Material viscosity

      Due to the large amount of adhesive applied to self-adhesive materials, die-cutting is difficult and the probability of problems is high. Therefore, I compared the materials of two suppliers and found that the initial viscosity of the material with the label removed by die-cutting was significantly higher than that of the material without the label removed by die-cutting. By observing the adhesive surface of the two materials through refraction, I felt that the adhesive weight of the former was also significantly greater than that of the latter.

Types of adhesives

      Different adhesives have different compositions, internal stresses, and die-cutting characteristics. Some high-end hot melt adhesive materials have die-cutting characteristics similar to emulsion glue (water-based glue), and there are basically no die-cutting problems; However, some low-end and cheap hot melt adhesive materials often have problems with die-cutting. By comparison, it was found that the label printing company uses the same two materials for the paper surface and whiteness, but the color of the adhesive coating is slightly different, indicating that the adhesives used for the two materials are different.

Bottom paper thickness

      The dimensional accuracy of the die-cutting knife is determined by the thickness of the base paper, so the thickness of the base paper determines the accuracy of die-cutting. Comparing, it was found that the thickness of the base paper of the two suppliers' materials is basically the same.

On site temperature

      On the day of visiting the label printing company, it was cloudy with an outdoor temperature of 4 ℃. The workshop temperature was 8 ℃ at 9am and the highest temperature at noon was 16 ℃. When the workshop temperature is 8 ℃, the die-cutting marks are clearly removed, resulting in significant waste; When the temperature rises to 16 ℃, the phenomenon of die-cutting label shedding is significantly improved, but there are still 10% to 20% label shedding. This phenomenon indicates that the cutting off of the label is related to temperature and environmental conditions.

Precision of die-cutting knife

      When the label falls off during die-cutting, it indicates that there are areas where the adhesive layer is not completely cut through or cut off. One of the reasons for the label falling off is that the adhesive is not completely cut through. The label printing company uses circular magnetic die-cutting blades, and on-site observation shows that the die-cutting pressure has reached its maximum. Due to the fact that the die-cutting blade roller is a shoulder iron, it cannot be adjusted significantly and can only be fine tuned. When the die-cutting pressure has reached its maximum, the die-cutting device can only replace the die-cutting blade with a new one to solve the problem of incomplete cutting of the adhesive.

      Based on the above situation, I have analyzed that some of the materials from the two suppliers have lost their labels during die-cutting, while others do not. The main reason is that the two materials have different adhesive thicknesses; The second reason is that the adhesives of the two materials are different, and their characteristics are also different; The third reason is that low temperature has a greater impact on materials with thick coating, and a smaller impact on materials with thin coating.

Solution

raise the temperature

      Hot melt adhesive is a rubber based adhesive. At low temperatures, the adhesive film is in a semi-solid state, and the tension (cohesion) between the adhesive films is high. Therefore, some of the adhesive films are not completely cut through, and the adhesive used for waste disposal is connected to the adhesive at the edge of the label, and the label is peeled off together during waste disposal. If the temperature of the environment rises, the film of hot melt adhesive becomes softer, the cohesion decreases, and it is easy to break. Even if the adhesive is not completely cut through, the situation of waste labels after die-cutting will be improved. At the same time, as the ambient temperature increases, the initial viscosity of the adhesive increases, which can also increase the release force of the overall material, thereby reducing the phenomenon of label drop during die-cutting.

      The ideal situation is to change the ambient temperature of the production workshop to achieve ideal processing conditions, and pre place the adhesive material at room temperature for 24 hours, so that the material is at the same ambient temperature. But in reality, there are many difficulties for printing factories to do so. In the winter in the south, there are no heating facilities, and insulation in the workshop increases costs. Therefore, the best solution is to increase the surface temperature of the materials during processing.

The surface temperature of materials can be increased through the following measures.

      1. Add drying channels or heating plates to the equipment to increase the material temperature. There are similar devices abroad that activate heating ovens or heating plates in winter to increase the temperature of materials and improve die-cutting processing characteristics. Label printing companies can contact equipment suppliers to add this configuration.

      2. Preheat the adhesive material before processing. Place the materials in a room with air conditioning or heating equipment, preheat them, and use them one by one during die-cutting to ensure the temperature of the materials.