In the label industry, the ink layer of the printed label is not scratch-resistant, so it usually requires protection after printing. When varnishing fails to achieve the desired brightness or matte effect, lamination is the most direct method. Lamination involves heating and pressurizing a plastic film coated with adhesive onto the printed surface of the label. After lamination, the label is covered with a layer of plastic film, making the surface smoother and shinier. This not only extends the label's lifespan and improves its gloss and firmness, but also provides protective effects such as waterproofing, moisture-proofing, anti-fouling, wear resistance, and chemical corrosion resistance.
However, labels often encounter issues after lamination, such as lamination bubbles, impurities, and other problems that complicate usage. In this article, the author introduces several common lamination issues based on years of practical experience, hoping to help enterprises prevent these problems before they occur.
A. Lamination Bubbles
Film Quality Problems
Some film materials are of poor quality when they leave the factory and may already contain bubbles. These bubbles typically occur in the glue layer of the film itself. When encountering such defective raw materials, the solution is to frequently check during the production process, identify the issues in time, and replace the materials as necessary.
1. Uneven Surface of the Material
The uneven surface of the self-adhesive label material coated with film can also cause lamination bubbles. Since film materials are applied over the surface of the printed self-adhesive label, any unevenness on the label's surface may lead to bubbles. There are various reasons for uneven surfaces, such as defects in the material or poor printing quality.
Solution: Carefully observe the lamination bubbles to identify any patterns, and check whether the surface of the self-adhesive label is flat under different lighting conditions. If any uneven areas are found, verify whether the location of the bubbles corresponds to these uneven spots.
If the bubbles align with the irregularities, it is likely that the uneven surface of the self-adhesive label material is causing the lamination bubbles. Next, investigate the root causes of the surface irregularities, such as foreign objects on the paper pressing roller that may create pits, or defects in the raw materials. Based on the findings, develop a solution to thoroughly address the issue.
2. Aging of the Pressure Roller
As mentioned earlier, an aging pressure roller may fail to press the film material and printed label together effectively, leading to bubbles.
Solution: Check for signs of aging in the pressure roller. If wear is detected, replacing the pressure roller will resolve the problem.
B. Coating Impurities
1. Dirty Material Surface
Dirt, dust, paper fibers, and paper scraps on the surface of the self-adhesive label material can cause coating impurities. Therefore, the material's surface must be cleaned during the production process.
Solution: A dust cloth or dust roller can be used to remove contaminants. The dust roller, which features a weakly sticky polyurethane roller, effectively bonds dust to the surface of the material, reducing dust issues during printing and coating. Notably, some printing machines on the market already come with dust rollers as a standard feature, reducing the need for additional measures.
Additionally, paper-based self-adhesive materials may generate paper powder, which can lead to lamination impurities. Paper powder often arises due to the insufficient surface strength of the material, making it difficult to fully remove. When encountering low-surface-energy materials, and if replacing the material isn't feasible, bottom coating can be a useful approach. First, print a layer of ink or diluent on the material's surface, and then print other colors. This process significantly reduces the adhesion of paper fibers, improving both the printing quality and the lamination quality.
First, print a layer of ink or diluent on the surface of the material, and then print other colors. This can significantly reduce the adhesion of paper fibers, improving not only the printing quality but also greatly enhancing the quality of subsequent lamination.
2. Printing Floating Dust
The quality of the printing workshop environment has a significant impact on lamination quality. If there is too much dust in the workshop, it can lead to lamination impurities. In principle, you should change your shoes before entering the printing workshop and mop the floor at least twice a day to ensure cleanliness and minimize dust generation.
3. Printing Static Electricity
When printing on film self-adhesive materials, a lot of static electricity is generated. Static electricity can attract dust from the workshop environment, causing impurities in the lamination process. Therefore, in addition to keeping the workshop clean, it is necessary to control the humidity. Ideally, the relative humidity should be maintained at around 50-60%. For enterprises with sufficient resources, it is recommended to use industrial humidifiers to regulate workshop humidity. For enterprises without such conditions, mopping the floor can help mitigate static electricity.
C. Lamination Curling
1. Lamination Tension
Generally speaking, there are two main types of label curling after lamination: upward curling and downward curling. If the label curls upward, it means the film tension is too high; if it curls downward, the film tension is too low. During production, the tension of the film changes continuously. When the film is first unrolled, the tension is relatively low. The closer the film gets to the core of the roll, the greater the tension.
Therefore, during lamination, the film tension needs to be adjusted accordingly. Increase the tension when unrolling the film, and reduce it when the film is near the end of the roll. Here's a method to check if the lamination tension is correct: after lamination, use a utility knife to cut the lamination material into several pieces according to the size of the finished label. Then, remove the label from the base paper to check if it lies flat.
If the label is flat, it means the film tension is correct. If the label curls up or down, it means the film tension is inappropriate and needs adjustment according to the specific situation.
2. Equipment Issues
The design of the laminating device in some older printing equipment is relatively simple, and the laminating tension cannot be adjusted, or the adjustment range is limited. This can cause problems for the operator. If the laminating tension is inappropriate, it cannot be effectively adjusted, which can lead to curling issues.
Many modern printing machines now use servo motors to adjust laminating tension, which effectively addresses this problem. Therefore, selecting the right laminating equipment is crucial.
