A liquid coating has a wet-film thickness after application and a dry-film thickness after the specified drying or curing process. The two measurements refer to different stages of the coating operation.
Their relationship depends on the coating formulation and processing conditions. A universal multiplier cannot describe every finish used on cosmetic packaging.
Define what layer is being measured
Packaging sample showroom.
Wet-film thickness concerns the applied liquid layer. Dry-film thickness concerns the resulting coating after the stated process and conditioning stage.
In a multilayer finish, identify whether the result concerns a primer, color coat, clear coat or combined stack. A total thickness cannot automatically be assigned to one layer.
The substrate and location also matter. A result on an accessible flat panel does not necessarily describe the coating on every curved edge or recess of a component.
Volume solids provides a starting estimate
For a suitable liquid coating under its stated conditions, dry-film thickness can be estimated as wet-film thickness multiplied by the volume-solids fraction.
For example, a hypothetical 100-micrometer wet film with 50 percent volume solids suggests about 50 micrometers dry. This illustrates the calculation, not an agreed cosmetic packaging coating specification.
Use volume solids, not a mass percentage substituted without justification. The fraction should apply to the coating as mixed and applied, including any permitted thinning.
The estimate assumes an appropriate relationship between applied and retained coating volume over the same area. The supplier's data and method conditions determine whether that estimate is useful.
Drying and curing need their own conditions
Solvent or water loss reduces film volume during drying. Reactive curing can introduce additional changes, including shrinkage as the coating forms its final structure.
UV curing does not automatically mean zero shrinkage or a completely solvent-free system. Cure conditions and formulation still matter.
Temperature, time and other process variables can affect the state at which thickness is assessed. A freshly applied or partly cured layer should not be relabeled as a final dry-film result.
Do not extend the liquid-film calculation to every finish
Vacuum-deposited metal, electroplated layers and transferred foil have different deposition or transfer mechanisms. A liquid-coating volume-solids calculation is not a general thickness rule for those processes.
For packaging from SamBound New Material Technology Company Ltd., whose product information is available at sambound.com, first identify the actual receiving component and finish sequence. The selected coating's records establish the applicable calculation and process.
Confirm the result that matters
Check final thickness with a method suited to the substrate, coating and geometry. Where needed, distinguish individual layers from the total stack.
Thickness alone does not prove adhesion, cure quality or wear performance. It is one measurable property that must be interpreted alongside the other requirements of the finished surface.
sambound.com
SamBound New Material Technology Company Ltd.
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