HAA HARDENER

HAA Hardener is the common name of beta-hydroxyalkylamide crosslinkers, white crystalline powders or granules such as N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide (CAS No 6334-25-4), used to cure carboxyl-functional polyester resins in TGIC-free thermosetting powder coatings for architectural, appliance, furniture, agricultural and general industrial finishes.
The beta-hydroxyalkylamide crosslinker has become the main alternative to TGIC in polyester powder coatings because it gives excellent outdoor durability, good flexibility and good transfer efficiency with a much milder hazard labelling than TGIC, which is classified in the EU as a mutagen (Muta. 1B, H340) and listed as a substance of very high concern.
The HAA curing agent works through its four reactive beta-hydroxyl groups, which esterify the carboxyl end groups of the polyester at baking temperatures of roughly 160–200 °C without a catalyst, building a three-dimensional network while releasing water as a condensation by-product.

Chemical type: Beta-hydroxyalkylamide (β-HAA), tetra-functional
CAS No (hydroxyethyl type): 6334-25-4
CAS No (hydroxypropyl type): 57843-53-5
Appearance: White powder or granules
Melting range (hydroxyethyl type): approx. 120–125 °C
Hydroxyl equivalent weight (hydroxyethyl type): approx. 80–84 g/eq
Volatile matter: typically max. approx. 0.5 %
Typical polyester : HAA ratio: approx. 95:5

COMMON PRODUCT & CHEMICAL NAMES OF HAA HARDENER:

HAA Hardener, HAA, β-HAA, Beta-Hydroxyalkylamide, β-Hydroxyalkylamide Hardener, Hydroxyalkylamide, Hydroxyalkyl Amide, Hydroxyalkylamide Hardener, Hydroxyalkylamide Curing Agent, Hydroxyalkylamide Crosslinker, HAA Curing Agent, HAA Crosslinker, TGIC-Free Hardener, Non-TGIC Hardener, Primid-Type Hardener, Polyester Powder Coating Hardener, N,N,N',N'-Tetrakis(2-hydroxyethyl)adipamide, Tetrakis(2-hydroxyethyl)hexanediamide, N,N,N',N'-Tetrakis(2-hydroxypropyl)adipamide, Bis[N,N-di(β-hydroxyethyl)]adipamide, Primid XL-552, Primid QM-1260, HAA XL-552 Type, HAA QM-1260 Type

"HAA Hardener" is a generic product name, not a single brand. It covers several beta-hydroxyalkylamide molecules, of which two dominate the market. The hydroxyethyl type, N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide (CAS 6334-25-4), is the classic Primid XL-552 type, the hydroxypropyl type, N,N,N',N'-tetrakis(2-hydroxypropyl)adipamide (CAS 57843-53-5), is the Primid QM-1260 type. Primid is the brand of the original producer, many manufacturers offer equivalent grades under their own codes.
The hydroxyalkylamide hardener is not an epoxy hardener and is not used for epoxy resins, adhesives or composites. It also should not be confused with TGIC (triglycidyl isocyanurate, an epoxy crosslinker), with glycidyl ester TGIC substitutes, or with the carboxyl polyester resins it cures. When ordering, the exact chemical type, CAS number and hydroxyl equivalent weight of the HAA Hardener should be stated.

WHAT IS HAA HARDENER?

Beta-hydroxyalkylamides are amides whose nitrogen atoms carry 2-hydroxyalkyl groups. In the most common HAA Hardener, an adipic acid backbone carries two amide groups, and each amide nitrogen carries two 2-hydroxyethyl groups, giving four hydroxyl groups per molecule (molecular weight approx. 320 g/mol, theoretical hydroxyl equivalent weight approx. 80 g/eq).
The special feature of HAA Hardener is the position of the hydroxyl group beta to the amide nitrogen. This allows the amide to assist the reaction (via a cyclic intermediate) so that esterification with carboxylic acids is fast at powder baking temperatures, much faster than with ordinary alcohols, and needs no catalyst.
The HAA curing agent is produced by aminolysis of an adipic acid diester (for example dimethyl adipate) with diethanolamine (hydroxyethyl type) or diisopropanolamine (hydroxypropyl type), followed by crystallisation and drying.

Polyester powder coatings for outdoor use were for decades cured almost exclusively with TGIC. In Europe, TGIC-based powders must carry strict hazard labelling, and TGIC was added to the REACH Candidate List in 2012, so the industry moved strongly to HAA Hardener. Today, HAA–polyester systems are standard for architectural aluminium, façades, window frames and many general industrial applications, and they are increasingly used worldwide.
For the powder producer, HAA Hardener brings several practical benefits besides labelling. HAA powders generally charge well in electrostatic spraying, give good transfer efficiency and penetrate corners and Faraday cage areas better than many TGIC powders. Mechanical properties such as flexibility and impact resistance are very good, and suitably designed HAA polyesters meet demanding exterior durability standards.
The beta-hydroxyalkylamide crosslinker also has limitations that formulators must manage: water is released during cure, which limits film build and can cause pinholes, light colours tend to yellow more on overbake than TGIC systems, the minimum cure temperature is usually somewhat higher, and chemical and corrosion resistance are often rated slightly below TGIC.

Where HAA Hardener-based powders are used: aluminium extrusions and architectural profiles, curtain walls, window and door frames, balcony railings, outdoor furniture, garden and agricultural equipment, construction machinery, appliance housings, metal office furniture, shelving, lighting, electrical enclosures, bicycles, fitness equipment and general steel parts.

CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION OF HAA HARDENER

HYDROXYETHYL TYPE (PRIMID XL-552 TYPE):
Chemical name: N,N,N',N'-Tetrakis(2-hydroxyethyl)adipamide
CAS No: 6334-25-4
EC No: 405-370-0
Molecular formula: C14H28N2O6
Molecular weight: approx. 320.4 g/mol
Functionality: 4 hydroxyl groups

HYDROXYPROPYL TYPE (PRIMID QM-1260 TYPE):
Chemical name: N,N,N',N'-Tetrakis(2-hydroxypropyl)adipamide
CAS No: 57843-53-5
Molecular formula: C18H36N2O6
Molecular weight: approx. 376.5 g/mol
Functionality: 4 hydroxyl groups

Chemical class: Beta-hydroxyalkylamide, polyfunctional hydroxyl amide crosslinker
Main function: Curing agent for carboxyl-functional polyester powder coatings

TYPICAL PROPERTIES OF HAA HARDENER

Typical values for a hydroxyethyl-type (XL-552 type) HAA Hardener, values differ by producer and type:
Appearance: White granules or powder
Odour: Practically odourless
Melting range: approx. 120–125 °C
Hydroxyl equivalent weight: approx. 80–84 g/eq
Volatile matter: max. approx. 0.5 %
Solubility: Soluble in water, reacts in the polyester melt during cure
Recommended extrusion temperature: approx. 100–110 °C (up to approx. 120 °C barrel temperature)
Typical cure: approx. 10 minutes at 180 °C or 5 minutes at 200 °C object temperature (resin-dependent)
Packaging (typical): 25 kg PE-lined bags
Storage: Dry, tightly closed, approx. 15–30 °C, hygroscopic

The hydroxypropyl type reacts more slowly. It is used where longer flow time, better degassing or different overbake behaviour is required, often with polyesters designed for it. The TDS of the HAA Hardener grade supplied is available on request from Ataman Kimya.

CALCULATING THE AMOUNT OF HAA HARDENER

Because HAA Hardener is used at low levels, the ratio must be calculated rather than estimated. The basis is the acid value of the polyester (mg KOH/g) and the hydroxyl equivalent weight of the HAA Hardener.

Step 1: Acid equivalent weight of the polyester = 56,100 / acid value.
Step 2: Equivalents of COOH per 100 g resin = 100 / acid equivalent weight.
Step 3: Grams of HAA Hardener per 100 g resin = equivalents × HAA equivalent weight (for a 1:1 ratio).

Worked example: polyester acid value 33 mg KOH/g, HAA Hardener equivalent weight 82 g/eq.
Acid equivalent weight = 56,100 / 33 = 1,700 g/eq.
COOH equivalents per 100 g resin = 100 / 1,700 = 0.0588 eq.
HAA Hardener needed = 0.0588 × 82 ≈ 4.8 g per 100 g resin, which corresponds to a polyester : HAA ratio of about 95.4 : 4.6.

This is why typical HAA polyesters with acid values around 30–35 mg KOH/g are formulated at about 95:5. Producers often work at a slight under- or over-stoichiometry to fine-tune properties, following the resin supplier's recommendation.

HAA HARDENER VERSUS TGIC – A PRACTICAL COMPARISON

Reactive group: HAA Hardener – hydroxyl (beta-hydroxyalkylamide), TGIC – glycidyl (epoxy).
Functionality: HAA Hardener – 4, TGIC – 3.
Equivalent weight: HAA Hardener – approx. 80–90 g/eq, TGIC – approx. 110 g/eq.
Cure mechanism: HAA Hardener – condensation, water released, TGIC – addition, no volatiles.
Typical polyester : crosslinker ratio: HAA Hardener – approx. 95:5, TGIC – approx. 93:7.
Typical maximum pinhole-free film build: HAA Hardener – traditionally about 100–125 µm (4–5 mils), higher with modern resins, TGIC – considerably higher.
Overbake colour stability: HAA Hardener – fair, light colours can yellow, TGIC – very good.
Minimum cure temperature: HAA Hardener – usually somewhat higher, TGIC – lower cure possible.
Chemical and corrosion resistance: HAA Hardener – good, TGIC – very good.
Transfer efficiency and Faraday cage penetration: HAA Hardener – often better.
Hazard labelling: HAA Hardener – mild, mainly dust-related, TGIC – Muta. 1B (H340) and further hazards, SVHC.

Switching from TGIC to HAA Hardener is therefore not a drop-in replacement: the polyester, additives, film thickness and bake schedule all need to be reviewed.

EXAMPLE: A PUBLISHED POLYESTER/HAA FORMULATION

A published laboratory example for an outdoor anthracite grey (RAL 7016) polyester/HAA powder used approximately 75.0 % carboxylated polyester, 3.6 % HAA Hardener (Primid XL-552), 0.3 % micronised PE wax, 6.9 % pigments, 1.0 % levelling additive, 0.4 % benzoin and 12.8 % filler. The premix was extruded on a twin-screw extruder with zone temperatures of 50/80/120/120/120 °C, ground and sieved at 125 µm, and cured for 10 minutes at 180 °C peak metal temperature at 70–80 µm film thickness. The coatings passed typical mechanical tests (mandrel bending, cross cut, cupping) and showed good gloss retention in accelerated weathering, with results influenced by the filler choice. This example shows the typical structure of an HAA powder, actual formulations must be developed with the selected resin.

COMPONENT PERCENTAGES OF THE LABORATORY EXAMPLE
Carboxylated polyester: 75.0 %
HAA Hardener (Primid XL-552): 3.6 %
Micronised PE wax: 0.3 %
Pigments: 6.9 %
Levelling additive: 1.0 %
Benzoin: 0.4 %
Filler: 12.8 %
Total: 100.0 %
These percentages restate the laboratory example above as an illustrative starting mixture, not a validated commercial recipe. Optimise and test with the selected resin and process.

TROUBLESHOOTING HAA HARDENER POWDER COATINGS

Pinholes and bubbles: caused by water released during cure, trapped air or moisture. Reduce film thickness, add or increase degassing agent (for example benzoin), use a resin with a longer flow window or a slower HAA type, and adjust the heating rate of the oven.
Overbake yellowing: reduce peak temperature and time, use resins and antioxidants recommended for overbake stability, consider the hydroxypropyl HAA type, and test whites carefully.
Poor flow or orange peel: check gel time, particle size distribution and flow additive level, avoid excess HAA Hardener, which can accelerate gelation.
Insufficient cure (poor solvent rub resistance, low impact): check the ratio calculation against the actual acid value, verify object temperature with data loggers and ensure homogeneous dispersion in the extruder.
Gloss variations: check dispersion, cure uniformity and the matting system.
Caking of powder: protect HAA Hardener and the finished powder from moisture and heat during storage and transport.

THINGS TO CONSIDER WHEN USING HAA HARDENER

- Choose a polyester designed for HAA cure (typical acid value approx. 30–35 mg KOH/g for standard systems).
- Calculate the ratio from actual analytical values, not nominal ones.
- Keep extrusion temperatures moderate (about 100–120 °C) to avoid pre-reaction.
- Plan film thickness and degassing to accommodate water release.
- Check overbake behaviour if the coating line can overbake.
- Test chemical and corrosion resistance against the specification, especially when replacing TGIC.
- Store HAA Hardener dry, it is hygroscopic and moisture affects dosing and appearance.
- Confirm the type (hydroxyethyl or hydroxypropyl) on every delivery, because they are not interchangeable without reformulation.

ALTERNATIVES TO HAA HARDENER

TGIC: epoxy crosslinker for polyester powders, no water release, strict hazard classification.
Glycidyl ester blends (TGIC substitutes such as PT 910/912 types): epoxy-type crosslinkers with addition cure.
Epoxy resins: crosslinkers in polyester–epoxy hybrid powders for interior use.
Blocked isocyanates and uretdiones: for polyurethane powders based on hydroxyl polyester.
Glycoluril crosslinkers (such as tetramethoxymethyl glycoluril): for hydroxyl polyester powders.
Other HAA products: hydroxyethyl and hydroxypropyl types and proprietary modified HAA hardeners from various producers.

HOW DOES HAA HARDENER WORK AT THE MOLECULAR LEVEL?
 
HAA Hardener is a β-hydroxyalkylamide crosslinker for carboxyl-terminated polyester resins, used mainly in powder coatings. The most common representatives are adipic acid diamides in which each amide nitrogen carries two hydroxyalkyl groups, for example tetrakis(2-hydroxyethyl)adipamide or its 2-hydroxypropyl analogue. The chemistry is easiest to follow by tracing what happens to the molecule from the moment the powder enters the oven until the coated part cools.
 
Before heating – a stable, solid blend: In the powder, the hydroxyalkylamide and the polyester are present as separate solid particles or as a solid melt-mixed blend. At room temperature, molecular mobility is too low for the hydroxyl and carboxyl groups to meet and react, so the powder remains storage-stable as long as it is kept dry and below its sintering temperature.
 
Melting and wetting: As the part heats up, the polyester melts and the hydroxyalkylamide dissolves or disperses in it. The polar hydroxyl and amide groups of the hardener interact with the carboxyl groups of the resin through hydrogen bonding, bringing the reactive partners into close contact. At this stage the melt has low viscosity and begins to flow over the substrate.
 
Activation through the neighbouring amide: When the temperature reaches the curing range, the hydroxyl group on the carbon β to the amide nitrogen becomes activated. The adjacent amide group participates intramolecularly, and an oxazolinium-type intermediate forms. This internal assistance makes the hydroxyalkylamide much more reactive toward carboxylic acids than ordinary diols or polyols, so no external catalyst is required.
 
Ester formation and water release: A carboxyl group of the polyester opens the activated intermediate and forms an ester linkage; one molecule of water is released for every bond created. Since the hardener has several hydroxyalkyl arms and the resin has several carboxyl ends, the reaction connects chains in many directions and quickly builds molecular weight. Viscosity rises sharply, flow stops and a crosslinked network develops.
 
Escape of water vapour: The water formed during crosslinking must diffuse out of the film while it is still soft enough to let vapour pass. If the surface gels too early, or the film is very thick, bubbles and pinholes can form. Hydroxypropyl-type HAA hardeners react somewhat more slowly than hydroxyethyl types, which gives the vapour more time to escape and can allow higher film builds with fewer surface defects.
 
Network completion: As stoving continues, remaining hydroxyl and carboxyl groups react until mobility becomes too low for further esterification. A balanced ratio of hydroxyl to carboxyl groups leaves few dangling ends and produces a dense network with good hardness, flexibility, impact strength and chemical resistance. An unbalanced ratio leaves free polar groups that make the film more sensitive to water and weathering.
 
Cooling and final properties: On cooling, the crosslinked polyester solidifies into a glassy film that no longer melts or dissolves. With saturated polyester resins, the ester backbone does not contain strong UV-absorbing aromatic amine or epoxy-derived structures, which supports long-term gloss and colour retention in outdoor use. This is why β-hydroxyalkylamides are widely used as an alternative to triglycidyl isocyanurate (TGIC) in exterior powder coatings.
 
Comparison with epoxy-based curing: In TGIC or glycidyl ester systems, carboxyl groups open epoxide rings in an addition reaction that releases no by-product. HAA Hardener instead works by condensation, which explains both its main limitation, outgassing of water, and its main advantage, a crosslinker chemistry free of epoxide groups.
 
Sensitivity to moisture: The numerous hydroxyl and amide groups also attract water from the air. Moisture taken up during storage can impair powder flow and fluidisation and may add to outgassing during cure, so the hardener and finished powders are kept in dry, closed packaging.
 
Final coating performance depends on the resin acid value, hardener-to-resin ratio, film thickness, heating rate, stoving temperature and time, and the pigments and additives used. HAA Hardener dosage and process conditions should therefore be confirmed through laboratory trials.

QUALITY CONTROL AND PURCHASING CRITERIA FOR HAA HARDENER

- chemical type and CAS number (6334-25-4 or 57843-53-5, or as stated by the producer)
- hydroxyl equivalent weight or hydroxyl value
- melting range
- volatile matter / moisture
- appearance and colour
- particle or granule size
- free amine or residual raw material content, where specified
- batch COA, TDS, SDS and recommended polyester types and ratios

Specifications and documents for the HAA Hardener grades supplied are available on request from Ataman Kimya.

STORAGE AND HANDLING OF HAA HARDENER

Store HAA Hardener in tightly closed original bags in a cool, dry, well-ventilated place, typically at about 15–30 °C, away from moisture, heat and direct sunlight. Close opened bags immediately because HAA Hardener absorbs moisture. Use clean, dry equipment, avoid dust generation when weighing and premixing, and ground equipment to prevent static discharge, since organic dusts can form explosive mixtures with air. Use stock on a first-in, first-out basis. Shelf life depends on the producer and is available on request from Ataman Kimya.

SAFETY OF HAA HARDENER

Beta-hydroxyalkylamide hardeners generally carry much milder hazard labelling than TGIC, in many cases the main practical concern is dust. Avoid inhaling dust and avoid contact with eyes. Wear safety glasses, gloves and a dust mask during bulk handling and use local exhaust ventilation.
First aid: after inhalation, move to fresh air, after skin contact, wash with soap and water, after eye contact, rinse with water for several minutes, removing contact lenses, after swallowing, rinse the mouth and seek medical advice if discomfort occurs.
Spills: sweep or vacuum up without raising dust, collect for reuse or disposal according to local regulations.
The classification of each HAA Hardener grade is given in the SDS, available on request from Ataman Kimya.

BUYING HAA HARDENER

The hydroxyalkylamide hardener is usually supplied as powder or granules in 25 kg PE-lined bags. When requesting HAA Hardener, please state the required type (hydroxyethyl or hydroxypropyl, or the reference grade), the resin system and acid value, the application and the annual volume. Grades, packaging and lead times are available on request from Ataman Kimya.

SUPPLY OF HAA HARDENER FROM ATAMAN KIMYA

Ataman Kimya supplies HAA Hardener grades for powder coating producers. Ataman Kimya provides TDS, SDS and COA documents, supports ratio calculation and TGIC-to-HAA transition questions, and helps customers choose between HAA types and other TGIC-free hardeners. For quotations, please contact Ataman Kimya.

FREQUENTLY ASKED QUESTIONS ABOUT HAA HARDENER

CAN HAA HARDENER BE USED FOR EPOXY RESINS?
No. HAA Hardener cures carboxyl-functional polyester resins in powder coatings, it is not an epoxy hardener.

WHY IS HAA HARDENER USED INSTEAD OF TGIC?
TGIC is classified as a mutagen (Muta. 1B, H340) and is an SVHC, so HAA Hardener allows TGIC-free exterior polyester powders with milder labelling.

HOW MUCH HAA HARDENER IS NEEDED?
Typically about 5 parts per 95 parts polyester, calculated exactly from the polyester acid value and the HAA equivalent weight.

WHAT CAUSES PINHOLES IN HAA POWDERS?
Water released during the cure reaction, film thickness, degassing agents and bake profile must be controlled.

WHAT IS THE DIFFERENCE BETWEEN XL-552-TYPE AND QM-1260-TYPE HAA HARDENER?
XL-552 type is the hydroxyethyl adipamide (CAS 6334-25-4), QM-1260 type is the hydroxypropyl adipamide (CAS 57843-53-5), which reacts more slowly and can improve degassing and overbake behaviour in suitable systems.

DOES HAA HARDENER NEED A CATALYST?
No. The beta-hydroxyalkylamide structure reacts without added catalyst at normal baking temperatures.

WHICH CURE SCHEDULE IS TYPICAL?
About 10 minutes at 180 °C or 5 minutes at 200 °C object temperature for standard systems, low-bake HAA polyesters can cure at lower temperatures according to the resin supplier.

HAA HARDENER – TECHNICAL SUMMARY

Product name: HAA Hardener
Chemical type: Beta-hydroxyalkylamide (tetra-functional)
Main types: Tetrakis(2-hydroxyethyl)adipamide, CAS 6334-25-4 (EC 405-370-0), Tetrakis(2-hydroxypropyl)adipamide, CAS 57843-53-5
Appearance: White powder or granules
Melting range (hydroxyethyl type): approx. 120–125 °C
Hydroxyl equivalent weight (hydroxyethyl type): approx. 80–84 g/eq
Volatile matter: max. approx. 0.5 %
Reaction partner: Carboxyl polyester (acid value typically approx. 30–35 mg KOH/g)
Typical ratio: approx. 95:5 polyester : HAA
Typical cure: approx. 10 min at 180 °C or 5 min at 200 °C
Cure by-product: Water
Main uses: TGIC-free outdoor and indoor polyester powder coatings
Storage: Dry, tightly closed, approx. 15–30 °C

HAA Hardener can be sourced from ATAMAN KİMYA. For further information and supply inquiries about HAA Hardener, please contact ATAMAN KİMYA.