JP4568209B2 - Backlight and liquid crystal display device using the same - Google Patents

Description

  The present invention relates to a backlight using a light-emitting diode as a light source and a liquid crystal display device using the same, and more particularly to a backlight and a liquid crystal display device that can reduce the outer shape of the display device while reducing the thickness. .

  A liquid crystal display device has low power consumption, is lightweight, suitable for thinning and downsizing, and is widely used as various monitors for personal computers, television receivers, portable terminals, navigation systems, and the like. In such a liquid crystal display device, there are a reflective liquid crystal display device and a transmissive liquid crystal display device, but a transmissive liquid crystal display device is often used in terms of brightness. In this transmissive liquid crystal display device, a backlight using a light emitting diode (LED) as a light source is used. This backlight is configured such that a circuit board on which an LED is mounted is disposed on the liquid crystal panel side, and the LED is opposed to one side of the light guide plate (see, for example, Patent Document 1).

  In the backlight having such a configuration, since the circuit board is located on the upper side of the light guide plate, there is a problem that the heat of the LED is easily trapped and sufficient heat dissipation cannot be performed.

  Contrary to this arrangement, a configuration is also adopted in which a circuit board on which LEDs are mounted is arranged below the light guide plate (see, for example, Patent Document 2).

  Thus, when the circuit board is disposed on the back surface side of the reflection sheet disposed on the back surface side of the light guide plate, it is easy to dissipate heat to the housing of a personal computer or the like incorporating the liquid crystal display device. There is.

However, when applied to a personal computer or the like having a large display screen size, if the reflective sheet is thin, peeling will occur between the light guide plate. If a thick reflective sheet with increased deformation strength is used, There arises a problem that a deviation occurs between the central axis in the thickness direction and the optical axis of the LED light source.
Japanese Patent Laying-Open No. 2005-134666 (FIG. 1) Japanese Patent Laying-Open No. 2005-115335 (FIGS. 2 and 4)

  As described above, when the LED is used as the light source and the circuit board on which the LED is mounted is disposed on the lower side of the reflection sheet from the heat radiation surface, the distance between the optical axis of the LED light source and the central axis in the thickness direction of the light guide plate This causes a problem that the light incident efficiency of the light guide plate is lowered and the screen brightness of the liquid crystal display device is lowered.

  In addition, since the circuit board is disposed on the back side of the reflection sheet, there is a problem that the thickness of the backlight itself increases.

  An object of the present invention is to provide a backlight and a liquid crystal display device in which the light entrance efficiency from the LED light source to the light guide plate is improved while achieving a reduction in thickness.

A backlight according to the present invention is provided with a plurality of light emitting diodes arranged in a line on a circuit board, a light guide plate disposed with one side faced to the light emitting diodes, and a rear surface side of the light guide plate. In the backlight including the reflective sheet , a thin portion in which the thickness in the end face direction on the light emitting diode side is reduced is formed on the reflective sheet.

  The liquid crystal display device according to the present invention includes an array substrate in which a plurality of pixel electrodes are disposed on a glass substrate, a counter substrate in which a common electrode is disposed to face the array substrate, and an enclosure between the substrates. A liquid crystal panel having a liquid crystal member formed thereon, a light guide plate disposed on the back side of the liquid crystal panel for irradiating the liquid crystal panel, and disposed on a circuit board facing at least one side surface of the light guide plate In a liquid crystal display device comprising a backlight having a plurality of light emitting diodes arranged in parallel and a reflective sheet disposed on the back side of the light guide plate, the thickness of the reflective sheet on the light emitting diode side in the end face direction is reduced. The thin part was formed.

According to the present invention, the thickness of the backlight is reduced by forming a thin portion with a reduced thickness in the end face direction on the light emitting diode side on the reflection sheet and arranging the circuit board on which the LED is mounted on the thin portion. In order to reduce the thickness of the light guide plate and minimize the deviation between the center axis of the light guide plate in the thickness direction and the optical axis of the LED light source, the light incident efficiency from the LED to the light guide plate can be improved and the screen luminance can be reduced. A backlight and a liquid crystal display device that can be increased can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As schematically shown in FIG. 1, the liquid crystal display device according to the present invention includes a liquid crystal panel 11 and a backlight 13 having a plurality of light emitting diodes (LEDs) 12 as light sources.

The liquid crystal panel 11 has a rectangular array substrate 14 and a counter substrate 15, and is stretched through a sealing material 16 printed on the array substrate 14 so as to surround the outside of the display area of the array substrate 14. By being combined, they are arranged facing each other with a gap of about 5 μm or less, and a liquid crystal member (not shown) is sealed in this gap.

  The array substrate 14 has a rectangular glass substrate 17, and although not shown in the figure, a large number of signal lines and scanning lines are arranged orthogonally to each other. In addition, a plurality of auxiliary capacitance lines are arranged substantially parallel to the scanning lines. A protective film, an alignment film (not shown) and the like are further laminated on the inner surface of the glass substrate 17, and a polarizing plate (not shown) is attached to the outer surface side to constitute the array substrate 14.

  On the other hand, the counter substrate 15 facing the array substrate 14 includes a rectangular glass substrate 18 which is actually formed in a smaller size than the glass substrate 17 constituting the array substrate 14, and the inner surface of the glass substrate 18. Although not shown above, in the case of a color liquid crystal display device, a black matrix and a color filter are provided, and a counter electrode and an alignment film made of ITO are laminated to form a glass substrate 18. A polarizing plate (not shown) is attached to the outer surface side to constitute the counter substrate 15.

  TFTs (not shown) as switching elements are formed in the vicinity of the intersections between the signal lines and the scanning lines provided on the glass substrate 17 of the array substrate 14, and the gate electrodes of the TFTs are used as the scanning lines. In addition, the source electrode is connected to the signal line, the drain electrode of each TFT is connected to a pixel electrode (not shown) made of ITO, and between each auxiliary capacitance line and the pixel electrode facing it. An auxiliary capacity is formed.

  A driving circuit for supplying a video signal and a scanning signal to the signal line and the scanning line and supplying a reference voltage and the like to the auxiliary capacitance line is a multi-layered structure in which the driving circuit is spaced along one long side of the array substrate 14 Is mounted on the printed circuit board 19. The printed circuit board 19 and the liquid crystal panel 11 are connected by three flexible printed wiring boards 21 on which a source driver 20 is mounted with TAB (Tape Automated Bonding). This is because the number of wirings is reduced by making the driving of the liquid crystal panel 11 multi-selective driving. If the number is up to three, the component mounting area is between the flexible printed wiring boards 21 on the printed circuit board 19. It has been found that can be formed.

  The printed circuit board 19 of this multilayer laminated structure is formed to have a width of about 10 mm with 6 to 8 layers. If the number of multilayers is increased, the width of the printed circuit board 19 can be made narrower, and conversely the number of layers can be reduced. For example, the width of the printed board 19 can be increased, and can be set according to the product specifications.

  On the surface of the printed board 19 where the flexible printed wiring board 21 does not exist, electrical components 22 such as a system LSI, various semiconductors, a chip resistor, a chip capacitor, and a connector are arranged.

  On one side of the liquid crystal panel 11 on which the three flexible printed wiring boards 21 are provided, on the remaining three side surfaces from the two side edge portions outside the flexible printed wiring board 21, synthetic resin or rubber material is provided. A frame body 23 made of a flexible elastic material such as the like is fitted to hold the side surface and protect the end surface of the liquid crystal panel 11.

  A backlight 13 is disposed on the back surface side of the liquid crystal panel 11 so as to face the liquid crystal panel 11 configured as described above. The backlight 13 includes a plurality of LEDs 12 and a light guide plate 24 in which the LEDs 12 are disposed on one side surface and set to a plate thickness of 1 mm or less. The light emitted from the LED 12 is reflected by the inner surface of the light guide plate 24 and propagates in the light guide plate 24, and the light is led out toward the liquid crystal panel 11 by the light guide plate 24. For this purpose, the light guide plate 24 is provided with a sawtooth reflection surface on the bottom surface or the lead-out surface of the light guide plate 24 or a prism-like reflection surface in order to efficiently guide light to the liquid crystal panel 11 side. Is used in combination to improve the light propagation efficiency.

  Further, the outer surface of the bottom surface of the light guide plate 24 is mirror-finished by depositing aluminum, silver, or the like on the surface of white paper or synthetic resin, or by sticking such a sheet so that there is relatively little deflection. For example, a reflective sheet 25 made of a slightly thick material of about 230 μm is disposed. If the amount of light is sufficiently secured, it is possible to use the reflection sheet 25 whose inner surface is white.

  On the other hand, an optical sheet 26 such as a diffusion sheet or a prism sheet is disposed on the light exit surface side of the light guide plate 24. The LED 12, the light guide plate 24, the optical sheet 26, and the reflection sheet 25 are made of metal such as stainless steel. Is housed in a frame-like back case 27. The LED 12 serving as the light source is mounted on a circuit board 28 made of a flexible printed wiring board, and the backlight 13 is constituted by these.

  The backlight 13 and the liquid crystal panel 11 thus configured are positioned by superposing the liquid crystal panel 11 on the back case 27 of the backlight 13. Thereafter, the liquid crystal panel 11 and the backlight 13 are integrated to form a liquid crystal display device by adhering the three side surfaces of the overlapped liquid crystal panel 11 and the backlight 13 with an adhesive tape 29. .

  As shown in FIG. 2, the liquid crystal display device is bent and held by a flexible printed wiring board 21 so as to be wrapped and wrapped by a flexible printed wiring board 21, so that the liquid crystal panel 11 and the backlight 13 have one side thereof. The width direction is held so as to be parallel to the planar direction of the liquid crystal panel 11 and the backlight 13. Since this printed circuit board 19 is composed of the multilayer laminated printed circuit board 19, the thickness in the thickness direction is thicker than that of the single-layer wiring board, but the length in the width direction is shortened accordingly. Therefore, the size of the frame portion can be reduced.

  Moreover, even if the length of the printed board 19 in the width direction is shortened, the flexible printed wiring board 21 that connects the printed board 19 and the liquid crystal panel 11 can be constituted by three pieces. It is possible to dispose an electrical component 22 such as a system LSI, various semiconductors, resistors, and capacitors constituting a drive circuit in an intermediate space where no flexible printed wiring board 21 exists.

  Therefore, even if the width of the printed board 19 is reduced to 10 mm, the number of the flexible printed wiring boards 21 used is set to be 3 or less, and the surface of the printed board 19 is still In addition, it is possible to secure a sufficient component arrangement space, and it is possible to promote reduction in thickness and size.

  The relationship between the liquid crystal panel 11 and the backlight 13 using the LEDs 12 will be described in more detail with reference to FIG. Note that the same components as those described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  That is, FIG. 3 is a partially cutaway sectional view of the portions of the liquid crystal panel 11 and the backlight 13, and the liquid crystal panel 11 provided with the polarizing plates 30 and 31 on both sides is engaged with one end of the light guide plate 24. The side surface of the back case 27 and the adhesive tape 34 are fixed. The back case 27 is formed in a U-shaped cross section on the inner side of the end surface on which the LED 12 is disposed, and one end of the light guide plate 24 is inserted into the U-shaped. An optical sheet 26 is disposed on the light guide plate 24 on the liquid crystal panel 11 side, and a reflective sheet 25 is formed on the opposite surface side. In order to form the thin portion 35, the thickness of the reflective sheet 25 is reduced by partially pressing the portion of the reflective sheet 25 where the thin portion 35 is formed, or the reflective sheet 25 is formed in multiple layers. A method such as a single layer configuration of only the portion 35 may be employed.

  A plurality of LEDs 12 connected and fixed by a wiring pattern are arranged in a line on the surface of the circuit board 28 made of a flexible printed wiring board in the space between one end of the light guide plate 24 and the side surface of the back case 27. Yes.

  That is, in the light source using the LED 12, as shown in FIG. 4, the emission surface 40 faces the light guide plate 24 side in a horizontal row on one surface of the circuit board 28 on which the plurality of LEDs 12 are formed in a tape shape. It is installed side by side.

  As shown in FIG. 5, the LED 12 is connected to an LED circuit 42 in which a plurality of LEDs 12 are connected in series to a lighting control drive circuit 41 so as to form a plurality of rows such as two rows. The current flowing through the LED circuit 42 is adjusted by the resistor 43, and current fluctuation is detected from one resistor 43, and the detected voltage is fed back to the lighting control drive circuit 41, thereby controlling a constant current. is doing.

  The LED circuit 42 can be driven by a driving method such as direct current driving or pulse voltage driving. Each LED 12 is driven by being connected to a circuit pattern formed on the circuit board 28. At this time, in order to improve the brightness and reduce the variation in brightness, it is possible to connect adjacent LEDs 12 so that the LEDs 12 of other LED circuits 42 are alternately arranged. This is achieved by forming a wiring pattern for driving the respective LED circuits 42 in 28 and alternately connecting the LEDs 12 thereto.

  The circuit board 28 is disposed so as to be positioned in the thin portion 35 portion of the reflection sheet 25. That is, the reflection sheet 25 forms a thin portion 35 by thinning only the end surface portion on the LED 12 side, and the remaining portion is formed thick.

  Accordingly, since the thin portion 35 has a step, the flat surface is positioned on the light guide plate 24 side, and the circuit board 28 is positioned on the surface where the step exists. In this way, the circuit board 28 and the bottom surface of the back case 27 are fixed by the adhesive tape 36 so that the optical axis as the light source of the LED 12 coincides with the central axis portion in the end face thickness direction of the light guide plate 24.

  A method for matching the optical axis of the LED 12 with the central axis of the light guide plate 24 in the thickness direction will be described with reference to FIGS.

  FIG. 6 shows a comparative example in which the entire thickness of the reflection sheet 25 attached to the light guide plate 24 is the same.

  Now, assuming that the thickness of the light guide plate 24 is a, the central axis A in the thickness direction is located at a / 2. Further, the thickness of the reflection sheet 25 is b. On the other hand, assuming that the height of the LED 12 is c and the optical axis B is at a position of c / 2, the amount of deviation between the central axis A and the optical axis B is AB.

For example, if a = 650 μm, b = 230 μm, and c = 600 μm, the deviation is
A-B = 325-300 = 25 μm
It becomes a gap of.

  However, since the circuit board 28 on which the LED 12 is mounted is located below the reflection sheet 25, b = 230 μm corresponding to the thickness of the reflection sheet 25 becomes an error.

Therefore, the virtual center line A ′ viewed from the optical axis B of the LED 12 is
A ′ = (650 + 230) / 2 = 440 μm
Will be present at
A′−B = 440−300 = 140 μm
This means that there is a deviation.

On the other hand, as shown in FIG. 7, when considering the case where the thin portion 35 is formed on the reflection sheet 25 and the circuit board 28 is disposed on the thin portion 35, the thickness of the thin portion 35 is d, Set d = 30 μm. In this case, as described above, since a = 650 μm, b = 230 μm, c = 600 μm, and d = 30 μm, the virtual central axis A ′ of the light guide plate 24 viewed from the optical axis B of the LED 12 is
A ′ = (650 + 30) / 2 = 340 μm
It becomes.

Therefore, the amount of deviation between the virtual center axis A ′ and the optical axis B is
A′−B = 340−300 = 40 μm
Thus, the amount of deviation between the actual center axis A and the optical axis B can be greatly improved.

  As a result, it is possible to greatly improve the light incident efficiency from the LED 12 to the light guide plate 24, to suppress a decrease in screen display luminance of the liquid crystal display device, and to reduce the thickness as the backlight. .

  The back case 27 is formed in a wide U-shape on one side where the LEDs 12 are arranged, including the bottom plate side, but the portion corresponding to the other side is merely formed in an L-shape. Thus, the width is only enough to allow the reflection sheet 25 to be locked. For this reason, since the back case 27 has only an L-shaped frame as a member corresponding to the bottom plate, the weight of the metal back case 27 can be greatly reduced, This is suitable for mold products.

  A non-display portion on the front side of the liquid crystal panel 11 is covered with a front case 37, and the front case 37 is fitted and fixed to the back case 27. The entire liquid crystal display device is fixed to a housing 39 such as a personal computer by an adhesive tape 38.

  The present invention is not limited to the above-described embodiment, but can be applied to a monochrome type liquid crystal display device. The back case has been described as having a frame shape. It is also possible to use a configuration in which a reinforcing bar is passed in a cross or a X shape so as to pass through the center of the frame and the mechanical strength is improved, or a box with a bottom is used.

  Furthermore, if the surface between the liquid crystal panel and the printed board including the flexible printed wiring board is covered with a transparent sheet or the like, dust and moisture adhere to and penetrate the flexible printed wiring board and the wiring part of the printed board. The product quality can be improved. Moreover, it is also possible to arrange | position LED on the some side of a light-guide plate depending on goods form.

1 is an exploded perspective view showing an overview of a backlight and a liquid crystal display device according to the present invention. The front view of a liquid crystal display device similarly. FIG. 3 is a partially cutaway cross-sectional view showing main parts of the backlight and the liquid crystal display device. The perspective view which similarly shows an LED light source. The circuit diagram which similarly shows an LED circuit. Explanatory drawing of the comparative example for demonstrating the relationship between a light-guide plate and LED. Explanatory drawing for demonstrating the relationship between the light-guide plate and LED of this invention.

Explanation of symbols

11 ... Liquid crystal panel 12 ... Light emitting diode (LED)
DESCRIPTION OF SYMBOLS 13 ... Backlight 14 ... Array substrate 15 ... Opposite substrate 24 ... Light guide plate 25 ... Reflective sheet 28 ... Circuit board 35 ... Thin part

Claims (4)

A backlight including a plurality of light emitting diodes arranged in a line on a circuit board, a light guide plate arranged to face one side of the light emitting diodes, and a reflection sheet arranged on the back side of the light guide plate In
A backlight having a thinned portion formed by reducing a thickness in an end surface direction on the light emitting diode side on the reflection sheet . The backlight according to claim 1, wherein the reflective sheet is disposed so that a thin portion is on an outer side, and the circuit board is disposed on the thin portion . A liquid crystal panel having an array substrate in which a plurality of pixel electrodes are disposed on a glass substrate, a counter substrate in which a common electrode is disposed to face the array substrate, and a liquid crystal member sealed between the substrates;
A light guide plate disposed on the back side of the liquid crystal panel for irradiating the liquid crystal panel, and a plurality of light emitting elements disposed in parallel with each other on at least one side surface of the light guide plate. In a liquid crystal display device comprising a diode and a backlight having a reflective sheet disposed on the back side of the light guide plate,
A liquid crystal display device, wherein a thin portion having a reduced thickness in an end face direction on the light emitting diode side is formed on the reflection sheet. 4. The liquid crystal display device according to claim 3, wherein the reflective sheet is disposed such that a thin portion is on an outer side, and the circuit board is disposed on the thin portion.

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