Generally speaking, the outer layer material of composite packaging materials should have a high melting point, good heat resistance, not easy to scratch or grind, good printing performance, and good optical performance. Commonly used materials include paper, aluminum foil, glass paper, polycarbonate, nylon, polyester, polypropylene, etc.
The inner layer material should have properties 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 usually uses materials with good properties such as gas and moisture barrier, light shielding, and high mechanical strength, such as aluminum foil, polyvinylidene chloride, glass paper, paper, polyethylene, etc.
Adhesive is applied between layers for bonding. Generally, solvent based thermosetting polyurethane adhesive is used between the treatment layer and the middle layer, and modified polypropylene lotion adhesive or specially modified carbonyl propylene copolymer resin is used between the inner layer and the middle layer. The adhesive used for the outer layer 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, odorless, and does not affect the nutritional content of the food. It can effectively maintain the color, aroma, and taste of the food.
In recent years, foreign countries have developed a method of uniformly coating a layer of coating agent on the surface of substrate films to improve the airtightness, oil resistance, and chemical stability of packaging materials, making them suitable for various food packaging applications. Common coating agents include polyvinylidene chloride resin and polypropylene polyvinylidene chloride resin. The coating methods include single-sided coating and double-sided coating.
