I. Overview and Applicable Scenarios
Pressure-sensitive gaskets are a type of sealing material composed of pressure-sensitive adhesive and foamed substrate (commonly PS) activated by torque during capping. They eliminate the need for additional equipment such as electromagnetic induction sealing machines or heat shrink tape. A typical structure consists of a printed layer/foam layer/self-adhesive layer, suitable for glass, plastic, and metal containers. They are widely used for moisture-proof, leak-proof, and tamper-proof sealing of powders, desiccants, granules, and pastes. Their advantages include simple process, low cost, and easy installation, making them suitable for production lines requiring small to medium batch production and rapid SKU changeover.
II. Standard Operating Procedures
• Size Matching and Selection: Select the specification according to the inner diameter of the bottle mouth and the diameter of the inner sealing surface of the cap. The gasket diameter is usually about 0.5 mm larger than the inner diameter of the cap; the common thickness is about 1.0 mm, but specifications of 0.25–1.2 mm are also available to balance sealing performance and sealing force.
• Pre-treatment: Ensure the bottle neck is dry, oil-free, and dust-free, and the inner sealing surface of the cap is flat and without gaps; if necessary, wipe and dry the threads and rim to avoid reduced adhesion due to contamination or minor defects.
• Gasket Placement and Orientation: Place the gasket inside the cap, usually with the printed side facing the bottom of the cap, so that the self-adhesive side contacts the bottle neck; orientation markings may vary between suppliers, refer to the product markings.
• Capping and Activation: Tighten to the specified torque to achieve zero-gap contact between the cap bottom and the bottle neck; torque-activated pressure-sensitive adhesive begins to migrate and wet after tightening, requiring 12–24 hours to complete final bonding.
• Opening and Reuse: After the first opening, the gasket usually remains at the bottle neck to form a one-time seal; if resealing is required, the residual gasket can be retained inside the cap, but the sealing force will be significantly reduced, and repeated use is not recommended.
III. Key Parameters and Acceptance
• Settling Time: The pressure-sensitive gasket should be left to stand for 12–24 hours after capping before opening to achieve stable adhesion. Opening too early may cause the gasket to detach from the cap, affecting the seal integrity.
• Compatible Media: Preferably used for non-oil or low-oil products such as powders, dry materials, and pastes. Oily or highly volatile contents will reduce interfacial adhesion, leading to leakage or delamination.
• Temperature Conditions: Application and storage are recommended below 21°C (70°F) to avoid high temperatures accelerating adhesive migration or failure. PS foam material is not heat-resistant and is not suitable for high-temperature cooking or hot-filling scenarios.
• Dimensions and Thickness: The gasket diameter is approximately +0.5 mm larger than the cap's inner diameter; the thickness is selected according to the cap's internal clearance and the characteristics of the contents, commonly around 1.0 mm, but can be customized within the range of 0.25–1.2 mm upon request.
• Sealing Verification: An initial inspection can be performed 2 hours after capping (observing whether the gasket detaches with the cap and whether the opening is evenly wetted). A second inspection is conducted after 24 hours to confirm the final sealing effect and leakage risk.
IV. Common Problems and Improvement Methods
• Insufficient adhesion or easy detachment: This is often caused by damp/oil stains at the bottle opening, foreign objects inside the cap, insufficient torque, or insufficient settling time. Ensure the bottle opening is clean and dry, tighten according to specifications, and allow it to stand for ≥12–24 hours before opening.
• Gasket breakage or fragment detachment: This is commonly seen when PS foam becomes brittle under low temperature or aging conditions, or when there are burrs/notches on the bottle opening edge. It is recommended to optimize the bottle opening processing quality, control storage temperature, and avoid operation in low-temperature environments.
• Not suitable for oily contents: Pressure-sensitive gaskets are sensitive to oils and highly migrating substances, easily causing interface slippage and detachment. For such applications, aluminum foil induction gaskets or other heat-sealing/cold-sealing solutions should be considered.
• Storage and Shelf Life: Pressure-sensitive liners (such as PS22) are recommended for use within 6 months. Storage conditions: 60–80°F (approximately 15–27°C), relative humidity 40–60%, protected from light. Exceeding this period or improper storage will lead to a decline in the torque-activated coating's effectiveness and reduced sealing consistency.
V. Selection Recommendations and Structural Configuration
• Structural Types:
• PS Foam Pressure-Sensitive Liners: General-purpose, widely adaptable, low-cost, suitable for powder/dry products; usually left at the bottle opening after opening, providing a one-time seal.
• Pressure-Sensitive Aluminum Foil Composite Liners: Aluminum foil and sealing film are laminated onto PS foam or paper base, balancing barrier properties and sealing strength, suitable for higher protection requirements; some structures are two-piece, with the aluminum foil remaining at the bottle opening and the backing inside the cap after opening.
• Specifications and Customization: Supports customization of diameters from 15–120 mm and thicknesses from 0.25–1.2 mm. Custom printing such as "SEALED for YOUR PROTECTION" is available. Roll stock is commonly supplied in widths of 330/350/660/700 mm, facilitating automatic feeding and high-speed capping.
• Compatible Containers: Suitable for glass, various plastics (PET/PE/PP/PS, etc.), metal containers, and screw cap systems. High requirements are placed on the flatness of the bottle neck and the cleanliness of the cap interior to ensure uniform pressure and reliable adhesion.
