Yellow to Purple Photochromic Pigment, UV Reactive – KT-PMC-02-YP

Yellow to Purple Photochromic Pigment, UV Reactive – KT-PMC-02-YP

Special Effect Pigments › Photochromic Pigment Series

KT-PMC-02-YP is a Yellow/Purple photochromic pigment in the fine 1–10μm particle size range — a UV-reactive organic pigment that appears pale yellow in the absence of UV light and shifts to a deep purple within approximately one second of exposure to direct sunlight or UV illumination. The color change is fully reversible: the purple fades back to yellow within seconds of moving out of UV exposure. At 1–10μm, KT-PMC-02-YP disperses in printing inks, coatings, nail lacquer, and plastic systems without visible particle texture, making it suitable for any application where a clean UV-activated yellow-to-purple color shift is the design brief.

How Photochromic Pigments Work — and How They Differ from Thermochromic and Fluorescent Grades

Photochromic pigments use organic molecular switches — typically spiropyrans, naphthopyrans, or diarylethene compounds — that undergo a reversible structural isomerization under UV irradiation. In the UV-absent state, the molecule adopts a ring-closed (colorless or pale) conformation. UV exposure opens the ring and generates a chromophore that absorbs visible light, producing the colored state. Removal of UV allows thermal or photochemical reversion to the closed form. The transition is fast — seconds for activation, seconds to minutes for reversion depending on temperature and specific chemistry.

Key distinctions from related pigment types: Thermochromic pigments (KTP series) respond to temperature, not UV. Fluorescent pigments (KT-FDS series) require continuous incident light to produce their effect but do not change color in response to UV — they emit at a fixed wavelength. Glow-in-the-dark pigments store energy and emit in the dark. Photochromic pigments are UV-specific color changers — they are pale or colorless indoors under standard artificial lighting (which contains minimal UV) and become deeply colored in direct sunlight or near UV-lamp exposure.

Kolortek Photochromic Series — Full Color Range at 1–10μm

All Kolortek photochromic grades are at 1–10μm standard particle size. Single-color activated grades (KT-PMC-12-PA through KT-PMC-28-B) appear pale or colorless indoors and shift to their designated color under UV. Two-color shift grades (KT-PMC-01-YG through KT-PMC-07-GR) are visibly colored in both UV-off and UV-on states.

Technical Specifications — KT-PMC-02-YP

Key Technical Characteristics

Yellow-to-purple — the maximum color wheel distance in the two-color photochromic range: Yellow and purple sit on near-opposite sides of the visible color spectrum. Among the Kolortek two-color photochromic grades, KT-PMC-02-YP produces one of the highest contrast shifts available — the visual change between the yellow UV-off state and the purple UV-on state is immediately apparent to the eye without requiring close inspection. For applications where the color change needs to be clearly visible and functionally obvious — outdoor apparel, consumer novelty products, promotional packaging — the yellow/purple shift provides strong visual communication of UV exposure.

Indoor vs. outdoor — the UV dependency that defines the product category: Standard indoor artificial lighting — LED, fluorescent, incandescent — contains minimal UV. KT-PMC-02-YP remains yellow under these conditions. Direct sunlight, outdoor daylight (even on overcast days to a lesser degree), and UV lamps (blacklight, 365nm) provide sufficient UV to activate the purple state. This means the product reads yellow in the home, office, or retail environment and purple in direct outdoor light — a clean visual UV indicator. The activation is not gradual; it is fast (approximately one second in direct sun) and the color shift is clear.

UV fatigue — the primary durability limitation of organic photochromic pigments: Photochromic organic molecules gradually lose switching efficiency with cumulative UV exposure over time. The color depth in the activated state decreases, and the reversion speed may change. The rate of fatigue depends on the UV intensity, the binder system, protective additives (UV absorbers at the right wavelength can either compete with the photochromic or protect it depending on concentration), temperature, and oxygen exposure. For outdoor applications with high cumulative UV load — apparel, exterior surfaces — fatigue testing under your specific conditions is necessary to establish expected product service life. For shorter-cycle applications — promotional products, seasonal use, novelty items — fatigue rate is less likely to be a limiting factor within the product lifecycle.

UV-curable system compatibility note: Photochromic pigments can be formulated in UV-curable binders, but the UV cure step must be managed carefully. A high-dose UV cure applied to the uncured film will activate the photochromic pigment — the film may appear purple during cure and transition back to yellow as the binder cures and the pigment reverts. This is a cosmetic issue during production rather than a functional problem in the cured film, but it can make color quality assessment during production difficult. Confirm the cure protocol and its effect on final film color with bench testing before production specification.

Application Range

Frequently Asked Questions

Q: Will KT-PMC-02-YP activate under indoor LED or fluorescent lighting?
A: Standard indoor artificial lighting — LED, fluorescent, incandescent — contains insufficient UV to activate photochromic pigments under normal conditions. KT-PMC-02-YP remains in its yellow state indoors under these light sources. Direct sunlight, outdoor daylight (including partially cloudy days), and UV lamps (365nm blacklight) provide sufficient UV for activation. UV output varies by specific light source — some specialized LED fixtures emit UV and may partially activate the pigment, but standard commercial and residential lighting does not. This UV-specificity is the core functional characteristic of photochromic pigments and should be communicated to end users of products containing KT-PMC-02-YP.

Q: How does KT-PMC-02-YP (two-color yellow/purple) differ from KT-PMC-12-PA (colorless/purple)?
A: KT-PMC-12-PA appears pale or colorless indoors and shifts to purple under UV — indoors the product has no significant body color. KT-PMC-02-YP appears yellow indoors and shifts to purple under UV — the product is visibly yellow at all times and purple under UV. Choose KT-PMC-12-PA when you want the product to appear neutral or colorless indoors and only show color outdoors. Choose KT-PMC-02-YP when you want the product to have a warm yellow indoor color that dramatically shifts to purple in sunlight — the product is always colored, just differently by environment.

Q: How long does the purple color last once the product moves out of direct sunlight?
A: Reversion from purple back to yellow begins immediately upon UV removal. The rate depends primarily on ambient temperature — warmer temperatures accelerate reversion; cooler temperatures slow it. In typical outdoor conditions moving from direct sun to shade, visible reversion begins within seconds and the yellow state is substantially restored within 1–5 minutes. In a cool, dark indoor environment, reversion may take slightly longer. This means the purple state is not persistent — it is present only when the product is actively exposed to UV.

Request Samples or Technical Data

Photochromic color change performance — activation speed, purple depth, and reversion behavior — should be evaluated in your specific formulation system and under your actual UV conditions. Contact Kolortek to request a sample of KT-PMC-02-YP alongside other photochromic grades, download the TDS, or discuss the full photochromic series for your application.