An Acrylic resin is a polymeric material (in solution, dispersion or solid) containing acrylic monomers. These monomers are usually esters of acrylic, methacrylic acids or their derivatives, and can be functionalized by introducing different chemical groups (R groups). Others monomers can also be incorporated in the polymer chains in order to obtain resins with different properties or lower cost.
In general acrylic resin show good chemical and photochemical resistance. They are commonly used in many different applications, from solvent-based and water-based industrial coatings to architectural coatings.
Key parameters of an acrylic resin are:
• Tg (Glass transition temparature),
• Average Molecular weight of the polymers, and
• Polymer molecular weight distribution.
These parameters have an impact on the resin properties (viscosity , dispersion ) and on the final film/coating obtained (flexibility/hardness...).
[caption id="attachment_139641" align="aligncenter" width="652"]
Figure 1. Typical Acrylic Monomers[/caption]
Thermoplastic Acrylic Resins
In thermoplastic resins, the polymers composing the resin do not contain any reactive group. Thus in these resins the polymer chains are not cross-linked. To improve the interaction between the different polymer chains, high molecular weight polymers are
used.
Thermoplastic resins normally soften and can be reshaped when the temperature is increased. This property makes these resins the ideal candidates for some industrial processes, as injection molding, compression molding or extrusion. Main use of these resin include inks and adhesives.
Cross-linking Resins
Crosslinking resins can be cured to promote chemical interactions between different polymer chains. Curing, which can lead to more complex polymeric structures, and thus to stronger. materials, can occur in different conditions, that will depend mainly
on the active group present in the polymers.
When reactive groups are present, acrylic resins can be cross-linked by allowing the interaction between two different polymer chains. This can occur in specific conditions, as for instance at a certain temperature or under UV light. A catalyst may also be added
to promote and accelerate the chemical reaction.
We can distinguish between two types of crosslinking systems:
• Externally-cross-linked resins, which require a curing agent, i.e. a chemical that will react with the polymers, and
• Self-crosslinking resins.
In the first case the R group is commonly a hydroxyl-functionalized chain allowing the reaction with melamine or isocyanate curing agents. This kind of formulation (resin + curing agent) can be provided where they are already mixed together as:
• Two components system (2K) or
• One component system 1K.
The 2K are used in particular when heating in an oven is not possible. In 1K, isocyanate curing agents can be “blocked”, or made unreactive at room temperature, and curing of the resin will occur only at higher temperature in an oven (stoving coatings).
In addition to hydroxyl functions, carboxyl groups are also normally present on the polymer chains of crosslinking resins (or as free acrylic acids): they can act as catalysts for the curing reaction and improve coating adhesion. Moreover other curing agents like epoxies,
which can react with the carboxyl groups, could also be used in this case.
These acrylic resins can be provided in solvent phase but if the number of carboxyl group on the polymers is high enough, they can be soluble in water. In this case they are commonly identified as water-thinnable. In water-based systems a co-solvent can also be present to improve resin compatibility. Finally, emulsions of thermoset acrylic resins are also available. Emulsions usually allow higher solid content at same viscosity compared to water-thinnable ones and the alkali resistance is usually better as less carboxyl group are
needed.
Finally acrylic resins can be available as self-crosslinking version (rather solvent-based or water-based). In these type of resins some R groups in the copolymer structure are blocked amide (alkoxymethyl acrylamides) groups like N,N-bis-butoxy-methylamide.
During curing process (usually in an oven at elevated temperatures), these groups react with the hydroxyl groups also available on the copolymers leading to a crosslinked network. These type of resins usually have increased hardness, gloss and chemical resistance compared to resins cross-linked with curing agents.
Hydroxyl Value Number
The hydroxyl value is an indicator of the reactivity of the acrylic resins functionalized with hydroxyl functions (ie the number of OH group available). It is usually expressed as the KOH mass in mg equivalent to the amount of acetic acid reacting during the acetylation of 1g of resin. The higher the hydroxyl value, the higher the reactivity (and thus the cross-linking possibilities).
Acid Value
The acid is an indicator of the number of carboxyl group present on in the copolymer. It is usually expressed as the amount of KOH needed to neutralize 1g of resin (See DIN 53402 or ISO 2114). The number of carboxyl group has an impact on the adhesion properties of the resin and on the solubility in water. The higher the acid value, the higher the number of
carboxyl groups.
Minimum Film-forming Temperature for Acrylic Dispersion
The Minimum Film-forming Temperature (MFT) is the minimum temperature under which the acrylic latex will lead to a cracked material rather than a continuous film.
• For acrylic latexes designed for architectural applications (wall paints) the MFT is usually below 5°C.
• For latexes designed for industrial applications, where oven curing is used, the MFT can be higher.
Attacryl A 144; as a thermoplastic acrylic resin, is characterized by excellent pigment wetting ability and high pigment filling. It is compatible with all pigments and fillers commonly used in the paint industry.
Usage Areas:
• Road marking paints,
• Concrete coatings,
• Stone varnish,
• Paint and surface coating,
• Metal paints.
Attacryl A-HF 060; It is a two-component thermosetting resin curable with polyisocyanate, 60% dissolved in Shellsol A. Resin combined with aliphatic polyisocyanate for two-component industrial coatings for hot and cold drying, with good mechanical properties, chemical and weather resistance.
Usage Areas:
• Industrial coatings,
• Automotive primers,
• Metal and glass surfaces,
• Abs surfaces.
Attacryl A 077; It is an air and oven drying two component resin in combination with aliphatic polyisocyanates in 60% xylene.
Usage Areas:
• Primer,
• PU systems,
• Anticorrosive floor coating,
• Industrial flooring.
Attacryl A-HF 097; It is an air and oven drying two component resin in combination with aliphatic polyisocyanates, also for 70% butyl acetate.
Usage Areas:
• Two component coatings,
• Auto repair paints and topcoats,
• Topcoats for agricultural machinery,
• Anticorrosive industrial paints.
Extremely successful results were obtained in the varnish study carried out in the laboratory with Attacryl A 077 and Attacryl A-HF 097 from the acrylic resin product range. Density in the prepared varnish solutions is between reference values (0.95 – 1.03 g/
cm3) and has been tested.
Tests made;
• Bending Test,
• Impact Test,
• Cross-cut Test,
• Gloss Test.
All the results obtained in these tests were within the desired reference value range.
Kader Maraşlı
Account Manager
Günkem
Aytaç Ayhan
Account Manager
Günkem
