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Did you know? In general, blow molding is used to manufacture plastic bottles. However, each type of plastic bottle product requires applying a different type of blow molding.
Types and manufacturing processes for plastic bottles
Types of plastic for making plastic bottles
The four most popular types of plastic used as materials for making plastic bottles are PET, PE, PP, and PC. For more information on this topic, check out the following points below.
1. PETE or PET (Polyethylene Terephthalate)
Polyethylene terephthalate (PET) is commonly used for the manufacture of bottled drinking water. Such as drinking bottles, soda bottles, oil bottles, and sauce bottles. Recycling symbol with numeric code 1 and PETE or PET code at the bottom. This symbol indicates that a plastic is made of Polyethylene Terephthalate. This type of plastic can only be used once. It is not recommended to use repeatedly, let alone fill it with warm water, because the polymer coating and carcinogenic substances on the plastic can dissolve (loose) and cause cancer in human organs.
2. PC (polycarbonate)
PC (polycarbonate), one of the most common plastics. This material itself is non-toxic, especially for making baby bottles, space cups and so on. It is controversial because it contains BPA. In theory, as long as 100% of BPA is converted into plastic structure in the PC manufacturing process, it means that there is no BPA in the product, and it will not be a threat to health. However, if a small amount of BPA is not converted into PC plastic structure, it can released into food or drink, which threatens the health and safety of users, especially teenagers.
3. PE (Polyethylene)
Polyethylene is one of the most versatile plastics. Therefore, it is not surprising that PE plastic is very popular in the world. High-density polyethylene (HDPE) is widely used for the manufacture of rigid plastic bottles, detergent bottles for example, while low-density polyethylene (LDPE) is used for the manufacture of sauce bottles.
The basic monomer used to make PE plastic is ethylene, a gaseous hydrocarbon. This compound is very stable, so the polymerization process into PE can only be continued in the presence of a catalyst, such as titanium chloride. Most PE plastic manufacturing industries use coordination polymerization which requires metal salts, such as chlorides and oxidants.
4. PP (Polypropylene)
Polypropylene or PP can be used to make pill bottles, syrup bottles, yogurt bottles, plastic straws, duct tape, and plastic rope. Plastic items with this symbol are good for use as food and beverage containers, because they are made of polypropylene which is very strong and quite safe to use even at hot temperatures.
Plastic bottles manufacturing process
As mentioned earlier, blow molding is the technique most often used in the manufacture of plastic bottles. However, there are specifically three types of blow molding processes used to make bottle-shaped plastic products, namely reheat and blow molding, extrusion blow molding, and reciprocating blow molding.
1. Reheat and Blow Molding
The first stage of the Reheat and Blow Machine (RBM) process for making bottles is injection molding. Plastic pellets are fed into the barrel of an injection molding machine where the plastic is heated until it melts. The melted plastic is then flowed into a mold to be molded into a long tube—commonly called a parison.
Parison then goes through a reheating process using a blow molding machine. At this stage, a thin steel rod, called a mandrel, is inserted into the neck of the parison to circulate the parison with high pressure air, until the outside of the parison sticks to the inside of the mold.
This process produces so-called bi-axially oriented bottles that have a CO2 barrier that is ideal for holding carbonated drinks. After that, the mold must be quickly cooled so that the plastic component has an optimal shape.
2. Extrusion Blow Molding
Extrusion blow molding combines the parison manufacturing process and the blow molding process in one step. In the extrusion blow molding process, the parison is formed vertically and the wall thickness is varied by changing the size of the hole through which the parison is extruded.
The mold portion that already contains the parison is then transferred to a blow molding station where the bottles are shaped as in the second step of the RBM process described above.
3. Reciprocating Blow Molding
Another manufacturing process is to use a reciprocating blow molding machine. This machine moves the screw linearly inside the injector barrel to collect the shot. Then, the screw will push the shot above the mandrel to make a parison which is then formed into a plastic bottle.
If you are wondering to get information regarding bottles manufacturer and production, Imajin can give you insights and ideas. We can connect you to specific vendors for each materials and processing.