1. Why Industry Needs “Visible” Temperature Indication
In metal heat treatment, electronics soldering, paint baking, composite curing and other industrial processes, temperature and holding time directly determine product quality. Thermocouples and thermal cameras are accurate, but costly, and cannot cover every workpiece or every position inside a furnace, let alone keep records for every unit of mass production.
200°C temperature indicator ink (heat indicator ink / irreversible thermochromic ink) offers a low-cost, intuitive, recordable solution: coat or print it on the workpiece surface, let it experience the process temperature together with the product, then judge by visual color change whether the process temperature was reached or an over-temperature event occurred — like a one-time “temperature record card” attached to every part.
2. What Is 200°C Indicator Ink? Color-Change Characteristics
200°C indicator ink is a specialty thermochromic ink designed for a 200°C threshold. The ink starts green and undergoes an irreversible color transition as exposure temperature and time increase:
| Condition | Color Change | Description |
|---|---|---|
| Initial state | Green | Green immediately after coating/printing |
| Below 180°C, exposed 180 min (3 h) | Stays green | Longer time = greener; indicates no over-temperature event |
| 200°C or above, exposed 90+ min | Turns blue | Longer time = bluer; over-temperature history recorded |
| After change | Blue (permanent) | Irreversible; color remains after cooling |
Easy to remember: green = safe (no over-temperature), blue = over-temperature experienced (200°C+ for 90+ min). The shade also roughly indicates how long the over-temperature lasted.
3. How It Works: Irreversible Thermochromic Mechanism
The ink uses a composite system of an inorganic color base plus a specific organic colorant:
- Low-temperature region (below 180°C): the colorant remains stable and the ink stays green; as holding time increases, the coating reacts more fully and the green becomes more saturated.
- High-temperature region (200°C and above): once the colorant exceeds its thermal stability threshold, it undergoes irreversible evaporation/decomposition, gradually exposing the underlying color base. After 90+ minutes of exposure, a clear green-to-blue shift is visible; the longer the exposure, the deeper the blue.
- Irreversibility: the evaporated or decomposed colorant cannot be restored, so the color change is a one-time record — the core value of a thermal history indicator.
4. Advantages of the Process
4.1 Visual Inspection, No Instruments Needed
Read the color with the naked eye after cooling — no thermocouples, thermal cameras or chemical analysis required. Production-line workers can judge in seconds.
4.2 Irreversible Record for Later Verification
Once changed, the color never reverts, giving every workpiece a permanent over-temperature profile — ideal for quality traceability and after-sales dispute resolution.
4.3 Extremely Low Cost for Mass Production
Per-unit coating cost is negligible compared with installing temperature sensors on every part — perfect for line-by-line verification in mass production.
4.4 Records the Actual Process History
The ink experiences the same temperature curve as the workpiece in the same furnace, recording true thermal history rather than a representative sampling point.
4.5 Flexible Application on Various Substrates
Can be applied by dotting, pen, screen printing or spraying, on metal, ceramics, glass, heat-resistant plastics and parts of various shapes.
5. Applications
- Metal heat treatment & annealing: verify furnace temperature uniformity and whether parts reached the required temperature and holding time.
- Electronics manufacturing: thermal history monitoring and over-temperature warning in reflow soldering, wave soldering and curing ovens.
- Paint baking / powder coating curing: confirm baking temperature is reached to avoid under-cured, peeling coatings.
- Ovens / drying equipment: multi-point verification of temperature distribution uniformity.
- Insulated pipes / vessel over-temperature monitoring: attach under insulation or on pipe surfaces to check for past over-temperature events during maintenance.
- Motor / bearing / transformer overheat indication: in preventive maintenance, determine whether equipment experienced abnormal high temperature.
- Automotive / aerospace parts: process verification and record-keeping for critical heat treatment and curing steps.
- Glass / ceramic firing, composite curing: confirm firing or curing temperature and time.
- Quality record & traceability: ship products with thermal history recorded; quickly trace process steps when quality disputes arise.
6. How to Use and Precautions
- Application: dotting, pen, screen printing or spraying; uniform coating is sufficient.
- Reading time: after the part cools to room temperature, judge by visual color comparison — the color is final.
- Interpretation: green = no over-temperature above 200°C; blue = over-temperature of 200°C+ for 90+ minutes, deeper blue = longer over-temperature.
- Scope: this ink indicates “whether the temperature threshold + duration was reached” for process verification and over-temperature warning; it is not a substitute for precise temperature instruments.
- Selection: since actual temperature profiles and substrates vary, we recommend sampling first to confirm the color-change time and contrast meet your requirements before mass use.
7. FAQ
Q1: Can the ink return to green after turning blue?
No. The change is irreversible — that is exactly why it is used to record over-temperature history: once overheated, permanently marked.
Q2: How do I read the color?
Visual comparison after cooling: green means no over-temperature above 200°C; blue means 200°C+ for 90+ minutes, with deeper blue indicating longer over-temperature.
Q3: Can it be used for processes below 180°C?
This product is designed for a 200°C threshold; it stays green below 180°C even after long exposure (only deeper in shade), suitable for indicating “not overheated”. Other temperature thresholds can be customized.
Q4: What substrates can it be applied to?
Metal, ceramics, glass and heat-resistant plastics; the binder and formulation are selected according to the substrate.
Q5: Advantages over thermocouples?
Lower cost, coverage of every part, synchronized recording with the process, no wiring — ideal for per-part verification in mass production; the limitation is that it indicates a threshold rather than precise temperature.
Q6: Can other color-change temperatures be customized?
Yes. The threshold temperature and color-change time can be customized to your process; contact us for sampling.
Q7: Storage conditions and shelf life?
Store away from light, sealed, in a cool place; shelf life is typically 12 months. Keep containers tightly sealed after opening.
8. About Shenzhen SJH Ink Co., Ltd.
Shenzhen SJH Ink Co., Ltd. specializes in anti-counterfeit inks and specialty functional inks. It is a member of the China Radiation Curing Branch with an annual output of nearly 1,000 tons. Besides 200°C temperature indicator ink, our product lines include IR excitation ink, UV invisible fluorescent ink, OVI optically variable ink, water-based thermochromic ink, photochromic ink and glow-in-the-dark ink. We support custom formulations (threshold temperature and color-change time) and free samples, with products compliant with EN71.3 and REACH.
- Website: www.sjhink.com
- Tel: +86 13510998453
- Email: sz_qhy@hotmail.com
- Address: No.14 Fuxing Road, Pinghu, Longgang District, Shenzhen, China
If you are planning heat-treatment verification, over-temperature monitoring or process record-keeping, welcome to request free samples to test the actual color-change performance of our 200°C indicator ink. Browse our product center or contact us for a quote.
Published by Shenzhen SJH Ink Co., Ltd. Reproduction with attribution required.