Under the development trend of injection, drawing

2022-08-10
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Development trend of PET bottle injection, drawing and blowing technology (Part 2)

cooling of embryo mold because the crystallization rate of pet is very small, the melt can be cooled quickly, and transparent bottle embryo can be obtained through the crystallization temperature zone quickly. For example, rapidly cooling PET melt at 285 ℃ to 77 ℃ ~80 ℃ can make the crystallinity less than 5%. The bottle embryo obtained by slowly cooling the melt is opaque

in order to make the PET melt with high temperature cool and solidify in a short time, the bottle embryo mold is required to have a high cooling capacity, which can be adjusted by cooling water. When the wall thickness of the bottle embryo is less than 4mm, the cooling water temperature of the mold should be 10 ℃ ~15 ℃, and then the transparent bottle embryo can be obtained; For bottle embryos with wall thickness greater than 4mm, the water temperature should be as low as 2 ℃ ~5 ℃. However, if the mold temperature is too low, sometimes water droplets will form on the mold cavity or mandrel due to condensation, which will affect the molding performance and bottle embryo performance

2). Reheating and temperature regulation of bottle embryo in the reheating process of PET bottle embryo, the bottle embryo is sent to the stretch blow molding machine to make it do continuous rotary movement in the oven to heat it evenly. After the bottle embryo is reheated, the temperature distribution along its wall thickness direction is usually uneven, that is, the outer wall temperature is higher and the inner wall temperature is lower, which is detrimental to the stretching and blow molding of the bottle embryo. It will cause defects such as spherulites, voids or delamination in the bottle wall, which will affect the performance of the bottle, especially significantly reduce the impermeability of the bottle. Therefore, before stretching and blowing the bottle embryo, the temperature distribution of the bottle embryo in the wall thickness direction should be adjusted, that is, through the heat conduction in the bottle embryo wall, the heat accumulated near the outer wall is transferred to the inner wall, and the outer wall is properly cooled due to contact with the outside air. This adjustment can ensure that the bottle embryo has a relatively uniform temperature distribution in the wall thickness direction. In addition, the circumferential stretching ratio of the inner wall of the bottle embryo is larger than that of the outer wall. For example, the inner and outer diameters of the bottle embryo used to stretch the blow molded 1.5L PET bottle (the outer diameter of the bottle body is 85mm) are 18 mm and 26mm respectively, resulting in the circumferential stretching ratios of the inner and outer walls of the bottle embryo being 4.7:1 and 3.3:1 respectively. In order to facilitate stretch blow molding, the temperature of the inner wall of the bottle embryo should be higher than that of the outer wall

one step injection, drawing and blowing also need to adjust the temperature of the bottle embryo, but welcome to call and support! Compared with two-step injection, drawing and blowing, it is easier to adjust the temperature of the bottle embryo, because after the bottle embryo in one-step is cooled by the mold, its thickness direction has a more symmetrical temperature distribution

3). Stretch and blow molding of PET bottle embryo. The bottle embryo should be stretched and blown under appropriate temperature and stretching ratio. For PET bottles (such as carbonated beverage bottles) to bear internal pressure, the total tensile ratio should be 10:1 or greater, in which the circumferential tensile ratio is (4~7):1, and the axial tensile ratio is (1.4~2.6):1. Excessive stretching ratio will cause stress whitening of the bottle

if the orientation temperature of the bottle embryo is set low, the tensile stress will be significantly increased, which will make the PET bottle appear stress whitening; If the orientation temperature is set high, the bottle will appear crystal mist. Pet can be oriented at 88 ℃ ~115 ℃, but in order to obtain bottles with high transparency, the orientation temperature range should be narrower. Some studies have shown that the optimal orientation temperature of pet is about 105 ℃, while others believe that it is 95 ℃. The bottle embryo can be inflated with single-stage compressed air with a pressure of about 2MPa, or two-stage compressed air can be adjusted out of the cluster during use, that is, inject low-pressure (1.0 ~ 1.5MPa) air first, and then inject high-pressure (2.5 ~ 3.0MPa, some up to 4MPa) air after the bottle embryo is inflated to contact the mold cavity, so that the bottle is in close contact with the mold cavity and can be cooled and shaped quickly. The temperature of the stretch blow mold should generally be lower (3 ℃ ~10 ℃), which helps to shorten the forming cycle. Sometimes, in order to improve the heat resistance of the bottle, the mold temperature can be higher (80 ℃ ~105 ℃) to heat set the bottle

development status and trend of pet injection, stretch and blow technology in recent years, the development of pet injection, stretch and blow technology is reflected in increasing output, broadening the scope of application, improving container performance and reducing bottle wall thickness. For example, at present, the maximum output of PET bottle (volume 0.5L) stretch blow molding has reached 60000~65000/h. In order to adapt to the increase of the output of reheating stretch blow molding equipment, bottle embryo injection molding machine manufacturers have been trying to increase the number of mold cavities of bottle embryo mold. The number of cavities of the injection mold for single-layer PET bottle embryo reached 144 four years ago. At present, manufacturers have launched a co injection system with 144 cavities. In addition, in recent years, the manufacturers of stretch blow molding machines are constantly improving the process control and product quality inspection technology of stretch blow molding. Using intelligent detection and closed-loop feedback technology, the stretch blow molding machine can realize automatic adjustment; Installing a camera on the stretch blow molding machine and cooperating with the lighting and other systems can detect the bottle embryo and the defects of the neck, bottom, seal, surface and naked eye of the bottle in real time during the production process. Unqualified containers can be automatically eliminated, and the optical properties of PET bottle embryo can also be detected; The non-contact infrared technology can quickly (6S) detect the wall thickness distribution of the bottle

the main development direction of stretch blow molded PET bottles is to improve their impermeability and heat resistance. This paper mainly introduces the impermeability prevention technology of PET bottles. About five years ago, people had high expectations for impermeable PET beer bottles, thinking that beer could be filled with PET bottles soon, but in the process of implementation, people found that it was much more difficult than they expected. In fact, less than 0.1% of the 250billion beer bottles used in the world in 2002 were PET bottles. Therefore, blow molding manufacturers turn their main efforts to develop impermeable PET bottles for fruit juice, carbonated beverages and hot filling products, and the volume of the bottles is concentrated in 200~1000ml. The packaging requirements of these products are obviously much lower than that of beer

by improving the permeability of O2 and CO2 of PET bottles, the shelf life can be extended and the flavor and nutritional value of beverages can be maintained. At present, the technologies to improve the impermeability of PET bottles can be divided into the following categories

1. Co injection stretch blow molding the bottle embryo formed by this technology has a multi-layer structure, that is, pet is used as the structural layer, and an impermeable layer is set between the inner and outer pet structural layers. At present, about 70% of impermeable PET bottles adopt this multilayer structure. The resins that can be used as impermeable layers are mainly MXD6 nylon and EVOH, and their prices are about $5.5/kg and $7.7/kg. MXD6 nylon is a transparent high impermeability resin, which can withstand the temperature of hot filling; EVOH has higher CO2 penetration resistance than MXD6 nylon, and it also has excellent flavor preservation. In addition, nanocomposite plastic can also be used as the impermeable layer of multilayer bottles. Recently, an updated method has emerged, that is, MXD6 nylon is blended with a cobalt based oxygen scavenger, and then the blend is used as the core material of stretch blow molded multi-layer PET bottles. The shelf life of fruit juice can be as long as one year by using PET bottles with this multi-layer structure to contain fruit juice, supplemented by PP impermeable sealing caps. The reason why the shelf life of this package is so long is that cobalt based oxygen capture agent can not only block the channel of O2 entering the bottle from the outside, but also balance the O2 already in the bottle

2. Surface coating technology this method refers to coating an extremely thin impermeable layer (some of which are smaller than the diameter of human hair) on the inner or outer surface of a single-layer PET bottle. Although single-layer PET bottles with low cost can be used in this technology, the cost of coating equipment is generally high. There are many kinds of materials that can be used for coating, including inorganic materials and organic materials

carbon. ACTIS cold plasma technology of French Sidel company was originally developed for beer bottles. Coating a thin carbon layer on the inner surface of the bottle can improve its impermeability to O2 and CO2 by 30 times and 7 times respectively. In order to reduce costs, the company has also recently developed a new ACTIS Lite coating technology for PET bottles with low requirements (such as juice, carbonated beverages and hot filled products). In addition, four Japanese companies have jointly developed a low-temperature plasma technology, which can coat a material called "diamond like carbon" on the surface of PET bottles without pretreatment before coating. The coating thickness is 0.02~0.04mm, which can improve the impermeability of bottles to gas by 30 times

silicon oxide (SiOx). A thin layer of transparent glass like silica (SiO2) with a thickness of 0.01mm ~0.1mm is deposited on the inner surface of PET bottles by using special plasma technology. The cost of this method is only 20% higher than that of untreated PET bottles, but the resistance to CO2 and O2 penetration of bottles can be increased by 25 times and 17 times respectively. SiO2 coating has high elasticity (cracking resistance), which can ensure that the bottle can still maintain good impermeability in case of expansion and contraction during filling. At the same time, because the coating is located on the inner surface of the bottle, it ensures that the coating will not be worn during filling and transportation

in addition, SiO2 can also be coated on the outer surface of PET bottles by physical vacuum coating between the stretch blow molding and filling processes. The advantage of this method is that the output is large, up to 20000/h. In order to prevent the coating from being worn, a protective layer can be coated on the SiO2 layer

epoxy amino resin. Spray the liquid epoxy amino resin on the outer surface of the PET bottle, and then place it in the oven for crosslinking and curing. The 1~6mm thick crosslinking layer not only has good gloss, but also has good impermeability to CO2 and O2, so that the shelf life can be extended by 2.5~3 times. In addition, the bottle can also be pasteurized or used for hot filling of fruit juice. Due to the good lubricity of the coating resin, when this technology is used for continuous coating, the output can reach 45000/h

combustion chemical vapor (the number of communication base stations in China in 2016 was nearly 6million deposits). This is a relatively new technology, which uses organic or inorganic impermeable materials. First, spray the coating solution with low steam pressure into a fog, and then dry it by flame and solidify it at the same time. This coating will not affect the transparency of the bottle. Compared with other coating methods, this technology does not need a vacuum box, has simple operation, low cost, and is environmentally friendly

3. Blending method: pet is blended with high impermeability resin (such as EVOH) or oxygen trapping agent or both, and then the blend material is used to inject a single-layer bottle embryo for stretch blow molding. This method requires neither multi-layer co injection molding process nor coating equipment, and the freedom of bottle design is large, but the price of suitable impermeable resin is very high

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