Theoretical Guidance and Calculation Methods for Volume Solids and Spreading Rate in Solvent-Based and Water-Based Paints

1. Theoretical Information

Unlike many materials used in daily life and industry, paints undergo changes following application; • Shape/appearance, • Structure, • Dimensions, and transform into a dry film or coating on the surface to which they are applied. This transformation process is defined as "Film Formation" and depending on the paint type includes: • Physical drying (volatiles leaving the film), • Chemical drying (film formers curing through a chemical reaction), one or both of these processes. To better understand the importance and effect of solids content by volume during this transformation, the following summary information on solvent and water-based paints will be useful. Volume solids content (VSC) is the ratio of the total non-volatile portions of wet paints to total volume. Solvent and water-based paints are fundamentally created as a result of mixing the following inputs through appropriate processes: 1. Resins (film formers), 2. Pigments and fillers (provide color, hiding power and economy in raw material cost), 3. Additives (anti-settling agents, rheology agents, spreading, matting and surface wetting agents etc.), 4. Volatiles (solvents and/or water). After the paint is applied by any application method, the volatiles used in the formulation, together with volatiles carried by the resin and additives, begin to leave the wet film depending on their boiling points, evaporation rates and solubility. During this physical drying process, the volume solids content ratio of the film thickness increases (Figure 1). During the transition from wet film to dry film, volumetric shrinkage occurs in the paint film and this shrinkage continues until all volatiles leave the film (Figure 2). Figure 1. % VSC increase over time during the transition from wet film to dry film in the film formation process in the paint film Figure 2. Volume shrinkage in the film during film formation process A: Wet paint state at application viscosity at zero time, h1: Wet film thickness resulting immediately after application, B: Paint film state at any point during physical drying process, h2: Wet film thickness at any point during physical drying process, C: Paint film state when physical drying is complete, h3: Dry paint film thickness when physical drying is complete, D: In chemically drying paints (reactions where by-products such as condensation, polyurethane etc. are formed), the completion period of the chemical reaction, h4: Dry film thickness after the curing reaction is complete in chemically drying paints, since the difference (h4-h3) is generally negligibly small, it is assumed equal in theoretical VSC calculations. We will also assume it equal in our calculation methods here and refer to it as h3. The smaller the value of (h3-h1): • The higher our paint's VSC value will be, • The lower the paint and application costs will be, • The lower the negative effects on the environment and human health will be. Paints are classified as follows according to their VSC ratios:

2. Volume Solids Content Calculation Methods

Paint volume solids content can be calculated using the following methods: 2.1. Theoretical VSC % = (Sum of individual VSC of inputs / Paint volume) * 100 This method can be used by paint manufacturers since it requires knowledge of the paint formulation and physical properties of the inputs. 2.2. Experimental VSC % = (h3 / h1) * 100 Paint at application viscosity is applied with the aid of an applicator to a panel at a known wet paint thickness (h1). It is dried/cured under conditions conforming to specifications. After curing, dry film thickness is measured from at least 5 points in different areas of the panel, and the average is taken (h3). 2.3. ISO 3233-1:2013: Based on the principle of measuring dry film density of a painted test panel according to Archimedes' principle.

2.4. Calculation method;

VSC % = {[(1000/db) – 1000 (1 - xk) / ds] / (1000 / db)} * 100 db= Paint density at 20°C, g/cm³; must be measured in the laboratory or requested from the paint manufacturer, ds= Average density of solvents in paint and thinner at 20°C, g/cm³; must be requested from the paint manufacturer, xk= Weight solids fraction of the paint (weight % solids / 100); must be measured in the laboratory or requested from the paint manufacturer. Especially for users, when selecting paints where the visual, functional, physical and chemical performance of paints meets expectations, the most important criterion is the high ratio of volume solids content and therefore the ability to calculate and compare how much area can be painted with 1 kg or 1 Lt of paint. Especially for users, when selecting paints where the visual, functional, physical and chemical performance of paints meets expectations, the most important criterion is the high ratio of volume solids content and therefore the ability to calculate and compare how much area can be painted with 1 kg or 1 Lt of paint. Another important point to consider when comparing multiple paints using volume solids content calculation is the necessity of thinning both paints at the same ratio with thinner to bring them to application viscosity. If there is a significant difference between the thinning ratios of competing paints (> ± 3%), accounting for the thinners, volume solids content and consequently paintable areas of thinned paints at equal viscosity should be compared. The effect of thinning ratio difference on final cost should be calculated separately. Paintable area with 1 kg of paint, A = [(1000 / db) - 1000 (1-xk) / ds] / h m² h = Average dry film thickness to be applied, microns

3. Conclusions

3.1. The volume solids content of a paint is equal to the dry film volume obtained after application. 3.2. As the thinning ratio of a paint increases, the volume solids content ratio decreases. This means: • Higher material cost, • Higher application cost, • Greater negative impact on human health, the environment and workplace safety. 3.3. The basic inputs determining the VSC ratios of paints are the resins used in the paint formulation and the solubilizing power of the selected solvents, and as the molecular weight of resins increases, their viscosities increase and VSC decreases. Paints produced with resins that contain less solvent and can be thinned to application viscosity with less solvent will have higher VSC, so resin manufacturers continue to intensively pursue R&D projects to develop lower molecular weight and higher solids resins without reducing physical and chemical resistance, and increasingly stringent regulations especially targeting emission values further enhance the importance of these efforts. Muhammet Demirkıran / Sales Director, Paints, Inks and Adhesives Group / Kempro Kimyasal Mad. ve Dış Tic. A.Ş.

4. References 1. BASF Handbook on Basics of Coating Technology; by Prof.Dr.A.Goldschmidtand Dr.H.-J.Streitberger,2003 2. Organic Coatings: Scienceand Technology; by Zeno W. Wicks,2007 3. European Coatings Handbook; by Thomas Brock, Michael Groteklaes, Peter Mischke,2000 4. Surface Coatings: Raw materials and their usage; Surface Coatings Association Australia, Oil and Color Chemist's Association,1993