Study on Paper Plastic Composite Adhesive

Paper-plastic composite products are widely used composite materials in the modern packaging industry and are mainly used in post-print finishing and packaging materials. The book cover, exquisite pictures, maps, new pictures, advertisements, gift bags, and advanced packaging boxes made by laminating the paper prints not only look bright and colorful, but also prevent moisture, stain, wear, decoration and practicality. Greatly improved; for the packaging of cement, coal powder, inorganic minerals and other products of paper-plastic composite packaging materials, the paper's toughness, hygroscopicity and plastic film extension, moisture resistance, higher tensile strength, etc., Has a good overall performance.

Paper-plastic composite adhesive (abbreviated as laminating adhesive) is the key to the composite process of paper and plastic film. Modern industrial countries have used laminating adhesive for more than 30 years. Non-polar non-stick materials such as polypropylene (PP), polyethylene (PE) and other plastic films and polar paper bonding have many special requirements. Laminating adhesives are mainly solvent-based and water-based. Although hot-melt adhesives have been reported, they are currently not widely used.

1 Research status of solvent-based paper-plastic composite adhesives

Solvent-based paper-plastic composite adhesives are generally based on polyurethanes, styrene butadiene styrene block copolymers (SBS), ethylene vinyl acetate copolymers (EVA), polyacrylates, etc., and toluene, ethyl acetate, and gasoline. Such as solvent, supplemented by tackifier resin, plasticizers, antioxidants and other additives. Due to the volatilization of organic solvents, there are disadvantages of flammability, toxicity, and environmental pollution. Solvent-based superplasticizers are no longer the focus of current research and development, but because they have good adhesion properties and high impact resistance, they are quite long. Can still exist during the period.

1.1 Polyurethane adhesive

The main raw materials of polyurethane laminating adhesive are toluene diisocyanate (TDI), diphenylmethane 4,4'-diisocyanate (MDI), polyether polyol, trimethylol propane and glycol, etc. Points, with low viscosity, high bonding strength, good flexibility, film formation and other characteristics. Because of its excellent heat resistance and aging resistance, it is still indispensable in some high-end printing products. Li Xizhong] The main agent was prepared by reacting TDI with polyether diol, 1,4-butanediol, and ethylene glycol with ethyl acetate as a solvent, and reacted with polyether polyol, polyol and 1,6 hexamethylene diisocyanate. To get the curing agent, this two-component polyurethane adhesive can be applied to compound film dry compounding including paper-plastic compounding. It has good initial tackiness, high bonding strength and high transparency.

1.2 EVA adhesive

EVA-type laminating adhesives are commonly used in the market with large amounts. EVA resin is not ideal for polyolefin adhesive properties, poor adhesion to polar materials, can be modified by solution grafting reactions with unsaturated monomers. Yang Huirong and others have developed a new type of EVA-type superplasticizer, in which toluene and ethyl acetate or butyl acetate are mixed solvents, and modified resins such as modified pine rosin and other tackifying resins, grafted SBS modified materials, etc. are added to EVA resin. Anti-oxidant ethylene terephthalate (BHT), homemade PP tackifier, etc., the performance of the product made to the level of similar products in Japan, in full compliance with the requirements of the upper machine laminating film production.

1 3 SBS adhesive

The superplasticized rubber with thermoplastic elastomer SBS as the main resin has the advantages of light color and transparency, excellent frost resistance and pressure resistance, simple preparation process and low cost, and the market has a large sales volume. Zhang Jianying uses toluene and ethyl acetate as solvents, and adds 3 kinds of tackifying resins with a mass ratio of 1:1:1 in SBS 792 resin, supplemented with anti-aging agent and dispersant to make a solid content of 38% to 40% (adhesive). The adhesive content of the material content is the mass fraction, the same below), and its products are praised by users. Yang Huirong and others developed a modified SBS adhesive for the problems of poor aging resistance and poor ink affinity of SBS rubber. The addition of 5 to 10 parts of a self-made polymer resin modifier in 10 to 20 parts of SBS 791 resin to modify it greatly improves its aging resistance, and then adds a modified rosin with a mass fraction of 15%. The affinity and penetration of the ink layer. After aging under intense light, ventilation and 60°C for 500 hours, the adhesive strength of the samples with the modified SBS glue only decreased by 20%, while the use of commercially available SBS glue decreased by 85%.

1 4 polyacrylic adhesive

Solvent-based polyacrylic adhesives for paper-plastic composites can be prepared by solution copolymerization, and the selection of solvents is based on low toxicity and low cost. The soft and hard monomers, functional monomers and solvents selected for some laminating adhesive formulations are shown in Table 1.

2 Research status of water-based paper-plastic composite adhesives

The water-insoluble polymer material overcomes the disadvantages of solvent-based laminating adhesives such as flammability, toxicity, high energy consumption, and environmental pollution by emulsifying the water-based paper-plastic composite adhesive evenly dispersed in water, and the viscosity and molecular weight of the emulsion are high and low. Irrelevant, so become the focus of current research.

2.1 Acrylic water-based adhesive

There are many studies on acrylic water-based adhesives, many of which have been patented. The patent [8] reported a water-emulsion paper-plastic composite glue, which was obtained through the copolymerization of acrylate monomers with styrene and acrylonitrile to obtain a glue solution with a solid content of 50%, which is an ideal solvent-based glue replacement product. The patent also reported an emulsion laminating adhesive containing polyacrylates and modifiers with high bonding strength and good toughness. Zou Benlian et al. used butyl acrylate as a soft monomer, vinyl acetate as a hard monomer, and a small amount of modified monomers to initiate polymerization in a non-ionic anionic composite emulsifying system to obtain a high lamination film with high brightness and adhesive strength. High, no blistering, no yellowing. Ye Xianke and others synthesized an acrylic emulsion adhesive, in which acrylic acid and acrylonitrile were used as functional monomers to significantly improve the adhesive strength of laminating adhesive to BOPP (biaxially oriented polypropylene) and paper. The best mass fractions of acrylonitrile and acrylic acid are 4% and 5% to 8%, respectively. Xu Zushun took acrylic acid ester, methacrylic ester, styrene and acrylonitrile as main monomers, and used acrylic acid, hydroxyethyl acrylate and hydroxypropyl acrylate as active functional monomers to synthesize a kind of semi-continuous seeded emulsion polymerization method. Laminating adhesive, which is suitable for the composite of various ink prints and polypropylene or polyester film, with high adhesive strength and resistance to organic solvents.

2.2 VAE water-based adhesive

Wang Jinliang and others have developed BST 7 water-based superplasticizers, using ethylene vinyl acetate copolymer emulsion (VAE) as the main body, adding appropriate tackifier resins, and using organic phosphate esters as softeners. Comparative tests show that the performance of BST 7-type rubber is comparable to that of imported ARO COAT, and the peel strength is significantly higher than that of the latter, and the price is significantly lower than that of the latter. Zhao Guofa will have a mass fraction of 46% VAE emulsion, 58% butyl acrylate, 2% vinyl acetate, 6% rosin, 12% polyvinyl alcohol, 19% pure water, 05% copolymerization catalyst, etc. Formulated with a VAE emulsion at a specific temperature, it has the advantages of folding resistance, water solubility, high strength, and easy recycling.

2.3 Blending Emulsion Adhesives

The patent [15] reported that the blended emulsion was prepared from a styrene butadiene rubber emulsion, an ethylene vinyl acetate and acrylate or vinyl chloride terpolymer emulsion, and a polyacrylate emulsion mixed in proportion and blended with a modifier. It contains only a small amount of organic solvents for the compounding of polypropylene film and paper prints. Yeh Sike et al [16] blended acrylate emulsion and VAE emulsion, and used a synthetic bisamide curing agent NL 1 for crosslinking. The adhesive film has a solid content of 50% and a viscosity of 3 Pa·s. When the paper-plastic compound is used, there is no need for hot pressing or pollution, and the cost is reduced.

3 research trends of paper-plastic composite adhesives

Since the 1990s, due to the improvement of people’s environmental awareness and the increasingly stringent government environmental regulations, the gradual replacement of solvent-based adhesives by water-based adhesives and hot-melt adhesives is an inevitable trend. The United States is the largest adhesive market in the world. In 1999, the adhesive industry had sales of approximately US$9.2 billion, of which the largest market for packaging adhesives was about 42% of the total. At present, the solvent market in the US adhesive market accounts for only 92%, water-based glue accounts for 59.3%, hot-melt adhesives account for 20%, and others account for 115%. As far as the paper-plastic composite adhesives are concerned, with the development of research and development, the following trends have emerged in its development.

3.1 Full Development of Environmental Friendly Adhesives

Water-based polyacrylate emulsions and polyurethane dispersions have previously been limited in their application due to a large gap in heat and moisture resistance compared to solvent-based glues. In recent years, some improved cross-linking agents have been developed, such as dispersible isocyanates, polyfunctional aziridines, and polyfunctional carbodiimides, which have enabled water-based adhesives to narrow the performance gap with solvent-based adhesives and have achieved significant results. The required performance standards for composite materials. Germany reported exclusively a polymer dispersion crosslinked with a polyisocyanate, the main component being a polymer prepared by emulsion polymerization of an unsaturated vinyl monomer in the presence of a protective colloid. This adhesive can be used on a variety of substrates with excellent adhesion properties. With the improvement of the performance of water-based adhesives, its application range will be increasingly expanded. "Green Chemicals" is the development direction of chemical technology in the 21st century. Degradable plastic packaging is a hot topic, and adhesives with biodegradable polyolefin composites have also attracted people's attention. A LIONS macromolecule has been synthesized abroad, which contains a glucose group and a polymerizable double bond in the molecule. It can be emulsion-polymerized with a vinyl monomer to prepare a LIONS copolymer emulsion having high adhesion to a hard-to-stick substrate. The main chain of the copolymer contains glucose units, which are biodegradable and widely used. Although biodegradable adhesives used for paper-plastic composites have not been reported yet, biodegradable paper-plastic composite adhesives that can be combined with biodegradable plastics should have good prospects for development.

3.2 Development of high solids content

There is no clear definition of emulsion with high solids content. It is generally believed that a solids content of more than 60% is a high solids emulsion. Compared with conventional emulsions with solids content below 50%, it has high production efficiency, low transportation costs, and quick drying. Low energy consumption and other advantages have become a research hotspot for many researchers. Ai Zhaoquan et al.] developed a high-solids water emulsion plastic-wood composite adhesive, which can also be used for paper-plastic composites. The crosslinkable prepolymer is obtained by reacting TDI with hydroxypropyl acrylate, and then it is prepared by emulsion polymerization with butyl acrylate, styrene, acrylonitrile, etc., and its solid content is 60%±1%. Xu Zushun et al [12] researched and developed the emulsion type paper-plastic composite adhesive with a solid content of 62%±1%.

3.2 Development of Functional Paper-plastic Composite Adhesives for Special Requirements

Increasingly stringent environmental regulations and changing consumer demands have drastically shortened the life cycle of adhesive products. Continuous development of functional adhesives suitable for different requirements has become a current development direction. After the emulsion adhesive is dried and formed into a film, the high-molecular polymer cannot be dissolved in water, which brings a lot of inconvenience to the process operations such as equipment cleaning, and the water-soluble adhesive comes into being. Zou Benlian and others developed a water-soluble paper-plastic composite adhesive, and added saponified rosin to butyl acrylate, vinyl acetate, and acrylic copolymer latex to control the proportion of water-insoluble and water-soluble components, so that the obtained Latex not only maintains the adhesive properties of plastics, but also overcomes the disadvantages of polymer emulsions that are insoluble in water after being dried and formed into films, and is easy to use.

Has been developed specifically for the non-baking cold pressure paper plastic composite new process adhesive film. The water-based laminating adhesives researched and developed by Ye Xianke, etc. have the characteristics of high solid content and high viscosity. The emulsion is applied to the surface of plastic film, and it is quickly attached to paper in a wet state, and is directly wound by a cold roll to save energy. To eliminate pollution. In addition, paper-plastic composite adhesives that are excellent in solvent resistance, water resistance, and anti-aging properties through different cross-linking methods are also subjects of general interest.

Source: 21st Century Fine Chemicals Network