TWI435121B - Diffusing film and backlight module utilizing the same - Google Patents

Description

Diffusion sheet and backlight module

The invention relates to a diffusion sheet, in particular to a diffusion sheet which utilizes surface roughness to cause atomization effect of light and a backlight module using the diffusion sheet.

Liquid crystal display devices have been widely used in various electronic devices, such as notebook type, because of their advantages of thinness, light weight, low power consumption, no radiation pollution, and compatibility with semiconductor process technology. Computers, mobile phones, digital cameras, personal digital assistants, etc. The liquid crystal display device provides light to the display panel through the backlight module to display a picture. In general, a backlight module typically has a combination of light sources and an optical film combination. The light source combination is used to provide light, and the optical film combination is used to improve the optical properties of the light. The optical film included in the optical film combination is, for example, a crepe sheet, a diffusion sheet, or the like.

Please refer to FIG. 1. FIG. 1 is a schematic view of a diffusion sheet 10 of the prior art. As shown in Fig. 1, the diffusion sheet 10 is composed of a substrate 100 (for example, polyethylene terephthalate PET) and diffusion layers 120 and 140 coated on the upper and lower surfaces of the substrate 100. The prior art is doped with a plurality of beads 160 (e.g., polymethyl methacrylate PMMA) in the diffusion layers 120, 140 to impart a fogging effect to the light passing through the diffusion sheet 10. However, when the backlight module or the display device provided with the diffusion sheet 10 is shaken or vibrated, the beads 160 in the diffusion layers 120, 140 easily fall off or scratch the upper and lower surfaces of the substrate 100, or when the diffusion sheet 10 is applied When the device is displayed, adjacent optical sheets or objects are scratched, and an interference fringe phenomenon (mura) appears on the display screen. In addition, the diffusion sheet 10 doped with the plurality of beads 160 also affects the grade characteristics of the display device, so that the viewing comfort of the user is lowered, and an unknown pattern caused by the beads 160 is easily observed from the display device.

One of the objects of the present invention is to provide a diffusion sheet and a backlight module using the same to solve the above problems.

According to an embodiment, the diffusion sheet of the present invention comprises a substrate, a first diffusion layer and a second diffusion layer. The first diffusion layer is disposed on the substrate, and the second diffusion layer is disposed on the first diffusion layer. The first diffusion layer includes a first surface structure, and the first surface structure has a first peak count value of roughness (Rpc). The second diffusion layer includes a second surface structure and a third surface structure, wherein the second surface structure and the third surface structure are respectively formed on opposite sides of the second diffusion layer, and the third surface structure coincides with the first surface structure . The second surface structure has a second roughness peak value, and the second roughness peak value is greater than or equal to the first roughness peak value.

According to another embodiment, a backlight module of the present invention includes an optical film combination and a light source combination. The optical film assembly includes a first diffusion sheet, and the first diffusion sheet is located at the outermost side of the optical film assembly. The first diffusion sheet comprises a substrate, a first diffusion layer and a second diffusion layer. The first diffusion layer is disposed on the substrate, and the second diffusion layer is disposed on the first diffusion layer. The first diffusion layer includes a first surface structure, and the first surface structure has a first roughness peak value. The second diffusion layer includes a second surface structure and a third surface structure, wherein the second surface structure and the third surface structure are respectively formed on opposite sides of the second diffusion layer, and the third surface structure coincides with the first surface structure . The second surface structure has a second roughness peak value, and the second roughness peak value is greater than or equal to the first roughness peak value.

In summary, the present invention is characterized in that different diffusion layers respectively form surface structures having different or the same roughness peak values, so that the light passing through the diffusion sheet produces an atomization effect. Therefore, the diffusion sheet of the present invention does not need to dope the beads in the diffusion layer, thereby avoiding problems such as falling off of the beads or scratching the surface of the substrate.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

Please refer to FIG. 2, which is a schematic diagram of a backlight module 3 according to an embodiment of the invention. As shown in FIG. 2, the backlight module 3 includes an optical film assembly 30 and a light source combination 32, wherein the optical film assembly 30 is disposed on the light source assembly 32. The backlight module 3 can be applied to a liquid crystal display. The optical film assembly 30 includes a first diffusion sheet 300, a first gusset 302, a second gusset 304, and a second diffusion sheet 306. The first die 302 is disposed under the first die 302, the second die 304 is disposed under the first die 302, and the second diffuser 306 is disposed under the second die 304. In other words, the first diffusion sheet 300 is located at the outermost side of the optical film assembly 30.

In this embodiment, the backlight module 3 is a one-side optical backlight module. Therefore, the light source assembly 32 includes a light guide plate 320, a reflection sheet 322, a light source 324, and a reflection plate 326. The light guide plate 320 is disposed under the second diffusion sheet 306 of the optical film assembly 30. The reflection sheet 322 is disposed under the light guide plate 320. The light source 324 is disposed on one side of the light guide plate 320, and the reflection plate 326 is disposed around the light source 324. In practical applications, the light source 324 can be a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED). It should be noted that the working principle of the edge-lit backlight module is well known to those skilled in the art and will not be described herein.

Please refer to FIG. 3 and FIG. 4, FIG. 3 is a schematic view of the first diffusion sheet 300 in FIG. 2, and FIG. 4 is an exploded view of the first diffusion sheet 300 in FIG. As shown in FIGS. 3 and 4, the first diffusion sheet 300 includes a substrate 3000, a first diffusion layer 3002, and a second diffusion layer 3004. Substrate 3000 can be made of any transparent material that allows light to pass through. For example, the substrate 3000 may be polyethylene terephthalate (PET), but is not limited thereto. The first diffusion layer 3002 is disposed on the substrate 3000, and the second diffusion layer 3004 is disposed on the first diffusion layer 3002.

The first diffusion layer 3002 includes a first surface structure S1, and the first surface structure S1 has a first roughness peak value Rpc_1. The second diffusion layer 3004 includes a second surface structure S2 and a third surface structure S3, wherein the second surface structure S2 and the third surface structure S3 are respectively formed on opposite sides of the second diffusion layer 3004. When the second diffusion layer 3004 is disposed on the first diffusion layer 3002, the third surface structure S3 of the second diffusion layer 3004 coincides with the first surface structure S1 of the first diffusion layer 3002, in other words, the first surface structure S1 and the first surface structure S1 The three surface structures S3 are complementary in shape such that the first surface structure S1 can be attached to the third surface structure S3. The second surface structure S2 has a second roughness peak value Rpc_2. It should be noted that the peak count value of roughness (Rpc) is defined as the number of peaks within a unit distance. Since the roughness peak value Rpc is well known to those skilled in the art, no further details are provided herein.

In this embodiment, the first surface structure S1, the second surface structure S2, and the third surface structure S3 are all irregular surface structures. In other words, the first surface structure S1, the second surface structure S2, and the third surface structure S3 are The width, height or structure has a non-periodic distribution. In addition, the second roughness peak value Rpc_2 of the second surface structure S2 is greater than or equal to the first roughness peak value Rpc_1 of the first surface structure S1 (ie, Rpc_2≧Rpc_1). Since the third surface structure S3 coincides with the first surface structure S1, the roughness peak value of the third surface structure S3 is the same as the roughness peak value of the first surface structure S1.

When the light passes through the surface having roughness, it diffuses to disperse the light, and the atomization effect is obtained. Therefore, when the light passes through the surface having two layers of roughness, better atomization can be obtained. Meanwhile, when the roughness peak value of the second surface structure S2 is greater than or equal to the roughness peak value of the first surface structure S1, the light first undergoes preliminary diffusion through the first surface structure S1 having a small roughness peak value, and then The diffusion is further performed by the second surface structure S2 having a larger roughness peak value to enhance the atomization effect by the second surface structure S2 having a larger roughness peak value. Therefore, through the above structural design, when the light passes through the first diffusion sheet 300, a good atomization effect can be obtained.

In addition, when the first diffusion sheet 300 is applied to the display device, the second surface structure S2 may affect the grade characteristics, in other words, the second surface structure S2 may affect the clarity of the user when viewing the display device. When the roughness peak value of the second surface structure S2 is smaller, the surface structure is relatively larger, and the surface structure is more easily observed. Conversely, the larger the roughness peak value of the second surface structure S2, the less likely it is. The surface relief structure is observed, so that the more the user views, the less likely the surface structure of the first diffusion sheet 300 is seen to increase the clarity to obtain a better grade. Preferably, the first roughness peak value Rpc_1 per millimeter and the second roughness peak value Rpc_2 per millimeter are both greater than 15.

Further, the first surface structure S1 may have a first center line average surface roughness value Ra_1, and the second surface structure S2 may have a second center line average surface roughness value Ra_2. The present invention can further make the second center line average surface roughness value Ra_2 of the second surface structure S2 smaller than or equal to the first center line average surface roughness value Ra_1 of the first surface structure S1 (that is, Ra_2≦Ra_1). Since the third surface structure S3 coincides with the first surface structure S1, the center line average surface roughness value of the third surface structure S3 is the same as the center line average surface roughness value of the first surface structure S1. Thereby, when the light passes through the first diffusion sheet 300, a good atomization effect can be obtained. Preferably, the first centerline average surface roughness value Ra_1 may be between 0.15 micrometers and 50 micrometers, and the second centerline average surface roughness value Ra_2 may be between 0.15 micrometers and 20 micrometers.

It should be noted that the centerline average surface roughness (Ra) is defined as the average value of the absolute distance from the point to the contour centerline of the actual contour of the measured surface within the sampling length. Since the centerline average surface roughness value Ra is well known to those skilled in the art, no further details are provided herein.

Further, the first surface structure S1 may have a first maximum peak-to-valley height difference Rz_1, and the second surface structure S2 may have a second maximum peak-to-valley height difference Rz_2. The present invention may further cause the second maximum peak-to-valley height difference Rz_2 of the second surface structure S2 to be less than or equal to the first maximum peak-to-valley height difference Rz_1 of the first surface structure S1 (ie, Rz_2≦Rz_1). Since the third surface structure S3 coincides with the first surface structure S1, the maximum peak-to-valley height difference of the third surface structure S3 is the same as the maximum peak-to-valley height difference of the first surface structure S1. Thereby, when the light passes through the first diffusion sheet 300, a good atomization effect can be obtained. Preferably, the first maximum peak-to-valley height difference Rz_1 and the second maximum peak-to-valley height difference Rz_2 are both greater than 0.6 micrometers.

It should be noted that the maximum peak to valley height (Rz) is defined as the maximum peak-to-valley height difference within the length of the contour sample. Since the maximum peak-to-valley height difference Rz is well known to those skilled in the art, no further details are provided herein.

In addition, the present invention can further make the refractive index n2 of the second diffusion layer 3004 larger than the refractive index n1 of the first diffusion layer 3002, and the refractive index n1 of the first diffusion layer 3002 is greater than the refractive index n0 of the substrate 3000 (ie, n2> N1>n0). Thereby, when the light passes through the first diffusion sheet 300, a good atomization effect can be obtained.

It should be noted that although the first diffusion sheet 300 is described by two diffusion layers, the invention is not limited thereto. In other embodiments of the present invention, the diffusion sheet may also be composed of two or more diffusion layers stacked on the substrate, wherein the roughness peak value Rpc and the refractive index of each diffusion layer are decreased from top to bottom, and the center The line average surface roughness value Ra and the maximum peak-to-valley height difference Rz are increased from top to bottom. Thereby, when the light passes through the diffusion sheet composed of the diffusion layer of two or more layers, a good atomization effect can be obtained.

In addition, the structure of the second diffusion sheet 306 in FIG. 2 may be the same as that of the first diffusion sheet 300 described above to increase the atomization effect of light.

Please refer to FIG. 5. FIG. 5 is a schematic diagram of a backlight module 3' according to another embodiment of the present invention. The main difference between the backlight module 3' and the backlight module 3 described above is that the backlight module 3' is a continuous backlight module. Therefore, the light source assembly 32' includes a light source 328 and a reflective plate 329. The light source 328 is disposed under the second diffusion sheet 306, and the reflection plate 329 is disposed under the light source 328. In practical applications, the light source 328 can be a cold cathode tube or a light emitting diode. It should be noted that the working principle of the direct type backlight module is well known to those skilled in the art and will not be described herein. In addition, the components of the same reference numerals as those shown in FIG. 2 are the same, and the detailed principles are not described herein.

Compared with the prior art, the present invention is characterized in that different diffusion layers respectively form surface structures having different or the same roughness peak value, center line average surface roughness value, maximum peak-to-valley height difference and/or refractive index, The light passing through the diffuser produces an atomizing effect. Therefore, the diffusion sheet of the present invention does not need to dope the beads in the diffusion layer, thereby avoiding problems such as falling off of the beads or scratching the surface of the substrate.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

3, 3'. . . Backlight module

10. . . Diffusion sheet

30. . . Optical film combination

32, 32'. . . Light source combination

100, 3000. . . Substrate

120, 140. . . Diffusion layer

160. . . Bead

300. . . First diffuser

302. . . First picture

304. . . Second picture

306. . . Second diffuser

320. . . Light guide

322. . . A reflective sheet

324, 328. . . light source

326, 329. . . Reflective plate

3002. . . First diffusion layer

3004. . . Second diffusion layer

S1. . . First surface structure

S2. . . Second surface structure

S3. . . Third surface structure

Figure 1 is a schematic illustration of a prior art diffuser.

FIG. 2 is a schematic diagram of a backlight module according to an embodiment of the invention.

Fig. 3 is a schematic view of the first diffusion sheet in Fig. 2.

Fig. 4 is an exploded view of the first diffusion sheet in Fig. 3.

FIG. 5 is a schematic diagram of a backlight module according to another embodiment of the present invention.

300. . . First diffuser

3000. . . Substrate

3002. . . First diffusion layer

3004. . . Second diffusion layer

S1. . . First surface structure

S2. . . Second surface structure

S3. . . Third surface structure

Claims (17)

A diffusion sheet comprising: a substrate; a first diffusion layer disposed on the substrate, the first diffusion layer comprising a first surface structure having a first roughness peak value (peak And a second diffusion layer is disposed on the first diffusion layer, the second diffusion layer includes a second surface structure and a third surface structure, the second surface structure and the second surface structure The three surface structures are respectively formed on opposite sides of the second diffusion layer, the third surface structure is coincident with the first surface structure, and the second surface structure has a second roughness peak value, and the second roughness peak value Greater than or equal to the first roughness peak value. The diffusion sheet of claim 1, wherein the first roughness peak value per millimeter and the second roughness peak value per millimeter are greater than 15. The diffusion sheet of claim 1, wherein the first surface structure has a first centerline average surface roughness (Ra), and the second surface structure has a second centerline average surface roughness And a second centerline average surface roughness value less than or equal to the first centerline average surface roughness value. The diffusion sheet of claim 3, wherein the first center line has an average surface roughness value between 0.15 micrometers and 50 micrometers, and the second centerline average surface roughness value is between 0.15 micrometers and 20 micrometers. between. The diffusion sheet of claim 1, wherein the first surface structure has a first maximum peak to valley height (Rz), and the second surface structure has a second maximum peak-to-valley height difference a value, the second maximum peak-to-valley height difference is less than or equal to the first maximum peak-to-valley height difference. The diffusion sheet of claim 5, wherein the difference between the first maximum peak-to-valley height difference and the second maximum peak-to-valley height is greater than 0.6 micrometers. The diffusion sheet of claim 1, wherein the first surface structure, the second surface structure, and the third surface structure are irregular surface structures. The diffusion sheet of claim 1, wherein the second diffusion layer has a refractive index greater than a refractive index of the first diffusion layer, and the first diffusion layer has a refractive index greater than a refractive index of the substrate. A backlight module comprising: a light source combination; and an optical film combination disposed on the light source combination, the optical film assembly comprising a first diffusion sheet, the first diffusion sheet being located at the highest of the optical film combination The first diffusion sheet comprises: a substrate; a first diffusion layer disposed on the substrate, the first diffusion layer comprising a first surface structure, the first surface structure having a first roughness peak And a second diffusion layer is disposed on the first diffusion layer, the second diffusion layer includes a second surface structure and a third surface structure, the third surface structure Coincident with the first surface structure, the second surface structure is opposite to the third surface structure, the second surface structure has a second roughness peak value, the second roughness peak value being greater than or equal to the first roughness Peak value. The backlight module of claim 9, wherein the first roughness peak value per millimeter and the second roughness peak value per millimeter are greater than 15. The backlight module of claim 9, wherein the first surface structure has a first centerline average surface roughness (Ra), and the second surface structure has a second centerline average surface. a roughness value, the second centerline average surface roughness value being less than or equal to the first centerline average surface roughness value. The backlight module of claim 11, wherein the first center line has an average surface roughness value between 0.15 micrometers and 50 micrometers, and the second centerline average surface roughness value is between 0.15 micrometers and 20 micrometers. between. The backlight module of claim 9, wherein the first surface structure has a first maximum peak to valley height (Rz), and the second surface structure has a second maximum peak-to-valley height The difference, the second maximum peak-to-valley height difference is less than or equal to the first maximum peak-to-valley height difference. The backlight module of claim 13, wherein the difference between the first maximum peak-to-valley height difference and the second maximum peak-to-valley height is greater than 0.6 micrometers. The backlight module of claim 9, wherein the first surface structure, the second surface structure, and the third surface structure are irregular surface structures. The backlight module of claim 9, wherein the second diffusion layer has a refractive index greater than a refractive index of the first diffusion layer, and the first diffusion layer has a refractive index greater than a refractive index of the substrate. The backlight module of claim 9, wherein the optical film assembly further comprises: a first cymbal sheet disposed under the first diffusion sheet; and a second cymbal sheet disposed under the first cymbal sheet; And a second diffusion sheet disposed under the second cymbal, wherein the structure of the second diffusion sheet is the same as the structure of the first diffusion sheet.