Ruitang Patent | Double-Wall Rotomolded Products Anti-Delamination Molding Technology

Double-wall rotomolded products feature separated functional layers and composite properties. They are widely used in anti-corrosion storage tanks, insulated containers, impermeable fuel tanks and other applications. However, the conventional production methods for double-wall rotomolded parts have long suffered from common industrial challenges:

▫️ Complicated production procedures. Most mainstream processes adopt separate feeding and multi-stage molding, which require repeated mold opening and closing and parameter adjustment. The production cycle is long and labor costs are high.

▫️ Weak interlayer bonding. For products made by multi-step molding, the two layers are bonded secondarily at the interface. The bonding strength is low, and delamination or peeling may occur during long-term service, impairing product performance.

▫️ Difficult yield control. Multi-time feeding relies heavily on workers’ experience. Uniform wall thickness and tight interlayer lamination are hard to stabilize, leading to defects such as material shortage, bubbles and delamination, and low qualified rate.

▫️ Restrictions on complex shapes. For double-wall products with special-shaped and curved surfaces, separate feeding hardly guarantees uniform wall thickness across all areas, limiting design freedom.

▫️ Low production efficiency. Multi-stage molding extends the cycle per mold, reduces equipment utilization and makes it difficult to fulfill bulk orders on time.

To solve the above pain points, the Ruitang Plastic Group R&D team started with the melting characteristics of raw materials, innovatively developed a molding concept based on melt adhesion temperature difference, and realized double-wall rotomolded products with one-time feeding. This technology has obtained national invention patent authorization.

Patent No.: ZL 2019 1 0924320.9

Patent Name: A double-wall rotomolded product manufactured based on melt adhesion temperature difference and its preparation methodCore Technical Highlights

✅ Delamination molding via one-time feeding by utilizing melt adhesion temperature difference. Two powder materials with different melt adhesion temperatures are mixed and fed into the mold at one time. During heating, the material with lower melt adhesion temperature melts first and adheres to the mold cavity to form the outer layer. The material with higher melt adhesion temperature melts later to form the inner layer. Double-wall structures can be obtained through one rotation molding without separate feeding.

✅ Tight interlayer bonding with low risk of delamination and peeling. The two layers fuse naturally in molten state. The interfacial bonding strength is much higher than secondary bonding and multi-step molding solutions. The finished products are structurally stable and resistant to interlayer peeling in long-term use.

✅ Controllable and uniform wall thickness for higher yield. Natural delamination depends on the melting properties of materials instead of manual feeding errors. Wall thickness consistency is improved, and molding defects like material shortage and bubbles are reduced to raise the qualified rate.

✅ Suitable for double-wall products with complex shapes. Special-shaped, curved and multi-cavity double-wall rotomolded parts can be stably molded by the one-time feeding process. It breaks the shape limitation of separate feeding and expands the design scope of double-wall rotomolded products.

✅ Simplified workflow for higher productivity. Repeated mold opening and separate feeding steps are eliminated. The cycle time per part is shortened, equipment utilization and labor output are improved, and the overall cost of mass production is reduced.

✅ Flexible formula for customized functional layers. Raw materials of different performances can be matched for inner and outer layers as required. It is available to achieve combinations such as chemical-resistant inner layer + weather-resistant outer layer, food-grade inner layer + high-strength outer layer.Applicable Scenarios

Scenario 1: Double-wall anti-corrosion rotomolded storage tanks for chemical industry

For storage tanks containing corrosive chemical media. The inner layer uses chemical-resistant raw materials while the outer layer adopts weather-resistant and impact-resistant formula. One-piece rotomolding ensures tight interlayer bonding and prevents leakage caused by delamination, suitable for chemical, printing and dyeing, electroplating industries.

Scenario 2: Double-wall impermeable fuel / urea tanks for vehicles

Double-wall fuel tanks and urea tanks for commercial vehicles and construction machinery. The inner layer provides medium resistance and impermeability, and the outer layer enhances structural impact resistance. Seamless one-piece molding reduces leakage risks and meets strict safety requirements for automotive components.

Scenario 3: Insulated double-wall rotomolded containers

Insulated storage containers for cold chain transportation and outdoor use. An air insulation layer can be formed between the two shells and filled with thermal insulation materials to improve heat preservation performance. The integrated structure avoids sealing failure common in traditional spliced insulation boxes.

Scenario 4: Food-grade double-wall storage and transportation containers

Storage tanks and turnover barrels for food and pharmaceutical industries. The inner layer is made of food-contact grade material to meet hygiene standards, and the outer layer uses high-strength formula for anti-drop and compression resistance, applicable to food processing and pharmaceutical warehousing and logistics.

Scenario 5: Double-wall components for outdoor play equipment

Double-wall shells of large outdoor rotomolded amusement facilities. The inner layer ensures toughness and safety, and the outer layer is formulated with UV resistance. The integrated structure resists delamination, slows aging and fading outdoors, and extends service life and safety of play equipment.

Scenario 6: Special protective double-wall housings

Protective covers for instruments and outdoor communication equipment. The inner layer is designed for energy absorption and buffering while the outer layer provides weather resistance and impact resistance. Custom special shapes are supported to satisfy protection requirements of special equipment.Core Benefits for Customers

🔹 Simplify production process to cut cost and boost efficiency. Eliminate separate feeding and repeated mold opening, shorten production cycle, increase equipment capacity, reduce manual operations and lower overall manufacturing costs.

🔹 Improve structural reliability and reduce after-sales troubles. The molten fused interface delivers far stronger bonding than traditional processes. Delamination and peeling rarely occur in long-term service, cutting after-sales repair rate and building better market reputation.

🔹 Stabilize molding quality and raise yield. Material-driven automatic layering minimizes quality fluctuation from manual operation. Wall thickness consistency is optimized to reduce material waste and defective products.

🔹 Expand product design boundaries and enrich product portfolio. Complex special-shaped double-wall products can be mass-produced stably, helping rotomolders develop high-value double-wall products and explore new business and customer groups.

🔹 Flexible functional combinations for customized orders. Inner and outer materials can be freely matched for anti-corrosion, weather resistance, food contact and high strength, quickly responding to customized requirements.

This invention represents a technological leap of rotomolding process from multi-step manufacturing to one-shot molding. It also reflects Ruitang’s continuous research on rotomolding mechanism and material application. Centered on real manufacturing pain points of rotomolders, Ruitang’s R&D team solves the industry bottlenecks of complicated procedures, easy delamination and low yield of double-wall products by material and process innovation, empowering rotomolding manufacturers to achieve higher quality and efficiency.

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