Reference flame retardant formulation for adhesives

The flame retardant formulation design for adhesives needs to be customized based on the adhesive’s base material type (such as epoxy resin, polyurethane, acrylic, etc.) and application scenarios (such as construction, electronics, automotive, etc.). Below are common adhesive flame retardant formulation components and their functions, covering both halogenated and halogen-free flame retardant solutions.

1. Principles of Adhesive Flame Retardant Formulation Design

• High Efficiency: Meet UL 94 V0 or V2.
• Compatibility: The flame retardant should be compatible with the adhesive base material without affecting bonding performance.
• Environmental Friendliness: Prioritize halogen-free flame retardants to comply with environmental regulations.
• Processability: The flame retardant should not interfere with the adhesive’s curing process or flowability.

2. Halogenated Flame Retardant Adhesive Formulation

Halogenated flame retardants (e.g., brominated) interrupt the combustion chain reaction by releasing halogen radicals, offering high flame retardant efficiency.

Formulation Components:

• Adhesive Base Material: Epoxy resin, polyurethane, or acrylic.
• Brominated Flame Retardant: 10–20% (e.g., decabromodiphenyl ether, brominated polystyrene).
• Antimony Trioxide (Synergist): 3–5% (enhances flame retardant effect).
• Plasticizer: 1–3% (improves flexibility).
• Curing Agent: Selected based on adhesive type (e.g., amine-based for epoxy resin).
• Solvent: As needed (adjusts viscosity).

Characteristics:

• Advantages: High flame retardant efficiency, low additive amount.
• Disadvantages: May produce toxic gases during combustion; environmental concerns.

3. Halogen-Free Flame Retardant Adhesive Formulation

Halogen-free flame retardants (e.g., phosphorus-based, nitrogen-based, or inorganic hydroxides) work through endothermic reactions or protective layer formation, offering better environmental performance.

Formulation Components:

• Adhesive Base Material: Epoxy resin, polyurethane, or acrylic.
• Phosphorus-Based Flame Retardant: 10–15% (e.g., ammonium polyphosphate APP or red phosphorus).
• Nitrogen-Based Flame Retardant: 5–10% (e.g., melamine cyanurate MCA).
• Inorganic Hydroxides: 20–30% (e.g., aluminum hydroxide or magnesium hydroxide).
• Plasticizer: 1–3% (improves flexibility).
• Curing Agent: Selected based on adhesive type.
• Solvent: As needed (adjusts viscosity).

Characteristics:

• Advantages: Environmentally friendly, no toxic gas emissions, compliant with regulations.
• Disadvantages: Lower flame retardant efficiency, higher additive amounts, may affect mechanical properties.

4. Key Considerations in Formulation Design

• Flame Retardant Selection:
  • Halogenated: High efficiency but poses environmental and health risks.
  • Halogen-Free: Eco-friendly but requires larger quantities.
• Compatibility: Ensure the flame retardant does not cause delamination or reduce bonding performance.
• Processability: Avoid interference with curing and flowability.
• Environmental Compliance: Prefer halogen-free options to meet RoHS, REACH, etc.

5. Typical Applications

• Construction: Fire-resistant sealants, structural adhesives.
• Electronics: Circuit board encapsulation adhesives, conductive adhesives.
• Automotive: Headlight adhesives, interior adhesives.

6. Formulation Optimization Recommendations

• Enhancing Flame Retardancy:
  • Synergistic combinations (e.g., halogen-antimony, phosphorus-nitrogen).
  • Nano flame retardants (e.g., nano magnesium hydroxide or nano clay) to improve efficiency and reduce additive amounts.
• Improving Mechanical Properties:
  • Tougheners (e.g., POE or EPDM) to enhance flexibility and impact resistance.
  • Reinforcing fillers (e.g., glass fiber) to increase strength and rigidity.
• Cost Reduction:
  • Optimize flame retardant ratios to minimize usage while meeting requirements.
  • Select cost-effective materials (e.g., domestic or blended flame retardants).

7. Environmental and Regulatory Requirements

• Halogenated Flame Retardants: Restricted under RoHS, REACH, etc.; use cautiously.
• Halogen-Free Flame Retardants: Compliant with regulations; future trend.

8. Summary

Adhesive flame retardant formulations should be designed based on specific applications and regulatory requirements, choosing between halogenated or halogen-free options. Halogenated flame retardants offer high efficiency but pose environmental risks, while halogen-free alternatives are eco-friendly but require higher additive amounts. By optimizing formulations and processes, high-performance, environmentally friendly, and cost-effective flame retardant adhesives can be developed for construction, electronics, automotive, and other industries.

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