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Blow Molding

We actively collaborate with the Customer throughout all process stages to resolve defects such as sagging (preform collapse), gate blush, and poor pinch-off quality, while simultaneously improving overall productivity. We work to develop solutions that do not interfere with the process by addressing the root causes of defects. For example, we introduce nucleating agents to increase crystallinity and improve top load resistance, anti-sagging additives to increase melt strength and reduce hot creep, or impact modifiers to enhance drop impact resistance. The result is a synergy that reduces waste and generates value.

We actively collaborate with the Customer throughout all process stages to resolve defects such as sagging (preform collapse), gate blush, and poor pinch-off quality, while simultaneously improving overall productivity. We work to develop solutions that do not interfere with the process by addressing the root causes of defects. For example, we introduce nucleating agents to increase crystallinity and improve top load resistance, anti-sagging additives to increase melt strength and reduce hot creep, or impact modifiers to enhance drop impact resistance. The result is a synergy that reduces waste and generates value.

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Rifra - Blow molding - transparent bottles
Rifra blow molding production detail
Rifra blow molding production process
Rifra blow molding products
Rifra - Blow molding - milk bottle

Phase one

1. Material preparation and drying

Blow molding is a transformation process that enables the production of hollow containers through the expansion of a preform or a tubular extrudate (parison) inside a mold using compressed air. There are three main variants: extrusion blow molding (EBM), injection blow molding (IBM), and injection stretch blow molding (ISBM). The first stage is material preparation. The polymer granules are loaded into the hopper of the extruder or injector. For hygroscopic polymers such as PET and PC, drying is mandatory to avoid hydrolysis and the resulting reduction in intrinsic viscosity. Similarly, the Masterbatches must be treated if they are made on hygroscopic carriers. IV drop due to hydrolysis irreversibly reduces the barrier and mechanical properties of the finished container. In this phase, the three essential conditions to monitor (for potentially hygroscopic polymers) are:

Residual moisture verified before each processing run.

Intrinsic viscosity of the incoming material.

Drying temperature and residence time in the silo maintained according to the supplier’s specifications.

Phase two

2. Parison formation (EBM) or preform injection (ISBM/IBM)

In extrusion blow molding, the molten polymer is extruded continuously or discontinuously (head accumulation) to form the parison. In the ISBM process, the preform is injected into a dedicated mold. In both cases, controlling thickness distribution is critical. Parison programming (varying thickness along the parison axis via gap control) is critical in EBM to compensate for non-uniform stretching during the blowing phase. A preform with non-uniform thickness generates containers with irregular wall distributions, weak points, and aesthetic defects. In this phase, it is essential to manage:

A parison design optimized for the container geometry, with a validated thickness distribution map.

Adequate melt strength for the polymer appropriate for EBM to limit sagging (structural collapse of the parison).

Uniform and stable extrusion head temperature to avoid viscosity variations in the parison.

The main critical elements of this phase are summarized as follows:

Parison programming

Dynamic control of parison thickness along the vertical axis via a hydraulic actuator.

Preform sagging

Elongation of the parison due to gravity during mold opening, causing thickness variations.

Elastic viscosity of the melt

Melt tensile strength (important for EBM with long parisons).

Preform design

Preform geometry in ISBM and its correlation with the thickness distribution of the finished container.

Gate blush

Aesthetic defect around the injection point in the preform due to melt stress.

Phase three

3. Mold closing and blowing

The mold closes around the parison/preform and compressed air is blown in to expand the polymer against the mold walls. In the ISBM technique, axial stretching (stretch rod) occurs first, followed by radial blowing. In ISBM technology, the stretch ratio (axial and radial) is decisive for the biaxial orientation of the polymer and consequently for the barrier, mechanical, and optical properties of the container. Bubbles or inclusions in the parison generate defects in the container wall. The pinch-off (sealing of the flaps) must have adequate strength. In this phase, the three optimal conditions to manage are:

Uniform preform temperature across the entire section before blowing.

Axial and radial stretch ratios within the natural stretch ratio of the processed polymer to maximize orientation without stress whitening.

Blowing pressure and air injection speed optimized to ensure complete mold filling without air entrapment defects.

The main critical issues are:

Stretch ratio

Axial and circumferential stretch ratio in ISBM, decisive for biaxial orientation.

Pinch-off sealing quality

Quality of the parison flap welding in the EBM mold, resistance to separation.

Blowing pressure and time

Blowing pressure and time and their effect on mold filling and cooling.

Biaxial orientation

Biaxial orientation of polymer chains, improving barrier and mechanical properties of the polymer.

Whitening

Whitening of the polymer due to excessive stretching or non-optimal temperature.

Phase four

4. Cooling, extraction, and finishing

The container is cooled on the mold walls, extracted, and sent to finishing operations: mechanical deflashing, punching of ventilation holes (in the case of drums), visual and dimensional inspection. A container extracted too early still has a high temperature and may deform (hot creep). In food containers, additive migration or the presence of acetaldehyde requires specific tests. Mechanical deflashing of the flaps must be complete to ensure the integrity of the joints. In this phase, the three essential conditions to keep under control are:

Container extraction temperature to avoid hot creep deformation.

Automatic deflashing system with calibrated tools and periodic replacement to ensure consistency of the trim line.

100% container inspection with vision systems for aesthetic defects and sample dimensional testing.

In this final phase, the critical issues to manage are:

Cooling temperature

Cooling time in the mold and its influence on post-extraction deformation.

Hot deformation

Deformation of the container while still hot under its own weight or external pressures.

Flash removal

Mechanical removal of flash (flaps) and quality of the trim line.

Top load resistance / Drop impact resistance

Functional tests for top load resistance and drop impact resistance.

Migration

Migration tests for containers in contact with food and beverages.

Markets

Markets for blow molding

Success in the blow molding of containers and hollow components depends on the ability to meet the specific needs of each sector. Effective solutions arise from an engineered approach calibrated to the specific final application. From managing rheological properties to prevent unwanted deformations, to the precision of mold closing and sealing. From accurate finishing to mechanical resistance and full compliance with industry standards, including those for food and chemical contact. Pigments and dyes are also essential to ensure excellent dispersion in the molten polymer without altering the material’s rheology or compromising mechanical performance. Our expertise supports applications in high-tech and regulated industrial contexts.

Rifra - Mercati - Cosmetica

Cosmetics

Rifra - Mercati - Food packaging

Food Packaging

Rifra - Mercati - Cassalinghi

Housewares

Rifra - Mercati - Medicale

Medical

Rifra - Mercati - Non food packaging

Non-Food Packaging

Products

Product line for blow molding

Rifra works alongside processors who create containers and hollow components through blow molding, in applications where thickness uniformity, mechanical resistance, aesthetic quality, and regulatory compliance must coexist in balance. In-depth knowledge of the typical criticalities of this process – from moisture and intrinsic viscosity control in hygroscopic polymers, to parison or preform management, through to the optimization of stretch ratio, pinch-off quality, cooling, and finishing – allows for the development of color Masterbatches and additives that do not merely satisfy aesthetic or functional requirements, but contribute directly to process stability and the quality of the finished container. Every solution is designed to improve productivity, reliability, and in-service performance, with constant attention to sustainability and the circular economy.

Color Masterbatches

Our design rules for color formulations

Rifra has always chosen not to focus on the production of standard formulas but to support the Customer in ad hoc developments that maximize color performance in the specific intended use. Not codes that can be used for everything, but a selection of colors that enhance the value the Customer wants to give to their product. The following table relates the needs of different sectors with Rifra formulation solutions: for each field, the value required for the manufactured item is translated into a concrete formulation lever, so that color becomes an active factor in product performance, reliability, and recognition.

Regulated and high-performance sectors Values for manufactured items How to obtain value from Rifra formulas
Food packaging Containers for water, juices, oil. Maximum organoleptic neutrality and mandatory regulatory compliance. Formulations compliant with EU Reg. 10/2011 and FDA.
Medical Bottles for pharmaceuticals, supplements, medical devices. Maximum requirements for purity, absence of migration, and chemical stability. Regulatory documentation. Maximum traceability. Formulations designed according to the sterilization technology.
Sectors with high aesthetic impact and durability Value for manufactured goods How to obtain value from Rifra formulas
Cosmetics Bottles for shampoo, detergents, cosmetics, and household products. High aesthetic quality, vibrant colors, and range chromatic consistency required. High opacity with optimized TiO2. Metamerism control. Pearlescent and metallic effects. Colorimetric repeatability for range productions.
Housewares Containers specifically designed to meet style and design requirements. Formulations created with colors developed in direct contact with the Customer’s designers; wide range of special effects and customizable solutions.
Specialized high-stress sectors Value for manufactured goods How to obtain value from Rifra formulas
Non-food packaging Jerry cans, drums, and tanks for aggressive chemical products (acids, bases, solvents). Bottles and containers for lubricants, paints, professional products. Mechanical and chemical resistance with visual identification of contents. Pigments with resistance to hydrocarbons and solvents. Uniform opacity. Standardized color codes for rapid identification of content.

Additive Masterbatches

Our long-standing additive solutions

When it is necessary to provide the manufactured item with specific characteristics, Rifra develops dedicated solutions by collaborating with active ingredient suppliers and verifying with Customers the best balance between the amount of active ingredient in the finished product and the desired performance.

Value for manufactured items Process benefits Properties
Container with uniform wall and absence of thin areas or fragile points. The flow modifier regulates the viscosity profile of the parison in EBM, reducing sagging and allowing for more stable thickness programming along the axis. MELT STRENGTH ENHANCER
Container with a brilliant external surface free of streaks. PPA reduces pressure at the extrusion head and die build-up on the lips of the annular die, eliminating longitudinal streaks (die lines) on the finished container. PROCESS AID ADDITIVE (PPA)
Container with stable color, without post-molding yellowing. Antioxidant protection prevents thermal degradation of the polymer in the barrel and blow head, maintaining constant color tone lot-to-lot. ANTIOXIDANT
Outdoor container with color and mechanical properties preserved over time. The appropriate UV/HALS selection for the intended use balances solar protection with minimal interference on polymer properties and the parison. UV STABILIZER HALS
Barrier container with low permeability to oxygen or hydrocarbons. The scavenger system integrated into the masterbatch absorbs residual oxygen in the container cavity during filling, extending the product’s shelf life. OXYGEN SCAVENGER BARRIER ADDITIVE

Complex Masterbatches

Our best formulations: the COMPLEX range

As in all well-made things, the best result is obtained by working as a team. Rifra translates this motto into a preference for solutions that combine color formulation with the most high-performing chemistries, providing “all-in-one” additivated structures directly in the plant.

Rifra solutions Synergistic advantage Guaranteed efficiency
RIFRACHEM CX PPA + ANTIOX Colored container with an external surface free of die lines and polymer protected from thermal degradation. PPA stabilizes the flow at the blow head; the antioxidant prevents yellowing during color changes. Elimination of surface streaks, reduction of machine downtime for head cleaning, maintenance of stable color tone over long cycles.
RIFRACHEM CX UV + ANTIOX Colored container with thermal protection during processing and solar protection during service. Formulation designed for jerry cans and outdoor containers requiring multi-year chromatic and mechanical durability. Prolonged outdoor color stability. Resistance to UV-oxidative degradation. Maintenance of mechanical properties (ESCR) for containers for aggressive chemical products.
RIFRACHEM CX MELT STRENGTH + UV EBM container with a stable parison and no sagging, and integrated UV protection for outdoor use. The synergy stabilizes the production process and ensures the durability of the finished container. Reduction of waste from unstable parisons in EBM with long parisons. UV protection for agricultural jerry cans and outdoor tanks. Stable color after years of exposure.