JPH065462B2 - Backlight device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a backlight device useful as a display in industrial and office equipment, a display device using liquid crystal, and the like.

(Prior Art and Problems Thereof) In a conventional liquid crystal or display backlight device, as shown in FIG. 6, a light diffusion filter b such as white frosted glass or a white plastic sheet is provided below the liquid crystal or display a. A concave reflecting mirror c is provided through
One in which a cold cathode tube d is arranged at the center thereof, or as shown in FIG. 7, a light diffusion filter b as described above, a plurality of cold cathode tubes d ... There is known one in which mirrors e are sequentially provided.

However, in the former device, only the central part of the liquid crystal is particularly bright and the peripheral part is dark. Therefore, in order to brighten the whole, the concave portion of the concave reflecting mirror c must be deepened to increase the focal length, and as a result, There is a drawback that the entire device becomes thick, and since the latter device uses a large number of light sources, there is a problem that it consumes a large amount of electric power and easily generates heat.

(Means for Solving Problems) The present invention has been achieved by focusing on the fact that these problems can be easily solved by using a fine interdigital sheet as a reflector in a backlight device. The invention is directed to a backing which uses a fine interdigital sheet having a large number of ridges parallel to each other at a fine interval on at least one surface of a transparent sheet, which is used as a reflecting plate by being arranged between a liquid crystal display element or display and a light source. The gist of the present invention is that it is a light device, and the second aspect of the present invention is that a fine interdigital sheet formed by providing a large number of parallel ridges between two parallel transparent sheets at a fine interval is used as a liquid crystal. The backlight device is provided between the display element or display and the light source and used as a reflector.

Hereinafter, the present invention will be described based on the embodiment shown in FIG. 1 and FIG. The backlight device according to FIG. 1 has a fine interdigital sheet 3a having a large number of ridges 2 ...
A flat reflecting mirror 4 is provided below the sheet 1, and a cold cathode tube 5 as a light source is provided laterally outside the sheet 1.
A liquid crystal 6 is arranged directly above this device. In this device, the light from the light source is uniformly diffused without being attenuated and is uniformly irradiated on the entire liquid crystal, so that there is an advantage that only one light source is required. In this example, the device may be arranged in the same manner except that the fine interdigital sheet 3a is turned upside down depending on its use.

FIG. 2 shows a display 7 instead of the liquid crystal 6 above a fine interdigital sheet 3b in which a large number of parallel ridges 2 are provided between two parallel transparent sheets 1 and 1 at a fine interval.
In addition to arranging the above, the device having the same configuration is intended to irradiate the display 7 by totally reflecting and diffusing the light from the light source.

Next, the operation of the backlight device according to the present invention will be described below.
Let us consider this in more detail based on the figure. The figure shows a fine interdigital sheet 3b in which a large number of parallel protrusions 2 are provided between two parallel transparent sheets 1 and 1 at a fine interval. Here, the refractive index at each portion is shown. N ₁ , n ₂ ...
Then, the critical angle φ (degree) at the interface between n ₁ and n ₂ is sin φ = n ₁ / n ₂ ……… Therefore, the angle of incidence inside n ₂ is φ <sin ⁻¹ (n ₁ / n ₂ ) ... The maximum angle condition of the louver angle θ is when the light beam incident near the critical angle becomes almost parallel to the light beam in the matrix having the refractive index of n ₃ , so θ <sin ⁻¹ (n ₁ / N ₃ · sinφ) ……, when the incident angle (degree) is 0 ≦ φ <sin ⁻¹ (n ₁ / n ₂ ), 0 ≦ θ <sin ⁻¹ (n ₁ ² / n ₂ · n ₃ ) It becomes.

The conditions for total reflection at the n ₃ and n ₄ interfaces are shown in FIG. 1) Since when n ₁ is air which is n ₁ = 1, the incident angle ^{condition: φ <sin -1 (1 /} n 2) louvers angle ^{conditions: 0 ≦ θ <sin -1 (} 1 / n 2 · n ₃₎ louvers interface total reflection condition: sin ^{[90-θ-sin -1 (sinφ} / n 3) ]> the n ₃ / n _4.

2) When n ₁ and n ₃ are air, n ₁ = n ₃ = 1 and the same incident angle condition: 1) Louver angle condition: 0 ≦ θ <sin ⁻¹ (1 / n ₂ ) Louver interface Total reflection condition of: sin (90−θ−φ)> 1 / n ₄ 3) n ₁ = n ₂ = 1 when n ₁ and n ₂ are air, and condition of incident angle: φ <sin ⁻¹ ( 1 / n ₃ ) Louver angle condition: 0 ≦ θ <sin ⁻¹ (1 / n ₃ ) Total reflection condition of louver interface: sin [90−θ−sin ⁻¹ (sin φ / n ₃ )]> n ₃ / n ₄ 4) When n ₁ , n ₂ and n ₃ are air, n ₁ = n ₂ = n ₃ = 1 and the condition of the incident angle: φ> sin ⁻¹ (1 / n ₄ ) The condition of the louver angle: 0 ≦ θ <90 Total reflection condition of louver interface: φ> sin ⁻¹ (1 / n ₄ ).

This will be further described with reference to FIG. 4. The figure shows a fine comb-shaped sheet 3b made entirely of polycarbonate in which a large number of parallel ridges are provided at fine intervals between two parallel transparent sheets. , Liquid crystal display element (not shown)
And a cold cathode tube 5 as a light source. In this case, if the incident angle of the light from the cold cathode fluorescent lamp 5 is 36 °, and if the louver has an inclination of 18 °, all the light goes out to the upper side of the sheet 1. In this case, the relationship of causing total reflection is such that if the refractive index of the material forming the transparent sheet is n, and if the incident angle θ <sin ⁻¹ (1 / n ₁ ), then total reflection occurs. That is, the range in which total reflection occurs is widened by using a material having a large difference in refractive index from air.

The material for forming such a transparent sheet is made of transparent plastic, rubber or alloys thereof, and also a mixture thereof, and when these materials and their refractive indexes [(in brackets)] are exemplified, they are thermoplastic polymers. Vinyl chloride (hard molding: 1.52 to 1.55), polystyrene (1.59 to 1.5)
60), polyamide (nylon 66 molded product: 1.53), polybutyral, polyacetylbutyral, and cellulosic resin (1.47 to 1.51), polycarbonate (1.55 to 1.5)
9), polyester (1.65), polysulfone (1.60), polyethylene (1.51 to 1.54), polypropylene (1.49), poly-
4-ethylenepentene-1 and polyvinyl acetate (1.45
~ 1.47), polymethylmethacrylate (1.49), tetrafluoroethylene (1.35), other plastic alloys, etc., or thermosetting epoxy resin (1.61), polyurethane (1.42)
~ 1.60), silicone rubber (1.42), acrylic resin (1.50 ~
1.58), polyester resin (1.52 to 1.57), and further glass (1.48 to 1.55).

The fine interdigital sheet 3 used in the present invention may have various shapes shown in FIG. That is, the one shown in Fig. (A) is a transparent sheet 1 provided with a large number of ridges 2 ...
(b) further has a large number of parallel protrusions 8 ... Further, FIG. (C) is a figure in which a large number of parallel ridges 2 ... Are provided at a fine interval between two parallel transparent sheets 1, 1, and FIG. (D) is a figure (b) on the other surface. A large number of parallel ridges 8 ...

These fine interdigital sheets can be obtained by means such as profile extrusion, compression molding with a mold, casting molding, injection molding, etching with light, and cutting from a molded product.

The obtained fine comb-shaped sheet can be provided as a backlight device by disposing it between a liquid crystal display element or display and a light source and using it as a reflector.

(Effect of the Invention) According to the present invention, the liquid crystal display element can be made thin.

Energy can be saved when using liquid crystal.

The difference in light and darkness of the display device is reduced and the display becomes clear.

Since the characteristics as a display device are improved, its industrial value is extremely large.

[Brief description of drawings]

1 to 5 relate to an embodiment of the present invention, FIGS. 1 and 2 are explanatory views of a backlight device of different modes, and FIGS. 3 and 4 are of different modes. In the backlight device, an explanatory view showing the relationship between the inclination angle of the louver of the fine interlaced sheet and the position of the light source, and FIGS. 5 (a) to (d) are cross-sectional views showing different embodiments of the fine interleaved sheet. FIG. 6, FIG. 6 and FIG. 7 are explanatory views of conventional examples of different modes. (Explanation of Main Codes) 1 ... Transparent sheet, 2 ... Ridges, 3 ... Fine interdigitated sheet, 5 ... Light source, 6 ... Liquid crystal display element, 7 ... Display.

Claims (3)

[Claims] 1. A fine interdigital sheet having a plurality of parallel ridges provided on at least one surface of a transparent sheet in parallel with a fine interval, is provided as a reflection plate between a liquid crystal display element or display and a light source. A backlight device characterized by being used. 2. A fine interdigital sheet comprising a plurality of parallel ridges arranged at a fine interval between two parallel transparent sheets is provided between a liquid crystal display element or display and a light source and reflected. A backlight device characterized by being used as a plate. 3. The backlight according to claim 1, wherein the transparent sheet has a large number of parallel ridges having a serrated cross section on the opposite surface having a large number of ridges. apparatus.