Ulllted States Patent [19]
`Hira et al.
`
`US005961198A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,961,198
`Oct. 5, 1999
`
`[54] LIQUID CRYSTAL DISPLAY DEVICE AND
`METHOD OF MANUFACTURING
`BACKLIGHTING LIGHT GUIDE PANEL
`
`9/1995 Yokoyama et a1. ..................... .. 362/31
`5,450,292
`5,461,547 10/1995 Ciupke et al. ..
`362/31
`giaoket atl
`
`THEREFOR
`
`
`
`
`
`, , 5,521,796
`
`
`
`1up e e a. .. 5/1996 Osakada e161. ........................ .. 362/31
`
`_
`
`.
`
`_
`
`.
`
`.
`
`.
`
`.
`
`[75] Inventors. Yasuo Hlra, HItOISIhI Tanlguchl, both
`of Yokohama; YuJl M°“>_M0bara;
`Y?shle K?dera, chlgasakl, all Of Japan
`
`[73] Assignee: Hitachi, Ltd., Tokyo, Japan
`
`[21] Appl. No.: 08/791,513
`
`[22]
`
`F1led.
`
`Jan. 30, 1997
`
`[30]
`
`Foreign Application Priority Data
`
`Japan .................................. .. 8-017335
`[JP]
`Feb. 2, 1996
`[51]
`Int. Cl? ........................... .. F21V 7/04; G02F 1/1335
`[52] U S C]
`362/31_ 362/561_ 349/65
`,'
`'
`' """"""""""""""""" "
`’
`’
`[58] Field of Search ......................... .. 362/31, 32; 349/65
`.
`References Clted
`U,S, PATENT DOCUMENTS
`1/1992 N k
`a..ayama """""""""""""""" "
`ffgtlsrggztoaliui"
`_ _ _ _ __ 36261
`3/1995 Ketchpel _ _ _ _ _ _ _ _ _ _
`.. 362/31
`4/1995 Murase et al. ..... ..
`.. 362/31
`4/1995 Kobayashi et a1.
`5/1995 DuNah et al. .......................... .. 362/31
`
`[56]
`
`5 079 675
`’
`’
`
`5:396j406
`5,40s,3s7
`5,408,388
`5,420,761
`
`362/31
`
`5,575,549 11/1996 Ishikawa et a1. ....................... .. 362/31
`
`362/31
`575847556 12/1996 Yokoyama et a1‘ '
`362/31
`5,608,837
`3/1997 Tai et a1. ....... ..
`5,649,754
`7/1997 Matsumoto ............................. .. 362/31
`Primary Examiner—Stephen Husar
`Assistant Examiner—MattheW J. Spark
`Attorney, Agent, or Firm—Antonelli, Terry, Stout & Kraus,
`LLP
`[57]
`
`ABSTRACT
`
`_
`_
`_
`_
`_
`_
`_
`A l1ght guide panel and l1qu1d crystal d1splay dev1ce 1nclud
`ing a liquid crystal cell array, a light guide panel or plate
`disPosed 0“ a m? Surface of the liquid, Crystal Ce11_arraY> and
`a l1ght source d1sposed at a lateral s1de of the l1ght guide
`panel or plate. The light guide panel or plate has a light
`incident Surface on which light rays emitted from the light
`source are incident, a li ht-transrnissive surface throu h
`Which the incident light rgays exit the light guide panel gor
`plate toWard the liquid crystal cell array, and a plurality of
`re?ecting slant portions for directing the incident light rays
`toWard the light-transmissive surface, Wherein the re?ecting
`slant portions are constituted by conveXes or concaves
`which are substantially rectangular in plan vieW and sub
`stantially trapeloidal in Sectional View
`
`8 Claims, 18 Drawing Sheets
`
`35
`'
`31"“
`l\\\\\\ \\\\\j\\§\ \\\\ \\\\\XX]’/\
`34
`VII/llWWWFWMM??/????l[##M?Wl/M/?/?m??/_f
`32//I‘////// //////////// //////////
`5/31
`I
`
`LGE_001210
`
`LG Electronics Ex. 1037
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 1 of 18
`
`5,961,198
`
`FIG. 1
`
`11
`
`FIG. 2
`
`FIG. 3
`PRIOR ART
`
`K\\\\\\l M4
`I///L////////Z///////
`J\3
`
`|\\\
`
`LGE_001211
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 2 of 18
`
`5,961,198
`
`F|G.4
`r
`PRIORART 99999999999999999999999999
`
`LGE_001212
`
`

`
`U.S. Patent
`
`Oct. 5, 1999
`
`Sheet 3 of 18
`
`5,961,198
`
`FIG. 5
`LIGHT RAYS
`UNDERGONE
`9 TOTAL REFLECTION 18
`1
`1
`\“\:\_‘f//
`\
`
`1
`
`16
`
`- \
`
`\2
`
`‘
`
`7
`
`12 13
`
`IGH\T RAYS
`2
`11 L
`UNDERGONE
`TOTAL REFLECTION
`
`‘O 14 ‘5
`
`FIG. 6
`
`_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ y _ _ _ L‘. _
`
`- i
`
`LGE_001213
`
`

`
`U.S. Patent
`
`Sheet 4 0f 18
`
`0a. 5, 1999
`FIG. 7
`
`5,961,198
`
`ITO‘ 1 I115‘ ' '25 I '25 “310' '35 ' A0
`
`SPREAD ANGLE OF INCIDENT LIGHT RAYS a (deg)
`(REFLECTION AT SIDE WALL OF SMALL CONVEX)
`
`
`FIEFLECTED AT SMALL CONVEX 8 (deg) REFLECTED AT SMALL CONVEX 8 (deg)
`
`
`
`
`
`
`
`EXIT ANGLE OF LIGHT RAYS EXIT ANGLE OF LIGHT RAYS
`
`FIG. 8
`
`'60 ‘ "'I'HIII'I'YTTI"I'HITTIT'H
`O 510 15 2025303540
`SPREAD ANGLE OF INCIDENT LIGHT RAYS 0: (deg)
`(REFLECTION AT SIDE WALL OF SMALL CONVEX)
`
`LGE_001214
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 5 of 18
`
`5,961,198
`
`FIG. 9
`
`FIG. 10
`
`SPREAD ANGLE
`OF INCIDENT
`LIGHT RAYS
`
`FIG. 11
`
`16
`\
`
`18
`\\
`
`/
`
`LIGHT RAYS
`UNDERGONE
`TOTAL EFLECTION
`
`LIGHT RAYS
`UNDERGONE
`TOTAL REFLECTION
`
`LGE_001215
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 6 of 18
`
`5,961,198
`
`D“ u ((3%
`Y / 10
`
`__/‘1 1
`
`FIG. 12(a)
`
`FIG. 12(1))
`
`FIG. 12(a)
`
`FIG. 12(e)
`
`LGE_001216
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 7 of 18
`
`5,961,198
`
`FIG. 13(a)
`
`FIG. 13(b)
`
`FIG. 13(0)
`
`FIG. 13(d)
`
`FIG. 13(e)
`
`FIG. 13(f)
`
`LGE_001217
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 8 of 18
`
`5,961,198
`
`FIG. 14
`
`FIG.15
`
`FIG.16
`
`SPREAD ANGLE
`OF INCIDENT
`LIGHT RAYS
`)
`
`1O
`I'///////////////j~8
`
`LIGHT FIAYS
`UNDERGONE
`I
`fW/ TOTAL REFLECTION
`
`4
`
`//'////X////////1
`|f/////|//////////'/'
`/
`LIGHT RAYS
`UNDERGONE
`TOTAL REFLECTION
`
`(I8
`
`LGE_001218
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 9 of 18
`
`5,961,198
`
`FIG. 17(a)
`
`“2
`w'
`
`V///////////////////'l\/8
`
`FIG. 17(1))
`
`“2
`
`\ >C1O v
`v/////////1////////g\,8
`
`FIG. 17(0)
`
`’\“2
`W}
`
`V//////////l///////LI\/8
`
`FIG. 17(d)
`
`“P
`—_\_>Go—'
`
`l/j//[///////Z///////I\/8
`
`LGE_001219
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 10 of 18
`
`5,961,198
`
`FIG. 18
`
`FIG. 19
`
`1
`
`l
`
`%
`
`LGE_001220
`
`

`
`U.S. Patent
`
`0
`
`18
`
`5,961,198
`
`FIG. 20(0) FIG. 20(0)
`
`LGE_001221
`
`

`
`U.S. Patent
`
`0m. 5, 1999
`
`Sheet 12 0f 18
`
`5,961,198
`
`FIG. 21 (a)
`
`—_/—\______
`
`__/\____
`
`'IIIIIIIIIIIIIIIIJ TIIIIIIIIIIZ
`
`8
`
`1 0'
`
`LGE_001222
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 13 of 18
`
`5,961,198
`
`FIG.22
`
`FIG. 23
`
`LGE_001223
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 14 of 18
`
`5,961,198
`
`FIG. 24
`
`I
`/
`
`4
`
`/
`/
`6P1 9p2 _ / '
`
`//
`
`FIG. 25
`
`1O
`
`8
`
`FIG. 26(a)
`
`FIG. 26(b)
`
`LUMINANCE
`
`W|THOUT
`PRISM SHEET
`
`LUMINANCE T wlTH
`PRISM SHEET
`
`I
`I
`I
`I
`30
`O
`-60 -30
`ANGLE (deg)
`
`I
`60
`
`I
`I
`I
`30
`0
`-60 -3O
`ANGLE (deg)
`
`l
`60
`
`LGE_001224
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 15 of 18
`
`5,961,198
`
`FIG. 27(a)
`
`///////////////~/‘21
`\20
`
`FIG.
`
`l V/A VA] WA V/A V/H V/A V/A VA
`
`mm) ummmvw
`
`/////////////
`
`FIG. 27(d) MW\ 3;)
`
`N24
`FIG, 27(9) m
`
`FIG. 27(f)
`
`LGE_001225
`
`

`
`U S Patent
`
`FIG. 28
`
`5,961,198
`
`FIG. 28(b)
`
`IIIIIIIIII
`
`23
`
`Y///////////////////A
`I\\\\\\\\\\\\\\\\\\\\\\\\ \\I/_‘ 30
`
`llnmmunnmmg
`
`21
`
`ION BEAM OBLIQUE ION MILLING
`///////////
`
`///////////
`
`SURFACE POLISHING
`
`INJECTION MOLDING
`
`LGE_001226
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 17 of 18
`
`5,961,198
`
`FIG. 29(a) @20
`
`7/////// / /// / //
`
`F|G_29(b) IIIIIIIIIII“23
`
`'IAIWAIV/AIV/JIVAIWI'IAIV/AIV/J‘i? // //////////////// 2
`
`f O
`
`mmlzlmrzlmmmm
`
`21
`\20
`
`ION BEAM OBLIOUE ION MILLING
`
`2O
`
`H619“) {arm/@4444
`ION BEAM
`////
`
`I '- " I’
`
`I I. -
`
`IW'WWWI
`
`NI-PLATING
`FIG. 29(d)
`
`26
`
`26
`DELAMINATION WW
`
`FIG. 29(e)
`
`INJECTION MOLDING
`
`LGE_001227
`
`

`
`U.S. Patent
`
`0a. 5, 1999
`
`Sheet 18 of 18
`
`5,961,198
`
`FIG. 30
`
`32//I‘/////////////////// //////////
`4/31
`
`l
`
`LGE_001228
`
`

`
`1
`LIQUID CRYSTAL DISPLAY DEVICE AND
`METHOD OF MANUFACTURING
`BACKLIGHTING LIGHT GUIDE PANEL
`THEREFOR
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a liquid crystal display
`device and a method of manufacturing a backlighting light
`guide panel for the same.
`In recent years, implementation of personal computers
`inclusive of so-called Word processors in a small siZe has
`been promoted, and portable type personal computers
`knoWn as lap-top type or notebook type computers are
`Widely used. In such portable type personal computer, a
`liquid crystal device is commonly used as a display unit. In
`this conjunction, there is an increasing tendency for adopt
`ing color display in the portable type personal computers. In
`accompanying With such trend, a backlighting type display
`device is coming into Wide use, in Which a light source is
`disposed at a rear side of a liquid crystal display screen for
`lighting the Whole display screen from the rear or back side.
`Needless to say, the backlighting light source for the color
`liquid crystal display device is required to emit light With
`high luminance. Besides, it is necessary to illuminate the
`display screen With uniform luminance over the Whole
`planar surface thereof. Luminance of the backlighting can
`easily be increased by increasing that of the light source.
`HoWever, taking into consideration the fact that the portable
`type personal computer or Word processor or the like are
`usually operated by using a battery or cell, limitation is
`necessarily imposed to the attempt for increasing the lumi
`nance of the light source. To say in another Way, there has
`been proposed no effective method or measures for increas
`ing the luminance of the liquid crystal display screen.
`For having better understanding of the present invention,
`description Will ?rst be made in some detail of conventional
`liquid crystal display devices such as disclosed, for example,
`in JP-A-4-162002 and JP-A-6-67004. FIG. 3 shoWs a lateral
`source type backlighting device employed conventionally in
`the liquid crystal display device knoWn heretofore. Refer
`ring to the ?gure, a lamp such as a cold-cathode discharge
`tube or a hot-cathode discharge tube is employed as a light
`source 1 Which is disposed at and along one lateral side of
`a light guide plate (also knoWn as optical Waveguide plate)
`2 Which is made of a light-transmissive material, Wherein a
`diffusing sheet 3 formed of a synthetic resin of milk-White
`color having a light scattering effect is mounted over a top
`surface of the light guide plate 2 With a vieW to uniformiZing
`luminance of the backlight over the Whole display screen.
`Additionally, there are disposed on the diffusing sheet 3 a
`?rst prism sheet 4 and a second prism sheet 5 for the purpose
`of enhancing axial luminance (luminance in the direction
`orthogonal to the display screen) of the display device by
`converging diffused light rays.
`In addition, a light scattering layer 6 is deposited over a
`rear surface of the light guide plate 2 at a side opposite to the
`light exit side in order to scatter the light rays traveling
`through the light guide plate 2 in the direction toWard the
`diffusing sheet 3. In this conjunction, the light scattering
`layer 6 is manufactured in a speci?c structure described
`beloW With the aim to further uniformiZe luminance distri
`bution of the light rays exiting the light scattering layer 6.
`FIG. 4 of the accompanying draWing shoWs a structure of
`the light scattering layer 6. As can be seen in this ?gure, the
`light scattering layer 6 is formed by a plurality of light
`scattering dots by depositing titanium oxide or the like over
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`5,961,198
`
`2
`the rear surface of the light guide plate 2 by resorting to eg
`a printing technique. Parenthetically, it Will readily be under
`stood that the intensity of light emitted from the light source
`1 becomes loWer as the distance from the light source 1
`increases. Accordingly, the light scattering dots of the light
`scattering layer 6 deposited over the bottom surface of the
`light guide plate 2 are so formed that the area of a given dot
`increases as the position of the given dot becomes more
`remote from the light source 1. Furthermore, a re?ecting
`sheet 8 is disposed on a bottom surface of the light scattering
`layer 6, as can be seen in FIG. 3.
`According to another proposal disclosed, for example, in
`JP-A-7-294745, grating grooves are formed in the bottom
`surface of the light guide.
`As is apparent from the foregoing description, in the
`conventional backlighting devices for the liquid crystal
`display device knoWn heretofore, light emitted from the
`light source 1 and introduced into the optical Waveguide or
`light guide plate 2 undergoes scattering at the light scattering
`dots forming the light scattering layer 6 so that the scattered
`light rays can be re?ected back again into the light guide
`plate 2 under the action of the re?ecting sheet 8 to thereby
`illuminate the liquid crystal cell after transmission through
`the diffusing sheet 3 and the tWo prism sheets 4 and 5. It can
`readily be understood that the structure of the conventional
`backlighting optical Waveguide or light guide panel for the
`liquid crystal display device is much complicated.
`Besides, because the diffusing sheet 3 of a light absorbing
`material is disposed over the top surface of the light guide
`plate 2, the conventional liquid crystal display device suffers
`a draWback that the luminance of the liquid crystal display
`device becomes loWer as a Whole although nonuniform
`distribution of luminance can certainly be suppressed to
`some extent. In other Words, With the structure of the
`conventional backlighting device, the attempt for increasing
`the luminance is incompatible With the attempt for uni
`formiZation of luminance distribution. To say in another
`Way, it is impossible to meet simultaneously both require
`ments for increasing the luminance on one hand and for
`uniformiZing the luminance distribution on the other hand.
`Furthermore, in the case of the conventional liquid crystal
`display device in Which the grating grooves are provided in
`the light guide, the pattern of the grating grooves re?ected
`to the light rays exiting the light guide panel Will interfere
`With a regular pattern of elements such as that of liquid
`crystal cell constituting the liquid crystal display device,
`giving rise to a problem that moiré phenomenon makes
`appearance. In order to solve this problem, a sheet for
`diffusing the light rays has to be additionally provided, to
`another disadvantage.
`Furthermore, With the structure of the conventional back
`lighting optical Waveguide or light guide panel, dif?culty is
`encountered in mounting ?xedly and stationarily the re?ect
`ing sheet 8 because of difference in the thermal expansion
`coef?cient betWeen the light guide plate 2 and the re?ecting
`sheet 8 due to heat transfer from the light source 1, resulting
`in variation in the distance betWeen the re?ecting sheet 8 and
`the rear or bottom surface of the light guide plate 2 due to
`vibration, thermal deformation or the like phenomena,
`Which in turn brings about a problem that nonuniformness of
`luminance distribution is likely to occur due to variation in
`the light utiliZation ef?ciency, as brought about by invasion
`and deposition of dusts betWeen the re?ecting sheet 8 and
`the light guide plate 2.
`SUMMARY OF THE INVENTION
`In the light of the state of the art described above, it is an
`object of the present invention to provide a liquid crystal
`
`LGE_001229
`
`

`
`5,961,198
`
`3
`display device which is essentially immune to the problems
`of the conventional liquid crystal display devices described
`above and which can ensure increased luminance without
`need for increasing luminance of a light source.
`It is also an object of the invention to provide a method
`of manufacturing a backlighting optical waveguide or light
`guide panel for the liquid crystal display device mentioned
`above.
`
`In view of the above and other objects which will become
`apparent as the description proceeds,
`there is provided
`according to a general aspect of the present invention a
`liquid crystal display device including a light guide plate in
`which a plurality of reflecting slant portions constituted by
`a corresponding number of small convexes or small con-
`caves are formed in a bottom surface for translating travel-
`ing directions of light rays incident on the light guide plate
`toward a light-transmissive surface at predetermined angles
`of the light guide plate. In a preferred mode for carrying out
`the invention, a reflecting film may be formed on the bottom
`surface along the reflecting slant portions. Alternatively, a
`reflecting sheet may be disposed below the bottom surface
`of the light guide plate. Further,
`in the case where the
`reflecting sheet is employed, a prism sheet formed with
`individual prism elements each having an appropriate vertex
`angle should preferably be provided on a top surface of the
`light guide plate so that the liquid crystal cell can be lighted
`with illuminating rays exiting the light guide plate with an
`optimal distribution of exit angles.
`When the reflecting film is formed along the reflecting
`slant portions, sectional shape thereof is so determined that
`the light rays exit the light guide plate through the light-
`transmissive surface in such directions that
`luminance
`
`becomes highest in the direction perpendicular to the light-
`transmissive surface of the light guide plate.
`On the other hand, unless the reflecting film is formed on
`the bottom surface of the light guide plate, the traveling
`directions of the incident light rays are translated primarily
`under the effect of total reflection within the light guide
`plate. In that case, sectional shape of the reflecting slant
`portions is so determined that the light rays exit the light
`guide plate through the light-transmissive surface in such
`directions that luminance becomes highest in the direction
`perpendicular to the light-transmissive surface of the light
`guide plate. By disposing the prism sheet on the top surface
`of the light guide plate in the manner described above, the
`vertex angle of the prism elements is so determined that the
`axial luminance, i.e., luminance emanating from the light
`guide plate in the orthogonal direction in which user views
`the liquid crystal display screen becomes highest.
`The above and other objects, features and attendant
`advantages of the present invention will more easily be
`understood by reading the following description of the
`preferred embodiments thereof taken, only by way of
`example, in conjunction with the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the course of the description which follows, reference
`is made to the drawings, in which:
`FIG. 1 is a perspective view showing a backlighting light
`guide panel for a liquid crystal display according to an
`embodiment of the present invention;
`FIG. 2 is a fragmentary perspective view showing small
`convexes formed in a bottom surface of a light guide plate
`shown in FIG. 1;
`FIG. 3 is a view showing a backlighting light guide panel
`employed conventionally in a liquid crystal display device
`known heretofore;
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`FIG. 4 is a schematic view for illustrating disposition of
`light scattering dots in a light scattering layer formed in the
`backlighting light guide panel shown in FIG. 3;
`FIG. 5 is a schematic diagram for illustrating paths along
`which light rays incident on a light guide plate travel
`therethrough in the backlighting light guide panel shown in
`FIG. 1;
`FIG. 6 is a schematic diagram for illustrating refiections
`of light rays at a reflecting slant portion or convex formed in
`the light guide plate;
`FIG. 7 is a view for illustrating graphically relations
`between a spread angle (X of incident light rays and an exit
`angle 5 of light ray reflected at a side wall of a convex;
`FIG. 8 is a view for illustrating graphically relations
`between the spread angle (X and the exit angle 5 of light ray
`reflected at a bottom wall of the convex;
`FIG. 9 is a fragmentary perspective view showing a
`structure of the light guide plate according to another
`embodiment of the invention;
`FIG. 10 is a partial sectional view showing a small convex
`formed in the light guide plate shown in FIG. 9;
`FIG. 11 is a schematic diagram for illustrating paths
`followed by light rays traveling through the light guide panel
`of the structure shown in FIG. 10;
`FIGS. 12(a) to 12(6) are views for illustrating geometries
`or shapes of small convexes formed in light guide plates as
`reflecting slant portions according to exemplary embodi-
`ments of the invention, respectively;
`FIGS. 13(a) to 13()‘) are views showing backlighting light
`guide panels according to six other embodiments of the
`invention, respectively;
`FIG. 14 is a view showing partially a backlighting light
`guide panel employed in a liquid crystal display device
`according to another embodiment of the invention;
`FIG. 15 illustrates a positional relationship between a
`small convex and a reflecting sheet in the backlighting light
`guide panel shown in FIG. 14;
`FIG. 16 is a schematic diagram for illustrating paths
`followed by light rays traveling through the light guide plate
`shown in FIGS. 14 and 15;
`FIGS. 17(a) to 17(LO are sectional views showing sec-
`tional shapes of small convexes according to four other
`embodiments of the invention, respectively;
`FIG. 18 is a perspective view showing partially a light
`guide plate for a liquid crystal display device according to a
`further embodiment of the present invention;
`FIG. 19 is a perspective view showing a structure of a
`light guide plate employed in a backlighting light guide
`panel for a liquid crystal display device according to yet
`another embodiment of the invention;
`FIG. 20(a) is a plan view for illustrating geometrical
`factors of a small convex of substantially rectangular shape
`formed in the light guide plate shown in FIG. 19 and FIGS.
`20(b) and 20(c) are side views along the short and long sides
`of rectangular shape, respectively;
`FIGS. 21(a) to 21(c) are view for illustrating three exem-
`plary sectional shapes of a small concave formed in the light
`guide plate shown in FIG. 19;
`FIG. 22 is a schematic diagram for illustrating paths
`followed by light rays traveling through a light guide plate
`shown in FIG. 21(b);
`FIG. 23 is a top plan view showing an array of dots or
`small concaves formed in a light guide plate according to an
`embodiment of the invention;
`
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`5,961,198
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`5
`FIG. 24 is a fragmentary sectional View showing a struc-
`ture of a prism sheet which can be used in a backlighting
`light guide panel according to another embodiment of the
`invention;
`
`6
`slant portions or dots and density distribution thereof, and
`auxiliary data concerning important components of the light
`guide panel according to the invention.
`
`TABLE 1
`
`PRESENT
`
`ABSENT
`
`SMALL CONVEX
`OR
`SMALL CONCAVE
`35 2 10°
`
`SMALL CONVEX
`OR
`SMALL CONCAVE
`35 2 15°
`OF EXIT ANGLE
`SMALLER AS CLOSER TO LIGHT
`SOURCE
`2 to 40 ,um
`
`SUBSTANTIALLY
`CIRCLE,
`OBLONG, etc.
`OBLONG, etc.
`DIAMETER § 4: 200 ,um
`IN CIRCULAR DOT
`SHORT SIDE LENGTH § 200 ,um
`IN OBLONG OR OTHER SHAPE
`AT RANDOM
`
`REFLECTING
`FILM
`
`TYPES
`OF
`DOTS
`INCLINATION
`ANGLE OF DOT
`VIEWED IN
`SECTION
`DEPTH OR
`HEIGHT
`OF DOT
`
`SHAPE OF DOT
`
`DOT SIZE
`
`DOT
`DISPOSITION
`
`DOT DENSITY
`DISTRIBUTION
`
`AUXILLIARY
`COMPONENTS
`
`—
`
`WHEN PLANAR DOT SHAPE IS
`OBLONG, LONG SIDES OF DOTS
`EXTEND SUBSTANTIALLY
`PARALLEL TO LIGHT SOURCE
`LOWER AS CLOSER TO LIGHT
`SOURCE
`
`REFLECTING
`SHEET
`SPECIAL
`PRISM SHEET
`
`EFFECTS
`
`—
`
`OPTIMIZATION
`
`INCREASE OF
`LUMINANCE
`UNIFORMIZATION
`OF LUMINANCE
`DISTRIBUTION
`MOLDABILITY
`INCREASE OF
`LUMINANCE
`PREVENTION OF
`VISUAL
`PERCEPTION OF
`DOTS
`PREVENTION OF
`MOIRE
`OPTIMIZATION
`OF EXIT ANGLE
`
`UNIFORMIZATION
`OF LUMINANCE
`DISTRIBUTION
`INCREASE OF
`LUMINANCE
`OPTIMIZATION
`OF EXIT ANGLE
`
`FIG. 25 is a partial sectional View showing a structure of
`a backlighting light guide panel according to a further
`embodiment of the invention;
`
`FIGS. 26(a) and 26(b) are views for illustrating graphi-
`cally luminance characteristics of the backlighting light
`guide panel shown in FIG. 25;
`FIGS. 27(a) to 27()‘) are views for illustrating processing
`steps in a method of manufacturing a light guide plate
`according to an embodiment of the invention;
`FIGS. 28(a) to 28(6) are views for illustrating a method of
`manufacturing a light guide plate according to another
`embodiment of the present invention;
`FIGS. 29(a) to 29(6) are process diagrams showing a
`method of manufacturing a light guide plate according to a
`still another embodiment of the present invention; and
`FIG. 30 is a View showing schematically a structure of a
`liquid crystal display device according to an embodiment of
`the present invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`General Description
`
`Before entering into detailed description of the preferred
`or exemplary embodiments of the present invention, general
`features thereof will first be described.
`
`In Table 1 shown below, there are listed in summarization
`the data concerning inclination angle of the reflecting slant
`portions or dots constituted by convexes or concaves, height
`or depth, planar forms thereof, disposition of the reflecting
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`The present invention may be carried out in a mode in
`which a reflecting film is formed on a rear or bottom surface
`of the light guide plate or a mode in which the reflecting film
`is not provided. The angle of inclination (also referred to as
`inclination angle) of the reflecting slant portion or dot
`constituted by a small convex or a small concave as viewed
`in section should preferably be selected in a range of 20° to
`50° and more preferably in a range of 35:10°. In particular,
`in the backlighting light guide panel in which the reflecting
`film is provided, the inclination angle should be in a range
`of 35:10° while in the case of the backlighting light guide
`panel
`in which the reflecting film is not provided,
`the
`inclination angle within a range of 35:15° is preferred. By
`regulating the inclination angle of the dot in section to the
`ranges mentioned above, distribution of angles at which
`light rays traveling through the light guide plate exit the
`latter can be optimized and at
`the same time the axial
`luminance (i.e., luminance as viewed in the direction per-
`pendicular to the light-transmissive surface or a coextensive
`plane of the backlighting light guide panel) can be increased
`while suppressing the quantity of light rays exiting obliquely
`the light guide plate.
`The height or depth of the reflecting slant portion or dot
`should preferably be selected from a range of 2 to 40 gm.
`When the height or depth mentioned above is greater than 40
`gm, luminance will become excessively high in a region
`close to a cold cathode-discharge tube employed as the light
`source, incurring ultimately nonuniformness of luminance
`or light intensity distribution. Besides, when the depth or
`height mentioned above is smaller than 40 gm, difficulty will
`be encountered in molding the light guide plate because then
`
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`7
`dot-like small convexes or small concaves formed in a
`
`stamper serving as a die become difficult to be filled or
`injected with a plastic material, making it difficult to form
`the reflecting slant portions or dots in a desired shape by the
`molding. On the other hand, in case the height or a depth of
`the reflecting slant portion or dot is smaller than 2 gm, then
`light reflection efficiency of the backlighting light guide
`panel will be degraded, making it difficult or impossible to
`ensure desired luminance or light intensity.
`With regard to the top plan shape of the reflecting slant
`portion or dot (i.e., shape of the reflecting slant portion or dot
`when viewed perpendicularly to the light guide plate), it is
`preferred to form the reflecting slant portion or dot in the
`form of a circle or rectangle when the reflecting film is
`provided, although the dot may be implemented in other
`shapes without departing from the spirit of the invention.
`Parenthetically, with the expression “substantially in a rect-
`angular form” or the like, it is contemplated that not only the
`intrinsically rectangle but also a shape approximating a
`trapezium is to be covered. In the backlighting light guide
`panel
`in which the reflecting film is not provided,
`the
`substantially rectangular form of the reflecting slant portion
`or dot (i.e., convex or concave) is preferred because the
`scattered light rays within the light guide plate can be
`suppressed with the luminance of the backlighting light
`guide panel being enhanced correspondingly.
`When the shape of the reflecting slant portion or dot is of
`a circular form, the diameter thereof should preferably be
`shorter than 200 gm. On the other hand, in the case of the
`reflecting slant portion or dot of rectangular shape,
`the
`length of the short side thereof should preferably be shorter
`than 200 gm. If otherwise, the shape of the dots or reflecting
`slant portion of the light guide plate can visually be per-
`ceived by a user, making it difficult for the user to discrimi-
`natively identify characters and graphics to be visually
`identified. The lower limit of the size of the dot or reflecting
`slant portion should be limited to 10 gm. If otherwise, the
`number of dots increases too excessively to manufacture the
`backlighting light guide panel with ease.
`The dots or reflecting slant portions should preferably be
`disposed at ransom. If otherwise, moire phenomenon will
`make appearance due to interference of the dot array with
`other regular pattern such as of liquid crystal cells, color
`filter, TFT pattern (thin-film transistor pattern) and/or a
`black stripe array. When the dot or reflecting slant portion is
`essentially of a rectangular shape, the dots or reflecting slant
`portions should preferably be so disposed that long sides of
`the dots or reflecting slant portions extend substantially in
`parallel with the light source which may be constituted by a
`discharge tube as mentioned hereinbefore.
`In that case,
`optimization of the exit angle distribution can be realized
`more easily.
`Distribution of the dots or reflecting slant portions should
`preferably be such that
`the dot density is lower at
`the
`location closer to the light source.
`As the auxiliary members constituting the backlighting
`light guide panel for the liquid crystal display device accord-
`ing to the present invention,
`there may be mentioned a
`reflecting sheet and (or) a prism sheet employed in the
`backlighting light guide panel where the reflecting film is
`not provided. These auxiliary members should be provided
`in order to optimize luminance and exit angle of light rays
`exiting the light guide plate.
`At this juncture, it should however be mentioned that the
`auxiliary elements such as the prism sheet,
`the diffusing
`sheet and others employed in the conventional backlighting
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`light guide panel for the liquid crystal display device are
`effective for enhancing luminance and optimizing lumi-
`nance distribution as well as the exit angles of the light rays,
`etc. regardless of presence or absence of the reflecting film.
`
`Exemplary Embodiments
`
`Now, the present invention will be described in detail in
`conjunction with what is presently considered as preferred
`or typical embodiments thereof by reference to the drawings.
`In the following description, like reference characters des-
`ignate like or corresponding parts throughout the several
`views. Also in the following description, it is to be under-
`stood that such terms as “left”, “right”, “top”, “bottom”,
`“convex”, “concave”, “height”, “depth” and the like are
`words of convenience and are not to be construed as limiting
`terms.
`
`FIG. 1 is a perspective view showing a backlighting light
`guide panel used in a liquid crystal display device according
`to an embodiment of the present invention, and FIG. 2 is a
`fragmentary perspective view showing a reflection layer of
`the light guide plate 2 of FIG. 1. The backlighting light guide
`panel for the liquid crystal display device according to the
`instant embodiment of the invention includes as primary
`components at least a light source 1, a light guide plate 2 and
`a reflecting film 11 or a reflecting sheet 8 (not shown in
`FIGS. 1 and 2 but shown in FIG. 3). In the light guide plate
`2, there are formed in a bottom or rear surface thereof a
`number of oblique reflecting surfaces (reflecting slant
`portions) 10 in the form of truncated cones (hereinafter also
`referred to as the small convexes 10), wherein the reflecting
`film 11 is formed along the small convexes 10. Basically, the
`reflecting slant portions or small convexes 10 may be
`disposed at random.
`FIG. 5 is a schematic diagram for illustrating paths along
`which light rays emitted from the light source 1 travel
`through the light guide plate 2. Referring to FIG. 5, light rays
`emanating from the light source 1 are incident on a left-hand
`end face 7 of the light guide plate 2 as incident light rays 9
`and travel through the light guide plate 2 as travelling light
`rays 12 which travel in the direction toward the other or
`right-hand end face of the light guide plate 2 while under-
`going repetitionally total refiections at a bottom surface 13
`of the light guide plate 2 and at a light-transmissive surface
`16. Those of the traveling light rays 12 incident on slant
`surfaces 15 of the small convexes 10 (reflecting slant
`portions) are reflected toward the light-transmissive surface
`16, whereon the light rays exist the light-transmissive sur-
`face 16 after refraction to enter the liquid crystal display
`device for the backlighting thereof. On the