How does the injection blowing process achieve precise integration of the bottle thread and the bottle body through "one-shot molding"?
Publish Time: 2025-08-20
In the manufacturing of hollow plastic products, the precision and sealing of the bottle neck structure are directly related to the product's functionality and safety. This is particularly true in pharmaceutical, cosmetic, and high-end food packaging, where the bottle neck thread must seamlessly align with the bottle cap to ensure leak-proof, contamination-resistant, and long-lasting sealing. Traditional extrusion blow molding often struggles to meet these high-precision requirements due to issues such as parting lines, flash, and secondary thread processing. The injection blowing process, with its unique "one-shot molding" process, successfully achieves seamless and precise integration of the bottle neck thread and the bottle body, making it the preferred technology for manufacturing high-demand containers.
1. The Core of "One-Shot Molding": Precision Forming of the Bottle Neck During the Injection Stage
The first step in the injection blowing process is "injection molding." Molten resin (such as PE, PP, or PET) is precisely injected under high pressure into a closed parison mold. The mold cavity not only determines the parison's shape but, more importantly, incorporates a high-precision thread core. During the injection process, the plastic completely fills the thread cavity, and upon cooling, a bottle finish with a complete, precise thread structure is formed. Because this process is directly molded using a precision metal mold, the thread's dimensional tolerance can be controlled within ±0.05mm, resulting in a smooth, burr-free surface and no subsequent processing, truly achieving "one-shot molding, one-step completion."
2. Mandrel Transfer: Maintaining the Parison's Temperature and Structural Integrity
After injection, the parison with the complete bottle finish is not directly removed from the mold. Instead, it is securely secured to a metal "mandrel." This mandrel not only supports the parison but also provides temperature control, maintaining the parison within the optimal inflation temperature range (typically softened but not fully cooled). The mandrel then rotates or translates the parison to the blow molding station. This entire process eliminates manual intervention or mechanical damage, ensuring that the bottle finish is not deformed during transfer and its precise geometric integrity is maintained.
3. Blow Molding: The bottle body is formed without interfering with the already formed bottle finish.
In the blow molding station, the parison is placed into the blow mold and closed. At this point, the bottle mouth is precisely positioned by the clamping structure at the top of the mold, while the bottle body is positioned within the mold cavity. When compressed air is injected into the parison through the internal channel of the core rod, the parison expands evenly under pressure, conforming to the inner wall of the blow mold and forming the desired bottle shape. Because the bottle mouth is clamped and isolated by the mold, the inflation process affects only the bottle body, without stretching, twisting, or deforming the already formed thread structure. The blow mold is rapidly cooled by circulating cooling water, allowing the bottle body to set its shape before the mold is opened and the finished product is removed.
4. Integrated Advantages: No Parting Line, No Flash, and High Sealing Performance
Thanks to the step-by-step process of "injection molding the bottle mouth first, then blow molding the bottle body," injection blowing process products completely avoid the parting line and flash issues common in traditional extrusion blow molding. There are no seams or weak points between the bottle mouth and the body, resulting in a high overall structural strength and excellent sealing performance. This integrated design is particularly suitable for applications requiring high cleanliness and long-term sealing, such as antibiotic bottles, eye drop bottles, and essential oil bottles, effectively preventing microbial intrusion and volatilization of contents.
5. Application Value: Meeting the Stringent Requirements of High-End Packaging
The injection blowing process's "one-shot" molding capability gives it irreplaceable advantages in the pharmaceutical, cosmetic, and baby product sectors. For example, in sterile pharmaceutical packaging, the bottle neck must achieve an airtight fit with the aluminum-plastic combination cap or pump head; in high-end perfume bottles, the threads must precisely mate with the metal nozzle to embody the brand's premium quality. Theinjection blowing processnot only meets these functional requirements but also achieves high transparency and a high finish, elevating the product's quality.
The injection blowing process achieves truly integrated manufacturing of the bottle neck threads and bottle body through the three-step process of "injection molding the bottle neck + mandrel transfer + blow molding the bottle body." This "one-shot" molding process not only simplifies the process but also comprehensively improves precision, cleanliness, and reliability. It integrates polymer materials, precision molds, and automated control technologies, providing solid technical support for modern high-end hollow containers.
