The adhesive of the composite aluminum foil is carried out on the adhesive machine, which is provided with an open scroll of aluminum foil and paper (or plastic film) and a winding shaft of the composite aluminum foil, a plate for holding the binder, a roll system for coating the binder, and also includes a guide roller, a flattening roller, a pressing roller, a heating roller, a cooling roller and a temperature and tension adjustment device.

The adhesive methods of composite aluminum foil are wet method, dry method and thermosetting method.

Wet bonding

Wet bonding is a method of pasting aluminum foil and composite layer together in a wet state with water solvent or water dispersed binder, and then drying and evaporating water, so the composite layer is required to have a certain permeability and porosity.

Wet bonding is often used for laminating. Binders should be soluble in water or dilute with water. They can be protein binders such as glue, animal glue and casuran, or carbohydrate binders such as starch, dextrin and cellulose. Organic or inorganic binders such as water glass, acrylic acid, denatured vinyl acetate and ethylene-vinyl acetate copolymers can also be used. The binder is usually neutral, but it can also be slightly alkaline, which corrodes the aluminum foil slightly and thus sticks firmly.

The most used binders are sodium silicate (sodium silicate, foaming alkali) and vinyl acetate. Water glass is cheap, but it becomes brittle after drying and turns yellow after long-term storage. Vinyl acetate is strong, soft and resistant to water, but it is expensive.

Dry bonding

Dry bonding is used to bond plastic films that are not breathable. Binder is divided into three kinds: vinyl acetate, vinyl chloride and other solvent-based; Cellulose nitrate, acetaldehyde cellulose, formaldehyde cellulose and other fiber types; Synthetic rubber and acrylic resin copolymer and other types.

Dry bonding first dissolve the binder in a volatile solvent, such as acetone and ethanol, coated on aluminum foil, dried, and then pressed together with the film with a certain pressure. Considering that the drying temperature (about 240 -- 250 ° C) exceeds the temperature tolerance of the plastic film and the physical and chemical action of the solvent on the plastic film, the binder is usually coated on the aluminum foil. In order to improve the pasting fastness, the plastic film should be treated by corona before pasting.

In wet and dry pasting, the variety, concentration, viscosity, solid content (kg/m3), operating temperature and coating amount of the binder all affect the bonding fastness and operation speed, which should be determined according to the characteristics of the composite layer material.

Thermosetting bonding

Thermosetting bonding is divided into two kinds: coated wax bonding and coated polyethylene bonding.

Wax-coating bonding is to paste the paper onto the aluminum foil with molten paraffin as the adhesive. According to the melting temperature of wax during processing, it can be divided into low melting point (66 -- 99℃), medium melting point (100 -- 149℃) and high melting point (150 -- 230℃) adhesive. In order to prevent the surface caking, about 5% polyethylene can be added to the paraffin, and the use temperature at this time is 8 ° C higher than its turbidity point. Paraffin foil has good elasticity and flexibility, can be used for packaging candy, snacks, cream, bread and other cooked food, can also be packaged small metal products, meters, instruments and photographic equipment.

When applying polyethylene paste, because the melting point of polyethylene is higher than the wax, it can not be used for roller coating, and the extrusion method is used for coating: the granular polyethylene is continuously added to the spiral extruder, heated and softened, extruded from the gap of the mold, coated between the paper and the aluminum foil, and they are pasted together. Polyethylene is divided into low, medium and high 3 grades according to density. Low density polyethylene should be used for bonding, the melting temperature is 260-280 ℃, the preheating temperature is 310℃, and the temperature of the paste part is 205℃, and the temperature should be controlled when pasting. Paste fastness is related to the thickness of the coating, generally 0.01-0.07mm, thick paste fastness is large. In addition, this method is best to use degreased soft aluminum foil. Due to the high pasting temperature, it can also be used to paste the hard aluminum foil without oil, at this time, the temperature and speed should be mastered, in addition to ensuring the firm paste, but also to achieve the highest productivity.

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