What Is Stretch Blow Molding & How Does It Work?

Stretch Blow Molding (SBM) is a popular manufacturing process used to make plastic containers, commonly polyethylene terephthalate (PET) bottles and jars. As the name suggests, this process involves creating containers by stretching and blowing a preform into the mold shape.

The stretch blow mold process has many benefits, both in terms of manufacturing efficiency and container properties. Dive into our easy-to-follow exploration of SBM, and discover how it results in some of our most trusted, strongest bottles and jars.

Stretch blow molding is a versatile method for creating plastic bottles and jars. It is frequently used to manufacture food, beverage, household, pharmaceutical and personal care containers. 

From resin pellets to full-formed containers, the SBM process creates uniform, reliable containers with a few easy steps.

There are two approaches towards the stretch blow mold process– single-stage and two-stage.

Single-stage stretch blow molding achieves the entire process in one continuous operation, from preform creation to final product stretching and blowing. This allows preforms to remain warm and directly enter the stretch blow mold process. This method is efficient, precise, and excellent for smaller batches.

The two-stage process separates the preform creation and final product creation. This allows manufacturers to cool and store their preforms, or source them elsewhere. This method allows for lower equipment cost, flexibility, and large-scale production.

Injection Stretch Blow Molding (ISBM), a type of SBM, specifies that the preform must be created using the injection molding process, during which melted resin is injected into a preform mold. Alternatively, some SBM (but non-ISBM) preforms may be created by a process called extrusion.

Stretch blow molding boasts advantages for consumers and manufacturers alike.

During the stretch blow mold process, preforms are expanded biaxially – stretched vertically (axial) and blown into a wider circumference (hoop). This biaxial stretch leads to several improved characteristics:

• Strength - Containers are more durable and impact-resistant.

• Barrier Performance - Containers are less susceptible to gas and moisture permeation, increasing product freshness.

• Finish - Containers boast even clarity and a high-quality, smooth finish.

• Weight - Containers tend to be more lightweight.

Thought leaders in the plastic industry recognize stretch blow molding as relatively cost-efficient for mass production. The process is also highly efficient, producing consistently good and accurate containers.

Polyethylene terephthalate (PET), the most common type of plastic used in SBM, is considered 100% recyclable because it maintains its quality through cycles of reuse. If properly recycled, PET containers can be broken down into post-consumer resin (PCR). PCR can be mixed with new, virgin resin during the preform creation process, decreasing the need for new plastic production. 

Throughout the manufacturing process, excess trim can also be salvaged for recycling. Generally, SBM produces less waste than other plastic molding techniques due to its precision practices and lighter, thinner containers.

Custom container molds allow brands to create unique containers that capture attention on the shelf.

The SBM process is versatile and can be used with several plastic types, the most common of which are PET, HDPE, and PP. 

• Polyethylene Terephthalate (PET) - Popular for food, personal care, and pharmaceutical applications, PET is a clear, strong, and lightweight plastic.

• High-Density Polyethylene (HDPE) - Naturally a translucent hue, HDPE boasts durability and chemical resistance which makes it well-suited for chemical containers.

• Polypropylene (PP) - PP is a versatile plastic used by cosmetic, food, personal care, and other industries. It has excellent chemical and impact resistance. 

To maintain high-quality stretch blow mold results, proper maintenance and quality assurance are crucial.

• Machinery Maintenance - Regular machinery maintenance ensures that your stretch blow molding machines are running to the best of their ability, producing consistent and high-quality containers. This helps eliminate costly product loss.

• Quality & Testing - It is important to inspect resin as well as finished products for any defects and inconsistencies.

• Proper Training & Documentation - Proper operator training and documentation ensure that your SBM process is in good hands, held to high standards by knowledgeable professionals.

The stretch blow molding process is just one of several methods used to create the plastic containers we rely on every day. At The Cary Company, we do the quality assurance for you, connecting you with reliable containers from trusted manufacturers. 

Have any further questions? Our container experts are here to assist you every step of the way. Contact our sales team at 630.629.6600 or email sales@thecarycompany.com! Find out more about packaging and containers, as well as compatible lids, caps and closures at The Cary Company!