(12) United States Patent
`Masaki et al.
`
`US006505959B2
`US 6,505,959 B2
`Jan. 14, 2003
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54) DIRECTIONAL DIFFUSING FILM
`
`(56)
`
`References Cited
`
`(75) Inventors: Tadahiro Masaki, Tokyo-To (JP);
`Fumihiro Arakawa, Tokyo-To (JP)
`
`(73) Assignee: Dai Nippon Printing Co., Ltd. (JP)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/839,691
`(22) Filed:
`Apr. 23, 2001
`(65)
`Prior Publication Data
`
`US 2001/0046134 A1 Nov. 29, 2001
`Foreign Application Priority Data
`
`(30)
`
`Apr. 27, 2000
`
`(JP) ..................................... .. 2000-127528
`
`(51) Int. Cl.7 ................................................ .. F21V 5/02
`
`(52) US. Cl. ......................... .. 362/339; 362/31; 349/64;
`349/112; 264/167
`
`(58) Field of Search ............................ .. 362/26, 27, 31,
`362/337, 339; 349/64, 112; 359/599, 621,
`622, 623, 624; 264/467, 167
`
`U.S. PATENT DOCUMENTS
`
`5,552,907 A * 9/1996 Yokota et al. ............ .. 349/112
`
`* cited by examiner
`Primary Examiner—Sandra O’Shea
`Assistant Examiner—Guiyoung Lee
`(74) Attorney, Agent, or Firm—Parkhurst & Wendel, L.L.P.
`(57)
`ABSTRACT
`
`A directional diffusing ?lm of the invention includes a base
`?lm, and a plurality of convex directionality-providing
`elements regularly arranged on at least one surface of the
`base ?lm. A section of a ?rst directionality-providing ele
`ment in a ?rst plane including a top of the directionality
`providing element has a shape of a substantially triangle, and
`a section of the directionality-providing element in a second
`plane including the top of the directionality-providing ele
`ment and perpendicular to the ?rst plane has a top of a
`second directionality-providing element and a shape of a
`continuous Wave. The directional diffusing ?lm having
`characteristics speci?ed by the invention can diffuse light in
`proper directionally diffused light, While maintaining high
`light-diffusing ability. The directional diffusing ?lm utilizes
`light highly ef?ciently as compared With conventional dif
`fusing ?lms.
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`11 Claims, 7 Drawing Sheets
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`LGE_001196
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`LG Electronics Ex. 1036
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`US 6,505,959 B2
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`1
`DIRECTIONAL DIFFUSING FILM
`
`TECHNICAL FIELD
`
`The present invention relates to a directional diffusing
`?lm and, more particularly, to a directional diffusing ?lm
`that can diffuse light in a controlled diffusion mode, a
`method of manufacturing the directional diffusing ?lm, a
`surface light source unit and a liquid crystal display.
`
`10
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`BACKGROUND ART
`
`2
`unsatisfactorily in a base material of the light diffusing ?lms
`or a coating material of the light diffusing ?lms. In addition,
`it is dif?cult to maintain the light diffusing ?lms in a
`satisfactory appearance. Furthermore, productivity (yield) in
`manufacturing the light diffusing ?lms is loW.
`In addition, it is possible that the beads fall off edges of
`the light diffusing ?lms When punching or cutting the light
`diffusing ?lm into a desired siZe or When assembling the
`punched or cut light diffusing ?lms, Which can produce dust
`and foreign matters.
`The beads diffuse light in all directions. Consequently, the
`amount of light can be reduced by internal absorption and
`some part of light can be re?ected toWard the light guide
`plate 122. Thus, the amount of light emitted in the normal
`(front) direction can be reduced, that is, ef?ciency of utili
`Zation of the light emitted by the light sources 121 may be
`loW, and luminance of the surface light source unit 120 may
`be also loW.
`
`DISCLOSURE OF THE INVENTION
`It is an object of the present invention to provide a
`directional diffusing ?lm that can utiliZe light at a high
`ef?ciency and that can be produced at a high productivity
`free from producing dust and foreign matters, and a method
`of manufacturing such a directional diffusing ?lm.
`According to the present invention, a directional diffusing
`?lm includes a base ?lm, and a plurality of convex
`directionality-providing elements regularly arranged on at
`least one surface of the base ?lm; Wherein a section of a ?rst
`directionality-providing element in a ?rst plane including a
`top of the directionality-providing element has a shape of a
`substantially triangle, and a section of the directionality
`providing element in a second plane including the top of the
`directionality-providing element and perpendicular to the
`?rst plane has a top of a second directionality-providing
`element and a shape of a continuous Wave.
`The directional diffusing ?lm having characteristics
`speci?ed by the present invention can diffuse light in proper
`directionally diffused light, While maintaining high light
`diffusing ability. The directional diffusing ?lm utiliZes light
`highly ef?ciently as compared With conventional diffusing
`?lms.
`Preferably, the shape of the continuous Wave is a periodic
`Waveform having a period corresponding to each of the
`directionality-providing elements. For example, the periodic
`Waveform may be a substantially sinusoidal Waveform.
`The shape of continuous Wave may be a periodic Wave
`form having Wavy parts corresponding to the directionality
`providing elements and straight parts respectively extending
`betWeen the adjacent Wavy parts.
`Preferably, the section of the directionality-providing
`element in the ?rst plane has a shape of a substantially
`isosceles triangle. Preferably, the substantially triangle has a
`vertex angle of a range of 80° to 100°. Preferably, the
`substantially triangle has a vertex Which is rounded and/or a
`predetermined amount of Which is cut off.
`Preferably, the plurality of convex directionality
`providing elements are arranged on a light emitting surface
`of the base ?lm so that incident light of incident angles in a
`range of 70° to 80° leaves the directional diffusing ?lm at
`outgoing angles including a maximum outgoing angle in a
`range of 25° to 40°. In the case, light that is difficult to be
`emitted out in prior art can be ef?ciently emitted out toWard
`the front direction.
`Preferably, the plurality of convex directionality
`providing elements are arranged on a light emitting surface
`
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`Generally, a surface light source unit is provided With a
`light diffusing ?lm. The light diffusing ?lm is disposed on a
`light-emitting side of the surface light source unit to diffuse
`illuminating light emitted by a light source of the surface
`light source unit.
`Aconventional light diffusing ?lm is formed of a material
`prepared by dispersing a light diffusing matter such as
`organic or inorganic beads in a transparent resin base, or is
`formed by coating a transparent resin base With an ink
`containing a dispersing matter such as organic or inorganic
`beads.
`FIG. 8 is a sectional vieW of a liquid crystal display 135
`provided With an edge-type surface light source unit 120 as
`an example of a conventional surface light source unit
`employing a conventional light diffusing ?lm.
`As shoWn in FIG. 8, the surface light source unit 120
`includes, as principal components, tWo light sources 121, a
`light guide plate 122, a re?ecting ?lm 124, and three light
`diffusing ?lms 110-1, 110-2 and 110-3 that have the same
`parameters.
`The light guide plate 122 is a surface light emitting means
`and has a light-emitting surface 122a, a not light-emitting
`surface opposite the light-emitting surface 122a, and oppo
`site side surfaces. The light sources 121 are disposed beside
`the opposite side surfaces, respectively. A dot pattern 123 is
`formed on the not light-emitting surface in order to diffuse
`light emitted by the light sources 121 toWard the light
`emitting surface 122a. The re?ecting ?lm 124 is disposed so
`as to face the not light-emitting surface of the light guide
`plate 122 to intercept light rays traveling in undesired
`directions and to re?ect back the same in a predetermined
`direction.
`The diffusing ?lms 110-1, 110-2 and 110-3 disposed on
`the side of the light emitting surface 122a of the light guide
`plate 122 diffuse light emitted by the surface light source
`unit 120 to enhance the uniformity of light. The diffusing
`?lms 110-1, 110-2 and 110-3 conceal the dot pattern 123. A
`50
`single diffusing ?lm is unable to diffuse light satisfactorily
`and diffuses light irregularly. Usually, three diffusing plate or
`so are necessary to achieve satisfactory diffusion and to
`enhance front luminance.
`A transparent liquid crystal display unit 133 is disposed
`on the light emitting side of the surface light source unit 120.
`The liquid crystal display unit 133 has a loWer substrate 132,
`an upper substrate 131 and a liquid crystal layer 130
`sandWiched betWeen the substrates 131 and 132. In the
`liquid crystal display 135 shoWn in FIG. 8, the liquid crystal
`display unit 133 is illuminated from behind by the surface
`light source unit 120.
`The light diffusing ?lms included in the aforesaid con
`ventional liquid crystal display contain beads as a diffusing
`matter. Therefore, light-diffusing characteristic of the light
`diffusing ?lms is unsatisfactory if particle siZes of the beads
`are irregularly distributed or if the beads are dispersed
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`of the base ?lm so that a haze value is in a range of 70 to 90
`When light falls on a light receiving surface of the base ?lm.
`Thus, luminous intensity (density) of diffused light in a
`necessary range can be increased.
`According to the present invention, a method of manu
`facturing a directional diffusing ?lm having the aforesaid
`characteristics comprises: a preparing step of preparing a
`cylinder having a molding pattern of a shape complementary
`to the plurality of convex directionality providing elements;
`and a molding step of molding the plurality of convex
`directionality providing elements by introducing a resin into
`the molding pattern of the cylinder.
`According to the present invention, the directional dif
`fusing ?lm having the aforesaid characteristics can be manu
`factured at a manufacturing cost comparable to that of the
`conventional diffusing ?lm. In addition, shape-repeatability
`and productivity are improved.
`Preferably, the molding step includes: a step of introduc
`ing an ioniZing radiation hardening resin into the molding
`pattern of the cylinder; and a step of setting the ioniZing
`radiation hardening resin by irradiating ioniZing radiation.
`For example, the preparing step includes a step of forming
`the molding pattern of the shape complementary to the
`plurality of convex directionality providing elements by
`cell-engraving by means of an electronic engraving machine
`provided With a diamond stylus having a point angle in a
`range of 80° to 100°. Preferably, the diamond stylus has a tip
`that is rounded and /or cut by a predetermined amount.
`In addition, this invention is a surface light unit compris
`ing: a light source, a surface light emitting means having a
`light-emitting surface that can emit a light from the light
`source in a predetermined direction, and a directional dif
`fusing ?lm that includes a base ?lm, and a plurality of
`convex directionality-providing elements regularly arranged
`on at least one surface of the base ?lm, Wherein a section of
`a ?rst directionality-providing element in a ?rst plane
`including a top of the directionality-providing element has a
`shape of a substantially triangle, and a section of the
`directionality-providing element in a second plane including
`the top of the directionality-providing element and perpen
`dicular to the ?rst plane has a top of a second directionality
`providing element and a shape of a continuous Wave.
`Alternately, this invention is a liquid crystal display
`comprising: a light source, a surface light emitting means
`having a light-emitting surface that can emit a light from the
`light source in a predetermined direction, a directional
`diffusing ?lm that includes a base ?lm, and a plurality of
`convex directionality-providing elements regularly arranged
`on at least one surface of the base ?lm, and a transparent
`liquid-crystal element arranged on a light-emitting side of
`the directional diffusing ?lm, Wherein a section of a ?rst
`directionality-providing element in a ?rst plane including a
`top of the directionality-providing element has a shape of a
`substantially triangle, and a section of the directionality
`providing element in a second plane including the top of the
`directionality-providing element and perpendicular to the
`?rst plane has a top of a second directionality-providing
`element and a shape of a continuous Wave.
`The surface light source unit and the liquid crystal display
`are able to enhance luminance ef?ciently in a practical range
`of luminance, and the liquid crystal display is also capable
`of clearly displaying images or the like, even if the number
`of the directional diffusing ?lms is small. The surface light
`source unit and the liquid crystal display can be formed in
`smaller thicknesses and can be sold at loWer prices, respec
`tively.
`
`4
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1A is an enlarged, fragmentary perspective vieW of
`a directional diffusing ?lm in a preferred embodiment
`according to the present invention;
`FIG. 1B is an enlarged, fragmentary perspective vieW of
`the directional diffusing ?lm of FIG. 1A as seen in a
`direction of an arroW A in FIG. 1A;
`FIG. 2A is a schematic plan vieW of the directional
`diffusing ?lm in the preferred embodiment;
`FIG. 2B is a schematic sectional vieW taken along the line
`C—C (?rst plane) in FIG. 2A;
`FIG. 2C is a schematic sectional vieW taken along the line
`D—D (second plane) in FIG. 2A;
`FIG. 3 is a schematic vieW for explaining steps of forming
`convex directionality-providing elements included in the
`directional diffusing ?lm of the embodiment;
`FIG. 4 is a schematic vieW for explaining a method of
`forming a concave pattern in a circumference of a cylinder;
`FIG. 5 is a schematic sectional vieW of a liquid crystal
`display provided With a surface light source unit employing
`directional diffusing ?lms of the embodiment;
`FIG. 6 is a perspective vieW for explaining directions for
`measurements of luminous intensity distribution;
`FIG. 7A is a graph shoWing measured luminous intensity
`distribution With respect to a direction perpendicular to the
`lamps;
`FIG. 7B is a graph shoWing measured luminous intensity
`distribution With respect to a direction parallel to the lamps;
`and
`FIG. 8 is a schematic sectional vieW of a liquid crystal
`display provided With a surface light source unit employing
`conventional light diffusing ?lms.
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`BEST MODE FOR CARRYING OUT THE
`INVENTION
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`Preferred embodiments of the present invention Will be
`described With reference to the accompanying draWings.
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`Directional Diffusing Film
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`FIG. 1 is an enlarged, fragmentary perspective vieW of a
`directional diffusing ?lm 10 in a preferred embodiment
`according to the present invention. FIG. 1A is a perspective
`vieW seen in a direction of an arroW B in FIG. 1B, and FIG.
`1B is a perspective vieW seen in a direction of an arroW A
`in FIG. 1A.
`The directional diffusing ?lm 10 has a base ?lm 11 and a
`plurality of directionality-providing elements 12. In FIG. 1,
`the directionality-providing elements 12 are magni?ed
`greatly for exaggeration. Actually, the convex directionality
`providing elements 12 are very small projections.
`The base ?lm 11 is formed of a transparent resin. The base
`?lm 11 may be an oriented or nonoriented ?lm of a ther
`moplastic resin, such as cellulose triacetate, a polyester,
`polyamide, polyimide, polypropylene, poly(methyl
`pentene), poly(vinyl chloride), poly(vinyl aceta), poly
`(methyl methacrylate), polycarbonate or polyurethane.
`Although dependent on rigidity, it is preferable that a
`thickness of the base ?lm 11 is in a range of 50 to 200 pm,
`from a vieWpoint of processing and/or handling it. In
`addition, in vieW of ?rmly and stably bonding the convex
`directionality-providing elements 12 to the base ?lm 11, it is
`preferable to ?nish a surface of the base ?lm 11 to Which the
`convex directionality-providing elements 12 are to be
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`bonded, by an adhesion improving process such as a corona
`discharge process.
`FIGS. 2A, 2B and 2C are a plan vieW and sectional vieWs
`of the directional diffusing ?lm 10. FIG. 2A is a plan vieW
`taken from the side of the light emitting surface of the
`directional diffusing ?lm 10, FIG. 2B shoWs a section CC
`included in a ?rst plane and extending in the direction of the
`arroW B, and FIG. 2C is a section DD included in a second
`plane and extending in the direction of the arroW A. As
`shoWn in FIG. 2C, an outline 12a of the section DD of the
`convex directionality-providing elements 12 included in the
`second plane is gently curved. The outline 12a of the section
`DD of the convex directionality-providing elements 12 may
`have straight lines dependently on a method and/or a con
`dition for forming a molding cylinder 88.
`As shoWn in FIG. 2B, the outline of the section CC of the
`convex directionality-providing elements 12 included in the
`?rst plane and extending in the direction of the arroW B has
`a shape of isosceles triangles each having a vertex angle
`ot=90°. The ?rst plane including the section CC includes
`tops of the convex directionality-providing elements 12.
`Shapes of sections of the convex directionality-providing
`elements 12 included in planes parallel to the ?rst plane and
`not including the tops of the convex directionality-providing
`elements 12 are substantially similar to and loWer than the
`shape of the section CC of the convex directionality
`providing elements 12 included in the ?rst plane and extend
`ing in the direction of the arroW B.
`The shape of the section CC of the convex directionality
`providing elements 12 included in the ?rst plane and extend
`ing in the direction of the arroW B does not need to be that
`of isosceles triangles and may be that of any triangles other
`than isosceles triangles.
`The outline 12a of the section DD included in the second
`plane including the tops of the convex directionality
`providing elements 12 has a sinusoidal Waveform. A three
`dimensional shape of the convex directionality-providing
`elements 12 is folloWed by moving the section CC of
`isosceles triangles extending in the direction of the arroW B
`along the substantially sinusoidal Waveform.
`Referring to FIGS. 2A, 2B and 2C, each of the convex
`directionality-providing elements 12 has a vertex angle a in
`a range of 80° to 100°, a height H in a range of 15 to 120
`pm and lengths L1 and L2 of the bottom in a range of 40 to
`200 pm. Spaces D1 and D2 betWeen adjacent convex
`directionality-providing elements 12 are 15 pm or beloW,
`respectively. Thus, the convex directionality-providing ele
`ments 12 are arranged in the highest possible density. The
`values of the parameters L1, L2 and H are determined
`dependently on operating conditions of the electronic
`engraving machine, Which Will be described later. If the
`vertex angle 0t is outside the aforesaid range, front lumi
`nance is greatly reduced.
`In the directional diffusing ?lm 10 shoWn in FIG. 2, the
`length L1 and L2 are approximately equal to each other.
`HoWever, the lengths L1 and L2 need not be equal to each
`other and may be of any suitable values, respectively.
`The tops of the convex directionality-providing elements
`12 may be rounded and/or cut by a predetermined amount.
`HoWever, luminance tends to be reduced When the tops are
`rounded and/or cut by a predetermined amount.
`The convex directionality-providing elements 12 are
`formed of a mixture of an oligomer, such as (meth)acrylate
`(hereinafter acrylate and methacrylate Will be referred to
`inclusively as “(meth)acrylate” of a polyfunctional
`compound, such as any polyhydric alcohol, or a prepolymer,
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`and a comparatively large amount of a reactive diluent.
`Suitable diluents include monofunctional monomers, such
`as ethyl (meth)acrylate, ethylhexyl (meth)acrylate, styrene,
`vinyltoluene and N-vinylpyrrolidone, and multifunctional
`monomers, such as trimethylolpropane tri(meth)acrylate,
`hexanediol (meth) acrylate, tripropylene glycol di (meth)
`acrylate, diethylene glycol di(meth)acrylate pentaerythritol
`tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6
`hexane diol (meth)acrylate and neopentyl glycol di(meth)
`acrylate.
`When the aforesaid mixture contains a photo
`polymeriZation initiator, such as acetophenone,
`benZophenoe, Michler’s benZoyl benZoate, ot-amyloxime
`ester or thioxanthone, and a photosensitiZer, such as
`n-butylamine, triethylamine or tri-n-butylphosphine, the
`same can be used as an ultraviolet hardening resin.
`The mixture may contain, as an ioniZing radiation hard
`ening resin, an active organic silicon compound expressed
`by RmSi(OR‘)n, Where R‘ is an alkyl group having a carbon
`number in a range of 1 to 10, and m and n are integers
`meeting m+n=4. Concretely, the organic silicon compound
`may be tetramethoxysilane, tetraethoxysilane, tetra-iso
`propoxysilane, tetra-n-propoxysilane, tetra-n-butoxysilane,
`tetra-sec-butoxysilane, tetra-tert-butoxysilane,
`tetrapentaethoxysilane, tetrapenta-iso-propoxysilane,
`tetrapenta-n-propoxy-silane, tetrapenta-n-butoxysilane,
`tetrapenta-sec-butoxysilane, tetrapenta-tert-butoxysilane,
`methyl trimethoxysilane, methyl triethoxysilane, methyl
`tripropoxysilane, methyl tributoxysilane, dimethyl
`dimethoxysilaane, dimethyl diethoxysilane, dimethyl
`ethoxysilane, dimethyl methoxysilane, dimethyl
`propoxysilane, dimethyl butoxysilane, methyl
`dimethoxysilane, methyl diethoxysilane, or hexyl trimethox
`ysilane.
`The convex directionality-providing elements 12 may be
`formed of a thermoplastic resin instead of the aforesaid
`reaction hardening resin. Possible thermoplastic resins are,
`for instance, acrylic resins, such as methyl methacrylate and
`ethyl methacrylate, polyester resins, such as polyethylene
`terephthalate, polybutylene terephthalate and polyethylene
`naphthalate, polycarbonate resins, polyhydrocarbon resins,
`such as polystyrene, polypropylene and polymethylpentene,
`polyamide resins, such as nylon 66 and nylon 6, saponi?ed
`ethylene-vinyl acetate copolymers, polyimide resins,
`polysulfone resins, polyvinyl chloride resins, and cellulose
`acetate resins.
`In this embodiment, the base ?lm 11 and the convex
`directionality-providing elements 12 are formed of the fol
`loWing materials.
`The base ?lm 11 is a PET ?lm With a thickness t=100 pm
`(A4300, commercially available from Toyobo).
`The convex directionality-providing elements 12 are
`formed of an ultraviolet hardening resin (RC19-793, com
`mercially available from Dai Nippon Inki Kagaku Kogyo
`
`Method of Manufacturing Directional Diffusing
`Film
`The directional diffusing ?lm 10 Was made by forming the
`convex directionality-providing elements 12 on the base ?lm
`11.
`Referring to FIG. 3, the molding cylinder 88 is provided
`in its circumference With cavities (a concave pattern) 88a
`having a shape complementary to that of the convex
`directionality-providing elements 12, in a regular arrange
`ment corresponding to that of the convex directionality
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`LGE_001206
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`

`
`US 6,505,959 B2
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`7
`providing elements 12 of the directional diffusing ?lm 10.
`An ionizing radiation hardening resin 82 is fed to a die head
`86 by a pump 87 and is extruded through the die head 86
`evenly into the cavities 88a. The base ?lm 11 is pressed
`closely against the circumference of the molding cylinder 88
`by means of an inlet nip roller 83. The ioniZing radiation
`hardening resin 82 ?lling up the cavities 88a is irradiated
`through the base ?lm 11 With ioniZing radiation radiated by
`an ioniZing radiation irradiation unit 85 (D-valve UV lamp,
`commercially available from Fusion) to set the ioniZing
`radiation hardening resin 82 into a cured (set) resin 81 and
`to bond the cured resin 81 to the base ?lm 11. Then, the
`convex directionality-providing elements 12 integrally com
`bined With the base ?lm 11 are separated from the molding
`cylinder 88 by means of an outlet nip roller 84 in order to
`obtain the directional diffusing ?lm 10.
`FIG. 4 is a vieW of assistance in explaining a method of
`forming the cavities 88a in the circumference of the molding
`cylinder 88 in an arrangement corresponding to the regular
`arrangement of the convex directionality-providing ele
`ments 12. In FIG. 4, directions indicated by arroWs A and B
`correspond to those indicated by arroWs A and B in FIGS. 1
`and 2, respectively.
`The cavities 88a Were formed by a cell-engraving process
`using a gravure electronic engraving machine
`(commercially available from Heidelberg Japan) provided
`With a double-negative diamond stylus having a point angle
`ot=90°.
`A diamond stylus 90 is supported on a fulcrum 90a for
`minute oscillation at a frequency of the order of several
`thousands hertZ. An amplitude of the minute oscillation is
`controlled according to a rotating speed of the molding
`cylinder 88 in such a manner that the amplitude traces a
`substantially sinusoidal Waveform. Thus, the cavities 88a
`are formed correspondingly to the convex directionality
`providing elements 12 arranged in a substantially sinusoidal
`Waveform. In the embodiment, the tip of the diamond stylus
`90 Was cut by 5 pm beforehand in order to prevent breakage
`thereof during the engraving process. The cavities 88a Were
`formed on the molding cylinder 88 in 100 lines/cm and at an
`angle of 4°.
`
`Surface Light Source Unit and Liquid Crystal
`Display
`FIG. 5 is a sectional vieW of a liquid crystal display 35
`provided With a surface light source unit 20 employing the
`directional diffusing ?lms 10 of the embodiment.
`As shoWn in FIG. 5, the surface light source unit 20
`includes tWo light sources 21, a light guide plate 22, a
`re?ecting ?lm 24 and tWo directional diffusing ?lms 10A
`and 10B. The directional diffusing ?lms 10A and 10B are the
`foregoing directional diffusing ?lms 10 and have the same
`parameters. The directional diffusing ?lms 10A and 10B are
`disposed in such a manner that four sides of each bottom of
`the convex directionality-providing elements 12 thereof
`(FIG. 2) extend at an angle of about 45° respectively With
`respect to four sides of a light emitting surface 22a of the
`rectangular light guide plate 22 (With respect to a direction
`perpendicular to the lamp and a direction parallel to the
`lamp).
`The light guide plate 22, i.e., a surface light projecting
`means, has the light-emitting surface 22a, a not light
`emitting surface opposite the light-emitting surface 22a, and
`opposite side surfaces. The light sources 21 are disposed
`near the opposite side surfaces, respectively. The not light
`emitting surface is provided With a dot pattern 23 in order to
`
`10
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`15
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`25
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`35
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`45
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`55
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`65
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`8
`diffuse light emitted by the light sources 21 toWard the light
`emitting surface 22a. The re?ecting ?lm 24 faces the not
`light-emitting surface of the light guide plate 22 to intercept
`light rays traveling in unnecessary directions and to re?ect
`back the light rays in a predetermined direction.
`A transparent liquid crystal display unit 33 is disposed on
`the light emitting side of the surface light source unit 20. The
`liquid crystal display unit 33 includes a loWer substrate 32,
`an upper substrate 31, and a liquid crystal layer 30 sand
`Wiched betWeen the upper substrate 31 and the loWer
`substrate 32. As shoWn in FIG. 5, the surface light source
`unit 20 illuminates the liquid crystal display unit 33 from the
`back side of the same.
`
`Performance Evaluation Tests
`
`The directional diffusing ?lm 10 and the surface light
`source unit 20 including the directional diffusing ?lm 10
`Were evaluated in terms of front luminance, particle falling,
`and luminous intensity distribution in comparison With a
`conventional directional diffusing ?lm and a conventional
`surface light source unit including the conventional direc
`tional diffusing ?lm.
`Herein, the conventional surface light source
`(comparative example) is the surface light source unit 120
`explained in connection With FIG. 8, Which employs direc
`tional diffusing ?lms D121 commercially available from
`Tujiden as the conventional directional diffusing ?lms 110
`1, 110-2 and 110-3.
`A haZe value, Which is a ratio of luminance of an object
`as observed through a diffusing medium to that of the object
`as observed directly, Was used as an index of a level of light
`diffusion. The directional diffusing ?lm 10 of the embodi
`ment had a satisfactory haZe value in the range of 70 to 90.
`More concretely, the light sources 21 and 121 Were turned
`on and the front luminances of the surface light source units
`20 and 120 Were measured from a direction normal to the
`front surfaces of the respective surface light source units 20
`and 120 by a luminance meter (BM-7, angle of ?eld: 2°,
`made by Topcon).
`Particle falling Was evaluated by the number of foreign
`matters found When cutting the directional diffusing ?lms in
`a predetermined siZe and incorporating the cut ?lms into the
`surface light source units.
`Results of measurement of the front luminance and par
`ticle falling are shoWn in Table 1.
`
`TABLE 1
`
`FRONT LUMINANCE PARTICLE FALLING
`
`EMBODIMENT
`COMPARATIVE
`
`1495 cd/m2 (102.1%)
`1465 cd/m2 (100.0%)
`
`0 (NOT FOUND)
`x (FOUND)
`
`The front luminance of the surface light source unit of the
`embodiment Was greater than that of the comparative
`example by about 2%. In addition, as resin fragments and
`?ne particles fell from the comparative example, but nothing
`fell at all from the surface light source unit of the embodi
`ment.
`Luminous intensities of the surface light source units 20
`and 120 With respect to tWo perpendicular directions Were
`measured in the angular range of —80° to 80° at angular
`intervals of 1° by the luminance meter (BM-7, angle of ?eld:
`20, made by Topcon)
`FIG. 6 shoWs the directions for the measurement of
`luminous intensity distribution characteristics. In FIG. 6, a
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`LGE_001207
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`US 6,505,959 B2
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`vertical direction perpendicular to the respective light
`sources (lamps) 21 is indicated by an arroW V and a
`horizontal direction perpendicular to the vertical direction is
`indicted by an arroW H. Luminous intensity distribution
`characteristics Were measured With respect to those tWo
`directions.
`FIG. 7A is a graph shoWing the luminous intensity dis
`tribution characteristics With respect to the vertical direction
`perpendicular to the lamps, and FIG. 7B is a graph shoWing
`the luminous intensity distribution characteristics With
`respect to the horiZontal direction parallel to the lamps.
`As shoWn in FIG. 7A, the luminance of the surface light
`source unit 20 of the embodiment With respect to the vertical
`direction is higher than that of the comparative example in
`the range of 140° With respect to the front (axial) direction
`(0° direction).
`As shoWn in FIG. 7B, the luminance of the surface light
`source unit 20 of the embodiment With respect to the
`horiZontal direction is higher than that of the comparative
`example in substantially all the angular range.
`As described above, the embodiment can achieve a high
`light diffus