Multi preform injection molding technology for imp

2022-10-02
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Multiple preform injection molding technology to improve barrier performance

various barrier technologies have been adopted in the pet industry. However, one of the technologies, multiple injection molding of PET bottle blanks, has not been successful. With the joint efforts of partners, Netstal Maschinen AG has further developed this technology that can produce high-quality bottle blanks

in the pet industry, barrier technology has been paid more and more attention. In order to make PET packaging have satisfactory barrier effect, three proven barrier solutions have been adopted by people. Among them, the multi-layer method (also known as composite injection molding) is to inject the pet substrate first, and then inject the barrier material through the hot mold core to form an intermediate barrier layer. This method requires high skills of operators and strict quality control. Another barrier solution is to mix barrier materials directly into PET raw materials. Its advantage is that the mixed material can be processed by the standard bottle blank production system without any other technological measures, and the operator does not need to master any other knowledge. But its disadvantage is that the mixed barrier material is easy to make pet opaque. The third method is called coating method, that is, plasma coating is carried out on the inside or outside of the blow formed hollow body or bottle blank. This process is usually complex

in addition, there are other technical solutions related to the barrier of pet preforms, such as multiple injection molding, which is characterized by: starting with inner injection molding, and then multi-layer injection molding during parallel processing. Unfortunately, this technology has been ignored in recent years

in the industry, the multiple injection molding process for manufacturing bottle blanks is usually considered to be both difficult and complex for the following reasons: first, each layer of bottle blanks must be very thin. However, in actual production, the mold core may deviate from the center under the effect of pressure difference, so the uniform distribution of wall thickness cannot be achieved. In addition, when the first molding cycle is completed, the bottle blank must be transferred to another mold cavity for injection molding of the next layer. But so far, this process is still completed by rotation, which is easy to lead to delamination between layers

in order to solve these problems, Netstal Maschinen AG, in close cooperation with molmasa, a mold manufacturer with a cathode material output of 161600 tons in Spain in 2016, and novapet, a raw material manufacturer in Spain, has successfully made the multiple injection molding process economical, reliable and renewable through intensive work

now, the moulds and machines after innovation and transformation can produce bottle blanks with a wall thickness of only 1.2 mm in the first production cycle. Due to the progress of raw material technology, the risk of delamination and delamination is also avoided. When the mold cavity needs to be changed, several rows of mold cores can move in parallel, thus replacing the original complex rotation movement. In short, these technological advances have paved the way for the implementation of various barrier schemes and the application of other technologies. In the future, a mixture of stretched polyethylene (OPP) and barrier materials can even be used. In addition, in order to obtain different color effects, other materials can also be adhered to the first layer

prelactia bottle blank

in the k2007 exhibition, a kind of bottle blank called prelactia (bottle blank that absorbs light through carbon titanium additives) was first introduced to the world. It is a dairy bottle blank that can block light produced by multiple injection molding process

generally, in order to make the PET container reflect UV light, white and TiO2 must be added, and the added concentration is generally about 12%. As an additive with high wear resistance, TiO2 can reduce the wear of containers. However, due to the high cost of TiO2, gray or black can generally be added to reduce its dosage. However, gray or black milk bottles do not sell well in the dairy market, which vigorously promotes enterprise innovation. In order to solve these problems, multiple injection molding is an ideal solution

multiple injection molding process

in the multiple injection molding production of prelactia bottle blanks, a synergy 2c/900 injection molding machine with two injection devices is used, and the raw materials are from novapet company, which is the raw materials specially produced by the company for manufacturing prelactia bottle blanks, known as dairy2 complex. The material is ready to use, and only 7.2% TiO2 is added in the polymerization process. For each thin layer of bottle blank, it provides very ideal fluidity and avoids delamination. In addition, the bottle blank also adopts the carbon gray liquid color specially developed for it as its inner layer, and the outer layer is still white. With this carbon gray liquid color, after stretching and blowing, a metal gray surface is formed in the bottle, which is the key factor to fully absorb light

Molmasa has designed and manufactured an efficient mold for this multiple injection molding process, which will not move with the rotation of the mold core mentioned above. The core transfer is carried out according to the displacement principle, which means that the whole core plate will move up and down along a row of cavities. In this way, the mold core first enters the mold cavity for injection molding of the first layer, and then enters the adjacent mold cavity in the second production cycle to start the injection molding of the second layer. When the first part is completed, the mold is opened and the mold core moves parallel to the adjacent large mold cavity row

generally, the bottle blank produced in the first production cycle has no bottleneck, its wall thickness is 1.2mm, and there are three small holes in the base area. In fact, these are the results of mold core support, which can prevent the mold core from moving when filling the mold cavity and the longer it is used, thus ensuring the uniformity of the first layer wall thickness. At present, this solution has been patented. In addition, when several rows of cores are transferred for the second production cycle, the cores that have just been released again will enter the cavity for the first layer of injection molding. In the second production stage, the bottle body, which is still gray, will be coated with a layer of 2mm thick bright white, and the bottleneck and thread will be generated. At the same time, the three holes on the base will also be filled

cutting edge valve technology is another innovation of this multiple injection molding process. With this technology, the outermost two rows of mold cores inserted only in the second production cycle can be alternately filled with melt. With the final opening of the mold, the preform is ejected, and the thickness of the inner and outer layers is uniform and complete

perfect dairy packaging bottle

in order to test the practical effect brought by this innovative bottle blank concept, Netstal Maschinen Ag first asked PDG plastics company of valley value country to try out the pretia bottle blank. PDG plastics has many blow molding machines and is very familiar with the production process of dairy packaging. The company quickly blew the preform of prelactia into bottles and then tested it. Six months later, 1000 bottles containing UHT milk were evaluated according to strict testing standards. The results showed that its barrier performance was better than that of single-layer bottles, and none of the bottles made the milk smell. Based on this, in the autumn of 2007, PDG plastics successfully put its first Netstal preform injection molding system into the manufacturing of preforms in prelactia

when holding a bottle blow molded from the preform of prelactia, although its inner layer is gray, the bottle still stands pure white. Compared with bottles with multi-layer method, the gray inner layer is generally invisible. If the bottle is cut, the matching of materials can be seen, and this matching also avoids the possibility of delamination. The light measurement results show that the light absorbed by the bottle can be as high as 99.99% and can reflect light with a wavelength of 700nm

obviously, multiple injection molding is a perfect solution developed by Netstal Maschinen Ag and its partners for PET packaging of dairy products

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