The increase in release force (i.e., higher peeling force and greater difficulty in peeling) of release films after aging is a common issue. The core cause lies in the physical and chemical changes of the release layer (typically a silicone coating) and the substrate under the influence of time and environmental factors (such as heat, oxygen, light, and humidity).
The specific reasons are as follows:
- Cause: For release agents (especially addition-curing silicones), the cross-linking reaction may not be fully completed during the coating and curing process. Over time, under the action of trace residual catalysts, heat, or environmental moisture, the remaining reactive groups (e.g., Si-H and Si-Vinyl) continue to react slowly.
- Impact: Increased cross-linking degree makes the network structure of the silicone coating denser and more rigid. The low-molecular-weight siloxane segments or unreacted components that originally play a "lubricating" role are more tightly bound in the cross-linked network. Although the surface free energy of the coating decreases (becoming more "non-adhesive"), the interfacial slip property reduces, resulting in higher force required during peeling.
- Cause: Low-molecular-weight siloxanes (LMW) contained in the release agent coating are not firmly bonded to the cross-linked network and are key substances for surface lubrication and reducing peeling force.
- Impact: During the aging process (especially at relatively high temperatures), LMW decreases through the following ways:
- Volatilization: Direct evaporation into the air;
- Migration: Diffusion and migration into the coating interior or substrate interior (being absorbed);
- Exudation: Absorption by the contacted adhesive.
- Result: The effective lubricating substances on the surface decrease, the interfacial friction between the release layer and the adhesive increases, and the release force rises.
- Cause: The substrate of the release film (e.g., PET, PP, PE, etc.) itself ages and may undergo the following changes under the action of heat or light:
- Increased crystallinity (rearrangement of polymer molecular segments);
- Changes in surface energy (introduction of oxygen-containing groups or structural changes);
- Shrinkage or deformation (dimensional changes caused by long-term stress or temperature variations).
- Impact:
- Changes in substrate crystallinity or surface energy affect the adhesion to the silicone coating, indirectly undermining the stability of release performance;
- Substrate shrinkage and deformation exert stress on the silicone coating, altering the surface state or microstructure;
- Low-molecular-weight substances generated by substrate aging migrate to the silicone layer or interface, interfering with release performance.
Environmental factors synergistically lead to increased release force by accelerating physical and chemical changes:
- Heat: The most significant accelerating factor, promoting further cross-linking of silicones, volatilization/migration of LMW, and substrate aging;
- Oxygen: Under extreme conditions or in the presence of impurities, it may cause oxidation of silicones or substrates, generating polar groups and changing surface properties;
- Humidity: Affects the stability of condensation-curing silicones, promotes moisture absorption, deformation, or hydrolysis of the substrate, and may also participate in the slow post-curing of silicones;
- Light (UV): Triggers the degradation of silicones and substrates, damages molecular chains, generates free radicals and oxidation products, and alters material properties.
- Cause: Release films are usually used in conjunction with tapes (pressure-sensitive adhesives), and the adhesives themselves also age (e.g., increased cross-linking degree, migration of plasticizers).
- Impact: Aged adhesives may become harder, have higher cohesive strength, or exhibit enhanced interaction with the surface of the release layer (e.g., the release layer generates slight polarity due to aging), leading to higher force required for peeling.
- Summary: The core mechanism behind the increased release force of release films after aging lies in changes in the silicone release layer itself, particularly the further densification of the cross-linked network and the loss of lubricating low-molecular-weight siloxanes. Substrate aging, environmental factors (heat, oxygen, moisture, light), and the aging of the contacted adhesive synergistically exacerbate this phenomenon.
- Select a release agent system with good stability, complete curing, and low migration;
- Optimize the curing process to ensure full curing of silicones and reduce residual reactive groups and low-molecular-weight substances;
- Strictly control storage conditions: store release films in a cool (recommended below 25°C), dry, and light-proof environment; manage inventory turnover, avoid long-term stockpiling, and follow the "first-in, first-out" principle;
- Choose substrates with good aging resistance (e.g., high-quality PET is generally more stable than BOPP).
Topwin is one of the leading professional manufacturers and solution providers with more than 20 years of experience, and has domestic top-level engineers in the silicone surfactant industry. Specializing in research and development, production, sales, and marketing of silicone-based special functional performance materials, Topwin also serves as a professional provider of technical services. Our products are mainly used in Polyurethane Foam, Corp Protection, Coatings and Inks, Leather & Textile, Silicone Release Coating for Paper and Film, Personal Care, and others.
