Microprism reflective material and its application prospect
Microprism reflective material is a new functional composite material developed in recent 50 years. The micro prism type reflective film developed in the late 80s. Because of its high brightness, good durability and low material cost, it overcomes the shortcomings of small angle of effective incidence, small angle of observation, and asymmetry of reflected light beam in the past, so it is becoming more and more widely used in high brightness Road traffic.
Reflective Tape Supplier – WEALLIGHT
WEALLIGHT is a reflective tape supplier. The main products include the Custom Reflective Tape, DOT C2 Reflective Tape, ECE 104 E-Mark Reflective Tape, SOLAS Reflective Tape, Custom Reflective Stickers, Reflective Fabric Tape, Reflective Heat Transfer Vinyl and Glow in the Dark Material etc.
1 Microprism reflective material Reflection principle and structure composition
1.1 Microprism reflective material principles
The reflection principle of the micro prism reflective film is based on the light incident in a three-dimensional space, from a certain angle, and 3 reflections on the 3 planes perpendicular to each other, and then reflected back along the original direction of incidence, as shown in Figure 1.
According to the different manufacturing processes, there are two kinds of reflection on the prism surface: one is the air – resin interface (full) reflection, the other is the reflection of the aluminum resin interface.
1.2 Microprism reflective material classification according to structure
According to the different types of reflection, the structure of the micro prism reflective film can be divided into two kinds (see Figure 2, figure 3): the coating type reflective film (called Type V Sheeting in ASTM4956) and the non-coating reflective film (called Type IV Sheeting in ASTM 4956). Because of the dull color of the coated reflective film, the market prospect is dim.
The structural differences of these two kinds of reflective films are as follows:
(1) the non-coated reflective film pyramid behind the pyramid is air, so the reflection is a mainly full internal reflection, which requires a stable air layer after the pyramid, so there is a layer of the closed layer (Sealing film) in the non-coated reflective film (see Figure 2), to prevent the impurities such as moisture and dust into the air layer, resulting in the decrease of the inverse reflection coefficient.
(2) There is a layer of metal on the coated pyramid, which is usually aluminum. The reflection is mainly carried out at the resin – aluminum interface. There is no sealing layer in the coating type reflective film.
(3) Since the uncoated reflective film needs to be closed, there are supporting walls. From the front side, there are diamond or hexagonal lattices. But there is no coating type reflective film.
2 Performance of microprism reflective film
2.1 Microprism reflective material optical properties
In terms of reflective intensity and wide angle, the micro prism reflective film has been greatly improved than that of the lens type reflective film. Fig. 4 is a comparison of the initial value of reflective intensity of 3 types of products of 3M Company (0.2 degree observation angle).
The reflected light cone of the former microprism reflective film is asymmetrical and the effective incidence angle is small, but through the design of the reflection unit and its array, these problems have been basically solved.
2.2 Microprism reflective material weatherability
The reverse reflection coefficient decreased by 50%, although the reverse reflection coefficient of the microprism film decreased by 50%, but the reverse reflection coefficient was still kept in the 400cd LX ~ m ~ (-4) film, which was much higher than that of the other two kinds of reflective films, as shown in Figure 5 (0.2 degree angle, -4 degree angle).
3 key technology and latest development of micro prism reflective film
3.1 key technologies
Although the basic principle of reflective film of microprism type reflective film is simple, its manufacturing technology involves many fields, such as materials science, optics, precision machinery manufacturing and so on. To sum up, there are 4 key technologies for making micro prism reflective film.
3.1.1 Unit structure and its array design
The traditional prism retroreflective material mainly has the following disadvantages:
(1) The effective angle of incidence is small. When the incidence angle is greater than 20 degrees, the reflection brightness is almost lost due to the total internal reflection phenomenon.
(2) The observation angle is small, that is, people can see the opposite light in the distance, but not in the near future.
(3) Because of the three side properties of the reflection unit, the reverse reflected light cone has an undesirable asymmetric shape, and the results have different reverse reflection luminance when observed from different scanning angles.
The methods to solve these problems are mainly based on the design of the inverse reflection unit and array, such as changing the angle of the angle between the 3 planes, making it distributed, or arranging the unit array according to a certain rule. However, due to the complicated design of the structure and array, it is difficult to make motherboards, reproduce them, and demolde them after molding.
3.1.2 Making and replicating of motherboard
Because the height of the micro prism type reflection unit is 0.003 ~ 0.015in (0.0782 ~ 0.381mm), and the shape is irregular, the arrangement on the plane also has some regularity, and the degree of smoothness of the forming surface is very high, so the motherboard needs to be machined precisely. The motherboard itself is not directly involved in molding, the processing price is high, the area is limited, and the mold usage cycle is not high. The replica can be produced by duplication of the motherboard and spliced into any size so as to facilitate industrial production.
3.1.3 Determination of base material
As a micro prism reflective film, its main material is engineering plastics. According to the different requirements of its performance, different plastic substrates are chosen. The main targets and problems to be solved are: weathering properties of materials, preheating properties and rheological properties of plastic sheets. 3M is using polycarbonate.
3.1.4 Compression technique
Because of the high demand for optical properties of the microprism reflective film, the precision of its press grain is also very high. In the process of compression, the defects such as poor flow, bubbles and scratches are not allowed, and the requirements of the process conditions, such as temperature and pressure, are also very demanding.
3.2 Microprism reflective material recent progress
WEALLIGHT is a reflective tape manufacturer, which can produce a microprism reflective film and a glass bead type reflective film. The non-coated microprism reflective film is produced by a reverse reflection coefficient of 900 CD. LX to m. And the shape and array of the reflected structural units are unique, basically solving the reflection light distribution. The disadvantage of unevenness and poor wide angle. Now, the reports on micro prism reflective films are mainly focused on the design of reflective elements and their arrays.
4 Microprism reflective material Application prospects
Because of the high reflective intensity and good wide angle performance of the micro prism reflective film, with the continuous improvement of the speed of motor vehicles, the continuous growth of high grade highways and the complexity of the road conditions, the application market of the microprism reflective film will be more and more extensive. On the highway in California, the border and pattern of the logo have been changed into diamond grade products. However, other problems caused by high strength, such as dazzling, and the contrast between the pattern and the background in practical applications, determine that the micro prism reflective film cannot completely replace the glass bead type reflective tape.
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