WO2012070765A1

WO2012070765A1 - Method for manufacturing backlight unit

Info

Publication number: WO2012070765A1
Application number: PCT/KR2011/007345
Authority: WO
Inventors: Jong Sun Kim; Sang Jun Park; Jae Hyuk Jang; Hyung Min Park; Kyoung Soo Ahn; Jeong Oh Lee; Yong In Lee
Original assignee: LG Innotek Co Ltd
Current assignee: LG Innotek Co Ltd
Priority date: 2010-11-22
Filing date: 2011-10-05
Publication date: 2012-05-31
Anticipated expiration: 2013-05-22
Also published as: TWI475296B; KR20120054765A; TW201222101A; KR101279471B1

Abstract

Provided is a method for manufacturing a backlight unit. The method includes forming one or more reception grooves at a light guide plate, aligning one or more LEDs at positions corresponding to the reception grooves and coupling a PCB thereto, and filling one surface of the light guide plate and the reception grooves with a resin material. Accordingly, it is possible to provide a method for manufacturing a backlight unit, which forms a reception groove in a light guide plate to receive a LED and fills the reception groove with a fluid resin material, thus preventing the damage to the LED caused by the difference between the thermal expansion rates of components such as a light guide plate, a reflection film and a PCB. In particular, it is possible to manufacture a backlight unit that can simplify the manufacturing process by filling a reception groove of a light guide plate with a resin material by a coating process and can efficiently extract and transmit light by the light diffusing, refracting and scattering characteristics of the resin material.

Description

METHOD FOR MANUFACTURING BACKLIGHT UNIT

The present invention relates to a method for manufacturing a backlight unit, and more particularly, to a method for manufacturing a backlight unit that can prevent the damage to a Light Emitting Diode (LED) caused by heat and shock, remove hot spots, and improve optical efficiency.

A backlight unit uniformly illuminates a rear side of a Liquid Crystal Display (LCD), which is not self-luminous, in order to show a display image. A light guide plate is included in the backlight unit to provide uniform illumination and brightness, which may be a plastic lens that uniformly transmits light, emitted by a light source (e.g., an LED), to the entire surface of the LCD.

FIG. 1 illustrates a structure of a backlight unit using an LED as a light source. As illustrated in FIG. 1, a plurality of LEDs 20 are provided on a printed circuit board (PCB) 10, and a light guide plate 30 is provided to transmit light, emitted by the LEDs 20, to the top of the backlight unit. Recently, continuous attempts are made to use LEDs as a light source to perform a uniform surface light emission on the entire light emission surface. In this case, a plurality of LEDs are arranged on a plane surface, and are inserted into concave holes formed at a light guide plate.

However, if an LED is inserted into a light guide plate, a hot spot X occurs due to heat at a surface near to the LED. This hot spot X relatively increases the brightness in a region near to the LED, causing a brightness spot.

Also, the high-temperature heat or thermal shock occurring at the LED causes the thermal expansion of a light guide plate, a reflection film and a PCB. In this case, the LED is damaged by the difference between the thermal expansion rates of the respective components.

An aspect of the present invention is directed to a method for manufacturing a backlight unit, which forms a reception groove in a light guide plate to receive a LED and fills the reception groove with a fluid resin material, thus preventing the damage to the LED caused by the difference between the thermal expansion rates of components such as a light guide plate, a reflection film and a PCB.

Another aspect of the present invention is directed to a method for manufacturing a backlight unit, which can simplify the manufacturing process by filling a reception groove of a light guide plate with a resin material by a coating process, and can efficiently extract and transmit light by the light diffusing, refracting and scattering characteristics of the resin material.

The present invention is to provide a method for manufacturing a backlight unit that includes a PCB mounted with a plurality of LEDs and a light guide plate with a plurality of reception grooves receiving the LEDs and has the reception grooves filled with a resin material.

According to an embodiment of the present invention, a method for manufacturing a backlight unit, including: forming one or more reception grooves at a light guide plate; aligning one or more LEDs at positions corresponding to the reception grooves and coupling a PCB thereto; and filling the reception grooves with a resin material.

The resin material may include a UV-curing resin material and may further include a plurality of beads. The optical efficiency can be improved by controlling the weight of the beads.

In addition, the light extraction efficiency can be improved by controlling the density of various optical patterns on the light guide plate, and the optical efficiency can be improved by stacking an optical film layer on the top surface of the light guide plate.

As described above, the present invention can provide a method for manufacturing a backlight unit, which forms a reception groove in a light guide plate to receive a LED and fills the reception groove with a fluid resin material, thus preventing the damage to the LED caused by the difference between the thermal expansion rates of components such as a light guide plate, a reflection film and a PCB.

In particular, the present invention can manufacture a backlight unit that can simplify the manufacturing process by filling a reception groove of a light guide plate with a resin material by a coating process, and can efficiently extract and transmit light by the light diffusing, refracting and scattering characteristics of the resin material.

In addition, the present invention can manufacture a backlight unit that can significantly reduce hot spots by implementing a microlens array film having diffusion patterns or diffusion beads and a light diffusing function of a resin material used in the manufacturing process.

The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a structure of a backlight unit using an LED as a light source;

FIGS. 2 to 4 are a flow diagram and cross-sectional conceptual diagrams illustrating a backlight unit manufacturing process according to an embodiment of the present invention;

FIG. 5 is a cross-sectional conceptual diagram illustrating a structure of a backlight unit according to another embodiment of the present invention;

FIGS. 6 to 8 illustrate optical patterns in a backlight unit according to embodiments of the present invention; and

FIGS. 9 to 11 illustrate examples of optical patterns according to embodiments of the present invention.

110: Printed circuit board

120: LED

130: Light guide plate

140: Reception groove

150: Resin material

151: Bead

160: Optical film layer

Y1: First density pattern region

Y2: Second density pattern region

X1: Third density pattern region

X2: Fourth density pattern region

Z1: Fifth density pattern region

Z2: Sixth density pattern region

The present invention is to provide a method for manufacturing a backlight unit, which forms a reception groove in a light guide plate to receive a LED and fills the reception groove with a fluid resin material, thus preventing the damage to the LED caused by the difference between the thermal expansion rates of components such as a light guide plate, a reflection film and a PCB.

To this end, the present invention provides a method for manufacturing a backlight unit, including: forming one or more reception grooves at a light guide plate; aligning one or more LEDs at positions corresponding to the reception grooves and coupling a PCB thereto; and filling the reception grooves with a resin material.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Wherever possible, the same reference numerals will be used to refer to the same elements throughout the specification, and a duplicated description thereof will be omitted. It will be understood that although the terms "first", "second", etc. are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

FIGS. 2 and 3 are a flow diagram and a cross-sectional conceptual diagram illustrating a backlight unit manufacturing process according to an embodiment of the present invention.

Referring to FIGS. 2 and 3, a method for manufacturing a backlight unit according to an embodiment of the present invention may include: forming one or more reception grooves at a light guide plate; aligning one or more LEDs at positions corresponding to the reception grooves and coupling a PCB thereto; and filling the reception grooves with a resin material.

The backlight unit manufacturing process will be described below in detail with reference to FIG. 3.

First, the backlight unit manufacturing process according to the present invention may include fabricating a light guide plate and a PCB separately. The light guide plate and the PCB are fabricated separately and are coupled together.

In step S1, a LED 120 is mounted on a PCB 110 according to the present invention. The LED 120 may be a side view LED that has a light emission surface 121 is formed in the direction of the sidewall of a reception groove 140. That is, the light emitted by an LED source 130 does not travel directly to the top but travels toward the sidewall. A reflection film having various reflection patterns (not illustrated) may be further provided on the top surface of the PCB 110.

In step S2, a reception groove is formed at a light guide plate 130. Steps S1 and S2 may be performed sequentially or separately as described above.

The reception groove 140 may be formed through a mechanical process to pierce the light guide plate 130, and the reception groove 140 may be formed to be wider than the LED. In addition, a first density pattern region Y1 and a second density pattern region Y2 having a higher pattern density than the first density pattern region Y1 may be formed on the other surface of the light guide plate facing the PCB.

Also,

optical patterns

131 and 132 may be formed on the other surface (bottom surface) of the light guide plate of the backlight unit. Specifically, optical patterns may be formed on the other surface (bottom surface) of the light guide plate 130, wherein they may be formed on the surface of a region where the reception groove is not formed.

Specifically, a first density pattern region Y1 and a second density pattern region Y2 having a higher pattern density than the first density pattern region Y1 are formed on the other surface of the light guide plate 130, and the first density pattern region Y1 may be nearer to the light emission surface of the LED than the second density pattern region Y2. In this case, the first and second density pattern regions may include a plurality of independent concave patterns that overlap each other or are spaced apart from each other.

That is, the first and second density pattern regions of the light guide plate 130 may be formed to have various sectional shapes (e.g., semicircle, ellipse, and an irregular shape) toward the inside of the surface of the light guide plate. In an exemplary embodiment of the present invention, the first and second density pattern regions may include polygonal pyramid patterns or hemispherical patterns.

In particular, the first density pattern region Y1 can improve the extraction efficiency of light from the LED to increase the light uniformity. Also, the second density pattern region Y2 can have a higher pattern density than the first density pattern region, to improve the light diffusion and scattering.

In step S3, the PCB and the light guide plate fabricated in steps S1 and S2 are coupled together. In this case, the sidewall surface of the light guide plate having the reception groove 140 may be spaced apart from the LED 120 by a predetermined distance.

In step S4, one surface of the light guide plate 130 and the reception groove 140 are filled with a resin material 150. The resin material may be filled by a coating process. In this case, the resin material 150 may be a fluid UV-curing resin material. However, the resin material 150 is not limited thereto and may be any resin material that can diffuse light and has a predetermined fluidity. In particular, since the resin material 150 is filled in the reception groove contacting the light emission surface of the LED, it may have a light diffusing function of a transparent material. To this end, diffusion beads 151 may be further included in the resin material 150. The diffusion beads may be included at 0.01% to 0.3% with respect to the total weight of the resin material. The light emitted by the LED in the lateral direction is diffused and reflected by the resin material 150 and the beads 151 and travels upwards, thus making it possible to significantly reduce a hot-spot phenomenon while increasing a diffusion phenomenon. The directions of arrows over the resin material layer illustrated in FIG. 2 represent the buffering operation of the resin material in a thermal expansion process.

In step S5, an optical pattern is formed on the top surface of the resin material. Specifically, an optical pattern may be further formed on the top surface of the resin material 150. That is, an optical pattern may be formed on the top surface of a layer of the resin material 150 formed on one surface of the light guide plate 130. Specifically, a third density pattern region X1 and a fourth density pattern region X2 having a higher pattern density than the third density pattern region are formed, the fourth density pattern region X2 may be nearer to the light emission surface of the LED than the third density pattern region X1. Although it is illustrated that the PCB 110 and the other surface of the light guide plate 130 are spaced apart from each other, they adhere closely to each other in the final structure.

Specifically, a third density pattern region X1 and a fourth density pattern region X2 having a higher pattern density than the first density pattern region are formed on the resin layer stacked on one surface (the top surface) of the light guide plate 130. In this case, the fourth density pattern region may be nearer to the light emission surface of the LED.

The optical patterns constituting the third and fourth density pattern regions X1 and X2 may include a plurality of convex protrusion patterns that overlap each other or are spaced apart from each other. For example, the second density pattern region X2 has a higher pattern density than the first density pattern region X1, wherein the convex protrusion patterns may be formed more densely or some of the protrusion patterns may overlap each other to control the pattern density.

In this case, the fourth density pattern region may be nearer to the light emission surface of the LED. That is, the fourth density pattern region X2 may be formed at the side near to the light emission surface of the LED, and the third density pattern region X1 may be formed at the side remote from the light emission surface of the LED. The fourth density pattern region X1 formed on the top surface of the light guide plate is implemented in a high-density pattern or an overlapping pattern, and is disposed near the light emission surface of the LED to greatly diffuse or scatter the incident strong light, thus making it possible to reduce the formation of hot spots. In addition, the fourth density pattern region X2 is formed on the surface of the light guide plate of the vertically upper direction of the formation position of the reception groove, and may be formed in a region within 1/5 of a first distance d1 to the adjacent reception groove. The formation limit point of the fourth density pattern is formed at a distance X3 within 10 mm from the light emission surface of the LED to remove the occurrence of hot spots.

On the other hand, the third density pattern region X1 is formed to have a single structure including an independent convex protrusion pattern, thus making it possible to reduce the pattern density, transmit the emitted light to a longer distance, increase the light extraction efficiency, and improve the light uniformity.

FIG. 4 illustrates a backlight unit manufacturing process according to another embodiment of the present invention

Referring to FIG. 4, a reception groove 140 is formed at a light guide plate 130 such that the reception groove 140 does not pierce the light guide plate (Q1). Thereafter, the reception groove 140 is filled with a resin material 150 and beads 151 (Q2).

Then, a PCB 110 mounted with LEDs 120 is coupled to the light guide plate 130 (Q3 ~ Q4).

Referring to FIG. 5, among the steps of FIG. 3, the step S5 of forming the optical pattern 170 on the top surface of the resin material layer 150 may be modified into a different step. In a modified embodiment, it may be modified into a structure including an optical film layer 160 including a microlens array pattern 161 stacked on the top surface of the resin material layer 150 stacked on one surface of the light guide plate 130.

In this case, the microlens array pattern 161 may include various optical patterns to diffuse light.

The arrangement density of the microlens array pattern 161 may be controlled to form a fifth density pattern region Z1 and a sixth density pattern region Z2 having a higher pattern density than the fifth density pattern region Z1, and to dispose the sixth density pattern region nearer to the light emission surface of the LED than the fifth density pattern region Z1.

The structure of the fourth embodiment including the optical film layer 160 including the microlens array pattern 161 may also be applied to the structure of FIG. 4 of the first embodiment as illustrated in FIG. 7. Moreover, as illustrated in FIG. 8, the structure of stacking the optical film layer 160 including the microlens array pattern 161 may also be applied to the structure of FIG. 3.

Embodiments of the optical patterns constituting the first and second density pattern regions formed on the other surface of the light guide plate or the third and fourth density pattern regions formed on the top surface of the resin layer or the top surface of the optical film layer in the backlight unit manufacturing process will be described below in detail.

In the above embodiments, the optical patterns of the first and second density pattern regions include convex protrusion patterns, and the optical patterns of the third and fourth density pattern regions include concave patterns. However, the optical patterns of the first and second density pattern regions may have the same pattern shape as the optical patterns of the third and fourth density pattern regions, with the exception of a difference in the concave/convex structure.

FIG. 9A illustrates tetragonal pyramid patterns as an example of the polygonal pyramid patterns in the density pattern region. The left of FIG. 9A illustrates a structure of tetragonal pyramid patterns that are integrated at a high density, and the right of FIG. 9A illustrates a structure of tetragonal pyramid patterns that are disposed to partially overlap each other to increase the pattern density. Other examples of the polygonal pyramid pattern include a triangular pyramid pattern, a hexagonal pyramid pattern, and an octagonal pyramid pattern. Herein, the term 'tetragonal pyramid' is used to denote a pyramid having a pointed vertex.

In addition, as illustrated in FIG. 9B, the optical patterns may include hemispherical patterns. The hemispherical patterns may be integrated at a high density or may be disposed to partially overlap each other to increase the pattern density. Other examples of the hemispherical pattern include a hemi ellipsoidal pattern and various three-dimensional patterns that do not have a pointed vertex.

FIGS. 10A and 10B illustrate examples of arranging tetragonal pyramid patterns or hemispherical patterns at a low density in FIG. 5.

If the optical patterns include convex or concave polygonal pyramid patterns as illustrated in FIG. 11A, a bottom inclination angle σ of the polygonal pyramid pattern may have a value of 35 to 70 degrees as illustrated in FIG. 11B. Herein, the bottom inclination angle may be controlled to control the pattern density.

For example, in the case of the tetragonal pyramid pattern, the pattern may be formed to have a bottom inclination angle of 35 to 50 degrees for low-density arrangement, and may be formed to have a bottom inclination angle of 50 to 70 degrees for high-density arrangement.

As the subject matter of the present invention, the resin layer formed in the reception groove and on one surface of the light guide plate may be formed of various resin materials other than the above-described resin material. The resin material stacked in and on the reception groove may be various UV-curing fluid resins, and may be formed of the following material in order to improve the light diffusion and reduce the occurrence of hot spots.

For example, the resin material may include a resin having urethane acrylate oligomer as a main material. For example, the resin material may include a mixture of urethane acrylate oligomer (compound oligomer) and polymer type (polyacryl). The resin material may further include a monomer that is a mixture of low-boiling-point diluted reactive monomers such as IBOA (isobornyl acrylate), HPA (Hydroxylpropyl acrylate), and 2-HEA (2-hydroxyethyl acrylate), and a photo initiator (e.g., 1-hydroxycyclohexyl phenyl-ketone) or an antioxidant may be mixed as an additive.

Specifically, the resin layer may include a synthetic resin including a mixture of oligomer, polymer resin (polymer type), and monomer. In this case, the oligomer and the polymer resin may include a mixture of 10~21 % urethane acrylate oligomer and 10~21% polyacryl. In addition, the monomer is a low-boiling-point diluted reactive monomer and may include a mixture of 10~21% IBOA (isobornyl Acrylate), 10~21% HPA (Hydroxypropyl Acrylate), and 10~21% 2-HEA (2-Hydroxyethyl Acrylate). Herein, 1~5% photo initiator may be added to initiate the photo reactivity, and 1~5% antioxidant may be added to improve a yellowing phenomenon.

The use of the above resin material can remove a hot-spot phenomenon caused by a light diffusion effect, prevent a decrease in the surface adhesion of the oligomer type, and prevent a decrease in the mass production rate caused by longtime curing, thus making it possible to satisfy the mass production rate, the reliability and the adhesion characteristics with respect to the hot spot removing groove of the light guide plate.

While the invention has been shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Claims

A method for manufacturing a backlight unit, comprising:

forming one or more reception grooves at a light guide plate;

aligning one or more Light Emitting Diodes (LEDs) at positions corresponding to the reception grooves and coupling a Printed Circuit Board (PCB) thereto; and

filling the reception grooves with a resin material.
The method of claim 1, wherein the reception grooves are formed to pierce the light guide plate, and the filling of the reception grooves with the resin material comprises forming the resin material on one surface of the light guide plate.
The method of claim 1, wherein the forming of the reception grooves at the light guide plate comprises:

forming the reception grooves through a mechanical process; and

forming a first density pattern region and a second density pattern region, which has a higher pattern density than the first density pattern region, on the other surface of the light guide plate facing the PCB.
The method of claim 3, wherein the forming of the reception grooves through the mechanical process forms the first density pattern region to be nearer to the light emission surface of the LED than the second density pattern region.
The method of claim 4, wherein the first density pattern region and the second density pattern region comprise a plurality of concave patterns that overlap each other or are spaced apart from each other.
The method of claim 5, wherein the concave patterns comprise concave polygonal pyramid patterns or hemispherical patterns toward the inside of the surface of the light guide plate.
The method of claim 4, wherein the filling of the reception grooves with the resin material fills the resin material by a coating process, and a plurality of light-diffusing beads are further included in the resin material.
The method of claim 7, wherein the beads are included at 0.01% to 0.3% with respect to the total weight of the resin material.
The method of claim 7, wherein the resin material comprises an ultraviolet (UV)-curing material.
The method of claim 3, further comprising forming a third density pattern region and a fourth density pattern region, which has a higher pattern density than the third density pattern region, on the top surface of a resin material layer formed on one surface of the light guide plate, after the filling the reception grooves with the resin material.
The method of claim 10, wherein the forming of the third density pattern region and the fourth density pattern region forms the fourth density pattern region to be nearer to the light emission surface of the LED than the third density pattern region.
The method of claim 11, wherein the third density pattern region and the fourth density pattern region comprise a plurality of convex patterns that overlap each other or are spaced apart from each other.
The method of claim 12, wherein the convex patterns comprise polygonal pyramid patterns or hemispherical patterns.
The method of claim 12, wherein the first to fourth density pattern regions comprise convex or concave polygonal pyramid patterns, wherein a bottom inclination angle of the polygonal pyramid pattern has a value of 35 to 70 degrees.
The method of claim 3, wherein the first density patter region and the second density pattern region comprise convex polygonal pyramid patterns, wherein a bottom inclination angle of the polygonal pyramid pattern of the first density pattern region has a value of 35 to 50 degrees and a bottom inclination angle of the polygonal pyramid pattern of the second density pattern region has a value of 50 to 70 degrees.
The method of claim 3, further comprising stacking an optical film layer, which comprises a microlens array pattern, on the top surface of a resin material layer formed on one surface of the light guide plate, after the filling of the reception grooves with the resin material.
The method of claim 15, wherein the optical film layer comprises a fifth density pattern region and a sixth density pattern region having a higher pattern density than the fifth density pattern region, and the sixth density pattern region is nearer to the light emission surface of the LED than the fifth density pattern region.