Development Status and Trend of Polyurethane Adhesives for Composite Packaging (1)

The composite flexible packaging material is a composite material in which two or more different types of substrates (films) have different properties and are tightly adhered by an adhesive. At present, China's most used and best performing adhesives in composite flexible packaging materials are solvent-based two-component polyurethane adhesives. This type of adhesive has been applied in foreign countries for 50 to 60 years. However, in China, there are only 25 years of application history. It was imported from abroad to manufacture composite flexible packaging materials in the early 1980s. In 1981, Shanghai's research results passed national-level technical appraisal, and in 1984 it achieved industrial production. After more than 20 years of development, there are currently hundreds of companies in China producing this product, with an annual production capacity of about 100,000 tons. The actual output last year was about 3,560 tons. The products provided are both general and functional; both resistant to low temperatures and resistant to temperatures up to 135°C; used for both food and pharmaceutical packaging, but also resistant to liquid pesticides; both aromatic, There are also aliphatic; both solvent-based and solvent-free; both ester-soluble and alcohol-soluble. In general, other countries have, we have.

The following is a detailed analysis of the history, status quo and development trend of polyurethane adhesive for composite packaging in China.

The development of composite flexible packaging materials in China started later than abroad. In the second half of the 70s of the last century, Shanghai began researching composite materials for food packaging using extrusion compounding and dry compounding. In 1982, Shanghai, Dalian, and Wuxi took the lead in introducing advanced large-scale flexible packaging production equipment from Japan, forming a complete set of intaglio printing machines, dry laminating machines, extrusion laminators, slitting machines, bag making machines, and testing equipment. The production system also began to use imported aluminum foil, polyester film, polypropylene, inks and adhesives.

At the end of 1984, China used the technology approved by the state in 1981 to build the first factory to produce solvent-based two-component polyurethane adhesives for food packaging, which made people see the prospect of localization of adhesives, and from then on In the short period of two to three years, more than ten adhesive production enterprises have rapidly developed and the scale is relatively large. The annual output is 200 to 500 tons.

In the early 90s of the last century, China's packaging industry made rapid progress, and imported flexible packaging lines emerged everywhere. Enticing the huge market, adhesive production plants are also rapidly developing. According to recent statistics, about 300 companies across the country have produced dry compound adhesives with an annual production capacity of about 100,000 tons. Two-component polyurethane adhesives have been localized for more than 20 years. Not only are there a lot of manufacturers, product models have also been enriched, and the quality of certain brands has reached the international level. In recent years, domestic products have accounted for more than 85% of the total domestic consumption.

In order to occupy the Chinese market, many foreign companies have invested in factories in China. Japan's Takeda Pharmaceutical Co., Ltd. has already started production at its production facility in Suzhou and provides ordinary low-cost adhesives to the Chinese market. Rohm and Haas Company of the United States has also set up a factory in Shanghai. After the acquisition of Morton, in addition to promoting water-based adhesives, it also sells solvent-based adhesives. Henkel's factory in Shanghai has put into production of UK2860 polyurethane compound adhesive.

Among domestic adhesives, research and development and product quality in Shanghai and Beijing have always been ahead of others. From a historical point of view, from the development of common adhesives to hot and acid resistant media resistant adhesives, from room temperature adhesives to boiling resistant to high temperature cooking adhesives, from general adhesives to functional Adhesives, from solvent-based adhesives to solvent-free adhesives, from aromatic adhesives to aliphatic polyurethane adhesives, to anti-corrosive adhesives adapted to certain liquid EC pesticide packaging, from non- From flame-retardant adhesives to fully-flame-retardant adhesives, Shanghai's scientific and technical personnel have played an important role in pioneering and the quality of products is at the forefront. Products manufactured using Shanghai technology can not only replace imports but also receive foreign materials. With the approval of users, the export of domestic polyurethane adhesives was realized in the early 1990s.

Now, Shanghai, Beijing, Zhejiang, Jiangsu, and Guangdong can provide polyurethane adhesives for composite food packaging materials with various properties and meet various packaging requirements. Among them, Shanghai Lianyin Chemical Co., Ltd. can produce high temperature resistance and resistance at the same time. LY-50A/LY-50AH adhesive with dielectric erosion properties and LY-103A/LY-103B functional aluminum composite film adhesive, and LY-9850R that can be used for aluminum foil structure and 121-135°C high temperature cooking /LY-9875R, LY-135A/LY-135B adhesives and LY-9850F/LY-9875F aliphatic urethane adhesives that are compliant with FDA regulations and resistant to 121 to 124°C, and LY-50VR And LY-50VN Liquid Emulsion Pesticide Packaging Adhesive, and in 2001 it successfully developed LY-75FT/LY-75FTH Adhesive with fast curing and no increase in the coefficient of friction of the composite film, shortening the curing time and reducing The two factors of friction coefficient and good openness are not inferior to those of similar imported products. Beijing Research Institute of Chemical Industry has UK2850/UK5000 plastic/plastic compound resistant to 121°C, 30 minute cooking adhesive and UK8150/UK7330 solvent free adhesive. Guangdong Zhongshan Kanghe Company has a special aluminum adhesive film adhesive KH-VM80. The European and American companies in Shenzhen have ECO501A/B and ECO751A/B alcohol-soluble adhesives, and Beijing Gaomeng Chemical has YH502 high temperature cooking adhesives.

The development trend of adhesives for composite flexible packaging has the following six directions.

1. Towards high solids, low viscosity adhesives

The earliest two-component polyurethane adhesive whose solid content of the main agent is 35% or 50% has now been increased to 75% or 80%. The European region has increased to 88%, and it is almost solvent-free! The solid content of the curing agent also increased from the original 60%, 75% to about 80%. This is mainly to reduce the amount of solvent emissions and reduce production costs.

In the past, due to the relationship between the equipment and the process, the adhesive was required to have excellent initial tack to ensure that the composite did not produce wrinkles or "tunneling" defects at the time under the equipment and process conditions, so the molecular weight of the adhesive Very high viscosity, and the concentration of the operating solution during compounding is relatively low, (mostly 20% to 30%), to ensure that the pre-set amount of glue and the uniform coating effect, as well as the composite product quality. Obviously, this low-concentration coating will inevitably lead to a large amount of solvent volatilization into the atmosphere, for example, the concentration of the operating solution is 20%, the amount of glue is 3.5g/m2, then, the coating is applied on a per square meter basis. The weight of the adhesive on the film is 3.5/0.20=17.5 (g). When dry, 14 g of solvent per square meter becomes air discharged into the air, leaving only 3.5 g of dry-based adhesive. This situation will lead to two big problems.

First, a large amount of organic solvent (specifically ethyl acetate) is emitted into the atmosphere, causing air pollution. This is obviously not feasible under the increasing trend of protecting the environment and preventing pollution.

Second, during the gluing process, the role of the solvent is only to help the rubber material to be transferred to the surface of the glued substrate easily and evenly. Once this mission is completed, it must be completely left so that the compound can be compounded in the dry state. Obviously, the solvent does not play a role in the level of adhesion. If you do not consider the role it was previously talking about, it is simply superfluous from the standpoint of adhesion and peel strength. As mentioned above, the concentration of the operating solution is 20%, and when the glue requirement is 3.5g/m2, the ethyl acetate consumed per square meter is as much as 14g. According to the current price of 9 yuan per kilogram, acetic acid is consumed per square meter. The cost of ethyl ester is 0.126 yuan. This 0.126 yuan went to the air to "wasted" away. High-solids, low-viscosity adhesives can be formulated to a higher concentration of the operating solution while still maintaining the desired amount of glue and achieving a uniform transfer. It can be operated at a concentration of 40% to 45%. For example, if the amount of the solution is 3.5g/m2, if the concentration of the solution is increased to 45%, the weight of the adhesive applied to the base film per square meter should be 3.5/0.45 = 7.78 (g). The ethyl acetate evaporated to the air after drying was only 4.28g/m2, which was 9.72g/m2 less than the previous 14g/m2. The cost of ethyl acetate consumed per square meter was only 0.03852 yuan, which was lower than the previous 0.126 yuan. For 0.08748 yuan, if you add the heat energy cost of driving off 9.72g of ethyl acetate, the cost savings will be even greater.

This shows that these two reasons are the driving force behind the development of high-solids, low-viscosity adhesives. However, there is a problem that must be paid attention to. That is, after the solid content is increased and the viscosity is reduced, the initial adhesive force of the adhesive should not be reduced. As an adhesive manufacturer, it is not possible to increase the solid content and maintain a lower viscosity of the adhesive by simply reducing the molecular weight. Instead, it should be considered from the molecular structure of the adhesive to produce a higher initial viscosity. High solid content, low viscosity products come. According to our experience, when the initial adhesive strength (peeling strength) is 1.0N/15mm or less, the composite can easily cause wrinkles, "tunnel" and other failures; initial adhesion is 1.0 ~ 1.8N/15mm, the failure may occur; When the initial adhesive force is greater than 1.8N/15mm, no wrinkles or “tunneling” failures will occur.