Road marking lines serve as warning signs during road traffic, primarily playing a role in guiding and reminding drivers, making them a crucial aspect of road traffic management. One key aspect of road marking lines is their requirement to provide effective reflectivity even during night or rainy conditions to ensure traffic safety and prevent accidents. Therefore, the reflectivity of road marking lines is vital for safe driving. The core component that enables road marking lines to reflect is glass microspheres with refractive indices, which offer nighttime reflectivity to the road system, enhancing driving convenience and safety during night-time transportation. The choice of glass microspheres is crucial. This article analyzes the main factors affecting the reflectivity of road marking lines, including the selection of glass microspheres, construction techniques, and types of markings. It then proposes several methods to improve the reflectivity of road marking lines and offers an initial analysis of the development trends in road marking reflectivity.
1. Factors Affecting the Reflectivity of Road Marking Paint
1.1 Selection of Glass Microspheres
1.1.1 Roundness and Diameter of Glass Microspheres
The roundness of glass microspheres directly affects the retroreflective ability of road markings. The higher the roundness, the better the retroreflective effect. Only glass microspheres with a roundness greater than 90% can ensure that incident light is reflected back to the driver's eyes, thus maintaining the retroreflective direction and improving the retroreflective coefficient. Glass microspheres with low roundness cause multiple irregular refractions of light within the spheres, losing most of the light and failing to produce a good retroreflective effect. This leads to light deviating from the driver's field of view, poor retroreflectivity, and increased risk of accidents.
On the other hand, glass beads may experience varying degrees of wear and fall off during road commuting. To ensure the bonding performance and reflective continuity of the road marking paint mixed with glass, the particle size of the glass beads must be graded to guarantee optimal reflective performance of the markings. If the diameter is too large, the beads will be less deeply embedded in the marking and more prone to falling off under external forces; if too small, they may all sink into the marking, resulting in poor reflective effects; and if unevenly sized, the smaller glass microbeads are easily obscured by the larger ones, preventing the reception of light from vehicle headlights and failing to create effective retroreflective patterns. Therefore, selecting glass microbeads with the appropriate particle size is crucial for the reflective performance of road markings.
1.2 The Impact of Construction Techniques on the Reflectivity of Road Markings
1.2.1 Embedding Degree of Glass Microspheres
The embedding degree of glass microspheres in the coating film affects the visibility and retroreflective coefficient of the markings, directly reflecting the intensity of the regressive reflection. Experiments show that when the embedding degree is between 40% and 50%, the regressive reflection is poor; at around 60%, the effect is good; and it decreases when reaching 60% to 80%. Generally, the embedding degree of glass microspheres is highly related to the application time, the viscosity of the coating, and the density of the glass microspheres. When the coating viscosity is high, the density of the glass microspheres is low, and the application time is late, the embedding degree is shallow, and some glass microspheres become floating beads, easily falling off under external forces, causing a rapid decrease in the retroreflective coefficient of the markings and shortening the effective lifespan of the reflective markings. Conversely, when the coating viscosity is low, the density of the glass microspheres is high, and the application time is early, the embedding degree may be too deep, causing multiple reflections of light within the glass microspheres and preventing refraction. Therefore, only glass microspheres with appropriate coating viscosity, density, and application time can achieve a suitable embedding degree and form effective regressive reflection.
2.2.2 Spraying Amount of Microspheres
The amount of glass beads scattered is equally influential on the reflective performance of road markings as the degree of embedding. Insufficient scattering of glass beads prevents the formation of a concentrated reflective return from the incident light source, resulting in poor reflective performance of the road markings. Excessive scattering can lead to overly dense refraction, causing bead accumulation and overlapping, with some beads embedding less deeply into the coating. This leads to repeated refraction of light between the beads, preventing the light from returning to the driver's eyes after several refractions, thus compromising the reflective performance of the road markings. Issues such as darkened markings and easily falling glass beads arise, and this also increases the cost of road marking installation. Research indicates that an appropriate amount of glass bead scattering is between 0.37-0.45 Kg/m³.
Method to Improve Line Marking Reflectivity
2.1 High-refractive glass microspheres adopted
The higher the refractive index of glass microspheres, the better the reflective performance of the road markings. Considering the impact of the refractive index of glass microspheres on the reflective performance of road markings, it is advisable to choose glass microspheres with a roundness of over 90% and a high refractive index to better achieve the reflective performance of road markings in rainy and night conditions, thereby enhancing their nighttime visibility.
2.2 Utilizing new type of line marking paint
2.2.1 Two-component line marking paint
The two-component road marking paint offers excellent adhesion to both cement and asphalt surfaces, dries quickly, and has a long effective lifespan. After curing, it exhibits strong hardness and mechanical strength, as well as a robust bond with glass beads, making it an environmentally friendly and durable road marking paint. In the past, China extensively used epoxy resin as the matrix resin for road marking paints, but due to slow development, primitive equipment, and an immature construction process, it eventually temporarily exited the road marking paint market. The German Road Research Institute conducted numerous experiments, with data indicating that two-component road marking paint is a high-performance coating. Among them, acrylic-based two-component road marking paints have seen rapid development, requiring no heating during application. After mixing the base material with the hardener, a chemical cross-linking reaction forms a hard coating, which has strong adhesion to the road surface and glass beads, dries quickly, and has a long effective lifespan. Since the coating of the two-component paint is cross-linked, it boasts excellent durability and ease of re-coating. However, two-component road marking paints are more expensive, have strict application standards, and must be mixed and used immediately.
2.2.2 Water-Based Line Paint
Water-based road marking paint uses water-based resins as the base material, featuring excellent reflective properties, high application efficiency, short drying time, long service life, low construction costs, and strong adhesion to glass beads. It can provide reflective visibility in rainy nights and has good recoating performance with good temperature resistance. Notably, the VOC content of this paint is below 125g/L, meeting current market demands. Currently, as the technology for water-based road marking paint in our country is still in the stage of continuous development and trial use, although water-based road marking paint has been promoted for a long time in China, its application is limited due to high prices, longer drying times, poor water resistance, and issues like yellowing during application. It is believed that with the increasing awareness of environmental protection and the increasingly severe environmental situation, water-based road marking paint will undoubtedly become the mainstream in the next few years.
2.3 Implementing new construction techniques
Whether it's hot melt road marking paint, two-component road marking paint, or water-based road marking paint, the main construction techniques are scraping and spraying. Spraying offers excellent durability, no cracking, strong reflectivity, high anti-slip value, and good recoating performance. Especially in recent years, the development of high-pressure airless spraying technology has created conditions for the application of high-viscosity paints and two-component paints with short curing times. This process has high coating efficiency, fewer spraying times, and superior film quality, even without the need for thinner, reducing environmental pollution.
