JPH0968614A - Production of surface illuminator and light transmission plate for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the light transmission plate of a surface illuminator, such as a back light, as a total surface uniformly light emitting plate by a simple method by forming a reflective printing through the use of many printing dots by an ink jet printing. SOLUTION: A reflective printing 14 is provided on the back surface of a transparent light transmission plate so that the light beams emitted from an LED light source to the inside of the plate are irregularly reflected. The printing 14 is constituted by fine dots 14a and the color of the dots is white. The density of the dots 14a is coarse in the region which is close to the light source and is dance in the region which is far from the light source. Moreover, the dots 14a are printing-formed by an ink jet printing method. This printing is conducted by jetting fine ink droplets in accordance with printing data from the plural nozzle holes provided in an ink jet print head and adhering the droplets onto the printing object surface.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a surface lighting device suitable for use as a so-called backlight, and a method for manufacturing a light guide plate for the surface lighting device.

[0002]

2. Description of the Related Art Liquid crystal display devices have come to be widely used in various electronic devices, mobile phones, and the like because they can display various displays. This liquid crystal display device
Liquid crystal is enclosed in a minute gap sandwiched between two glass plates, and a patterned transparent electrode is arranged on the inner surface of the glass plate. By energizing the selected electrode, The liquid crystal matching the shape of this electrode loses its light-transmitting property and is displayed in black. In order to improve the visibility of such a liquid crystal display device, a backlight is often arranged behind it. As the device becomes smaller, the backlight is required to be thinner. A conventional example of such a thinned backlight a is shown in FIGS.
4 shows.

LE is attached to the edge of the transparent light guide plate b having a predetermined thickness.
The D light source c is incorporated. This LED light source c has a case h in which an LED chip i sealed with a transparent resin is incorporated, and is incorporated in a slit d formed in the transparent light guide plate b with the case opening facing sideways. As shown in FIGS. 14 (B) and 14 (C), the back surface of the transparent light guide plate b is provided with fine recesses (textures) e for irregularly reflecting light inside the light guide plate b. LED light source c
Light incident on the light guide plate b from its side surface is
Repeating the total reflection on the front surface and the diffuse reflection on the back surface, the light is spread over the entire area of the light guide plate b. As a result, when viewed from the outside, the entire surface of the light guide plate b seems to be shining.

In order to make the brightness of the surface of the light guide plate b uniform, the size of the fine recesses e formed on the back surface of the light guide plate b is varied depending on the distance from the LED light source c. . That is, the recess e is small when it is close to the LED light source c, and the size of the recess e is increased as the distance from the LED light source c increases. The reason is that near the LED light source c, the amount of light reflected by the recess e is at least sufficiently bright, but when it is far from the LED light source c, the size of the recess is increased to increase the amount of light reflected. L
It compensates for the decrease in brightness due to the distance from the ED light source.

[0005]

The light guide plate b can be obtained by molding acrylic or polycarbonate by, for example, an injection molding method. Therefore, as described above, the fine concave portion e to be formed on the back surface of the light guide plate b is formed by forming the fine convex portion f on the mold g.

By the way, it is difficult to set the size of the convex portion f that can be formed on the mold to a certain value or less.
Further, the finer the convex portion, the more time and cost it takes to process it. Moreover, even if the size of the small recess e is determined as a function of the distance from the light source, if the LED light source c is not actually mounted and light is emitted, whether the surface of the light guide plate b is uniformly illuminated or not is determined. do not know.
Therefore, in the past, based on a certain prediction, the above-mentioned fine recess e
After forming the convex portion f for the mold on the mold g, it is inevitable to correct the fine convex portion f on the mold by repeating trial and error. Such work is also time consuming and expensive.

Further, in Japanese Utility Model Laid-Open No. 5-55103,
Instead of the fine recesses e for irregular reflection formed on the back surface of the transparent light guide plate b, printing for irregular reflection on the back surface of the transparent light guide plate (hereinafter, such printing is referred to as “reflection printing” in the present specification). .) Is disclosed.
In this case, the size of the circular printed pattern to be provided on the back surface of the light guide plate is changed depending on the distance from the light source. The method for forming the printed pattern disclosed in the publication is so-called screen printing. In case of screen printing, it is necessary to make a printing screen,
Then, in order to obtain the uniformity of the light from the entire area of the light guide plate by repeating trial and error, as in the case where the fine recesses are formed by the mold as described above, it is necessary to repeatedly modify the screen. Is also very time consuming and expensive. Then, as long as the screen printing is used, the size of the print pattern cannot be made smaller than a predetermined size. Further, in the case of screen printing, proper printing cannot be performed unless the back surface of the light guide plate is a flat surface.

Furthermore, what can be said in common to the above-mentioned two types of conventional examples is that it is not possible to form a smaller size than a predetermined size, whether it is a fine recess on the back surface of the light guide plate or a printed pattern. Therefore, the brightness of the entire surface of the light guide plate cannot be made completely uniform, and unevenness may occur. Then, there may be a problem that a so-called diffusion sheet has to be arranged on the surface of the light guide plate b.
When the diffusion sheet is added, the cost increase due to the increase in the number of parts and the cost increase due to the increase in the number of work steps are inevitable, and the manufacturing cost of the backlight increases as a whole.

The present invention has been devised under such circumstances, and it is assumed that a light guide plate in a surface illumination device such as a backlight can emit light uniformly over the entire surface by a simple method. The task is to do.

[0010]

DISCLOSURE OF THE INVENTION In order to solve the above problems, the present invention employs the following technical means.

According to a first aspect of the present invention, there is provided a surface lighting device used as, for example, a backlight,
This surface illuminating device is a surface illuminating device including a light guide plate having a front surface as an illumination light irradiation surface and a reflective print on the back surface, and a light source for supplying light to the light guide plate. Is characterized by being formed by a large number of printing dots by inkjet printing.

[0012] In a preferred embodiment, the density of the printed dots becomes higher as the distance from the light source increases.

Further, in a preferred embodiment, an LED as a light source is arranged on the peripheral portion of the light guide plate. That is, this embodiment is a so-called LED backlight.

In the present invention, the ink jet printing method is adopted as the reflection printing method to be formed on the back surface of the light guide plate. This inkjet printing method
This is a method in which fine ink droplets are ejected from a plurality of nozzle holes provided in an inkjet printhead according to print data and are attached to a print target surface. As means for ejecting ink droplets from the nozzle, a means for applying instantaneous pressure by a piezoelectric element to a pressure chamber provided behind the nozzle, or for instantaneously heating the pressure chamber at high temperature to generate bubbles, There is a means for causing ink droplets to fly by increasing the pressure due to the generation of bubbles.

In such an ink jet printing method, it is possible to perform printing according to print data without contacting the surface to be printed. Therefore, even if unevenness such as a girder portion is formed on the back surface of the light guide plate to incline the light guide plate, the reflection printing can be performed on the back surface of the light guide plate without any problem. You can

Further, in this ink jet printing method, if only print data is created, it is possible to drive an ink jet printer according to this print data. Therefore, it is not necessary to make a printing screen as is the case with screen printing. Further, by checking the light emitting state of the light guide plate which has been subjected to the reflection printing by the ink jet printing method, it is possible to easily correct the print data for the reflection printing on a personal computer, for example. Therefore, the correction of the dot pattern of the reflection printing for making the entire surface emit light uniformly by trial and error does not take much time.

Furthermore, due to recent technological advances in ink jet print heads, for example, 600 dpi and 12
Printing with a resolution of 00 dpi can be performed. Therefore, the print dots constituting the reflection printing can be made significantly smaller than that in the case of screen printing. As a result, uniform light emission on the entire surface of the light guide plate is further promoted, and uniform light emission can be achieved. Then, even if a transparent material is adopted as the light guide plate, it is possible to eliminate the need to attach a diffusion sheet to the front surface side, and in this case, the surface lighting device of the present invention further reduces its manufacturing cost. You can

The density of the printed dots is usually made higher as the distance from the light source increases. What is characteristic here is that the density of each printed dot is changed while the size of each printed dot is kept small, and the size of the dot is not changed. Then, as described above, it is possible to conveniently correct the difference in luminous intensity due to the difference in the distance from the light source while preventing the occurrence of uneven light emission, and achieve uniform light emission on the entire surface of the light guide plate.

Further, L as a light source is provided on the peripheral portion of the light guide plate.
When the ED is arranged, since the LED chip is extremely small, for example, the LED can be arranged within the thickness dimension of the light guide plate, and the thin surface illumination device (L
ED backlight) is realized.

According to a second aspect of the present invention, there is provided a method of manufacturing a light guide plate for a surface illuminating device, which comprises a front surface as an illuminating light emitting surface and a back surface having reflective printing. A method of manufacturing a light guide plate for a device, wherein print data is created such that the dot density changes according to the distance from the position where the light source is to be arranged, and a large number of print dots are formed by an inkjet printing method according to the print data. Is formed on the back surface of the light guide plate.

It is apparent that the light guide plate for the surface lighting device manufactured by the manufacturing method according to the second aspect also has the same advantages as those described above.

According to the third aspect of the present invention, there is also provided a method of manufacturing a light guide plate for a surface lighting device, which method comprises:
A method of manufacturing a light guide plate for a surface lighting device, the front surface of which is an illuminating light emitting surface, and the back surface of which is reflectively printed. Step of forming a prototype light guide plate with a large number of printing dots printed on the back surface by an inkjet printing method according to this print data, measuring the luminous intensity at each position on the surface of the prototype light guide plate, and measuring the light intensity at each position. A step of correcting the print data so that the luminosity of the light is averaged, and a step of performing main printing of a large number of print dots on the back surface of the light guide plate by an inkjet printing method according to the corrected print data. Is characterized by.

According to this method, the ink jet printing method can print a desired print pattern according to the print data without going through the production of a printing screen or the like, and the print data can be printed by a personal computer, for example. This method focuses on the fact that it can be easily created or modified.

If it is easy to create print data for trial production, the luminous intensity at each position of the trial light guide plate is measured,
It is also easy to modify the print data so that the luminosity is averaged.

Therefore, according to this method, the light guide plate for a surface lighting device having the above-mentioned characteristics can be manufactured very easily.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall perspective view of a light guide plate 11 for constituting an LED backlight 10 which is an embodiment of the surface lighting device of the present invention. This light guide plate 11
Can be obtained, for example, by molding a transparent acrylic resin or polycarbonate. As a whole, the light guide plate 11 has a constant thickness, and at the four corners of the back surface, there are integrally formed girder portions 12 for incorporating the light guide plate 11 into devices with a predetermined inclination. In addition, this light guide plate 1
A slit 13 for mounting an LED light source 20 described later is formed on the left and right side edge portions of 0. The front surface side and the back surface side may be smooth flat surfaces.

FIG. 2 shows an L attached to the slit 13.
The ED light source 20 is shown. A predetermined number of LED chips 22 are bonded to the bottom surface of the box-shaped reflection case 21 whose sides are open. A wiring pattern 24 connected to the lead wire 23 is formed on the bottom of the case 21. The bonded LED chip 22 and the wiring pattern are connected by wire bonding. Then, the internal space of the reflection case 21 is
A transparent resin 25 such as an epoxy resin is filled.

Now, on the back side of the transparent light guide plate 11,
Reflective printing 14 is applied to diffusely reflect the light emitted from the LED light source 20 into the light guide plate 11. This reflective print 14, as shown in FIGS. 4 and 6,
It is composed of fine dots 14a, and the color of the dots is white. The density of the white dots 14a is
4 (D) and 6 (D ') are coarse in the area close to the LED light source 20, and are denser in the area far from the LED light source 20 (FIGS. 4 (E) and 6 (E'). Then, in the present invention, such white dots 14a are printed and formed by the inkjet printing method.

Based on the characteristics of the LED light source 20, the transparency of the light guide plate 11, the distance from the LED light source in consideration of the characteristics of the LED light source 20, and the like, first, print data representing a dot pattern is created on a personal computer, for example. (FIG. 8, S1). The print data is created by the software that takes into consideration the rule of thumb from the characteristics of the LED light source 20, the transparency of the light guide plate 11 or the size thereof, the arrangement position of the LED light source on the light guide plate, and the like as described above. It is created so that the light intensity from each part of the surface of 11 is uniform.

Then, based on the print data thus created, a prototype in which a dot pattern is printed on the back surface of the light guide plate 11 is manufactured by the inkjet printing method (FIG. 8, S2).

L is added to the prototype light guide plate 11 'thus manufactured.
With the ED light source 20 attached and the LED light source 20 emitting light, the light emission on the surface of the light guide plate is checked. For example, in the LED driving state, the surface of the light guide plate 11 'is scanned with an optical sensor, and light intensity distribution data on the surface of the light guide plate 11' is collected (FIG. 8, S3).

The print data is corrected based on the luminous intensity distribution data (FIGS. 8, S4 and S5). Specifically, the dot density is made coarser for the areas brighter than the average luminous intensity, and the dot density is made denser for the areas darker than the average luminous intensity. This correction may be performed by, for example, displaying the dot pattern based on the data and the measured luminous intensity distribution on the screen and allowing the operator to manually correct the above data, or automatically with the help of software. You may make corrections.

Based on the print data thus corrected,
Printing is again performed on the back surface of the light guide plate 11 by the inkjet printing method (FIG. 8, S2), and the light guide plate on which the dot pattern is printed again is checked for the same luminous intensity distribution as above (FIG. 8, S2). S3, S4). If this distribution is within the allowable range (YES in S4 of FIG. 8),
The corrected print data is confirmed as data for main printing (FIG. 8, S5), and large-scale printing as main printing is performed based on the corrected data (FIG. 8, S7).

As described above, the ink jet printing method is a method in which the ink jet print head is driven to perform printing based on print data. The ink jet print head 30, as schematically shown in FIG. 7, ejects ink introduced into a minute pressure chamber 31 into a nozzle 32.
It is a printing method in which the print material is ejected from the surface and is attached to the print target. As a method of increasing the pressure of the pressure chamber 31, a piezoelectric element is actuated or a temperature of a part of the pressure chamber is instantaneously raised to generate bubbles, and ink droplets are caused to fly by the pressure generated by the bubbles. There are things. Then, as shown in FIG. 7, this inkjet printing method
This is a method in which printing can be performed with the inkjet print head 30 separated from the print target S.

Therefore, as in the embodiment shown in the drawing, even on the light guide plate 11 having the projections and depressions such as the girders 12 on the back surface, accurate printing can be performed according to the print data without any problem. Of.

Due to the recent technological progress, the resolution of the ink jet print head 30 has reached 600 dpi to 1200 dpi. Therefore, the smallest unit dot forming the image can be extremely small. Therefore, the size of each white dot forming the dot pattern can be greatly reduced as compared with the case of screen printing or the like. In the present invention, the density of the individual white dots is changed depending on the distance from the LED light source without changing the size of the individual white dots.

The light guide plate 11 emitted from the LED light source 20
The light incident on the inside from the side surface repeats total reflection on the surface of the light guide plate 11, total reflection on a portion other than the white dot printing portion on the back surface, and diffuse reflection on a portion where the white dots 14a are printed. , Over the entire area of the light guide plate 11. Of these, light traveling at an incident angle of a predetermined angle or less with respect to the normal to the surface of the light guide plate 11 is emitted to the outside, but when viewed from the outside, the light is spread over the entire area of the light guide plate. The light emitted to the outside as described above seems to shine over the entire surface of the light guide plate.

Since the density of the white dots 14a increases as the distance from the LED light source 20 increases, the distance from the LED light source 20, that is, the central portion in the embodiment shown in the drawing, is reduced. The light escaping from the back surface of the light plate 11 is reduced to compensate for the decrease in the front side luminous intensity due to the distance from the LED light source, and the entire surface of the light guide plate appears to shine evenly. Moreover, since the size of each white dot is small, it is possible to conveniently avoid unevenness in the luminous intensity on the surface side.

Of course, the scope of the present invention is shown in the figures,
And it is not limited to the above-mentioned embodiment. In the embodiment, the size of each white dot is made constant, and the density thereof is changed. However, according to the inkjet printing method, it is possible to form any print pattern, and the specific form of the dot pattern is various. It can be changed. In short, the present invention can enjoy the advantages of directly driving the print head to perform printing by correcting the data without intervening an intermediate such as a printing screen.

Further, in the embodiment shown in the drawings, the slits 13 are provided on the left and right side edges of the light guide plate 11, and the LED light source 20 is incorporated in the slits. However, the light guide plate 11 and the LED light source are provided separately, The case where the LED light source is arranged in the peripheral portion of the light guide plate is of course included in the scope of the present invention.
In this case, in addition to a light source having a case in which an LED chip is incorporated in a transparent resin as a light source, as shown in FIG. 9, the LED chip 22 is bonded to a substrate 26 and the bonding portion is resin-sealed. And Fig. 10
It is also possible to use a so-called LED lamp 27 as shown in FIG.
The case of adopting 8 and arranging it in the peripheral portion of the light guide plate 11 having a predetermined shape is of course included in the scope of the present invention.

[Brief description of drawings]

FIG. 1 is an embodiment of an LE of an area lighting device of the present invention.
It is a whole perspective view of an example of a D backlight.

FIG. 2 is an LE incorporated in the LED backlight of FIG.
It is an expansion perspective view which shows D light source.

FIG. 3 is a sectional view taken along the line III-III in FIG.

4 (D) is an enlarged cross-sectional view of part D in FIG.
FIG.

5 is a bottom view of the LED backlight shown in FIG. 1. FIG.

6 (D ') is an enlarged view of a D'portion in FIG. 5, and (E') is an enlarged view of an E'portion in FIG.

FIG. 7 is a schematic diagram for explaining a printing principle by an inkjet print head.

FIG. 8 is a flow chart for explaining one embodiment of a method for manufacturing a light guide plate of the present invention.

FIG. 9 is an explanatory diagram of another example of the LED light source.

FIG. 10 is an explanatory diagram of still another example of the LED light source.

FIG. 11 is an explanatory diagram of still another example of the LED light source.

FIG. 12 is a perspective view showing an example of a conventional LED backlight.

FIG. 13 is a sectional view taken along the line XIII-XIII of FIG.

14 (A) is an enlarged sectional view of part A in FIG. 13, and FIG. 14 (B) is FIG.
3 is an enlarged sectional view of a B portion of FIG. 3, and FIG.

[Explanation of symbols]

 10 LED Backlight 11 Light Guide Plate 14 Reflective Printing 14a Printing Dot 20 LED Light Source

Claims (4)

[Claims] 1. A surface illuminating device comprising a light guide plate having a front surface as an illuminating light emitting surface, and a back surface on which reflection printing is applied, and a light source for supplying light to the light guide plate, wherein the reflection printing is performed. A surface lighting device, which is formed by a large number of printing dots formed by inkjet printing. 2. The surface lighting device according to claim 1, wherein the density of the print dots becomes higher as the distance from the light source increases. 3. A method of manufacturing a light guide plate for a surface lighting device, the front surface of which is an illumination light emitting surface and the back surface of which is reflectively printed, wherein the dot density changes according to the distance from the position where the light source is to be arranged. Print data is created as described above, and a large number of print dots are formed on the back surface of the light guide plate by an inkjet printing method according to the print data. 4. A method of manufacturing a light guide plate for a surface lighting device, the front surface of which is an illumination light emitting surface and the back surface of which is reflectively printed, wherein the dot density changes according to the distance from the position where the light source is to be arranged. Print data as described above, and a step of forming a prototype light guide plate with a large number of printing dots printed on the back surface by an inkjet printing method according to the print data, measuring the luminous intensity at each position on the surface of the prototype light guide plate. Then, a step of correcting the print data so that the luminosity at each position is averaged, and main printing of a large number of print dots is performed on the back surface of the light guide plate by an inkjet printing method according to the corrected print data. Characterized by including a step,
A method for manufacturing a light guide plate for a surface lighting device.