The resin in fiberglass reinforced plastic (FRP) products securely bonds the glass fibers together, transmits and distributes loads, and determines the product's chemical resistance, heat resistance, aging resistance, and ultimate mechanical properties.
The three most commonly used thermosetting resins in FRP products are:
1. Unsaturated Polyester Resin - The most versatile and commonly used resin.
● This is the most widely used and lowest-cost resin type. It offers low cost and good economics.
● It has excellent processability and is suitable for various processes such as hand lay-up, winding, spraying, and molding.
● It cures quickly and offers high production efficiency.
● There are many different types, and different properties can be achieved through formulation adjustments.
● Main Types: Ortho-phthalate (Ortho-phthalate): A general-purpose resin used for general products.
Iso-phthalate (ISO-phthalate): Offers improved water and chemical resistance and is commonly used in corrosion-resistant storage tanks and pipes.
Bisphenol A: Offers excellent corrosion resistance, especially alkali resistance, making it suitable for chemical environments. Vinyl ester resin: Its performance lies between that of unsaturated polyester and epoxy, often classified separately (see below).
2. Vinyl ester resin - "High-performance" unsaturated polyester
It is modified from epoxy resin and combines the excellent processability of unsaturated polyester with the superior corrosion resistance of epoxy resin.
Advantages:
● Excellent corrosion resistance, with better resistance to acids, alkalis, and solvents than unsaturated polyester.
● Good toughness and resistance to microcracking.
● Strong bond to glass fiber.
● Low shrinkage.
Disadvantages:
● Higher cost than unsaturated polyester.
● Can have higher viscosity, sometimes requiring heating or the addition of a diluent.
Applications:
● It is the material of choice for chemical corrosion protection applications (such as large storage tanks, scrubbers, and chimneys).
● Epoxy resin - A high-performance resin
● Known for its excellent mechanical properties and bond strength.
Advantages:
● Extremely high mechanical strength and stiffness.
● Excellent bond strength, with excellent adhesion to various fibers. Low shrinkage (1-3%), precise product dimensions, and low internal stress.
● Excellent chemical and heat resistance.
Disadvantages:
● Highest cost.
● Long curing cycle, often requiring heat post-curing for optimal performance.
● Some curing agents are toxic, requiring careful protection.
● Requires stringent process environment (temperature and humidity).
Applications: Aerospace, military, high-performance sports equipment (such as fishing rods and bicycle frames), electronic insulation, and corrosion protection projects requiring extreme strength and durability.
How to Choose a Resin?
First, determine the performance level
If your product does not require high strength and corrosion resistance and seeks maximum economic efficiency, unsaturated polyester resin is a good starting point. If you seek extreme mechanical properties, consider epoxy resin directly. If you need excellent corrosion resistance and toughness between the two, vinyl ester resin is an ideal choice.
Refine within the same resin category
After determining the broad resin category, select subcategories based on specific needs. For example, in the corrosion protection field, a clear performance-cost gradient has been established, from isophthalic acid/bisphenol A in unsaturated polyesters to more advanced vinyl ester resins.
Final Confirmation
After locking in the general direction, communication with material suppliers is still necessary to determine the most suitable resin grade based on the specific process method, curing conditions, and product usage environment (media and temperature).
Key Components of a Resin System
What we commonly refer to as "resin" is actually a system, including:
Resin base: The main component.
Curing agent: The substance that initiates the crosslinking reaction.
Accelerator: In unsaturated polyester/vinyl ester systems, it is combined with the curing agent (usually a peroxide) to achieve room temperature curing.
Additives:
Pigments/Colorants: Provide color to the product.
Fillers: Such as calcium carbonate and aluminum hydroxide, used to reduce cost, reduce shrinkage, and improve flame retardancy.
Flame retardants: Improve the product's fire rating.
UV absorbers: Improve weather resistance.
Summary
For economy and versatility -> Unsaturated polyester resin
For harsh chemical environments -> Vinyl ester resin
For extreme strength and performance -> Epoxy resin
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