What is the role of the resin in paint?
The resin is typically the bulk component of paint and is responsible for binding / holding all the ingredients together. The resin functions by forming a continuous film that gives protection to the substrate and to the components within the film. The resin in paint also imparts key properties such as adhesion to the substrate, gloss, durability, flexibility and toughness. There are various synthetic and natural resin systems, the typical types include alkyds, polyesters, silicates, epoxies, polyurethane, oils, melamine resin, etc. and depending upon the substrate and end application, one or more basic resin or polymer systems can be used.
What are the main constituents of a paint?
A typical paint comprises of 4 main categories of ingredients:
a) Pigment – to give hiding and colour
b) Resin or binder – to bind pigment together and promote adhesion to substrate
c) Solvent – to modify viscosity, drying in certain systems and also render ease of application.
d) Additives - made up of numerous ingredients such as driers, rheology additives, flow agents , waxes, etc. , that are added in small quantities to modify & optimise the performance of the coating
Why does my paint exhibit cracking after application?
Cracking normal occurs when the top coat of paint is unable to expand to the same degree as the previous coating. This occurs commonly when an undercoat has not been given sufficient time to dry, or indeed if a paint is encouraged to dry too quickly, for example by increasing the temperature in a room or if decorating exterior surfaces in excessive heat.
Why does my paint form bubbles on the surface after drying and what can I do to rectify this?
Bubbles formed on the surface of a coating is refered to as Blistering. This can be due to either/ or too much paint being applied in one go, moisture trapped in the underlying plaster, using non-heat-resistant paints near sources of extreme heat. To rectify, the blistered paint must be removed, and the surface made clean and dry prior to repainting with an appropriate paint, either one that is permeable (where damp) or heat-resistant if required.
What is the difference between non-convertible and convertible coatings?
A non-convertible coating when applied and during the drying process, be it air dry or stoving, no chemical reaction takes place, and there is no change in the resin characteristics and performance. A convertible coating after applied and during the drying process, be it air dry or stoving, there is a chemical reaction such crosslinking and is not reversible.
Why is there a thick rubbery like layer on the surface of my alkyd based air drying finish paint when I open a container after storage?
This rubbery like layer is usually referred to as skin. This forms by an oxygen catalyzed alkyd cross linking reaction between the alkyd containing paint and the oxygen entrapped in the air space of the container. Skin formation can be drastically reduced by the incorporation of a small amount (0.1-0.4% it varies depending on paint viscosity, production method, resin type and level) of a volatile Anti-oxidant –the most common being Methyl Ethyl Ketoxime (also known as MEKO or anti-skin) . The quantity added into the paint is also crucial since too little will cause skinning and too much will result in drying problems.
Can I premix the MEKO with the driers and then add to my alkyd containing paint ?
No, never premix MEKO with the oxidative driers as this combination is known to lead to fires or explosions.
How do I know if I’m adding the correct amount of catalyst to my 2K Hydrox Acrylic paint?
A hydroxy functional acrylic resin is designed to cross link at room temperature with suitable isocyanate. The mixing ratio of the hydroxy functional resin to the Isocynate catalyst is crucial to the performance of the coating. This ratio is calculated from the hydroxyl equivalent weight of the acrylic resin and the isocyanate equivalent weight of the isocyanate adduct. For example if you using an acrylic resin with the equivalent weight of 425 and the isocyanate adduct with the equivalent weight of 191, then the mixing ratio will be:
- 425 parts of Hydroxy Acrylic Resin to 191 parts of Isocyanate Adduct.
It is important to note whether the hydroxyl equivalent is quoted on solids or solution and adjustment in calculation should be performed accordingly.
What is the difference between individual driers and mixed drier?
Driers for alkyd based paints can be classified into 3 main groups i.e. Primary ,Secondary or through and Auxiliary driers ,each group performing a specific function in the drying process. A mixed drier is a careful blend of primary, secondary and auxiliary driers stabilized in a single mixture to give maximum catalytic effect.