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Polyester resins are a broad family of polymers obtained by the polycondensation of polybasic acids with polyhydric alcohols and carrying the ester linkage (–CO–O–) in their chain. They do not describe a single chemical; the family covers unsaturated polyesters, powder coating and coil coating polyesters, alkyds and water-based polyester dispersions. Their most common field of use is glass fiber reinforced plastic; they serve as the main binder in the production of boats, tanks, pipes, facade panels, artificial marble and solid surfaces.
Unsaturated polyester resin is supplied dissolved in styrene and, when an organic peroxide and a cobalt accelerator are added, cures at room temperature into a hard, crosslinked network. It is used in lamination, in the production of gelcoat and automotive putty, and in polymer concrete and casting applications. With its orthophthalic, isophthalic, neopentyl glycol-based and DCPD-based types, the balance of mechanical strength, chemical resistance and cost is adjusted.
Powder coating polyester, with its saturated carboxyl- or hydroxyl-functional structure, gives outdoor-durable, glossy and flexible films in the coating of aluminum profiles, facades, white goods and metal furniture. Alkyd resin, in turn, is a polyester modified with fatty acids and is used in wood and metal paints, primers and enamels. These products can be supplied from ATAMAN KİMYA; for technical information and requests, contacting ATAMAN KİMYA is recommended.
WHAT ARE POLYESTER RESINS?
Polyester resins are polymers in which the ester linkages formed by the reaction of diols or polyols with dicarboxylic acids or anhydrides repeat along the chain. In terms of chemical class, they are among the polycondensation polymers.
The name denotes not a single substance but a product family that varies with the choice of raw materials. The properties of the family are determined by the acid type, the alcohol type, the type of functional group and, where present, a common component such as a fatty acid or styrene.
Unsaturated polyesters, which carry double bonds in the chain, cure by a radical reaction. Saturated polyesters form a film by reacting with crosslinkers through their carboxyl or hydroxyl ends, and alkyds by reacting with oxygen in the air.
Commercial products are supplied as styrene solutions, organic solvent solutions, water-based dispersions, granules and solvent-free resins. Thermoplastic polyesters such as PET and PBT are a separate product group used as fibers, bottles and engineering plastics.
COMMON PRODUCT AND CHEMICAL NAMES OF POLYESTER RESINS:
Polyester
Polyester resin
Polyester resin (alternative spelling)
Polyester resins
Unsaturated polyester resin
Saturated polyester resin
Orthophthalic polyester resin
Isophthalic polyester resin
Neopentyl glycol polyester resin
DCPD-based polyester resin
Terephthalic polyester resin
Styrenated polyester resin
Glass fiber reinforced plastic resin
Lamination polyester
Gelcoat resin
Casting polyester
Putty polyester
Polymer concrete polyester
Carboxyl polyester
Hydroxyl polyester
Oil-free polyester
Powder coating polyester
Coil coating polyester
Alkyd resin
Oil-modified polyester
Water-based polyester dispersion
Sulfopolyester
Polyester binder
Polyester polymer
Coating polyester
Trade names vary by manufacturer. Among unsaturated polyesters the Polylite, Norsodyne, Polipol and Polijel series are seen, among powder coating polyesters Reafree, among alkyds and oil-free polyesters Synolac, and among water-dispersible sulfopolyesters the Eastman AQ and Eastek series.
CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION OF POLYESTER RESINS
Product name: Polyester resins
Common abbreviation: UP or UPR for unsaturated polyester resins; OFPE for oil-free polyester
Chemical name: Polyester (polycondensation polymer of polybasic acids with polyhydric alcohols)
INCI name: There is no single INCI name for industrial resins; special polyester polymers developed for cosmetic purposes are registered under separate INCI names
CAS No: There is no single number; 26123-45-5 is frequently seen in sources for unsaturated polyester, and products carry different numbers depending on composition
EC / EINECS No: Since it is a polymer, no single number is given for the resin itself; the raw materials have their own numbers
Molecular formula: There is no fixed formula; the general repeating unit is shown as –[O–R–O–CO–R′–CO]n–
Molecular weight: Depends on the product type; unsaturated polyesters and alkyds are at the oligomer level, and detailed values are given in the manufacturer’s documents
Chemical class: Polymer, polycondensation polymer containing the ester linkage
Main functions: Binder, film former, composite matrix resin, casting resin
SUBFAMILIES OF POLYESTER RESINS
Polyester resins should be evaluated not as a single product but as a whole made up of subfamilies with different properties. Below, five main subfamilies are summarized with their chemical structures, typical properties and fields of use.
The values given are example product data published by the manufacturers concerned and general literature ranges. The technical data sheet of each product should be taken as the basis.
1. UNSATURATED POLYESTER RESINS
Unsaturated polyester resins are produced by the esterification of acids carrying double bonds, such as maleic anhydride, with phthalic anhydride, isophthalic acid and glycols. The resin is supplied dissolved in styrene; styrene both provides flowability and acts as the crosslinker during curing.
Curing is started by an organic peroxide and a cobalt accelerator. The double bonds in the chain copolymerize with styrene by a radical route and an irreversible network forms. The reaction is exothermic; the gel time depends on temperature and catalyst ratio.
The acid and glycol type determines performance. Orthophthalic types are general purpose and economical. Isophthalic and neopentyl glycol-based types give higher water, chemical and heat resistance; DCPD-based types are preferred for low shrinkage and low-styrene-emission lamination.
Example manufacturer data, Polylite 720-700 (Polynt, isophthalic): Viscosity 900–1,100 mPa·s (23 °C, Brookfield); non-volatile content 53.5–57.5 percent; acid value below 14 mg KOH/g; gel time 15–25 minutes (1 percent MEKP50, 23 °C); density 1.1 g/cm³; shelf life 6 months (23 °C, in the dark).
Example manufacturer data, Polylite 720-700, cured unreinforced resin: Tensile strength 76 MPa; tensile modulus 3,650 MPa; elongation at break 3.5 percent; flexural strength 140 MPa; HDT 86 °C; Barcol hardness 45; volumetric shrinkage 7.5 percent.
Example manufacturer data, Norsodyne H 13212 (Polynt, orthophthalic): Viscosity 450–650 mPa·s; gel time 14–18 minutes (1 percent MEKP50, 23 °C); density 1.10 g/cm³; tensile strength 57 MPa; elongation at break 2.3 percent; flexural strength 98 MPa; HDT 64 °C.
Example manufacturer data, Polipol 3453 and 3813 (Poliya, casting type): For orthophthalic 3453, viscosity 560–650 mPa·s, gel time 7–9 minutes, HDT 58 °C; for isophthalic/neopentyl glycol-based 3813, viscosity 600–800 mPa·s, gel time 10–12 minutes, HDT 80 °C, Barcol hardness 48.
Example manufacturer data, Polres GMP (DCPD-based putty polyester): Viscosity 500–550 cps; acid value 14–20 mg KOH/g; gel time 10–16 minutes (2 g benzoyl peroxide paste per 100 g resin); density 1.10–1.20 g/cm³; shelf life 4 months.
Example manufacturer data, Polipol 3570-PB (Poliya, terephthalic, polymer concrete): Viscosity 250–300 mPa·s; gel time 10–12 minutes; tensile strength 71 MPa; flexural strength 129 MPa; HDT 86 °C; Barcol hardness 40. Acrylic-modified Polipol 383-G, on the other hand, has been developed for high UV, heat and chemical resistance.
Example manufacturer data, Norsodyne H 13223 TAEP (Polynt, pigmented orthophthalic): It is pre-accelerated and thixotropic; gel time 14–18 minutes (1.5 percent MEKP50, 23 °C), peak temperature 95–115 °C; shelf life 3 months (23 °C, in the dark).
In manufacturer data, hand lay-up and spray-up methods are stated for general purpose orthophthalic and isophthalic types. The resin is stored below 25 °C, in the shade and away from direct sunlight; shelf life shortens as temperature rises.
Vinyl ester resins are epoxy-based, and their mechanical strength is lower than that of epoxy and higher than that of polyester. In one manufacturer’s grating example, it has been reported that chemical resistance falls markedly for polyester above 38 °C, while vinyl ester shows no significant loss up to 71 °C.
According to market research, the unsaturated polyester resin market reached about 14.6 billion dollars in 2025. Orthophthalic types hold a share of about 35.7 percent, and the construction sector is the largest field of use with about 36.7 percent.
Main fields of use:
• Lamination of boats, tanks, pipes and facade panels
• Gelcoat, automotive putty and repair products
• Casting of artificial marble, solid surface, sinks and countertops
• Polymer concrete, drainage channels and garden furniture
Strengths:
• Easy wetting of fibers and fillers thanks to low viscosity
• Curing at room temperature and wide adjustability
• Low cost compared with epoxy and vinyl ester
Limitations:
• Volumetric shrinkage of about 7 percent during curing
• Flammability and occupational health requirements because of styrene
• Low elongation at break and brittle structure of the cured product
2. CARBOXYL-FUNCTIONAL SATURATED POLYESTERS AND POWDER COATING POLYESTERS
Powder coating polyesters are solid resins obtained from terephthalic and isophthalic acid and glycols such as neopentyl glycol, with ends carrying carboxyl groups. They are supplied as pale granules and contain no solvent.
The resin is mixed in an extruder with a hardener of the TGIC or β-hydroxyalkylamide type, ground and applied electrostatically. In the oven it melts, flows and is crosslinked as a result of the reaction of the carboxyl ends with the hardener.
The glass transition temperature determines the balance between storage stability and film flow. The acid value, in turn, affects the hardener requirement and the crosslink density. Types free of trimellitic anhydride, known as TMA free, are also available.
Example manufacturer data, Reafree 4784-S (Arkema): Acid value 30–36 mg KOH/g; Tg about 72 °C; viscosity 80–125 Pa·s (165 °C); ratio of 93/7 with TGIC and 95/5 with Primid XL-552; cure 12 minutes at 180 °C; shelf life more than three years.
Example manufacturer data, Reafree 5700: Acid value 32–38 mg KOH/g; Tg about 61 °C; viscosity 9–20 Pa·s (165 °C); cure of 10 minutes at 200 °C with TGIC and 20 minutes at 160 °C with HAA; 25 kg polyethylene bag.
Example manufacturer data, Reafree 4781 and 4760-S: Acid value 33–38 and 30–36 mg KOH/g respectively; Tg about 68 and 60 °C; viscosity 20–35 and 12–25 Pa·s (165 °C).
Example manufacturer data, application results (Reafree 4784-S and 4760-S): At 60–80 micron film, 60° gloss above 90 percent; cupping above 8 mm; direct and reverse impact above 80 kg·cm; adhesion Gt0.
Extrusion conditions are given in the example as 80 °C with TGIC, 105 °C with Primid and 200 rpm. Reafree 4784-S is highlighted for its strong texturing property, and Reafree 5700 for its very good flow, high gloss and salt spray resistance.
The durability class is decisive in selection. Standard durability resins are preferred for general use, and superdurable resins for surfaces exposed to the outdoors for a long time, such as facades and aluminum profiles.
In powder coating production, the resin, hardener, pigment, filler and flow additives are mixed in an extruder, cooled, broken and ground. The resulting powder is applied with an electrostatic gun and cured in an oven.
In systems containing TGIC, the hardener is evaluated separately because of its classification in the safety data sheet. Systems with β-hydroxyalkylamide hardeners cure at a lower temperature; since water is released in the reaction, film thickness is limited according to the manufacturer’s recommendation.
These data are typical values; they should not be accepted as sales specifications. A dry environment, a temperature below 30 °C and protection from direct sunlight are recommended for storage.
Main fields of use:
• Aluminum profile and facade coatings
• White goods, metal furniture and lighting housings
• Outdoor-durable industrial metal surfaces
Strengths:
• Solvent-free application, low emission and recovery of overspray
• High gloss, good flow and outdoor durability
• The possibility of building a TGIC-free system with suitable resin selection
Limitations:
• Need for a high curing temperature, not suitable for heat-sensitive surfaces
• Need for line cleaning on color changes and special application equipment
• Separate evaluation of hardener selection for safety and regulation
3. HYDROXYL-FUNCTIONAL OIL-FREE POLYESTERS
Oil-free polyesters are saturated polyesters that contain no fatty acid. They carry hydroxyl groups at their ends and, together with crosslinkers such as melamine or isocyanate, work as binders in coil coating, can decoration and general industrial enamel systems.
They are supplied as solvent-based solutions. The hydroxyl value affects the amount of crosslinker, and the acid value affects the catalyst requirement and pigment wetting. Low hydroxyl value types give flexible films, high hydroxyl value types harder films.
With melamine, the reaction takes place at oven temperature in the presence of an acid catalyst; with its balance of flexibility, adhesion and hardness, the film is used on metal surfaces that can be bent and formed.
Example manufacturer data, Synolac 9763 N 65 (Arkema): Hydroxyl number 30, that is 0.9 percent hydroxyl; acid value 7 mg KOH/g; solids 65 percent; solvent Solvent Aromatic 150; viscosity Z1–Z2 Gardner-Holdt; 0T/1T flexibility potential in coil coating.
Example manufacturer data, Synolac 5069S-65: Hydroxyl number 25–35; acid value at most 10 mg KOH/g; solids 63–67 percent; viscosity 25–35 P (25 °C); density 1.06 g/ml; color at most 2 Gardner; shelf life 12 months from production.
Example manufacturer data, Synolac 5069S-65, crosslinker recommendation: Resin/melamine solids ratio of 70:30–85:15 with hexamethoxymethyl melamine; 85:15–80:20 in coil coating; 1–5 percent p-toluenesulfonic acid on melamine solids as acid catalyst.
In an alternative system, the resin, melamine and epoxy are mixed at 72:18:10 and 2 percent acid catalyst on amino solids is used. In general industrial enamels, a resin/melamine ratio of 70:30–80:20 has been given.
Benzoguanamine can speed up the curing reaction; partially methylated melamine can also be used in general industrial enamels. Depending on the intended use, it can also work together with isocyanate.
In coil coating, 0T/1T flexibility means that the painted sheet can be bent with a radius equal to its own thickness. This performance is achieved by adjusting resin selection, crosslinker ratio and baking conditions together.
The resin is stored in the original, closed container, in a dry environment and below 30 °C; in the example product, shelf life is 12 months from production. For polyesters to be used in coatings for metal packaging in contact with food, a separate regulatory check is required.
Main fields of use:
• Coil coating and prepainted sheet
• Can decoration and general industrial enamels
• Protective metal coatings
Strengths:
• Balance of flexibility, adhesion and hardness
• Light-colored, non-yellowing structure suitable for outdoor durability
• Film properties adjustable by melamine ratio
Limitations:
• Need for oven temperature, solvent content
• Sensitivity to crosslinker and catalyst ratio
• Higher cost than alkyds
4. ALKYD RESINS
Alkyd resins are oil-modified polyesters obtained by modifying polyols and polybasic acids with fatty acids. Oil length is classified as short, medium and long; as it increases, flexibility and drying capability rise, while hardness and gloss behavior change.
Types carrying drying fatty acids are crosslinked by oxidation with oxygen in the air; driers such as cobalt, zirconium and calcium speed up this process. Types that do not show oxidative drying are baked with melamine or isocyanate.
Example manufacturer data, Synolac 7210 X 60 (Arkema, short oil): Based on dehydrated castor oil; solids 58–62 percent; viscosity 2,700–6,000 mPa·s; acid value at most 17 mg KOH/g; solvent xylene; flash point 24 °C; density 1.03 g/ml; in primers and enamels with amino resins.
Example manufacturer data, Synolac 1949 X 70: Fatty acid content 32 percent; solids 69–71 percent; acid value 5–10 mg KOH/g; viscosity 5,500–7,500 mPa·s; in high-gloss two-component polyurethane varnishes and enamels for wood.
Example manufacturer data, Synolac 5053 WD 50 (medium oil): Solids 48.5–51.5 percent; acid value at most 12 mg KOH/g; viscosity 50–80 dPa·s; solvent white spirit; in general purpose and anticorrosive paints.
Example manufacturer data, Synolac 7500 (very long oil, high solids): Solids at least 98 percent, solvent-free; linseed oil fatty acid 75 percent; acid value 3–10 mg KOH/g; density 0.99 g/ml; oxidizing type; shelf life 12 months.
For Synolac 7500, 0.05 percent cobalt and 0.15 percent zirconium as metal on solid resin are recommended as driers. Where there is concern about drier absorption onto pigments or polluted air, calcium can be added up to 0.2 percent; 0.1 percent methyl ethyl ketoxime in the total paint is advised to prevent skinning.
Short oil Synolac 7210 X 60 is soluble in aromatic hydrocarbons, esters, ketones and glycol ethers. It is compatible with amino resins, nitrocellulose and styrenated alkyds; it is only partially compatible with long oil alkyds.
For medium oil Synolac 5053 WD 50, a good balance between surface drying and hard drying and good brush application have been reported. The high-solids very long oil type is targeted at wood primers, wood stains and industrial wood coatings.
The choice of oil length determines the application. Short oil types give hardness and gloss in baked systems, while long oil types give flexibility and brush application in air-drying paints.
Alkyd resins are stored in the original, unopened container, in a dry environment and generally below 30–35 °C, away from direct sunlight.
Main fields of use:
• Primers, paints and enamels for wood and metal
• Anticorrosive paints and general industrial coatings
• Wood varnishes, stains and furniture coatings
Strengths:
• Economical cost and wide formulation flexibility
• Good flow and surface wetting in brush and roller application
• Drying and flexibility adjustable through oil length
Limitations:
• Slow curing because of oxidative drying, tendency to yellow over time
• Susceptibility of the ester linkage to hydrolysis in water and alkaline environments
• Volatile organic compound emission in solvent-based types
5. WATER-BASED POLYESTER DISPERSIONS AND WATER-DISPERSIBLE POLYESTERS
Water-based polyesters are polyesters that disperse in water thanks to ionic groups bound to the chain. Types with carboxyl groups are neutralized with an amine, and sulfonated types disperse in water through sulfonate groups bound to the chain.
Sulfopolyesters are produced from glycols and aromatic diacids; the Eastman AQ and Eastek series can be given as examples. They are supplied as solid resin or as ready dispersions and are used in coatings, inks, adhesives and textile sizing.
Example manufacturer data, Eastman AQ and Eastek series: Glass transition temperature 3–63 °C; 3 °C for AQ 1950, 29 °C for Eastek 1400, 38 °C for AQ 38S, 55 °C for AQ 55S, 63 °C for AQ 65S; charge density 0.33–0.89 meq/g.
Up to 30 percent solids the viscosity is below 100 cP; above this level it rises rapidly. It has been reported that the minimum film formation temperature is about 20 °C below the glass transition temperature, so extra plasticizer is often unnecessary.
Types with a glass transition temperature above 45 °C give thin, hard films of low tack. Types below 35 °C are flexible and moderately tacky. As charge density increases, water and moisture resistance decrease; dispersion cannot be achieved in solutions of high ionic strength.
Sulfopolyester dispersions provide fast drying and smooth, glossy films thanks to small particle aggregates. The wide Tg range allows flexibility and tack to be adjusted to the application.
AQ 1950 is designed for repulpable hot melt adhesives. Low-Tg types such as Eastek 1000 and AQ 38S provide flexibility and slip in textile sizing and reduce yarn breakage in weaving.
The choice of plasticizer affects water resistance. Hydrophobic plasticizers increase water resistance, and hydrophilic ones decrease it. In types with carboxyl groups, the degree of neutralization and the amount of co-solvent determine dispersion stability and film formation.
Water-based polyesters can also be used with crosslinkers such as melamine or isocyanate when required; in this case water and solvent resistance is increased. Low volatile organic compound targets are increasing the interest of this family in coatings and inks.
In storage, protection from freezing and high temperature, management of the risk of microbial contamination and compliance with the shelf life in the product document are required.
Main fields of use:
• Water-based inks and printing varnishes
• Hot melt adhesives, repulpable packaging adhesives
• Textile sizing and finishing applications
Strengths:
• Low solvent content and low volatile organic compound emission
• Film formation at low temperature and fast drying
• Flexibility and tack adjustable through Tg
Limitations:
• Lower water and moisture resistance than solvent-based systems
• Rapid viscosity increase above 30 percent solids
• Need for protection against freezing, high temperature and microbial contamination
CHEMICAL STRUCTURE AND MOLECULAR PROPERTIES OF POLYESTER RESINS
The basic unit of polyester is the ester linkage (–CO–O–) formed by the reaction of the carboxyl group with the hydroxyl group. The ester linkage is polar; the carbonyl oxygen behaves as a hydrogen bond acceptor, and the dipole interactions between chains contribute to mechanical strength.
The backbone of the chain varies with the acid and alcohol type used. Aromatic acids give hardness and heat resistance, aliphatic acids flexibility. Branched glycols such as neopentyl glycol protect the ester linkage sterically and thereby increase hydrolysis resistance.
In unsaturated polyesters, the maleate and fumarate double bonds are the points where the network is built. The degree of isomerization from maleic to fumaric and the styrene ratio determine the crosslink density. In saturated polyesters, the crosslink points are the carboxyl or hydroxyl groups at the chain ends.
In alkyds, the unsaturated fatty acids bound to the chain react with oxygen to build the network. Ester linkages are susceptible to hydrolysis; for this reason polyesters can degrade over time in hot, humid, acidic and basic environments.
Polyesters are not soluble in water. Water-based types remain dispersed through carboxylate or sulfonate groups bound to the chain.
PHYSICAL AND CHEMICAL PROPERTIES OF POLYESTER RESINS
Physical appearance: Unsaturated polyesters are styrene-containing, viscous, light yellow to amber liquids; powder coating polyesters are pale-colored granules; oil-free polyesters and alkyds are solvent-based solutions; sulfopolyesters are solid resin or dispersion
Chemical character: Polar polymer; contains the ester linkage and is susceptible to hydrolysis in hot and humid environments
Molecular formula: There is no fixed formula; it consists of repeating units containing the ester linkage
Molecular weight: Depends on the product type; unsaturated polyesters and alkyds are at the oligomer level
CAS No: There is no single number; 26123-45-5 is frequently used for unsaturated polyester
EC / EINECS No: There is no single number because it is a polymer
Solids content: In styrene-containing unsaturated polyesters about 53–62 percent in example products; in oil-free polyester solutions about 63–67 percent; in alkyds about 48–71 percent, above 98 percent in solvent-free types; 100 percent in powder coating polyesters
Density: In styrene-containing unsaturated polyesters about 1.1 g/cm³ as an example; in alkyd and oil-free polyester solutions about 0.99–1.06 g/ml
Viscosity: In unsaturated polyesters 450–1,100 mPa·s (23 °C) as an example; in oil-free polyester 25–35 P (25 °C); in short oil alkyds 2,700–7,500 mPa·s; in powder coating polyesters 9–125 Pa·s (165 °C)
Acid value: In unsaturated polyesters in the range of 14–20 mg KOH/g or below as an example; in alkyds and oil-free polyesters 3–17; in powder coating polyesters 30–38
Hydroxyl value: 25–35 in example products of oil-free polyesters; in carboxyl-functional powder coating polyesters the acid value is the main parameter
Styrene content: In unsaturated polyesters it is given in safety data sheets in the range of about 25–50 percent by weight
Gel time: In example unsaturated polyesters about 14–25 minutes at 23 °C with 1 percent MEKP50; it depends on temperature, accelerator and catalyst
Glass transition temperature: About 60–72 °C in example powder coating polyesters; 3–63 °C in sulfopolyesters
Flash point: 31–32 °C in example safety data sheets for styrene-containing resins; 24 °C in a xylene-based alkyd solution
Solubility in water: Insoluble; sulfopolyesters and neutralized carboxyl polyesters disperse in water
pH (aqueous solution): Meaningful only for water-based types; the value depends on the product
Decomposition: Hydrolysis of ester linkages and thermal decomposition; carbon oxides and hydrocarbons form on burning
Moisture: Powder coating and solution products are stored in a dry environment; water-based types are protected from freezing
Reactivity: Unsaturated polyesters cure by a radical route with peroxide and accelerator; heat and light shorten shelf life
Short Description of Physical Properties
In technical data sheets, solids content, viscosity, acid and hydroxyl value, gel time, Tg and shelf life are monitored most. Since these values vary with the manufacturer and the batch, the document of each product should be consulted.
HOW DO POLYESTER RESINS WORK AT THE MOLECULAR LEVEL?
In the synthesis of polyester, an acid or anhydride esterifies with a hydroxyl and water is released. The reaction proceeds at high temperature with removal of the water. Unsaturated products are subsequently diluted with styrene.
In unsaturated polyester, the redox reaction between peroxide and cobalt produces free radicals. The radical starts the addition polymerization of styrene and of the double bonds in the polyester chain. The chains are linked by styrene bridges, heat is released, and the resin first gels and then hardens.
In carboxyl-functional powder coating polyester, the carboxyl ends open the epoxy ring of TGIC. With a β-hydroxyalkylamide hardener, esterification occurs with the hydroxyl groups and water is released. In both cases a network forms at oven temperature.
Hydroxyl-functional polyester reacts with the methoxy groups of melamine in the presence of an acid catalyst and methanol is released. When used together with isocyanate, a urethane linkage forms.
In alkyd, the allylic hydrogens in the chain react with oxygen to give hydroperoxide. Driers such as cobalt speed up their decomposition and permanent bonds are built between the chains.
In water-based polyester, the ionic groups on the particle surface make the particles repel one another. During evaporation the particles coalesce and a continuous film forms.
IN WHICH SECTORS ARE POLYESTER RESINS USED?
Composites and chemical equipment: Boats, tanks, pipes, facade panels, pools and towers
Construction: Artificial marble, solid surface, sinks, countertops, polymer concrete and drainage channels
Automotive and repair: Gelcoat, body putty and repair products
Paint and coating: Powder coating, coil coating, wood and metal paints, alkyd primers and enamels
Metal and packaging: Can decoration and food-contact-compliant metal packaging coatings
Ink, adhesives and textile: Water-based ink, hot melt adhesive and textile sizing
Electrical and heating-cooling: Unsaturated polyester molding compounds with high arc resistance or flame retardant properties
ARE POLYESTER RESINS USED IN COSMETIC, FOOD AND PHARMACEUTICAL APPLICATIONS?
Cosmetics: Industrial polyester resins are not used in cosmetics. Special polyester polymers developed for cosmetic purposes are registered under separate INCI names and may take part with functions such as film former. Styrene-containing, powder coating or alkyd resins cannot be used for this purpose.
Food: It is not used as a direct food additive. On metal surfaces in contact with food, resinous and polymeric coatings are evaluated in the United States under 21 CFR 175.300, and polyester resins are among the components formed from the acids and alcohols listed in this provision.
In this provision, some tin catalysts are limited to 0.2 percent of the resin, and 2,2-dimethyl-1,3-propanediol can be used only in coatings in contact with non-alcoholic foods. In Europe there is no single harmonized legislation for coatings; Regulation (EC) No 1935/2004 and national rules apply. Compliance with Turkish and EU requirements must be verified product by product.
Pharmaceuticals: It is not used as an active substance or excipient. If a use in contact with pharmaceuticals or medical applications is being considered, product-specific documents and biocompatibility tests are required.
INDUSTRIAL APPLICATIONS OF POLYESTER RESINS
In composite production, unsaturated polyester wets the glass fiber and, when cured, gives hard, lightweight and corrosion-resistant parts. Boats, tanks and panels are produced by hand lay-up and spray-up methods; isophthalic and neopentyl glycol-based types are preferred for chemical environments.
In powder coating, the polyester resin forms an outdoor-durable, glossy and flexible film without using solvent. Superdurable types stand out in facades and aluminum profiles, standard durability types in general metal products.
In coil coating, oil-free polyester and melamine provide a balance of flexibility and hardness for painted sheet that is bent and formed. Alkyd resins, on the other hand, offer economical, easily applied primers and enamels in wood and metal paints.
POINTS TO CONSIDER WHEN USING POLYESTER RESINS
• The manufacturer’s technical data sheet and safety data sheet should be read before use
• In unsaturated polyesters, the peroxide and the cobalt accelerator must not be mixed directly with each other and must be added to the resin separately and according to the instructions
• Gel time is sensitive to temperature, catalyst ratio and mass thickness; trials should be carried out under actual conditions
• The work area should be ventilated because of styrene vapor, and ignition sources should be kept away
• In powder coating and coil coating systems, the resin, crosslinker and baking conditions should be selected together
• Water-based types should be protected against freezing, high temperature and microbial contamination
STARTING FORMULATION APPROACHES FOR POLYESTER RESINS
The approaches in this section are short starting examples showing how the product family can be evaluated in casting, powder coating and coil coating applications. The examples are not verified commercial recipes or final formulas; the proportions are for preliminary laboratory trials, and the total of each formula is 100%.
The amounts of hardener, catalyst and accelerator are determined according to the resin manufacturer’s recommendation. In every application, occupational safety and regulatory checks must be carried out.
EXAMPLE 1: EFFECT OF FILLER RATIO ON VISCOSITY AND CURING HEAT IN A FILLED CASTING POLYESTER
Purpose: To monitor the effect of the ratio of unsaturated polyester resin to mineral filler on viscosity, peak temperature and surface quality in artificial marble and solid surface casting.
Starting approach:
Unsaturated polyester casting resin: about 30.0%
Calcium carbonate or dolomite filler: about 66.0%
Pigment paste: about 2.0%
Cobalt accelerator solution: about 0.5%
Organic peroxide hardener: about 1.0%
Air release and wetting additive: about 0.5%
Application approach:
• The filler ratio is tested at about 60%, 66% and 70%; the resin, filler and pigment are mixed, and after the accelerator is added, the peroxide is added last and separately.
• The mixture is poured into the mold and deaerated; gel time, peak temperature, Barcol hardness, shrinkage and surface defects are monitored.
• Direct contact of the peroxide with the accelerator is avoided and ventilation is provided against styrene vapor.
EXAMPLE 2: EFFECT OF HARDENER RATIO ON FILM APPEARANCE IN A TGIC-FREE POLYESTER POWDER COATING
Purpose: To monitor the effect of the resin/hardener ratio on flow, gloss and mechanical strength in a powder coating based on carboxyl-functional polyester and a β-hydroxyalkylamide hardener.
Starting approach (white powder coating):
Carboxyl-functional polyester: about 56.0%
β-Hydroxyalkylamide hardener: about 3.0%
Titanium dioxide: about 28.0%
Barium sulfate filler: about 11.0%
Flow additive: about 1.5%
Degassing additive: about 0.5%
Application approach:
• The resin/hardener ratio is tested at about 96/4, 95/5 and 94/6; the components are mixed in an extruder, cooled and ground.
• The powder is applied electrostatically and baked at the temperature and time given in the manufacturer’s data; for one example resin, 20 minutes at 160 °C with HAA has been reported.
• Flow, gloss, impact, flexibility and adhesion are monitored; grounding and ventilation are applied against the formation of dust clouds.
EXAMPLE 3: EFFECT OF OIL-FREE POLYESTER TO MELAMINE RATIO ON FLEXIBILITY AND HARDNESS IN COIL COATING
Purpose: To monitor the effect of the resin/melamine ratio on flexibility, hardness and solvent resistance in a paint made of hydroxyl-functional oil-free polyester with a melamine crosslinker.
Starting approach:
Oil-free polyester solution (about 65% solids): about 45.0%
Hexamethoxymethyl melamine: about 7.0%
Titanium dioxide: about 25.0%
Solvent mixture: about 21.5%
Acid catalyst solution: about 0.5%
Flow and surface additive: about 1.0%
Application approach:
• The resin/melamine solids ratio is tested at about 85:15, 80:20 and 70:30; the amount of acid catalyst is adjusted on melamine solids according to the manufacturer’s recommendation.
• The paint is applied to a metal panel at constant thickness and baked at the temperature and time suitable for the manufacturer’s data.
• Flexibility, hardness, solvent rub resistance and adhesion are monitored; ventilation and flammable material precautions are applied against solvent vapor.
SIMILAR PRODUCTS AND ALTERNATIVES TO POLYESTER RESINS
Vinyl ester resins are epoxy-based resins used in place of unsaturated polyester in heavier chemical service and at high temperature. Their mechanical strength is higher than that of polyester; their cost is generally higher.
Epoxy resins give higher adhesion, low shrinkage and high strength in coatings and composites, but their curing is slower and their cost is high. In powder coating, epoxy-polyester hybrid systems are used; their outdoor durability is more limited than that of pure polyester.
Polyurethane coatings, through the combination of a polyol with an isocyanate, provide flexibility and abrasion resistance; polyester polyol is also a common component of these systems. Acrylic resins and dispersions stand out with UV resistance and color stability, and may lag behind polyester in chemical resistance and hardness.
In metal packaging, water-based phenol/epoxy precondensates are also used as sole binder. For one example product, baking for 12 minutes at 200 °C for interior and exterior coating has been reported.
No alternative replaces polyester in every application. Performance, cost, compatibility and regulation should be evaluated together.
QUALITY CONTROL AND PURCHASING CRITERIA FOR POLYESTER RESINS
• Solids content, viscosity and density
• Acid value and hydroxyl value, for example by ISO 2114 or ASTM D1639
• In unsaturated polyesters, gel time, peak temperature and shelf life
• In powder coating polyesters, glass transition temperature, melt viscosity and color
• Solvent or styrene content, flash point; in water-based types, pH and particle size
Manufacturers’ typical values are not considered binding specifications unless confirmed in a written contract. A certificate of analysis, a safety data sheet and a technical data sheet should be requested with every batch.
STORAGE AND TRANSPORT OF POLYESTER RESINS
Styrene-containing unsaturated polyesters are generally stored below 25 °C, in the shade and in the dark. In example products shelf life is given as 3–6 months and shortens as temperature rises. The peroxide and the cobalt accelerator are stored separately and under suitable conditions.
Powder coating polyesters are stored in a dry environment, below 30 °C, in the original closed bag; in example products shelf life is more than three years. Alkyd and oil-free polyester solutions are kept in closed containers, in a dry environment and below 30–35 °C; water-based types are protected from freezing.
Transport classification depends on the product. For an example styrene-containing polyester resin, UN 1866, class 3, packing group III has been reported. Section 14 of the safety data sheet of each product should be checked.
SAFETY INFORMATION ON POLYESTER RESINS
Safety should be separated between cured and uncured product. Cured polyester is a largely inert solid. Uncured styrene-containing resin and solvent-based alkyd and oil-free polyester solutions are flammable and call for attention from a health standpoint.
In example safety data sheets, the statements flammable liquid (H226), causes skin irritation (H315), causes serious eye irritation (H319), harmful if inhaled (H332), damage to hearing organs through prolonged or repeated exposure (H372) and harmful to aquatic life with long lasting effects (H412) appear. In some sheets there is also suspected of damaging the unborn child (H361d). The flash point is 31–32 °C.
Occupational exposure limits for styrene vary by country; in example sheets, values between 10 ppm and 100 ppm are seen as an 8-hour average. The applicable limit should be checked in the legislation of the country of work.
As gloves, neoprene, nitrile, Viton or polyvinyl alcohol complying with EN 374 are used; for the eyes, safety glasses with side shields or protective goggles; where ventilation is insufficient, a type A filter. Antistatic clothing and working away from ignition sources are recommended.
In a fire, dry chemical, foam or carbon dioxide is used; a water jet is not recommended. Vapors are heavier than air and can collect in low places. Carbon monoxide and carbon dioxide form on burning.
Accelerators such as cobalt bis(2-ethylhexanoate) may contain components with high bioaccumulation potential. Waste is disposed of according to local legislation and is not released into the drain. Powder coating dust contains fine respirable particles, and a dust cloud may also carry a fire and explosion risk.
In case of eye contact, rinse with water for at least 10 minutes and consult a doctor. This section is for general information; it does not replace the safety data sheet.
WHAT SHOULD BE CONSIDERED WHEN BUYING POLYESTER RESINS?
• Correct product identity: unsaturated or saturated, orthophthalic, isophthalic or neopentyl glycol-based, carboxyl- or hydroxyl-functional, solvent-based or water-based
• Technical specifications: solids content, viscosity, acid or hydroxyl value, gel time, Tg
• Suitability for the intended use: indoor or outdoor, chemical and heat exposure, method and baking conditions
• Packaging, shelf life, batch consistency and certificate of analysis
• The supplier’s technical support, regulatory requirements and conformity documents for food-contact uses
• Total cost of supply: cost per unit of solids, waste and processing cost should be evaluated together
SUPPLY OF POLYESTER RESINS FROM ATAMAN KİMYA
Which type, grade and packaging of polyester resin can be supplied varies by product. Product selection is made according to the application, the method to be used and the performance desired.
For up-to-date information on stock, origin, documents, delivery time and technical support, contacting ATAMAN KİMYA is recommended.
FREQUENTLY ASKED QUESTIONS ABOUT POLYESTER RESINS
What are polyester resins?
They are a family of polymers carrying the ester linkage, formed by the polycondensation of polybasic acids with alcohols.
What does polyester resin mean?
The name comes from the ester linkages in the polymer chain.
What is the CAS number of polyester resins?
There is no single number; 26123-45-5 is often used for unsaturated polyester.
What is the EC / EINECS number of polyester resins?
Because it is a polymer, there is no single number; the raw materials have separate numbers.
What is the chemical formula of polyester resins?
There is no fixed formula; it consists of repeating units containing the ester linkage.
What is the INCI name of polyester resins?
For industrial resins there is no single INCI name; special grades for cosmetic purposes are known by their own INCI names.
Are polyester resins used in cosmetics?
Industrial types are not used; only special grades developed for cosmetic purposes are used.
What is the difference between polyester resins and vinyl ester resins?
Vinyl ester is epoxy-based and gives higher chemical resistance and strength; polyester is more economical.
What are polyester resins used for?
They are used for composite production, coating, casting and bonding.
In which sectors are polyester resins used?
They are used in composites, construction, automotive, paint, metal coating, ink and textile.
How do unsaturated polyester resins cure?
They cure by crosslinking radically with styrene using a peroxide and a cobalt accelerator.
What are polyester resins good for?
They form hard, durable and chemical-resistant parts and coatings.
How do polyester resins work in powder coating?
The carboxyl ends react with the hardener in the oven and form a crosslinked film.
Are polyester resins soluble in water?
No; water-based types are present dispersed in water.
How much peroxide is used during curing?
Manufacturers’ tests are generally carried out with 1–1.5 percent MEKP50; the actual amount is determined by the manufacturer’s instructions according to the resin and conditions.
Are polyester resins hazardous substances?
The cured product is low risk; uncured styrene-containing resin is flammable and carries a health hazard.
Why can styrene pose a risk in polyester resins?
Its vapor is harmful if inhaled and, with repeated exposure, can damage organs and hearing.
Are polyester resins registered under REACH?
Polymers are generally exempt from registration; monomers such as styrene are assessed separately.
What is the physical appearance of polyester resins?
Unsaturated polyester is a viscous liquid, powder coating polyester is pale granules, and alkyd is in solution form.
What is the UN number of polyester resins?
There is no single number; UN 1866 has been reported in an example safety data sheet for styrene-containing solutions.
Why are acid value and gel time important in polyester resins?
Acid value determines the hardener requirement and stability, and gel time determines the working time.
What does the price of polyester resin depend on?
It depends on the type of acid and glycol, the styrene content, the solids content and raw material prices.
Is there an alternative to polyester resins?
Yes; vinyl ester, epoxy, polyurethane and acrylic resins can be alternatives in some applications.
How should polyester resins be stored?
In the original closed container, cool and in the shade, generally below 25–30 °C, away from heat and moisture.
Which documents should be requested when buying polyester resins?
Safety data sheet, technical data sheet and certificate of analysis.
Which technical properties are important when buying polyester resins?
Resin type, solids content, viscosity, acid or hydroxyl value, gel time and shelf life.
POLYESTER RESINS – TECHNICAL SUMMARY
Chemical name: Polyester (polycondensation polymer of polybasic acids with alcohols)
CAS number: No single number; often 26123-45-5 for unsaturated polyester
Chemical class: Polymer, polycondensation polymer containing the ester linkage
Main functions: Binder, film former, composite matrix resin, casting resin
Important fields of application: Composites, artificial marble, powder coating, coil coating, wood and metal paint
Parameters critical for quality control: Solids content, viscosity, acid or hydroxyl value, gel time
Storage: In the original closed container, cool, dry and in the shade, generally below 25–30 °C.
