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How to Make Rigid Polyurethane Foam?

Rigid polyurethane foam, commonly called rigid PU foam, is produced through the reaction of rigid foam polyether polyol and isocyanate (also known as black material). Rigid PU foam is characterized by a high closed-cell rate and low thermal conductivity, making it one of the most widely used and best-performing insulation materials in the construction industry today.

Regarding building panels, rigid polyurethane foam boards can be categorized into continuous and intermittent types based on the foaming and molding process. This article will introduce the production processes of these two types of polyurethane boards and how to select their raw materials, such as polyether polyol, and polyol blend.

Continuous Rigid Polyurethane Foam Board Production Process

The continuous production of rigid polyurethane foam boards has greatly improved production efficiency.

Production Process

After the raw materials are mixed in the foaming machine, they are injected into a uniformly moving substrate for foaming. The upper substrate covers the foam, forming a board with substrates on both sides. Common substrates include aluminum foil or metal materials. During the foaming process, the rigid polyurethane foam cures between double-layered pressurized panels, and the board is then cut to the required length.

During production, material distribution must be even, typically achieved by reciprocating pouring with a mixing head at a production speed of about 9–10 m/min. If the speed is too high or the pouring is too fast, excess material may accumulate at the edges or cause operational difficulties. Using two or more mixing heads can reduce the pouring volume of each head, but a pressure roller or similar device is needed to ensure even material distribution.

The thickness of the board can be adjusted by modifying the spacing between the conveyor belts of the forming machine and the thickness of the side sealing blocks, with a range of 20mm to 250mm. The conveyor belt speed can be adjusted between 1.0m/min and 25m/min, and the board width can be adjusted within a range of 600mm to 1200mm.

Precautions for Raw Materials

Additionally, it is important to note that in the high-speed continuous composite foaming process, the reaction speed is highly sensitive to temperature changes, especially in the polyisocyanurate foam system. Therefore, to reduce the system’s sensitivity to temperature, it is recommended to use high-viscosity grade isocyanates during production.

Intermittent Rigid Polyurethane Foam Board Production Process

Production of Injection-Molded Boards

The production method for injection-molded boards is an intermittent process.

Specifically, the raw materials are mixed in a foaming machine and then injected into the mold cavity (with the substrate already in place) through an injection port. After the foam cures, the board is removed from the mold. This method involves simple equipment and is suitable for producing a variety of products, especially boards with different surface layer requirements. During production, it is necessary to adjust the foaming time and formulation based on the length of the board, particularly for longer boards.

The gelation speed significantly affects the quality of the finished product. If gelation occurs too quickly, the mold cavity may not be filled evenly, potentially leading to inconsistent density or voids. In such cases, adjusting the polyether polyol blend formulation becomes crucial.

Selection of Raw Materials

The selection of raw materials has a significant impact on the various properties of rigid polyurethane foam boards. So, how can one choose the appropriate raw materials to ensure that the resulting rigid polyurethane foam exhibit superior performance?

Selection of Polyether Polyol

First and foremost, selecting the appropriate polyether polyol is crucial. Polyether polyol is one of the fundamental raw materials for rigid polyurethane foam, and it affects the physical and mechanical properties, dimensional stability, and foaming process performance of the resulting foam core material. Once the type of polyether is determined based on the requirements for the initiator, hydroxyl value, and viscosity, it is recommended to choose a polyether polyol with a low potassium ion content.

Selection of Blowing Agents

The primary function of foam stabilizers (also known as blowing agents) is to control the size of the foam cells, maintain their stability, and prevent collapse. It is recommended to choose foam stabilizers with strong emulsifying capabilities. Silicone-based foam stabilizers are particularly effective, and their dosage can be adjusted within the range of 1.5% to 2.5% (by mass). Additionally, the type and amount of blowing agent directly influence the density, strength, and other physical properties of rigid polyurethane foam.

Blowing agents not only help adjust and control the foam’s density and performance but also reduce the viscosity of the polyether blend, improve the foaming process, and enhance foam flowability, which aids in foam shaping.

Selection of Catalysts

For catalysts, a delayed catalytic system can be selected to extend the time between the cream phase and the gel phase, effectively improving the activity of the foaming system and enhancing foam performance to suit production process requirements.

Additionally, factors such as whether the foam is evenly distributed within the cavity, the fineness of the foam, and the closed-cell rate significantly affect the overall insulation performance of the board. These factors are related to the adhesion strength between the foam and cavity walls, as well as the dimensional stability of the foam.

Use of Flame Retardants

The use of flame retardants can significantly enhance the fire resistance of rigid polyurethane foam. However, flame retardants may have a detrimental effect on the foam during the foaming process. Therefore, it is crucial to strictly control the amount of catalyst added to ensure that while improving the flame-retardant properties of rigid polyurethane foam, its performance and dimensional stability are not compromised.

Selection of Isocyanates

The choice of isocyanate is fixed, but its dosage can impact the performance of rigid polyurethane foam products. As the amount of isocyanate increases, the crosslinking density of the foam increases, leading to higher rigidity and strength. However, if too much isocyanate is used, the foam can become brittle, making the core material prone to cracking.

Conclusion

In conclusion, the production of rigid polyurethane foam boards, whether through intermittent or continuous methods, heavily relies on the quality and selection of raw materials. The choice of polyether polyols, foam stabilizers, catalysts, and other additives plays a crucial role in determining the foam’s physical properties, such as density, strength, and thermal insulation performance.

As the industry continues to evolve, further advancements in raw material formulations will be key to improving both production efficiency and the overall performance of polyurethane foam boards in various applications. As a manufacturer of rigid polyurethane foam raw materials, we at LECRON SHARE will continue to optimize the quality of raw materials and contribute to a better rigid polyurethane foam market in the future.

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We provide detailed product information covering various aspects, including technical specifications, performance indicators, application cases, etc. These materials will help you better understand the characteristics and advantages of our products in order to make wise decisions.

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