Outdoor TFT LCD display modules operate in significantly different environments than regular consumer display modules, thus placing more specific performance requirements on them.
These requirements include high brightness, waterproofing, prevention of accidental touches, anti-glare, high reliability, and resistance to ultraviolet (UV) radiation.
Among these requirements, "UV resistance" is frequently mentioned, but many people are not familiar with its specific implementation methods.
When discussing UV protection solutions for outdoor LCD display modules, many may be familiar with "UV-resistant OCA," but what other methods are available?
This article will systematically introduce common UV protection solutions for TFT LCD display modules, hoping to help you make more appropriate choices during the design and selection process.
Regarding UV light
Before introducing the specific solutions, let's first have a basic understanding of ultraviolet (UV) light.
Light can be divided into several categories according to its wavelength: visible light generally has a wavelength between 380 and 780 nm; ultraviolet (UV) light has a wavelength range of 100 to 400 nm (partially overlapping with visible light); wavelengths less than 100 nm are X-rays; and wavelengths greater than 780 nm belong to infrared radiation.
Ultraviolet (UV) light can be further classified by wavelength as follows:
Long-wave UVA (315~400nm)
Medium-wave UVB (280~315nm)
Short-wave UVC (100~280nm)
From an energy perspective, UV-C > UV-B > UV-A; however, in terms of distribution in the natural environment, UV-A accounts for over 95%, UV-B less than 5%, and UV-C is almost entirely absorbed by the ozone layer and is virtually non-existent in the natural environment.
Therefore, when we talk about LCD UV protection, we are mainly referring to protection against long-wave UVA.
After learning the basics of ultraviolet radiation, let's take a look at the commonly used UV protection solutions in outdoor LCD display modules.
Anti-UV OCA Optical Adhesive
Anti-UV OCA optical adhesive, also commonly known as "UV CUT OCA," is almost standard equipment for outdoor LCD display modules and is one of the most widely used UV protection methods. It's important to note that this type of OCA is usually non-UV (self-curing).
Besides outdoor LCD display modules, anti-UV OCA is also widely used in EPD electronic paper modules with front lights, display modules requiring UV blocking, and curved or irregularly shaped display modules.
The Working Principle of Anti-UV OCA
Ordinary OCA optical adhesives mainly consist of base resin, crosslinking agents, initiators, coupling agents, and functional additives, and do not inherently possess UV protection capabilities.
Anti-UV OCA, however, adds "anti-UV additives" to this structure. These additives effectively absorb high-energy ultraviolet rays and convert them into harmless heat energy, thereby preventing UV light from damaging the LCD panel.
UV OCA Blocking Capability
Specifications typically provide transmittance data for the 340~380nm wavelength range. UV transmittance below 340nm is essentially zero. For specific wavelength blocking requirements, transmittance can be tested accordingly.
There are two common ways to express this:
a. UV (340~380nm) transmittance < 0~1%: The lower the value, the better the blocking effect.
b. UV (340~380nm) absorption/blocking rate > 97~99%: The higher the value, the stronger the blocking capability.
UV-resistant inks
Using UV-resistant inks in outdoor LCD modules is not mandatory; their selection depends on actual product requirements and cost considerations.
However, because outdoor products are often exposed to sunlight, rain, and even corrosive environments (such as charging station displays at the beach), the inks selected for the glass cover (CG) must meet requirements for resistance to salt spray, sweat, and chemicals.
Recommended Application Scenarios
UV-resistant inks are recommended in the following situations:
When the customer has specific UV resistance testing requirements for the CG cover plate;
When the customer requires the LCD module to achieve a "uniform black" effect;
When the ink color is prone to yellowing after UV irradiation, affecting the consistency of appearance, such as with white cover plates.
Mechanism of UV-resistant Inks
Ordinary inks mainly consist of pigments, binders, and functional additives:
Pigments: Determine the color, such as carbon black (black) and titanium dioxide (white). Some pigments have stable structures and possess a certain degree of lightfastness.
Binders: Such as epoxy resins and polyesters, they act as carriers for the pigments and form a protective film after curing.
Functional additives: Such as curing agents and leveling agents, used to adjust the ink's properties.
UV-resistant inks, in addition to these components, incorporate light stabilizers. These stabilizers preferentially absorb ultraviolet light and convert it into heat energy, thus protecting the ink layer from damage.
Anti-UV Polarizing Film (POL)
Whether a polarizing film has anti-UV properties is something many people are unaware of. In fact, polarizing films can be divided into anti-UV and non-anti-UV types.
Anti-UV polarizing films incorporate UV absorbers into the TAC layer, thus blocking UV rays. When selecting a polarizing film, it's essential to confirm with the supplier whether it supports UV protection.
Currently, the commonly used protective layer materials for polarizing films are TAC, PMMA, COP, and PET. Among them:
COP: Weakest UV protection performance
PET: Slightly better than COP
PMMA and TAC: Good UV protection performance
PMMA has low cost but poor water absorption, and is mostly used in large-size TVs; TAC is mainly used in small and medium-sized high-reliability modules.
UV-resistant glass covers
UV-resistant glass covers are widely used in the automotive industry (such as sunroofs and windshields), but less so in outdoor and consumer displays, although their use has been gradually increasing in recent years.
The principle behind them is the addition of metal oxides such as cerium oxide, titanium oxide, and iron oxide to the glass material. These components effectively absorb ultraviolet rays, but also affect the visible light transmittance and color of the glass.
Generally speaking, the visible light transmittance of UV-resistant glass is about half that of ordinary glass; the UV blocking effect is related to the glass thickness-the greater the thickness, the lower the UV transmittance.
Decision Guide: How to Choose and Combine?
Basic Applications: UV-resistant OCA is a must.
High Requirements for Appearance and Weather Resistance: Add UV-resistant ink to the OCA base.
Extremely High Reliability Requirements: Simultaneous use of UV-resistant OCA + UV-resistant polarizer can create "dual protection."
Pursuing Ultimate Performance and Integration: Consider using a UV-resistant glass cover and adjust other supporting solutions accordingly.
Ultimately, the optimal solution is always the result of balancing product positioning, testing standards, and cost budget. Understanding the mechanism and positioning of each solution is crucial for flexible combinations and designing reliable and economical outdoor display products.
