2/6/2019 Acrylic resin fundamentals: Coating functions and benefits Acrylic Resin Fundamentals Posted on April 22, 2016 by Ron Lewarchik Coatings utilizing acrylic resins are the leading polymer technology in the coatings industry. Historically alkyd finishes have held the leading position in coatings for decades. Acrylics are utilized in architectural coatings, product finishes for original equipment manufacture including automotive (OEM) and refinish, as well as special-purpose coatings. Acrylic resins are primarily based on acrylate and methacrylate monomers and provide good weather resistance, resistance to hydrolysis, gloss and color retention in exterior applications. Due to their versatility and performance, acrylic coatings account for over 25% of all coatings and global sales approaching $25 billion. Acrylic resins can be thermoplastic or thermosett and are used in organic solvent born, waterborne, powder and radiation-curable coatings Three broad classes of liquid coatings utilizing acrylic resins include thermoplastic, thermoset and waterborne. Many acrylic resins may also include other vinyl monomers such as styrene or vinyl acetate primarily to reduce cost. Acrylic monomers have a lower Tg than their analogous methacrylate monomers (for example compare the Tg for n-butyl acrylate versus n-butyl methacrylate see Table I and Table II). As Table II suggests, the glass transition temperature of the monomers selected for synthesis of a resin can be selected to enhance multiple properties that may include Table I – Tg of Nonfunctional Homopolymers weather resistance, moisture resistance, oxygen permeability, flexibility reactivity, cure and hardness. In addition, acrylics can be functionalized with a variety of monomers to provide improved adhesion to metal, or to react for example with aminoplast or isocyanate crosslinkers. Thermoplastic acrylic polymers (TPA) in general have excellent properties including exterior durability. Such resins were widely used in automotive OEM and Refinish topcoats from the 50’s to the 70’s, but their use has dramatically declined due to the high molecular weight necessary to provide properties, they require a high amount of organic solvent to enable air atomized spray application. Accordingly https://knowledge.ulprospector.com/4320/pc-acrylic-resin-fundamentals/?utm_source=strongmail&utm_medium=email&utm_campaign=New+Trend+T… 1/4 2/6/2019 Acrylic resin fundamentals: Coating functions and benefits these paints apply at about 20% weight solids. Thermoplastic resins typically use a high level of methyl methacrylate in their polymer backbone to provide excellent hardness and exterior durability. Table II Relationship of Tg to Physical Properties Figure I – Structure of poly MMA and poly MA Thermosetting acrylic resins (TSA) are designed with functional monomers to either react with themselves when exposed to heat or moisture, or with that of a cross-linker to form a cross-linked film. Thermoset resins as a group are lower molecular weight and thus have higher application solids. Once cross-linked, as a class they offer films with excellent resistance to organic solvents, moisture and UV light and do not soften appreciably when exposed to moderately high temperatures as thermoplastics do. An example of acrylic monomers with functional groups that can be used to functionalize acrylic polymers to provide properties such as crosslinking, self-crosslinking, improved adhesion or pigment wetting are provided in Table III. Being able to functionalize an acrylic resin with a wide range of reactive moieties provides the ability to tailor the performance of the resin backbone to provide improved adhesion over a variety of substrates, improved pigment wetting and/or the ability to provide crosslinking or selfcrosslinking. Other acrylic monomers are also available to impart sulfonic acid, or phosphoric acid functionality to the acrylic resin. Table III – Functional Acrylic Monomers https://knowledge.ulprospector.com/4320/pc-acrylic-resin-fundamentals/?utm_source=strongmail&utm_medium=email&utm_campaign=New+Trend+T… 2/4 2/6/2019 Acrylic resin fundamentals: Coating functions and benefits Being able to functionalize an acrylic resin with a wide range of reactive moieties provides the ability to tailor the performance of the resin backbone to provide improved adhesion over a variety of substrates, improved pigment wetting and/or the ability to provide crosslinking or self-crosslinking. Other acrylic monomers are also available to impart sulfonic acid, or phosphoric acid functionality to the acrylic resin. Looking for acrylic resins for your coatings formulations? Prospector has over a thousand listings for acrylic resin materials. View product data sheets, request samples and more now… Search Acrylic Resins Carbamate functional acrylics can also be made for example by reacting an isocyanate functional acrylic with hydroxypropyl carbamate. Many of the acrylics in the category of functionalized acrylic resins are used in automotive OEM and refinish clearcoats to provide an excellent combination of mar resistance, chemical resistance and light stability. Acrylic polymers are also used extensively to make water reducible and emulsion resins. Water reducible acrylic resins typically have acid numbers of 40 to 60. An example of a water reducible TSA would have a resin composition comprised of MMA/STY/BA/HEMA/AA in a weight ratio of 40/20/22/10/ 8 prepared by free radical polymerization in a water reducible solvent such as a glycol ether solvent like 2butoxy ethanol with butyl alcohol. To begin the process of making paint, a suitable amine is used to neutralize the acrylic acid in the resin backbone to provide an acid salt. The amine is used at less than the theoretical level of neutralization using for example 2-(dimethyl amino) ethanol (DMEA) or 2-Amino2-methyl-1-propanol (AMP). The next step in the paint making process involves the addition of water. Please refer to a previous Prospector article concerning waterborne resins: https://knowledge.ulprospector.com/3069/pc-fundamentals-waterborne-resin-technology/ as well as additional information on viscosity versus reduction characteristics of waterborne resins: https://knowledge.ulprospector.com/639/flow-leveling-viscosity-control-water-born-coatings/. Acrylic emulsion polymerization is carried out in water with monomers, a water soluble initiator and surfactants. Many of the same monomers are used in emulsion polymerization as that in solution polymerization, however the properties of the latex can be greatly affected by changes in the: polymerization conditions, monomer structure and solubility, monomer concentration, surfactant type and level, temperature, initiator type and initiator concentration are all variables that can effect the emulsion particle size, structure and molecular weight of the final polymer. A detailed examination of latex https://knowledge.ulprospector.com/4320/pc-acrylic-resin-fundamentals/?utm_source=strongmail&utm_medium=email&utm_campaign=New+Trend+T… 3/4 2/6/2019 Acrylic resin fundamentals: Coating functions and benefits polymerization is a significantly large subject and is thus out of scope for this article. Acrylic polymers are also used in powder coatings along with acrylate functional acrylic resins for radiation cure coatings. The fundamental influence of monomer Tg, molecular weight and functional monomers remain the same for all the applications described herein. In summary it is the goal of this article to provide a heightened understanding of acrylic resin technology and its ramifications on paint performance characteristics and mechanical properties. The views, opinions and technical analyses presented here are those of the author or advertiser, and are not necessarily those of UL’s Prospector.com or UL LLC. All content is subject to copyright and may not be reproduced without prior authorization from UL or the advertiser. While the editors of this site may verify the accuracy of its content from time to time, we assume no responsibility for errors made by the author, editorial staff or any other contributor. Filed Under: Paint & Coatings About Ron Lewarchik Ronald J. Lewarchik, President and CEO of Chemical Dynamics, LLC, brings 40 years of paint and coatings industry expertise to his role as a contributing author with the Prospector Knowledge Center. As a contributing writer, Ron pens articles on topics relevant to formulators in the coatings industry. He also serves as a consultant for the Prospector materials search engine, advising on issues related to optimization and organization materials within the database. 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