[DESCRIPTION] [Invention Title]

SECURITY FILM FOR DISPLAY DEVICE AND METHOD OF MANUFACTURING THE SAME [Technical Field]

The present invention relates to a security film for a display device and a method of manufacturing the same. [Background Art]

A portable information communication device such as a notebook computer, a personal digital assistant (PDA) or a mobile phone, an automated teller machine (ATM) such as a financial institution is used to store or input various data and personal information. The data and information are displayed and inputted through a display screen of the corresponding device.

However, since a conventional display screen has been developed to enhance a wide viewing angle and high luminance, others can easily observe a screen from a side of a display device. Therefore, there was a serious security problem that personal information and important data may be exposed to others.

Recently, a security film for a display device has been developed in order to solve such a problem. As shown in Fig. 1, a conventional security film 100 for a display device has a structure in which transparent light-transmissive portions 110 and opaque non- transmissive portions 120 are alternately formed along a horizontal direction of the security film 100.

Fig. 2 is a view illustrating a process of manufacturing the security film 100 having such a structure. A plurality of light-transmissive films 101 and a plurality of non- transmissive films 102 alternately adhere to each other and then cut in a predetermined thickness, thereby manufacturing the security film 100 in which the light-transmissive portions 110 and the non-transmissive portions 120 are alternately formed.

As shown in Figs. 3 and 4, the security film 100 manufactured as described above prevents side emission of light in a state where the security film 100 adheres to a front surface of a liquid crystal panel 200 of a display device, so that the viewing angle θ of

the liquid crystal panel 200 is reduced. Accordingly, it is possible to prevent images displayed on the liquid crystal panel of the display device from being exposed to others.

However, in the method of manufacturing the conventional security film 100 for a display device, the alternately adhering and stacking process is performed after preparing all of the light-transmissive films 101 and the non-transmissive films 102, and the cutting process is then performed. For this reason, an increase in the number of materials and manufacturing processes is unavoidable. Therefore, productivity of security films may be lowered, and price of products may be increased.

Further, in the cutting process after the light-transmissive films 101 and the non- transmissive films 102 are alternately bonded to each other, it is extremely difficult to secure uniformity of products. [Disclosure] [Technical Problem]

Accordingly, an object of the present invention is to provide a security film for a display device and a method of manufacturing the same, which can improve productivity, lower price of products and maintain uniformity thereof. [Technical Solution]

According to an aspect of the present invention for achieving the object, there is provided a security film for a display device, which comprises a birefringent layer formed of a material having a birefringence property and having a plurality of linear protrusion portions and a plurality of linear groove portions alternately arranged on an exit surface thereof, wherein the plurality of linear protrusion portions allow polarization of incident light to be changed and then the light to be transmitted and the plurality of linear groove portions allow polarization of incident light not to be changed or to be changed less than the linear protrusion portions and then the light to be transmitted; and a polarizing layer provided on the exit surface of the birefringent layer, wherein the polarizing layer allows the polarized light transmitted through any one of the protrusion and groove portions to be transmitted but the polarized light transmitted through the other of the protrusion and groove portions not to be transmitted. Here, it is preferable that a phase delay value A of the protrusion portion, a phase

delay value B of the groove portion and maximum and minimum wavelengths λ _max and λ _m i _n of light incident on the birefringent layer have a relation as follows: A - B| ≥ a x λ _min - lOOnm and |A - B| < a x λ _mjn + 100nm where "a" is an integer. In addition, the width w and height h of the linear protrusion portion may have a relation of w/h≤l, and the width w of the linear protrusion portion and width w' of the groove portion may have a relation of w/w' ≤ 1.

In the meantime, the polarizing layer may adhere to the exit surface of the birefringent layer, or be disposed to be spaced apart from the exit surface of the birefringent layer. A light-transmissive transparent reinforcement layer may adhere to at least one of an incident surface of the birefringent layer and an exit surface of the polarizing layer.

A method of manufacturing a security film for a display device according to the present invention comprises the steps of forming a birefringent layer formed of a material having birefringence a property and having a plurality of linear protrusion portions and a plurality of linear groove portions alternately arranged on an exit surface thereof, wherein the plurality of linear protrusion portions allow polarization of incident light to be changed and then the light to be transmitted and the plurality of linear groove portions allow polarization of incident light not to be changed or to be changed less than the linear protrusion portions and then the light to be transmitted; and forming a polarizing layer provided on the exit surface of the birefringent layer, wherein the polarizing layer allows the polarized light transmitted through any one of the protrusion and groove portions to be transmitted but the polarized light transmitted through the other of the protrusion and groove portions not to be transmitted. In addition, the method according to the present invention may further comprise a step of allowing a light-transmissive transparent reinforcement layer to adhere to at least one of an incident surface of the birefringent layer and an exit surface of the polarizing layer. [Advantageous Effects]

As described above, a security film according to the present invention has a simple structure and makes it difficult for others to observe a display screen from a side of a display device. In addition, the simple structure makes it possible to improve productivity of security films and simplify a manufacturing process. [Description of Drawings]

Fig. 1 is a perspective view of a conventional security film for a display device. Fig. 2 is a view illustrating a process of manufacturing the security film for a display device shown in Fig. 1.

Fig. 3 is a perspective view showing a use state of the security film for a display device shown in Fig. 1.

Fig. 4 is a partial sectional view of a liquid crystal panel of a display device and the security film shown in Fig. 3.

Fig. 5 is an exploded perspective view of a security film for a display device according to the present invention. Fig. 6 is a sectional view of the security film in a state where components shown in Fig. 5 are assembled.

Fig. 7 is a view illustrating the optical operation of the security film for a display device shown in Fig. 5.

Fig. 8 is a sectional view of a security film for a display device according to another embodiment of the present invention.

Fig. 9 is a flowchart illustrating a process of manufacturing a security film for a display device according to the present invention.

Fig. 10 is a partial sectional view showing the security film for a display device according to the present invention adhering to a liquid crystal panel of a display device. Fig. 11 is a graph showing a simulation result for a viewing angle of the security film according to the present invention. [Best Mode]

Fig. 5 is an exploded perspective view of a security film for a display device according to the present invention. Fig. 6 is a sectional view of the security film in a state where components shown in Fig. 5 are assembled. Fig. 7 is a view illustrating the optical

operation of the security film for a display device shown in Fig. 5.

As shown in these figures, a security film 1 for a display device according to the present invention comprises a birefringent layer 10 made of a birefringent resin film, and a polarizing layer 20 adhering to an exit surface of the birefringent layer 10. The birefringent layer 10 comprises an incident surface on which light emitted from a display device (a liquid crystal panel) is incident, and an exit surface from which the light exits. The birefringent layer 10 has a concavo-convex structure in which a plurality of linear protrusion portions lib and a plurality of linear groove portions 11a are formed on any one surface of the birefringent layer 10. The plurality of linear protrusion portions lib and the plurality of linear groove portions 11a of the concavo-convex structure extend in the same direction and are disposed alternately.

Here, the surface having the plurality of linear protrusion portions lib and the plurality of linear groove portions 11a formed thereon is preferably used as the exit surface.

As shown in Fig. 7, in the birefringent layer 10 having the aforementioned structure, the linear protrusion portions lib allow polarization of incident light to be changed and the light to exit, and the linear groove portions 11a allow polarization of incident light not to be changed or to be changed less than the linear protrusion portions lib.

At this time, each of the protrusion portions lib and the groove portions 11a has a phase delay value, which is adjusted by allowing polarization of incident light to be phase delayed. In the present invention, a phase delay value A of the protrusion portion lib, a phase delay value B of the groove portion 11a and maximum and minimum wavelengths λ _max and λ _m i _n of incident light have a relation of the following expressions 1 and 2: A - B| ≥ ax λ _min - 100nm (1) |A - B| < a x λ _min + 100nm (2) where "a" is an integer, and AíB.

Expression 1 is a condition for ensuring a transmittance of 10% or more, at which when the security film 1 is attached on a liquid crystal panel 40 (see Fig. 10) of a display device, a user can observe images displayed on the liquid crystal panel 40.

Meanwhile, width w and height h of each of the protrusion portions lib have a relation of w/h≤l, and the width w of each of the protrusion portions l ib and width w' of each of the groove portions 11a have a relation of w/w'≤l, so that a viewing angle θ of the security film 1 can be effectively restricted. Fig. 11 is a graph showing a simulation result for a viewing angle obtained when w/h≤ 1 and w/w' ≤ 1 in the security film according to the present invention. Generally, a security film satisfies its left and right viewing angles of 45 degrees or less. In the present invention, it can be seen that the security film 1 provides a viewing angle of 45 degrees or less when w/h≤ 1 and w/w' ≤ 1. In the meantime, the hot embossing method may be used as a method of forming the aforementioned birefringent layer 10 having the concavo-convex structure. That is, a hot embossing method using a mold or wire stamper is performed on a birefringent resin film that is a raw material of the birefringent layer 10, so that the linear groove portions 11a and the linear protrusion portions lib are alternately formed on the exit surface of the birefringent layer 10.

Here, the birefringent layer 10 may be manufactured by forming a plurality of linear groove portions 11a and a plurality of linear protrusion portions lib on a single resin film. Alternatively, the birefringent layer 10 may also be manufactured by applying a resin film that is a raw material to a light-transmissive substrate and then forming the linear groove and protrusion portions 11a and lib constituting a concavo-convex structure on one surface (exit surface) of the birefringent layer 10 using the aforementioned hot embossing method.

The polarizing layer 20 is formed of a polarizing film, through which the polarized light changed in the birefringent layer 10 is transmitted and the polarized light not or less changed therein is not transmitted. The polarizing layer 20 is positioned on the exit surface of the birefringent layer 10.

At this time, the polarizing layer 20 may directly adhere to the exit surface on which the concavo-convex structure (the plurality of linear protrusion portions lib and the plurality of linear groove portions Ha) of the birefringent layer 10 is formed. Although not shown, the polarizing layer 20 may be manufactured as a separate optical component

and disposed to be spaced apart from the exit surface of the birefringent layer 10.

The polarized light exiting from the birefringent layer 10 exits through regions corresponding to the linear protrusion portions lib in the polarizing layer 20. Therefore, when light is two-dimensionally viewed from the exit surface of the polarizing layer 20, a plurality of bright regions 21b and a plurality of dark regions 21a are linearly arranged in parallel with each other and alternately, wherein the plurality of bright regions 21b correspond to the plurality of linear protrusion portions lib of the birefringent layer 10, and the plurality of dark regions 21a correspond to the plurality of linear groove portions 11a of the birefringent layer 10. It will be apparent that if the direction of the polarizing layer 20 is changed, the polarized light changed in the linear protrusion portions l ib is not transmitted through the polarizing layer 20, and the polarized light which is not or less changed in the linear groove portions 11a is transmitted through the polarizing layer 20. Accordingly, the polarized light exiting through the polarizing layer 20 exits through the regions corresponding to the linear groove portions 11 a formed in the birefringent layer 10. Thus, when light is two-dimensionally viewed from the exit surface of the polarizing layer 20, dark and bright regions, which correspond to the linear protrusion portions lib and the linear groove portions 11a, can be linearly arranged in parallel with each other and alternately. Fig. 8 is a sectional view of a security film for a display device according to another embodiment of the present invention. The security film 1 according to the present invention may further comprise a reinforcement layer 30 such as a light- transmissive transparent substrate adhering to the incident surface of the birefringent layer 10 and/or the exit surface of the polarizing layer 20 so as to enhance strength of the security film 1.

A method of manufacturing the security film 1 for a display device with such an optical structure according to the present invention comprises a step SOl of forming a birefringent layer 10 having a concavo-convex structure in which a plurality of linear protrusion portions l ib and a plurality of linear groove portions 1 Ia are formed on any one surface of a resin film; and a step S02 of forming a polarizing layer 20 on the surface on

which the linear protrusion portions lib and the linear groove portions 11a of the birefringent layer 10 are formed.

In the step SOl of forming the birefringent layer 10 having the plurality of linear protrusion portions lib and the plurality of linear groove portions 11a, the plurality of linear protrusion portions l ib and the plurality of linear groove portions 11a are formed on any one surface of a resin film having a birefringence property using the hot embossing method, as described above.

If the linear protrusion portions lib and the linear groove portions 11a are formed, the light incident on the linear groove portions 11a of the birefringent layer 10 is not or less changed in polarization due to the birefringence property and then exits therefrom. The light incident on the linear protrusion portions lib of the birefringent layer 10 is changed in polarization and then exits therefrom.

In the step S02 of forming the polarizing layer 20 of the birefringent layer 10, a polarizing film having an optical property, which allows the polarized light changed in the birefringent layer 10 to be transmitted but the polarized light not or less changed in the birefringent layer 10 not to be transmitted, is optically coupled to the exit surface of the birefringent layer 10, i.e., the surface on which the linear protrusion portions lib and the linear groove portions 11a are formed.

At this time, the polarizing layer 20 may be optically coupled to the surface of the birefringent layer 10 (the surface on which the linear protrusion portions lib and the linear groove portions 11a are formed) by an adhesive material or the like. Alternatively, the polarizing layer 20 may be directly attached on the birefringent layer 10 before the birefringent layer 10 is cured.

As described above, the polarizing layer 20 may be manufactured as a separate optical component and disposed to be spaced apart from the exit surface of the birefringent layer 10. By changing the direction in which the polarizing layer is optically coupled, the polarizing layer 20 allows the polarized light changed in the birefringent layer 10 not to be transmitted but the polarized light not or less changed in the birefringent layer 10 to be transmitted. Meanwhile, in order to enhance the strength of the security film 1 , the method of

manufacturing a security film according to the present invention may further comprise a step of forming the reinforcement layer 30 such as a light-transmissive transparent substrate adhering to the incident surface of the birefringent layer 10 and/or the exit surface of the polarizing layer 20. As shown in Fig. 10, in the security film 1 configured and manufactured as described above, bright regions 21b and dark regions 21a respectively corresponding to the plurality of linear protrusion portions lib of the birefringent layer 10 and the plurality of linear groove portions 11a are formed in a state where the security film 1 adheres to a liquid crystal panel 40 of a display device. Therefore, the dark regions 21a prevent the light from laterally exiting from the liquid crystal panel 40 of the display panel, thereby decreasing a viewing angle θ of the liquid crystal panel 40.

Accordingly, images displayed on the liquid crystal panel 40 of the display device are not observed from a side of the display panel, so that it is possible to prevent the images from being exposed to others, and security of the images can be maintained. As described above, in a security film for a display device and a method of manufacturing the same according to the present invention, a birefringent layer having a plurality of linear protrusion portions and a plurality of linear groove portions is formed using a hot embossing method, and a polarizing layer is formed on the surface on which the plurality of linear protrusion portions and the plurality of linear groove portions are formed, whereby the number of materials and manufacturing processes can be remarkably decreased. Accordingly, productivity of security films can be improved, and price of products can be lowered.

Further, a plurality of linear protrusion portions and a plurality of linear groove portions are formed on one surface of a birefringent layer by a hot embossing method using a mold or stamper, and a polarizing layer is formed on the surface of the birefringent layer, so that a variation of products can be remarkably reduced. Accordingly, uniformity of products can be maintained.