Humidity indicator cards are mainly classified into several types based on their moisture-sensitive materials, color-changing characteristics, and application scenarios. The following is a classification explanation based on technical principles and practical applications:
1. Classification by Moisture-Sensitive Material
(1) Cobalt-based Humidity Indicator Cards
Principle: Uses cobalt chloride (CoCl₂) as the moisture-sensitive substance. It is blue when dry ([Co(H₂O)₄Cl₂]), and turns pink after absorbing moisture ([Co(H₂O)₆]²⁺). The color change is reversible.
Characteristics: Obvious color change, low cost, and was once widely used in electronic component packaging.
Restrictions: Cobalt chloride is classified as a Group 2 carcinogen under EU Regulation 2004/73/EC. It does not comply with RoHS and REACH environmental standards and has been gradually phased out. It is not suitable for export products.
(2) Cobalt-Free Humidity Indicator Card
Principle: Uses environmentally friendly chemicals to replace cobalt chloride, achieving color changes. Common combinations include blue to pink, yellow to green, and brown to blue.
Features: Safe and non-toxic, compliant with EU RoHS directives and industry standards such as IPC/JEDEC J-STD-033D, suitable for scenarios with high environmental protection requirements.
Applications: Widely used in moisture-proof packaging in electronics, medical, and food industries, especially suitable for export goods.