Application of adhesives 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 commodities in the supermarket, it can be learned that various kinds of beautiful plastic flexible packaging have become 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, as the country vigorously advocates 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, as far as possible the use of some easy post-treatment materials, so that the packaging can be recycled and reused, paper and plastic composite packaging came into being. 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 very good. The betel nut and salt packaging generally use OPP printing, paper, and/or PE (CPP). The tea bag packaging generally uses a paper printing composite CPP aluminum coating structure. The melon seed bag packaging generally uses a paper printing composite PE structure.

Sporadic paper-plastic composite bags emerged more than ten years ago. The adhesive used in the compounding process was a one-component adhesive with toluene as the solvent. With the enhancement of national hygiene awareness, one-component adhesives using toluene as the solvent were used. Because it does not meet the hygienic requirements for food packaging, it was gradually replaced by two-component polyurethane adhesives. 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, but when two-component polyurethane adhesives are used in paper-plastic composites, they are used improperly and often have some quality problems. The most common ones are poor peel strength and foaming at heat seals. , curling, etc.

Many of the reasons for the quality problems are mutual influences, such as blistering at the heat seal, poor peel strength, and creases. Therefore, when we use two-component polyurethane adhesive composite paper and plastic, in the compounding should pay attention to the following questions.

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

2, the paper surface is rough, more pores, relative to the plastic composite, the amount of glue is relatively large, otherwise it will affect the composite strength or produce bubbles.

3, the use of composite paper moisture is too large, it will also cause the composite film blistering.

The author once met a case in Hunan. A soft package manufacturer produced a paper-plastic packaging bag that was packed with betel nut products. The structure was OPP printing, paper, and/or PE. The composite product had no appearance or peel strength. Can be picky, but in the process of making bags, there are bubbles appearing in the heat-sealing area. This phenomenon occurs in the position of the middle hot knife, and no air bubbles appear in the heat-sealed areas on both sides. Through analysis, the reason is that this composite film has too high moisture content in the paper, and the water vapor expands during the heat sealing. The moisture at the heat seals on the two sides can run out of the incision, and the water vapor can only be heard due to no incision in the middle. Bubbles inside. The bag making process of the package is two bags that are formed at one time in the bag making process. The hot knife on both sides is narrow, and the middle hot knife is wider. After the heat sealing, the bag is cut into two bags. Bubbles are generated in the middle of the wide heat seal, and the other side of the heat seal will not appear bubbles. Later, through adjustment, when the bag was made, the composite film was first cut with a blade in the middle of the two bags, and then the air bubble disappeared by heat sealing.

4. Because the polyurethane adhesive is a reactive two-component adhesive, the relative initial adhesive force is poor in the composite paper. After compounding the plastic film, the drying temperature should not be too high, the tension should not be too high, and the composite roll temperature should not be too high. 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, waterborne adhesives from Zhongshan Kanghe and Beijing Gaomeng. Has been launched in the market. This will affect the transformation of some paper-plastic composite flexible packaging. Currently, waterborne acrylate adhesives and water-based one-component polyurethane adhesives have been successfully launched on the market. Compared to two-component polyurethane adhesives, the compounding cost is lower and the composite odor is smaller, which is increasingly favored by flexible packaging manufacturers.

Existing waterborne adhesives have the following advantages:

1. The paper-plastic composite film with water-based adhesive is relatively smooth, curling rarely occurs, and the adaptability is good.
2. The water-based adhesive compound product has good hygienic performance, no residual solvent, convenient cleaning and simple operation.
3. The initial peel strength of the composite product is good. After the machine matures for 1 to 2 hours, it can be slit and rewind.
4, to solve the paper-plastic composite film prone to blistering, wrinkling phenomenon.
5. Solvent-free evaporation (volatilization of water) improves the composite environment.

From the technical point of view of current water-based adhesives, the disadvantage of water-based adhesives is that the peel strength is lower 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 strength. Higher composite products, plastic transparent packaging and boiled cooking packaging.

From the current soft 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.