What is reflective material made of?

What is reflective material made of? Most of the reflective material is a membrane structure consisting of layers (protective film), reflection layer (functional layer), base (bearing layer), adhesive layer and bottom layer (protective layer). But different types of reflective materials have different composition.

According to the type of reflective material, it can be divided into: embedded reflective film, sealed reflective film, micro prism reflective film, all prism reflective film.

The specific structure of different types of reflective materials refer to the development of reflective materials.

Reflective materials and their applications

The regressive original reflective material is a new type of optical composite developed rapidly in the world in recent years. It has a unique reflective performance. It can reflect the light from the light source to the direction of the original light source, and keep it in a small corner cone.

Moreover, when the angle between incident light and reflective surface normal varies within a certain range, this reflection property remains unchanged. Therefore, reflective material is a very popular night mark material. Because it does not have an external power supply, it can play a good role in indicating, and so it is also an important energy saving material.

1. The principle and requirement of retro reflective

When a beam of light is projected onto an object, the rest will be reflected or scattered by the surface other than some energy absorbed. If the surface is very smooth and clean, the reflection angle and the incidence angle are the same. The surface is called the mirror surface, and the reflection on the mirror surface is called the mirror reflection.

Some surfaces can reflect the projective light indiscriminately in all directions. This surface is called diffuse reflection surface, and its reflection is called diffuse reflection.

The difference between retro reflection and specular reflection and diffuse reflection is that it can reflect the direction of the light beam in the direction of the original light source. When the angle between incident light and the normal surface of the reflection surface is controlled within a certain range, the reflection property remains unchanged (Fig. 1).

Fig. 1 a schematic diagram of three different reflective optical paths

For a practical retro reflective material, bright reflectivity and good wide angle are two indispensable elements. According to the theoretical analysis, when the reflector cone angle is designed for an hour, 98% of the reflected light can be concentrated in the three-dimensional angle of 3~4°, so that the observer near the light source can see very bright reflected light.

The reflective intensity of ordinary reflective materials is hundreds of times higher than that of ordinary diffuse white paint. For the sake of practicality, the greater the angle variable range of the incident light and the reflection surface, the better the better the return reflection can be under the optimal regression reflection, generally not less than ±50°.

2. Optical path analysis and design of retro reflective materials

To achieve the purpose of retro reflection, we must design and process materials carefully. In essence, the microscopic structure of the regressive material is a “refraction – reflection” optical unit, and numerous optical units are densely joined together to form a reflective surface. For illustrative purposes, taking the engineering grade reflective material (reflective fabric work) as an example, the optical path structure is analyzed and the design elements are introduced.

The microstructure of the lens reflective material is shown in Figure 2. It is a composite optical system consisting of glass beads, binders, spherical reflectors and substrates.

optical road map of a reflective optical unit

The refraction is shown in Figure 3. The incident light parallel to the light axis enters the glass bead from the air. Through the refraction, the intersection of light and light axis happens on the intersection point A of the bottom of the glass microsphere. As the bottom of the glass bead is set with the reflection layer, the light is reflected on the A point. At this time, the incident light path and the reflected light path are located on both sides of the optical axis, forming a symmetrical figure, so the reflected light is parallel to the incident light and returns to the direction of the light source.

In view of the fact that the reflective layer is a half spherical surface, the reflection characteristics are unchanged when the incident direction changes within a certain range.

n’/S’-n/S=(n’-n)/r    (1)

Among them, n is the refractive index of the image cube, that is, the refractive index of the glass bead; S’ is the image distance, that is, the diameter of the glass bead (S’ = 2r).

N is the refractive index of the object, that is, the refractive index of the air; S is the distance between objects, that is, the distance from the measuring point to the reflected surface.

In the case of n=1, and S=∞, the formula (1) can be simplified to:

n’/2r=(n’-1)/r   (2)

Get n ‘=2. That is to say, if the light is refracted and just focused on the A point, the refractive index of the glass bead must be equal to 2.

Due to the existence of the spherical aberration, only the near axis light can be focused accurately. With the increase of the distance between the incident light and the optical axis, the focus will be offset longitudinally, which leads to a angle θ between the reflected light and the incident light, and the reflected light is turned into a cone beam. As in Figure 4, θ is called the diffusion angle.

Rule: when the reflected light deviates from the optical axis and has no intersection point with the optical axis, θ is positive, as shown in figure 5-a; while the reflected light is biased towards the optical axis, and when it intersects with the optical axis, θ is negative, as shown in figure 5-b. The diffusion angle is a very important factor for the regression reflection intensity. The absolute value of θ is large, but the intensity of the regression reflection is low, but the visible range is large. Vice versa. Therefore, in the design of optical path, we must control θ angle according to the requirement of use so as to get different reflective effects.

Fig. 4 the longitudinal spherical aberration shows

There is a function relationship between θ angle and refractive index n ‘and incident angle α.

Θ =4arcsin (sin α /n ‘) -2 α

When the refractive index of glass bead is n ‘, the θ angle is a function of α angle. Figure 6 shows the influence of five different folding rate glass beads on the diffusion angle (θ) and incidence angle of the retroreflective materials. It can be seen from Fig. 6 that the maximum values of θ =f (α) are different due to the different refractive indices of microbeads, which provides a choice for different reflective requirements. The intensity of reflection is a psychophysical parameter for the human eye.

There is no strict mathematical boundary for the determination of the value of θ. At present, the best empirical data in the world can be obtained at θ max=1° in the design of the optical path of the far distance regression reflective material. After setting a θ max value, the refractive index (n ‘) of the glass beads can be determined by calculation: conversely, the maximum value of the diffusion angle of the reflective material can be designed from the known glass refractive index (n’).

Fig. 6

The following is a brief introduction to the design method of the optical path. Θ =f (α, n) is a bivariate function. Its geometric meaning is a surface (see M in Figure 7).

θ≤α≤90°   1≤n≤+∞ (practical use 1.5≤n≤2.2)

Fig. 7

A plane N perpendicular to θ uranium is analyzed by θ =1 degree, and the relationship between θ =f (d) and N is analyzed.

The maximum value of θ =f (α) is greater than 1°, and then there are two intersections with N.

(2) The maximum value of θ =f (α) is less than 1°, and there is no intersection point with N.

(3) The maximum value of θ =f (α) is equal to 1°, then there is an intersection point with N, which is the extreme point of the intersection of plane N and surface M. The intersection line between N and M can be expressed as follows:

N=sin α /sin [(θ +2 α) /4] (3)

At θ =1°, n=sin α /sin [(1 degree +2 a) /4] (4)

N Max can be obtained by making dn/d α =0. So it can be solved by numerical approximation method in practice.

Table 1

n max=1.922504 can be seen from the above table, so the best long-range reflectivity can be obtained by using glass beads with refractive index equal to 1.922504. In practice, the accuracy of refractive index is only about 1.92. The application formula (4) can find the corresponding microbead refractive index after setting the maximum value of the θ. For example, the maximum value of θ =f (α) is 7~9, and the refractive index of the microsphere can be calculated by the formula (4), and the refractive index of the microsphere is about 1.70.

3. Types and uses of Retro reflective materials

With the development of science and technology and the expansion of application area, the design of light path for returning the reflective materials is becoming more and more perfect and the variety of materials is increasing. So far, the materials have been developed into practical value. There are lens exposed reflective film, flat top type reflective film, air flat top reflective film, prism reflective film, and microprism reflective film, Reflective coatings, reflective fabric, collinear reflectors, reflective sheeting, transmittance reflective films, reflective heat transfer vinyl, etc.

4. Development and Application

Retroreflective materials, which are increasingly updated due to their adaptability to performance and application, have been developed into series products. The market of reflective materials: its application involves sea, land and air traffic safety, national defense, scientific research and civilian use.

First, we focus on safety devices for road signs. The reflective properties of the reflective material, return and reflection after the light of the automobile headlights, have the effect of far distance reflection. Therefore, it effectively avoids the heavy loss of the car, which is called “lifesaving film”. As a traffic safety facility, it has great economic and social benefits.

At present, countries with advanced technology are competing against reflective materials. In order to participate in international competition, we start with improving product quality. Taking the regression directional reflector as an example, we analyze the function of the spherical aberration to the optical path when we design the optical path, and obtain the function relation between the parameters in the optical path, thus deriving a set of calculation formulas for the optical path design, which improves the effective reflector area of the reflective unit. In theory, it is 17% higher than the international level and can be improved by 12% by the measurement. In the process, the process of model once forming is unique and novel.

Second, the collinear reflector, the test products compared with the international similar products, has the advantages of high reflective intensity and small diffusion angle, and it is one of our potential high quality products.

Third, the series of products that return to reflective materials belong to the night reflective safety signs, and are widely used energy-saving products. The main problems that need to be further explored and studied are:

(1) Regression analysis and design of light path system for reflective materials to study the transmission characteristics of light in various media.

(2) To carry out the material scientific research on the regressive reflective materials, in particular, we should pay special attention to the study of the transmittance and refraction of the glass beads, the transmittance and stability of the polymers, the reflective properties of the metal materials, and the stability of the color.

(3) In view of the characteristics of regressive reflective materials, special technological technologies are developed, such as microbead planting technology, film plating technology, optical liner technology, surface coating technology and continuous production technology.

(4) Establish specialized testing methods and standards, including refractive index determination, wide-angle measurement, reflection intensity measurement and chromaticity determination.

At the same time, we have developed and produced a series of products of reflective materials. We introduce a lot of colorful, diamond shaped and flickering “diamond film” products. It is mainly used to print various patterns and characters. Its characteristic is that ink can be obtained without printing preprocessing, and can be used for decoration and environmental layout directly.

Reflective materials manufacturer – WEALLIGHT

WEALLIGHT is a reflective material manufacturer, providing reflective materials customized services, custom reflective tape and custom reflective stickers. Our main products include reflective tape, reflective fabric, reflective thermal transfer vinyl, rainbow reflective thermal transfer material, luminous material, etc.

Now contact us for samples of free reflective materials.

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