Color-Changing Bags: How UV Photochromic Printing Transforms Everyday Style

UV Photochromic Printing: a new printing option for bags

UV photochromic printing is a special printing method which applies Sunlight or UV (ultraviolet) light properties to realize color change effect of printed matters.

Principle of Photochromic Color Change

Ultraviolet light is invisible light in the violet range of the spectrum in the electromagnetic spectrum. The key point of UV photochromic printing is the application of special photochromic inks. Such inks include photochromic materials which have chemical reaction capabilities. Under the effect of the ultraviolet ray, the molecular structure of the photochromic matter in the ink varies so that a color change is achieved.

After printing photochromic ink, it needs to be coated with UV after printing, but the printing process is the same as that of ordinary ink. During the curing process, the ultraviolet light emitted by the UV lamp activates the photochromic substances in the ink, priming them for a color change. Once the printed material is later exposed to natural sunlight or a specific ultraviolet light source, the color-changing effect appears. 

Because of photochromic color principle (the rate of discoloration will also change depending on the environment that the product is used.) Factors including light, application environment etc. may have a direct effect on life span depending on the product being used.

Application environment: Photochromic substances are easily oxidized by oxygen in the air. The photochromic material which has resistivity to the oxidation is effective to maintain the performance for a long time. Special processed or antioxidative type of photochromic ink has longer life than a regular ink.

The life of the photochromic content is also influenced by temperature and humidity. Chemical reactions are accelerated by high temperatures and high humidity that cause the colouring of the photochromic materials to age. For example, the duration of stability of the photochromic materials may be shorter in humid tropical zones as compred to dry moderate zones.

Light Intensity: High intensity of ultraviolet light, the photochromic chemicals reaction speed is faster, the chemical process will more quickly, and aging of photochromic lens. For instance, when exposed to the natural sunlight, sometimes the service life of photochromic materials is very short. Their life span is relatively long since they are in the indoor environment with lower light intensity.

Usage Frequency: Usage frequency is the frequency with which the photochromic materials are actuated (ie, exposed to the ultraviolet or particular light source) in a given period of time. The photochromic materials are gradually damaged by the exposure of UV. Any single exposure results in some tiny alteration in molecular structure, and these miniscule changes add up over time and can be observed as deterioration in performance. The service life of photochromatic materials is extremely short at high frequency of use. One example of this is that a product which is used ten times per day with UV exposure, may have a photochromic life of a few months, while a product used once a day may last 1-2 years.

When this special principle of photosensitive color change is applied to photochromic printing technology, the application prospect is very broad. More directly, it introduces a new visual experience and surprises to bags, fashion and creativity and brings new visual effects to the product. For instance, patterns printed with UV photochromic inks on T-shirts, tote bags, backpacks, phone cases and other items can change their color under sunlight, which makes the product more fun and attractive. It is to be noted that the color switch effect is adjustable and difficult to be replicated by others, so it is very reliable to product anti-counterfeiting. As long as it continues to develop technologically, and becomes cheaper to use, it is just going to spread into more areas.

Special note at the end, it should be noted that this printing process has to be done in particular conditions e.g. not to be disturbed by natural light etc. Proper drying temperature and drying time can avoid damages of the photochromic substances during printing, which contributes to the effect of color change to be precise and stable. Similar premature aging of the photochromic substances can occur when the drying condition is such that the drying temperature is unduly high or the drying time is unduly long.

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