JPH07181488A - Surface illuminator for liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent irregular color and the difference of lightness from occurring on a liquid crystal display screen and further to reinforce the protection of a light source from external load by effectively utilizing light emitted from a light source, improving the lightness of the background of the liquid crystal display screen and eliminating the interposition of an air layer. CONSTITUTION:This surface illuminator 10 is a device for illuminating the background of the liquid crystal display screen equipped with a light transmission plate 11 arranged on the back surface of a liquid crystal cell 2 and the light source 12 arranged on the side of the plate 11. Especially, in this illuminator, a transmitted light cushioning layer 13 is formed to cover the light source 12 and a reflecting function layer 14 is formed at one part or all of the outer surface of the layer 13.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device for background lighting of a liquid crystal display screen provided in a liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device, which is a light-receiving display device, is provided with an illuminating device, which is generally called a backlight, for background illumination of a liquid crystal display screen. This one is used for the purpose of clearly distinguishing the liquid crystal display such as characters and figures displayed on the screen and brightening the screen.
It is used in a wide range of fields such as LCD TVs, vehicle instrument panels, and liquid crystal displays for personal computers and word processors.

Further, such an illuminating device is made as compact as possible in association with the trend toward miniaturization and thinning of the main body side of a personal computer, word processor, etc. (which is a remarkable example of the increase in lap top models). It is required to be as thin as possible. Accordingly, many of the current models have a light guide plate 11 'on the back surface of the liquid crystal cell 2 as shown in FIG.
A configuration in which the light source 12 is arranged on the side of 1'is generally adopted.

However, when such a structure is adopted, not all of the light emitted from the light source 12 is used as the backlight of the liquid crystal display, but the light emitted from the light source 12 to the surroundings is guided. Most of the light except for the part facing the light plate 11 'is not used at all, or the presence of an air layer existing between the light guide plate 11' and the light source 12 causes confusion of light and is not effectively used. In addition, there is a problem in that color unevenness and a difference in brightness are caused. In addition to this, the above configuration alone does not protect the light source 12 against external vibration or impact, and there is a problem to be solved in this respect as well.

[0005]

The present invention has been made in view of such a background. By eliminating the air layer, the light emitted from the light source is effectively used, and the optical characteristics are improved. It is an object of the present invention to propose a novel planar illumination device in a liquid crystal display device which solves the above problems by protecting the light source.

[0006]

[Constitution of the invention]

That is, a surface illumination device in a liquid crystal display device as a first invention according to the present application includes a light guide plate arranged on the back surface of a liquid crystal cell and a light source arranged on the side of the light guide plate. In a device for background lighting of a liquid crystal display screen, the device comprises a light-transmitting buffer layer so as to cover at least a light source, and a reflective functional layer is formed on a part or all of an outer surface of the light-transmitting buffer layer. It is characterized by being done.

In addition to the above requirements, the planar lighting device in the liquid crystal display device according to the second invention of the present application is characterized in that the light guide plate is formed of a light transmitting buffer layer. .

Furthermore, in addition to the above-mentioned requirements, in the planar lighting device in the liquid crystal display device according to the third invention of the present application, the light-transmitting buffer layer is formed of silicone gel or silicone rubber as a material. It is a feature. The invention is intended to achieve the above object by means.

[0009]

That is, in the planar lighting device in the liquid crystal display device according to the first invention of the present application, the light-transmitting buffer layer is formed so as to cover at least the light source, and a part of the outer surface of the light-transmitting buffer layer is formed. Alternatively, the reflective function layer is formed on the entire surface. As a result, by covering the light source with the light-transmitting buffer layer, the air layer existing between the light guide plate and the light source is eliminated, and the confusion of light caused by the presence of this air layer is prevented and the light is emitted around the light source. The reflected light enters the light guide plate directly through the translucent buffer layer, and other light is repeatedly reflected between the reflective function layer and the light source, and finally most of the light emitted from the light source is conducted. Guided by a light board. Further, the light transmitting buffer layer also has a function of protecting the light source from external vibration and impact.

The planar illumination device in the liquid crystal display device according to the second invention of the present application has a structure in which the light guide plate is formed of a light transmission buffer layer. By this, in addition to the above-described action, the light-transmitting buffer layer portion covering the light source and the light guide plate have exactly the same refractive index, and the confusion of light caused by the difference in the refractive index is prevented. It can be used.

Furthermore, in the planar lighting device in the liquid crystal display device according to the third invention of the present application, the light transmissive buffer layer is formed of silicone gel or silicone rubber. With this, in addition to the above-mentioned action, the cushioning property of the silicone gel or the silicone rubber further protects the light source, and there is almost no difference in the refractive index compared with acrylic or the like used as the material of the light guide plate. Effective use of light can also be achieved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A planar illumination device in a liquid crystal display device of the present invention will be specifically described below with reference to the drawings. In the description, first of all, an outline of the liquid crystal display device will be described centering on the portion where the planar lighting device of the present invention is provided, and then the configuration of the basic embodiment of the planar lighting device of the present invention will be described. Reference will be made to other embodiments with different partial configurations. Following this, a brief description will be given of the manufacturing method of the basic embodiment of the planar lighting device of the present invention.

First, an outline of a liquid crystal display device to which the planar lighting device of the present invention is applied will be described. As is well known, the liquid crystal display device 1 is used in a wide range of fields such as wristwatches, calculators, word processors, small television displays, display screens of CD players, VCRs and the like. To explain the principle, the smectic, nematic, and cholesteric liquid crystals, which are classified according to the difference in crystal arrangement, have the property that their molecular arrangement changes when a voltage is applied to them. By turning on / off the light to be turned on or controlling the wavelength of the light that can pass through, characters and figures are displayed as a display and are raised on the screen.

Further, the basic structure of the liquid crystal display device 1 is a liquid crystal cell 2 formed by sandwiching the above liquid crystal between two transparent electrode plates, and a liquid crystal cell 2 provided on the front surface side for protecting the liquid crystal cell 2. The backlight type liquid crystal display device 1 includes a protection panel (not shown) and the planar lighting device 10 of the present invention provided on the back side of the liquid crystal cell 2 with the buffer layer 3 interposed therebetween. Made by. Although illustration is omitted, in addition to these members, a holding frame for holding these members, a polarizing plate and a reflection plate which are necessary due to a difference in a display operation method, and further, for the purpose of preventing ultraviolet ray cut and surface reflection. The various filters used, the sealing material used to seal the periphery of the liquid crystal cell 2, the sealant used to seal the liquid crystal injection hole, and the like are also used in the liquid crystal display device 1.
Is provided in.

Of these, the liquid crystal cell 2 is formed by sandwiching the liquid crystal between two transparent electrode plates as described above. Here, the structure of the transparent electrode plate used for this will be supplemented. The transparent electrode plate is formed by using a synthetic resin plate such as a glass plate or an acrylic plate as a support plate, and attaching a transparent conductive film such as indium oxide or tin oxide as an electrode to the support plate. By adjusting the surface treatment of the electrodes, it is possible to arrange the liquid crystal molecules so that the arrangement is perpendicular to the support plate, parallel to the support plate, inclined, or a combination thereof to have an twist.

Next, the protection panel will be described. The protective panel serves to protect the liquid crystal cell 2 as described above, but at the same time, it has a good light transmittance and can clearly recognize characters, figures and the like appearing on the surface of the liquid crystal cell 2 from the outside. Must. Therefore, as a material of this protective panel, a colorless transparent or colored transparent glass plate, an acrylic plate, or another synthetic resin plate is applied.

In addition to the above-mentioned function of protecting the liquid crystal cell 2, the protection panel can have a function as a touch panel. Specifically, it is configured by laminating a touch input pattern film to a protective panel made of the above material. By the way, when inputting characters or figures on such a protection panel, the character or figure you want to display should be touched directly on the protection panel or by touching the pen tip and drawn on the protection panel. Is detected and recognized as a character or a figure, and the information is sent to the liquid crystal cell 2 and displayed as a character or a figure on the display screen.

A fixed gap is provided between the liquid crystal cell 2 and the planar lighting device 10 of the present invention, and the buffer layer 3 is formed in this gap. The buffer layer 3 has a basic function of blocking transmission of an external load applied to the light guide plate 11 to the liquid crystal cell 2 and preventing the liquid crystal display from being distorted, and also prevents reflection and absorption of incident light, It also has the function of brightly and clearly displaying characters and figures appearing on the display screen by preventing the confusion of light caused by the refraction of light. Specifically, it is desirable that the material forming the buffer layer 3 has excellent buffering characteristics, has a refractive index equal to that of the material forming the light guide plate 11 to be described later, and does not absorb or reflect light. The same material as that of the light-transmitting buffer layer 13 described later can be applied.

The planar illumination device 10 provided in the liquid crystal display device 1 functions as a so-called backlight used for background illumination of the liquid crystal display screen and is provided on the back surface of the liquid crystal cell 2. A light guide plate 11 provided via the buffer layer 3, a light source 12 disposed on the side of the light guide plate 11, a light transmitting buffer layer 13 formed so as to cover at least the light source 12, and the light transmitting plate. Buffer layer 1
Reflective function layer 14 formed on a part or all of the outer surface of No. 3
It is basically composed of and.

Of these, the light guide plate 11 plays a role of converting point-like or line-like light emitted from the light source 12 into plane-like light having substantially the same area as the liquid crystal cell 2 and supplying the light. As an example, it is formed by cutting a synthetic resin material such as a colorless and transparent acrylic plate having excellent translucency, or glass into approximately the same size as the liquid crystal cell 2. Although illustration is omitted in the light guide plate 11, a reflection mirror or the like for switching the optical path can be appropriately provided, and the light guide plate 11 can be provided inside the thin light plate 11 or as shown in FIG. 4C. It is also possible to form itself as an inclined surface prism P that becomes higher as the distance from the light source 12 increases, and to consider the diffusion efficiency of light.

The light source 12 is, for example, a cold cathode or hot cathode type fluorescent lamp, a halogen lamp, or an LE.
D and the like can be applied, and when a cold cathode type fluorescent lamp is used, since the liquid crystal cell 2 is driven by a DC voltage, it is converted to AC by high frequency DA
An inverter is required separately.

The light-transmitting buffer layer 13 is a portion which constitutes the characteristic structure of the present invention. In the embodiment shown in FIGS. 1 and 2, the light-transmitting buffer layer 13 covers the periphery of the light source 12, and the light guide plate 11 and the light source 12 are provided. It is provided to fill the space. Hereinafter, the light transmitting buffer layer 1
Materials constituting No. 3 will be described.

First, as an example of the material of the light transmitting buffer layer 13, silicone gel can be mentioned. Further, as the silicone gel used in the present invention, those having a reduced content of volatile low molecular weight substances are preferable, and there is a risk that if the undiluted solution of the silicone gel is too low in viscosity, it will penetrate into the details due to capillary phenomenon. There is a possibility that it will flow out before curing, and on the other hand, if the viscosity is too high, there is a risk that it will not fully sneak into the entire filling area, and the workability will deteriorate. It is necessary that the property is high (the degree of expressing the phenomenon of thixotropy).

Therefore, such a silicone gel is, for example, a diorganopolysiloxane (hereinafter referred to as component A) which is a stock solution of the silicone gel represented by the following formula [1]: RR ¹ ₂ SiO— (R ² ₂ SiO) _n SiR ¹ ₂ R ... [1] [wherein R is an alkenyl group, R ¹ is a monovalent hydrocarbon group having no aliphatic unsaturated bond, and R ² is a monovalent aliphatic hydrocarbon group (R ^At least 50 mol% of 2
Is a methyl group, and when it has an alkenyl group, its content is 10 mol% or less), and n is a number such that the viscosity of this component at 25 ° C. is 100 to 100000 cSt]. Viscosity at 25 ℃ 5000cS
It is less than or equal to t and is composed of organohydrogenpolysiloxane (component B) which is a stock solution of a silicone gel having hydrogen atoms directly bonded to at least two Si atoms in one molecule. Obtained by curing a mixture adjusted such that the ratio (molar ratio) of the total amount of alkenyl groups contained in the component A to the total amount of hydrogen atoms directly bonded is 0.1 to 0.2. Addition reaction type silicone copolymer, JIS K
Penetration measured with (K-2207-1980 50g load) is 5-25
The cured product is 0.

The silicone gel will be described in more detail. The component A has a linear molecular structure, and alkenyl groups R at both ends of the molecule are added to hydrogen atoms directly bonded to Si atoms in component B. And a compound capable of forming a crosslinked structure. The alkenyl group present at the terminal of this molecule is preferably a lower alkenyl group,
A vinyl group is particularly preferable in consideration of reactivity.

R ¹ existing at the terminal of the molecule is a monovalent monovalent hydrogen group having no aliphatic unsaturated bond, and specific examples of such a group include methyl group, propyl group and hexyl group. Examples thereof include alkyl groups, phenyl groups and fluoroalkyl groups.

In the above formula [1], R ² is a monovalent aliphatic hydrocarbon, and specific examples of such a group include:
Examples thereof include alkyl groups such as methyl group, propyl group and hexyl group, and lower alkenyl groups such as vinyl group. However, at least 50 mol% of R ²
Is a methyl group, and when R ² is an alkenyl group, the amount of the alkenyl group is preferably 10 mol% or less. If the amount of alkenyl groups exceeds 10 mol%, the crosslink density becomes too high and the viscosity tends to be high. Also, n is
The viscosity of this A component at 25 ° C. is usually 100 to 10
It is set to be within the range of 0000 cSt, preferably 200 to 20000 cSt.

The above-mentioned component B is a cross-linking agent for the component A and is Si
The hydrogen atom directly bonded to the atom is added to the alkenyl group in the A component to cure the A component. The component B has only to have the above-described action, and as the component B, those having various molecular structures such as linear, branched, cyclic or network can be used.

In addition to the hydrogen atom, an organic group is bonded to the Si atom in the component B, and this organic group is usually a lower alkyl group such as a methyl group. Further, the viscosity of component B at 25 ° C. is usually 5000 cSt or less, preferably 50
It is less than 0 cSt. Examples of such component B include organohydrogenpolysiloxanes having both ends of the molecule blocked with triorganosiloxy groups, copolymers of diorganosiloxane and organohydrogensiloxane,
Tetraorganotetrahydrogencyclotetrasiloxane, copolymerized siloxane composed of HR ¹ ₂ SiO 1/2 units and SiO 4/2 units, and HR ¹ ₂ SiO 1/2 units and R ¹ ₃ SiO
Mention may be made of a copolymer polysiloxane composed of 1/2 units and SiO 4/2 units. However, in the above formula, R
¹ has the same meaning as above.

The ratio of the total molar amount of alkenyl groups in the component A to the total molar amount of hydrogen atoms directly bonded to Si in the component B is usually 0.1 to 2.0, preferably It is produced by mixing the component A and the component B so as to be in the range of 0.1 to 1.0 and curing the mixture.

The curing reaction in this case is usually carried out using a catalyst. The catalyst used here is preferably a platinum-based catalyst, and examples thereof include finely pulverized elemental platinum, chloroplatinic acid, platinum oxide, platinum and olefin complex salts, platinum alcoholates, and chloroplatinic acid and vinylsiloxane. And complex salts with. Such a complex salt is usually used in an amount of 0.1 ppm (platinum equivalent, the same applies below) or more, preferably 0.5 ppm or more based on the total weight of the components A and B. The upper limit of the amount of such a catalyst is not particularly limited, but when the catalyst is in a liquid state or can be used as a solution, an amount of 200 ppm or less is sufficient.

The components A, B and the catalyst as described above are mixed and left to stand at room temperature or heated to cure to form the silicone gel used in the present invention. The silicone gel thus obtained is JIS K
Penetration measured with (K-2207-1980 50g load) is usually 5
Has 250. The hardness of such a silicone gel varies depending on the cross-linking structure formed by the A component and the B component.

The viscosity of the silicone gel before curing and the degree of penetration after curing are 5 to 75% by weight based on the silicone gel obtained, with a silicone oil having methyl groups at both ends.
It can be adjusted by adding in advance in an amount within the range. Thus, the silicone gel can be prepared as described above, or a commercially available one can be used.

Examples of commercially available products that can be used in the present invention include CF5027, TOUGH-3 and TOUGH.
-4, TOUGH-5, TOUGH-6, TOUGH-
7, (Tore Dow Corning Silicone) or X3
2-902 / cat 1300 (made by Shin-Etsu Chemical Co., Ltd.), F250-121 (made by Nippon Unica Co., Ltd.), etc. can be mentioned.

Further, a more preferable silicone gel is a silicone gel produced by using a diorganopolysiloxane, which is a stock solution of silicone gel, in which low molecular weight substances are reduced. That is, the component A contains two or more silicon atom-bonded alkenyl groups in one molecule, has a viscosity at 25 ° C. of 50 to 100,000 centipoise, and has 4 to 20 parts by weight of a cyclic diorganopolysiloxane. It is the one to which the diorganopolysiloxane having a content of 0.5% by weight or less is applied. In addition to the above silicone gel, it is possible to use, for example, a film or sheet that has already been formed, a type of silicone rubber that is cured by ultraviolet light, or a silicone gel. As an example of the commercially available product, SOTEFA7
0, SOTEFA50 (made by Toray Dow Corning Silicone) and X-31-7006 (made by Shin-Etsu Chemical Co., Ltd.)
The former is a silicone film adhesive that has already been semi-cured into a film, and is said to strongly adhere to glass, acrylic, polycarbonate, etc. by heat curing, and the latter is It is a one-component silicone gel that is cured in a few seconds by irradiation with ultraviolet rays and has excellent adhesiveness. And if you use these, you can use directly from the seat state,
For curing, ultraviolet rays that can be easily controlled and can be cured in a short time can be used.

As the material of the light transmitting buffer layer 13, in addition to such silicone gel or silicone rubber, polyurethane elastomer, thermoplastic resin or thermosetting resin can be applied. The polyurethane elastomer is crosslinked and cured by the reaction between the prepolymer and the polyisocyanate. These may be supplied as a mixed solution or may be sprayed and supplied while being mixed in a spray state while being mixed at the nozzle tip. Suitable for the latter is a solventless quick-hardening urethane resin manufactured by Nippon Synthetic Chemical Industry Co., Ltd.

Further, as the material of the light transmitting buffer layer 13, a photocurable resin can be applied. As the photocurable resin, a photosensitive resin obtained by introducing a styrylpyridinium group into a polyvinyl acetate / polyvinyl alcohol emulsion as a photosensitive group, and other natural water-soluble polymers such as carrageenan and gelatin, carboxymethyl cellulose, ammonium alginate, Photopolymerization type consisting of semi-synthetic water-soluble polymer such as starch and methylaminopropyl ether and photopolymerization initiator such as benzophenone, thioxanthone and benzoin ether, and monomer, dichromate, diazo resin, bisazide compound And a photo-crosslinking agent. If an ultraviolet curable resin is used as the photocurable resin, it is convenient because it can be cured in a short time by irradiation of ultraviolet rays which is easy to control.

The term "photocuring" of the photocurable resin means that when it is irradiated with electromagnetic waves having high energy such as visible light, ultraviolet rays, X-rays and electron beams, it absorbs energy and causes crosslinking, curing and insolubilization. The term "light" is a general term for electromagnetic waves with high energy.

As these polyurethane elastomers and ultraviolet curable resins, those having high transparency before and after curing are applied so as to reduce the light quantity of the light source 12 as much as possible. In addition, in the present invention, since the cushioning property is also an essential requirement, a cured product having an appropriate elasticity and capable of satisfying other physical properties required for this type of apparatus are applied.

Such a light-transmitting buffer layer 13 can also be applied to the light guide plate 11 as shown in FIG. 3, and in this case, the light-transmitting buffer layer 13 covering the light source 12 and the light guide plate 11 are combined. The light-transmitting buffer layer 13 to be formed is integrated with the structure.
Incidentally, when such a light guide plate 11 is formed of the light transmitting buffer layer 13, the buffering characteristics of the light transmitting buffer layer 13 can sufficiently cope with an external load received by the liquid crystal cell 2, so that the liquid crystal cell 2 and the light guide plate 11 are accommodated. It is also possible to eliminate the buffer layer 3 provided between and. The light-transmitting buffer layer 13 has the same refractive index as that of the light guide plate 11 and the same optical characteristics as described above.
There is no problem even if it is formed by 3.

Further, the reflection function layer 14 collects the light emitted from the light source 12 which does not reach the light guide plate 11 directly and is emitted to the outside through the light transmitting buffer layer 13 as described above.
These serve to guide these into the light guide plate 11. In the embodiment shown in FIGS. 2 and 3, the reflection function layer 14 is composed of a reflection sheet 16 made of a metal foil having a relatively high reflectance such as an aluminum foil. The reflective functional layer 14 is formed by
The light source 12 may be provided so as to cover only the periphery of the light source 12, as shown in FIG. 3, or may be extended so as to also cover the bottom surface of the light guide plate 11.

Further, the light transmitting buffer layer 13 and the reflection function layer 1
4 applies the principle of an optical fiber as shown in FIGS. 4 (a) and 4 (b), and a light-transmitting buffer layer 13 having a high refractive index is provided outside the light source 12, for example, corresponding to the core layer of the optical fiber.
It is also possible to adopt a configuration in which a reflection function layer 14 having a low refractive index is provided on the outer side thereof in correspondence with the cladding layer of the optical fiber. Then, the light emitted from the light source 12 propagates toward the light guide plate 11 without being attenuated by being totally reflected at the boundary surface between the light transmissive buffer layer 13 functioning as a core layer and the reflective function layer 14 functioning as a cladding layer. To be done.

Incidentally, the light transmitting buffer layer 13 and the reflection function layer 14 in this case are formed by laminating a solid sheet resin. However, in order to enhance the protection of the light source 12 from external vibration or impact, the above-mentioned is adopted. It is desirable to apply a material having excellent buffering properties such as a silicone gel or silicone rubber.

The translucent buffer layer 13 and the reflective function layer 14 may be provided so as to cover only the periphery of the light source 12 as shown in FIG. 4A, or as shown in FIG. 4B. It is also possible to further extend this so as to cover the bottom surface of the light guide plate 11.

The above is the basic structure of the present invention, but if necessary, the light amount adjusting sheet 5 and the reflecting film 6 shown in FIG.
Depending on the case, a diffusion plate (a plate having a matt surface) on or below the buffer layer 3 (between the liquid crystal cell 2 and the light guide plate 11).
It is also possible to provide. The light amount adjusting sheet 5 is bright in a portion where the light entering the light guide plate 11 is close to the light source 12,
Since it becomes dark in a distant portion, this is improved, and it is provided so as to supply a uniform amount of light to the back surface of the liquid crystal cell 2. In the illustrated embodiment, the size of the dot d that reflects light is small in the portion close to the light source 12,
By arranging so as to be large in a portion far from the light source 12, and adjusting the amount of light that escapes to the bottom surface of the light guide plate 11 out of the light that has entered the light guide plate 11, the amount of light that illuminates the back surface of the liquid crystal cell 2 I am trying to make adjustments.

The reflection film 6 has the same function as that of the reflection sheet 16 so that the light emitted from the light source 12 is not missed as much as possible and all of them are applied to the background illumination of the liquid crystal display. It is provided for this purpose. In the case where such a reflective film 6 is used, when the above-mentioned light amount adjustment is performed, the light guide plate 11 is used.
The light amount may be adjusted by devising the shape of the light source (see FIG. 4C) or by providing the light amount adjusting sheet 5 on the upper surface of the light guide plate 11. Incidentally, when the light quantity adjusting sheet 5 is used, the arrangement of the dots d provided on the bottom surface of the light guide plate 11 may be set to the reverse arrangement.

Next, the manufacturing method of the planar lighting device 10 of the present invention will be briefly described with reference to the embodiments shown in FIGS. First, a light guide plate 11, a light source 12, and a reflection sheet 16 as a reflection function layer 14 on which a light transmission buffer layer 13 is laminated are prepared. Next, the light source 12 is exposed to the side of the light guide plate 11, and as shown in FIG. 5, the light transmitting buffer layer 13 and the reflecting function which are laminated with the light transmitting buffer layer 13 inside so as to cover the light source 12 from the outside. The layer 14 may be covered and the end portion of the reflective function layer 14 may be fixed to the light guide plate 11.

Incidentally, since the light transmitting buffer layer 13 can freely change its shape, the space formed by the reflective function layer 14, the light guide plate 11 and the light source 12 is filled with the light transmitting buffer layer 13. However, no air layer is formed between them.

[0049]

The planar illumination device in the liquid crystal display device of the present invention has the above-mentioned structure, and by having such a structure, the following effects are exhibited. That is, the planar illumination device in the liquid crystal display device according to the first invention of the present application includes at least the light source 12
The light transmissive buffer layer 13 is formed so as to cover the light transmissive buffer layer 13, and the reflective function layer 1 is formed on part or all of the outer surface of the light transmissive buffer layer 13.
4 is formed. Thus, by covering the light source 12 with the light-transmitting buffer layer 13, the air layer existing between the light guide plate 11 and the light source 12 is eliminated, and the light confusion caused by the existence of the air layer is prevented, and the light source is prevented. 1
The light emitted to the periphery of 2 directly enters the light guide plate 11 through the light transmission buffer layer 13, and the other light is also reflected by the functional layer 1.
4 and the light source 12 are repeatedly reflected, and finally, most of the light emitted from the light source 12 is guided to the light guide plate 11.
Therefore, the liquid crystal display screen does not have color unevenness or difference in brightness and darkness, and the liquid crystal display becomes easier to see, and the background of the liquid crystal display screen becomes brighter, and the liquid crystal display can be clearly recognized. Further, by covering the light source 12 with the light transmitting buffer layer 13 in this manner, a heat retaining effect of the light source 12 can be expected, and the light source 1
2. Promote high efficiency light emission. Further, the light transmission buffer layer 13 is provided on the light guide plate 1.
1 is extended to cover the bottom surface of the light guide plate 11 as well.
Further, the heating effect of the liquid crystal cell 2 laminated via the buffer layer 3 can be expected, and the performance deterioration of the liquid crystal cell 2 at low temperature can be prevented. Further, since the light-transmitting buffer layer 13 has excellent buffering characteristics, it also exerts an effect of protecting the light source 12 from external vibration and impact.

The planar illumination device in the liquid crystal display device according to the second invention of the present application has a structure in which the light guide plate 11 is formed of the light transmission buffer layer 13. As a result, in addition to the above effects, the light-transmitting buffer layer 1 covering the light source 12
3 and the light guide plate 11 have the same refractive index,
The confusion of light caused by the difference in refractive index is prevented, more effective use of light is achieved, and the amount of light in the background of the liquid crystal display screen can be further increased.

Furthermore, in the planar illumination device in the liquid crystal display device according to the third invention of the present application, the light transmission buffer layer 13 is formed of silicone gel or silicone rubber. As a result, in addition to the above effects, the cushioning property of the silicone gel or silicone rubber further protects the light source against external loads, and the refractive index is lower than that of acrylic used as the material of the light guide plate 11. There is almost no difference, effective use of light can be achieved, and it can contribute to improvement of the brightness of the background of the liquid crystal display screen.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a liquid crystal display device to which a planar lighting device of the present invention is applied.

FIG. 2 is a vertical sectional side view showing the planar lighting device of the present invention.

FIG. 3 is a vertical sectional side view showing another embodiment of the above.

FIG. 4 is a vertical sectional side view showing still another embodiment of the same.

FIG. 5 is a vertical cross-sectional side view showing a state during manufacturing of the planar lighting device of the present invention.

FIG. 6 is a skeletal vertical side view showing the basic structure of a conventional planar lighting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal cell 3 Buffer layer 5 Light intensity adjustment sheet 6 Reflective film 10 Planar lighting device 11 Light guide plate 12 Light source 13 Translucent buffer layer 14 Reflective function layer 16 Reflective sheet d Dot P Slope prism

Claims (3)

[Claims] 1. A device for background illumination of a liquid crystal display screen, comprising a light guide plate arranged on the back surface of a liquid crystal cell and a light source arranged on the side of the light guide plate, wherein the device covers at least the light source. A planar illuminating device in a liquid crystal display device, wherein a light-transmitting buffer layer is formed on the light-transmitting buffer layer, and a reflective function layer is formed on part or all of the outer surface of the light-transmitting buffer layer. 2. The planar illumination device in a liquid crystal display device according to claim 1, wherein the light guide plate is formed of a light transmitting buffer layer. 3. The planar illumination device in a liquid crystal display device according to claim 1, wherein the light-transmitting buffer layer is made of silicone gel or silicone rubber.