Will printed materials fade when placed outdoors? This has always been a difficult question in the printing industry, because inks will inevitably fade over time. It's similar to how some people tan easily while others don't tan at all regardless of how much sun they get. Such ambiguous issues are hard to answer clearly.
In addition to sunlight causing fading, display lights (halogen lamps) in stores can also cause ink to fade. The primary factor causing ink to fade is ultraviolet (UV) light, which refers to the invisible light spectrum with wavelengths close to violet light. Based on the wavelength, UV light can be roughly divided into UVA, UVB, and UVC. UVC is mainly used for sterilization, while UVA and UVB, which range from about 280-400nm, are responsible for material aging and ink fading. Therefore, environmental tests generally evaluate the ink's fading condition under UVA or UVB exposure.
In the past, the solution for lightfastness in the printing industry was "screen printing" because it allows for thicker ink layers, making fading less noticeable or extending the duration before fading occurs. Nowadays, other printing methods also offer lightfast, fade-resistant solutions, with the main factors being "ink," "lamination," and "material."
Can lamination protect ink and prevent printed materials from fading?
A simple solution is to add an anti-UV (ultraviolet) protective layer on the printed materials, similar to how people apply sunscreen. Don't doubt it; anti-UV coatings don't have to be opaque or silver-colored; they can also be transparent!
Whether it is glossy or matte film, the most common material is OPP. However, OPP can only block about 10% of ultraviolet light, so it does not have lightfast or fade-resistant properties. Another common transparent film is PVC. This material has better print adhesion and is often made into transparent stickers. But PVC only has a 20% UV blocking rate, so it also does not have lightfast or fade-resistant properties.
Transparent holographic film is a thicker PET material with a transparent reflective coating on the surface, achieving up to 50% UV blocking rate! It's the best among common transparent films. In addition to preventing UV penetration and fading, it also has anti-counterfeiting functions, often used for parking permits, ID cards, and boat certificates. There are also protective films and coating materials specifically designed for UV resistance, blocking about 99% of UV light, depending on the needs.
Summary of the UV protection effectiveness of printing protective layers:
Anti-UV film > Transparent holographic film > PVC > OPP film
Are there lightfast, fade-resistant printing inks?
Inks can be divided into heat-set inks and UV inks based on their curing methods. Heat-set inks cure by drying or natural drying, while UV inks require UV light exposure to cure. Generally, UV inks have better sun resistance than heat-set inks, but for exposure exceeding six months, many UV inks will still noticeably fade.
Among common printing inks, toner-based inks are more resistant to UV light. According to ISO 12040, most toner-based inks can reach Level 5 or higher, meaning full sun exposure (8hr/day) for about 2 years or more. In comparison, general heat-set offset inks can only reach a minimum of Level 3, equivalent to about 3 months. It's worth noting that the lightfastness of inks varies by color, with black (K) and blue (C) typically being more lightfast than yellow (Y) and red (M).
Offset printing also offers specialized lightfast inks. According to ISO 12040, lightfastness is rated on an 8-level scale, with levels 4-6 being medium, roughly equivalent to toner-based inks, and levels 7-8 being higher-end lightfast inks. The characteristics and prices of different lightfast inks vary accordingly.
Summary of the UV fading resistance of inks:
Lightfast inks > Toner-based inks > UV inks > Heat-set inks
Weather-Resistant (Lightfast) Stickers
Paper boxes usually do not have the problem of being exposed to the sun for too long outdoors, but stickers might. PET and PVC are more resistant to UV exposure. PVC is more effective than PET, but PVC has environmental concerns. PVC is polyvinyl chloride, and because it contains "chlorine," it can produce dioxins when burned, increasing the risk of cancer. Many countries have banned the import of PVC printed products. Synthetic paper, pearl paper, and other PP materials are prone to aging and cracking. Mold paper and coated paper have long paper fibers and are not easily cracking, but they are susceptible to moisture, making them unsuitable for long-term outdoor use.
Summary of the UV resistance of printing materials:
PVC > PET > PP
High (Low) Temperature Resistant Stickers | Frozen Stickers | Waterproof Stickers
Stickers used outdoors often need to be temperature resistant and waterproof, which we have detailed in another article. Please see: High (Low) Temperature Resistant Labels | Freezer Labels | Waterproof Labels
You might wonder, since there are specialized solutions for sun protection, why not directly use specialized materials and inks for printing? The reason is that printing purposes and equipment are very diverse and complex, and different situations may require different inks or printing materials. We can only adopt the most suitable solution at the time. For example, although there are specialized lightfast inks for offset printing, their color performance differs from regular inks and may not meet the client's expectations in terms of color management, not to mention the cost! Furthermore, "variable data printing" like serial numbers requires digital printing processes, which use completely different inks!
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