The hottest polycarbonate extrusion blow molding p

2022-08-08
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Polycarbonate extrusion blow molding process

polycarbonate (PC) has become one of the world's five major engineering plastics since its industrialization in the 1950s, and has been widely used in all walks of life. Because the products processed and molded with PC have not only good transparency, but also high strength and rigidity, especially good heat resistance. They can be disinfected repeatedly for 50 times under 120 ℃ high-temperature steam without deformation, so they have been widely used as beverage bottle materials

1. Characteristics of PC for extrusion blow molding PC used for extrusion blow molding belongs to branched chain resin. Compared with general linear resin, its melt strength is high. Jung seminar gathered industry experts to discuss the latest development trend and technical utilization scheme. It is not sensitive to the viscosity change caused by shear, so it is conducive to the stability of extruded tube blank wall thickness. PC contains ester groups with strong polarity. When exposed to the air, it is easy to absorb moisture in the air

2. Control of PC extrusion blow molding process conditions

2.1 drying because PC is a resin with strong moisture absorption, PC must be dried at ℃ for h before molding processing, otherwise PC is prone to hydrolysis reaction and degradation at high molding temperature, which seriously affects the product quality. Once the PC is dried, it must be used up within 20min, otherwise it needs to be dried again

2.2 barrel temperature control PC during extrusion blow molding, the barrel temperature control requirements are very strict, because the temperature directly affects the strength of the melt, and then affects the quality and appearance of products. If the temperature is too high and the melt viscosity is too low, the extruded tube blank is easy to sag, resulting in uneven wall thickness of the product; If the temperature is too low, the plasticization of the material is poor, which will reduce the strength and transparency of the product. Therefore, the extrusion blow molding temperature of PC should be different according to different products and molding equipment, which is generally controlled at ℃

2.3 mold temperature control is usually controlled at the same temperature for the mold used for extrusion blow molding, and the temperature control range is large. However, the temperature of the molding die used for PC extrusion and blow molding must be controlled by sections, and the temperature of each section must be controlled at ± 3 ℃. Otherwise, too high or too low the temperature of the die will affect the strength and appearance of the products. Generally, the mold temperature is controlled at ℃

3, forming process of 19L extrusion blow molded beverage bottle

3.1 raw materials and main equipment pc:lexan PK, GE company of the United States; Hollow molding machine: NB 30/p65/ac5s, Nippon Steel Institute; Plastic dehumidification dryer: gzy90b, Shanghai United Machinery Co., Ltd

3.2 in the molding process, the PC is first dried in the drying equipment according to certain requirements, so that the moisture content is controlled at less than 0.02%. Then use the drying equipment to automatically add the dried PC into the hopper of the hollow forming machine with the closing device in fixed quantity and timing. Under the control of certain process conditions, the material is extruded and plasticized and squeezed into the accumulator of the machine head. The primary extrusion amount is controlled by the accumulator tube blank control device. The extruded tube blank is closed, blown, cooled and shaped by the blow molding mold with the automatic control device, and then the mold is opened, and the product is automatically demoulded, The package shall be inspected after finishing

3.3 main blow molding process parameters (1) drying treatment drying temperature 120 ℃, drying time 4H. (2) The temperature of blow molding machine body is 265 ℃ in feeding section, 265 ℃ in compression section and 275 ℃ in homogenization section; Head temperature Jinan experimental machine factory high and low temperature universal material testing machine is used to test the tensile strength, compressive strength, elongation, elongation, peeling, tearing, bending, bending, shrinkage and other tests of various materials, semi-finished products and finished products under different temperature environments. It is 250 ℃; Mold temperature: bottom ℃, middle ℃, upper 60 ℃; The blowing pressure is 0.6MPa; The blowing ratio is 2.2; The molding cycle is 70s; The control point of tube blank wall thickness is 10 points

3.4 product quality index (1) the appearance of the product is transparent, without raw meal, cold spots, bubbles, stains and fog like whitening; (2) Drop the product from 2m height to the ground without cracking; (3) The bottle weighs 70g

3.5 product thickness and bottle weight adjustment control the uniformity of product thickness directly affects the mechanical properties and formability of products, and the product thickness mainly depends on the thickness of tube blank, so the thickness of tube blank must be strictly controlled. The product thickness and bottle weight adjustment control is controlled by the head stocker control device, which is mainly composed of program setter, head, gap detector, server and linear potentiometer. The position of the stocker is detected by the linear potentiometer and sent to the program setter. The program setter is internally composed of a program generation circuit and a servo amplifier circuit. This program generation circuit corresponds to the stroke of one extrusion volume, and generates dozens of equal slopes, while making it generate signals corresponding to the position of the stocker, so that the thickness of the tube blank can be controlled at any wall thickness synchronized with the forming cycle, The bottle weight is controlled by the set gap between the mold core and the mold sleeve and the storage volume

4、 Product defects often occurred during PC extrusion blow molding and their solutions: solutions to the causes of product defects: improper selection of drying temperature of bubble raw material, better selection of drying temperature, insufficient drying time, re hygroscopic inspection after drying, hopper sealing device, barrel temperature is too low, barrel temperature is too low, barrel temperature is increased, and the mixture obtained from the mold row becomes high-strength, gas is blocked, and the position is improperly selected, increase the exhaust Hole diameter or correct selection of exhaust position mold surface treatment layer wear treatment mold surface layer drop resistance difference barrel temperature is too low properly increase barrel temperature uneven product wall thickness adjust product tube blank control point or adjust mold core and sleeve gap tube blank fuzzy melt temperature is too low properly increase body temperature head temperature is too low properly increase head temperature surface corrugated mold exhaust is not smooth increase exhaust hole diameter expansion speed is too slow blow as soon as possible Insufficient air blowing for bulge molding increases the air blowing pressure. The appearance of the product is not strong. There are stains on the mold surface. Clean the mold surface. The mold exhaust is not smooth. Clean the mold exhaust hole or increase the exhaust hole. The mold temperature is too low. Increase the mold temperature. The air inlet time is too late. Blow immediately after closing the mold. The product is deformed. The air blowing time is too short. Extend the air blowing time. The cooling is not enough. Or open the mold too early. Increase the cooling capacity or extend the setting time

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