In the production process of prepainted steel coils, coating
materials are selected based on application requirements such as
weather resistance, corrosion resistance, and glossiness. They are
mainly categorized into three types: primers, topcoats, and
backcoats. Their specific types and characteristics are as follows:
Primers act directly on pretreated metal substrates (such as
cold-rolled steel plates and galvanized steel plates). Their core
functions are anti-corrosion and improving interlayer adhesion.
Common types include:
- Epoxy Primer: It has extremely strong adhesion, good compatibility with
galvanized steel plates and cold-rolled steel plates, and excellent
chemical corrosion resistance. It can effectively block the contact
between the substrate and external moisture and salt, making it the
mainstream primer in the home appliance and building materials
fields.
- Polyester Primer: It has high compatibility with polyester topcoats and good coating
flexibility. Suitable for deep processing scenarios that require
subsequent bending and stamping, it balances anti-corrosion and
processing performance.
As the "surface barrier" of prepainted steel coils, topcoats
directly affect the appearance (color, glossiness) and service
durability, and should be selected according to the application
environment. Mainstream types are:
- General Polyester Topcoat: It has high cost-effectiveness and optional glossiness (high gloss,
flat gloss). With moderate weather resistance, it is suitable for
non-outdoor scenarios such as indoor home appliances (refrigerator
side panels, washing machine casings) and indoor decorative parts.
- Silicon-Modified Polyester (SMP) Topcoat: Silicon resin is introduced into polyester, significantly improving
weather resistance (no easy fading or chalking after 5-8 years of
outdoor exposure). It also has good solvent resistance and is often
used in outdoor light steel structures (workshop cornices, exterior
walls of temporary buildings).
- Polyvinylidene Fluoride (PVDF) Topcoat: It has top-tier weather resistance (15-20 years of outdoor service
life), excellent UV resistance, acid rain resistance, and high-low
temperature resistance (-40℃~150℃). With strong color stability, it
is mostly used in high-end outdoor scenarios, such as large
building curtain walls and exterior walls of airport terminals.
- Acrylic Topcoat: It has high glossiness and bright colors. Its weather resistance is
better than that of general polyester but weaker than SMP. It is
suitable for lightweight indoor and outdoor applications with high
appearance requirements (such as advertising signs and decorative
panels).
Although backcoats are not directly exposed to the outside, they
need to protect the back of coils from scratches and corrosion
while improving overall structural stability. Common types are:
- Epoxy Backcoat: It has strong corrosion resistance and good adhesion to substrates,
suitable for humid environments (such as cold storage and basement
ceilings).
- Polyester Backcoat: It has good flexibility, no easy cracking during coil winding and
transportation, and is compatible with most general scenarios. Its
cost is lower than that of epoxy backcoats.
