Why Is pH Important in Paint Formulation?

Here’s why pH is important in paint formulations:

• Binder and Resin Stability: Adjusting the pH is important to achieve the desired paint consistency. Highly basic and acidic pH affects the paint density and the strength of binders to stick together. Acrylic, alkyd, epoxy, and vinyl resins work at 7 to 9 pH. Too high pH (>10) and too low pH (<4) cause orange peel and poor adhesion. 
• Pigment Dispersion: Paint pH has a direct relation with pigment dispersion. Too High and too low pH increases the paint surface tension and attracts the pigment particles inward. They don’t spread easily and leave a poor finish behind. Iron oxide, ultramarine blue, and phthalocyanine green pigments preserve their original color only in alkaline environments. They fade or change their color in unfavorable pH conditions.
• Corrosion Control: Paint pH changes the corrosion-resistant abilities of paint. Acidic paints (<4 pH) contribute to electrochemical reactions, which increase the metal corrosion and rusting. Likewise, too high paint pH causes the water to react with paint, which corrodes the metal surface. Maintain the optimum temperature (neutral or >7) to maintain the anticorrosive properties of paint.
• Drying Time: Acidic pH changes the viscosity of paint to runny and thin. It does not stick well to the substrate, which slows down the drying time. Highly alkaline pH of paint speeds up the curing process and takes less time to dry as they are thick. 
• Mildew and Microbial Resistance: Acidic conditions work well for killing bacteria but not for fungus (mildew). Paint with a low pH <5 increases the mildew growth. Use water-based paints (latex, epoxy) or oil-based paints with a pH range of above 7 to protect against mildew. 

How is Paint pH Measured?

Here is how to measure the pH of paint:

• Benchtop pH Meter: A pH meter consists of an electrode, a digital display system, and a stand. A storage tube with potassium chloride (KCl) solution is attached with an electrode to keep it moisturized. Remove this first to calibrate the pH meter with buffer solutions of pH 4, 7, and 10. It is done to check the impact of environmental conditions on the readings. After calibration, rinse the electrode and dip it into the paint sample. Make sure it does not touch the ground or sides of the sample container for accurate readings. Let the readings stabilize and then note them down from the digital panel. 
• pH Test Strips: It is the most common and least precise method to measure the pH of liquids. Dip the test strip (litmus paper) into a sample beaker and keep it submerged for recommended time. Remove the strips and compare the changed color with the reference pH color chart. 
• Slurry Testing: Slurry testing method requires a pH meter and a sample to measure the pH. Mix the paint with water in equal ratios to create a slurry (pigment paste with distilled water). Allow the solid paint particles to settle down and stain the slurry in another beaker. Dip the digital pH meter in the sample slurry to get accurate pH values. 

How Does pH Control Influence Specific Paint Applications?

Here is how pH control affects the specific paint applications:

• Anti-Corrosive Coatings: Low pH paint contains a high concentration of hydrogen ions, which increase the oxidation process and damage the protective metal layers. It damages the anti-corrosive coatings on steel beams, iron railings, and metal bridges.
• Masonry Paints: Masonry paints have a highly alkaline pH of more than 11. It is important to neutralize the cement, bricks, and plaster walls to avoid bubble formation and frequent repainting. Adjust the pH with neutral additives or alkali-resistant primers.
• Wood Coatings: Using highly acidic or basic nature paints causes grain rising in wooden doors, furniture, and wooden wall panels. Wood is highly acidic from inside, so apply the paint with a balanced pH (7 to 9) for smooth results.
• Acrylic Paints: Maintain the pH of acrylic paints for pigment longevity on canvas, plastic surfaces, and interior walls. Low or high potential of hydrogen fades away natural colors quickly.