When it comes to the characteristics of reflective markings, it is inseparable from the types of coatings that make up reflective markings. At present, the road traffic markings in China are divided according to the material of marking paint. There are solvent-based, hot melt, water-based coatings and two-component marking, and there is also a newly used reflective marking tape. According to China's Standard of Pavement Marking Coatings (JT/T 280-2004), road traffic marking materials can be divided into four categories: solvent-based road traffic marking materials, hot-melt road traffic marking materials, two-component road traffic marking materials and water-based road traffic marking materials.
Solvent-based coatings, the first used road traffic sign coatings, mainly include acrylic acid and chlorinated rubber. After years of development and application, it has been widely recognized and accepted by people. Generally speaking, the construction is simple and easy, with strong adaptability. The second painting of the old logo is relatively easy, and a new coating can be directly painted on the old coating. Fast drying time, low price, easy maintenance and less one-time investment. However, due to its short service life, a large number of organic solvents in the coating volatilize during construction, which seriously pollutes the environment and endangers the health of construction workers. The increasingly strict environmental protection requirements and limited service life greatly limit the development of this kind of coating, and it has shown a downward application trend in recent years. In some economically underdeveloped areas, small and medium-sized towns and rural roads, there is still a certain market for such products.
Hot-melt marking coatings first developed in Europe in 1950s, and developed rapidly because of its beautiful line shape and durability. In recent years, hot-melt marking coatings have been widely used in high-grade highways and urban roads in China. The high-quality products in this kind of coatings have good reflective effect, good durability, long service life and fast drying time. However, it also has its weaknesses, mainly due to the need for special heating equipment during construction, large emissions, high construction cost, almost accounting for 1/3 of the total cost, low construction efficiency, difficulty in polishing the marking, and the pollution resistance is greatly affected by the construction quality and pavement quality, which is sometimes not ideal.
Waterborne road traffic marking coatings have been developed for a long time in the United States and western Europe, and have been applied to a certain extent. Waterborne paint is a kind of environmental protection paint, and its main advantages are: low volatile organic compounds content, non-flammability, no pollution to the environment, and no harm to the health and safety of construction personnel; No need to clean up the old line, no need to maintain, and the update is safe and convenient; Mechanical equipment is easy to clean. The main disadvantages are: water resistance and adhesion to concrete floor need to be further improved, and construction is greatly affected by environment and weather. It can only be carried out under the conditions that the temperature is above 10 degree, the relative humidity is below 80%, there is no rain within 24 hours, and the road surface is free of water and sand.
Two-component road traffic sign materials are also called reactive road traffic sign materials. Two-component road traffic marking paint is a new solvent-free and environment-friendly road traffic marking material. China began to use epoxy resin in the 1970s, but it was not widely used because of the immature equipment development and construction technology at that time. The basic principle is that the base material and curing agent are mixed in proportion, and chemical reaction takes place in a short time, curing into a tough paint film. At present, two-component road traffic marking materials have been successfully applied in the United States, Germany and other western countries, and some of them have been successfully applied in Shanxi and other places in China, which is a new trend in the development of road traffic marking materials.
Sign tape is a kind of adhesive product. Its biggest feature is that the construction is very simple. High-quality marking tape, made of very good chemical synthetic materials, is hard and soft, easy to construct and has excellent underwater reflection function. Some products can also be freely pasted and removed without damaging the road surface. At present, in the United States, Western Europe, Japan and other developed countries, marking tape is widely used. Due to the cost problem, road traffic markings in China have not been widely used, mainly used in zebra crossings, waterways, stop lines, lane indicator arrows and other non-lane markings. Photo 16 shows the hot-melt zebra crossing and parking line at both ends of the sidewalk near Wuxiang Square in Nanning, Guangxi, which are all-weather rainy night marking belts. On rainy nights, the reflective effect is very ideal. The picture shows 17 road construction workers in Nanning, Guangxi sticking the cut all-weather rainy night marking tape. All-weather reflective marking, with the progress of society and the development of science and technology, the development trend of road traffic marking materials has several characteristics: (1) reducing the pollution of material manufacturing and use to the surrounding environment; Extend the service life of the marking line to make it economical and practical; Improve the visibility of signs —— Improve the visibility of signs at night by premixing reflective materials such as glass beads in the sign paint, especially by upgrading the materials of reflective devices, and provide the visibility of signs in wet environment and rainy night conditions.
With the emergence of all-weather reflective marking technology, the traditional technical standard of measuring marking not only examines the adhesion, wear resistance, weather resistance, anti-fouling and anti-discoloration, anti-skid performance and construction performance of marking, but also increases the reflective performance and brightness performance index in rainy night.
Conventional reflective coatings for road traffic signs use ordinary glass beads. This retro-reflective material has already introduced its reflective characteristics. When light enters another medium from one medium, it will be refracted. Therefore, when the road surface is dry, the light of the car lamp directly enters the glass beads from the air and then reflects back into the air. In the absence of other media, the reflected light can be directly transmitted to the vicinity of the light source and found by the driver, as shown in figure18; But once it rains or the ground is wet, the light of this traditional marking needs to pass through the water film after passing through the air, thus changing the reflection path of the light, as shown in figure 19. The light irradiation path when water film appears on the surface of glass beads is shown in Figure 20. When there is a water film on the glass beads, a lot of light cannot penetrate through the water film to form retroreflection, which affects the retroreflection ability. Without the retroreflection function, the marking line will not be bright, and drivers can't see the roads and lanes clearly, which may easily lead to traffic accidents on rainy nights. How to ensure that traffic markings have the same reflective efficiency when it rains or not is always an insurmountable problem in the traffic marking material industry.
In 2007, the all-weather reflective traffic paint with real underwater reflective ability came out. As the name implies, all-weather reflection means that this marking can reflect light not only in sunny nights and daytime, but also in rainy nights, prompting road users to drive routes, which is conducive to reducing the incidence of traffic accidents at night in rainy days.
The reflective element used in all-weather rainy night marking is no longer a single reflective element structure, but a retro-reflective system composed of two reflective elements. One is glass beads that can achieve retroreflection in dry environment, and the other is special synthetic microcrystalline ceramic beads that can't achieve retroreflection in dry environment. It reflects light at an off-angle and requires the participation of water film to complete retroreflection, so that light can return to the direction of light source, thus completing the process of retroreflection. Fig. 2 1 shows microcrystalline ceramic beads. Under the action of water film, the light bends directionally, resulting in retroreflection effect.
All-weather reflective road traffic signs can be water-based coatings, hot-melt coatings, two-component coatings and signs. According to the climate characteristics and road environmental conditions in the use area, the marking can reflect light under water and dry road by matching the ratio of reflective ceramic beads with unique reflective performance on rainy nights with ordinary reflective glass beads. See fig. 22 and fig. 23 for the experimental and practical effects of all-weather reflective road traffic markings in water. Fig. 24 is the stipulation of the angle and distance in the measurement of the retroreflective coefficient of the marking in the national standard of China. Correctly distinguish the related technical concepts of road traffic reflective marking
In recent years, the development of road traffic reflective markings in China has made great progress. Of course, it is not difficult to find that due to the rapid development of roads, there is a huge demand for traffic markings. This rapid growth has also led to the premature use of some marking products and technologies, resulting in some problems such as marking quality, marking technology and service life. These difficulties not only lead to road traffic safety hazards, but also affect the confidence of people in the industry in reflective marking. To solve this problem quickly and make China's road marking industry develop quickly and well, we must establish the following technical concepts.
(1) The life of road traffic marking materials and the life of reflective brightness of road traffic marking materials are two different concepts.
The service life of road traffic marking material refers to the time when the indicator line material is worn away, which is also called wear resistance. Different marking materials have different film-forming substances (components), fillers and thicknesses, and the wear resistance is affected.
As far as the film-forming material itself is concerned, the film-forming of one-component material is generally not as good as that of two-component or multi-component reaction, but the film-forming thickness can greatly change the wear resistance of one-component film-forming material. Usually we are talking about the life of the marking material itself, not the life of the reflective brightness. The life of reflective brightness refers to the time when the reflective performance of traffic marking materials reaches the standard brightness, that is, the durability of reflective brightness of traffic marking materials is different from the life of traffic marking materials themselves. For example, cold paint, cold paint markings are completely worn off on the road for 3-5 months, but their reflective brightness life is zero; The wear life of hot melt paint is 2 years, but its reflective brightness life is only 3-6 months. Table 2 shows the comparison of reflective brightness of different paints (reticle data comes from 380IES reticle of American 3M company).
Table 2 Life span of different marking materials and their reflective brightness Life span of marking materials and reflective brightness of two-component coatings Life span of marking materials with cold paint and hot melt paint (months) 3 ~ 5 24 24 48 Reflective brightness life span (months)
(≥ 100 MCD/Lx * m)0 3 ~ 6 & gt； 12 48 at present, the durability of reflective brightness of traffic marking coatings is still measured by wear resistance in the standard of pavement marking coatings in China (JT/T 280-2004). The United States, Australia, Finland, New Zealand and other countries have regulations on the retroreflectivity of marking. When the requirement is lower than 100mcd/Lx*m, the marking line must be redrawn, not whether the marking material itself is still intact.
(2) The requirements of road traffic signs for reflective performance should be continuous.
With the development of highways in China, the speed is getting faster and faster, and there are more and more elderly drivers. This change objectively greatly increases the demand for traffic marking brightness. The experimental results show that at the speed of 100km/h, the standard reflective brightness of the marking only gives the driver a recognition time of 3.9 seconds, which is only a normal reaction time. Tired or older drivers need higher reflective brightness. At present, the standard of reflective brightness formulated by most developed countries is the reflective brightness of the road surface 30 meters away from the vehicle.
Besides the interference of water film, the brightness of reflective markings will also be affected by many other aspects. Among them, the typical reflective element is damaged and falls off with the natural aging and wear of the marking paint. Therefore, for the sake of safety, reflective signs should be tested and maintained regularly.
The three micrographs in Figure 25, from left to right, show the surface wear of microcrystalline ceramic beads, high-quality glass beads and ordinary glass beads after 24 months of use in marking. The comparative experiment was conducted by 3M Company and Nevada Department of Transportation on the freeway in Las Vegas, with a daily traffic volume of 65,438+00,000 vehicles.
At present, the road traffic marking materials of expressways in China are basically hot-melt materials. If the road design documents put forward the reflective requirements of the marking, the construction unit will buy hot-melt marking materials with glass beads. The reflective function of this reflective logo will fluctuate and eventually be lost with the loss of the logo. The reason is that the reflective glass beads on the surface of hot-melt materials are easy to be worn off, and the glass beads "buried" inside the hot-melt marking need a certain time, and only after the hot-melt materials on them are worn off again can they be exposed to play a reflective role, which makes the reflective brightness of the marking sometimes poor and unstable. At the same time, in view of this change, it is necessary to find and establish more scientific evaluation and detection standards for reflective markings to meet the higher requirements of safety visual recognition.
For the reflective performance of marking, it is a basic task of road safety and a long-term road maintenance work to continuously check the reflective coefficient of marking and maintain it at any time. Ignore this work, it will form a driving safety hazard.
(3) Establish the concept of reflection brightness in different states.
Road traffic markings should have the following characteristics: clearly visible day and night, concise instructions, eye-catching symbols, and clear identification at high speed; At the same time, it should be able to have certain visibility and reflectivity in rainy days and bad weather, and ensure sufficient sight distance to give the driver a certain time to distinguish. This requires that traffic markings have the lowest reflective brightness to ensure safe driving at different times and in different weather environments, and different reflective brightness values should be stipulated in the standard according to different conditions.
The European marking standard (EN- 1436- 1997) "Road traffic marking materials-performance of road traffic signs" clearly distinguishes the reflective brightness values under dry conditions, rainy days and wet conditions. The measurement methods and requirements of retroreflective coefficient under rainy and humid conditions are also formulated in American measurement standards for marking materials (ASTM 2 176 and ASTM 2 177).
Fig. 26 is a sign with high reflective brightness sprayed with traffic sign paint. Clear road traffic markings can ensure better driving guidance and improve driving safety.
At present, there are only parameters of drying conditions in relevant standards in China. From the point of view of existing traffic conditions and driving safety, it is necessary to formulate the standard of reflective brightness of marking lines in wet and rainy days, and add corresponding detection equipment to the road maintenance system.
British statistics show that although it rains only 65,438+00% of the time, the traffic volume will also decrease during this 65,438+00% of the time, but half of the accidents occur on rainy nights, mostly because the signs are almost unrecognizable after being covered with water on rainy days.
According to the statistics of national road traffic accidents in 2007 (note: White Paper on Traffic Accidents in 2007 by the Traffic Management Bureau of the Ministry of Public Security), although the traffic volume at night is less than 30% of the traffic volume during the day, the number of traffic accidents at night accounts for more than 40% of the total number of accidents, and the number of traffic accidents deaths accounts for 47.8% of the total number; The death toll from traffic accidents in bad weather such as rain, snow and fog accounts for 2 1.6% of the total. Therefore, it is an objective need to improve the standard value of reflective brightness of traffic marking coatings in China to meet the traffic safety needs under all-weather conditions.