Composite aluminum foil pasting device and method
The bonding of the composite aluminum foil is carried out on a bonding machine, which is provided with an open reel of aluminum foil and paper (or plastic film), a take-up shaft of a composite aluminum foil, a plate for holding an adhesive, and a roller system for applying an adhesive, and It includes a guide roller, a flattening roller, a pressure roller, a heating roller, a cooling roller, and a temperature and tension adjusting device.
There are three methods of sticking composite aluminum foil: wet method, dry method and thermosetting method.
Wet bonding is a method in which a water-based solvent or a water-dispersible binder is used to adhere an aluminum foil and a composite layer together in a wet state, followed by drying to evaporate water, and thus the composite layer is required to have a certain gas permeability and porosity. .
Wet bonding is commonly used for crepe paper. The binder should be soluble in water or diluted with water. They can be protein-based binders such as glue, animal glue and casein. They can also be carbohydrate-based binders such as starch, dextrin and cellulose. An organic or inorganic binder such as water glass, acrylic acid, denatured vinyl acetate, and ethylene-vinyl acetate copolymer may also be used. The binder is often neutral, but it can also be slightly alkaline, slightly corroded to the aluminum foil and adhered firmly.
More water used in the binder is water glass (sodium silicate, foaming base) and vinyl acetate. Water glass is cheap, but becomes brittle after drying and turns yellow after long-term resettlement; vinyl acetate has strong adhesion, softness and water resistance, but the price is higher.
Dry bonding is used for the bonding of airtight plastic films. There are three types of binders: solvent type such as vinyl acetate and vinyl chloride; fiber type such as nitrocellulose, acetaldehyde cellulose, and formaldehyde cellulose; and copolymers of synthetic rubber and propylene resin.
The dry bonding first dissolves the binder in a volatile solvent such as acetone and ethanol, coats it on an aluminum foil, dries it, and then presses it together with the film under a certain pressure. Considering that the drying temperature (about 240-250 ° C) exceeds the temperature resistance of the plastic film and the physical and chemical effects of the solvent on the plastic film, the binder is usually coated on the aluminum foil. In order to improve the adhesion fastness, the plastic film is corona treated before being pasted.
When wet and dry paste, the type, concentration, viscosity, solid content (kg/m3), operating temperature and coating amount of the binder affect the adhesion fastness and operation speed, and should be based on the composite layer material. Characteristics to determine.
Thermosetting bonding is divided into two types: wax bonding and polyethylene bonding.
Wax bonding is the application of molten paraffin as a sticking agent to the aluminum foil. According to the melting temperature of the wax during processing, it can be divided into low melting point (66-99 ° C), medium melting point (100 - 149 ° C) and high melting point (150 - 230 ° C) adhesive. In order to prevent surface agglomeration, about 5% of polyethylene can be added to the paraffin, and the use temperature is 8 ° C higher than the cloud point. Paraffin paper foil has good elasticity and flexibility. It can be used to package desserts such as candy, snacks, butter, bread, etc. It can also be used to package small metal products, instruments, instruments and photographic equipment.
When the polyethylene is pasted, since the melting point of the polyethylene is higher than that of the wax, the roll coating cannot be used, and the extrusion coating method is adopted: the granular polyethylene is continuously added to the screw extruder, and the mixture is heated and softened. It is extruded from the gap of the mold, coated between paper and aluminum foil, and pasted together. Polyethylene is divided into three grades according to density, medium and high. Low-density polyethylene should be used for bonding. The melting temperature is 260-280 ° C, the preheating temperature is 310 ° C, and the bonding temperature is 205 ° C. The temperature should be controlled when pasting. The fastness of the paste is related to the thickness of the coating, generally 0.01-0.07 mm, and the adhesion is thick. In addition, this method preferably uses a degreased soft aluminum foil. Since the pasting temperature is high, it can also be directly pasted with the hard aluminum foil which is not degreased. At this time, the temperature and speed should be mastered, and in addition to ensuring the firmness of the sticking, the productivity should be high.