Prism sheet and backlight module incorporating same

A prism sheet (10) includes a substrate (12) and a plurality of prism structures (14). The substrate includes a plurality of diffusing particles (122) dispersed therein. The prism structures are at a light output side of the substrate. The diffusing particles can diffuse light beams traveling through the substrate. This configuration performs the same function as that of a diffusing sheet of a conventional backlight module. The prism structures can gather light beams to improve a brightness of a backlight module (6) incorporating the prism sheet. Thus, the backlight module can provide bright and uniform light at a low cost and while having a reduced thickness.

FIELD OF THE INVENTION

The present invention relates to a prism sheet and a backlight module for an apparatus such as a liquid crystal display device.

GENERAL BACKGROUND

Liquid crystal displays (LCDs) are commonly used as display devices for compact electronic apparatuses, because they not only provide good quality images with little power but are also very thin. The liquid crystal molecules in an LCD do not emit any light themselves. The liquid crystal molecules have to be lit by a light source so as to clearly and sharply display text and images. Thus, a backlight module for an LCD is generally needed. A prism sheet is generally needed in a backlight module for improving a brightness of the backlight module.

Referring toFIG. 7, a conventional prism sheet70includes a substrate72having a plurality of prism structures74integrally formed at a light output surface thereof. The prism sheet70can gather light beams to improve a brightness of an associated backlight module (not shown). However, the prism sheet70generally needs to cooperate with a diffusing sheet (not shown) in order to provide uniform light beams, which adds to the overall thickness and the cost of the backlight module.

Referring toFIG. 8, another conventional prism sheet80includes a plurality of prism structures82, a substrate84, and a diffusing layer86arranged in that order from top to bottom. The diffusing layer86includes a plurality of diffusing particles861formed therein, which enables the prism sheet80to uniformly emit light beams out from the prism structures82. However, the diffusing layer86is generally a structure formed separately from the substrate84, and therefore adds to the overall thickness of the prism sheet80.

What is needed, therefore, is a prism sheet that can overcome the above-described deficiencies.

SUMMARY

A prism sheet includes a substrate and a plurality of prism structures. The substrate includes a plurality of diffusing particles dispersed therein. The prism structures are at a light output side of the substrate. The diffusing particles can diffuse light beams traveling through the substrate. The prism structures can gather light beams to improve a brightness of a backlight module incorporating the prism sheet.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe the preferred embodiments in detail.

FIG. 1is a side cross-sectional view of part of a prism sheet according to a first embodiment of the present invention. The prism sheet10includes a substrate12and a plurality of prism structures14integrally formed thereon. The prism structures14are parallel to each other. Each prism structure14includes a portion142having a triangular cross-section. The triangular cross-section defines an acute apex angle α. In the illustrated embodiment, the triangle of the triangular cross-section is an isosceles triangle. The substrate12includes a plurality of spherical diffusing particles122randomly dispersed therein, and a planar bottom surface124opposite to the prism structures14.

The diffusing particles122can be formed together with the substrate12by an injection molding method, or be formed by a laser method or an ultrasonic method after injection molding of the substrate12. The substrate12can be made from transparent material with a high refraction index and a high light transmission index, such as polyester, polycarbonate (PC) or polymethyl methacrylate (PMMA). The diffusing particles122can be made from silicon dioxide (SiO2), aluminum oxide (Al2O3), or a same material as that of the substrate12.

Advantageously, in the first embodiment, the prism sheet10includes the plurality of diffusing particles122formed in the substrate12. The diffusing particles122can diffuse light beams traveling therethrough. Thus, the prism sheet10can diffuse light beams while having a reduced thickness.

FIG. 2is a side cross-sectional view of part of a prism sheet according to a second embodiment of the present invention. The prism sheet20is similar to the prism sheet10. However, a substrate22of the prism sheet20includes a plurality of hemispherical diffusing particles222dispersed therein.

FIG. 3is a side cross-sectional view of part of a prism sheet according to a third embodiment of the present invention. The prism sheet30is similar to the prism sheet10. However, a substrate32of the prism sheet30includes a plurality of conical diffusing particles322dispersed therein.

FIG. 4is a side cross-sectional view of part of a prism sheet according to a fourth embodiment of the present invention. The prism sheet40is similar to the prism sheet10. However, each of prism structures44of the prism sheet40includes a portion442having a cross-section with tapering sides and a curved top. In the illustrated embodiment, the tapering sides are straight and symmetrical with respect to each other, and the curved top is arcuate.

FIG. 5is a side cross-sectional view of part of a prism sheet according to a fifth embodiment of the present invention. The prism sheet50is similar to the prism sheet10. However, a substrate52of the prism sheet50includes a wavy bottom surface524.

Referring toFIG. 6, a backlight module6includes the prism sheet10, a light guide plate62, a reflective sheet64, and a light source66. The light guide plate62includes a light incident surface622, a light emitting surface624adjoining the light incident surface622, and a bottom surface626opposite to the light emitting surface624. The light source66is disposed adjacent to the light incident surface622of the light guide plate62. The prism sheet10is disposed adjacent to the light emitting surface624of the light guide plate62. The reflective sheet64is disposed adjacent to the bottom surface626of the light guide plate62.

Light beams emitted from the light source66enter the light guide plate62through the light incident surface622. Some light beams emit directly out from the light guide plate62through the light emitting surface624and into the prism sheet10. Other light beams emit from the light guide plate62through the bottom surface626and transmit to the reflective sheet64. These light beams are reflected back to light guide plate62, and finally emit from the light guide plate62through the light emitting surface624and into the prism sheet10. The diffusing particles122in the substrate12can diffuse light beams traveling through the substrate12. This configuration performs a similar function to that of a diffusing sheet of a conventional backlight module, therefore the backlight module6does not need a diffusing sheet. In addition, the prism sheet10can gather light beams to improve a brightness of the backlight module6. Thus, the backlight module6can provide bright and uniform light at a low cost and while having a reduced thickness.

In alternative embodiments of various of the above-described embodiments, the apex angle of the cross-section portion of each prism structure can be a right angle or an obtuse angle. The sizes, density and distribution of the diffusing particles can be configured according to different requirements of various applications.