Water-Based Building Topcoat Paints and Expectations

Water-Based Architectural Topcoats and Expectations Paints Mixtures with protective and decorative properties are generally known as paints (1). Although the protective properties of paint are not usually emphasized, actual competition takes place on the basis of this characteristic. As protective functions; mechanical properties (abrasion resistance), resistance to chemicals, water/moisture and UV resistance, and cleanability of the painted surface are the first characteristics that come to mind. The decorative function of paint highlights coverage and 'color'.

When paints are examined from a sectoral perspective, generally:

• Architectural Paints, • Automotive Paints, • Industrial Paints, • Paints Used in Other Fields can be classified, although they can be further divided into the sub-applications shown in Figure 1 (2). [caption id="" align="alignnone"] paint chart[/caption] Figure 1. Major application areas of paints by sector in Turkey

Although the surface to which the paint is to be applied and the types of paint vary on a unit formula basis, the general components found in a paint formulation (1):

Binder (Latex) Solvent (Water/Organic) Pigment/Extender/Filler Additives: Wetting and Dispersing Agent (Surfactant), Thickener, Defoamer, Biocide, Buffer, Neutralizing Agent, Anti-settling Agents, UV Protectant, Optical Brightener, Drier, Matting Agent, Anti-skinning Agent, etc.

Binder (Latex)

Emulsion polymers (latex) are considered ideal dispersed systems, in other words systems in which particles are completely separated. However, if a good emulsion is not formed, aggregation or agglomeration can occur. Water-based emulsion polymers can be divided into three groups: poly(acrylic), poly(urethane), and poly(epoxide), and within the context of compatibility with other raw materials, they generally have an effect on the paint's abrasion resistance, UV resistance, and alkali resistance. Acrylic paints dry quickly due to their structure. Colors can be mixed with each other and can be diluted with water if necessary. Poly(urethane) paints have fast-drying properties, are two-component, and have a semi-matte appearance. They are characterized by high UV, mechanical and chemical resistance, elasticity, and wet-on-wet application properties. Poly(epoxides) are known for their chemical and physical resistance, long storage time, and resistance to degradation even in polar solvents. Water-based poly(epoxides) are most notably characterized by fast drying, high humidity/moisture resistance, and ease of application to the substrate surface. Emulsion manufacturers stabilize their products in two ways:

a) Stabilization with Emulsifier (Surfactant) Only

In this case, very high abrasion resistance is provided, however, preference rates are low due to pH sensitivity in paint production and the requirement to use mill base. The desired resistance to shear stress also demonstrates that this stabilization technique remains open for further development.

b) Use of Protective Colloids as Stabilizing Agents

In this case, the disadvantages mentioned in the other method can be easily eliminated, however, high water absorption restricts the use of such colloids. The point that needs to be optimized here is the conversion of stabilizing solutions with colloidal structure into polymers with finer particle structure through different techniques. Furthermore, it could be a beneficial approach for R&D departments to cooperate with universities. Recent studies on high-segment emulsions made with pure acrylic monomers have shown that paint performance has been brought to very high levels. Studies in this area are promising in that higher-performance products can be achieved without complicating process conditions and without requiring additional infrastructure investments. Recent studies on paints show that polymers (emulsions) with low molecular weight and linear chain structure provide paint with much higher abrasion resistance (3). When specifically considered, in styrene-acrylic emulsions, linear chain is not as important as in vinyl acetate-based ones, but it retains the property of being a critical parameter on the paint's abrasion resistance. Regarding UV and alkali resistance of the final paint, vinyl acrylic emulsions compete with styrene acrylics. While vinyl acrylics excel in UV resistance, their low alkali resistance places them in second place compared to styrene acrylics.

Solvent

They form the volatile portion of the paint and are used to provide the final paint with desired application and appearance properties without changing the paint's characteristics. Solvents are also chemicals known as coalescent agents used to reduce the film formation temperature of paint. Their use is decreasing day by day because they increase the volatile organic compound (VOC) content of the paint and some national/international regulations (REACH, etc.) impose serious restrictions. In water-based paints, a mixture of several solvents that are generally miscible with water can also be used. Solvents can be divided into three main groups: a) Hydrophobic in nature: They act by swelling the latex particle. Their capacity to reduce minimum film formation temperature (MFFT) is weak. White spirit is among the most commonly used in this group. b) Hydrophobic/Hydrophilic in nature: Their capacity to reduce MFFT is high. Diesters, ester alcohols, etc. fall into this solvent group. c) Hydrophilic in nature: Their capacity to reduce MFFT is lower than hydrophobic ones. Monoethylene glycol (MEG) can be given as an example.

Pigment/Extender/Filler

Color (tone) and gloss (sheen) are the two most important properties that pigment adds to paint. In addition, coverage, resistance to weather conditions, and effects on mechanical properties should not be overlooked. Materials defined as extenders have similar functions to pigments. The distinction between the two is determined by refractive index. Those with a refractive index greater than 1.7 are called pigments, those with lower values are called extenders. Extenders are additionally important in that they provide paint with specific gravity and solids content. The properties of certain main extenders can be summarized as follows: Talc: Has strong adhesion and hydrophobic structure. Should be preferred in matte paints. Whiteness index is low. Kaolin: Provides the opportunity to obtain a smooth surface, however, has a low pH value.

Other Additives Wetting and Dispersing Agent (Surfactant)

Dispersants and/or surfactants directly affect the shelf life, pigment binding strength, and gloss of paint. Products dominating the market are ammonium and sodium salts of water-soluble polyelectrolytes. Although these synthetic polymers were initially synthesized only starting from methacrylic acid, products with copolymeric structure are also seen today. Polyphosphates also remain among the commonly used and effective dispersants in the market. If dispersants are chosen incorrectly/optimal quantities are not used, attachment to these auxiliary materials and web/network formation can occur. Otherwise, phase separation (formation of aggregates or agglomerates) is inevitable. Aggregate can be defined as planar and face-to-face contact of particles, while agglomerate is defined as contact of particles from corners and edges. As a result, the emulsifier moves toward the additive, pigment, and latex, and coagulation occurs. This is the clearest indication that paint quality is poor.

Thickener

Thickeners are as important a component of paint as latex (emulsion). In general, cellulosic ethers, particularly hydroxyethyl cellulose (HEC), retain the characteristic of being the most commonly used chemical for this purpose.

Acrylic Thickeners

These are emulsions with swelling properties in an alkaline environment (ASE). It is possible to modify these products hydrophobically with ethylene oxide and polyurethane. Recent studies again show that progress in this area is considerable (3). It is beneficial to include polyurethane and increasingly common inorganic thickeners such as hectorite/bentonite in this category as well.

Defoamer

Regarding defoamers used to prevent foam formation tendencies that emerge during the latex production phase, the most important points that can be written are the selection of the correct defoamer type and the determination of the optimal quantity. These critical values vary on a paint type basis and are aspects that should be carefully considered in terms of final paint quality.

Biocide

Studies on biocides have accelerated in recent years. Regulations and legal restrictions in recent years have triggered these studies.

Buffer and Neutralizing Agents

Their mechanisms of action are through emulsion, dispersing agent, and thickeners other than polyurethane (PUR). While amines are used for neutralization, caustic and potassium hydroxide are also used. For the required effectiveness to be achieved, the pH value must be greater than 8. Other Additives

Additives can be described as chemicals that have a direct effect on the rheological properties and ease of application of paint. These additives and auxiliary materials are very important for the quality of the final paint and must be selected carefully.

References 1. D. Stoye, W. Freitag, Editors, "Paints, coatings and solvents", 2. Completely Rev. Ed., Wiley-VCH, Weinheim, 1998. 2. "Recent Trends in the Paint and Raw Materials Sector in the World and Turkey", Paint Manufacturers Association Bosad Report, 2015, http://www.bosad.org.tr/images/pdf/2015-Bosad-sunum-TR.pdf 3. C. Elgin, A. Saraç, Unpublished Study, 2016.

  Prof. Dr. Ayfer Saraç / Chemical Engineer / Yıldız Technical University Cem Elgin / B.E.S. Chemistry Rubber / Chemistry Department / Yıldız Technical University