Six Key Plastic Bottle Processes
Did you know? Behind the ubiquitous plastic bottles we see in our daily lives are six core processes that determine their shape, performance, and purpose. Today, let's explore them!
1. Injection Molding: The Basics of "Preform First, Then Bottle"
Process Principle: Plastic pellets are heated and melted, then injected into a mold and pressed into a "preform" (similar to a small cylinder with a mouth). This process then requires additional processes (such as blow molding) to transform it into a complete bottle.
Applications: This process is used as a "pre-production" step for almost all plastic bottles with mouths (such as beverage bottles and skincare bottles), and can also directly produce accessories such as caps and bases.
Advantages: High mold precision, stable preform dimensions, and suitable for mass production.
Disadvantages: It cannot directly produce hollow bottles; multiple processes are required, resulting in a slightly higher cost.
2. Blow Molding: "Blowing air into the preform to form the desired shape."
Process Principle: The preform is heated and softened after injection molding, then "blown" into a mold with high-pressure air, forcing the plastic to adhere to the mold walls. After cooling, a hollow bottle is formed.
Sub-Types:
Extrusion Blow Molding: Suitable for containers without fixed necks (such as plastic buckets and large water bottles);
Stretch Blow Molding: Stretch the plastic during blow molding, resulting in lighter, thinner, and stronger bottles (commonly used in pet and mineral water bottles).
Applications: Over 90% of hollow plastic bottles (beverage, daily chemical, and food packaging), especially for transparent, thin-walled containers.
Advantages: High one-step molding efficiency, good bottle toughness, low weight, and manageable costs.
Disadvantages: Complex molds, high adjustment costs for design changes, and unsuitable for small-batch production.
3. Extrusion: "Making Bottles Like Noodles"
Process Principle: After plastic pellets are melted, they are continuously extruded through the extruder's die head into a tubular plastic blank. While still hot, the blank is placed into a mold, inflated with compressed air, and cooled to set the shape.
Applications: Production of simple-shaped containers without delicate necks (such as plastic bottles, hoses, and large-diameter packaging barrels). Plastic sheets and tubes can also be produced.
Advantages: Fast production speed, suitable for large-sized and non-standard-shaped bottles, and low equipment investment.
Disadvantages: Low neck precision, inability to produce delicate threaded necks, and slightly uneven bottle wall thickness.
4. Compression Molding: "Using Pressure to Form Plastic into Bottles"
Process Principle: Plastic pellets or powder are placed into the mold cavity. Heat is applied to melt the plastic. Pressure is then applied through the punch to force the plastic to fill the mold cavity. After cooling, the plastic is removed from the mold.
Applications: Producing thick-walled, high-strength plastic bottles (such as pharmaceutical bottles and chemical reagent bottles), or complex-shaped containers with embossed or decorative patterns (such as cosmetic cream bottles).
Advantages: Bottles with uniform wall thickness and high strength, capable of fine surface textures, suitable for high-temperature and high-pressure applications.
Disadvantages: Long production cycle, lower efficiency than blow molding, unsuitable for thin-walled, high-volume containers.
5. Thermoforming: "Suctioning Plastic Sheets into Shallow Containers"
Process Principle: After heating and softening a flat plastic sheet, a vacuum pump removes the air beneath the sheet, forcing it to adhere to the mold surface. After cooling, the sheet is cut into the desired shape.
Applications: Producing shallow, thin-walled plastic containers (such as yogurt lids, jelly cups, and cosmetic sample bottles). It is also commonly used for packaging liners and trays.
Advantages: Low mold cost, flexible design changes, suitable for small-batch, multi-style production.
Disadvantages: Can only produce shallow-cavity containers; cannot produce deep, hollow bottles. It also has low strength and is prone to deformation.
6. Rotomolding: "Letting Plastic 'Roll' into Shape in the Mold"
Process Principle: Plastic powder is poured into a mold, which is then continuously rotated about two perpendicular axes while being heated. Centrifugal force causes the powder to adhere evenly to the mold walls. After cooling, the mold is opened and the product is removed.
Applications: Production of large, specialized plastic containers (such as chemical storage tanks over 50L, children's toy buckets, and outdoor drinking water barrels), or products with asymmetrical shapes and high wall thickness requirements.
Advantages: Seamless, high strength, capable of producing large, complex containers, and low mold costs.
Disadvantages: Long production cycle (10-30 minutes per product), unsuitable for small, thin-walled bottles, and poor color uniformity.
�� As a plastic bottle supplier and bottle preform supplier, Hongyuan maintains strict product control and is committed to providing customers with high-quality PE bottles and preforms of varying weights. ��