Why Can’t Two-component Polyurethane Adhesives Be Stirred With A Round Rod?

Introduction

Two-component polyurethane adhesives are adhesives made up of two separate components that, when mixed together, react chemically to form a strong, durable bond. Two-component polyurethane adhesives are versatile and have high strength and flexibility, making them suitable for a variety of demanding applications. If mixed incorrectly, the adhesive may not cure properly, resulting in a weak bond and application failure. Therefore, it is important to understand the composition and correct use of two-component polyurethane adhesives. This article takes a deep look at two-component polyurethane adhesives, explores its composition and characteristics, and why it cannot be stirred with a round bar, and understands the correct use method to make it fully perform.

What Are Two-component Polyurethane Adhesives?

Two-component polyurethane adhesive is the most important category of polyurethane adhesives, with a wide range of uses and large dosage. It is usually composed of two components, A and B, which are packaged separately and can be prepared in a certain proportion before use. Component A (main agent) is a hydroxyl component, and component B (curing agent) is a component containing free isocyanate groups. Some main agents are polyurethane prepolymers with terminal NCO, and the curing agent is a low molecular weight polyol or polyamine. Component A and component B are mixed in a certain proportion to form a polyurethane resin.

Advantages Of Two-component Polyurethane Adhesives

1.Reactive—When the two components are mixed, a chemical reaction occurs, curing and forming a solid polyurethane.
2.Adjustable—The composition and molecular weight of the two components can be modified to achieve the desired viscosity, cure speed and mechanical properties.
3.Room Temperature Cure — Curing can be done at room temperature or heat can be used to accelerate the cure.
4.Flexible Mixing Ratio —the ratio of the two components can usually be adjusted within a certain range.
5.Strong Bond — with high bond strength
6.Chemical Resistance—Two-component polyurethanes typically have better chemical resistance compared to one-component versions.
7.Fast Cure — cures faster than one-component polyurethanes
8.Versatility—Two-component polyurethane adhesives can bond to a variety of substrates, including metal, glass, plastics and composites.
9.Customizable Curing Time —The curing speed can be adjusted by selecting specific raw materials or adding catalysts.
10.High-performance Properties—Excellent resistance to shock and vibration, and remains flexible at low temperatures.

Applications Of Two-component Polyurethane Adhesives

Automotive Industry

• In the automotive industry, two-component polyurethane adhesives are primarily used in the construction of composite panels in refrigerated truck beds to provide thermal insulation and structural integrity.

Architectural Decoration

• Ceilings and Wall Panels
  Aluminum Honeycomb Panels: Aluminum honeycomb panels for ceilings and wall panels. The lightweight and strong bond provided by the adhesive ensures durability and aesthetics.

• Interior Wall Panels
  Inorganic Fireproof Substrate: Used to bond various decorative panels such as CPL (Continuous Pressure Laminate) and aluminum panels to inorganic fireproof substrates. The adhesive ensures that the panels are firmly connected, providing fire resistance and structural stability.

• Exterior Wall Panels
  Insulation and Thermal Insulation Materials: Two-component polyurethane adhesives are used for inorganic fireproof panels for exterior wall insulation and thermal insulation. The adhesive provides a strong and weather-resistant bond.

• Rock Panels
  Backed Fiberglass: Two-component polyurethane adhesives are used to bond rock panels with backed fiberglass, ensuring that the panels are strong and impact-resistant.

Aerospace Industry

• In the aerospace industry, two-component polyurethane adhesives can be used to assemble and repair aircraft parts, and their light weight and high strength properties make the aircraft structure more complete.

Electronics

• Two-component polyurethane adhesives are used to pot and encapsulate electronic components, protecting them from moisture, dust and other environmental factors.

Composite Material Manufacturing

• Two-component polyurethane adhesives can also be used in the manufacture of composite materials, such as sports equipment and industrial machinery, to bond different materials together to form lightweight, high-strength composite structures.

Other Applications

• In the renewable energy sector, two-component polyurethane adhesives can also be used to bond components in wind turbines and solar panels.

The Reason Why Two-component Polyurethane Adhesive Cannot Be Stirred With A Round Rod

• Experienced professionals know that round rods have no friction, cannot mix evenly, and the adhesive attached to the bottom and wall of the barrel is not fully stirred, which will affect the performance of the glue binder. Specific reasons include:

• Inadequate mixing: Round rods cannot properly mix the two components of adhesive together. Adhesives need to be mixed consistently and evenly to ensure chemical reactions.

• Fast curing time: Once mixed, the two-component adhesive usually cures quickly; using round rods is very slow and may cause the mixture to begin to cure before it is fully mixed, failing to achieve the desired effect.

• Viscosity variation: The difference in thickness of the two-component adhesive may cause one component to mix faster than the other, resulting in uneven mixing and ineffective bonding.

• Air entrapment: Stirring with a round bar can introduce air bubbles into the mixture. The presence of air entrapment weakens the bond and creates voids in the cured material.

• Air entrapment: Stirring with a round bar can introduce air bubbles into the mixture. The presence of air entrapment weakens the bond and creates voids in the cured material.

• Inconsistent Adhesive Properties: If not mixed thoroughly and evenly, the properties of the adhesive may vary across the bond area, leading to unpredictable results.

  Correct Mixing Method For Two-component Polyurethane Adhesives

  Two-component polyurethane adhesives are not mixed with round rods but are usually mixed with specialized equipment, such as:

• Evacuated mixing bowl: Use an evacuated mixing bowl to add the components in the correct order. For example, add isocyanate and olamine activator, mix for a set time, and then evacuate to remove air bubbles. This method ensures thorough mixing and prevents air entrapment.

• Automated dispensing system: Use an automated dispensing system to mix in the correct proportions. This system adjusts the reactivity of the adhesive and provides consistent mixing.

• High shear mixer: Use a high shear mixer or impeller mixer to provide the shear and turbulence required for thorough mixing, which is more effective than manual mixing with a rod.

• Temperature control: Maintain the proper temperature during mixing. For solvent-free adhesives, the adhesive is typically heated to a specific range (e.g., 40°C to 60°C) to facilitate proper mixing and application.

By following these methods, you ensure that the two-component polyurethane adhesive is mixed correctly, leading to optimal performance and bonding strength.

Precautions For Using Two-component Polyurethane Adhesives

1 About storage: Generally placed in a dry and cool place, the storage temperature is usually: 10-30℃., open and use as soon as possible.

2 Before use, make sure that the surface of the bonded material is clean, flat and well lubricated.

3 The mixing ratio must be correct, sufficient and uniform, otherwise it will affect the bonding strength. By observing the color depth, you can judge whether it is uniform.

4 The glue should be applied evenly, without missing scrapes or accumulation.

5 After applying the glue, it should be laminated and pressed as soon as possible; it is recommended to pressurize the film until it reaches the transportable strength after lamination. The pressure of the adhesive layer is recommended to be 1-3kg/cm2; it depends on the type of material and flatness, to ensure that the bonding surface is in close contact and the force is uniform.
You can choose cold pressing or hot pressing according to your own situation. Hot pressing is generally 40-80C.

6 Before unloading the pressure, make sure that the adhesive has solidified and the film is not deformed by finger pressure.

Conclusion

Proper mixing tools and techniques are critical to the effectiveness of two-component polyurethane adhesives. Using the correct equipment ensures a thorough and uniform mix, which is essential for the adhesive to cure properly and provide the desired bond strength and durability. Inadequate mixing can result in incomplete cure, weak bonds, and inconsistent adhesive performance, compromising the integrity of the application. For best results, proper guidelines should be followed to ensure optimal performance.

Reference

What is two-component polyurethane adhesive from WINLONG
Related knowledge about two-component polyurethane adhesives from BOSTIK