Analysis of Common Problems in Paper Plastic Film

1 Proposed issue

Since the 1980s, China has widely adopted the internationally popular printing laminating technology to improve the quality of printed products. The so-called "printed film" is a layer of BOPP film laminated on the surface of the printed matter. This technology is widely used in book covers and product packaging boxes. The appearance of the laminating product is smooth, abrasion-resistant and water-resistant, so it is welcomed by consumers. However, due to the improper process or the improper selection of materials in the laminating process, it is easy to cause the phenomenon of “bubbling and wrinkling” on the surface of the laminated film print, which reduces the grade of the printed material and even results in waste products. Over the years, this problem has been plagued by printing film manufacturers, and manufacturers have also caused huge economic losses.

Many people have discussed this, but so far, this phenomenon is still frequent in most manufacturers.

During the years of application and promotion of laminating adhesives, we systematically analyzed and tested this phenomenon, solving the problems for many manufacturers and summarizing them.

2 Cause Analysis and Solution

The key to solving this problem is to understand the causes of foaming and wrinkling, find the crux of the quality problem, and then decide whether to change the process parameters or replace the raw materials. For the nowadays commonly used glue coating process, the equipment is a relatively stable factor. The factors affecting the product quality are only the adhesive, paper, ink (including additives) and process parameters.

2.1 Process parameters

As far as the process parameters are concerned, the main factors affecting the quality of the laminating film are the coating thickness, drying path temperature, vehicle speed, pressure roller temperature and pressure. The temperature of the drying tunnel is too low or the vehicle speed is too fast, so that the solvent in the solvent-based adhesive cannot completely volatilize, resulting in blistering and wrinkling. This has become the consensus of everyone. Therefore, in the production process, everyone should pay attention to the influence of process parameters, ensure that the solvent is completely volatilized, and try to avoid the quality problems caused by this. However, overcoming the drawbacks of process parameters may still cause blistering and wrinkling. Therefore, it is necessary to further explore other influencing factors.

2.2 Adhesives

The quality of the adhesive can directly affect the quality of the laminated product. This is undoubtedly true. Solvent-based adhesives that use high-boiling solvents such as xylene, etc., can make it difficult to completely volatilize after passing through the drying tunnel, resulting in blistering and wrinkling. The adhesive contains water (the appearance of the adhesive is turbid and opaque). It is worth noting that there is no coating on the surface, causing blistering, fogging, and snowflake. Many manufacturers have blistering and wrinkling, and adhesives should be considered first. Therefore, the adhesive film printing factory will strictly control the adhesive, select the high-quality adhesive, and be supplied by a more stable supplier. However, after choosing a good quality adhesive, the same batch of adhesive compounded different prints, some appeared blistering and wrinkling, while others did not. This indicates that the adhesive is not the only factor that causes blistering, wrinkling, and others. Influencing factors.

2.3 Paper

In addition to adhesives and process parameters that can cause blistering and wrinkling, other factors are paper, ink, and additives.

This is often easily overlooked by most people. According to our practice and exploration, these factors are crucial.

As paper, there are offset papers, copperplate papers, and so on. Although different paper quality products have different quality effects, this is based on the requirements of the publisher rather than the laminating process. But there is one factor that cannot be ignored - the humidity of paper (including the body of the book). The paper with a certain humidity is necessary for the printing process. It can adjust the thickness of printing ink and increase the printing speed, but it needs to be overcome for the lamination process. The reason is that the products after lamination tend to pile up and the water vapor is difficult to escape, so that it is easy to cause concentration and blistering under the BO PP film (under the combined influence of other factors). This is also one of the main reasons why it is not easy to blistering a stacked product and it is easy to produce blisters.

Therefore, it is recommended that the manufacturer dry or dry the printed matter for several days before laminating, and then perform lamination.

The humidity of the cover sheet of the book can be controlled. We can dry the pre-laminated film through a drying facility or naturally dry it before relaminating it. However, if the humidity of the text of the body of the book is not controlled, the cover sheet after the film will still appear. bubble.

This is the reason why the cover of the laminated film is not blistering, and the binding of bookbinding books and books is blistering after being stacked for a period of time. To overcome the dampness of the paper in the body of books and magazines, it may be difficult for most manufacturers to do so, but efforts must be made to overcome them.

As a result of the above process control, in addition to reducing moisture, it also includes incompletely dried volatiles in the printing ink.

It is worth noting that we dried the film to be laminating and then laminated the laminated product. We found that some printed products still had blistering and wrinkling. This is not a matter of paper moisture. Therefore, we must look for the cause from a deeper level, namely the ink and its additives.

2.4 Ink and its additives

The influence of ink and its additives on the quality of laminating products is also easily overlooked by most people. Through experiments, we found that inks and their additives have a great impact on the quality of laminated products. The reason is that inks and their additives, especially additives such as varnish, dry oil, diluting agent, dissolving agent, etc., contain high-boiling volatile organic solvents. These volatile organic solvents are used for most adhesives and BOPP films. The effect of dissolving or swelling causes the original adhesive strength of the adhesive to decrease, causing foaming under the action of water vapor and other residual volatile components, and wrinkling of the swelling effect of the BOPP film.

The commonly used paper-plastic compound solvent-based adhesives are mostly one-component rubber type and two-component polyurethane type, and most of them are single-component rubber types. The solvents in the inks and their auxiliaries dissolve or swell the solid components (styrene-butadiene rubber elastomers, etc.) of these adhesives. Therefore, it can be said that the adhesive system should be one of the important criteria for the quality of adhesives. This is the important reason why the results of the same batch of printed materials using different types of adhesive lamination are very different. From this perspective, the type of adhesive is particularly important.

In general, one-component rubber adhesives are more likely to be foamed than two-component polyurethane adhesives, hot melt adhesive precoat films, and aqueous emulsion adhesives that are easily dissolved or swelled by solvents in inks and their auxiliaries. For this reason, we used water-emulsion adhesives for comparative tests and found that the use of aqueous emulsion adhesives for lamination, blistering, and wrinkling problems were basically solved. The reason is that the organic solvent in the ink and its additives has a poor dissolution effect on the solid component (polyacrylate or polyethylene-vinyl acetate) of the glue, and therefore it is not easy to foam, and at the same time, Brightness is much better than one-component rubber adhesives. Due to the presence of the adhesive layer, the residual solvent on the printing surface is isolated from the BOPP film, and thus the wrinkle phenomenon is less likely to occur. In addition, the use of rubber adhesives is also far less resistant to aging than other types of adhesives. Therefore, we recommend the use of emulsion adhesives, two-component polyurethane adhesives, or hot melt adhesive precoats.

2.5 Stapling process

After discussing the factors that may cause quality problems in the laminating process, it is necessary to emphasize on the binding process of books and periodicals. When using PVA solution as the cover (upper cover), the temperature of the hot back process is not too high, otherwise, the adhesive The moisture in the solution quickly evaporates, and the adhesive strength of the adhesive that acts as a composite at this time is reduced, and blistering is also likely to occur. In the hot melt adhesive bonding process, the thickness of the hot melt adhesive is not so thick that the temperature is not too high, otherwise, the same quality problem will occur.

In short, there are many factors affecting the quality of laminating products, such as the factors of process parameters, the factors of adhesives, the influence of paper moisture, the influence of ink and its additives, and the impact of binding processes, etc. Each aspect should be highly valued. . We believe that the most important and most important factor to consider is the type of adhesive and ink (including additives). The above are just our experiences and perspectives. We hope that we can play a guiding role in printing laminated film manufacturers and are willing to further discuss with the people in the industry.




Author: Sun tall Zemin