Backlight module and brightness enhancement film thereof

A backlight module includes a light source, a light guide plate for guiding light from the light source, and a brightness enhancement film having a plurality of spherical surface microlenses for gathering light from the light guide plate. In contrast to traditional prism sheets, the brightness enhancement film having the plurality of spherical surface microlenses have better efficiency of light-gathering.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight module used in a liquid crystal display, and more particularly, to a backlight module with a brightness enhancement film having a plurality of spherical surface microlenses.

2. Description of the Related Art

A backlight module is a key component of a liquid crystal display (LCD). The purpose of the backlight module is to provide a sufficient-brightness and an even-distribution light surface to the LCD panel. Because the LCD is widely used in various electronic products such as a monitor, a notebook computer, a digital camera, and a projector, the demand for the backlight module has increased tremendously.

Please refer toFIG. 1, which shows a prior art of a backlight module20. The backlight module20comprises a light source22(such as a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light emitting diode), a light guide plate26, a reflector24disposed at a side of the light guide plate26, a diffusion sheet28, and prism sheets30and32. The reflector24is used for reflecting light from the light source22toward the light guide plate26. Then the light guide plate26guides light emitted from the light source22and light reflected from the reflector24as uniform planar light. Through the light-distributing of the diffusion sheet28and light-gathering of the prism sheets30and32, the light is fed into an LCD panel. The prism sheets30and32are formed by hardening an acrylic resin on a polyester film with a thickness of 125-μm by means of exposure under high energy UV light. The conventional prism sheets30and32are served as bar-alignment triangle prisms in characteristics of a vertex angle of substantial 90 degrees with an interval of 50 μm within each other. The prism sheets30and32can concentrate scatter light from the light guide plate26upward with substantial ±35 degrees with respect to a direction of an on-axis. Nevertheless, as shown inFIG. 1, the prism sheet30only concentrate light constituent of Y-axis upward, and the prism sheet32only concentrate light constituent of X-axis upward. Therefore, utilizing only a single prism sheet can enhance the brightness by 1.6 times, while, for better light-gathering quality, utilizing two prism sheets30and32with their prism alignments thereon being vertical to each other can enhance the brightness by 2 times or more. In other words, scatter light is gathered by means of prisms on the prism sheets30and32, therefore boosting the brightness of the LCD display by 2 times. In this manner, for the LCD display described above, power consumption is lowered and a life span of batteries is lengthened.

Consequently, using a single prism sheet fails to provide sufficient brightness, while using two prism sheets may result in more photo-energy consumption. Besides, using two prism sheets may induce higher cost for the backlight module as a result.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a backlight module comprising a brightness enhancement film with a plurality of spherical surface microlenses in lieu of a backlight module having two conventional prism sheets to solve the problem existing in prior art.

Briefly summarized, the invention provides a backlight module comprising a light source, a light guide plate for guiding light from the light source, and a brightness enhancement film comprising a plurality of spherical surface microlenses for gathering light from the light guide plate.

It is an advantage of the present invention that using one brightness enhancement film with a plurality of spherical surface microlenses thereon in lieu of the conventional structure of two prism sheets. The scatter light from the light guide plate can be concentrated toward a direction of an on-axis by the spherical surface microlenses, solving the conventional defect of needing to use two prism sheets to concentrate light.

The disclosed inventions will be described with references to the accompanying drawings, which show important example embodiments of the inventions and are incorporated in the specification hereof by related references.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Please refer toFIG. 2, which shows a backlight module50in accordance with the present invention. The backlight module50comprises a light source52(such as a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light emitting diode), a light guide plate56, a reflector54disposed at a side of the light guide plate56, and a brightness enhancement film60. The reflector54is used for reflecting light from the light source52toward the light guide plate56. The light guide plate56guides light emitted from the light source52and light reflected from the reflector54and distributes the light as a uniform planar light source. Through the light-distributing of the diffusion sheet58and light-gathering of the brightness enhancement film60, the light is fed into an LCD panel. InFIG. 2, the diffusion sheet58is preferably disposed between the brightness enhancement film60and the light guild plate56. In other embodiments, either disposing the diffusion sheet58over the brightness enhancement film60, or no diffusion sheet arrangement is also allowed.

Please refer toFIG. 3toFIG. 8.FIG. 3andFIG. 4, respectively, are an enlarged view and a side view of a first embodiment of the brightness enhancement film60depicted inFIG. 2. The brightness enhancement film60comprises a plurality of spherical surface microlenses62aand a plurality of carriers64a. Each spherical surface microlens62ais disposed on corresponding one of the plurality of carriers64a. Each of the plurality of carriers64ais closely disposed with each other. The plurality of carriers64aare substantially shaped as triangles.

FIG. 5andFIG. 6, respectively, are an enlarged view and a side view of a second embodiment of the brightness enhancement film60depicted inFIG. 2. The brightness enhancement film60comprises a plurality of spherical surface microlenses62band a plurality of carriers64b. Each spherical surface microlens62bis disposed on corresponding one of the plurality of carriers64b. Each of the plurality of carriers64bis closely disposed with each other. The plurality of carriers64bare substantially shaped as rectangles.

FIG. 7andFIG. 8, respectively, are an enlarged view and a side view of a third embodiment of the brightness enhancement film60depicted inFIG. 2. The brightness enhancement film60comprises a plurality of spherical surface microlenses62cand a plurality of carriers64c. Each spherical surface microlen62cis disposed on corresponding one of the plurality of carriers64c. Each of the plurality of carriers64cis closely disposed with each other. The plurality of carriers64care substantially shaped as hexagons.

A resolution for better light-gathering performance is to increase a thickness of the carriers64a,64bor64c, or cushioning the carriers64a,64bor64cwith another carrier to obtain a higher ratio of height and width (h/w) of the brightness enhancement film60.

Referring toFIG. 9, the spherical surface microlenses62can refract any light constituents from the light guide plate56upward.

Please refer toFIGS. 10A-10I, which illustrate a flow of forming the brightness enhancement film according to the present invention. First of all, as shown inFIG. 10A, a first photoresist210(e.g. Az9260) is spread on a substrate200in a spin-coating manner. Next, a second photoresist220(e.g. AZ4620) is also spread evenly on the first photoresist210in a spin-coating manner. It is appreciated that melting point of the first photoresist210should be higher than that of the second photoresist220. Then, as shown inFIG. 10B, etching the first photoresist210and the second photoresist220are performed to form an array pattern. As can be seen inFIG. 10C, in a process of reflowing the first photoresist210and the second photoresist220, due to the fact that the melting point of the first photoresist210is higher than that of the second photoresist220, it happens that the first photoresist210is not completely melted but the second photoresist220has already melted. In doing so, the melted second photoresist220forms a half-sphere due to surface tension as the first photoresist210does not melt completely. As shown inFIG. 10D, sputtering a nickel film230on the first photoresist210and the second photoresist220is executed after cooling the photoresists210and220.

Next, electroplating a Ni—Co film240on the nickel film230and sputtering an Au film250on the Ni—Co film240are illustrated inFIG. 10E. Furthermore, the first photoresist210and the second photoresist220, covering with metal films230,240,250, are electroformed to form a cast260, as shown inFIGS. 10F and 10GFinally, a metal mold270is obtained by re-electroforming the cast260. Accordingly, a mass production of the brightness enhancement film60with a plurality of spherical surface microlenses is possible by injecting plastic material280such as polyester or polycarbonate into the metal mold270, as shown inFIGS. 10H and 10I.

Preferably, spherical surface microlens62a,62b, and62care substantially shaped as spheres. However, in real process of forming the metal mold270, the appearance of the melted second photoresist220, due to incomplete melt of the first photoresist210, is as shown inFIG. 11, rather than a half-sphere. As a result, the appearance of the spherical surface microlenses of the brightness enhancement film60made by the metal mold270is similar to the appearance shown inFIG. 11.

In contrast to prior art, the present inventive backlight module uses a brightness enhancement film with a plurality of spherical surface microlenses thereon in lieu of the conventional structure of two prism sheets. The scatter light from the light guide plate can be concentrated toward a direction of an on-axis by the spherical surface microlenses, solving the defect of the use of two prism sheets. In addition, the present inventive brightness enhancement film has the function of light-gathering and light-distributing. Since the light only passes through a single brightness enhancement film, photo energy consumption is reduced. Therefore, the use of the present inventive brightness enhancement film not only lowers costs, but also reduces power consumption.

The present invention has been described with references to certain preferred and alternative embodiments which are intended to be exemplary only and not limiting to the full scope of the present invention as set forth in the appended claims.