1.How does permeability resistance affect the service life of corrugated board?
How it works: High-quality coatings have a tight molecular structure and uniform film formation, effectively preventing rain, dew, moisture from the air, and oxygen from penetrating the interface between the coating and the substrate. However, if the coating is highly permeable (e.g., with large molecular gaps or pinholes), moisture and oxygen will gradually penetrate and chemically react with the substrate (especially the galvanized layer or steel sheet) (e.g., oxidation of the galvanized layer and rusting of the steel sheet), ultimately causing blistering and peeling of the coating, exposing the substrate to rust.
Impact on Lifespan:
Highly permeable coatings (e.g., PVDF, SMP): Provide long-term (10-20 years) protection against moisture penetration, preventing rust on the substrate and extending its service life.
Low permeability coatings (e.g., standard PE, acrylic): After 3-5 years, localized permeability may occur, resulting in blistering of the coating and rust on the substrate, requiring repair or replacement.
2.How does adhesion affect the service life of corrugated board?
Working Principle: The adhesion between the coating and the substrate (or galvanized layer) determines whether the coating will peel due to temperature fluctuations (thermal expansion and contraction), external forces (such as wind and vibration), or minor impact. Poor adhesion can easily cause the coating to peel and flake, and direct exposure of the substrate to the environment can accelerate rust.
Key Indicator: The industry commonly uses the "cross-hatch" method to test adhesion (a grade of 0 indicates high quality if no coating peels after the cross-hatch test). PVDF and SMP coatings typically achieve adhesion levels of 0-1 due to the tight bond between the resin and the substrate. Ordinary PE coatings, if the curing process is poor, may only have adhesion levels of 2-3 and are prone to peeling.
Impact on Lifespan: Coatings with poor adhesion may experience extensive peeling within 5 years, shortening their service life by over 50%.
3.How does salt spray resistance affect the service life of corrugated board?
Core damage source: The air in coastal or high-humidity areas contains high levels of salt (chloride ions). Salt adheres to the coating surface with rain or fog. If the coating has poor salt spray resistance, the salt easily penetrates the substrate, accelerating the formation of "white rust" on the galvanized coating or "red rust" on the steel plate, leading to coating failure.
Key testing standard: The industry uses the "neutral salt spray test (NSS)" for evaluation. PVDF coatings can pass 1000-1500 hours of testing (no rust), SMP coatings can pass 500-800 hours, and ordinary PE coatings can only pass 200-300 hours.
Impact on lifespan: In coastal environments, PE coatings may fail due to salt spray erosion in 2-3 years, while PVDF coatings can provide stable service for over 15 years-a significant difference.
4.How does chemical resistance affect the lifespan of corrugated board?
Core sources of damage: Industrial areas (such as chemical plants, dyeing and printing mills, and mining areas) contain acidic and alkaline gases and dust in the air, or roofs may be exposed to oil, dirt, and cleaning agents. If the coating has poor chemical resistance, it is easily corroded (such as dissolution, discoloration, and pitting), losing its protective capabilities.
Performance Differences: PVDF coatings, due to the strong chemical stability of fluororesin, are resistant to most acids, bases, and solvents. SMP and PE coatings have weaker chemical resistance and may corrode within 3-6 months after exposure to strong acids and bases.
Impact on Lifespan: In industrial environments, coatings with poor chemical resistance can shorten the service life from 8-10 years to 2-3 years.
5.What effect does hardness have on the performance of corrugated board?
Application scenarios: Corrugated board is prone to bumps and scratches during installation (e.g., during handling, splicing, and when workers step on it). If the coating has a low hardness (e.g., ordinary PE coating), it can easily be scratched through to the baseboard, creating "exposed spots." These exposed spots become entry points for corrosion, accelerating corrosion of the baseboard and gradually spreading to surrounding areas.
Key indicators: Using the "pencil hardness test" used in the industry, PVDF and SMP coatings typically have a hardness of 2H-3H (scratch-resistant), while ordinary PE coatings typically have a hardness of HB (scratch-prone).
Impact on lifespan: If a coating with low hardness is extensively scratched after installation, its service life may be shortened from 5 years to 2-3 years.