Research and Application of Green Paper-plastic Adhesive

Abstract : The types of green paper-plastic adhesives are introduced. The researches on water-based acrylic adhesives, polyvinyl acetate-based water-based adhesives, water-based and solvent-free polyurethane adhesives and hot melt adhesives are reviewed, and the development trend of green paper-plastic packaging adhesives is pointed out.

Keywords: green paper plastic; water-based adhesive; solvent-free adhesive; hot melt adhesive

Green paper-plastic composite adhesive is a kind of adhesive commonly used in the packaging industry, referred to as green adhesive film, mainly refers to two types of water-based and hot-melt adhesives. Since the 1990s, water-based adhesives and hot-melt adhesives have been widely developed as people's awareness of environmental protection has increased and government regulations for environmental protection have become stricter. The United States is the largest adhesive market in the world. In 1999, the adhesive industry accounted for about 42% of the total adhesives. At present, the solvent market in the US adhesive market accounts for only 9.2%, water-based adhesives account for 59.3%, hot-melt adhesives account for 20%, and others account for 11.5%. It can be seen that the green paper-plastic compound adhesive occupies a pivotal position in the modern packaging industry.

1 Study on Green Paper-plastic Composite Adhesive

1.1 Water based acrylic adhesive

Water-based adhesives use water as the medium, non-toxic and non-flammable; they have good resistance to other substances and can be modified by various types of additives; the process is simple and easy to use. There are many studies on water-based acrylic adhesives, and there have been many reports. Adding a modifier to the acrylate gives a paper-plastic composite film adhesive with a strong bond strength and good toughness. Zou Benlian et al used butyl acrylate as a soft monomer, and vinyl acetate as a hard monomer with a small amount of monomer for modification. The resulting film adhesive had high brightness, high adhesive strength, no blistering, and no yellowing. For paper-plastic composite adhesives. Tang Hongke and others used acrylate as the main raw material to synthesize butyl acrylate vinyl acetate copolymer emulsion by semi-continuous emulsion polymerization and added a certain proportion of emulsified rosin tackifying resin to make a novel paper-plastic composite adhesive. Adhesive strength, stability, water resistance, etc. are greatly improved. Ye Xianke and others synthesized an acrylic emulsion adhesive, in which acrylic acid and acrylonitrile were used as functional monomers to significantly improve the bonding strength of the biaxially oriented polypropylene and paper BOPP.

1.2 polyvinyl acetate water-based adhesive
The emulsion adhesive includes a homopolymerization and a copolymerization emulsion, has a good initial bonding strength, can be arbitrarily adjusted in viscosity, is easily miscible with various additives, and can be formulated into a paper-plastic composite adhesive with various properties. Wang Jinliang et al. synthesized a polyacrylate emulsion with ethylene-vinyl acetate copolymer emulsion, which is suitable for high-speed automatic folder-gluer laminating. The adhesive effect is good, and it is fully applicable to laminated white cardboard. Whiteboard paper, ordinary glossy white paperboard products with automatic sealing and bonding. Xu Xiangbing et al. synthesized a kind of acrylic ester emulsion with self-made aqueous rosin emulsion and VAE emulsion to form a composite emulsion adhesive. It is used in the paper-plastic composite of the packaging industry and has a high peel strength. Adding the appropriate amount of aqueous rosin resin and VAE emulsion in the system can make the adhesive product water-soluble, improve the adhesive properties of the product, and reduce the "snowflake" phenomenon. Liu Changchun and other vinyl acetate and acrylic monomer, polymer and resin modified adhesives made of non-toxic, quick-drying, light color, water resistance, strong adhesion, suitable for the packaging industry.

1.3 Water-based and Solventless Polyurethane Adhesives

Water-based polyurethane adhesives were developed in response to the requirements of low toxicity and low pollution products in the 1970s. Water-based polyurethane adhesives are mainly produced by the following two methods: First, the original polyurethane adhesive is directly emulsified into a stable water-dispersed emulsion by adding an emulsifier; and secondly, hydrophilic ions are introduced into the molecular skeleton of the polyurethane. The group forms self-dispersing and self-emulsifying systems. The advantage of this system is that it does not contain emulsifiers, has good film formation, and can be blended with other anionic or cationic polymerization systems to reduce costs. Recent studies on it have been very active, mainly focusing on increasing solids content, increasing drying speed and bonding strength, increasing cross-linking, or introducing polyethers to increase their water resistance. The preparation method of ionic water dispersion polyurethane adhesives can be found in relevant patent reports. Due to the comprehensive performance of composite film packaging materials, it is increasingly welcomed by people. The amount of adhesive needed with it also increased accordingly, with the largest amount being polyurethane adhesive. It has been reported that the solventless polyurethane adhesive used in Europe for food packaging film bags is approximately 2.4 kt per year and the solvent type is approximately 2.2 kt per year. The average annual growth rate of adhesives for food composite film bags in the next five years will be 4% per year, and China may double. At present, polyurethane (PU) adhesives developed at home and abroad account for a large proportion of high-performance food packaging composite films, and one of the main development directions is waterborne polyurethane adhesives. Due to its non-contamination, low coating amount, and fast compounding speed, the processing cost is lower than that of the solvent type, and it is used for bonding plastic films having poor solvent resistance and high heat shrinkability. The application of plastic in the packaging field has broad prospects.

The use of solvent-free polyurethane adhesives for composite membranes began in Germany in 1974. The use of such solventless polyurethane adhesives to make composite membranes has accounted for more than 50% in Europe and the United States. Solvent-free polyurethane adhesives for the manufacture of composite membranes have now been developed to the third generation. Amino resins or etherified amino resins can be used in flexible packaging. Zhang Xueyin and other adhesives made of amino resin compounded with EVA, DBP, thinners, thickeners, and rosin-based compound tackifiers can meet the requirements of paper-plastic adhesives. Hu Xiaolan et al used poly(1,4-adipylene adipate) as raw material to prepare polyurethane adhesives with good resistance to cooking and adhesive properties. The adhesive has good adhesive property to PET film/Al foil composite structure and PET/PET structure. The adhesive layer has good transparency after cooking, stable quality, good repeatability and non-toxicity, and is suitable for bonding flexible packaging composite structural materials. .

1.4 Biodegradable Hot Melt Adhesives

The United States is the world's largest producer of hot-melt adhesives, with 614,000 tons in 1991 and 916,000 tons in 1996. The annual growth rate is above 5%, and its consumer market packaging industry accounts for 49%. China began to develop hot-melt adhesives in the 1970s, and the hot-melt adhesives developed rapidly at the end of the 20th century and began to be applied in the packaging industry. Hot-melt adhesives are mainly ethylene-vinyl acetate copolymers (EVA). In 1996, the production of such adhesives reached 12,000 tons. It was mainly used in the packaging industry, book binding, and bag making. Its advantages are fast bonding speed, no solvent, easy control of glue amount, and good gloss of products. U.S. patents describe the use of dihydroxy acids and ethers to synthesize polyesters containing hydroxymethyl groups as the substrate, and to produce biodegradable hot melt adhesives with good properties and can be used for paper-plastic bonding. Shark et al. used hydroxy-containing butyrate, valerate, cellulose, starch esters, etc. as sucrose ester as a tackifier for the substrate, and the biodegradable adhesive was effective in paper-plastic bonding.

In addition, He Lunying studied a kind of unsupported starch adhesive, which has good flowability, suitable viscosity, and good water retention performance. It can completely and uniformly infiltrate the surface of the adherend, has strong adhesion ability, stable performance, and is not easy to separate, gel, and decay. Etc., suitable for bonding corrugated cardboard. There is also an oxidized starch adhesive in the packaging industry.

2 Conclusion

Green adhesives are the development requirements of the packaging industry in the 21st century. In terms of the development level of green adhesives, China differs greatly in size and variety from foreign countries. High solids water-based emulsion adhesives, water-based and solvent-free polyurethane adhesives, biodegradable hot melt adhesives, and green multi-functional adhesives are the development trend of green paper and plastics in the future. They will strengthen the research of green environmental protection adhesive resins and develop new types of green paper. Plastic adhesive varieties have important significance for improving the quality of green and environmentally friendly packaging adhesives in China. (Wen/Fu Heqing Li Yongjin Huang Hong Chen Huanqin)