The causes and improvement solutions for the insufficient water-boiling resistance of flexible packaging composite films

Water boiling and high-temperature steam cooking packaging are the mainstream packaging forms for cooked foods, sauces, and marinated products, which have strict requirements for the water, heat, and hydrolysis resistance of polyurethane laminating adhesives. After water boiling, problems such as blistering, delamination, whitening, and a sharp drop in peel strength occur in the composite films, which are the most common failure forms in medium-high temperature steam cooking packaging, directly leading to leakage of the packaging, bag rupture, and product deterioration.

 

The core of water boiling failure lies in the insufficient crosslinking density of the adhesive layer and poor hydrolysis resistance. Ordinary general-purpose polyurethane laminating adhesives have a loose crosslinking structure, and water molecules can easily penetrate the adhesive layer, destroying the intermolecular forces, causing the adhesive layer to soften and detach. Low-quality adhesives contain a large number of low-molecular chain segments and hydrophilic groups, which are prone to hydrolysis and breakage in high-temperature water environments, completely losing their adhesive ability.

Inadequate process control will further exacerbate the water boiling failure. Deviation in the ratio of two components, uneven mixing of adhesives, insufficient curing temperature and time, will all cause incomplete gelation of the adhesive layer, with a large number of unreacted active groups, and rapid failure upon contact with water. Low coating amount and thin adhesive layer cannot form a dense waterproof protective layer; excessive humidity in the workshop causes slight hydrolysis of the adhesive, which also significantly reduces the water boiling resistance.

 

Improving the water boiling resistance requires the use of special high-temperature steam cooking polyurethane laminating adhesives, which have a high-density crosslinking structure that can resist the penetration of high-temperature water molecules. Precise control of adhesive ratio in production, ensuring sufficient curing reaction, improving the density and hydrolysis resistance of the adhesive layer. At the same time, matching standard coating dry weight and strictly controlling the humidity of the production environment, from raw materials and process to ensure the stability of the composite film's water boiling and steam cooking conditions.