Sunlight brings out the colors!


  • Large-format inkjet printing
photochromic printing

①Technical Overview | Product Specifications

This is a printing technology that can produce colors in the four primary colors (CMYK) of cyan, magenta, yellow, and black, and can produce strong colors with excitation light near 365 nm, which is the near ultraviolet light contained in sunlight.

Photochromic inks are reversible inks that change color in the presence or absence of ultraviolet light. It is printed with ink that changes color in response to ultraviolet light such as sunlight. The stronger the UV light, the darker the color.

photochromic ink

Indoors / Outdoors *The photo shows oil-based ink.


SOLAR PRINT is an eight-color simultaneous printing technology developed by SO-KEN that utilizes the above-mentioned ultraviolet color inks and uses both regular CMYK inks and ultraviolet color CMYK inks.

About Photochromics

  • Principle of Chromics
    • Photochromic dyes are synthetic dyes in the form of crystalline powders.
    • When dissolved in an organic solvent, the dyes exhibit a reversible effect from colorless to colored. The effect is reversible from colorless to colored when the dyes are dissolved in an organic solvent. The effect cannot be achieved unless the dyes are alone or dissolved.
    • As for the color return, the dissolved dye forms a matrix with the base material, so the speed of coloration → color loss is greatly affected by the base material.

Ink specifications and weather resistance

The original ink developed by our company is strongly colored by the excitation light around 365nm, which is the near ultraviolet light contained in the sunlight.

Irradiation verification under artificial sun, assuming 12:00 noon in midsummer!
Measurement conditions Artificial sun, irradiation distance 84cm
Measurement object Solvent inkjet printing,SOLAR PRINT, synthetic paper
Verification environment Irradiated by artificial sun assuming mid-summer daytime.

photochromic printing

Figure 1: (5-second irradiation)

photochromic printing

Figure 2: (55-second shutdown)

photochromic printing

Figure 3 (55-second shutdown)

The results of a test in which UV light was irradiated for 5 seconds (Figure 1), the color was generated, and then the UV light was blocked for 55 seconds to eliminate the color (Figure 2). As a result, the color halving was observed after about 5,760 times of irradiation. (Fig. 3) In the verification of continuous irradiation, the color halving was observed after about 4 to 5 hours of irradiation when the UV light was blocked on half the surface.

Please try to avoid continuous exposure to direct sunlight, which reduces the color of solar prints by half, and leave the prints unattended.

②Notes on installation and use

Sunlight by season and time

フォトクロミック 印刷

Time of day to enjoy the color of SOLAR PRINT
SOLAR PRINT, which can produce full-color prints using ultraviolet rays from sunlight, has the best time and period for reproducing the best color depending on the strength of the daily ultraviolet rays and the period of sunlight. The circle in the graph is the recommended time.

Changes in UV radiation levels over the course of a day

photochromic printing
Recommended time zone. The best full color reproduction can be enjoyed. The degree of coloration varies depending on the amount of ultraviolet light.
× Since the UV light is weakened, the color will be 10-30% lighter than the best full color 100%.

For UV radiation levels outside of summer and winter, please refer to the monthly graphs.

Change in UV radiation by month


Changes in UV radiation levels due to weather

This is the amount of UV radiation when the UV radiation in clear weather is 100%.

photochromic printing
good weather
Amount of ultraviolet rays 100%
photochromic printing
Amount of ultraviolet rays 98%-90%.
photochromic printing
slightly cloudy
Amount of ultraviolet rays About 80%
photochromic printing
Amount of ultraviolet rays About 60%
photochromic printing
Amount of ultraviolet rays About 30%

About UV-cut glass

photochromic printing

About glass windows with ultraviolet rays cutting and heat shielding effect performance

When checking the solar print near a window, the color effect of the SOLAR PRINT may be weaker than it should be because the transmission of ultraviolet rays is weakened indoors.

③About Triggers

Types of triggers to change the design of SOLAR PRINT

Trigger (1)
Just expose it to sunlight.
photochromic printing
Trigger (2)
Just shine a UV light on it.
photochromic printing