Polyacrylic Resins

In this article, we will address the subject of polyacrylates, or polyacrylic resins. We can discuss some of the differences of polyacrylates from other resins before moving on to their history. Acrylic resin (but not the acrylic emulsion that forms the basis of acrylic paint) is a thermoplastic, meaning it is one of a group of plastics that can be repeatedly heated and manipulated, whereas polyester resin and epoxy are thermosetting plastics that use heat or a catalyst to solidify into a solid mass that does not melt. Acrylic is mixed from acrylic polymer, a dry powder, a methyl methacrylate monomer, a thin liquid, and usually a type of organic peroxide hardener. For any sized piece, an autoclave or hydraulic press is required to reduce air bubbles and counteract the internal stresses created by the strong exothermic reaction. The powder, monomer and vapors are toxic. Organic peroxides are particularly toxic, some are explosive, and some cause instant blindness if they enter the eye. Acrylic resin has gained popularity in the solid surface manufacturing industry. It has many advantages, such as being more durable than polyester because it can be heated, bent and cooled without any physical impact. Additionally, acrylic resin can withstand heavier use. When made with acrylic cast resin materials, the seams of the product are much more robust than those of products made with the polyester equivalent. However, acrylic cast material exhibits less visual depth than polyester and is more expensive. Nevertheless, its advantages add more value for your money. When you look at real-world applications, acrylic resins provide better adhesion than other products found on the market. Water-based acrylic polymers are the smartest choice for superior product results. Acrylic resins are used everywhere: brake lights, car tires, dentures, phone screens, art and sculptures, and even themes and decorations.

History

Caspay and Tollens obtained alkyl esters of acrylic acid in 1873. While working on methyl ester of methacrylic acid, Otto Röhm received a German patent in 1915 for the use of the solution of acrylic acid ester in acetone as a varnish and binder instead of drying oils in paint, and for impregnation purposes in wood and similar materials. The function that Otto Röhm envisioned for acrylic acid at that time still sheds light on today's technology. Products obtained through polymerization of alkyl esters of acrylic and methacrylic acids are named differently. Even if we call it acrylic resin or acrylic resin, when phenol, melamine and ketone resins are considered, it seems more correct to call the polymers of acrylic and methacrylic acid, which are polymerization products, polyacrylic or polyacrylate due to their high molecular structures. This group also includes polymers of esters, nitriles and amides of acrylic and methacrylic acid. Polyacrylates used as resins in the paint industry have a much lower molecular length than polyacrylate-plastics used in the plastics industry. For this reason, although poly and resin suggest high molecular structure, it would be more correct to call those used in paints "polyacrylate resins" and those used in the plastics sector "polyacrylates." While the molecular weight of polyacrylic resins used in paints reaches 200,000, plastic-polyacrylates are 1,000,000 and above. Since we will examine the subject from the perspective of paint technology, we can continue by dividing polyacrylic resins into 2 main groups. • Thermoplastic, physically drying polyacrylic resins that do not contain functional groups and therefore cannot perform cross-linking. • Thermosetting polyacrylic resins that contain functional groups (-COOH, -CONH2, -CONH, -CH2OH, -CONHCH2OR, etc.) and can perform cross-linking. Now we can elaborate somewhat more on the two main groups.

Thermoplastic Polyacrylate Resins

They are used as paint binders. The small amounts of acrylic and/or methacrylic acid in their composition create the appropriate polarity that provides excellent adhesion to the substrate (especially to metals) and at the same time increase the wetting properties of pigments. They form a film on the applied surface as these solvents evaporate when applied as a solution with their solvents. Thermoplastic acrylic resins are superior to other binders in what we call mechanical properties, hardness and solubility. They have the best light fastness. This property applies within the thermosetting group. It should not be forgotten that styrene addition will reduce light fastness. Another property is excellent chemical resistance. When applying to metal surfaces, acid content should be increased. Their resistance to alkalis is high, but we cannot say the same for organic acids. Pigment wetting and dispersion properties of thermoplastics can be called mid-range. For this reason, wetting can be improved by the addition of a small amount of plasticizer or another resin. In general, they are incompatible with alkyds. Thermoplastic polymethacrylates, especially poly-n-butyl methacrylates, are used in the food industry packaging sector (heat-seal), in lacquers and inks. They are increasingly used in printing inks, adhesives, auto refinish paints, industrial and marine paints, and extensively in the construction sector. They provide excellent compatibility with plaster and concrete.

Thermosetting Polyacrylate Resins

Thermosetting polyacrylate resins form a network structure and harden through increasing temperature and polycondensation reaction compared to physically drying thermoplastics. This network structure provides the system with excellent film hardness and very good atmospheric and chemical resistance. Thermosets exhibit much better adhesion than thermoplastics. In these types of resins, the network structure is formed either between the resin's own molecules or between the resin's molecules and the molecules of the reaction partner. The most ideal for this is the use of melamine formaldehyde resins. By attaching the functional groups I will name below to the polyacrylate molecule, we can obtain polyacrylate resins with different functions.

Epoxy-amine-amide-anhydride-hydroxyl-methylol isocyanate

Thermosetting polyacrylic resins are used in automobile topcoat paints and are also extensively used in white goods coating due to their excellent chemical resistance and high pigment binding properties. Their reaction partners are usually melamine. If we also add epoxy resin to this, adhesion and chemical resistance increase further. After defining our resins, I would also like to mention network structure formation with polyisocyanates. Acrylic resins containing hydroxyl groups harden through chemical reaction (polyadduction) with an appropriate isocyanate at room temperature, resulting in excellent paint films. These films, also called polyacrylurethanes, have very high alkali and detergent resistance. The hardening reaction caused by polyadduction achieves dust-free touch in a few minutes and hand-hard set in a few hours. However, the final hardening where mechanical and chemical resistance are excellent can take several days. In contrast, at 110-130 degrees, final hardness can be achieved in 20-30 minutes. Cross-linking can be accelerated with a catalyst. Polyacrylurethanes show extraordinary corrosion resistance in salt spray testing and are highly resistant to gasoline and hydraulic oils. They are most commonly used in auto refinish paints and special metallic paints. In summary, we can say this. Polyacrylic paints that have formed a network structure with isocyanate exhibit performance equivalent to stoving paints despite being air-drying.    

Nigar Cangönül

Technical Sales Manager

Günkem