Substrate Holdout and Pinhole Formation in Inline Flexographic Coating
Substrate holdout and pinhole control require matching anilox coat weight delivery to sheet absorbency while regulating dynamic wetting and surface skinning.
ASTM E96 WVTR
Standard Specification
Quantitative measurement protocol for determining the rate at which water vapour passes through semi-permeable and permeable materials. Application of astm e96 wvtr ensures that packaging membranes provide sufficient moisture protection for dry goods or perishable items. This procedure involves sealing a specimen over a dish containing either desiccant or water and placing it in a controlled atmosphere to track weight change over time.
Testing Methodology
Choice of either the desiccant method or the water method determines the direction of vapour flow during the evaluation. Practitioners use the desiccant method when the interior of a package remains dry, while the water method simulates high humidity environments. Each calculation requires precise temperature control and specific relative humidity levels to yield a value in grams per square metre per 24 hours.
Stable air velocity across the specimen surface prevents the formation of stagnant boundary layers that might skew the final reading.
Material Performance
Resultant data from this test dictate the shelf life of moisture-sensitive products. High values suggest a porous structure unsuitable for hydroscopic powders or metal components prone to oxidation. Thin films and coated boards often show lower resistance when mechanical stress or creasing occurs during the converting process.