Interpret the selection of substrates and inks for dry composite technology

The composite flexible packaging industry began to develop in the middle of the 20th century, and it has increasingly shown its importance. The composite flexible packaging can not only make the goods undamaged or rot, but also beautiful, easy to store and transport. In recent years, the development speed of China's composite flexible packaging industry has even surpassed that of other industries.

The composite flexible packaging not only maintains the excellent characteristics of the single-layer film, but also overcomes their respective deficiencies. The new characteristics of the composite flexible packaging can meet the different requirements of different packaging contents on the film. According to different materials, we have classified soft packaging: wet packaging, sterilization packaging, vacuum packaging, frozen packaging and so on. According to different production processes, we divide it into a dry compound process, a wet compound process, and an extrusion compound process.

This article systematically discusses the application technology and other issues in the dry compound processing technology. The dry compound soft packaging technology is a necessary method for the manufacture of composite flexible packaging materials. It includes the composite substrate and adhesive (including the dilution used). Agent), composite machinery and processing technology. Therefore, to achieve a good composite flexible packaging effect, all factors that affect the quality of composite flexible packaging must be controlled.

(A) Composite Substrate and Printing Ink

Composite substrates include paper_, aluminum foil, aluminized film, various plastic films such as nylon film, PET, OPP, CPP, LDPE, etc. The most important indicator for the quality evaluation of the substrate is the surface tension of the film or the cleaning of the surface. Degree condition.

1. The aluminum foil used for compounding requires good cleanliness. If there is dust and oil on the surface of the aluminum foil, a barrier layer will be formed, which will hinder the adhesion and affect the composite strength. Therefore, we have a cleanliness requirement for aluminum foil, as if the surface of polypropylene, polyethylene film has a certain surface tension.

2. The surface tension of the plastic film is related to its own nature. When it is compounded, the surface tension of the film is required to be more favorable for the infiltration, leveling, and dispersion of the adhesive on the film surface. In general, the film is subjected to corona treatment prior to shipping to increase the surface tension. If the substrate is not corona treated, or the storage time is too long or for other reasons, the surface tension of the film is reduced, which will affect the composite fastness. . However, it does not mean that the higher the surface tension, the better. If the surface tension is too high, the strength (tensile strength and impact strength) of the film will be reduced, and the quality of the package will be affected.

The determination method is to use a cotton ball to draw the test solution and apply it on a film inclined at 30 degrees to leave a liquid film 1 cm wide and 10 cm long. If the liquid film does not shrink within 5 seconds, it is judged that the film reaches the surface you want to measure. Tension value, such as liquid film shrinkage, there is still a 0.8cm wide liquid film, it is judged to be close to the surface tension value you want to measure, such as the liquid film is completely broken, shrinkage into a grain or strip shape is less than 0.5cm width, It is judged that the film does not reach the surface tension value you want to measure.

3. The auxiliaries used in the film processing must have sufficient stability to avoid the migration phenomenon, otherwise it will affect the composite quality such as strength and heat sealability. In addition, the crystal point phenomenon is likely to occur in the composite. Therefore, the choice of the slip agent and plasticizer, as well as the size and stability of the addition amount, have a great influence on the composite strength.

4. Although the printing ink itself is not a composite substrate, the ink after printing is attached to the film substrate, and the ink has become a whole with the film, so the nature of the ink has a great influence on the composite, such as its adhesives. Compatibility, film formation, fastness, fineness, etc. have a great influence on the strength of the composite; in addition, the amount of residual solvent during printing also has some influence on the composite quality, such as peel strength, odor, sanitation, etc. .

(b) Use of adhesives

There are many kinds of adhesives at present, which can be divided into one-component adhesives and two-component adhesives.

One-component adhesive refers to a single component, and can be used to represent viscous glue without mixing with other components. Currently, rubber is the most common rubber on the market. One-component adhesives are generally used in the compounding of common materials and require less packaging materials. They are currently used in paper-plastic composite packaging. Two-component adhesives are generally used for packaging with high peel strength requirements, vacuum packaging, and retort sterilization packaging.

The two-component adhesive refers to a glue that shows the adhesiveness after the main component and the curing agent are mixed. At present, polyester and polyurethane-based adhesives are generally used. Polyurethane adhesives have good peel strength and shock resistance, and have certain resistance to acids, alkalis, solvents, oils, etc. Another outstanding feature is excellent low temperature resistance. At present, various polyurethane adhesives on the market have different internal molecular structures and different performances due to different manufacturers. Therefore, all kinds of adhesives have their own adaptation aspects and have different adaptability to different structural materials. Use it when choosing. If you need to cook, hot and sour, chemical resistant media, etc., must find the appropriate adhesive, otherwise it is difficult to guarantee the composite strength.

In the preparation of the glue to follow the correct sequence, first add the appropriate amount of diluent to the main agent, and stir evenly, and then add the curing agent and stir. Instead of mixing the main agent and the curing agent together with a thinner, the glue applied to the film during the compounding process is extremely uneven in molecular weight, which can easily cause uneven surface coating and other quality problems. The common point is the crystal point, rubber particles, but also affect the adhesive strength of the adhesive. The main reason is that the speed of the cross-linking reaction of polyurethane adhesives depends on the effective collision between molecules, and at the same temperature and pressure (such as at room temperature and pressure), the effective collision between molecules is related to its concentration. The higher the concentration, the better the probability of effective collisions. The bigger, the faster the reaction. The main agent and curing agent in the absence of diluent, the high concentration, the reaction speed, especially in high temperature and humidity weather, a longer time will generate larger molecules, causing the adhesive to increase the local viscosity. When the diluent is added first, the concentration decreases, and the reaction rate becomes slower, which is favorable for composite coating.