Halogen-free flame retardant reference formulation for water-based acrylic electronic adhesives

Halogen-free flame retardant reference formulation for water-based acrylic electronic adhesives

In water-based acrylic systems, the addition amounts of aluminum hypophosphite (AHP) and zinc borate (ZB) should be determined based on specific application requirements (such as flame retardancy rating, coating thickness, physical performance requirements, etc.) and their synergistic effects. Below are general recommendations and reference ranges:

I. Baseline Addition Amounts Reference

Table: Recommended Flame Retardant Additions and Descriptions

II. Optimization of Compound Ratios

1. Typical Compound Ratios:

• AHP:ZB = 2:1 ~ 4:1 (e.g., 15% AHP + 5% ZB, total 20%).
• Adjust ratios experimentally, for example:
• High flame retardancy demand: AHP 15%~20%, ZB 5%~8%.
• Balanced physical properties: AHP 10%~15%, ZB 3%~5%.

1. Synergistic Effects:

• Zinc borate enhances flame retardancy by:
• Stabilizing char formation (interacting with aluminum phosphate generated by AHP).
• Releasing bound water to absorb heat and dilute flammable gases.

III. Experimental Validation Steps

1. Stepwise Testing:

• Individual testing: First evaluate AHP (5%~20%) or ZB (5%~15%) separately for flame retardancy (UL-94, LOI) and coating performance (adhesion, hardness, water resistance).
• Compound optimization: After selecting a baseline AHP amount, incrementally add ZB (e.g., 3% to 8% when AHP is 15%) and observe improvements in flame retardancy and side effects.

1. Key Performance Indicators:

• Flame retardancy: LOI (target ≥28%), UL-94 rating (V-0/V-1), smoke density.
• Physical properties: Film formation, adhesion (ASTM D3359), water resistance (no delamination after 48h immersion).

IV. Key Considerations

• Dispersion Stability:
• AHP is hygroscopic—pre-dry or use surface-modified variants.
• Use dispersants (e.g., BYK-190, TEGO Dispers 750W) to improve uniformity and prevent sedimentation.
• pH Compatibility:
• Water-based acrylic systems typically have a pH of 8–9; ensure AHP and ZB remain stable (avoid hydrolysis or decomposition).
• Regulatory Compliance:
• AHP must meet halogen-free RoHS requirements; ZB should use low heavy-metal impurity grades.

V. Alternative or Supplemental Solutions

• Melamine Polyphosphate (MPP): Can further enhance flame retardancy when combined with AHP (e.g., 10% AHP + 5% MPP + 3% ZB).
• Nano Flame Retardants: Nano-grade ZB (addition reduced to 1%~3%) or layered double hydroxides (LDH) for improved barrier effects.

VI. Summary Recommendations

• Starting formulation: AHP 10%~15% + ZB 3%~5% (total 13%~20%), then optimize.
• Validation method: Test small-scale samples for LOI and UL-94 while evaluating mechanical properties.  

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