At present, the three most important environmental protection technologies for international flexible packaging are solvent-free composite technology, flexographic printing and co-extrusion compounding, among which solvent-free composite technology is the most environmentally friendly. At present, solvent-free composite technology has occupied a very important position in the European and American markets, accounting for 80% to 90% of new composite machine equipment.
In China, solvent-free composite technology began in the mid-to-late 1990s. In recent years, the development has been slightly faster. The number of existing installations does not exceed 40 (accounting for no more than 2% of the total number of composite machines), far lower than that of developed countries [1-7]. ]. Under such circumstances, how can domestic soft packaging enterprises and technicians engaged in flexible packaging work have a correct understanding of solvent-free composite technology and its products, and thus expand the market share of solvent-free composite technology in the domestic market has become the current domestic soft package The focus of the industry is on issues. Solvent freelamination is a relatively dry solvent-based compounding process and is another compounding process used in the flexible packaging industry. Solvent-free soft compounding is a film-like substrate (plastic film or paper, Al foil, etc.) which is adhered to each other by a solventless adhesive and a special composite device, and then subjected to chemical ripening reaction of the adhesive to cure the substrate. A composite way of bonding together. Both the solventless composite and the solvent-based dry composite are prepared by using an adhesive to obtain a composite film. The difference between the two types of processes is that the solvent-free composite adhesive does not contain any solvent, so the two-layer substrate does not need to be excluded from the drying tunnel as in the solvent dry composite process before bonding. Solvent-free composite and dry composite are practical industrial production methods that compete with each other and complement each other in plastic film composite production.
The solvent-free compounding process was first developed in 1974 by the German company Herberts. Due to its economical, safety and environmental advantages, it has become an important processing method for plastic composite films. In the developed countries of Europe and the United States, where environmental protection and energy conservation are strong, the number of composite films produced by the solventless composite process has significantly exceeded that of the dry process. Since the beginning of the 21st century, the number of new solventless composite devices in Europe has increased. More than 90% of the total number of composite equipment; Japan has introduced a solvent-free composite process since 1977, and more than 60 production lines have been built in the early 21st century, occupying a dominant position in the production of composite membranes; in the United States, the use of solvent-free adhesives accounted for 10% in 1977. In 1980, it reached 50%, and in the 1990s it rose to over 90%. Due to the lack of popularization of solvent-free composite equipment in China, its application is less.
1. Domestic solvent-free composite equipment. At present, the world's manufacturers of solvent-free composite equipment mainly include: W&H in Germany, Nordmecanica in Italy, Schiavi, Bielloni, DCM in France and Comexi in Spain. Many composite equipment manufacturers in China have also invested in the development and research of such equipment, and have made certain progress. In 1985, Beijing Research Institute of Chemical Industry introduced the first solvent-free coating compound testing machine manufactured by DCM Company, engaged in scientific research and production. Then in 1996, Tianjin Dingzheng Printing and Packaging Co., Ltd. introduced solvent-free equipment from Schiavi Company of Italy, and in the same year The commissioning was successfully put into production in August. Subsequently, Guangzhou Jinweilong Company, Dalian Shengdao Packaging, Shanghai Tiger Brand, Sanying, Hubei Salt Industry and other manufacturers have introduced more than a dozen solvent-free composite equipment from Italy, France, Germany and other countries. With the understanding and mastery of the new solvent-free composite technology in domestic composite packaging enterprises, this new composite process has obviously accelerated the development trend.
2, solvent-free equipment features, the typical configuration of the solvent-free composite machine includes: two unwinding devices, a winding device and a solvent-free adhesive coating composite device. Its biggest feature is that it can be directly integrated into the composite through a special coating device, without the need for drying tunnels. Solvent-free composite equipment is adapted to the need for solvent-free adhesive coating, so it has some significant differences from solvent dry composite equipment. Mainly in the coating device has a temperature rise, temperature control system, relying on adjusting the temperature to adjust the viscosity of the adhesive to facilitate coating and construction. The take-up device is provided with a closed-loop tension controller to strictly control the winding tension and prevent the "tunnel" effect in the production process of the composite film.
The feeding device has a high-precision mixing nozzle (suitable for the needs of two-component adhesive feeding) and a humidifier (to ensure the full curing of the one-component adhesive).
The coating system is different, there is no mixing pump; there is no drying tunnel, no drying is required; the vertical control system is more accurate than the solvent-based system. Compared with the dry composite, the following main differences are found on the equipment. :
(1) The long drying oven used for the solvent in the volatile adhesive is removed, the equipment is compact, and the equipment components are easy to clean and maintain;
(2) The material has a shorter film penetration distance on the device, which makes the material tension control more precise. Due to the compact structure of the device, all control keys are concentrated on the main control panel for easy monitoring by the operator;
(3) The gluing unit is the central part of the solventless laminating machine where the adhesive is mixed, heated, metered and coated;
(4) The rubberized head is generally a four-roll or five-roll design, which is a glue roller, a metering roller, a (floating roller), a rubber roller and a rubber roller. There is an accurately calculated angle between the roller and the roller to ensure accurate and constant amount of sizing.
3. Solvent-free composite characteristics. Compared with traditional dry method, solvent-free compound has many advantages in reducing cost, improving product quality, environmental protection, production safety and stability, etc. It is a kind of production worthy of advocacy and practical value. the way. Table 1 lists the performance comparison between solventless composite and dry composite.
3.1 Reducing the production cost The solvent-free composite equipment does not need to dry the drying tunnel, so the structure is compact, the occupied space is small, the equipment cost is low, and the cost of the composite film production can be significantly reduced.
3.2 Less rubber compound, low cost of rubber compounding. The coating amount of solvent-free composite unit area is about 40% of dry compounding. Although the relative cost of solvent-free composite adhesive is relatively high, the comprehensive cost is reduced by 30%. Area composite products have low production costs.
3.3 The equipment consumes low energy. The solvent-free equipment does not have a drying tunnel. It does not need to pass the drying tunnel to remove the solvent in the adhesive, which reduces energy consumption. At the same time, the longer drying oven used to volatilize the solvent in the adhesive eliminates the problem of material curling. The material has a short walk on the equipment and reduces waste generation.
3.4 The production line speed is high, the highest line speed of solvent-free compound is up to 480re/rain, generally about 300m/rain, the compound speed is fast, and the equipment production efficiency is high.
3.5 The product quality is guaranteed and the efficiency is improved. The solvent-free composite adhesive does not contain solvent, so it is not polluting the packaging material, and is more suitable for food packaging. At the same time, the composite film structure dimensional stability is not deformed after the composite. Good; in addition, the solvent-free composite equipment has an in-line corona treatment unit, which has good composite properties for a film with a reduced surface tension and a high lubricant content.
3.6 Reduce labor and safety protection costs, compact equipment, fewer operators, and reduce labor costs. In the solventless compounding process, no solvent is volatilized, and almost no waste material is produced, which avoids pollution of the environment and is conducive to clean production.
3.7 Good safety, solvent-free composite safety, can minimize fire and explosion hazards, no special fire and explosion-proof measures are required in the factory area and production workshop. In summary, the solvent-free composite processing cost is significantly lower than that of the dry process, and the production efficiency is improved, and the food packaging is not polluted, which is very beneficial for improving the market competitiveness of the enterprise.
4 The development of solvent-free composite adhesives, many countries in the world have conducted in-depth research on solvent-free polyurethane adhesives, and developed a variety of practical products that can meet the various performance requirements of food packaging composite film materials.
The development of this series of adhesives can be roughly divided into the following stages: (1) The first generation is a one-component solvent-free polyurethane adhesive, which can be divided into polyether polyurethane polyisocyanate and polyester polyurethane polyisocyanate, which relies on water in the air. The water adhered to the coated film is reacted and solidified, and the water is easily supplied insufficiently to cause curing failure, and at the same time, CO2 generated during curing tends to generate bubbles. (2) The second generation is a solvent-free two-component polyurethane adhesive, which can be cross-linked and cured by mutual reaction of two components to form a macromolecule. In terms of use, a film other than EVA, Nylon, and aluminum foil can be used. (3) The third-generation solvent-free adhesive is a two-component system improved on the second generation (using aromatic polyols to improve high temperature resistance), and can be resistant to high temperature cooking in a composite film containing an aluminum foil structure. It has the advantages of high initial adhesion, low viscosity, low operating temperature, and no limitation on the composite substrate. It can solve the problem of poor heat sealing of E and Nylon by the second generation adhesive, and the film with strong barrier is easy to wrinkle. Or the problem of easy peeling has also been solved.
(4) The fourth-generation UV-curable solvent-free adhesive, due to the continuous speed increase of the laminating machine, makes the curing speed of the general adhesive difficult to adapt, so the UV curing adhesive came into being. At present, the cationic curing products are mainly acid-catalyzed epoxy systems. Under the irradiation of ultraviolet rays, the photoinitiator of the adhesive decomposes, and the epoxy block polymerization is initiated to obtain a three-dimensional crosslinked structure of the epoxy resin. Under the premise of selecting an appropriate UV generator, the adhesive can quickly compound the polyester film and achieve a relatively high bonding strength in a few minutes to an hour, allowing the post-processing to proceed smoothly.
4.2 Characteristics of solvent-free polyurethane adhesives. One-component solvent-free adhesives are generally NCO-terminated polyisocyanate prepolymers. The curing process is completed by moisture. See Figure 3. The one-component adhesive after cross-linking curing is elastic. It is resistant to aging and can make the composite have good bonding strength and mechanical properties. However, due to its low molecular weight, the heat resistance is poor (<100 ° C); the curing speed of such adhesives is relatively slow, and it is greatly affected by moisture, and it is easy to generate CO: bubbles, when the coating amount is large or the water supply is insufficient. Poor curing. One-component solventless adhesives are mainly used in paper/plastic composites. The two-component solventless polyurethane adhesive is composed of a main agent and a curing agent. When compounding, the main agent and the curing agent are mixed in proportion, the viscosity is controlled to a suitable range by heating, and then applied to the substrate by a multi-roll coating system. The main components are polyether polyols and polyether polyol prepolymers modified with isocyanate or polyester polyols. A reaction mechanism similar to that of a solvent-based adhesive is shown in Figure 4. The low molecular weight polyether polyol is generally polypropylene glycol, polyoxypropylene triol, tetrahydrofuran propylene oxide copolyether triol, polytetrahydrofuran, and the like, and mixtures thereof. The isocyanate is generally selected from liquid linear hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI), and a tin catalyst may also be used. The low molecular weight polyester polyol may be an aliphatic polyol, a cyclic hydrocarbon polyol, and an aromatic polyol. At present, solvent-free adhesives are generally used in combination with polyester polyethers. Pure polyester type is generally difficult to control, especially solvent-free adhesives resistant to high temperature cooking, while polyether types are limited in terms of bonding properties and high temperature resistance. The third generation of two-component polyurethane solvent-free adhesives currently being developed is designed to be close to the performance of solvent-based adhesives. The third generation of solvent-free polyurethane adhesive products represented by Henkel Liofol has the following performance characteristics:
(1) High initial tack at room temperature conditions / relative to 2 generations;
(2) Basically no anti-seal effect;
(3) There is no restriction on the composite substrate (high slip agent compatibility, EVA, white PE, etc.);
(4) low content of isocyanate free monomer;
(5) Resistant to boiling water and high temperature cooking.
Since the solvent-free polyurethane adhesive has no solvent small molecules, the intermolecular force is large, and hydrogen bonds are formed, and the viscosity is high at normal temperature. The viscosity can be effectively reduced by raising the temperature. However, too high a temperature tends to cause gelation, resulting in a high molecular weight resin, resulting in difficulty in coating or uneven coating. Therefore, it is important to control the temperature at which the adhesive is applied during construction. Generally, the temperature of single-component solvent-free adhesive is controlled at 70 ° C ~ 100 ° C; the coating temperature of two-component adhesive is controlled at 40 ° C ~ 80 ° C. 4.3 solvent-free polyurethane adhesive suppliers, the world's main manufacturers of solvent-free polyurethane adhesives are Germany. Henkel Group, Germany Herberts, Morton, Japan Toyo Ink Manufacturing Co., Ltd. and France's AtoFindley Inc. Domestically, the Beijing Research Institute of Chemical Industry has also developed some solvent-free adhesives through product introduction. 5 solvent-free composite development trends and prospects, after decades of development and application, solvent-free composite technology is very mature. The use of solvent-free adhesive composite film can reduce energy consumption, increase production efficiency, improve product quality, and reduce overall production costs. Because it does not contain solvents, it helps to protect the environment and clean production, and ensures that the composite does not pollute the packaged foods & medicines. In recent years, with the enhancement of product quality and food hygiene and safety awareness in China, solvent-free compounding has been increasingly valued by people in the composite film packaging industry. Many solvent-free composite devices have been in operation in China, and most flexible packaging materials are currently available. Produced with solvent-free adhesives. With the increasing demand for packaging materials such as food in the country and the continuous improvement of production equipment, solvent-free compounding will show a booming situation.
Derma Roller,Microneedle Roller,Beauty Roller
Handsome Beauty Product Co., Limited , http://www.chinabeautyproduct.com