P

Paint
Material which, when applied as a liquid to a surface, forms a solid film for the purpose of decoration and/or protection. Generally a paint contains binders (resins), solvents, pigments, and additives.

Pass
Motion of a spray gun in one direction only.

Paste
High viscosity product that requires dilution prior to application. For example, it can be a concentrated pigment dispersion used for shading.

Pattern
Shape or stream of material coming from a spray gun.

Pearlescent pigment
Pigment exhibiting various colors depending on the angles of illumination and viewing, as observed in mother-of-pearl. Pearlescent pigments are also called nacreous pigments.

Peeling
Paint or coating lifting from the surface due to poor adhesion.

Percent Solids
Percentage mass of non-liquid components in paint.

Performance additive
Additive used to enhance various properties of the coating.
Examples of performance additives are: surface conditioners (slip aids, anti-blocking, anti-scratch additives...), light and heat stabilizers, corrosion inhibitors, adhesion promoters... .

Permeability
Abaility of a coating film to allow the passage or penetration of a liquid or gas.

Phase decomposition
Spontaneous separation of polymer solutions into two phases, forming polymer/polymer emulsion or double-layer system.
Syn. Phase separation

Phenolic resin
Thermosetting synthetic resin produced by the condensation of phenol with an aldehyde (particularly of with formaldehyde). Provides very good heat and water resistance.

Photoinitiator
Additive which, when exposed to a specific wavelength of energy, forms a reactive species which starts the chain reaction to cause polymer formation. Most commercial photo-iniators for radical curing reactions contain benzoil groups, which are mainly responsible for the absorption of energy from light.
Syn. Photo-curing material

pH
Measure of acidity and alkalinity. pH 1-7 is acid and pH 7-14 is alkali.

pH-Stabilizer
Additive use to stabilize the pH of a coating.

Pigment
Finely ground natural or synthetic, insoluble particle adding color and opacity or corrosion inhibition to a coating film.
Note: In contrast, a dye is soluble.

Pigment volume
Percent by volume occupied by pigment in the dried film of paint (expressed as a percentage).

Pinholing
Coating defect: small, pore-like holes in a coating film about the size of a pinpoint. Extend entirely through the film.

Plasticizer
Compounding material used to enhance the deformability of a paint, varnish or lacquer. A plasticizer is soluble in the polymer and decreases the glass transition temperature (Tg) value, softens and adds flexibility to the product.

Polyester
Synthetic resin in which the structural units are linked by ester grouping.

Polymer
Large organic molecule formed by combining many smaller molecules (monomers) in a regular pattern.

Polymerization
Chemical reaction that links monomers to form polymers.

Polyurethane
Polymer made by the reaction of polyols with a multi-functional isocyanate. Provides toughness, flexibility, weather resistance, chemical resistance, and abrasion resistance to the coating film. Commonly used to make topcoats.

Polyvinyl Chloride (PVC)
Hard tough plastic solid used for coatings, commonly known as vinyl. Produced by the polymerization of the gas vinyl chloride [CH₂CHCl].

Post-cure reaction
Crosslinking reaction which occurs in cured coating due to the presence of an excess of a hardener. Can cause coating defects such as internal stress, decreasing adhesion durability and flexibility.

Pot Life
Length of time a coating material is useable or sprayable after mixing. As mixed material reacts in the pot, the viscosity always increases.
Syn. Shelf life

Powder coating
100% solid coating generally applied by an electrostatic process as a fine, dry powder to the surface and then heated above its melting point so the powder particles flow together or cure.

Practical coverage
Spreading rate of a paint calculated at the recommended dry film thickness and assuming 15% material loss.

Preservative
Substance added to protect, prevent, or retard decay, discoloration, or spoilage under conditions of use or storage.
See Biocide, Fungicide

Primary drier
Drier containing Co, Mn or V ions.
Syn. Active drier

Primary particles
Smallest particles of pigments and extenders that can be obtained during production.

Primer
First of two or more coats of paint, varnish or lacquer system. Primer improves adhesion, corrosion resistance of the substrate, or increases compatibility with the topcoat.

Printing Ink
Colored or pigmented liquid or paste composition that dries to a solid film after application as a thin layer by printing machinery.

Process additive
Additive which improves the processability of a coating.
Examples of process additives are: defoamers, dispersants, emulsifiers, driers and catalysts, rheology control additives, or wetting agents.

Profile
Anchor pattern of a surface produced by sandblasting, acid etching, or similar method.

Protecting agent
Additive used to protect coating against light, corrosion or bacteria degradation.