Tubular blown film (sheet)
DATE：2022/4/2 8:36:46 / READ： / SOURCE：This station
Tubular blown film (sheet)
The tubular blown foam film (sheet) has an attractive appearance like mother of Pearl and can be used as a filling material with soft and high temperature strength. The raw material of this product is mainly LDPE. Recently, similar products have been made from high molecular weight polyethylene and can be used to replace oil impermeable paper. Both chemical foaming and physical foaming can be used for the molding of these tubular foaming films. The material to foaming method is mainly mechanical foaming. If expandable melt concentrate is used, fine and more stable cell structure can be obtained. The bubble of tubular blown film is closed cell foam. The final density of tubular blown foam film (sheet) is 0.3 ~ 0.4g/cm, which is independent of the foaming system. To achieve lower density, it is necessary to increase melt elasticity. The method of increasing melt elasticity can be carried out by mild crosslinking or adding compatible thermoplastic elastomer. The addition of thermoplastic elastomer can improve the inherent low tear strength of the material. However, this method will lead to the problem of yellowing of products. Film coating composite production line www.handern.com comThe key control parameters of this foamed product are still melt pressure and temperature. In addition, die design and polymer selection should be considered. In practical application, the basic form of die is still bottom center feeding and high-pressure spiral die. This kind of die is easy to obtain uniform die melt pressure. The choice of polymers is also critical. The main indexes are melt strength and elasticity. In order to maximize the elasticity of the melt and fix its composition after cooling, a polymer with low melt flow index (MI = 0.3 ~ 2.0g / 10min) must be selected. The problem that occurs in the production of monolayer is the shrinkage of the gel, which leads to tear on the surface of the film. However, the use of polymers with narrow molecular weight distribution will improve this problem. This is due to the migration of the low molecular weight part to the membrane surface, or due to the degradation of the polymer. Film coating composite production line www.handern.com com
The density of tubular blown foam film is directly related to the physical properties required for end use. Reducing the density by 20% will reduce the tear strength by 40%, unless EVA or rubber additives are used. Therefore, sometimes coextrusion can also be used to reduce the cost of raw materials.
There are two forms of LDPE foam film manufacturing line. One is the series extrusion unit shown in. The unit can automatically mix and measure DPE and foaming aid and then send them to the feeding port. After the material is basically materialized by the first stage extruder, the immature hair application gas (or hair train) is pressed into the extruder by the gas pump at the head of the first stage extruder, and then sent to the intersection through the connecting pipe between the two extruders after stirring. It is filtered by the filter screen of the end rod converter set at the intersection, and then sent to the second stage extruder (i.e. the stable cold unloading bridge extruder). The second stage extruder stirs and transports the resin added with foaming agent or gas again, and carries out stable extrusion foaming molding and cooling setting (similar to horizontal film blowing method). After shaping, the membrane tube is cut into two pieces by the blades on both sides and sent to the traction coiling part. According to the film size, the film is 1.1 ~ 1.2m wide and 1 ~ 4mm thick. The film manufacturing speed is 3 ~ 30m / MIM Foaming ratio 30 ~ 33. The combination of two series extruders is 65 / 90 or 90 / 120 (the numerator is the screw diameter of the first stage extruder and the denominator is the screw diameter of the second stage extruder). The length diameter ratio of the first stage extruder is 32:1, and the length diameter ratio of the second stage extruder is 25:1. The traction power of the tractor is 2.2kW. The diameter of the traction rubber roller is 305mm, the rubber roller material is neoprene, and the hardness is hs60 °. The maximum winding speed is 25kW / min and the winding speed is 800W / min. This LDPE foam film is mainly used as cushioning material for packing and packing. In addition, as long as the screw and die are replaced, the above machine can produce PS foaming film with foaming ratio of 8 ~ 14 times. Film coating composite production line www.handern.com com
Another form of LDPE foam film production line is the blow molding device shown in figure 5-79, and its main machine is an imported mixed extruder. The extrusion screw is of three-stage type, the length diameter ratio is greater than 24, and the compression ratio is 3:1 to 3.5:1. In order to ensure the plasticizing quality and constant die pressure, the length of the screw metering section is required to be 10 ~ 12 times the screw diameter. The spiral mandrel die with bottom feeding as shown in figure 5-79 can not only ensure sufficient die melt pressure, but also provide relatively uniform material flow. Film coating composite production line www.handern.com com
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