Determining if packaging paper has become damp can be done by observing its appearance, touching it, and testing its performance. Key signs include softening, deformation, curling of printed materials, or fading of colors.
Here are some simple and effective methods:
Appearance: Damp packaging paper may appear dull, lack luster, have slight water stains or mold spots, and its color may be yellowish or grayish, losing its original crispness. If the paper edges develop a "ruffled edge" (curled edges and a concave center), it's a typical sign of moisture absorption and deformation.
Touch: Dry paper feels crisp and elastic, quickly springing back when gently pressed. Damp paper feels soft, sticky, or damp, lacks resilience when squeezed, and may even crease or tear easily.
Feel: Listen to the Sound: Pick up a piece of paper and shake or bend it quickly. Dry paper will make a crisp "shh" sound; damp paper will make a dull sound, almost silent. This is an important sensory indicator of paper moisture content.
Test Use: During printing or packaging, if you find that the paper easily jams, the printed material curls, the ink adheres unevenly, or the color fades, it is likely due to fiber expansion and changes in surface tension caused by moisture.
Professional Testing (Optional): For bulk purchases or high-requirement scenarios, the Cobb method can be used to test the water absorption of cardboard. This method quantifies moisture resistance by measuring the amount of water absorbed per unit area. It is widely used in corrugated cardboard quality inspection and can accurately determine its moisture resistance.
