Discussion on the most popular factors affecting t

2022-10-02
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Discussion on the factors affecting the internal labeling and molding of injection mold and product design

people used to focus on the function of products. With the improvement of living standards, the consumer market has gradually developed to high quality, and consumers have higher requirements for the appearance and even texture of products, which makes appearance packaging particularly important. At present, the function, composition, manufacturer, shelf life, trademark and advertising language of the goods contained in the container are expressed on the packaging container products separately in the production process, that is, the products are made first, and then processed in the appearance. The common methods include printing, heat transfer printing, pad printing, vacuum electroplating, coating, etc. these methods not only add more processes to the process, making the program complex, but also because of the machines required by additional processes Labor and working time increase the production cost of products

with the improvement of the automation of injection molding equipment, a new type of in mold labeling (IML) technology is popular at home and abroad

in mold labeling products are generally favored by the industry because of their unique advantages in high definition, good three-dimensional sense, surface scratch resistance, increasing the aesthetics of packaging containers, improving economic benefits, environmental protection, and enhancing anti-counterfeiting. The following mainly introduces the process of internal labeling of injection mold, key points of mold design, common defects of molded thin-walled shell products and improvement methods

1 in mold labeling molding process and influencing factors

1.1 molding process

in mold labeling has two labeling molding methods: blow molding and injection molding. For in mold labeling of injection molding, the automatic manipulator attaches the label to the inner wall of the mold, injects and fills the mold after closing the mold, and melts the hot-melt adhesive resin on the back of the in mold label with the help of resin at high temperature, so as to integrate the label and the container. 80% of in mold labeling in Europe is through injection molding

1.2 influencing factors of in mold labeling

in the technology of in mold labeling, the main influencing factors include labels, molds, manipulators and molding equipment, of which the most important is injection molding production equipment

1.2.1 label

label is a very important link in production. The quality of the label they hope to sign is directly related to the quality of the product. The most important impact on the label is printing. If the inking property of the label is not good, it is easy to cause ink pollution to the mold, resulting in poor product quality

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

(2) sheet forming. Sheet material is the key to the success or failure of the in mold labeling mold. Generally, the material of sheet material is ethylene terephthalate, as well as organic glass (PMMA) and polycarbonate. However, polyethylene terephthalate has excellent molding and processing, and its surface gloss and wear resistance can also meet customer requirements. Therefore, it is widely used with a thickness of 125 μ M ethylene terephthalate sheet is the most commonly used. In the process of sheet heat setting, temperature control is very important, otherwise it is easy to deform and the scrap rate is high. The upper and lower moulds of the heat setting machine are equipped with heating plates to maintain a constant temperature during operation. After the movable heating plate is put into the sheet, move the top of the sheet to preheat it to make it soft, and then close the mold for heat setting treatment. The sheet size should be a little smaller than the final part size. Generally, the sheet size is 0.02 ~ 0.03 mm smaller than the single side of the part size. The sheet is not only easy to be placed in the cavity, but also can be fully extended

(3) ink. Ink is also very important for in mold labels. Before selecting ink, the adhesion, scratch resistance, chemical resistance and other properties of ink on label materials should be tested according to the requirements of final application. First of all, we 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 wear resistance of the ink layer. UV inks have higher ink layer strength than solvent based ones, which is more suitable for in mold labels. The label used for injection molding needs large pressure during injection molding, so the air between the label and the bottle body can be discharged without the embossing or frosted surface on the back of the material. The label for injection molding generally adopts the electrostatic label suction process in the mold, because the pressure generated during injection molding is very large. If the vacuum label suction process is adopted, the label will be punctured, thus affecting the continuity of production

1.2.2 mold

the quality of mold design is directly related to the output, quality and life of products, because mold accounts for a large part of the investment of the whole IML

(1) film forming mold design. Design formula of molding mold size: when male mold molding with female mold injection or female mold molding with male mold injection, the molding mold size is equal to the size of the injection mold, the sum of the thermal expansion and film shrinkage of the injection mold at 60 ~ 80 ℃ minus the thermal expansion and film thickness of the molding mold at the working temperature; When male mold molding with male mold injection or female mold molding with female mold injection, the size of the molding mold is equal to the size of the injection mold, the sum of the 60 ~ 80 ℃ thermal expansion and film shrinkage of the injection mold minus the thermal expansion of the molding mold at the working temperature. When the molding mold and the injection mold use the same materials and work at similar temperatures, the thermal expansion of the injection mold at 60 ~ 80 ℃ and the thermal expansion of the molding mold at the working temperature can offset each other. The formed film fillet must match the fillet of the injection mold, or the fillet with a smaller film must be extended to match the fillet of the injection mold

(2) injection mold design. Generally, the shrinkage of acrylonitrile butadiene styrene copolymer and PMMA is 0.5%. If you make an in mold labeling mold, because the product surface is covered with a layer of polyethylene terephthalate film, the two obviously have different heat shrinkage rates. The shrinkage of the products formed by the in mold labeling injection mold is smaller than that of the ordinary mold, and 0.3% is more appropriate. Because the plastic substrate is wrapped by the sheet during injection molding, which hinders the shrinkage of the plastic. In order to reduce vibration, deformation and other problems in forming, high rigid metal materials, such as H-13, are often used in mold manufacturing, but the cost is higher than 20% of the standard mold. Suitable stiffeners and template thickness can also be used to improve the rigidity of the mold

1.2.3 manipulator

in the whole production, the manipulator also plays a very important role. When placing the label, the manipulator should ensure that the label is placed in the correct position, so as to avoid rebranding of products with 3.3.1 strength level. Among them, the coordination and consistency of signal communication between automatic manipulator and injection molding machine and the safety protection function of electrical chain are particularly important, which is related to the safety of mold and manipulator and the efficiency of the whole production line. At the same time, the in mold labeling process requires the manipulator to embed the label into the mold with an accuracy of about (0.2) mm, and also requires high operation accuracy and good stability

1.2.4 injection molding equipment

injection molding equipment plays a crucial role in in mold labeling production. As the labeling system is a fully automated system, its requirements for molding equipment are fast injection speed, short molding cycle, high injection pressure, large mold opening stroke, and stable production, especially the accuracy and stability of injection molding machine, short production cycle and low wear rate. If the machine is not stable, the accuracy of mold opening position will be reduced, resulting in an increase in defective products. Since the wall thickness of the in mold labeling container is generally less than 1.0 mm, the minimum requirement for the injection molding machine is that the injection speed reaches 450 mm/s and the injection pressure reaches 300 MPa

injection molding machines generally adopt servo closed-loop control to improve control accuracy, while increasing accumulator to improve injection speed. The opening and closing of the formwork must be fast and stable. The proportional valve is used to open and close the formwork, which can play the braking function; In addition, the high rigidity frame is also helpful for braking. The formwork deformation will directly affect the thickness of the mold cavity. If the thickness of the finished product is 0.50 mm, the formwork deformation should be controlled below 0.05 mm. 2 common problems and improvement measures of in mold labeling products

2.1 product deformation

selection of label material shrinkage ratio plays an important role in the production process. The material shrinkage ratio of label paper is different, and the product will be affected and deformed (the bottle body bulges and both sides are concave). At present, the shrinkage of materials used in the in mold label material market after heat is the characteristic of most plastic films, but the shrinkage rates of different films are different. The plastic bottle body will also shrink when it is cooled. When the shrinkage rate is different from the shrinkage rate of the bottle body, the bottle body will be deformed. In order to solve the product deformation, the average thickness of the product is generally required to be less than 1.2 RAM (including the label thickness), and the wall thickness should be as uniform as possible. In addition, by adjusting the injection molding process and optimizing the mold structure design, the problem of product deformation can also be effectively solved

2.2 bubbles

the mold design structure is unreasonable, which is easy to cause product shape changes in the production process, which makes the degradable plastic still in the promotion stage, deformation, bulging, poor exhaust, resulting in bubbles in the labeling process. Unreasonable bottle shape design such as round bottle body and stepped bottle body and uneven labels caused by hot stamping are the main reasons for bubbles. Hot stamping is not easy to produce bubbles, and two hot and cold stamping technologies can be used for in mold labels. In order to avoid convex and concave deformation of the label material in the mold, poor exhaust and bubbles, on the premise that the customer accepts its visual effect, it is recommended to use the cold stamping technology. If the temperature during processing is low, the hot-melt adhesive will soon solidify with the molten plastic parison, and the volatile gas will not be smoothly eliminated to form bubbles

2.3 labeling problem

during labeling, the temperature of the molding compound, injection pressure, cooling temperature and other aspects should be strictly controlled. If the control is not good, the label paper will be separated from the bottle body. The problems in labeling are as follows

(1) rebranding. Two or more pieces of label paper are stuck on the bottle at the same time, which is very rare, but it can lead to the phenomenon of skew label, falling label and so on. The manipulator adsorbs labels in the way of vacuum adsorption. Excessive vacuum suction or excessive friction coefficient between labels are the main reasons for multiple or double labels. Adjusting the vacuum suction of the manipulator and effectively eliminating static electricity are effective methods to solve the problem of re marking

(2) off mark. In the process of transporting the label by the manipulator, it fell out of the suction cup halfway, and was not sent to the mold cavity at all or fell out of the mold cavity due to weak vacuum adsorption

(3) lack of bid. When the machine is started normally, there are no labels on the front and back sides, which is mainly caused by the problems of air pressure and label dropping. To solve the above problems, the first is the selection of labeling manipulator. The labeling accuracy and accuracy of robots produced by different manufacturers for in mold labeling are different, so we should compare them in many ways and choose products with good quality; The second is the choice of labels. The quality of labels produced by different in mold labels is also different. Generally speaking, in mold labels with good stiffness and less static electricity are conducive to the accuracy of label bonding; In addition, the influence of operation process and other factors can not be ignored; Finally, in terms of waste disposal, general methods cannot be used. Because the material of the label is the same as that of the bottle body, the label paper and the bottle body have been completely integrated after one-time molding in the production process. The mechanical properties of the label can still maintain the initial 80% after scraping the label first; 5. Weak acid resistance

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