Silicone oil alone cannot meet the comprehensive performance requirements of follower sealants. It must be blended with thickeners and additives to form qualified follower sealants.
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Core functions and performance requirements of follower sealantsFollower sealants, also known as tail plug oil or lithium base ester, are key materials for gel ink ballpoint pens with the following core functions and corresponding standards:(1) Sealing and leakage prevention: Block ink backflow and volatilization, avoid ink overflow after dropping, and maintain a clear interface without mutual dissolution with ink.(2) Follow-up performance: Move synchronously with the ink interface as writing proceeds to form a liquid piston and balance negative pressure inside the pen tube.(3) Thixotropy: Maintain high viscosity at rest to prevent leakage and turn fluid under shear force for smooth following without wall adhesion.(4) Long-term stability: Consistent performance under high and low temperatures, no bubble generation, low evaporation rate, and no stratification after long-term storage.
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Critical defects of single silicone oilAlthough dimethyl silicone oil serves as the base oil of follower sealants, it has fatal drawbacks when used independently:(1) Lack of gel structure and unbalanced sealing & follow-up performanceLow-viscosity silicone oil flows excessively, failing to block ink and causing backflow and leakage. High-viscosity silicone oil provides temporary sealing yet moves sluggishly during writing, easily breaking and leading to interrupted writing. Single silicone oil has no thixotropy and cannot switch between high static viscosity and low shear viscosity.(2) Unstable interface and severe wall creepingSilicone oil has a low surface tension of 20–21 mN/m, forming a large tension gap with ink (30–40 mN/m). It adheres weakly to PP pen tube walls and creeps upward easily, resulting in sealing failure. Without a network structure formed by thickeners, silicone oil cannot maintain integral continuity and will split into tiny droplets.(3) Poor shock resistance and insufficient evaporation inhibitionPure silicone oil in liquid state cannot buffer impact during dropping, so ink easily breaks through the silicone oil layer and leaks out. Despite its low volatility, pure silicone oil has far weaker evaporation resistance than gel-type follower sealants.
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Standard formulation of silicone oil-based follower sealantsSilicone oil needs to be compounded with the following components to produce qualified sealants:(1) Base oil: Provide basic viscosity, low volatility and ink incompatibility; common options include dimethyl silicone oil, methylphenyl silicone oil, polyisobutylene and liquid paraffin.(2) Thickener: Build gel networks and deliver thixotropy and stability; typical materials are hydrophobic fumed silica and lithium organic acid salts.(3) Additives: Adjust interfacial properties, fluidity and long-term stability, including surfactants and antioxidants.Typical mass ratio: 25–80 parts base oil + 3–16 parts thickener + 20–60 parts additives.
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Conclusion & supplementary notes(1) Core conclusion: Silicone oil alone cannot satisfy all standards for follower sealants. Thickeners are mandatory to form gel structures, matched with additives to optimize sealing and follow-up properties.(2) Special scenarios: Some high-viscosity oil-based ballpoint pen inks do not require follower sealants due to their inherent high viscosity and low backflow risk. Even silicone oil-based sealants must adopt high-viscosity, low-volatility silicone oils with strictly controlled formulation ratios.(3) Industrial standards: Follower sealants shall comply with specifications such as QB/T2776, with clear indicators for viscosity, follow-up performance, sealing capacity and anti-stratification property.
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