Red Thermochromic Pigment, Color Changing at 16°C, 1–10μm – KTP-16-BR

Red Thermochromic Pigment, Color Changing at 16°C, 1–10μm – KTP-16-BR

Special Effect Pigments › Thermochromic Pigment Series

KTP-16-BR is a Red thermochromic pigment with an activation temperature of 16°C, in the fine 1–10μm particle size range — a leuco dye-based color-changing pigment that is red below 16°C and becomes colorless as temperature rises above the activation threshold. The 16°C switching temperature is the lowest in the Kolortek thermochromic range, making KTP-16-BR specifically suited for applications that respond to cool or cold conditions — cold beverages, refrigerated packaging, outdoor temperature indicators, and smart labels designed to signal whether a product has been adequately chilled. At 1–10μm, it disperses in printing inks, coatings, and plastic systems without visible particle texture in thin films.

How KTP-16-BR Works — Color-to-Colorless at 16°C

KTP-16-BR belongs to the Colored-to-Colorless (C2C) class of thermochromic pigments. Below the activation temperature, the leuco dye within the microcapsule is in its colored (red) state. As temperature rises through the activation threshold (~16°C), an interaction within the encapsulated system causes the dye to adopt a colorless form — the red disappears and the underlying substrate, base coat, or design becomes visible. The effect is reversible: cooling below 16°C restores the red color. The transition is sharp and repeatable under normal use conditions.

The practical design implication is straightforward: at typical refrigerator temperature (4–8°C), KTP-16-BR is fully red. At room temperature (20°C+), it is fully colorless. The transition occurs across the 16°C threshold. Formulators can design graphics, text, or color layers that appear only when cold and disappear at ambient temperature — a temperature-responsive indicator built directly into the ink or coating.

Kolortek Thermochromic Series — Activation Temperatures and Colors

Color-to-color shift grades (e.g., KTP-30-BR Black-Red, KTP-30-GY Green-Yellow) and BPA Free food-grade grades (KTP-31-RBF, KTP-31-GBF and others) are available. Contact Kolortek for the full thermochromic color and temperature range.

Technical Specifications

Key Technical Characteristics

16°C activation — the cold-indicator specification: The 16°C threshold is positioned between typical refrigerator temperature (4–8°C) and ambient room temperature (20–25°C). This means KTP-16-BR is reliably red when a product is cold and reliably colorless at room temperature — a clean binary visual signal with a practical margin on both sides of the transition point. For cold beverage cans, bottle labels, and refrigerator-activated packaging, this threshold is more appropriate than the more common 31°C body-temperature grades, which would remain colored at refrigerator and ambient conditions without activating until warm skin contact.

Microencapsulation — the enabling technology: The leuco dye system in KTP-16-BR is contained within polymer microcapsules (1–10μm). The capsule provides the controlled chemical environment necessary for the thermochromic reaction and protects the active chemistry from direct contact with the binder, solvent, or substrate. Capsule integrity is critical to performance — high-shear mixing, grinding, or mechanical stress that ruptures the capsules permanently disables the thermochromic function. This is the primary processing constraint that distinguishes thermochromic pigments from conventional pigments.

Designing with color-to-colorless change: KTP-16-BR becomes colorless above 16°C, which means the visual design depends entirely on what is underneath. A white substrate produces a white surface at room temperature; a printed graphic under the thermochromic layer is revealed when the red disappears at warm temperatures. Conversely, a black base coat under KTP-16-BR produces a red surface when cold and reveals black (or whatever is printed) at room temperature. The base coat design is as important as the pigment specification — the thermochromic layer is a reveal mechanism, not a standalone color.

UV and heat stability — the durability constraints of leuco dye chemistry: Leuco dye thermochromic pigments are less UV-stable than conventional pigments. Extended outdoor UV exposure causes gradual fading of the color intensity and may affect the sharpness of the thermal transition over time. For indoor and point-of-sale applications, this is generally not a practical concern. For outdoor-exposed labels or packaging, UV-protective topcoats and avoiding direct prolonged sun exposure extend the functional service life. Contact Kolortek for specific stability data relevant to your application conditions.

Application Range

Formulation Notes

Low-shear mixing — non-negotiable for microencapsulated pigments: The thermochromic function of KTP-16-BR depends entirely on intact microcapsules. High-shear dispersers, ball mills, three-roll mills, and tight-clearance pumps will rupture the capsule walls, permanently destroying the color-change capability. Mix KTP-16-BR into the pre-dispersed ink or coating base using only low-shear paddle or anchor mixing. If the ink or coating contains other pigments or fillers that require high-shear dispersion, complete all high-shear steps before adding the thermochromic component at the end.

Solvent compatibility: Strong solvents — ketones, aromatic hydrocarbons at high concentration — can attack the polymer capsule wall over time and reduce thermochromic performance. Water-based and mild solvent-based systems generally provide better capsule longevity. UV-curable systems are compatible provided the UV cure step does not generate excessive heat that could activate the pigment during curing and affect final print quality. Contact Kolortek for specific solvent compatibility guidance.

Loading levels: Typical loading for printing inks runs 10–30% by weight of the ink phase depending on desired color intensity. In thinner ink films (gravure, flexo), higher loading compensates for reduced film thickness. For coatings, 15–25% in the wet film is a practical starting range for full color development. Color intensity at the cold state and the sharpness of the color transition are both loading-dependent — bench evaluation at your target film thickness is the most reliable method for establishing final loading levels.

Kolortek has supplied thermochromic pigments across the full temperature and color range for over 20 years, with consistent activation temperature and capsule quality across production batches. The thermochromic range covers activation temperatures from 16°C through 45°C, multiple colors including BPA Free food-grade grades (KTP-31-RBF, KTP-31-GBF, and others at 31°C), and color-to-color shift variants for more complex design requirements. TDS and SDS are available on request for KTP-16-BR.

Frequently Asked Questions

Q: Does the 16°C activation temperature mean the color changes only at exactly 16°C?
A: The activation temperature designates the midpoint of the color transition range. In practice, thermochromic pigments transition across a range of approximately 3–8°C around the activation point rather than switching instantaneously at a single degree. KTP-16-BR begins its transition slightly below 16°C and completes it slightly above. For visual indicator applications, this is a practical advantage — the transition is visible and progressive rather than abrupt. For applications requiring a very sharp specific threshold, this range should be confirmed against the TDS and evaluated in bench trials.

Q: Can KTP-16-BR be combined with non-thermochromic pigments in the same formulation?
A: Yes — thermochromic pigments can be combined with conventional pigments, pearlescent pigments, and other effect pigments in the same ink or coating. Adding a non-thermochromic base color alongside KTP-16-BR creates a bi-color effect: the base color is visible at all temperatures, while the thermochromic red is added when cold and disappears when warm. Layering approaches (thermochromic ink over a static base) give more design flexibility than blended single-layer systems. Ensure all conventional pigments are dispersed before KTP-16-BR is added via low-shear mixing.

Q: Is KTP-16-BR food-safe for direct food contact packaging?
A: KTP-16-BR is the standard grade and is not specifically formulated or certified for direct food contact applications. For food packaging applications requiring food safety compliance, specify the BPA Free series — KTP-31-RBF (Red, 31°C, BPA Free) or other BPA Free grades. The 16°C activation temperature is not currently available in the BPA Free series; contact Kolortek to discuss available food-grade temperature options.

Q: What happens if KTP-16-BR is exposed to temperatures well above the activation point for extended periods?
A: Brief exposure to temperatures significantly above the activation point (such as during summer shipping or storage) does not permanently damage the thermochromic function — the color returns when the pigment cools. Extended exposure to very high temperatures (above approximately 80–100°C depending on the specific binder and capsule chemistry) can cause irreversible capsule degradation. Storage and shipping temperatures should be kept below 40°C as a practical precaution. Contact Kolortek for specific thermal stability data for KTP-16-BR.

Request Samples or Technical Data

Thermochromic color-change effects must be evaluated in your specific ink or coating system and at your target film thickness — bench trials are the most reliable way to confirm activation temperature sharpness, color intensity, and thermal cycling durability before production commitment. Contact Kolortek to request a sample of KTP-16-BR, download the TDS with activation temperature data, or discuss the full thermochromic range including BPA Free and color-to-color shift grades.