TWI518385B - Light guide plate and backlight unit assembly - Google Patents

Description

Light guide plate and backlight unit assembly

The present invention relates to a light guide plate used in a liquid crystal display device and a backlight unit assembly including the same.

With the development of industrial society as a highly information age, the importance of electronic display devices has increased as a medium for displaying and transmitting various kinds of information. In particular, in the case of a liquid crystal display device (LCD), it is a device that is a combination of liquid crystal and semiconductor technology, and has the advantages of being thin, light, and low in power consumption. Therefore, research and development of its structure and manufacturing technology have been carried out, and Used in various fields.

In such a liquid crystal display (LCD) device, since the liquid crystal itself cannot emit light, a light source is additionally provided on the back surface of the device to construct a color and a picture.

A backlight unit (BLU) is widely used as the light-emitting device. With the recent trend of thinning the thickness of the liquid crystal display device, a light-emitting diode is used instead of the conventional cold cathode fluorescent lamp (CCFL). The situation of (LED, Light Emitting Diode) has increased dramatically. In addition, LED (Light Emitting Diode) has the advantage of not using mercury and excellent color reproduction.

The edge type BLU in which the LEDs are distributed on the side is superior to the direct type in which the LEDs are distributed in front of the backlight unit, and has advantages in power consumption and product thickness, and the application range thereof is expanding.

The use of a light source generated on the side to the front light guide plate is used in the edge type BLU. Light generated on the light source is incident from the side of the light guide plate to the inside of the light guide plate, and is emitted from the front side. In this manner, since the path of light passing through the light guide plate is long and the light loss is increased, in order to prevent such a phenomenon, a highly transmissive polymethyl methacrylate (PMMA, Polymethyl methacrylate) is mainly used. Series of materials. However, polymethyl methacrylate is structurally weak to moisture, and a light guide plate using polymethyl methacrylate has a problem of bending in a high-temperature, high-humidity environment and a decrease in dimensional stability.

An object of the present invention is to provide a light guide plate which is provided with a resin having excellent internal absorption rate to overcome bending defects and dimensional stability in order to overcome the structural disadvantage of polymethyl methacrylate which is weak to moisture.

According to a preferred first embodiment of the present invention, there is provided a light guide plate comprising: a base material layer; and a bottom layer provided on one surface of the base material layer, the moisture absorption rate being lower than the base material layer.

The substrate layer according to the above embodiment may be made of a polymethyl methacrylate resin.

The underlayer according to the above embodiment can be produced from a resin selected from a polycarbonate resin, a polystyrene resin, an acrylic resin, an olefin resin, a copolymer thereof, and a mixture thereof.

The underlayer according to the above embodiment may contain 0.1 to 10% by weight of glass fibers.

The glass fiber according to the above embodiment may have a shape that is long in one direction and has directionality.

The thickness of the underlayer according to the above embodiment may be 1 to 300 μm.

The light guide plate according to the above embodiment may have a structural layer which is a layer in which a plurality of three-dimensional structures are arranged on one surface of the base material layer on which the underlayer is not formed.

The structural layer according to the above embodiment can be produced from an ultraviolet curable resin or a thermosetting resin.

The height of the three-dimensional structure of the structural layer according to the above embodiment may be 25 to 300 μm.

The pitch of the three-dimensional structure of the structural layer according to the above embodiment may be 100 to 500 μm.

As another preferred second embodiment of the present invention, there is provided a backlight unit assembly having the above-described light guide plate.

According to the present invention, the resin having different moisture absorption rates and the glass fiber having the directivity are introduced into the light guide plate, whereby the bending and dimensional stability of the entire light guide plate can be improved even in an environment of high temperature and high humidity. In particular, the glass fiber is introduced into the bottom layer to scatter the light incident on the side surface, thereby preventing the brightness from decreasing.

The invention is described in detail below.

The present invention relates to a light guide plate comprising: a substrate layer; and a bottom layer disposed on one side of the substrate layer, having a lower moisture absorption rate than the substrate layer, and in particular, the light guide plate may be on the bottom layer Contains fiberglass.

The light guide plate of the present invention is characterized in that, in order to solve the disadvantage that the polymethyl methacrylate which is a material of the light guide plate is generally excellent in bending stability and dimensional stability in a high-temperature and high-humidity environment, the resin and glass excellent in internal absorption rate are used. The fibers are introduced into the light guide plate.

The base material layer can be made of a polymethyl methacrylate resin, and in order to solve the disadvantage that the polymethyl methacrylate resin is weak in a high-temperature and high-humidity environment, the water absorption rate can be formed on at least one side of the base material layer to be lower than that of the base material layer. The bottom layer.

The underlayer can be produced from a resin selected from a polycarbonate resin, a polystyrene resin, an acrylic resin, an olefin resin, or a copolymer and a mixture thereof, and the olefin resin can be a cyclic olefin polymer (COP) or Loop olefin copolymer (COC). The polymethyl methacrylate of the base material layer has a moisture absorption rate of 0.03%, and the resin used in the underlayer may have a moisture absorption rate of less than 0.03%.

Further, the thickness of the underlayer may be 1 to 300 μm, which may vary depending on the position of the LED lamp in the backlight unit. The light coming out of the LED lamp passes through the substrate layer to form a light path. If the thickness of the underlayer is less than 1 μm, the moisture absorption function of the underlayer is lowered. If the thickness of the underlayer exceeds 300 μm, when light passes through the underlayer, it is possible Will produce light loss.

Further, glass fibers may be contained in the underlayer, and the glass fibers may scatter light from the lower portion of the light guide plate to the upper portion, thereby preventing the bending and dimensional deformation of the light guide plate caused by heat or moisture.

The content of the above glass fiber may be 0.1 to 10% by weight, and if it is less than 0.1% by weight, the effect of preventing bending and dimensional deformation is not very good, and if it exceeds 10% by weight, scattering of light by glass fiber The degree is severe, thereby reducing the amount of light emitted from the front, resulting in a decrease in brightness.

In addition, the glass fiber has a shape that is long in one direction and can have directionality. Specifically, the glass fibers may be in the shape of a cylinder or a polygonal column, and the glass fibers can be aligned in the extrusion direction at the time of extrusion, in which case the glass fibers can be arranged perpendicular to the light source (Fig. 2).

In order to form the underlayer as described above, it may be produced by first forming a base material layer and then coating the resin forming the underlayer, or by extruding the base material layer and the base material layer and a structural layer described later. When the resin forming the underlayer is co-extruded together, it is manufactured.

After the glass fiber is stirred with the resin forming the underlayer, it is formed into a wafer shape by extrusion, and then can be co-extruded with the base material layer, and can be applied by mixing with the underlying resin on one surface of the base material layer.

The resin which forms the underlayer as described above can be selected from methyl methacrylate-styrene copolymer, polycarbonate resin, polystyrene resin, acrylic resin, olefin resin, copolymers and mixtures thereof.

The structural layer may be formed on one side of the substrate layer where the underlayer is not formed, and a plurality of three-dimensional structures are arranged on the structural layer. Further, the structural layer can be produced from an ultraviolet curable resin or a thermosetting resin.

In the light guide plate of the present invention, the shape of the three-dimensional structure arranged on the structural layer is preferably symmetrical with respect to the center line passing through the vertical direction of the peak point, but the shape is not limited thereto. Further, the three-dimensional structure may have a height of 25 μm to 300 μm and a pitch of 100 μm to 500 μm. In the light guide plate, light from the side passes through the inside of the light guide plate and exits from the front surface of the light guide plate, but has a large scattering of light and cannot be from the front as compared with the direct type having the lamp underneath. The characteristic that the amount of light that is emitted and is relatively large is relatively large. The pattern existing in the direction in which light is emitted enhances the straightness of light and increases the brightness. Therefore, the three-dimensional structure having the above-described height and pitch has an advantage of increasing straightness based on the pattern.

The structural layer as described above may be formed by co-extruding with the substrate layer. That is, it can be formed by co-extruding the molten base resin constituting the base material layer and the structural layer while passing through a pattern roll.

Specifically, as shown in Fig. 1, the base material layer 10 and the structural layer 30 can be easily produced from a single resin without distinguishing between layers. Although the extrusion temperature varies depending on the matrix resin, it is preferably extruded at 200 ° C to 300 ° C. At this time, the above-mentioned base resin can mainly use a polymethyl methacrylate resin.

When the light guide plate manufactured as described above is applied to the backlight unit assembly, it is possible to realize a backlight unit assembly that is structurally stable even in an environment of high temperature and high humidity.

Hereinafter, the present invention will be described in more detail based on examples, but the scope of the present invention is not limited to the examples described below.

<Example 1>

Co-extrusion was carried out using a polymethyl methacrylate resin as a base material layer and a methyl methacrylate-styrene copolymer as a base layer. The light guide plate was produced such that the thickness of the base material layer was 3 mm and the thickness of the underlayer was 100 μm. At this time, for the methyl methacrylate-styrene copolymer, a copolymer having a weight ratio of methyl methacrylate of 75 was used.

<Example 2>

A light guide plate was produced in the same manner as in Example 1 except that a copolymer having a weight ratio of methyl methacrylate of 60 was used for the methyl methacrylate-styrene copolymer.

<Example 3>

A light guide plate was produced in the same manner as in Example 1 except that a copolymer having a weight ratio of methyl methacrylate of 30 was used for the methyl methacrylate-styrene copolymer.

<Example 4>

A light guide plate was produced in the same manner as in Example 1 except that the thickness of the underlayer was 200 μm.

<Example 5>

A light guide plate was produced in the same manner as in Example 1 except that the thickness of the underlayer was 300 μm.

<Example 6>

A light guide plate was produced by using a polymethyl methacrylate resin as a base material layer and co-extruding as a base layer with a polycarbonate resin. The thickness of the base material layer was 3 mm, and the thickness of the underlayer was 100 μm.

<Example 7>

A light guide plate was produced in the same manner as in Example 6 except that the polystyrene resin was used as the underlayer.

<Example 8> to <Example 14>

When the underlayer was formed according to the glass fiber content described in Table 2, the same procedure as in Example 1 to Example 7 was carried out except that the methyl methacrylate-styrene copolymer and the glass fiber were co-extruded. Manufacturing a light guide plate.

<Comparative Example 1>

Although the light guide plate was produced in the same manner as in the above-described first embodiment, it was produced by using a polymethyl methacrylate resin in such a manner that no layer-to-layer distinction was made.

<Comparative Example 2>

Although the light guide plate was manufactured in the same manner as in the above-described Example 7, it was produced by using a polymethyl methacrylate resin in such a manner that no layer-to-layer distinction was made.

The physical quantity evaluation of the light guide plate prepared in the above examples and comparative examples was carried out in the following manner, and the results are shown in Table 2.

(1) Water absorption rate

The light guide plates in the examples and comparative examples were measured by the ASTM D570 test method. After drying in an oven at 50 ° C for 24 hours to measure the weight, it was immersed in water at 23 ° C for one day. The moisture absorption rate was measured by the ratio of the weight after drying to the weight after immersion in moisture.

(2) Measurement of the amount of bending deformation (degree of occurrence of bending)

The light guide plates in the examples and the comparative examples were stored at 50 ° C, 80% RH, and 96 hr, and the degree of occurrence of bending was measured. The degree of occurrence of the bending was measured using a displacement measuring instrument of Solartron, and as shown in Table 1, the degree of occurrence of the bending was divided into five stages to distinguish.

The light guide plates of the examples and the comparative examples were mounted on a backlight unit for a 42-inch liquid crystal display panel, and were measured using a luminance meter (TOPCON, BM-7). After measuring the brightness at any of the 17 locations, Out of the average. The brightness was changed at each measurement, so the brightness of Comparative Example 1 was made 100 to compare the relative values.

As shown in the above Table 1, it is understood that in the embodiment in which the acrylic copolymer having a low moisture absorption rate is used in the underlayer, the water absorption rate of the entire light guide plate is low, and the degree of occurrence of bending is reduced. In addition, the same level of effect can be obtained in terms of brightness.

However, the light guide plate of Comparative Example 1 in which the entire light guide plate was produced using a polymethyl methacrylate resin showed a relatively high moisture absorption rate and a degree of occurrence of warpage.

In addition, it was confirmed that the light guide plate was more stably bent by the added glass fibers.

As a result, when the resin having a low moisture absorption rate is introduced into the light guide plate, the bending and dimensional stability of the entire light guide plate are improved in an environment of high temperature and high humidity.

10. . . Substrate layer

20. . . Bottom layer

30. . . Structural layer

40. . . light source

50. . . glass fiber

1 is a longitudinal sectional view of a light guide plate according to an embodiment of the present invention;

Fig. 2 is a view showing glass fibers and an arrangement shape on a light guide plate according to an embodiment of the present invention.

10. . . Substrate layer

20. . . Bottom layer

30. . . Structural layer

40. . . light source

Claims (10)

A light guide plate having: a substrate layer; and a bottom layer disposed on one side of the substrate layer, having a lower moisture absorption rate than the substrate layer, wherein the bottom layer is made of a methyl methacrylate-styrene copolymer The weight ratio of methyl methacrylate in the methyl methacrylate-styrene copolymer is 30 to 75. The light guide plate of claim 1, wherein the substrate layer is made of a polymethyl methacrylate resin. The light guide plate of claim 1, wherein the bottom layer comprises 0.1 to 10% by weight of glass fibers. The light guide plate of claim 3, wherein the glass fiber has a shape that is long in one direction and has directionality. The light guide plate according to Item 1, wherein the underlayer has a thickness of 1 to 300 μm. The light guide plate according to claim 1, wherein the light guide plate further has a structural layer which is a layer in which a plurality of three-dimensional structures are arranged on one surface of the base material layer on which the underlayer is not formed. The light guide plate according to claim 6, wherein the structural layer is made of an ultraviolet curable resin or a thermosetting resin. The light guide plate according to Item 6, wherein the structural layer has a height of 25 to 300 μm. The light guide plate according to claim 6, wherein the structural layer has a three-dimensional structure having a pitch of 100 to 500 μm. A backlight unit assembly having the light guide plate according to any one of claims 1 to 9.