Acrylic Resin Fundamentals

Acrylic Resin Fundamentals, UL Prospector, Ronald Lewarchik, 4/2016:

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

Table I – Tg of Nonfunctional Homopolymers
Table I – Tg of Nonfunctional Homopolymers

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 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.

acrylics_table_2
Table II Relationship of Tg to Physical Properties

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 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.

Figure I – Structure of poly MMA and poly MA
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.

Table III – Functional Acrylic Monomers
Table III – Functional Acrylic Monomers

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.

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.

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.

To read the rest of Ron’s article, click here to head over to UL Prospector.

Certified Green Claims Increase Value & Brand Recognition in Coatings

Article written by Chemical Dynamics President, Ronald Lewarchik, originally published in UL Prospector.

Whether coatings are sold directly to consumers or business to business, UL’s study: Under the Lens: Claiming Green – The influence of green product claims on purchase intent and brand perception reveals that legitimate third-party, certified green claims contribute to the attractiveness of a product and command a higher price because of enhanced brand perception. The survey results are noteworthy, as 70% of Americans say they’re searching for greener products, and 67% of business decision makers indicate sustainability is an important factor when making decisions for their organizations.

Avoiding Misleading Claims

However, many manufacturers misrepresent their products by claiming they are green for the purposes of enhancing sales. In 2012, the Federal Trade Commission revised its Green Guides, the agency’s core set of guidelines to help marketers avoid making misleading environmental claims. The Guides are now more specific and prescriptive, making it easier for the FTC to prosecute “greenwashers.” Accordingly, if a green claim is considered to be deceptive in the eyes of the FTC, there is both a financial and a legal risk.

Read the full article here.

Flow, Leveling & Viscosity Control in Waterborne Coatings

Ron Lewarchik is a contributing author to UL Prospector and publishes articles monthly. Please read on for his expert findings on “Flow, Leveling & Viscosity Control in Waterborne Coatings”:

Flow, leveling and viscosity stability can be very challenging and problematic in waterborne ambient cure and baked finishes. These issues can affect not only package stability, but also have a profound effect on appearance during and after application. As the vast majority of waterborne coatings are anionic in nature (amine (EU) neutralized), this article will focus on amine neutralized resin types, although if resin polarity, for example from acid functionality, is high enough, anionic resin types can be dispersible or even water soluble without the use of neutralizing amine.

There are two major categories of waterborne paint technologies: water reducible (EU) and latex (EU). For the purpose of this article, water reducible resins are normally made in solvent and then reduced with water to form a resin dispersion in water. Latex resins are made by emulsion polymerization in water. The paints using emulsion resins most often utilize a small amount of organic cosolvent to improve coalescence of the latex particles, as well as substrate wetting.

Other types of waterborne paints utilize a growing number of resin types that include PUD (polyurethane dispersions (EU)) as well as microemulsions. Accordingly, multiple issues can influence the flow, leveling, and appearance of waterborne coatings. This article will primarily examine the impact of 1) resin type, 2) humidity and temperature variation, 3) wetting and 4) flow control. Appearance of the coating during and after application can be affected greatly by these issues.

Click here to read on for the full article at UL Prospector