1.What effect does low temperature have on scratch resistance?
Changes in coating state: The glass transition temperature of most organic coatings is 50-80℃. When the ambient temperature is much lower than Tg, the movement of the coating molecular chain is restricted, and it changes from a "flexible state" to a "glassy state" - the hardness increases, but the flexibility decreases sharply and the brittleness increases.
Scratch resistance performance:
When slightly scratched, the coating may "crack" due to high brittleness, resulting in deep and irregular scratches, and even coating fragments peeling off.
Different resins vary significantly: At -20℃, the pencil hardness of ordinary PE coatings may increase from 2H at room temperature to 3H, but the impact resistance decreases by more than 50%, and the risk of bottom exposure after scratching increases; while fluorocarbon coatings have strong molecular chain stability and less brittleness increase at low temperatures, making it easier to maintain coating integrity when scratched.
2.What effect does room temperature have on scratch resistance?
Coating state change: At this time, the coating is in the "optimal equilibrium state" - the molecular chain can move slightly, maintaining a certain hardness and having enough flexibility to buffer the scratch force.
Scratch resistance performance:
The scratch resistance is the most stable, basically in line with the design performance of the coating itself.
Most scratches are "linear shallow scratches" that are not easy to show the bottom, and the visual impact of scratches can be reduced by the lubricating additives in the coating.
3.What effect does high temperature have on scratch resistance?
Coating state changes: When the temperature approaches or exceeds the Tg of the coating, the molecular chain movement intensifies, the coating transitions from the "solid" to the "viscous flow state", the hardness decreases, and the flexibility is too high.
Scratch resistance performance:
The coating is easily "pressed" or "dragged" by hard objects, resulting in wide and shallow scratches, and even coating adhesion.
Different resins vary significantly: At 60°C, the pencil hardness of ordinary PE coating may drop from 2H at room temperature to 1H, and a light scratch with a key can leave obvious marks; while PVDF coating has a higher Tg and can still maintain a hardness of 3H below 80°C, and the scratch resistance is almost unchanged.
4.What effect does high humidity have on scratch resistance?
Changes in coating state: If the coating is not completely cured, high humidity will cause moisture to penetrate into the coating, destroying the intermolecular forces and reducing the cohesive force of the coating; at the same time, moisture may weaken the adhesion between the coating and the substrate, causing the coating to be "easy to peel off".
Scratch resistance performance:
When scratched, the coating is more likely to be "lifted" or "delaminated", resulting in a composite damage of "scratch + peeling".
For resins containing hydrophilic groups, the hardness may decrease by 10%-20% under high humidity, and the scratch resistance is significantly weakened; while PVDF has a hydrophobic molecular structure, and its performance is almost unchanged under high humidity.
5.What effect does low humidity have on scratch resistance?
Changes in coating state: Dry environment may accelerate the release of residual volatiles in the coating. If the coating itself is not tough enough, it may become slightly brittle due to "overdrying".
Scratch resistance:
Scratch resistance is slightly lower than normal temperature and humidity. It is easier to produce fine cracks when scratched, and scratches are easier to "whiten" due to surface dryness.
The impact is small, usually only slightly weakening thin coatings or low-toughness resins, and almost no effect on high-performance coatings such as PVDF.