Guide to Selecting Polyester Resins: How to Distinguish Their Uses? What Performance Indicators to Focus On?

In the field of industrial production and processing, polyester resins have become a fundamental material in various industries due to their versatile performance adaptability. However, faced with a wide range of products on the market, many purchasers and practitioners often struggle with questions such as "how to accurately distinguish polyester resins for different uses" and "which performance indicators must be focused on when making a purchase". This article will focus on these two core issues and provide readers with a clear reference direction through section-by-section analysis.

I. Classified by Application Scenarios, What Are the Core Differences Between Different Polyester Resins?

The classification of polyester resins is not a single-dimensional one. Their chemical structure and formula adjustments are directly tailored to different application scenarios. From the perspective of common fields, they can be mainly distinguished by their application characteristics into the following categories:

1. What Unique Properties Do Polyester Resins Used in the Coatings Industry Have?

Saturated polyester resins are commonly used in the coatings field. The most notable feature of this type of resin is its excellent weather resistance and gloss stability. In scenarios such as outdoor facilities and furniture surface coating, it is necessary to resist ultraviolet rays, temperature changes, and humidity for a long time. Therefore, this type of resin will have its molecular chain structure adjusted to reduce the risk of yellowing, while improving compatibility with pigments to ensure that the coating is uniform and not easy to peel off. Compared with resins for other uses, the curing speed of polyester resins for coatings is also adjusted according to construction needs. For example, industrial assembly line coating requires fast-curing resins, while manual coating requires a longer surface drying time.

2. How to Distinguish Polyester Resins for Composite Material Molding from Other Types?

Unsaturated polyester resins are widely used in the field of composite materials such as fiberglass-reinforced plastics (FRP) and artificial stone. Their core distinguishing points lie in "cross-linking and curing characteristics" and "mechanical performance adaptability". This type of resin needs to be combined with initiators and accelerators to complete cross-linking and curing at room temperature or medium temperature to form a three-dimensional network structure. Therefore, the curing shrinkage rate is a key distinguishing indicator. For example, resins for artificial stone require an extremely low shrinkage rate to avoid cracks after molding; while resins for FRP pipes pay more attention to the tensile strength and flexural strength after curing. In addition, polyester resins for composite materials will also have their corrosion resistance adjusted according to the service environment. For example, resins used in the chemical industry need to be acid and alkali resistant, while resins used in the construction industry need to be aging resistant.

3. What Are the Core Identification Points of Polyester Resins for Adhesives and Sealants?

Polyester resins used in adhesives and sealants are mostly low-molecular-weight saturated polyesters. Their key distinguishing points focus on "adhesive performance" and "flexibility". Compared with resins for coatings, this type of resin has a higher content of polar groups to enhance adhesion to bonded materials (such as metals, plastics, and wood); at the same time, flexible segments (such as adipic acid and ethylene glycol segments) are introduced into the molecular chain to prevent the adhesive layer from cracking due to temperature changes or external forces. In addition, polyester resins for sealants also need to have good medium resistance. For example, resins for automotive sealing need to be resistant to engine oil and gasoline erosion, while resins for construction sealing need to be resistant to water and ultraviolet rays.

II. When Purchasing Polyester Resins, Which Performance Indicators Are "Must-Check Items"?

After clarifying the purpose, the control of performance indicators directly determines the final effect of the product. The following types of indicators need to be focused on, and the priority of indicators varies according to different uses:

1. Why Do Curing-Related Indicators Play a Decisive Role in the Application Effect?

Curing indicators include curing temperature, curing time, and curing shrinkage rate, which are the core for distinguishing the applicability of different resins. For example, if a high-temperature curing resin is selected for the coating of large outdoor components, it will increase the construction difficulty and cost; if the curing time of the resin used for electronic component packaging is too long, it will affect production efficiency. The curing shrinkage rate is even more critical - an excessively high shrinkage rate will cause deformation and cracking of the product. For example, resins for precision molds require a shrinkage rate of less than 0.5%, while ordinary FRP products can accept a shrinkage rate of 1%-2%. In addition, the cross-linking density after curing also needs to be paid attention to. A high cross-linking density results in high resin hardness and good chemical resistance, but the flexibility will decrease, so a balance needs to be struck according to the application scenario.

2. How to Select Mechanical Performance Indicators According to the Purpose?

Mechanical indicators such as tensile strength, flexural strength, and impact strength are directly related to the durability of resin products. For resins used in composite materials, priority should be given to tensile strength and flexural strength. For example, FRP resins used in load-bearing structures require a tensile strength of ≥80MPa; while for resins used in adhesives, attention should be paid to shear strength. For example, resins used for metal-to-metal bonding require a shear strength of ≥15MPa. The impact strength corresponds to the anti-brittle fracture ability of the product. For example, resins used in low-temperature environments (such as parts of refrigeration equipment) need to have high low-temperature impact strength to avoid brittle fracture at low temperatures.

3. In Which Scenarios Must Environmental Resistance Indicators Be Focused On?

Environmental resistance indicators include weather resistance, chemical resistance, and temperature resistance, which need to be checked in a targeted manner according to the service environment. Resins for outdoor use (such as outdoor furniture and traffic signs) need to pass weather resistance tests (such as xenon lamp aging tests) to ensure no obvious loss of gloss, discoloration, or cracking after long-term exposure; resins used in the chemical industry need to be checked for acid resistance, alkali resistance, and solvent resistance. For example, equipment in contact with concentrated hydrochloric acid needs to use acid-resistant resins; resins used in high-temperature environments (such as parts around automobile engines) need to pay attention to the heat distortion temperature. Generally, the heat distortion temperature is required to be more than 20℃ higher than the service environment temperature to avoid softening and deformation at high temperatures.

4. Will Appearance and Processing Performance Indicators Affect Practical Application?

Appearance indicators (such as color and transparency) and processing performance indicators (such as viscosity and compatibility) do not directly determine the core performance of the product, but they will affect the processing process and the appearance of the final product. For example, high-end furniture coating requires the selection of high-transparency resins to ensure that the wood texture is clearly displayed; while resins for colored paints need to have good compatibility with pigments to avoid floating color and blooming. Viscosity is related to construction convenience. For example, manual brushing requires low-viscosity resins (easy to brush), while spraying resins need to have their viscosity controlled within a specific range (to avoid sagging or poor atomization).

III. Conclusion: What Is the Core Logic of Distinguishing and Selecting Polyester Resins?

In short, the distinction of polyester resins should take "application scenarios" as the core, and lock in the suitable type through differences in curing characteristics, mechanical performance, environmental resistance, and other aspects; while the selection should focus on "application needs" and prioritize the screening of key performance indicators. For example, outdoor coating needs to prioritize weather resistance and curing temperature, and composite material molding needs to prioritize mechanical strength and shrinkage rate. Only by combining the distinction of uses with the control of indicators can we accurately select suitable polyester resin products and avoid production losses or product quality problems caused by improper selection.