Analysis of Application of Adhesive for Paper-plastic Composite Flexible Packaging

At present, the development of China's flexible packaging printing industry can be said to be a steady step-by-step rise, and it has become an important pillar industry in China's economic development. From the packaging of various goods in the supermarket, you can learn that a variety of beautiful plastic flexible packaging is becoming the mainstream of commodity packaging.

With the rapid development of flexible packaging, various functional materials are used more and more widely. At the same time, due to the country's strong promotion of environmental protection, many domestic companies have begun to focus on the development of packaging materials that meet environmental requirements, especially materials that can be recycled. Therefore, in the selection of packaging materials, try to use some easy-to-handle materials so that the packaging can be recycled. Paper-plastic composite packaging came into being in this situation. According to investigations, the development of paper-plastic composite flexible packaging in Hunan is fast, and the packaging products include betel nut, salt and other food supplies, and the development momentum is fierce. The development of paper and plastic flexible packaging in Hebei, Fujian and Guangdong is also good. The betel nut and salt packaging generally use OPP printing/paper/PE (CPP) structure. The tea bag packaging generally adopts a paper printing composite CPP aluminum plating structure. The melon seed bag packaging generally uses a paper printing composite PE structure.

The paper-plastic composite bags that emerged more than ten years ago are compounded using a single-component adhesive with toluene as the solvent. With the increase of national health awareness, one-component adhesives using toluene as a solvent have gradually been replaced by two-component polyurethane adhesives because they do not meet the hygienic requirements for food packaging. Therefore, the paper-plastic composite packaging on the market is basically composed of two-component polyurethane adhesives.

Some people say that paper-plastic composites are easier than plastic-plastic composites. However, when two-component polyurethane adhesives are used improperly in paper-plastic composites, they often have some quality problems. The most common ones are poor peel strength, blistering and curling at the heat seal.

The reasons for the quality problems are mostly mutual influences, such as the blistering of heat seals, poor peel strength, and wrinkles. Therefore, when we use two-component polyurethane adhesive composite paper and plastic, we should pay attention to the following issues in the composite:

1. Two-component polyurethane adhesives are reactive adhesives and are extremely sensitive to the amount of water and alcohol in the solvent. At the same time, since the composite paper also has a certain amount of moisture, these will affect the full crosslinking of the polyurethane adhesive. Therefore, great care must be taken in compounding.

2. The surface of the paper is rough, and there are more pores. Compared with plastic-plastic composites, the amount of glue is large, otherwise it will affect the composite strength or generate bubbles.

3. Composite paper with the humidity. Too much moisture can cause blistering of the composite film. The author encountered a case in Hunan, a paper-plastic packaging bag made by a flexible packaging manufacturer for betel products, and the structure is OPP printing/paper/PE. The composite product was impeccable in both appearance and peel strength, but bubbles were found in the heat-seal during the bag making process. This phenomenon occurs in the middle of the hot knife, and there are no bubbles on the sides of the heat seal. The bag making process of forming two bags at a time is adopted. The hot knife on both sides is narrow, and the middle hot knife is wider. After heat sealing, the bag is slit into two bags. The bubbles are generated in the middle of a wide heat seal, and bubbles do not appear on the heat seals on both sides. Later, through the adjustment, during the bag making process, the composite film was first cut with blades in the middle of the two packages, and then the air bubbles disappeared by heat sealing. When the composite film is cut, the moisture content of the paper is too high, and the water vapor expands during the heat sealing. Narrower heat seals on both sides can run out of the incision, and in the middle, due to no incision, water gas can only cause bubbles inside the drum. .

4. Because polyurethane adhesives are reactive two-component adhesives, the relative initial tackiness is poor in composite paper. After compounding the plastic film, the drying tunnel temperature should not be too high, the tension should not be too large, and the composite roller temperature should not be too high. Otherwise it is prone to curling or wrinkling.

As waterborne adhesive technology has become more and more mature, many adhesive manufacturers have introduced waterborne adhesives, such as waterborne acrylic adhesives from Rohm and Haas in Germany, 8830 waterborne polyurethane adhesives from Zhejiang New Oriental, Zhongshan Kanghe, and Beijing Gaomeng's waterborne adhesives. Launched on the market. This will affect some of the changes in paper-plastic composite flexible packaging. Currently on the market water-based acrylate ester adhesive and water-based one-component polyurethane adhesive, compared to two-component polyurethane adhesive, the composite cost is lower, compound Smaller odor, more and more favored by the soft packaging manufacturers.

Today's waterborne adhesives have the following advantages:

1 The paper-plastic composite film with water-based adhesive is relatively smooth, with few curling phenomena and good adaptability.

2 The composite product with water-based adhesive has good hygienic properties, no residual solvent, easy cleaning, and easy operation

3 The initial peel strength of the composite product is good, the next machine matures for 1 hour - after 2 hours can be slit and rewind

4 Solved the phenomenon of blistering and wrinkling of paper-plastic composite film

5. Solvent-free evaporation (volatilization of water) improves the composite environment.

From the technical point of view of current water-based adhesives, the disadvantage is that the peel strength is poorer than that of solvent-based polyurethane adhesives, and the solution is a milky white emulsion. Therefore, it can only be applied to dry food packaging, aluminized packaging, light packaging, and cannot be applied to high-strength composites. Products, plastic transparent packaging and boiled cooking packaging.

From the current flexible packaging market, there are more and more manufacturers using water-based adhesives for aluminum-plated packaging and paper-plastic packaging, which will also be a development opportunity for water-based adhesives.

Author / (Xiao Haiyi)