the packaging materials of imported goods in the form of laws and regulations. For example, the United States stipulates that the packaging of imported goods must not use straw, otherwise it will be forcibly burned. The packaging of imported goods by the Ministry of Agriculture and Fisheries of Xinxi Temple shall not be hay, straw, bamboo mats, etc. For this reason, our country has done a lot of work. The first is to avoid the use of toxic materials. Pigments, dyes, and paints used on packaging containers or labels should be made of materials that do not contain heavy metals. Adhesives used as bonding materials should not only be toxic or toxic, but also be easily decomposed during separation. In addition, various governments have adopted corresponding measures in adapting to the green consumption boom. For example, the EU has promoted the use of packaging materials that cannot be reused or recycled since 2000, in order to promote the use of renewable and recycled packaging products.
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.
With China's accession to the WTO, China's more goods will go to the world, so the traditional relatively backward packaging industry will face a severe test, and packaging will also be one of the breakthroughs in changing the price of domestic goods in the international market. This will inevitably stimulate the rapid development of the domestic packaging industry to some extent.
Packaging adhesives
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 of adhesives are numerous. In view of space limitations, only a brief description of paper adhesives is given here:
There are many kinds of paper adhesives, such as water glass, starch adhesive, polyvinyl alcohol and polyvinyl acetate emulsion.
(1) Water glass, also known as silicate, is a soluble silicate composed of an alkali metal and silica containing different ratios. Water glass as a corrugated paperboard adhesive, its bond strength is acceptable, but there are many shortcomings. First, the drying speed is slow. Second, with basicity, the sodium oxide in the water glass absorbs the moisture in the air to form sodium hydroxide, which denuds the printing pattern on the surface of the box. Third, the generated sodium hydroxide can cause deliquescence. Loss of viscosity of water glass, cardboard and carton deformation; Fourth, the carton compressive strength, burst strength is low. Some advanced countries do not use it for corrugated board adhesives.
(2) Starch adhesive is a kind of adhesive commonly used at home and abroad. It is prepared by mixing starch as raw material and other auxiliary materials. Starch adhesive has strong adhesive force, good initial adhesion strength, and can guarantee that the corrugated liner does not turn back yellow and does not show defects, but it also has disadvantages such as slow drying speed.
(3) Polyvinyl alcohol (PVA) is a white crystalline polymer. When used as a corrugated paperboard adhesive, the paperboard is flat and straight, does not absorb moisture, does not corrode the product, and has a firm bond. Deformation, the carton made of a strong compressive ability. Polyvinyl alcohol has better adhesion than starch adhesives, but its cost is higher.
(4) Polyvinyl acetate emulsion, also known as milk white glue or PVAC emulsion, is divided into two types: solution type and emulsion type, which are generally used in the carton industry as emulsion type. Polyvinyl acetate emulsion has many advantages as a corrugated cardboard adhesive, such as fast curing at room temperature, high initial adhesive strength, high strength of cardboard, and long storage period. The disadvantage is that the water resistance and heat resistance are not ideal. In winter, freezing may affect the use and the cost is high. In addition, polyvinyl acetate emulsion can be used instead of galvanized flat iron wire to glue and seal cardboard boxes.
The adhesive used for paper packaging is mainly made of 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 silicates (also known as water glass), starch adhesives are being used because of their advantages such as high bond strength, large stiffness, no moisture absorption and softening, no corrosion, no pollution, and low cost of use. The more carton manufacturers use it. 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. Some carton manufacturers that still use silicates (sodium silicates) so far do not want to eliminate babbitines, but rather difficult to master the process of making starch binders. According to the author's understanding, many carton factories have used starch binders, and some have even spent thousands or even tens of thousands of yuan to buy starch compounding technology. The quality of starch adhesives produced is unstable and difficult to master. The phenomenon that the starch glue made of it has a water content of more than 80% and 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, squeaking, cutting, and even knives. Still not used, these phenomena have limited their use. Still using cerulosin that is prohibited by the state but has to be used.
Adhesives play an important role in the carton production process. How to use adhesive to bond the carton to improve the quality of the carton has become a hot topic in the carton manufacturing industry. With the continuous advancement of science and technology, many large cartons manufacturing companies have more advanced cardboard production lines, while most small and medium-sized enterprises still follow traditional single-sided machines and even stand-alone production of corrugated cardboard. Most of their adhesives are used. Still sodium silicate (water glass). For these manufacturers, the correct choice of starch adhesives is even more important.
Adhesives have really begun to produce with scale in our country, starting from 1958. In the 1980s, the development of adhesives had a climax. At present, there are more than 1,500 adhesives production enterprises in China, with more than 3,000 varieties, and it has become one of the fastest-growing key industries in China's chemical industry. The synthetic adhesive industry in the developed countries of the world has entered a highly developed stage. The average growth rate in the 1990s was about 3%, and the average growth in China was 19.5%. In 1998, global sales of synthetic adhesives were approximately 25 billion U.S. dollars, of which the United States accounted for about 35% of global sales, western Europe accounted for 25%, Japan accounted for 15%, and China accounted for only 7%. The global synthetic adhesive consumption structure accounts for 35% of the packaging industry, the construction industry accounts for 25%, the wood processing industry accounts for 20%, the automobile transportation industry accounts for 10%, and the others account for 10%.
From the adhesive application structure, it can be seen that the packaging industry is the largest industry for adhesives. It is widely distributed in various fields such as paper products, printing and decorating, plastics, and other packaging industries. At the same time, with the development of the adhesive industry, packaging products have also been improved. Quality and grade promote the development of the packaging industry.
No matter how you can produce a qualified paper adhesive, you need to have the nature of the adhesive. The principle of bonding, and the related knowledge of the use of objects have a more in-depth understanding.