Recently, an industry friend consulted the author a problem. When the company produces paper-plastic or paper-aluminum composite film (using the traditional solvent-based dry composite process), the bond strength is often insufficient, and bubbles and delamination occur during heat sealing. , the solvent residue is too high and so on. Through on-site inspection and analysis, the author finally found a solution to the problem. And this matter has also caused the author to think about it. With regard to paper-plastic or paper-aluminum composites, too many people in the industry know only one, and they don't know the real mechanism. Below, the author analyzes the problems that need to be paid attention to in paper-plastic or paper-aluminum composites. It is expected to help the industry to correctly view the importance of the composite structure production process and to help improve the quality of paper-plastic or paper-aluminum composite packaging.
a problem that needs attention
Objectively speaking, in all dry composite product structures, the bonding process with paper as a composite structure is relatively easy, which has reached consensus in the industry. However, many people in the industry often overlook an important issue, that is, there is a direct connection between the heat sealing of the paper-plastic or paper-aluminum composite film and the composite processing, that is, the setting of composite parameters, the adjustment of the composite process, and the adhesive. Selection may have a direct impact on the heat seal quality of the composite film and the later use of the composite package.
Depending on the type and amount of paper, the heat-sealing temperature set in the heat-sealing section should also be different. In addition, the heat conduction of the paper is relatively slow, so the heat-sealing temperature of the paper-plastic or paper-aluminum composite film is generally set at 200 °C. the above. However, since almost all the paper contains a certain amount of water inside, in the case of a high temperature, the moisture in the paper will instantly become a gas and expand, which causes bubbles and delamination of the composite film. Therefore, in order to ensure the heat-sealing quality of the composite film, the choice of paper-plastic or paper-aluminum composite process and adhesive should not be taken lightly.
How to choose a composite process and adhesive
1. Selection of composite process
Currently, there are three main processes for paper-plastic or paper-aluminum composites: cast composite, dry composite, and solvent-free composite.
The application of the casting compounding process is the earliest, relatively simple and mature, and there is no solvent residue problem, but the bonding strength is not high. Generally, it can only be used for the production of light packaging such as melon packaging, dry roasted and roasted goods packaging, and heavy packaging for salt. It often fails to meet the requirements of use (this is also a disadvantage of the solvent-free composite process).
The traditional dry composite process is much better in bonding strength than the other two processes, and can fully meet the needs of heavy-duty packaging, but it needs to coat a large amount of adhesive, which not only increases the composite production cost, but also is easy. A large amount of solvent residue and incomplete curing are generated.
Therefore, the author believes that the simple composite process selection can not achieve the purpose, the key is to choose the right adhesive to match.
2. Adhesive selection
Paper is a water-absorbent material, and its surface is rough relative to film materials, especially the reverse side of kraft paper. From the point of view of the bonding mechanism, the wet bonding of paper-plastic or paper-aluminum composite using water-based adhesive is the best bonding method. At the moment when the water-based adhesive is in contact with the paper, the moisture is absorbed by the paper, and at the same time, a part of the colloid is followed by the moisture entering the inside of the paper fiber, thereby achieving a good bonding effect. From the point of view of the bonding effect, there are many kinds of water-based adhesives on the market that can meet the composite requirements, but it is still necessary to choose the water-based adhesive according to the characteristics of the composite products. The author believes that the following two aspects can be referred to. .
(1) Application indicators
Different types of water-based adhesives have different preparation methods and production processes, and their chemical and physical properties are also different, that is, the application indexes are different. Water-based adhesive in packaging The more important application indicators in the printing industry mainly include four aspects: bond strength, high/low temperature resistance, moisture resistance and stickiness. Defects such as poor adhesion, degumming, and brittleness of the film that are often encountered in practical applications are basically caused by the failure of the above four application indicators. According to the characteristics of paper-plastic or paper-aluminum composite film, it is recommended to select a water-based adhesive product that is resistant to high temperature and has a strong viscosity.
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