Compared with the long-distance truncated micro-prism reflective film, the front brightness of the large-angle truncated micro-prism reflective film is relatively low, but its reflective brightness will not be greatly attenuated at large incident angle and large viewing angle. Large angles correspond to places with many lanes and bends, as well as signs with complex contents and long reading time, so this kind of reflective film is suitable for traffic signs on urban roads and wide roads. Although its front reflective brightness is average at a long distance (only compared with the prism level at a long distance, it can still reach more than twice the high intensity level), at a short distance (the distance to read the logo content), its reflective brightness is much higher than that of the long-distance reflective film. Its directivity is stronger than that of long-distance reflective film, and it can be adjusted according to the position and direction of the sign to meet the needs of reading. Fig. 6 shows the structure of VIP large-angle truncated microprism under microscope. VIP (visual impact prism), translated as visual impact prism, came out in the late 1980s and was once widely used. After the full prism technology appeared, it was discontinued. All-prism reflective film is a prism-type reflective film made of all-prism structure, and its characteristics have been introduced in chapter 2. In short, it is to remove the part of the traditional microprism structure that can't reflect light, so that the reflective film is all composed of prism structures that can realize total reflection. It combines the two characteristics of long-distance and large-angle micro-prism reflective films, and improves the reflection brightness at large incident angle and observation angle of 50-250 meters while maintaining high front brightness and being easy to find at a long distance.
The advent of this kind of all-prism reflective film breaks through the academic barrier that prism reflective film can not give consideration to both long-distance reflection ability and short-distance reflection ability at the same time. According to the path and mode of vehicle light propagation, it finds the angles (incident angle and observation angle) needed for sign recognition within an ideal distance, then determines the non-reflective areas on the traditional truncated microprism, and then removes these non-reflective areas, so as to realize the reflective structure area per unit area 100% on the reflective film, which is called "total reflection".
Of course, from the actual reflection effect, this is only the theoretical reflection efficiency 100%. In actual production, due to the limitation of materials and other conditions, the brightness of reflective headlights cannot reach 100%. At present, the best reflection efficiency is 58%, which is much higher than other types of reflective films, such as high-intensity reflective films, only 23%. And from the observation angle of 0.2? From the beginning to 2 o'clock? Its retroreflection efficiency is always above 50%. Fig. 7 is an electron micrograph of a full prism reflection film.
At present, after each microcrystalline cube is connected and arranged according to certain rules, there will be more than 930 units in a square centimeter of material area to control the path of light entering and reflecting. The lower layer of the microcrystal cube corner is sealed to form an air layer, and the incident light is totally reflected inside by the diffraction phenomenon of light, and the best reflection effect can be achieved without the help of a metal reflection layer. Compared with the traditional engineering-grade high-strength reflective film, the reflective film made of wear-resistant high-hardness polycarbonate material and microcrystalline cubic technology not only doubles the reflective performance, but also greatly improves the large-angle reflective performance. The front brightness of this full prism reflective film is more than 6 times that of engineering grade, and the front brightness of white film (0.2? /-4? ) is generally above 600 cd/lx/m, which is more than twice the high-strength grade, while under the measurement of the grand view angle (0.5? And second? When), the retroreflective performance is about two to four times higher.
All-prism reflective film is a kind of traffic sign material suitable for all grades of highways and urban roads. The application in the west has gradually replaced the investment and consumption of sign lighting. When making road signs, if the long-term investment benefit and safety benefit are considered, the full prism reflective film can replace any grade of reflective film. Under normal use conditions, after ten years of use, the retained brightness of the full prism is at least 80% of the initial brightness, that is, after ten years, it can still greatly exceed the retroreflection performance of the brand-new high-strength and engineering-grade reflective film, which is a more economical choice from the perspective of scientific development. At the same time, if the same ink is used, combined with screen printing technology, various traffic signs with patterns can be made.
All-prism reflective film is mainly used for guiding signs, prohibition signs, warning signs and indicating signs, especially for signs that need to be read for a long time, signs with complex visual environment, wide roads and high-grade highways, and its performance is particularly outstanding. The suitable bottom plate of diamond-grade reflective film is aluminum plate, and the processing temperature is generally required to be above 18 degrees Celsius.
Fig. 8 is a comparison of retroreflection brightness values of engineering-grade reflective film, high-intensity grade, truncated prism and total prism at various angles. With the progress of science and technology, the photometric performance of all-prism reflective film has been significantly improved at all angles. In recent years, under the condition that the structure of prism-type reflective film has not changed greatly, the focus of innovation has shifted more to achieve richer light control effect and rich material characteristics through different material processing technologies, so as to achieve different reflective ability and flexibility to meet the needs of different levels. The reflective films commonly known as "super", "super" and prism engineering grade (new super engineering grade) in the market are all new forms of prism reflective films. The truncated prism structures of these reflective films are basically the same, but the processing techniques of the materials are different, resulting in different reflection effects, superior weather resistance and processing adaptability, which meet different application requirements.
Among them, especially the super-strong reflective film, because it conforms to the market demand, it quickly became popular after it came out at the beginning of 2 1 century. Its original design intention is to give full play to the advantages of prism structure, and on the basis of ensuring that it can surpass all functions of high-strength reflective film, it can also have better retroreflective performance and superior cost performance under multi-angle conditions.
These new prism reflective films have very high strength and thickness, which eliminates the defects of easy tearing, wrinkling, bubbles and surface honeycomb protrusions in logo processing, greatly simplifies the construction difficulty, makes the logo processing process easier to control and reduces the losses caused by poor processing. At the same time, due to the large surface brightness factor of the reflective film, the retroreflection performance is greatly improved. It not only has superior retro-reflection coefficient at a long distance, but also can keep the sign bright at a large observation angle at a close distance under general visual requirements, so that the driver can find the sign earlier and read the sign content more clearly at a close distance. Fig. 9 is a schematic structural view of these prism-structured reflective films. Different retro-reflection effects can be formed by the material treatment difference between the resin layer and the cubic crystal surface.
The surface of this kind of reflective film is mostly made of polycarbonate, which is not only more wear-resistant and scratch-resistant, but also can be used with screen printing ink, and can also be used for thermal transfer to make color traffic signs. At the same time, due to the improvement of the surface brightness coefficient, the signboard is more eye-catching and bright during the day, and it also has better weather resistance.
It is worth mentioning that in the 2008 Beijing Olympic Games, which had strict requirements on all aspects of traffic signs, Beijing traffic management authorities used this reflective film to complete the preparation task of the event with high quality and high speed, making China the first country in the history of the Olympic Games to use this reflective film to make special lane warning signs. This also shows from one side that the production technology of traffic signs in China has rapidly approached the international advanced level. See figure 10.
Figure 10(a) is an ultra-high reflective film sign being installed, and the color part on it is printed by the printer. Figure (b) shows the super-reflective film being printed. The biggest difference on the surface of super reflective film is the unique stripe pattern, as shown in Figure (c). This is a characteristic that other reflective films do not have.
The prism engineering-grade reflective film that came out in 2008 is also a brand-new product concept. While ensuring the front brightness performance of traditional engineering-grade reflective film, it has made great progress in large-angle reflective performance, and its retroreflection ability even exceeds the parameters of high-intensity reflective film. At the same time, due to the use of polycarbonate, this kind of reflective film has the ability of hardness and high weatherability, which can greatly improve the construction efficiency and provide more technical choices for the application and popularization of retroreflective materials. After the full prism structure, there is no breakthrough in the structure of the reflective film. However, there is still a lot of room for development in terms of cost, materials and chemical coating. Fluorescent reflective film is a typical case, in which the coating technology has been improved to further optimize the function of reflective film. Fluorescent full prism reflective film is a kind of reflective film with special optical effect, which combines special fluorescent materials with excellent weather resistance (general fluorescent materials have poor weather resistance) with full prism technology. There is a unique weather-resistant fluorescent factor in the fluorescent reflective film, which can increase the activity after absorbing the energy of visible light and part of invisible light in the spectrum, thus converting the energy of invisible light into the energy of visible light, making the chromaticity and luminosity of the reflective film stronger during the day, thus increasing the distinctiveness of the sign.
Because the fluorescent reflective film can absorb the energy of invisible light in the spectrum and convert it, it can have better chromaticity and luminosity, which is called more vivid. This fluorescent reflective film is much brighter than ordinary colors in bad weather conditions and when the sun is not so strong, and it is easier to attract people's attention. The use of this fluorescent reflective film in traffic safety facilities is of great significance to ensure driving safety at dawn, dusk or in bad weather such as rain, snow and fog. At present, the application of fluorescent full prism reflective film has been very common in foreign countries, such as fluorescent warning signs, fluorescent linear delineator, and fluorescent signs in road construction areas. Yellow-green fluorescent full prism reflective film has been approved by the Federal Highway Bureau as a traffic sign for pedestrians, non-motor vehicles and school areas. Orange fluorescent full prism reflective film is often used for building area signs. Countries all over the world have also issued corresponding standards and specifications and technical conditions for fluorescent reflective films. Figure 1 1 is a comparison between fluorescent and non-fluorescent reflective films.
Fluorescent yellow reflective film and fluorescent yellow-green reflective film have been used in China since 2006. The fine acceptance and application of this new technology can be seen in the rainy and foggy section of Sichuan-Emeishan Expressway, the accident-prone section of Badaling Expressway in Beijing and the Olympic lane on the Fifth Ring Road in Beijing. See figure 12 and figure 13. Figure 3- 14 The sidewalk warning signs near the water stadium of the Beijing Olympic Games are made of fluorescent yellow-green full prism reflective materials to improve the visual recognition effect of the warning signs. Pay attention to the difference in luminosity and chromaticity of warning signs using ordinary reflective films next to them. In order to ensure the Olympic traffic, a speed warning device with fluorescent yellow-green full prism reflective film is being installed on the Fifth Ring Road (Figure 13). It is worth noting that other traffic signs are not good in chromaticity and luminosity under backlight, but the area of fluorescent yellow-green full prism reflective film is very eye-catching.
It should be noted that the fluorescent reflective film is a combination of weather-resistant fluorescent factor and prism reflective film. Advertising materials printed with lemon yellow do not belong to this technical category. Although the surface looks similar in chromatography, it does not have all the technical characteristics of fluorescent reflective films.