The "invisible technology film" on glasses: Unveiling the physical vacuum coating black technology of lenses and frame

When you wear lightweight and comfortable titanium alloy glasses that allow you to see clearly in strong light without causing eye strain, and the frame remains shiny and new even after long-term use, and your skin shows no allergic reaction, all of this is inseparable from a key technology - Physical Vacuum Deposition Coating (PVD). As the core surface treatment process in modern eyewear manufacturing, PVD technology simultaneously enhances both the lenses and the frames: giving the lenses practical functions such as anti-blue light and anti-reflection, and creating a durable, beautiful, and skin-friendly surface texture for the frames. This seemingly insignificant "invisible film" has already become the core support for improving the wearing experience of eyewear. Today, we will fully demystify the PVD technology behind eyewear lenses and frames.

To understand the physical vacuum coating technology in the eyewear field, one must first clarify its core definition: In a high vacuum environment, through physical methods such as magnetron sputtering and evaporation, the coating materials like metals, ceramics, and compounds are transformed into atomic and ionic states, and then deposited on the surface of eyeglass lenses or frames to form ultra-thin films. This technology is abbreviated as PVD (Physical Vapor Deposition) in English. Compared with traditional electroplating and chemical coating, its greatest advantage lies in the uniformity and density of the film layer, strong adhesion, environmental friendliness and no pollution (no emission of heavy metals), and the ability to precisely control the thickness and composition of the film layer, perfectly meeting the strict requirements of eyeglasses for precision, safety and durability. Whether it is the functional coating on the lens or the decorative and protective coating on the frame, PVD technology can achieve a "tailor-made" effect.

Let's first take a look at the physical vacuum coating of the eyeglass frame - its core value lies in "aesthetic upgrade + functional protection", and it is widely applied in mainstream materials such as titanium alloy and stainless steel. The frame, as a component that directly contacts the skin and is exposed to the external environment for a long time, has extremely high requirements for the wear resistance, corrosion resistance, and skin-friendly properties of the coating. And the PVD technology precisely meets these requirements. The core principle of PVD coating on the frame is to adjust the combination of the target material and the reactive gas to form different component film layers on the surface of the frame, thereby achieving various colors and protective functions. For example, for common titanium alloy frames, the base material is light gray. Through PVD coating, it can be transformed into various fashionable colors such as rose gold, champagne gold, and matte black, while forming a hard protective film that resists the erosion of sweat and cosmetics.

The common types of PVD coating for spectacle frames can be classified into two categories: decorative layers and functional layers. The decorative layers are the core for enhancing the appearance of the frames. They are achieved through the magnetron sputtering process: the rose gold effect is produced by combining a titanium target with nitrogen and a small amount of methane to form a carbon nitride (TiCN) layer; champagne gold is prepared by adjusting the ratio of nitrogen and argon, resulting in a more gentle tinted titanium nitride (TiN) layer; matte black is a carbonitride (TiC) layer formed by the reaction of a high concentration of methane with the titanium target, combined with the base material's sandblasting pretreatment to achieve a matte texture. The thickness of these layers is usually between 2 and 5 micrometers, which is only one-tenth of the diameter of a hair strand, yet they can give ordinary alloy frames the texture of high-end precious metals. The functional layers focus on practical needs. For example, the diamond-like carbon (DLC) layer is prepared through the arc ion plating process, with a hardness of over HV2000, which can make the frame surface wear-resistant and scratch-resistant, and even after long-term friction, it is unlikely to produce scratches; the anti-fingerprint layer is coated with a special fluorocarbon compound, making fingerprints difficult to adhere and making cleaning more convenient.

Unlike the frame which focuses on "decorative and protective" functions, the core of the physical vacuum coating of eyeglass lenses is "optical function optimization", aiming to enhance visual clarity and protect eye health. As a medium for light refraction, the surface reflection, light transmittance, and anti-fouling ability of the lens directly affect the visual experience. And the PVD technology can solve these optical problems by superimposing multiple layers of different functional films. The PVD coating of the lens usually adopts a multi-layer stacked structure, with each layer of film layer bearing different functions. Commonly seen ones include anti-reflective film, anti-blue light film, wear-resistant film, hydrophobic and anti-fouling film, etc. The total thickness of these film layers is only a few hundred nanometers, yet they can achieve an "1 + 1 > 2" optical effect.

The anti-reflection coating is the most fundamental and important PVD (Physical Vapor Deposition) layer of the lens, and it is equipped on almost all optical lenses. We know that when light hits the surface of the lens, it will produce reflection, which not only reduces the light transmittance and causes blurred vision, but also generates glare (such as the light glare during night driving). The anti-reflection coating deposits multiple layers of dielectric films such as silicon oxide and titanium oxide through the magnetron sputtering process, and utilizes the "film interference" principle to cancel out the reflection of light: when the film layer thickness is one quarter of the wavelength of the incident light, the reflected light will cancel each other out, thereby significantly improving the light transmittance. The light transmittance of an uncoated lens is approximately 91%, while after multi-layer anti-reflection PVD coating, the light transmittance can be increased to over 98%, making vision clearer and brighter. The anti-blue light coating is a functional layer developed to meet the needs of modern people who use electronic devices for a long time. By adding special metal oxides (such as niobium oxide) to the film layer and using the PVD process to precisely control the film layer structure, it can selectively absorb harmful blue light in the range of 400-450 nanometers, while ensuring the normal transmission of visible light and reducing the stimulation of blue light to the eyes, alleviating eye fatigue.

Apart from the optical functional coating layer, the wear-resistant coating and the hydrophobic anti-fouling coating of the lenses also rely on the support of PVD technology. Although resin lenses are lightweight and impact-resistant, their surface hardness is relatively low, making them prone to scratches and affecting the light transmittance. The wear-resistant coating is deposited with an oxide silicon or oxide aluminum film layer through the PVD process, increasing the surface hardness of the lenses from HB level to above H level. Even with daily wiping, it is unlikely to cause scratches. The hydrophobic anti-fouling coating is the "top-level protection" of the lenses. It is deposited with a fluorine-containing compound film layer through magnetron sputtering, making the surface of the lenses exhibit superhydrophobic properties, with a contact angle greater than 110 degrees. Water droplets falling on the lenses will automatically roll off, and at the same time, it can resist the attachment of oil, dust, and achieve the effects of "easy cleaning, anti-fogging, and anti-fingerprint". These functional coating layers are precisely superimposed through the PVD process, making the lenses both clear and durable, and also protecting the eyes' health.

It is worth noting that although the PVD coating processes for the lenses and the frames are of the same origin, due to the different material properties, there are significant differences in the process details. The frame base material is mostly metal (titanium, stainless steel, aluminum alloy), and before coating, plasma cleaning is required to remove surface oil and oxide layers to enhance the adhesion of the coating layer; while the lens base material is mostly resin or glass, which is more brittle. During the coating process, the cavity temperature needs to be strictly controlled (usually below 100°C) to avoid lens deformation. In terms of process selection, the decorative coating for the frame mainly uses magnetron sputtering to ensure uniform and fine coating layers; while the functional coating for the lens mostly adopts multi-target magnetron sputtering, which can precisely stack multiple layers of different components. In addition, the detection standards for the coating layers of the two are also different: the coating on the frame focuses on wear resistance, corrosion resistance, and color consistency, and needs to pass salt spray tests, friction tests, etc.; the coating on the lens focuses on optical performance, and needs to test optical indicators such as light transmittance, reflectance, and blue light blocking rate.

The physical vacuum coating technology not only enhances the performance and appearance of glasses, but also promotes the green development of the eyewear industry. The traditional electroplating process for frame production generates wastewater containing heavy metals, polluting the environment. However, the PVD process is carried out entirely in a high-vacuum environment, without the need for chemical electrolytes, resulting in zero emission of heavy metals and zero pollution, which aligns with the global environmental protection trend. For lenses, compared to traditional chemical coatings, PVD coating has a more uniform film layer, stronger adhesion, longer service life, and reduces the need for lens replacement due to coating detachment, indirectly reducing resource consumption. Nowadays, PVD coating has become a standard technology for mid-to-high-end eyewear. Whether it is a titanium alloy frame priced at a thousand yuan or a lens with anti-blue light function, they all rely on this black technology for support.

From the fashionable colors of the frame to the clear vision of the lenses, the physical vacuum deposition coating technology, with its precise micro-metric craftsmanship, has redefined the wearing experience of glasses. This "invisible technological film" may seem insignificant, but it embodies the integration and innovation of materials science and optical technology. It not only meets people's pursuit of the aesthetics of glasses, but also safeguards the health of the eyes. When we wear glasses next time, we might as well pay attention: the warm luster of the frame and the clear transparency of the lenses are all the "technological warmth" bestowed by the PVD technology. With the continuous advancement of technology, future PVD coating for glasses will achieve more precise functional customization, such as adaptive light-sensing intelligent coating and thinner multi-layer composite films, making glasses not only tools for correcting vision, but also wearable artworks that combine health, fashion and technology.