Coating Defects 150

ambient temperature

The nominal temperature of the air that surrounds devices and systems. Blisters may develop in a coating when using solvents that evaporate too quickly in the ambient temperature.

atomize

To become a fine spray or mist. Failure of a coating material to atomize during application is a common cause of orange peel.

batch

A specific quantity to be produced. One coating lot within a batch may vary in color from another, leading to color variation between parts.

blister

A small, dome-like bulge in the coating film or a small recess in a coating film. Typically blisters are caused by trapped moisture, rapid drying, and the use of improper solvents.

bubble

A type of blister that appears as a tiny raised area on a coating film. Bubbles most commonly form in coatings that are cured in an oven.

color variation

A defect in which parts coated with the same batch of coating deviate from their intended color. Color variation can be prevented through process control.

defect

A failing, deficiency, or imperfection in the specified and expected quality of the coating. Coating defects may be prevented through effective process control systems.

delamination

The loss of coating adhesion to a surface or between coating layers. Delamination tends to destroy a coating's strength and durability, as well as its aesthetic appearance.

dust

A small particle of a solid substance. Dust contaminates a coating mainly through dirty equipment and facilities, as well as sanding.

electrocoat bath

The conductive coating material into which the coating surface is immersed during electrocoating. During electrocoating, metal or adhesive contaminants often seep into a coating during the electrocoat bath.

electrocoating

A sophisticated form of dip coating that involves immersion of a conductive part into a conductive waterborne coating solution. During electrocoating, metal or adhesive contaminants often seep into a coating during the electrocoat bath.

electrode

A device within a circuit that conducts electricity. During a powder coating application, insufficient voltage in one of the electrodes often causes an excessively thin coating film or inadequate coverage of the coating surface.

electrostatic spraying

A coating process that involves using a spray gun to apply an electrical charge to powder particles while the part to be coated is grounded. Excessive electrostatic charge during electrostatic spraying causes a build-up of current on the substrate, which prevents good coating flow-out.

fast solvent

A type of solvent that evaporates quickly in its ambient temperature. Fast solvent often leads to blisters.

finishing line

The area in a coating facility in which a coating is applied to a surface. Isolating or enclosing the finishing line is an effective means of preventing coating contamination.

fisheye

A coating defect characterized by a small, recessed area in a coating film with a raised area in the middle. Fisheyes are usually caused by oil and grease on a coating substrate.

flash-off time

The amount of time necessary between coating application and baking of the coating to allow solvents sufficient evaporating time. Insufficient flash-off time may cause some types of blisters in a coating.

flow-out

The failure of a coating to flow uniformly across a surface. Poor flow-out typically is the result of problems with the spay gun or excessively high viscosity of the coating.

hiding power

The ability to hide the surface of an object. When applied too thin, a coating lacks the necessary hiding power.

lint

Fragments of fibers that fall off of cotton, paper, or linen. Lint is the most common contaminant found in a coating.

lot

A group of identical or similar parts or materials. One coating lot within a batch may deviate in color from another, leading to color variation between parts.

metallic flake coating

A type of coating containing tiny flakes of metal. Metallic flake coating is reflective over a wide range of wavelengths and may appear to change color when viewed from different angles.

mottle

A coating defect characterized by a ring-like blotch with a light-colored area in the center of the ring. Mottle typically occurs when metallic flake pigment is used in a coating.

operational procedure

The specific instructions for each stage of a manufacturing process. Designing and implementing effective operational procedures helps to prevent the occurrence of coating defects.

orange peel

Uneven, rough irregularities in the surface of a coating film. Orange peel often occurs when a binder fails to flow uniformly across an object's surface.

overspray

Coating material that has missed the surface being coated and has landed on other surfaces, including other coatings, in the finishing line. Overspray can be caused by drafts in the coating facility.

pigment

The microscopic, insoluble particle that gives a coating its color and opacity. Insufficient agitation of pigment often leads to pigment clustering.

pigment clustering

A condition in which pigment particles in a coating bunch together. Pigment clustering may trap solvent and prevent timely evaporation, leading to solvent pops.

pinhole

A small, sunken area that forms on a coating film after a bubble ruptures. Pinholes are typically larger and less abundant across a coating's surface than solvent pops.

porosity

The measure of the open spaces, or voids, in a material. Porosity in the substrate may trap moisture beneath the coating and cause blisters.

powder coating

A coating technology in which the coating is manufactured by blending the binder, pigment, and additives through a heated extrusion process. During a powder coating application, insufficient voltage in one of the electrodes often causes an excessively thin coating film or inadequate coverage of the coating surface.

process control

A method of checking product performance and batch consistency by regularly measuring and regulating processes that yield a product. Coating companies often seek to prevent coating defects through effective process control systems.

process requirement

Specific methods used during process control to ensure that a finished product meets product requirements. Understanding product requirements and process requirements helps to prevent the occurrence of coating defects.

product requirement

Specification from a potential consumer regarding how a product must conform to meet total quality standards. Product requirements help determine process requirements.

root cause

The true origin of a problem as opposed to the symptom of a prior cause. Troubleshooting focuses on identifying the root cause of a problem rather than simply addressing the symptoms.

run

A coating defect characterized by a streak of excess coating material that forms a line vertically down a coating surface. Also called a sag.

sag

A coating defect characterized by a streak of excess coating material that forms a line vertically down a coating surface. Also called a run.

silicone

A type of thermoset known for being both heat resistant and water repellant. Silicone is the most common type of grease found on coating surfaces.

solvent pop

A small, crater-like recess in a coated surface that forms typically when a pocket of solvent evaporates on a patch of film that has already dried. A solvent pop is a type of blister.

statistical process control

A method of measuring and controlling the processes that yield a product. In SPC, statistics are used to collect sample data and allow predictions of the overall process.

substrate

The surface upon which a coating is applied. Coating defects may be prevented through proper preparation of the substrate.

volatile

A changeable substance that can transform readily from solid to liquid to vapor at normal temperatures and pressures. Blisters usually contain some type of volatile, such as water, water vapor, solvent, or solvent vapor.

voltage

Electrical force or pressure that causes current to flow into a circuit. During a powder coating application, insufficient voltage in one of the electrodes often causes an excessively thin coating film or inadequate coverage of the coating surface.

wet

To cover with a liquid. When a partially dried coating does not adequately wet a surface, raised, solvent-filled areas often remain on the surface.