Solvents & Thinners for Paints & Coatings

“Solvent is a material whose molecules are capable of forming an intimate mixture with molecules of other material(s) and is present in higher percentage in the mixture”, and this mixture is known as solution, the other material is known as solute.

Such an intimate mixture depends upon

  • chemical character
  • size
  • shape
  • molecules

We can have solution of gases, liquids, and solids.

  • Gases: oxygen+ nitrogen + carbon dioxide = air
  • Liquids: sulfuric acid + water = acid solution
  • Solid: copper + tin = bronze
Pigments
Resins
Extenders
Solvents
Additives

Introduction

There is a saying “like dissolves like”.

Water + alcohol=solution but water + kerosene = separate   due to Role of Chemical character, size, and shape of molecules in solubility

  • Mutual attraction among molecules of polar and non-polar are large enough to prevent mixing of one in other.
  • In Water, Glucose, Carboxy methyl cellulose (CMC) and Cellulose
    • Glucose is small molecule and polar so soluble in water.
    • Cellulose is large and is made up of glucose anhydride is insoluble.
    • Cellulose is made more polar as in CMC become soluble though large.

Solvent introduction- please watch the video from start to 24 min.

Let us see the effect of shape, polarity, and size.

Solubility of alcohol in water (gm/100ml water) Methyl and ethyl alcohols are highly soluble in water but butyl and amyl alcohols are les soluble. Solubility decreases with increase in non-polar chain but increases with change in shape.

Similarly, a non-polar system as

  • Mineral spirits, mineral oil, Paraffin wax, Polyethylene

Here, small molecules of mineral oil are soluble in mineral spirit and paraffin wax is poorly soluble (large size of molecule) and polyethylene is insoluble (very large molecule)

But replace hydrogen (alternate) in polyethylene with OH it becomes polyvinyl alcohol which is highly polar and is soluble even in water.

In coating industry, the resins/binder are large to very large, non-polar to polar but the solubility in solvent is basic requirement. Accordingly, solvents are chosen. Solvents are generally small molecules compare to resin/binder.

Function of solvent

  • Reduce viscosity of resin –ease processing of resin and good wetting of pigments
  • Ease of application

Improve flow, level, gloss, and substrate wetting

Function of solvent- please watch the video from 24min to 32min.

Solvent characteristics

  • SOLVENT POWER
  • BOILING POINT
  • RATE OF EVAPORATION
  • FLASH POINT
  • FLAMMABILITY
  • CHEMICAL STABILITY
  • COLOUR
  • ODOUR
  • TOXICITY
  • CORROSION RESISTANCE
  • WT./LITER
  • COST PER Kg

Solvent characteristics P1- watch the video from 32min to the end.

Solvent characteristics P2- watch the video from start to 24min.

Types of volatile solvent

Solvents for coating industries may be classified as

  • Terpene solvents
  • Hydrocarbon solvents:
    • Aliphatic
    • Naphthenic
    • aromatic
  • Oxygenated solvents
    • Alcohols
    • Esters
    • Ketones
    • ether-alcohols
  • Chlorinated compounds
  • Nitroparaffins
  • Furans

Solvent classifications- please watch the video from 25min to the end.