Masterbatches for rotational molding

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Rotational molding

For every need of the rotational molding process

We actively collaborate with the Client throughout all phases of rotational molding to resolve defects and improve productivity. We work closely to fine-tune process conditions, exploring alternative additives and materials together that can address the primary causes of defects. The result is a synergy that significantly reduces waste and develops value in innovation starting from the expertise of both parties.

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Phase one

1. Material preparation and dosing

The polymer, typically in the form of finely ground powder, is weighed and introduced into the cold mold. If the polymer has not been pre-colored, the coloring Masterbatches or additive is dry-mixed with the base powder. Rifra supports this technology by offering the possibility to study granule size together or by working in collaboration with powder manufacturers for the sector. Rifra supports this technology by offering the opportunity to jointly study particle size or by collaborating with powder manufacturers in the industry. In this phase, the three essential conditions to control are:

Uniform particle size to ensure homogeneous melting.

Accurate Masterbatches / powder mixing with validated times and methods to avoid segregation.

Precise gravimetric dosing to control the nominal thickness of the product.

Phase two

2. Mold loading and closing

The dosed powder is introduced into the mold (generally made of cast aluminum or sheet steel). The mold is hermetically sealed and mounted on the rotating axis of the oven. In this phase, the mold seal is essential to avoid leakage of molten material. Mold deformations, wear of the sealing seats, and non-uniform tightening generate excessive flash, thickness variations, and defects on the parting lines. In this phase, it is essential that:

The mold is free of deformations and has regular, intact sealing seats.

Tightening is uniform across all closing points (checked with gauges or dynamometers).

Vents are correctly positioned and maintained to allow air to escape during melting.

Common defects related to this phase include:

Parting lines

Common defects related to this phase include:

Mold deformation

Repeated cycles can damage the mold; systematic checks contribute to the creation of high-quality products.

Flash

Excess material leaked from the seals; sometimes leakage is also a consequence of suboptimal tightening.

Phase three

3. Heating and biaxial rotation

The closed mold is rotated biaxially (primary and secondary rotation) inside a forced convection oven, at temperatures that vary depending on the polymer. The powder melts progressively and is deposited by gravity and centrifugation onto the mold walls.

Thermal management is fundamental in this phase. Overheating causes oxidative degradation of the polymer (yellowing, browning, loss of mechanical properties). A cycle that is too short leaves the powder incompletely sintered (internal bubbles, poor interlayer cohesion). The rotation ratio influences thickness distribution. In this phase, the three essential conditions to guarantee are:

Control and repeatability of the PIAT within ±5°C of the optimal process value for the polymer used.

Rotation ratio optimized for the mold geometry, verified through thickness distribution on the part.

Absence of excess oxygen in the mold: use of inert nitrogen or control of vent ports to limit oxidation.

The main critical issues are:

Maximum internal air temperature of the mold

A key process parameter to ensure that every part is cured uniformly, the mechanics are repeatable, and degradation or under-curing is avoided.

Sintering

Sintering of powder particles and formation of a cohesive, porosity-free film.

Ratio between primary and secondary speed

The ratio between primary and secondary rotation speed affects thickness distribution.

Hot spots

Localized overheating zones due to complex geometries or insufficient convection.

Bubbles

Entrapment of air bubbles due to premature melting of the surface.

Phase four

4. Cooling and demolding

The mold is removed from the oven and cooled using air jets, water mist, or a combination of both. After reaching the extraction temperature, the mold is opened and the product is extracted. Cooling that is too rapid at this stage generates residual stresses, warpage, and non-uniform shrinkage. Premature demolding causes structural collapse of the still-hot part. Insufficient draft angles generate extraction problems. In this phase, the three essential conditions to keep under control are:

Controlled and gradual cooling rate (avoiding thermal shocks) to minimize residual stresses.

Adherence to the specific demolding temperature for the polymer.

Mold geometry with adequate draft angles and suitable release agents.

The main critical issues are:

Cooling rate

The cooling rate influences the crystallinity and residual stresses on the product.

Distortions

Uncontrolled dimensional deformation of the part during cooling.

Shrinkage

Volumetric shrinkage of the polymer and dimensional tolerances of the product.

Removal temperature

Minimum temperature at which the part can be extracted without deformation.

Markets

Markets for rotational molding

Success in rotational molding is measured by the ability to respond to the unique challenges of each sector. Solutions that guarantee high productivity, consistent quality, and regulatory compliance are not universal, but must be engineered for the specific end application. Our expertise and products serve the most critical needs in a wide range of high-tech and regulated industrial sectors.

Products

Product line for rotational molding

Rifra offers a wide range of Color, Additive, and Complex formulations for every need of the rotational molding process, including UV stabilizers, nucleating agents, lubricants, and antistatic additives. Each product is developed to optimize the production process and ensure the best aesthetic and functional result, with a focus on sustainability and the circular economy.

Color Masterbatches

Our design rules for color formulations

Rifra’s approach has never been to propose standard formulas, but to develop tailor-made solutions together with the Client that enhance color performance in the specific application. Solutions designed to add value to the final product according to the Client’s needs. The following table stems from this continuous dialogue. It connects the value chain: what the Client wants to bring to the market as product and innovation is linked to what Rifra can do so that such value develops to its maximum potential. We are on the same side. Your production challenge is our priority.

Specialized high-stress sectors	Value for manufactured goods	How to obtain value from Rifra formulas
Agriculture	Cisterns, storage tanks for pesticides, collection basins, tanks for drip irrigation. Products that operate outdoors for decades.	Formulations with UV/HALS balanced with selected inorganic pigments. Guaranteed color stability even after years of prolonged solar exposure.
Non-food packaging	Tanks for acids, bases, and solvents. Drums and containers for aggressive products that require specific chemical resistance of the polymer and the colorant.	Selection of pigments with high chemical resistance. No migration in the presence of corrosive agents. Certified formulations for UN-approved containers.
Construction	Inspection chambers, manholes, water storage tanks. Products subject to cyclic mechanical loads, thermal shocks, and UV in urban environments.	High-durability UV/HALS systems. Inorganic pigments with full compatibility with polymer stabilizers. Stability in extreme heat and cold.
Nautical and Marine	Kayaks, canoes, floats, buoys, boat components. Prolonged use in salt water and in contact with intense UV and salt spray.	Formulations with pigments featuring very high lightfastness (7 on the wool scale) and HALS stabilizers for aggressive marine environments.

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Sectors with high aesthetic impact and durability	Value for manufactured goods	How to obtain value from Rifra formulas
Furniture	Planters, benches, playgrounds, swimming pools. Products in prolonged contact with people and natural environments: high aesthetic quality and safety required.	Metamerism control for vibrant colors. Pigments with certification for skin contact and children’s environments. Lot-to-lot color consistency.

Regulated and high-performance sectors	Value for manufactured goods	How to obtain value from Rifra formulas
Automotive	Fenders, fuel and fluid tanks, internal components, and bumpers for industrial and agricultural vehicles. Resistance to impact and thermal shocks.	REACH-compliant pigments, HAP-free, with thermal stability up to 200°C. Formulations validated on specific polymers to avoid altering mechanical properties.
Food Packaging	Drinking water tanks, food containers, beverage cisterns. Regulatory compliance and organoleptic neutrality are mandatory.	Pigments and additives compliant with EU Reg. 10/2011 and FDA standards. Migration testing. Formulations developed on food-grade LLDPE and HDPE.
Toys	Slides, swings, playhouses, small pools, playground elements. Products in prolonged contact with children, subject to solar exposure, weathering, and mechanical wear. High safety, weather resistance, and long-term aesthetic quality required.	Formulations with pigments certified for prolonged skin contact. UV/HALS stabilizers selected to ensure fade resistance and maintenance of mechanical properties even after years of outdoor exposure. Bright and brilliant colors with lot-to-lot color consistency for product identity.

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Additive Masterbatches

Our long-standing additive solutions

When it is necessary to give the product specific characteristics, Rifra studies dedicated solutions by collaborating with active ingredient suppliers and verifying with Clients the best balance between the amount of active ingredient in the finished product and the desired performance.

Value for manufactured goods	Benefits for the process	Properties
Product with uniform thickness and a smooth, porosity-free external surface.	The Masterbatches based on nucleating agents and flow modifiers regulates the melting speed of the powder on the chill roll, reducing the encapsulation of air bubbles.	FLOW MODIFIER NUCLEATING AGENT
Product resistant to thermal degradation from the oven cycle.	Antioxidant protection prevents polymer yellowing during long periods at process temperatures and reduces off-colors at the end of the cycle.	ANTIOXIDANT HEAT STABILIZER
Product with stable color that does not fade after years of outdoor exposure.	Correct selection of UV absorbers and HALS minimizes die build-up from stabilizer volatilization and maintains mechanical properties over time.	UV STABILIZER HALS
Product with a demoldable surface without external release agents.	Internal release agents integrated into the Masterbatches reduce cycle times and the use of release sprays, eliminating incompatibility with subsequent paints and adhesives.	INTERNAL MOLD RELEASE AGENT
Flame-retardant product, study of the most effective formula for passing the relevant industry standard.	The compatibility of the flame retardant with process conditions avoids its degradation and the decline of mechanical properties over repeated cycles.	FLAME RETARDANT

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Complex Masterbatches

Our design rules for color formulations

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 UV + MOLD RELEASE	Colored product with an optimal external surface for demolding and integrated UV protection. The synergy eliminates interference between the release agent and stabilizer, guaranteeing both performances in a single dosage.	Reduction of cycle times, no external release agents, long-term outdoor color stability. Ideal for furniture and containers.
RIFRACHEM CX ANTIOX + UV	Colored product with full thermal protection in the oven and resistance to solar degradation. Antioxidant protection safeguards the polymer during the high-temperature cycle; UV protection extends its outdoor life.	Prevention of yellowing during the cycle, color stability over time, maintenance of mechanical properties even on natural LLDPE and HDPE.
RIFRACHEM CX UV + ANTIMICROBIAL	Integrated solution for outdoor containers in contact with water or food: protection from solar degradation and antimicrobial properties within the polymer mass.	Double functionality in one master: guaranteed outdoor durability and product hygiene. Compliant for drinking water tanks (with certified pigments).

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