
Generally speaking, the basic structure of composite materials is that the
outer layer of composite packaging materials should be materials with high
melting point, good heat resistance, less scratches and burrs, good printing
function, and good optical function. Commonly used materials include paper,
aluminum foil, fiberglass, polycarbonate, nylon, polyester, polypropylene,
etc.
The inner layer materials should have functions such as heat sealing, good
adhesion, odorless, non-toxic, oil resistant, water resistant, and chemical
resistant, such as heat-resistant plastic materials such as polypropylene,
polyethylene, and polyvinylidene chloride. The middle layer of composite
materials with three or more layers generally uses materials with good functions
such as blocking gas and moisture, and shielding light, and high mechanical
strength, such as aluminum foil, polyvinylidene chloride, cellophane, paper,
polyethylene, etc.
Adhesive is applied between layers for bonding. Generally, solvent based
thermosetting polyurethane adhesive is used between the outer layer and the
middle layer, and modified polypropylene lotion adhesive or specially modified
carbonyl propylene containing resin is used between the inner layer and the
middle layer. The outer layer adhesive requires high bonding strength, simple
process, and low cost; The adhesive used for the inner layer requires high
temperature resistance, high peel strength, non-toxic, tasteless, and does not
affect the nutritional composition of the food, which can effectively maintain
the color, aroma, and taste of the food.
In recent years, foreign countries have developed a uniform coating agent on
the surface of the substrate film to improve the airtightness, oil resistance,
and chemical stability of packaging materials, making it suitable for various
food packaging. Commonly used coating agents include polyvinylidene chloride
resin and polypropylene polyvinylidene chloride resin. The methods of coating
include single-sided coating and double-sided coating.
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