Acrylic Resin

Acrylic Resin Acrylic resin is a polymeric material containing acrylic monomers (in solution, dispersion or solid form). These monomers are typically esters of acrylic and methacrylic acids or their derivatives and can be functionalized by adding different chemical groups (R groups). Other monomers can also be incorporated into polymer chains to obtain resins with different properties or at lower cost. Acrylic resins generally exhibit good chemical and photochemical resistance. They are widely used in many different applications ranging from solvent-based and water-based industrial coatings to architectural coatings. The basic parameters of acrylic resin are: • Tg (Glass transition temperature), • Average molecular weight of polymers, and • Polymer molecular weight distribution. These parameters have an effect on resin properties (viscosity, dispersion…) and the resulting final film/coating (flexibility/hardness…).

Thermoplastic Acrylic Resins

In thermoplastic resins, the polymers making up the resin contain no reactive groups. Therefore, in these resins the polymer chains are not cross-linked. High molecular weight polymers are used to improve the interaction between different polymer chains. Thermoplastic resins normally soften and can be reshaped when temperature is increased. This property makes these resins ideal candidates for some industrial processes such as injection molding, compression molding or extrusion. The main applications of this resin include inks and adhesives.

Cross-Linking Resins

Cross-linking resins can be hardened to promote chemical interactions between different polymer chains. Curing, which can lead to more complex polymeric structures and thus stronger materials, will essentially depend on the active groups present in the polymers and can take place under different conditions. When reactive groups are present, acrylic resins can be cross-linked by allowing interaction between two different polymer chains. This can occur under certain conditions, such as at a specific temperature or under UV light. A catalyst can also be added to support and accelerate the chemical reaction. We can distinguish between two types of cross-linking systems: • Externally cross-linked resins that require a curing agent, i.e. a chemical that will react with the polymers, and • Self-cross-linking resins. In the first case, the R group is typically a hydroxyl-functional chain that allows reaction with melamine or isocyanate curing agents. This type of formulation (resin + curing agent) can be provided where they are mixed as: • Two-component system (2K), or • Single-component system (1K). 2K is used particularly in situations where oven heating is not possible. In 1K, isocyanate curing agents can be "blocked" or rendered inert at room temperature and resin curing only occurs in an oven (oven coatings) at a higher temperature. In addition to hydroxyl functions, carboxyl groups are normally found in the polymer chains of cross-linking resins (or as free acrylic acids): they can serve as catalysts for the curing reaction and improve coating adhesion. In addition, other curing agents such as epoxies that can react with carboxyl groups can also be used in this case. These acrylic resins can be provided in solvent phase, but if the number of carboxyl groups on the polymers is sufficiently high they can be water-soluble. In this case they are usually defined as water-thinnable. In water-based systems, an auxiliary solvent may also be present to improve resin compatibility. Finally, emulsions of thermoset acrylic resins are also available. Emulsions generally allow higher solids content at the same viscosity compared to water-thinnable versions and usually have better alkali resistance since fewer carboxyl groups are needed. Finally, acrylic resins may be available as self-cross-linking versions (rather solvent-based or water-based). In these types of resins, some R groups in the copolymer structure are blocked amide groups (alkoxymethyl acrylamides) such as N,N-bis-butoxy-methylamide. During the curing process (usually in an oven at elevated temperatures), these groups react with hydroxyl groups also present in the copolymers, leading to a cross-linked network. These types of resins generally 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 acrylic resins functionalized with hydroxyl functions (i.e. the number of OH groups present). It is usually expressed as the mass of KOH in mg equivalent to the amount of acetic acid that reacts during acetylation of 1 g of resin. The higher the hydroxyl value, the higher the reactivity (and therefore the likelihood of cross-linking).

Acid Value

Acid value is an indicator of the number of carboxyl groups in the copolymer. It is usually expressed as the amount of KOH required to neutralize 1 g of resin (see DIN 53402 or ISO 2114). The number of carboxyl groups has an effect on the resin's adhesion properties and solubility in water. The higher the acid value, the higher the number of carboxyl groups.

Minimum Film Forming Temperature for Acrylic Dispersion

Minimum Film Forming Temperature (MFT) is the minimum temperature at which acrylic latex will not result in a cracked material rather than a continuous film. • For acrylic latexes designed for architectural applications (wall paints), MFT is typically below 5°C. • For latexes designed for industrial applications where oven curing is used, MFT may be higher. Attacryl A 144; as a thermoplastic acrylic resin, is characterized by excellent pigment wetting capacity and high pigment loading. It is compatible with all pigments and fillers commonly used in the paint sector. Applications: • Road line markings, • Concrete coatings, • Stone varnish, • Paints and surface coatings, • Metal paints. Attacryl A-HF 060; a two-component thermoset resin dissolved 60% in Shellsol A, curable with polyisocyanate. A resin combined with aliphatic polyisocyanate for two-component industrial coatings with good mechanical properties, resistant to chemicals and weather conditions, for hot and cold drying. Applications: • Industrial coatings, • Automotive primers, • Metal and glass surfaces, • ABS surfaces. Attacryl A 077; a two-component resin drying in air and in the oven containing 60% xylene in combination with aliphatic polyisocyanates. Applications: • Primer, • PU systems, • Anticorrosive floor coating, • Industrial floor coating. Attacryl A-HF 097; a two-component resin drying in air and in the oven, 70% in butyl acetate in combination with aliphatic polyisocyanates. Applications: • Two-component coatings, • Automotive refinish paints and topcoats, • Topcoats for agricultural machinery, • Anticorrosive industrial paints. Extremely successful results were obtained in varnish work conducted in the laboratory with Attacryl A 077 and Attacryl A-HF 097 from the acrylic resin product range. The varnish solutions prepared were tested after density values were found to be within reference ranges (0.95 – 1.03 g/cm³). Tests performed: • Bend-Flex Test, • Impact Test, • Adhesion Test, • Gloss Test. All results obtained in these tests came within the desired reference value range. Kader Maraşlı Sales Manager Günkem Aytaç Ayhan Sales Manager Günkem