Hollow plastic blow moulding can basically be divided into two categories: extrusion - blow moulding and injection - blow moulding. The main difference between the two is the preparation of the parison, and the blow molding process is essentially the same. On the basis of these two molding methods are: extrusion - stretching - blow molding (referred to as extrusion - pull - blowing), injection - stretching - blow molding (referred to - pull - blowing) and multilayer mapping Plastic and so on. Injection-blow molding (referred to as injection-blow) plastic bottles are made of plastics with bottomed parisons by injection molding, and then the parisons are heat-transferred to blow molds for blow molding hollow products. Note - The blown hollow container has no flash, the dimensional stability is good, the quality of the bottle mouth and the thread is excellent, the thickness of the parison can be pre-conditioned, the glossiness of the product is good, and the raw materials are saved. However, the injection-blow molding is not suitable for consuming large-scale and complicated-shaped containers, and because of the use of two injection and blow molds, the equipment investment is large. Note - The blow-through hollow container is mainly composed of a small bottle body with a single cylinder shape, which can be consumed with polyvinyl chloride, polyethylene, polypropylene and polystyrene, polyester, polyamide and other resins. Mainly used for the packaging of medicines, foods, cosmetic products, etc. The types of plastics used for hollow blow molding are polyethylene, polyvinyl chloride, polypropylene, polystyrene, linear polyester, polycarbonate, polyamide, cellulose acetate and Polyacetal resin, etc. Among them, the consumption of high-density polyethylene accounted for the first place. It is commonly used in the packaging of food, chemical and disposal liquids. High molecular weight polyethylene is suitable for the manufacture of large fuel tanks and barrels. Because of its good transparency and airtightness, polyvinyl chloride is widely used in the packaging of cosmetic products and detergents. With the development of non-toxic polyvinyl chloride resins and additives, and the development of stretch blow molding technology, the use of PVC containers in food packaging has increased rapidly and has been used in beer and other beverages containing carbon dioxide gas. package. Linear polyester data is a new type of material that has entered the hollow blow molding category in recent years. Because of its glossy appearance, excellent transparency, high mechanical strength, and good container storage, waste disposal does not pollute the environment, etc. Therefore, the development of bottles is fast, especially The use of pressure plastic food containers is the most common. Due to the improvement of its resin modification and processing technology, the use of polypropylene has also increased year by year.

The main raw material and typical formula

(l) Polyethylene is generally used for polyethylene resins with a melt index of 1 to 6.

(2) Polypropylene Ordinary Selective Polypropylene Resin with a melt index of 2-4.

(3) Polystyrene generally used universal or impact-type injection grade polystyrene resin.

(4) PVC hard transparent bottle formulation.

The main equipment and characteristics of plastic barrel production

(1) The extruder and head are essentially the same as the ordinary extrusion-blow method.

(2) Parison Disposal A tubular parison extruded from an extruder is installed to stop the cutting, the bottom fusion, and the neck processing through this installation to form a test tube-shaped bottomed parison.

(3) Parison heating installation parison heating installed oven, heating sleeve, heating channels and many other heating methods can be electric heating or infrared heating. However, the heating installation should be able to adjust the temperature and balance the heating, so as to minimize the temperature difference between the inside and the outside of the parison.

(4) Tensile installation of tensile mandrel and tensile clamp are two types.

1 Stretching mandrel Stretching mandrel is inserted from the upper part of the parison, under the action of hydraulic pressure, resists the bottom of the parison, stops the longitudinal stretching, and then the air hole in the mandrel passes through the compressed air to inflate and stops the radial stretching. Most stretch forming uses this type of tensile installation.

2 Tensile clamp The clamp is clamped from the outside to both ends of the tubular parison, and it stops under the action of hydraulic pressure in the longitudinal direction, and then blows to stop the radial tension. Both the neck and the bottom have flash trims that require trimming and the flash edge can be recycled after being broken.

(5) Extrusion-pulling-blown molding machines There are many types and specifications of extrusion-pull-blow molding machines in foreign countries. At present, there is no such special equipment in China.

Plastic barrel production process

Note - Blow molding practice consists of two processes: injection molding parisons and blow molding products, and injection molding parisons are the key to the entire consumer process.

(1) Process Control of Injection Molded Parts

1 injection temperature injection temperature and the original data types and characteristics, the type of injection molding machine and product thickness and other factors. For crystalline resins, such as polyethylene, polypropylene, etc., the injection temperature should be higher than its melting point. For amorphous polymers, such as polystyrene, polyvinyl chloride, the injection temperature is higher than its sticky temperature. Resins with low melt batches have higher resin injection temperatures than melt indexes. The use of plunger injection molding machine than the screw injection molding machine processing temperature is higher. Thin-walled parisons require higher injection temperatures than thick-walled parisons. Ordinary polystyrene injection temperature is 140 °C ~ 240 °C, polyethylene is 150 °C ~ 280 °C, polypropylene is 205 °C ~ 285 °C, polyvinyl chloride is 160 °C ~ 190 °C. Injection mold temperature is usually 40 °C ~ 80 °C.

2 Injection pressure Normal resin has a low melt index and a thin parison wall, requiring a higher injection pressure, and vice versa. Plunger injection molding machines require higher pressure than screw injection molding machines. Under the condition of ensuring the quality of production, use lower injection pressure as much as possible. Normal polystyrene injection pressure is 58.8 to 107.9 MPa, polyethylene is 58.8 to 98.06 MPa, polypropylene is 54.9 to 98.06 MPa, and polyvinyl chloride is 78.4 to 127.5 MPa. (2) The process control of blow molding is basically the same as the blow molding process of extrusion-blow molding.

Major equipment and features

(1) The structure of the parison injection machine is the same as that of an ordinary injection molding machine, but the injection pressure is low, and the length-to-diameter ratio of the screw can be smaller, and the compression ratio should not be too large.

(2) Molds include injection molds and blow molds. The information of the injection mould parison mold and the normal injection molds are the same as those of the processing request, but the core mold must be hollow in order to open the compressed air. The blow mold and the blow-molding mold are essentially the same.

(3) The demoulding installation is different from the extrusion-blow molding. After the blow molding process is completed, the blow mold is opened, the core mold with the molded product is sent to the stripping installation, and the product is separated from the core mold by the stripping template.

Product specification

Injection-blow plastic bottles currently have no national standard or department standard. Product specifications can refer to polyethylene blow barrel specifications and make necessary corrections. However, the injection-blow hollow container of the same kind of raw material is superior in performance to the squeeze-blow hollow container.

Large hollow containers generally refer to large-sized hollow products such as various plastic barrels, tanks, storage tanks, and boxes with a volume of more than 50L. The main raw material is polyethylene resin, and the molding process is mainly extrusion-blow molding and rotary molding.

Extrusion-blow molding of large containers is essentially the same as plastic barrels, with only slight differences in raw materials and equipment.

The main raw materials for plastic containers are generally low-density polyethylene resins or high- and low-density polyethylene resin mixtures, while large consumer containers are mainly high-density polyethylene and high-molecular-weight polyethylene resins.

Major equipment and features The extruders and blow-molding installations for consuming large containers are the same as those for consuming plastic barrels, but a stocker should be added between the extruder barrel and the head. Since the parisons of large products are also very large, if extruded by the extruder slowly, the parisons will exhibit serious draw-down phenomenon caused by self-weight, resulting in uneven wall thickness in the products. At the same time, due to the long extrusion time, the temperature of the parison is too low due to cooling, which also affects the quality of blow molding. After the additional hopper is installed, the extruder continuously extrudes the molten material into the hopper. When the stored material reaches a certain amount, the material is quickly pressed out by the ramming material to form a parison with the average thickness and the proper temperature. . Therefore, the addition of hoppers not only reduces the drawdown of the parisons and the temperature of the parisons, but also allows smaller extruders to consume large products.

Plastic barrel product standard

Extrusion-blow molding of large hollow containers is currently no national or ministry standard. The necessary amendments can be made with reference to GB 13508-92 polyethylene blow barrel standards. The PETP soft drink bottle implements the QB1868-93 standard.

Extrusion-stretch-blow (referred to as squeeze-pull-blow) plastic bottles are made of resin by extrusion into a tubular parison, then the bottom is fused to form a bottomed parison, and then the parison is processed to the plastic used. The ideal stretching temperature, a longitudinal product obtained by longitudinal stretching by an internal (stretch mandrel) or external (stretching jig) mechanical force, and at the same time or later compressed by compressed air to produce a hollow product. . After the plastic has been biaxially stretched, the molecules are redirected. Therefore, the impact toughness, low-temperature strength, transparency, surface glossiness, rigidity, and barrier properties of the products have all been significantly improved and improved. In addition, the thinning of the wall thickness of the product after stretching can save raw materials and reduce costs. At present, the plastics used in the production of extruded-pull-blow hollow containers are mainly polyvinyl chloride and polypropylene, and the products are mainly small-sized and thin-walled bottles, which are used for the packaging of food, beverages, cosmetics and daily chemical products.

Push-pull is divided into one step and two steps. One-step parison manufacturing, stretching, and blow molding are performed continuously in one facility, also known as hot parison process. The two-step parison manufacturing is carried out separately from heating, stretching, and blow molding in terms of time, position, and equipment, and is also called a cold billet method.

The requirements for the main raw materials and typical formulations for polypropylene resins and PVC containers are basically the same as those of the extrusion-blow molded containers.

The consumer process extrusion-pull-blowing process is essentially the same as the extrusion-blowing process in the control of the extrusion of the parison and the blow molding process. The following focuses on the process control of stretching.

(1) Stretching temperature control A suitable stretching temperature is the key to stopping the biaxial stretching, otherwise it will not achieve the purpose of aligning the plastic molecules. For non-crystalline polyvinyl chloride, if a one-step method is used, the parison can be cooled from 90°C to 200°C during extrusion and then cooled to 90°C to 100°C to stop stretching and blowing. At this time, it is 10°C to 20°C higher than its glass transition temperature, which is the most ideal stretching temperature. For crystalline polypropylene, if a one-step process is used, the parison must be cooled efficiently.

From the extrusion temperature of 210°C to 230°C, it is rapidly cooled to a crystallization temperature of between 90°C and 105°C, suppressing the spherulite structure, and then heating to 150°C to 160°C between the glass transition temperature and the melting point temperature. Biaxial stretching. Regardless of polyvinyl chloride or polypropylene, if a two-step process is used, it is required to reheat the pre-made parisons to their respective stretching temperatures before stopping the stretching and blowing.

(2) Stretching ratio In addition to the stretching temperature and other conditions, the molecular orientation state of the biaxially stretched product is determined by the stretching ratio, so that the stretching ratio determines the improvement of the product performance. The draw ratio is the product of draw ratio and blow ratio, and the draw ratio is the ratio of the length of the product to the length of the parison, ie, the draw ratio in the machine direction. The blow-up ratio is the ratio of the maximum diameter of the product to the parison diameter, which is the radial stretch rate. The stretch ratio is too low to achieve molecular reorientation and improve the performance of the product. If the stretching ratio is too high, the data will be damaged and the processing conditions will not be easily controlled. The draw ratio of ordinary polyvinyl chloride is 4-6, and that of polypropylene is 6-10.

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