There are two labeling molding methods for in-mold labeling: blow molding and injection molding. For injection molding in-mold labeling, an automated manipulator attaches the label to the inner wall of the mold. After the mold is closed, the mold is injected and filled. The hot-melt adhesive resin on the back of the in-mold label is melted by the high temperature of the resin, so that the label and container are integrated. , 80% of in-mold labeling in Europe is through injection molding.

In the in-mold labeling technology, the main influencing factors include labels, molds, robots, and molding equipment. The most important one is the injection production equipment.

1、Label

Labels are a very important link in production. The quality of the label is directly related to the quality of the product. The most important impact on the label is printing. If the ink of the label is not good, it will easily cause the ink to contaminate the mold, resulting in The product is of poor quality.

(a) Composition. Labels can be roughly divided into three layers: sheet (usually polyethylene terephthalate or polycarbonate), ink, and adhesive (mostly a special glue). When the injection molding is completed, the film and plastic are integrated, with the sheet on the outside, and the surface of the sheet is generally hardened.

(b) Sheet forming. Sheet material is the key to the success or failure of the in-mold labeling mold. Generally, the material of the sheet material is ethylene terephthalate, but also organic glass (PMMA) and polycarbonate. However, polyethylene terephthalate has excellent molding and processing, and its surface gloss and wear resistance can meet customer requirements. Therefore, it is widely used. Ethylene terephthalate sheets with a thickness of 125 μm are the most commonly used. . In the heat setting process of the sheet, temperature control is very important, otherwise it will be easily deformed and the scrap rate will be high. The upper and lower molds of the heat setting machine have heating plates to maintain a constant temperature during operation. After the movable heating plate is placed into the sheet, the top of the sheet is moved to preheat the sheet and make it soft before the mold can be closed for heat setting. The size of the sheet is a little smaller than the size of the final part. Generally, the size of the sheet is 0.02 to 0.03 mm smaller than the size of the part on one side. The sheet is not only easy to place into the cavity, but also can be fully stretched.

(c) Ink. Ink is also very important for in-mold labels. Before selecting ink, the adhesion, scratch resistance, chemical resistance and other properties of the ink on the label material should be tested according to the requirements of the final application. First, it must ensure good printing adaptability, secondly, meet the performance requirements of each stage (printing, labeling and final use), and finally require low cost and environmental protection. Labels have higher requirements for the abrasion resistance of the ink layer. Compared with solvent-based ones, UV ink has higher ink layer strength and is more suitable for in-mold labels. Labels for injection molding require high pressure during injection molding, so the air between the label and the bottle can be discharged without the need for an embossed or frosted surface on the back of the material. Labels for injection molding generally use an electrostatic label suction process in the mold. Because the pressure generated during injection molding is very large, if a vacuum label suction process is used, the label will be broken down, thus affecting the continuity of production.

2、Mold

The quality of mold design is directly related to the output, quality and life of the product, because molds account for a large part of the entire IML investment.

(a) Film forming mold design. Forming mold size design formula: When male molding is matched with female mold injection molding or female molding is matched with male mold injection molding, the size of the molding mold is equal to the size of the injection mold, the sum of the thermal expansion and film shrinkage of the injection mold at 60 to 80°C minus the working temperature of the mold Thermal expansion and film thickness under the conditions; when male molding is matched with male mold injection molding or female mold molding is matched with female mold injection molding, the mold size is equal to the size of the injection mold, the sum of the thermal expansion of the injection mold at 60 to 80°C and the film shrinkage minus the working temperature of the mold thermal expansion below. When the molding mold and the injection mold use the same material and operate at similar temperatures, the thermal expansion of the injection mold at 60 to 80°C and the thermal expansion of the molding mold at the operating temperature can cancel each other out. The formed film fillet must match the fillet of the injection mold or the slightly smaller fillet of the film must be stretched to match the fillet of the injection mold.

(b) Injection mold design. Generally, the shrinkage rate of acrylonitrile-butadiene-styrene copolymer and PMMA is 0.5%. If it is used as an in-mold labeling mold, the surface of the product is covered with a layer of polyethylene terephthalate film. Obviously the thermal shrinkage is different. The shrinkage rate of in-mold labeling injection molding products is smaller than that of ordinary molds, and 0.3% is more suitable. This is because the plastic substrate is wrapped in sheets during injection molding, which hinders the shrinkage of the plastic. In order to reduce problems such as vibration and deformation during molding, high-rigidity metal materials, such as H-13, are often used in mold manufacturing, but the cost is 20% higher than that of standard molds. Suitable reinforcement ribs and template thicknesses can also be used to improve mold rigidity.

3、Injection robot

In the entire production, the robot also plays a very important role. When placing labels, the robot must ensure that the labels are placed in the correct position to avoid relabeling of the product. Among them, the coordination and consistency of signal communication between the automated manipulator and the injection molding machine and the electrical interlock safety protection function are particularly important, which are related to the safety of the mold and manipulator and the efficiency of the entire production line. At the same time, the in-mold labeling process requires the accuracy of the robot to embed the label into the mold within approximately (±0.2) mm. It also requires high operating precision and good stability.

4、Injection molding equipment

Injection molding equipment plays a vital role in in-mold labeling production. Since the labeling system is a fully automated system, its requirements for the molding equipment are fast injection speed, short molding cycle, high injection pressure, large mold opening stroke, and stable production, especially the accuracy and accuracy of the injection molding machine. Stability, short production cycles and low wear rates are paramount. If the machine stability is not good, the accuracy of the mold opening position will decrease, resulting in an increase in defective products. Since the wall thickness of in-mold labeling containers is generally less than 1.0 mm, the minimum requirement for an injection molding machine is an injection speed of 450 mm/s and an injection pressure of 300 MPa.

Injection molding machines generally use servo closed-loop control to improve control accuracy, while adding a pressure accumulator to increase injection speed. The opening and closing of the template must be fast and stable. A proportional valve is used to open and close the mold, which can exert a braking function.