A humidity indicator card is a tool used to monitor the relative humidity inside sealed packaging. It visually reflects the ambient humidity through color changes at chemical indicator points and is widely used in moisture-proof packaging for humidity-sensitive products such as electronic components, semiconductors, and optical equipment. Its technical parameters mainly include the following aspects:
1. Color-Changing Principle and Chemical Basis
The core of the humidity indicator card is the moisture-sensing material, which can be divided into two categories based on whether it contains cobalt:
Cobalt-containing type: Uses cobalt chloride (CoCl₂) as an indicator. It is blue in a dry state ([Co(H₂O)₄Cl₂]) and turns pink after absorbing moisture ([Co(H₂O)₆]²⁺). The color change is reversible.
Cobalt-free type: Uses environmentally friendly alternative materials (specific components are mostly trade secrets), achieving various color-changing combinations such as yellow to green and blue to purple. It complies with EU RoHS and REACH regulations, avoiding carcinogenic risks.
Note: Due to cobalt chloride being classified as a Group 2 carcinogen by EU Regulation 2004/73/EC, cobalt-containing humidity cards are being phased out. Exported products should prioritize cobalt-free models.
2. Indicator Point Specifications and Humidity Range
Common types include three-point, four-point, and six-point cards, each corresponding to different humidity thresholds.
Typical configurations include three indicator points: 5% RH, 10% RH, and 60% RH, meeting industry standards such as JEDEC J-STD-033D.
The detection range generally covers 5%–95% RH, and specific gradients (e.g., 10%, 20%, 30%) can be customized upon request.
3. Physical Parameters
Material: Pure white paper substrate or wood pulp paper, impregnated with a moisture-sensing solution.
Dimensions: Common specifications are 103mm × 38mm × 0.04mm, but non-standard sizes such as 3 inches × 2 inches are also available. Thickness: Approximately 0.4 mm.
Packaging: Usually sealed in aluminum foil bags or tin cans, containing desiccant to prevent premature moisture absorption.