Solvent-free compound technology has occupied a very important position in the current European and American markets, accounting for 80-90% of the new compound machine equipment. In China, solvent-free compound technology began in the mid-to-late 1990s, and the number of existing installations does not exceed 40. The glue used in the traditional flexible packaging industry is mostly solvent glue. In 1996, Henkel took the lead in innovatively promoting solvent-free adhesives in the Chinese market. Compared with solvent glue, solvent-free glue not only has the advantages of environmental protection and low carbon, but also saves the amount of glue used, can apply faster machine lines, improve production efficiency, etc., and has a higher cost performance.
Features of solvent-free adhesives
1. Contains no solvent
Solvent-free adhesives are 100% active ingredient content. They are coated with different coating systems and do not use solvents, so there is no solvent volatilization throughout the compounding process, and there is no solvent residue in the compound section of the compound product, which is more in line with food safety. Requirements, and no emissions, in line with emission reduction and environmental protection requirements.
2. Not a flammable or explosive dangerous product
Good safety, no fire or explosion hazard, no solvent explosion-proof measures required; flux-free adhesives are not flammable and explosive, high corrosion and other dangerous goods, no explosion-proof considerations in transportation and storage, and no solvent The adhesive is 100% solids and occupies less storage space.
3. Small amount of coating
Because the flux-free agent has better cold flow characteristics, the coating amount of the solvent-free adhesive is generally between 0.8-2.5g / m2. For special materials such as paper, the coating amount can reach 4 g / m2. The coating amount of the solvent-based adhesive is generally 2.0-4.5 g / m2. This shows the cost advantages of solvent-free adhesives.
4. The molecular weight is relatively small
The molecular weight of solvent-free adhesives is much lower than that of solvent-based adhesives of the same grade, which makes it possible for the adhesive to infiltrate, diffuse, and penetrate the surface of the substrate at a suitable temperature without the participation of solvents. [next]
Types and development history of solvent-free polyurethane adhesives
Solvent-free composite processes, equipment and adhesives were developed in the 1970s. The first generation of solvent-free adhesives are single-component moisture-curing adhesives. The chemical structure of a one-component moisture-curable polyurethane solvent-free adhesive is a polyester or polyether with relatively short chain length isocyanate end groups, isocyanate (-NCO) and moisture in the substrate or environment A chemical reaction occurs, releasing CO2 for curing.
In order to overcome the shortcomings of single-component adhesives, two-component polyurethane solvent-free adhesives were developed. Two-component polyurethane solvent-free adhesives can be divided into second-generation and first-generation adhesives according to their initial adhesion and cooking resistance. Three-generation two-component polyurethane solvent-free adhesive.
The second generation of solvent-free adhesives was first applied to composite packaging materials in 1980.
The third-generation solvent-free adhesive overcomes the shortcomings of the second-generation solvent-free adhesive. It has the advantages of high initial tack, low viscosity, low operating temperature, and no restrictions on the composite substrate. It can solve the second-generation adhesive The problem of poor heat sealing of EVA and nylon by the mixture, and the problem of easy wrinkling or peeling of the film with strong barrier properties have also been solved. It can be applied to the compounding of various plastic films and foils, reducing the free The content and resistance to content are excellent, the bonding strength and heat resistance of the adhesive have also been improved, and the aluminum-plastic composite film products may have high cooking resistance.
The main features of the current third-generation products are:
(1) Adopt anti-catalysis system.
(2) Reduce the viscosity of the adhesive, improve the wettability of the adhesive to the film, and improve the coating and dispersion properties of the adhesive on the film surface. Therefore, it not only improves the quality of solvent-free adhesive composite products, but also increases machine speed and increases production efficiency.
Solvent-free polyurethane adhesives have been developed for nearly 30 years, and the performance of their products has gradually matured. Under the environment of green environmental protection and low-carbon economy, solvent-free adhesives have excellent economic performance, The advantages of safety and environmental protection, as well as the continuous development of composite processes and equipment, are favored in Germany, the United States, Japan and the world. In developed countries such as Europe and the United States, the use of solvent-free polyurethane adhesives has rapidly increased from 10% 20 years ago to more than half now. Japan has introduced the first solvent-free? X compound machine since 1977, and now it has grown to have more than 100 solvent-free compound equipment.
Due to the continuous speed-up of the laminating machine, the curing speed of general-purpose adhesives is difficult to adapt. The fourth generation of UV-curable solventless adhesives came into being. The currently used cationic curing products are mainly acid-catalyzed epoxy systems. Under ultraviolet irradiation, the photoinitiator of the adhesive decomposes to initiate block polymerization of the epoxy to obtain a three-dimensional cross-linked structure of the epoxy resin. Under the premise of selecting an appropriate UV generator, this adhesive can quickly compound polyester film, and can reach a fairly high bonding strength within a few minutes to an hour, making the post-processing process smooth. [next]
Features of solvent-free composite equipment
Compared with solvent-based composite equipment, solvent-free composite equipment has the following advantages:
1. No drying? X channel, low energy consumption
The drying capacity of solvent-type compound machine x is generally 150-250KW, and the average power consumption can reach 500,000-700,000 yuan a year. Even if steam drying is used, energy consumption is not small. The total power of the solvent-free machine is low and there is no drying tunnel. According to the information provided by Italy Nordmeccanica, the energy consumption of the solvent-free is almost one-twentieth of the solvent type.
2. Fast compound speed
Solvent-free compounding does not require baking? X, no residual solvent restrictions, high production efficiency, average compounding speed 250m / min, up to 600m / min, one compounding machine can meet the production of two printing machines.
3. High degree of automation
The solvent-free laminating machine adopts proprietary equipment to automatically feed glue, automatically control the ratio of the two components of A and B, automatically control the temperature, and adjust the coating amount online. The equipment is compact and saves manpower.
Key points of solvent-free compounding process
At present, the commonly used base materials for solvent-free composites mainly include BOPP, PET, OPA, VMCPP, VMPET, CPP, PE, aluminum foil, etc. When compounding, materials with high rigidity and good coating performance (PET, BOPP, OPA, VMPET, etc.) are generally placed in the main unwinding station; materials that are easy to stretch (PE, CPP, VMCPP, etc.) are placed in the secondary unwinding Station. However, it is not static, and can be flexibly selected according to the actual production situation. For example, when the printed film is compounded with the aluminum plating material, in order to ensure the composite quality and production efficiency, the aluminum plating material can be placed in the main unwinding station.
There are many factors to consider when choosing an adhesive. The first is the type of packaging content and the type of film material used. Secondly, if the printing ink is in contact with the adhesive, the compatibility of the two must also be considered; peel strength requirements And heat sealing conditions also have a great influence on the choice of adhesive.
In addition, two issues need to be noted: First, the MDI type isocyanate compound will gradually migrate to the inner layer surface through the inner film, and react with moisture to form a polyurea heat-resistant seal layer, which affects the heat sealing of the packaging bag quality. This problem is likely to occur when the quality of the polyethylene film is poor or the adhesive is not properly selected, especially when using two-component adhesives. Second, when a film with a high content of slip agent is compounded, the slip agent may migrate into the adhesive layer, which may cause problems such as poor peel strength, poor heat sealing, and increased friction coefficient, affecting its operation on the packaging production line. Sex. When compounding such films, attention must be paid to the choice of adhesive. [next]
The future of solvent-free adhesives
After decades of development and application, solvent-free adhesives and solvent-free composite technologies have become very mature. The use of solvent-free adhesive composite films can reduce energy consumption, increase production efficiency, improve product quality, and reduce overall production costs. Because it does not contain solvents, it is conducive to protecting the environment and clean production, and ensures that the compound does not pollute packaged foods and medicines.
We believe that with China's increased awareness of the quality of composite products and food hygiene and safety, and the increased awareness of energy conservation and environmental protection, solvent-free compounding will surely attract more and more attention from people in the compound packaging industry. The good operation of the existing solvent-free compounding equipment in China will surely accelerate the flexible packaging industry's transition from solvent-based compounding to solvent-free compounding.
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