Classification of Unsaturated Polyester Resins

Unsaturated polyester resins come in a wide variety of types and specifications, which can be designed and adjusted according to specific application needs. Typically, the classification of unsaturated polyester resins is based on different molding methods and performance characteristics.

Classification by Molding Method:

· Hand Lay-Up Resin: Suitable for manual operation and small-scale production.

· Spray-Up Resin: Used in spray-up molding, offering higher efficiency.

· Molding Resin: Suitable for molding processes, typically used in mass production.

· Pultrusion Resin: Used in continuous pultrusion molding, commonly applied in long fiber-reinforced composites.

· Sheet Molding Compound (SMC)/Bulk Molding Compound (BMC) Resin: Used in sheet or bulk molding processes, suitable for complex-shaped products.

· Casting Resin: Applicable for precision castings.

· Continuous Lamination Resin: Used for producing continuous sheets or plates.

Classification by Performance Characteristics:

· General-Purpose Resin: Suitable for general applications.

· Chemical-Resistant Resin: Exhibits excellent resistance to corrosion.

· Flame-Retardant Resin: Suitable for applications with high fire safety requirements.

· Flexible Resin: Provides good flexibility.

· Transparent Resin: Used in products requiring high transparency.

· Artificial Marble/Onyx Resin: Used for the production of artificial stone.

· Button Resin: Specifically used for button manufacturing.

· Gel Coat Resin: Applied as a surface coating, providing a smooth finish.

· Foaming Resin: Used for producing lightweight foam products.

· Pigment Carrier Resin: Used for pigment dispersion and stabilization.

Other Classifications:

· By Reactivity: Can be categorized into high-reactivity, medium-reactivity, and low-reactivity resins.

· By Promotion State: Includes pre-promoted (with added promoters) and non-promoted resins.

· By Thixotropy: Includes thixotropic and non-thixotropic resins.

· By Wax Content: Includes wax-containing and non-wax-containing resins.

· By Light Stability: Includes resins with and without light stabilizers.

Additionally, the viscosity of unsaturated polyester resins can vary widely, from 0.3 Pa·s to over 3 Pa·s, and can be adjusted according to user requirements. Some resin manufacturers add color indicators to the resin, which change color during the curing process to indicate the degree of cure. Common curing indicators include:

· Phenothiazine: Changes from brown to green.

· N,N'-Diphenyl-p-phenylenediamine: Changes from reddish-brown to orange-yellow.

· N,N'-Bis(1-ethyl-3-methylpentyl)-p-phenylenediamine: Changes from blue to red.

The gel time, cure time (time to exothermic peak), and exothermic peak temperature of unsaturated polyester resins can be adjusted according to specific requirements, resulting in different variants of the same resin.