Research Progress of Waterborne Paper-plastic Laminating Adhesive

1 Preface

In recent years, most of the art prints, packaging papers, advertising paintings, book covers, and packaging paper carton boxes have been coated with a polypropylene film to improve the appearance of paper or printed products and to increase their useful life. The color printing paper after the film is called paste paper, also known as film paper, its colorful eye-catching, and has moisture, anti-fouling performance, deeply loved by consumers. Adhesives that can bond PP films to paper products are called paper-plastic composite adhesives, and are referred to as laminating adhesives. Commercially available laminating adhesives have the following main varieties: polyurethane two-component adhesives, EVA adhesives, SBS adhesives, and polyacrylate adhesives.

At present, there are mainly three types of paper-plastic composite adhesives: solvent-based, water-based (or emulsion-type) and solid-type. Waterborne laminating adhesive has the characteristics of non-toxicity, low taste, no pollution, easy coating, low cost, etc. It is the development direction of paper-plastic laminating adhesive. There are many types of such adhesives, and new types of adhesives with improved initial viscosity, drying speed, and water resistance are being developed. Waterborne laminating adhesives include polyvinyl alcohol (PVA) acetals, polyvinyl acetate, waterborne two-component polyurethanes, neoprene latex, composite emulsions, and acrylic water-based adhesives. Among them, the research and application of aqueous acrylate adhesives are the most widely used.

2 Polyvinyl alcohol (PVA) and its acetal water-based adhesive

PVAc is saponified and hydrolyzed to form PVA. PVA used for water-based laminating adhesives is a hydrolysate with a low degree of saponification. For example, a certain proportion of aldehydes (such as formaldehyde) are added to polyvinyl alcohol, under certain conditions, with aldehydes. Condensation can be obtained with water resistance, frost resistance, good adhesion, simple process, lower cost of the composite film adhesive. For example, an aqueous adhesive film prepared with polyvinyl formal as base material does not gel below 0°C without adding antifreeze agent.

3 Polyvinyl acetate based water-based adhesive

Polyvinyl acetate emulsion has a long history of use, low price, good stability, good initial tack strength, easy adjustment of viscosity by adding fillers, plasticizers, good mixing, no environmental pollution, and easy application. The application of a wider range of paper plastic film adhesive. The BST-7 aqueous laminating adhesive developed by Wang Jinliang et al. was prepared by adding vinyl acetate-ethylene copolymer emulsion (VAE) as the main component, adding appropriate amount of tackifier resin and using phosphate ester as softener. Tests have shown that the BST-7 laminating adhesive has the same index as imported ARO COAT laminating adhesive, and the peel strength is obviously higher than the latter, and the price is lower. Zhao Guofa [12] will have a mass fraction of 46% VAE emulsion, 5.8% butyl acrylate, 2% vinyl acetate, 6% rosin, 12% polyvinyl alcohol, 19% pure water, 0.05% copolymerization Catalysts, etc., are formulated into VAE-based laminating adhesives at specific temperatures, which are characterized by their resistance to folding and high strength. Although polyvinyl acetate-based water-based superplasticizers have obvious advantages, they also have poor water resistance and easy creep of the adhesive layer, which affects their use and development.

Since the 1950s, scientists at home and abroad have done a lot of work to improve the performance of polyvinyl acetate-based water-based superplasticizers and have achieved some results. For example, a new type of adhesive has been developed by acetalizing emulsion stabilizers, copolymerizing vinyl acetate with methyl methacrylate emulsions, and adding hydrophobic rosin modified resins to polymerized monomers. Water-resistant polyvinyl acetate water-based adhesive). Zhang Qihui et al. added two kinds of complementary modifiers [18]. The obtained water-based laminating adhesive has good water resistance, surpasses the Japanese second-class product standard, and has a simple production process. The raw materials are easily available, and the cost is homogenous with common vinyl acetate. The emulsion is similar.

4 Waterborne two-component polyurethane adhesive

Water-based vinyl polyurethane adhesives] are two-component, mainly based on a mixture of aqueous vinyl resins, fillers or surfactants, and a mixture of a polyisocyanate (and its prepolymer) and a stabilizer as a crosslinking agent. The two components are mixed before use and heated for rapid curing or cold pressing for rapid curing. The polymethylene polyphenyl polyisocyanate solution was added to the modified polyvinyl acetate emulsion in a certain proportion to obtain a two-component waterborne vinyl urethane adhesive]. The adhesive can replace ordinary polyvinyl acetate laminating adhesive, and has been widely used in the paper-plastic composites. It can also be used in printing, wood processing and other aspects, and has good water and solvent resistance.

5 Neoprene emulsion adhesive neoprene latex

CRL-403 or CRL-503 can be made into a variety of adhesives by combining different tackifiers, vulcanizers, fillers, stabilizers, antioxidants, etc., and can be used for paper-plastic composites as well as paper, fiber, and poly. Vinyl chloride and leather.

6 Composite Emulsion Water-based Laminating Adhesive

The mixture of SBS and epoxy resin [2 mass ratio is (1- 3.5) : 1] as the base material, MMA as modified diluent, polyvinyl acetate emulsion as water-soluble carrier, rosin and dimerized rosin as viscosifier The agent can be formulated into a water-based paper-plastic composite adhesive. Polyvinyl acetate emulsion accounts for about 60% of the total mass of the adhesive. There are special reports] that an adhesive made of styrene butadiene latex, ethylene-vinyl acetate and acrylate or vinyl chloride ternary complex emulsion, acrylate emulsion mixed in a certain proportion and combined with a modifier, can be used for polypropylene film Composite with paper prints. Yeh Sike et al. blended acrylate emulsions and VAE emulsions and used a synthetic bisamide curing agent NL-1 for cross-linking. The obtained adhesive film had a solid content of 50%, a viscosity of 3 Pa·s, and a paper-plastic composite. No need for hot pressing, low cost and no pollution. This new type of composite emulsion type adhesive has been widely used in paper-plastic composites.

7 Acrylate System Water-based Laminating Adhesive

There are many studies on acrylic water-based adhesives. A paper-plastic laminate adhesive was reported in the literature. It is an ideal solvent-based laminating adhesive replacement product by copolymerizing acrylate monomers with styrene and acrylonitrile to obtain a solid content of 50%. The literature also reported an emulsion laminating adhesive containing polyacrylates and modifiers, with strong adhesion and good toughness. Xu Zushun took acrylate, methacrylate, styrene and acrylonitrile as the main monomers, and used acrylic acid, hydroxyethyl acrylate and hydroxypropyl acrylate as functional monomers to synthesize a kind of semi-continuous seeded emulsion polymerization. Acrylic adhesive film, which is suitable for the combination of various ink prints and polypropylene or polyester film, high adhesive strength and resistance to organic solvents. Acrylate systems generally use copolymers. With methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc. mixed to adjust the softening point, toughness or copolymerization with acrylonitrile, styrene, VAc, MMA, etc. to meet the needs of different uses. Acrylic copolymers are widely used in the field of paper-plastic laminating adhesives due to their thermal stability, good optical stability, strong antioxidant resistance, good transparency, and high adhesion to many materials.

7.1 Polyacrylate Water-based Laminate Polyacrylate Water-based Laminating Adhesives can be easily prepared using standard composite equipment. The adhesive properties of various films are good, and the film's cleanliness and stability to light are both well. In the one-component system, each reactant exists in the same emulsion, but no reaction occurs. After the film is formed, the active groups in the polymer particles react with the active groups in the aqueous phase to cause cross-linking and solidification, thus having a longer pot life. Tang Hongke et al. used a multi-component copolyacrylate emulsion and water-based adhesive film made of emulsified rosin as a tackifier. It has strong adhesion, good stability, and excellent water and moisture resistance.

7.2 Rapidly Compounded Polyacrylate Water-Based Laminating Adhesive In laminating adhesive technology, it is necessary to make the paper-plastic bonding firm and the bonding speed fast. There are also many researches in this area. For example, the high-speed sealing glue of plastic-plastic carton developed by Jiao Jian et al. uses acrylic emulsion as the main material, adding a certain amount of ethylene-propylene emulsion, rosin, compound emulsifier, antioxidant and Filler and other compounded, in all kinds of climatic conditions have excellent adhesive properties, has a high value of promotion and application.

7.3 Modified Acrylic Aqueous Laminates A polymer emulsion with a core/shell structure is a polymer emulsion in which two or more monomers with different properties are polymerized in stages under certain conditions. Its emulsion particles contain different components inside and outside, giving the adhesive different properties. Polysiloxanes and acrylic esters, which have two different chemical structures, differ greatly in polarity, and have different reactivity and compatibility, are obtained by emulsion polymerization and have both advantages. For example, octamethylcyclotetrasiloxane (D4) and butyl acrylate are the main monomers, and OP-10, sodium lauryl sulfate are used as emulsifiers, and potassium persulfate is used as an initiator for emulsion polymerization. A modified water-based paper-plastic laminate was prepared. By changing the amount of silicone and acrylate can adjust the product's performance.

7.4 Milkless acrylic water-based adhesives The emulsion-type adhesives contain small-molecule emulsifiers. The emulsifiers migrate to the surface in the product and glue, which results in a decrease in the physical properties such as water resistance and adhesiveness of the product. In order to eliminate the adverse effects caused by emulsifiers, a new process for the production of non-emulsion paper-plastic adhesives has been developed.] Using olefins containing -SO4Na as emulsifying monomers, the water-based acrylate copolymer paper-plastic laminating adhesive prepared by the emulsion-free polymerization process is stable in storage and strong in adhesion. Milk-free polymerization to prepare water-based acrylate copolymer paper-plastic adhesive is a promising new product.

8 Conclusion “Green Project” is the development direction of chemical technology in the 21st century. Safe, non-toxic, non-polluting, fast-curing waterborne laminating adhesives have received extensive attention. Composites made with this glue do not turn yellow and do not roll straight. In addition, the use of water-based adhesives and corresponding equipment for paper-plastic composites, less investment, low energy consumption, low cost, has important environmental protection value and considerable economic benefits.

Source: 21st Century Fine Chemicals Network