I. Core Premise: Define Sealing Requirements in a “Scenario-Based” Way
The quality of sealing has no universal standard. It must first be defined based on the product characteristics and usage environment—this definition of sealing objectives is the starting point of all design decisions. Different application scenarios demand very different sealing performances. A misaligned requirement definition often leads to either overdesign or outright failure:
Food / pharmaceutical scenarios: Core needs are barrier + safety. Stickers must block oxygen (anti-oxidation), water vapor (anti-moisture/mold), and microorganisms (anti-contamination). At the same time, materials must meet food-contact standards (e.g., FDA, GB 4806), avoiding migration of plasticizers or adhesives.
Electronics / precision components: Core needs are dustproof + moisture-proof. Stickers must prevent tiny dust particles from clogging interfaces and moisture from short-circuiting PCBs. Sealing must balance “high barrier” with “reopenability” (for maintenance).
Liquids / pastes (e.g., shampoo samples, sauce packs): Core needs are leak prevention + compression resistance. Stickers must withstand both the osmotic pressure of the contents and external squeezing, avoiding adhesive failure along edges due to liquid infiltration.
Outdoor / transportation scenarios: Core need is resistance to environmental aging. Stickers must withstand temperature cycling (–20 ℃ to 60 ℃), UV exposure, and humidity variation, preventing material embrittlement or adhesive breakdown.
Only by clarifying “what to protect against, and to what degree” can materials and structures be selected effectively. For example, even within food packaging, biscuits (moisture-sensitive) versus meat (oxygen-sensitive) demand entirely different sealing logics—biscuits require water vapor barriers, while meat requires oxygen barriers.
II. Material Selection: Building the “First Line of Defense” for Sealing
Material is the foundation of sealing. A sealing sticker’s material system typically consists of three layers: substrate layer, adhesive layer, and coating/treatment layer. The compatibility of these three layers directly determines sealing performance. A high-sealing design must move beyond the misconception that “thicker substrate” or “stronger adhesive” is always better, and instead pursue layer synergy + scenario adaptation.
Substrate Layer: Choose the Right “Barrier Backbone” to Define Baseline Performance
The substrate is the sticker’s “skeleton.” Its physical properties (density, extensibility, permeability) directly affect barrier ability and structural stability. Different materials should be selected according to sealing goals:
High-barrier substrates: For oxygen/moisture-sensitive applications (e.g., baked goods, electronics), multilayer composites outperform single plastics.
PET/aluminum foil composite: Aluminum foil provides near-total oxygen and water vapor barrier; PET adds high strength (tear resistance). Suitable for long-shelf-life food or precision components. The aluminum layer must be pinhole-free, and lamination must avoid bubbles to ensure barrier continuity.
EVOH composites: EVOH is one of the most cost-effective transparent high-barrier materials, with oxygen permeability just 1/1000 that of PE. It is also microwave-compatible, ideal for visible-window packaging requiring barrier performance.
Weather-resistant substrates: For outdoor or wide-temperature environments.
PP: Broad temperature range (–20 ℃ to 120 ℃), strong chemical resistance. Suitable for liquid packaging or outdoor labels. However, its low surface energy requires corona treatment to improve adhesive bonding.
PI (polyimide): Heat resistance up to 260 ℃, excellent UV resistance. Suitable for high-temperature sterilization (e.g., medical devices) or outdoor electronics, though relatively costly.
Flexible substrates: For irregular packaging shapes (e.g., curved bottles, special-shaped boxes).
PE: Good flexibility, conforms well to curved surfaces. Suitable for sauce bottles, cosmetic samples. Weak barrier properties mean it must be paired with barrier coatings (e.g., acrylic).
TPU: Excellent elasticity (up to 500% elongation), abrasion resistance. Suitable for resealable packaging (e.g., snack bags). Poor oil resistance, not suitable for oily contents.
Adhesive Layer: Ensure “Gap-Free Bonding” to Eliminate Seal Weak Points
The adhesive bonds the sticker to the packaging surface. Its tack, environmental resistance, and wetting behavior directly affect sealing. A high-sealing design must emphasize surface wetting ability and low migration risk:
Match adhesive type to packaging material (plastic, glass, metal) to avoid mismatch and detachment.
Pressure-sensitive adhesives (PSA): Work in most scenarios; no heating needed. Types include acrylic, rubber, and silicone. Acrylic PSAs offer excellent weather resistance (high/low temperature, aging resistance), are odorless, and meet food-contact standards—ideal for food/personal care packaging. Silicone PSAs tolerate extreme heat (>150 ℃) but are costlier and may bond poorly with low-energy plastics (e.g., PE).
Hot-melt adhesives: Applied molten, solidify on cooling to form high-strength bonds. Suitable for heavy-duty or high-leakage-risk packaging (e.g., large liquid packs). Their strong flow requires careful coating control (typically 0.1–0.3 mm) to prevent uneven sealing due to glue overflow.
