CN118655742A - A transparent optical film, a transparent rear projection film and a rear projection transparent display system - Google Patents

Abstract

The present invention relates to a transparent optical film, a transparent rear projection film and a rear projection transparent display system, wherein the optical film comprises: a dielectric layer, the dielectric layer is composed of an optically uniform and transparent medium, the dielectric layer comprises an incident surface and an exit surface opposite to each other; a plurality of scattering particles, the plurality of scattering particles are distributed in the dielectric layer to partially scatter the light incident into the optical film through the incident surface, and the scattered light is distributed on the incident surface side and the exit surface side of the optical film; wherein the refractive index of the scattering particles is different from the refractive index of the medium, and the total intensity of the scattered light on the exit surface side is at least 3 times the total intensity of the scattered light on the incident surface side. The brightness of the front image can be a preset multiple of the brightness of the back image, and can be used in privacy protection, virtual augmented reality and other occasions where a transparent display effect needs to be achieved through projection.

Description

A transparent optical film, a transparent rear projection film and a rear projection transparent display system

Technical Field

The present invention relates to the field of transparent projection technology, and in particular to a transparent optical film, a transparent rear projection film and a rear projection type transparent display system.

Background Art

Transparent display screens are display screens when in use, and can act as transparent glass or transparent plastic films when not in use. Therefore, they have great potential in the display business field, especially in retail display scenarios. Common transparent display technologies on the market include transparent LCD, OLED, Micro LED, 45° reflector and transparent projection display. Among them, transparent projection display technology is a transparent display technology that achieves the same display effect as LCD, OLED and other technologies by projecting images onto transparent projection films or transparent glass with transparent projection films. Compared with other technical solutions, transparent projection display technology has the advantages of low manufacturing cost, simple structure, simple manufacturing process, easy installation, large display area and wide application scenarios. It can be widely used in exhibitions, retail markets, stage choreography, transparent advertising displays, vehicle-mounted HUD, 3D screens, AR/MR and light field displays.

Although the transparent projection films (such as holographic films) in the prior art perform well in terms of transparency, viewing angle and clarity, when the rear projection films on the market are projected, the transparent projection films form images with basically the same brightness on the back and front, and cannot achieve a display effect in which the brightness of the front image is many times greater than that of the rear image. In some application scenarios, such as virtual reality and augmented reality, and some privacy protection environments, a transparent projection film with a significant brightness difference between the front and rear images is required. Even in some application scenarios, a transparent projection film is required in which only the front image can be seen, and the image is basically invisible on the back. In other words, there is a lack of a transparent projection film with a brightness difference between the front image and the rear image on the market, especially a transparent rear projection film whose brightness between the front image and the rear image can be carefully designed to achieve a quantifiable average brightness ratio, so as to be used in privacy protection, virtual augmented reality, and other occasions where a transparent display effect needs to be achieved through projection.

Summary of the invention

The purpose of the present application is to solve the technical problem that when a transparent rear-projection film is projected, the rear-projection film forms images with basically the same brightness on its back and front, but it is impossible to achieve a rear-projection projection film with a large and preset brightness difference between the front and back images while maintaining good transparency, viewing angle, picture clarity and brightness.

The purpose of the present invention is achieved by the following technical solutions:

To achieve the above-mentioned purpose, the present application first provides a transparent optical film, which includes: a dielectric layer, which is composed of an optically uniform and transparent medium, and the dielectric layer includes an incident surface and an exit surface opposite to each other; a plurality of scattering particles, which are distributed in the dielectric layer to partially scatter the light incident into the optical film through the incident surface, and the scattered light is distributed on the incident surface side and the exit surface side of the optical film; wherein the refractive index of the scattering particles is different from the refractive index of the medium, and the total intensity of the scattered light on the exit surface side is at least 3 times the total intensity of the scattered light on the incident surface side.

In some optional embodiments, the half-peak width angle of the scattered light intensity on one side of the exit surface is 30°-150°.

In some optional embodiments, the medium is selected from transparent high molecular polymers, and the scattering particles are selected from any one of polystyrene microspheres, PMMA microspheres, silica microspheres, silicone microspheres, latex microspheres and metal microspheres.

In some optional embodiments, the diameter of the microspheres is 0.05 μm to 50 μm.

In some optional embodiments, the scattering particles partially scatter the light incident into the optical film through the incident surface based on Mie scattering theory.

In some optional embodiments, a method for preparing a transparent optical film is provided. The method for preparing the transparent optical film is applicable to the transparent optical film described above, and the specific steps are as follows:

S101, preparing a particle liquid with a mass fraction of μ by mixing a plurality of scattering particles with water or an organic solvent;

S102, fully mixing the particle liquid and an uncured high molecular polymer solution having a solid content of g to obtain a high molecular polymer mixed solution;

S103, uniformly coating the high molecular polymer mixed solution on a transparent substrate film by a coating method to form a film;

S104, according to the polymerization characteristics of the high molecular polymer, the high molecular polymer mixed solution after film formation is heated and volatilized and then solidified to obtain a transparent optical film containing scattering particles.

In some optional embodiments, another method for preparing a transparent optical film is provided. The method for preparing the transparent optical film is applicable to the transparent optical film described above, and the specific steps are as follows:

S201, spreading a plurality of scattering particles on the surface of the transparent high molecular polymer film;

S202, heating the transparent high molecular polymer film until it softens;

S203, pressing the plurality of scattering particles spread on the surface of the transparent high molecular polymer film into the interior of the film;

S204, cooling the transparent high molecular polymer film containing the scattering particles to room temperature to obtain a transparent optical film containing scattering particles.

The present application also provides a transparent optical film, wherein the transparent rear projection film comprises any of the transparent optical films described above.

In some optional embodiments, the transparent rear projection film further includes a transparent base layer, and the transparent base layer is disposed on at least one side of the transparent optical film.

In some optional embodiments, the transparent base layer is selected from any one of PET, PMMA, PC, an anti-reflection film, and a high-absorption film.

In some optional embodiments, the transparent rear projection film further includes an anti-reflection layer, and the anti-reflection layer for reducing reflectivity is disposed on at least one side of the transparent optical film.

In some optional embodiments, the transparent display system includes the transparent rear projection film as described above, and the transparent display system also includes a projection device, and the projection device is used to generate a projection image through the transparent rear projection film.

The transparent optical film, transparent rear projection film and rear projection transparent display system provided by the present application have at least the following advantages:

The present application utilizes the difference in refractive index between scattering particles and the medium to produce a quantifiable difference in the scattered light intensity on both sides of the transparent optical film, so that the two sides of the transparent optical film can provide users with display effects of different image brightnesses, that is, the brightness of the front image of the rear projection film is much different from that of the back image, and the brightness of the front image can be a preset multiple of the brightness of the back image. It can be used in privacy protection, virtual augmented reality and other occasions where a transparent display effect needs to be achieved through projection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the structure of a transparent optical film of the present application.

FIG. 2 is a schematic diagram showing the meaning of technical indicators of the total intensity of scattered light emitted from the exit surface and the total intensity of scattered light emitted from the incident surface of the transparent optical film provided by the present application.

FIG3 is a schematic diagram showing the meaning of technical indicators of the forward scattered light intensity of the transparent optical film of the present application as a function of viewing angle and the half-peak width angle of the scattered light intensity.

FIG. 4 is a schematic flow chart of a method for preparing the transparent optical film of the present application.

FIG. 5 is a schematic flow chart of another method for preparing the transparent optical film of the present application.

FIG. 6 is a schematic diagram of the three-dimensional structure of the transparent rear projection film of Structure I of the present application.

FIG. 7 is a schematic diagram of the optical path of a transparent rear projection film of the present application.

FIG8 is a schematic diagram of the forward scattering characteristics of Mie scattering of the present application.

FIG9 is a schematic diagram of the cross-sectional structure of the transparent rear projection films of Structure I, Structure II, Structure III, Structure IV, and Structure V of the present application.

FIG. 10 is a back image rendering (a) and a front image rendering (b) of an experimental sample of the transparent rear projection film of the present application.

FIG. 11 is a transparency effect diagram of an experimental sample of the transparent rear projection film of the present application.

FIG. 12 is a schematic diagram of a rear-projection transparent display system of the present application.

In the figure: 100, transparent optical film; 101, dielectric layer; 102, scattering particles; 110, transparent base layer; 120, anti-reflection layer; 210, projector; 220, audience; 310, projector output light; 320, scattered light emitted from the output surface of the transparent optical film; 330, scattered light emitted from the incident surface of the transparent optical film; 500, incident light; 510, light scattered forward by the microspheres; 520, light scattered backward by the microspheres; 530, light not scattered by the microspheres.

DETAILED DESCRIPTION

In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be further described below in conjunction with the specific embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments, and are not intended to limit the scope of the present invention. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

The words expressing positions and directions described in the present invention are all explained by taking the drawings as examples, but they can be changed as needed, and the changes are all included in the protection scope of the present invention. The same reference numerals in the drawings represent the same or similar structures, and thus their repeated description will be omitted.

Below, firstly, a brief description is given of one of the application fields of the embodiment of the present application (eg, a rear-projection transparent display system in a shopping mall).

Rear projection film projection is a projection technology that is used to provide large-scale image support in a specific space without using the traditional front projection film mode. It is generally believed that a transparent rear projection film is set between the user and the projection device (such as a projector), and the light of the image projected by the projection device passes through the transparent rear projection film and is displayed in front of the user.

To improve the viewing experience of users, the incident surface brightness of the transparent rear projection film can be increased, and the front surface brightness of the transparent rear projection film can be increased. However, if the back and front of the transparent rear projection film form images with basically the same brightness, user privacy will be affected. If you try to change the external illumination, replace the emitter to reduce the amount of light, or use soft lamps, although the brightness of the back of the transparent rear projection film can be reduced, the quality of the front image facing the user will also be affected.

Based on this, in order to solve the technical problem that when a transparent rear-projection film is projected, the transparent rear-projection film forms images with basically the same brightness on its back and front, but cannot achieve a transparent rear-projection film with a large and quantifiable brightness difference between the front and back images while maintaining good transparency, viewing angle, picture clarity and brightness, the present application proposes a transparent optical film, a transparent rear-projection film and a rear-projection transparent display system. The technical solution of the embodiment of the present application and how the technical solution of the embodiment of the present application solves the above-mentioned technical problems will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

(Transparent optical film embodiment)

Referring to FIG. 1 , FIG. 1 shows a schematic structural diagram of a transparent optical film provided by the present application, wherein the optical film includes a dielectric layer and a plurality of scattering particles.

The medium layer is composed of an optically uniform and transparent medium, and comprises an incident surface and an exit surface which are opposite to each other.

The plurality of scattering particles are distributed in the dielectric layer to partially scatter the light incident into the optical film through the incident surface, and the scattered light is distributed on the incident surface side and the exit surface side of the optical film.

The refractive index of the scattering particles is different from the refractive index of the medium, and the total intensity of scattered light on the exit surface is at least 3 times the total intensity of scattered light on the incident surface.

Therefore, by utilizing the difference in refractive index between the scattering particles and the medium, and the corresponding relationship between the particle size of the scattering particles and the scattered light intensity distribution of Mie scattering, a quantifiable difference in the scattered light intensity on both sides of the transparent optical film is produced, so that the two sides of the transparent optical film can provide users with display effects of different image brightness.

On the one hand, the high brightness (exit surface) side of the transparent optical film can be used as the display surface for the user, and the image incident from the incident surface can be displayed in front of the user, giving the user a better visual experience. It can be understood that because the brightness of the exit surface is higher, more light can be emitted to the eyes, so that the image perceived by the user is clearer and more delicate, and the user experience is better.

On the other hand, the scattering intensity on the incident surface side is lower than that on the exit surface side, which reduces the brightness of the image on the incident surface. It can be understood that the user cannot perceive a clear image from the incident surface, which is conducive to privacy protection.

On the other hand, the transparent optical film in this embodiment can achieve a quantifiable brightness difference between the incident surface and the exit surface by controlling the refractive index ratio between the scattering particles and the medium, and the correspondence between the particle size of the scattering particles and the Mie scattering light intensity distribution.

In particular, when the total intensity of scattered light on the exit surface side is at least three times that of scattered light on the incident surface side, the exit surface side has better image brightness and picture clarity, while the brightness on the incident light side can be reduced to an ideal value, which is beneficial to privacy protection.

In summary, the transparent optical film provided in this embodiment achieves the effect that the brightness of the front image of the rear projection film is significantly different from that of the back image while maintaining good transparency, and can achieve the brightness of the front image being a preset multiple of the brightness of the back image. It can be used in privacy protection, virtual augmented reality and other occasions that require a transparent display effect through projection.

The shapes of the scattering particles can be spherical, ellipsoidal, square, rod-shaped, angular, or completely irregular.

In a specific application, a plurality of the scattering particles are evenly distributed in the dielectric layer. As light passes through the transparent optical film, it gradually attenuates and changes its diameter, causing the light beam to become multiple small light beams, thereby generating radiation spots. Large radiation spots can lead to scattering errors, and using evenly distributed scattering particles can reduce such errors.

Refer to FIG. 2 , which shows a schematic diagram of the meaning of technical indicators of the total intensity of scattered light emitted from the exit surface and the total intensity of scattered light emitted from the incident surface of the transparent optical film provided by the present application.

In some optional embodiments, the total intensity of scattered light on the exit surface side may be 10 times, 20 times, 30 times, etc., of the total intensity of scattered light on the incident surface side.

In some optional embodiments, the half-peak width angle of the scattered light intensity on one side of the exit surface is 30° to 150°.

Referring to FIG. 3 , FIG. 3 is a schematic diagram showing how the forward scattered light intensity of the transparent optical film of the present application changes with the viewing angle.

The half-peak width angle of scattered light intensity can be used to quantify the image viewing angle that can be achieved by the transparent optical film. See Figure 3. The ordinate represents the scattered light intensity on the front of the transparent optical film, and the abscissa represents the viewing angle of the audience. The vertical direction to the projection film is defined as 0°, the clockwise viewing angle is positive, and the counterclockwise viewing angle is negative. The half-peak width angle of scattered light intensity means the corresponding angle width when the scattered light intensity value on the front of the transparent optical film is half of the peak value. The half-peak width angle of scattered light intensity of the transparent optical film of the present invention is between 30° and 150°, so it has a larger viewing angle.

Therefore, under the above-mentioned scattered light intensity half-peak width angle, the transparent optical film of this embodiment can have a larger viewing angle.

In some optional embodiments, the medium is selected from transparent high molecular polymers, and the scattering particles are selected from any one of polystyrene microspheres, PMMA microspheres, silica microspheres, silicone microspheres, latex microspheres and metal microspheres.

Among them, high molecular polymer is used as the medium of transparent optical film. High molecular polymer has good heat resistance and durability, and can be used as the transparent optical film of transparent rear projection film for a long time; high molecular polymer has good UV resistance, is not easy to fade or yellow, and improves the service life of transparent rear projection film; high molecular polymer has low roughness, and it is easy to obtain a smoother surface, which improves the manufacturing yield of transparent optical film; high molecular polymer has low density, and after being made into a film as a medium, it has lower quality, higher deformation resistance and elongation.

When the scattering particles are selected from any one of polystyrene microspheres, PMMA microspheres, silica microspheres, silicone microspheres, latex microspheres and metal microspheres, the transparent optical film can have a certain anti-ultraviolet performance, which can effectively block part of the ultraviolet rays and protect the objects in the film layer from damage by ultraviolet rays; the above-mentioned scattering particles have good impact resistance, can absorb unexpected impacts, and improve the stability of the transparent optical film when subjected to external impacts.

In some optional embodiments, the thickness of the optical film is greater than the particle size of the microspheres, and the diameter of the microspheres is 0.05 μm to 50 μm.

Therefore, the microspheres within the above range do not increase the thickness of the transparent optical film, but can satisfy the scattering of light incident on the transparent optical film.

In some optional embodiments, the scattering particles partially scatter the light incident into the optical film through the incident surface based on Mie scattering theory.

In some optional embodiments, the mass fraction of the scattering particles in the transparent optical film can be 4% to 30%. This is because controlling the mass fraction of the scattering particles in the transparent optical film can ensure the light transmittance of the film and prevent the attenuation of the optical system. When the mass fraction of the scattering particles in the transparent optical film is in the range of 4% to 30%, the light transmittance of the film is good and the attenuation of the optical system is not likely to occur.

In some optional embodiments, referring to FIG. 4 , FIG. 4 is a schematic flow chart of a method for preparing a transparent optical film of the present application, wherein the transparent optical film is prepared by the following method:

S101, preparing a particle liquid with a mass fraction of μ by mixing a plurality of scattering particles with water or an organic solvent;

S102, fully mixing the particle liquid and an uncured high molecular polymer solution having a solid content of g to obtain a high molecular polymer mixed solution;

S103, uniformly coating the high molecular polymer mixed solution on a transparent substrate film by a coating method to form a film;

S104, according to the polymerization characteristics of the high molecular polymer, the high molecular polymer mixed solution after film formation is heated and volatilized and then solidified to obtain a transparent optical film containing scattering particles.

Thus, a particle liquid is prepared, and the particle liquid is mixed with a high molecular polymer solution to obtain a high molecular polymer mixed solution, which is coated on a substrate film by coating to obtain a cured transparent optical film, and the manufacturing process is simple. The coating and other methods involved in the manufacturing process are mature, and a high-precision transparent optical film can be obtained under the premise of reducing the manufacturing cost.

In some optional embodiments, referring to the flow diagram of FIG. 5 , FIG. 5 is a flow diagram of a method for preparing a transparent optical film of the present application, wherein the transparent optical film is prepared by the following method:

S201, spreading a plurality of scattering particles on the surface of the transparent high molecular polymer film;

S202, heating the transparent high molecular polymer film until it softens;

S203, pressing the plurality of scattering particles spread on the surface of the transparent high molecular polymer film into the interior of the film;

S204, cooling the transparent high molecular polymer film containing the scattering particles to room temperature to obtain a transparent optical film containing scattering particles.

Therefore, by taking advantage of the simple structure of the transparent optical film, the scattering particles are pressed into the softened transparent high molecular polymer film to directly prepare the transparent optical film, which has a fast preparation speed and is easy to promote in industry.

(Transparent rear projection film embodiment)

Referring to FIG. 6 , FIG. 6 shows a schematic diagram of the three-dimensional structure of a transparent rear projection film provided in the present application. The transparent rear projection film includes a transparent optical film, which has the same structure and function as the transparent optical film in the above transparent optical film embodiment, and will not be described in detail here.

In some optional embodiments, the transparent rear projection film further comprises a transparent base layer, and the transparent base layer is disposed on at least one side of the transparent optical film. It can be understood that the transparent base layer is a transparent film without scattering particles. The transparent base layer can be selected from any one of PET, PMMA, PC, anti-reflection film, and high absorption film.

Thus, on the one hand, the transparent base layer can be used as the transparent substrate film in the above step S103, and can also improve the mechanical strength of the transparent back-projection film, thereby improving the strength properties of the transparent back-projection film while reducing the difficulty of preparing the transparent back-projection film. On the other hand, the transparent base layer is arranged on at least one side of the transparent optical film, and the light flux of the forward and backward scattered light reaching the front and back sides of the transparent back-projection film can be adjusted by changing the light transmittance _T1 of the transparent base layer, thereby flexibly adjusting the brightness of the images on the front and back sides of the transparent back-projection film. The light transmittance _T1 can be calculated using the Fresnel formula, which will not be described in detail in this application.

In summary, by providing a transparent base layer on at least one side of the transparent optical film, the effect of adjusting the luminous flux of scattered light reaching the front and back sides of the transparent rear projection film can be achieved.

Refer to Figure 7, which is a schematic diagram of the optical path of a transparent back-projection film provided by the present application. In a specific application, the transparent back-projection film includes a transparent base layer 110 and a transparent optical film 100 which are arranged in sequence. The implementation principle is that, first, the projection light emitted by the projection device enters the transparent optical film 100 through the transparent base layer 110. A part of the incident light 500 entering the transparent optical film 100 will continue forward along the direction of the incident light without being scattered. This part of the unscattered light 530 will not contribute to the imaging of the transparent back-projection film and will no longer be paid attention to. The other part will be scattered by the scattering particles 102 in the transparent optical film 100. The light scattered by the scattering particles 102 is divided into forward scattered light 510 and backward scattered light 520. It can be considered that the scattering that occurs is similar to Mie scattering, and the forward scattered light is more than the backward scattered light, as shown in the forward scattering effect diagram shown in Figure 8.

The backscattered light 520 reaches the transparent base layer 110 and transmits through the transparent base layer 110 at a certain ratio to reach the back of the transparent rear projection film. It can be understood that the light flux transmitted through the transparent base layer 110 is determined by the average light transmittance _T1 of the transparent base layer 110.

In some optional embodiments, the transparent rear projection film further comprises an anti-reflection layer, and an anti-reflection layer for reducing reflectivity is disposed on at least one side of the transparent optical film. It can be understood that the anti-reflection layer is a transparent anti-reflection film that does not contain scattering particles and can reduce the reflectivity of incident light and increase the transmittance.

Thus, the interface between the transparent optical film and the anti-reflection layer can partially reflect the light back to the direction of the incident light, and the light flux emitted to the front and back of the transparent rear projection film can be adjusted by adjusting the average light transmittance _T2 of the anti-reflection layer. The light transmittance _T2 can be calculated using the Fresnel formula, which will not be described in detail in this application.

For example, when the anti-reflection layer is disposed on one side of the exit surface of the transparent optical film, the forward scattered light will reach the anti-reflection layer, and transmit through the anti-reflection layer at a certain ratio to reach the side of the transparent rear projection film facing the user. The ratio of the light flux transmitted through the anti-reflection layer and the light flux reflected back to the transparent rear projection film is determined by the average light transmittance _T2 of the anti-reflection layer. The greater the light transmittance _T2 of the anti-reflection layer, the more light will transmit through the anti-reflection layer and reach the user's field of view (the front of the transparent rear projection film), and the brighter the front image of the transparent rear projection film will be.

In a specific application, the anti-reflection layer, the transparent optical film and the transparent base layer can be combined in the following manner:

Structure I, as shown in a of FIG. 9 and the combination of layers shown in FIG. 6 , the transparent optical film is placed on the transparent base layer 110, and the anti-reflection layer 120 is placed on the transparent optical film 100, forming a three-layer structure rear projection film with the transparent optical film 100 located in the middle and the transparent base layer 110 and the anti-reflection layer 120 located on both sides thereof.

Structure II is a combination of layers as shown in b of FIG. 9 .

Structure III is the combination of layers as shown in c of FIG. 9 .

Structure IV is the combination of layers as shown in d of FIG. 9 .

Structure V is the combination of layers as shown in e of FIG. 9 .

The front and back scattered light flux ratio of the transparent rear projection film of the present application satisfies formula (1):

Wherein: Φ _r0 is the ratio of the forward and backward scattered light flux calculated by the ideal physical model used in this application, σ _r is the ratio of the total forward and backward scattering cross sections of the transparent optical film 100, ξ is the non-ideal factor,

It means that the physical model used in this application has simplified, approximated and idealized some factors.

Since the scattering that needs to occur in the transparent optical film 100 is mainly single scattering, in order to satisfy the brightness difference between the front and back projection images of the transparent back-projection film, the forward scattered light flux is greater than the backward scattered light flux after passing through the transparent optical film 100. Among them, the scattering particles 102 in the transparent optical film 100 can be randomly and evenly distributed in the transparent film 101, and incoherent scattering occurs, that is, when scattering, the total scattering effect is a simple superposition of the scattering of all scattering particles under the irradiation of incident light. Therefore, the ratio of the total forward scattering cross section to the backward scattering cross section of the transparent optical film 100 is approximately equal to the ratio of the forward scattering cross section to the backward scattering cross section of a single scattering particle. The ratio of the forward and backward cross sections of the transparent optical film 100 is expressed by the following formula (2):

Wherein: σ _f is the forward scattering cross section of Mie scattering of a single scattering particle, σ _b is the backward scattering cross section of Mie scattering of a single scattering particle, and σ _r is the ratio of the total forward and backward scattering cross sections of the transparent optical film 100.

Therefore, the difference between the front and back scattering light flux ratio _Φr of the actually prepared transparent back-projection film and the front and back scattering light flux ratio _Φr0 calculated and predicted by the model mainly depends on the scattering properties of the transparent base layer 110, the anti-reflection layer 120 and the transparent medium 101 of the transparent optical film 100, as well as the mass fraction ω of the scattering particles in the transparent optical film 100. _σr is the ratio of the total forward and backward scattering cross sections of the transparent optical film 100, _T1 is the average transmittance of the transparent base layer 110, and _T2 is the average transmittance of the anti-reflection layer 120. If there is no anti-reflection layer or transparent base layer in some projection film structures of the present application, the value of _T1 or _T2 is the transmittance of the interface between the optical film and the air, which can be calculated by the Fresnel formula and will not be repeated here. It can be seen from formula (1) that by selecting different combinations of _σr , _T1 , and _T2 , transparent back-projection films with different front and back scattering light flux ratios can be prepared. Wherein, _T1 and _T2 are determined by the material, thickness and structure of the transparent base layer 110 and the anti-reflection layer 120. The value of _σr is determined by three parameters: the refractive index of the transparent film 101 of the transparent optical film 100 is _m0 , the refractive index of the scattering particles is _m1 , and the particle size of the scattering particles is D. However, to obtain a transparent optical film with a specific _σr value, it is necessary to calculate the value combination of _m0 , _m1 and D that can achieve this _σr value through Mie scattering theory, and then use the calculated three parameter values to select the corresponding transparent film material and scattering particles to produce the transparent optical film.

The average light transmittance _T1 of the transparent base layer 110, the average light transmittance _T2 of the anti-reflection layer 120 and the ratio _σr of the forward scattering cross section to the backward scattering cross section of the transparent optical film 100 jointly determine the ratio of the scattered light flux of the front image to the back image of the transparent back-projection film, thereby achieving the brightness difference between the front and back sides of the transparent back-projection film and enabling the average brightness ratio of the front image to the back image of the transparent back-projection film to reach the expected ratio.

When the scattering particles partially scatter the light incident into the transparent optical film through the incident surface based on the Mie scattering theory, it also conforms to the above theory.

In addition, the transparency of the transparent back-projection film of the present application (transparency is described by transmittance and haze, the higher the transmittance and the lower the haze, the higher the transparency), the clarity and brightness of the projected image, and whether the transparent optical film 100 maintains single scattering are closely related to the mass fraction ω of the scattering particles in the transparent optical film 100 and the thickness h of the transparent optical film. The greater the concentration of the scattering particles, the greater the thickness of the transparent optical film, the lower the transparency of the transparent back-projection film, the higher the clarity and brightness of the projected image, but the greater the probability of multiple scattering in the transparent optical film 100. Therefore, the mass fraction of the scattering particles and the thickness of the transparent optical film can not only determine whether single scattering occurs in the transparent optical film 100, but also determine the transparency, picture clarity and brightness of the transparent back-projection film. Therefore, it is necessary to determine the appropriate mass fraction ω and thickness h, which can be easily determined by testing different ω and h values and then testing the results, which will not be elaborated here.

In some optional embodiments, a transparent rear projection film having a preset front and back image brightness difference is provided, the structure of which includes a transparent base layer 110, a transparent optical film 100 and an anti-reflection layer 120. The transparent optical film 100 includes a dielectric layer and a plurality of scattering particles.

The medium layer is composed of an optically uniform and transparent medium, and the medium layer includes an incident surface and an exit surface opposite to each other. The medium is selected from transparent high molecular polymers, and the scattering particles are selected from any one of polystyrene microspheres, PMMA microspheres, silica microspheres, silicone microspheres, latex microspheres and metal microspheres. The total intensity of scattered light on the exit surface side is 3-30 times the total intensity of scattered light on the incident surface side. The half-peak width angle of the scattered light intensity on the exit surface side is 30° to 150°. The diameter of the microsphere is 0.05μm to 50μm, and the scattering particles are based on the Mie scattering theory to partially scatter the light incident on the optical film through the incident surface.

A plurality of scattering particles are distributed in the medium layer to partially scatter the light incident into the optical film through the incident surface, and the scattered light is distributed on the incident surface side and the exit surface side of the optical film; the refractive index of the scattering particles is different from the refractive index of the medium, so that the total intensity of the scattered light on the exit surface side is greater than the total intensity of the scattered light on the incident surface side.

The transparent base layer is arranged on the incident surface side of the transparent optical film. The transparent base layer is selected from any one of PET, PMMA, PC, anti-reflection film and high absorption rate film.

The anti-reflection layer is disposed on at least one side of the transparent optical film to reduce reflectivity.

Thus, by combining the three factors of the transparent optical film with Mie scattering effect, the light transmittance of the transparent base layer and the light transmittance of the anti-reflection layer, and establishing the interaction and dependence relationship between the three factors, a transparent rear projection film with a preset front and back brightness difference can be achieved while maintaining good performance in terms of transparency, picture quality and viewing angle, not just achieving a brightness difference between the front and back. The transparent rear projection film of the present application has the advantages of simple structure, simple manufacturing process, low manufacturing cost, easy installation, and large display area, and is suitable for a variety of application scenarios.

The above embodiment achieves the effect of having a preset and large front and back brightness difference while maintaining a large viewing angle, good transparency, picture clarity and brightness. It not only achieves the brightness difference between the front and back, such as the back image brightness and front image brightness effects of the laboratory sample shown in Figures 10(a) and 10(b). The prior art does not have such an effect. Specifically, the light transmittance of the transparent back projection film of this embodiment can be greater than 70%, the haze is less than 20%, and it has good transparency, such as the transparency effect of the test sample shown in Figure 11. The image contrast of the transparent back projection film of this embodiment is above 40:1, the gain is above 1.0, and it has good picture clarity and brightness. The optical film and transparent back projection film of this embodiment have two main technical indicators, namely, the ratio of the front and back scattered light intensity and the half-peak width angle of the scattered light intensity, which respectively quantify and measure the front and back image brightness difference and viewing angle that the transparent back projection film of this application can achieve. As shown in Figure 1, the projector 210 emits light 310, which is projected onto the back projection film and generates scattered light in all directions. The ratio of the front and back scattered light intensities means the ratio of the total scattered light intensity 320 emitted from the front of the projection film to the air to the total scattered light intensity 330 emitted to the back of the projection film when the transparent rear projection film is projected.

In a specific application, this application provides 5 embodiments of transparent rear projection films, as follows:

Example 1

A water-soluble thermosetting adhesive with a refractive index m ₀ =1.45 was used as the transparent film material of the transparent optical film, and PS (polystyrene) microspheres with a particle size of D=600 nm and a refractive index m ₁ =1.6 were used.

PS microspheres are mixed with water to prepare a microsphere liquid with a mass fraction μ = 10%, a water-soluble thermosetting adhesive with a solid content g = 80% is taken, and the mass fraction of the microspheres in the transparent optical film after final curing is determined to be ω = 5%.

According to the mass ratio formula

Take 2 g of microsphere liquid and 5 g of water-soluble thermosetting adhesive, mix the two thoroughly by ultrasonic vibration, and prepare a mixed solution in which the microspheres are evenly distributed in the water-soluble thermosetting adhesive.

The mixed solution is coated on a PMMA transparent glass with a light transmittance of T ₁ = 95% by a coating machine, and then heated and cured to form a transparent optical film with any thickness between 1μm and 500μm, and an anti-reflection film with a light transmittance of T ₂ = 99% is attached to the transparent optical film to finally produce a transparent rear projection film.

The experimental results show that the ratio of total scattered light intensity between the front and back sides of this rear projection film is 23:1, the half-peak width angle of the scattered light intensity is 56°, the transmittance is 84%, the haze is 9%, the contrast is 42:1, and the gain is 1.3.

Example 2

(1) A water-soluble thermosetting adhesive with a refractive index m ₀ =1.40 is used as the transparent film material of the transparent optical film, and PMMA microspheres with a particle size of D =500 nm and a refractive index m ₁ =1.49 are used.

(2) PMMA microspheres are mixed with water to prepare a microsphere liquid with a mass fraction μ=10%, a water-soluble thermosetting adhesive with a solid content g=50% is taken, and the mass fraction of the microspheres in the transparent optical film after final curing is determined to be ω=10%,

(3) According to the mass ratio formula

Take 2 g of microsphere liquid and 3.6 g of water-soluble thermosetting adhesive, mix the two thoroughly by ultrasonic vibration, and prepare a mixed solution in which the microspheres are evenly distributed in the water-soluble thermosetting adhesive.

(4) Use a coating machine to coat a thin film of the mixed solution on a PC transparent plastic with a transmittance of T ₁ = 85%, and then heat and cure it to form a transparent optical film with any thickness between 1 μm and 500 μm, and then attach an anti-reflection film with a transmittance of T ₂ = 98% on the transparent optical film. Finally, a transparent rear projection film is made.

The experimental results show that the ratio of total scattered light intensity between the front and back sides of this rear projection film is 16:1, the half-peak width angle of the scattered light intensity is 73°, the transmittance is 77%, the haze is 14%, the contrast is 55:1, and the gain is 1.8.

Example 3

(1) A water-soluble thermosetting adhesive with a refractive index m ₀ =1.50 is used as the transparent film material of the transparent optical film, and PS (polystyrene) microspheres with a particle size of D =250 nm and a refractive index m ₁ =1.6 are used.

(2) PS microspheres are mixed with water to prepare a microsphere liquid with a mass fraction μ=20%, a water-soluble thermosetting adhesive with a solid content g=40% is taken, and the mass fraction of the microspheres in the transparent optical film after final curing is determined to be ω=15%,

(3) According to the mass ratio formula

Take 1.5 g of microsphere liquid and 4 g of water-soluble thermosetting adhesive, mix the two thoroughly by ultrasonic vibration, and prepare a mixed solution in which the microspheres are evenly distributed in the water-soluble thermosetting adhesive.

(4) Use a coating machine to coat a thin film of the mixed solution on a PC transparent plastic with a light transmittance of T ₁ = 80%, and then heat and cure it to form a transparent optical film with any thickness between 1 μm and 500 μm, and then attach an anti-reflection film with a light transmittance of T ₂ = 99% on the transparent optical film. Finally, a transparent rear projection film is made.

The experimental results show that the ratio of total scattered light intensity between the front and back sides of this rear projection film is 6:1, the half-peak width angle of the scattered light intensity is 175°, the transmittance is 72%, the haze is 18%, the contrast is 64:1, and the gain is 2.3.

Example 4

(1) A high molecular transparent plastic with a refractive index m ₀ =1.50 is used as a transparent film material for making a transparent optical film, and PS (polystyrene) microspheres with a particle size D =300 nm and a refractive index m ₁ =1.6 are used.

(2) A certain amount of PS microspheres with a particle size of 300 nm are spread evenly on the surface of a transparent polymer plastic.

(3) heating the polymer plastic to soften it, pressing the microspheres spread on the surface of the polymer plastic into the interior of the film, and then cooling the polymer plastic to room temperature, cooling and solidifying it to obtain a transparent optical film;

(4) An anti-reflection film with a light transmittance of T ₂ = 99% is laminated on the transparent optical film to finally produce a transparent two-layer rear projection film.

The experimental results show that the ratio of total scattered light intensity between the front and back sides of this rear projection film is 11:1, the half-peak width angle of scattered light intensity is 167°, the transmittance is 93%, the haze is 8%, the contrast is 44:1, and the gain is 1.9.

Example 5

(1) Now, a molecular transparent plastic with a refractive index of m ₀ =1.58 is used as a transparent film material for making a transparent optical film, and PS (polystyrene) microspheres with a particle size of D =10 μm and m ₁ =1.6 are used.

(2) A certain amount of PS microspheres with a particle size of 10 μm are spread evenly on the surface of a transparent polymer plastic.

(3) heating the polymer plastic to soften it, pressing the microspheres spread on the surface of the polymer plastic into the interior of the film, and then cooling the polymer plastic to room temperature, cooling and solidifying it to obtain a transparent optical film;

(4) An anti-reflection film with a light transmittance of T ₂ = 99% is laminated on the transparent optical film to finally produce a transparent two-layer rear projection film.

The experimental results show that the ratio of total scattered light intensity between the front and back sides of this rear projection film is 24:1, the half-peak width angle of the scattered light intensity is 39°, the transmittance is 91%, the haze is 7%, the contrast is 46:1, and the gain is 1.8.

(Rear projection transparent display system embodiment)

The transparent display system includes a transparent rear projection film, which has the same structure and function as the transparent rear projection film in the above transparent rear projection film embodiment, and will not be described in detail here.

The transparent display system further comprises a projection device, and the projection device is used to generate a projection image through the transparent rear projection film.

Referring to FIG. 12 , FIG. 12 shows a schematic diagram of a rear-projection transparent display system provided by the present application.

The surface of the transparent rear projection film facing away from the projector 210 in the transparent display system is the surface where the audience 220 views the image, and is also the front side of the transparent rear projection film. Correspondingly, the surface facing the projector 210 is the back side of the transparent rear projection film. The surface of the transparent optical film facing away from the projector 210 is the exit side, and correspondingly, the surface facing the projector 210 is the incident side.

Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims (12)

1. A transparent optical film, characterized in that the optical film comprises: A dielectric layer, the dielectric layer is composed of an optically uniform and transparent medium, and the dielectric layer includes an incident surface and an exit surface opposite to each other; A plurality of scattering particles, wherein the plurality of scattering particles are distributed in the dielectric layer to partially scatter the light incident into the optical film through the incident surface, and the scattered light is distributed on one side of the incident surface and one side of the exit surface of the optical film; The refractive index of the scattering particles is different from the refractive index of the medium, and the total intensity of scattered light on the exit surface is at least 3 times the total intensity of scattered light on the incident surface. 2 . The transparent optical film according to claim 1 , wherein the half-peak width angle of the scattered light intensity on the exit surface is 30°-150°. 3. The transparent optical film according to claim 1 or 2, characterized in that the medium is selected from transparent high molecular polymers, and the scattering particles are selected from any one of polystyrene microspheres, PMMA microspheres, silica microspheres, silicone microspheres, latex microspheres and metal microspheres. 4 . The transparent optical film according to claim 3 , wherein the diameter of the microspheres is 0.05 μm to 50 μm. 5 . The transparent optical film according to claim 1 , wherein the scattering particles partially scatter the light incident into the optical film through the incident surface based on Mie scattering theory. 6. A method for preparing a transparent optical film, characterized in that the method for preparing the transparent optical film is applicable to the transparent optical film according to any one of claims 3 to 5, and the specific steps are as follows: S101, preparing a particle liquid with a mass fraction of μ by mixing a plurality of scattering particles with water or an organic solvent; S102, fully mixing the particle liquid and an uncured high molecular polymer solution having a solid content of g to obtain a high molecular polymer mixed solution; S103, uniformly coating the high molecular polymer mixed solution on a transparent substrate film by a coating method to form a film; S104, according to the polymerization characteristics of the high molecular polymer, the high molecular polymer mixed solution after film formation is heated and volatilized and then solidified to obtain a transparent optical film containing scattering particles. 7. A method for preparing a transparent optical film, characterized in that the method for preparing the transparent optical film is applicable to the transparent optical film according to any one of claims 3 to 5, and the specific steps are as follows: S201, spreading a plurality of scattering particles on the surface of the transparent high molecular polymer film; S202, heating the transparent high molecular polymer film until it softens; S203, pressing the plurality of scattering particles spread on the surface of the transparent high molecular polymer film into the interior of the film; S204, cooling the transparent high molecular polymer film containing the scattering particles to room temperature to obtain a transparent optical film containing scattering particles. 8. A transparent rear projection film, characterized in that the transparent rear projection film comprises the transparent optical film according to any one of claims 1 to 5. 9 . The transparent rear projection film according to claim 8 , further comprising a transparent base layer, wherein the transparent base layer is disposed on at least one side of the transparent optical film. 10 . The transparent rear projection film according to claim 9 , wherein the transparent base layer is selected from any one of PET, PMMA, PC, an anti-reflection film and a high-absorption film. 11. The transparent rear projection film according to any one of claims 8 to 10, characterized in that the transparent rear projection film further comprises an anti-reflection layer, and the anti-reflection layer for reducing reflectivity is disposed on at least one side of the transparent optical film. 12. A rear-projection transparent display system, characterized in that the transparent display system comprises the transparent rear-projection film according to any one of claims 8 to 11, and the transparent display system further comprises a projection device, and the projection device is used to generate a projection image through the transparent rear-projection film.