The retroreflective principle of microprism reflective film is different from that of engineering grade (embedded lens) and high-strength grade (lens sealed) reflective films. Both engineering grade and high-strength grade reflective films adopt the glass bead reflection principle. The reflection principle of microprism reflective film is to use the refraction and reflection of microprisms. The main representative products of microprism reflective film can be divided into four categories in terms of retroreflective characteristics and structure: truncated prisms that focus on long-distance legibility, truncated prisms that focus on short-range and wide-angle legibility, and truncated prisms that focus on long-distance legibility. Full prisms with distance recognition performance and short-range reading performance, and new prism-type reflective films that combine these prism technologies with new material technologies. They are new reflective materials that comply with the diversification of application levels and have emerged in recent years to meet the needs of different levels. After the first generation of microprism reflective film came out, people discovered a problem. When a motor vehicle actually drove into the reading distance of the sign, that is, at a large viewing angle, the brightness of the sign attenuated so much that it Within the reading distance, the content of the sign cannot be read, or it may take longer to read. As a result, people used the large-angle truncated microprism structure to create large-angle truncated microprism reflective films (see Chapter 2) to solve the problem of maintaining two degrees of the mark within the reading distance. Therefore, this kind of large-angle reflective film is also a special prism-type reflective film described in terms of reflective performance.
Compared with the long-distance truncated microprism reflective film, the front brightness of the large-angle truncated microprism reflective film is relatively low, but at large incident angles and observation angles, its reflective brightness will not be as good. Great attenuation. The large angle corresponds to locations with multiple lanes and curves, as well as signs with complex content that require a long reading time, so this kind of reflective film is suitable for traffic signs on urban roads and wide roads. Although its frontal reflective brightness at a long distance is average (only compared to the long-distance prism level, it is still more than twice as high as the frontal brightness of the high-intensity level), but at close range (when reading the logo content is required) distance), its reflective brightness is much higher than that of long-distance reflective film. Its directionality 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. Figure 6 shows the structure diagram of the VIP large-angle truncated microprism under a microscope. VIP (Visual Impact Prismatic), translated as visual impact prism, came out in the late 1980s and was once widely used. It was discontinued after the emergence of full prism technology. Full-prism reflective film is a prism-type retroreflective material using a full-prism structure. Its characteristics have been introduced in Chapter 2. Simply put, it removes the non-reflective parts of the traditional micro-prism structure, so that the reflective film is entirely made of materials that can It is composed of a prism structure that achieves total reflection. It combines the two characteristics of long-distance and large-angle microprism reflective films. While maintaining high front brightness and easy detection at long distances, it improves the reflective brightness at large incident angles and observation angles at a distance of 50-250 meters. .
The advent of this full-prism reflective film breaks through the academic barrier that prismatic reflective films cannot take into account both long-distance and short-distance reflective capabilities. Based on the path and mode of car light propagation, it finds the angles (incident angle and observation angle) required for sign recognition within the ideal distance, then determines the non-reflective areas on the traditional truncated microprisms, and then converts these non-reflective areas into The area is removed, thereby achieving 100% of the reflective structure area per unit area of ??the reflective film, which is the so-called "total reflection".
Of course, judging from the actual reflective effect, this is only the theoretical reflective efficiency of 100%. In actual production, due to limitations of materials and other conditions, 100% of the brightness of reflective car lights cannot be achieved. Currently, the best reflection efficiency is 58%, which is much higher than other types of reflective films, such as high-intensity reflective films. Efficiency, only 23%. Moreover, from the observation angle of 0.2° to 2°, the retroreflection efficiency can always remain above 50%. Figure 7 is an electron micrograph of the full prism reflective film.
On the current full prism reflective film, after each microcrystalline cube is connected and arranged according to a certain rule, there will be more than 930 units on a square centimeter of material area to control the incidence of light. and reflected paths. The lower layer of the microcrystalline cube corner is sealed to form an air layer, which uses the diffraction phenomenon of light to form total internal reflection of the incident light, thereby achieving the best reflective effect without the need for a metal reflective layer.
Compared with traditional engineering-grade and high-strength grade reflective films, this kind of reflective film made of wear-resistant and high-hardness polycarbonate material and microcrystalline cube technology not only has doubled its reflective performance, but also has better large-angle reflective performance. Great improvement. The front brightness of this full-prism reflective film is more than six times that of the engineering grade. The front brightness of the white film (0.2?/-4?) is generally above 600 cd/lx/m, which is more than twice that of the high-intensity grade. Large observation The retroreflective performance at angles (0.5° and 2°) is about two to four times higher.
Full prism reflective film is a traffic sign material suitable for all grades of highways and urban roads. Applications in the West have gradually replaced the investment and consumption of sign lighting. When making road signs, if we consider long-term investment benefits and safety benefits, full-prism reflective film can replace any grade of reflective film. Under normal use conditions, the retained value of full-prism reflective brightness after ten years of use is at least 80% of the initial brightness value. That is, after ten years, it can still greatly exceed the retroreflection of new high-strength and engineering-grade reflective films. Performance is a more economical choice when viewed from the perspective of scientific development. At the same time, if the same type of ink is used, combined with screen printing technology, various types of traffic signs with patterns can be produced.
Full prism reflective film is mainly used in guide signs, prohibition signs, warning signs and instruction signs, especially signs that require a long time to read, signs with complex visual environment, as well as wide roads and high-grade On the road, its performance is particularly outstanding. The suitable base plate for diamond grade reflective film is aluminum plate, and the processing operating temperature is generally required to be above 18 degrees Celsius.
Figure 8 is a comparison of the retroreflective brightness values ??of engineering-grade reflective film, high-strength grade, truncated prism and full prism at various angles. With the advancement of technology, the photometric performance of full-prism reflective films at all angles has been significantly improved. In recent years, prismatic reflective films, without major changes in structure, have shifted the focus of innovation to achieving richer light control effects and rich material properties through different material processing technologies. Complete different retroreflective capabilities and different flexibility to meet the needs of different levels. Reflective films commonly known as "super-strength grade", "extra-strength grade" and prismatic engineering grade (new super engineering grade) in the market are all new forms of prismatic reflective film. The truncated prism structures of these reflective films are basically the same, but the material processing techniques are different, resulting in different reflective effects, superior weather resistance and processing adaptability to cope with different application needs.
Among them, especially the super-strong reflective film, it has quickly become popular after its advent in the early 21st century because it has complied with market demand. The original intention of its design is to take advantage of the prism structure, ensure that it can surpass all functions of high-strength reflective film, and also have better retroreflective performance and superior cost performance under multi-angle conditions.
These new prismatic reflective films have very high strength and thickness, which eliminate defects such as easy tearing, wrinkles, bubbles, and honeycomb protrusions on the surface of the reflective film during sign processing, greatly simplifying the difficulty of construction. , making the sign processing process easier to control and reducing losses caused by poor processing. At the same time, due to the large surface brightness factor of the reflective film, the retroreflective performance is greatly improved. It not only has a superior retroreflection coefficient at long distances, but under general visual recognition requirements, the large observation angle at close range can still maintain good brightness of the signs, allowing drivers to detect signs earlier and Read the signs more clearly at a closer distance. Figure 9 is a schematic structural diagram of these prism structure reflective films. Different retroreflective effects can be formed through differences in material processing of the resin layer and cubic crystal surface.
The surface layer of this type of reflective film is mostly made of polycarbonate material, which is not only more wear-resistant and scratch-resistant, but can also be used with screen printing inks and thermal transfer printing to produce colorful traffic signs. . At the same time, due to the increase in surface brightness factor, the signboard is more eye-catching and bright during the day, and it also has better weather resistance.
It is worth mentioning that at the 2008 Beijing Olympics, which had strict requirements on traffic signs in all aspects, the Beijing Municipal Traffic Management Bureau used this kind of reflective film to complete the preparations for the event with high quality and speed. mission, making China the first country in the history of the Olympic Games to use this kind of reflective film to make special lane prompt signs. This also shows from one aspect that China's traffic sign production technology has quickly approached the international advanced level. See Figure 10.
Figure 10(a) shows the super reflective film sign being installed. The colored part above is printed by a printer. Picture (b) shows the super reflective film being printed. The most distinctive feature of the super reflective film surface is the unique stripe pattern in Figure (c). This is a feature that other reflective films do not have.
The prism-type engineering-grade reflective film, which was only launched in 2008, is also a brand-new product concept. While ensuring the front brightness performance of traditional engineering-grade reflective films, it has made great progress in large-angle reflective performance. The retroreflective ability even surpasses the parameters of high-strength reflective films. At the same time, due to the use of polycarbonate materials , making this kind of reflective film hard and highly weather-resistant, which can greatly improve construction efficiency and provide more technical options for the application and promotion of retroreflective materials. Reflective films after the full prism structure have not yet made any structural breakthroughs. However, there is still a lot of room for development in the cost, material and chemical coating of reflective film. Fluorescent reflective film is a typical example of improving coating technology to further optimize the function of reflective film. Fluorescent full prism reflective film is a reflective film with special optical effects that 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 the invisible light in the spectrum, thereby converting the energy of invisible light into the energy of visible light, making the chromaticity of the reflective film and luminosity play out more powerfully during the day, thus increasing the conspicuity of the logo.
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 the so-called more vivid. This kind of fluorescent reflective film, under bad weather conditions and when the sun is not so strong, is much brighter than ordinary colors and 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 severe weather such as rain, snow, fog, etc. At present, fluorescent full-prism reflective films are widely used abroad, such as fluorescent warning signs, fluorescent linear delineators, fluorescent signs in road construction areas, etc. The yellow-green fluorescent full-prism reflective film has been approved by the US Federal Highway Administration for use in traffic signs for pedestrians, non-motor vehicles and school areas; the orange fluorescent full-prism reflective film is mostly used for construction area signs. Countries around the world have also introduced corresponding standards, specifications and technical conditions for fluorescent reflective films. Figure 11 is a comparison of fluorescent and non-fluorescent reflective films.
In China, since 2006, fluorescent yellow reflective films and fluorescent yellow-green reflective films have begun to have some applications. The Chinese traffic engineering community's detailed understanding of this new technology can be seen in the rainy and foggy section of the highway from Sichuan to Mount Emei, the accident-prone section of the Badaling Expressway in Beijing, and the Olympic-only lanes on the Fifth Ring Road in Beijing. and application play. See Figure 12 and Figure 13. Figure 3-14 The sidewalk warning signs near the Beijing Olympic water sports venue use fluorescent yellow-green full-prism reflective materials to improve the visual recognition of the warning signs. Pay attention to the difference in luminosity and chromaticity of warning signs using ordinary reflective film next to them. In order to ensure Olympic traffic, speed reminder equipment with fluorescent yellow-green full-prism reflective film is being installed on the Fifth Ring Road (Figure 13). It is worth noting that under backlighting, other traffic signs have poor chromaticity and luminosity, but fluorescent signs The yellow-green full-prism reflective film area is very eye-catching.
It should be noted that fluorescent reflective film is a combination of weather-resistant fluorescent factors and prism-type reflective film. Advertising materials printed with lemon yellow do not fall into this technical category, although the color spectrum appears to be close to , but does not have all the technical characteristics of fluorescent reflective film.