Formula Concept And Production Approach For Solvent Based PSA Adhesive For PVC Electrical Insulation

To formulate a rubber-based, solvent-based pressure-sensitive adhesive (PSA) for use in PVC electrical insulation tape with high cohesive strength and no residue upon removal, you need to focus on several key components and processing steps. Here's a formula concept and production approach:

Key Components

1. Elastomeric Base (Rubber)
• Natural rubber (NR) or synthetic rubber (e.g., Styrene-Butadiene Rubber - SBR): Natural rubber offers good flexibility and adhesion, while SBR provides better thermal stability and aging resistance, which is beneficial for electrical tapes.
• Butyl Rubber (IIR): Enhances moisture and air barrier properties, and provides good aging resistance.
2. Tackifiers
• Tackifiers are crucial for initial tack and bonding to PVC. Consider using:
• Hydrocarbon resin (C5/C9 aliphatic/aromatic)
• Rosin esters: Provide good compatibility with rubber and enhance adhesion to non-polar surfaces like PVC.
• The choice of tackifier affects the balance between adhesion and cohesive strength.
3. Plasticizers
• Mineral oil or naphthenic oil: Adjusts the softness and flexibility of the adhesive without compromising its performance. The plasticizer also helps control peel adhesion and reduces residue upon removal.
4. Fillers
• Fillers like calcium carbonate or silica can be used to adjust the viscosity, modify tack, and improve cohesive strength.
5. Antioxidants & UV Stabilizers
• To protect the rubber and tackifiers from oxidation and UV degradation, you might add:
• Hindered phenols (e.g., BHT - Butylated Hydroxytoluene)
• UV absorbers or hindered amine light stabilizers (HALS) to enhance outdoor stability.
6. Crosslinkers
• Crosslinkers improve cohesive strength, a critical factor for preventing residue upon removal. Suitable options include:
• Phenolic resins for increased internal strength.
• Sulfur-based crosslinkers can be used for vulcanizing the rubber to achieve higher cohesive strength without compromising tack.
7. Solvent
• Toluene or hexane are commonly used as solvents to dissolve the rubber, tackifiers, and plasticizers. Solvent choice will influence drying time, final viscosity, and safety considerations.

Performance Considerations

• High Cohesive Strength: The right balance of elastomer and tackifier ensures strong internal strength, reducing residue upon removal.
• Residue-Free Removal: A slightly lower tack with higher cohesive strength is necessary to minimize residue. The crosslinking level must be optimized to allow strong bonding without leaving adhesive behind on the surface.
• Peel Adhesion to PVC: The formulation should have strong adhesion to PVC but be designed for clean removal, requiring a careful balance of rubber, tackifiers, and plasticizers.

Here's a formulation for a rubber-based, solvent-based PSA suitable for PVC electrical insulation tape, designed to offer high cohesive strength and clean removal with no residue.

Please note: This formulation is a starting point, and adjustments may be required based on production conditions and specific requirements.

Complete Working Formulation (for 100 parts by weight)

1.    Natural Rubber (SMR-20 or RSS-1): 100 parts

• Acts as the primary elastomer, providing good flexibility, adhesion, and strength.

2.    Tackifier (C5 Hydrocarbon Resin): 80 parts

• Provides tack and improves bonding to non-polar surfaces like PVC.
• Example: Escorez 5380 (or equivalent).

3.    Plasticizer (Naphthenic Oil): 10 parts

• Helps adjust the softness and ensures flexibility.
• Example: Nyflex 820 (or equivalent).

4.    Crosslinker (Phenolic Resin): 5 parts

• Enhances cohesive strength and reduces the risk of residue.
• Example: SP-1068 phenolic resin (or equivalent).

5.    Antioxidant (Hindered Phenol - BHT): 1 part

• Protects the adhesive from oxidation and ensures stability during storage and application.
• Example: Butylated Hydroxytoluene (BHT).

6.    Filler (Calcium Carbonate): 15 parts

• Improves the internal strength and reduces overall costs.
• Example: OMYA BLR 2 or any finely ground calcium carbonate.

7.    Solvent (Toluene): 300 parts

• Acts as the primary solvent for dissolving the rubber and other components.
• Alternatively, you could use a blend of Toluene (200 parts) and Hexane (100 parts) to optimize drying speed and solvent evaporation.

Production Method

1.    Rubber Dissolution:

• Dissolve 100 parts of natural rubber in 150 parts of toluene (or toluene/hexane blend) in a high-shear mixer. The temperature should be controlled at 60-80°C to ensure efficient dissolution.

2.    Add Tackifier:

• Slowly add 80 parts of hydrocarbon resin tackifier while continuing to mix. Maintain temperature and mixing speed to prevent any phase separation.

3.    Add Plasticizer:

• Gradually introduce 10 parts of naphthenic oil to the solution. This will adjust the flexibility and ensure smooth coating during application.

4.    Add Crosslinker:

• Add 5 parts of phenolic resin. This step enhances cohesive strength and reduces residue upon removal. Ensure it's well-dispersed in the solution.

5.    Add Antioxidant and Filler:

• Add 1 part of BHT antioxidant to ensure the adhesive does not degrade over time. Mix thoroughly.
• Then add 15 parts of calcium carbonate filler slowly to prevent clumping. This will improve viscosity and enhance cohesive strength.

6.    Final Adjustment:

• Adjust the viscosity of the adhesive by adding more solvent if necessary, keeping the final solids content around 25-30%.

7.    Coating:

• The adhesive is coated onto PVC film using a knife-over-roll or gravure coating system. Ensure the coating is uniform to prevent defects in the final tape.

8.    Drying:

• Dry the adhesive-coated PVC film in an oven at around 60-100°C to remove the solvent completely. Drying time and temperature depend on the solvent system used.

9.    Slitting and Rewinding:

• After drying, slit the adhesive-coated PVC film into the desired tape widths. Rewind the tapes under appropriate tension to ensure no wrinkles or deformation.

Note: This formulation provides a robust starting point for producing a high-performance solvent-based rubber PSA suitable for PVC electrical insulation tapes. 

Here are some key considerations and tips for scaling up the production of your rubber-based, solvent-based PSA formulation for PVC electrical insulation tapes. These will help ensure a smooth transition from lab-scale to full-scale production.

1.    Raw Material Sourcing: Ensure consistent quality of natural rubber, tackifiers, and solvents. Work with reliable suppliers to avoid variations affecting performance.

2.    Solvent Handling: Use proper ventilation and solvent recovery systems to minimize hazards. Ensure compliance with local VOC regulations.

3.    Mixing Process: Utilize high-shear mixers for large batches, controlling heat and mixing time for even dispersion. Avoid excessive heat and air entrapment.

4.    Viscosity Control: Adjust solvent content and monitor viscosity throughout production to ensure uniform adhesive application.

5.    Coating Line Setup: Optimize coating thickness and line speed for efficient adhesive application and drying.

6.    Drying and Solvent Evaporation: Ensure ovens have adequate capacity for complete solvent removal without defects.

7.    Adhesive Thickness: Maintain uniform adhesive thickness to ensure consistent adhesion and electrical properties.

8.    Quality Control: Implement real-time tests for viscosity, coat weight, and finished product tests such as peel adhesion and electrical insulation.

9.    Slitting and Rewinding: Control tension and use precise slitting equipment to ensure clean, uniform tape.

10. Production Optimization: Optimize batch sizes and consider automated systems to monitor quality and improve efficiency.

Final remarks

By considering these factors, you can successfully scale up the production of your rubber-based, solvent-based PSA adhesive while maintaining quality and performance.