USRE48844E1 - Liquid crystal display apparatus - Google Patents

Abstract

A liquid crystal display apparatus is provided in which occurrence of a moiré pattern can be prevented without largely reducing front luminance. A liquid crystal display apparatus 1 includes a surface light source 4, a liquid crystal display panel 2, and first and second prism sheets 5 and 6 for condensing light emitted from the surface light source 4 and guiding the light toward the liquid crystal display panel. The first and second prism sheets 5 and 6 are disposed such that prism array directions thereof are orthogonal to each other. When a pixel pitch of the liquid crystal display panel 2 is defined as Pp [μm]; a prism array pitch of the first prism sheet 5 is defined as Px [μm]; and a prism array pitch of the second prism sheet 6 is defined as Py [μm], relationships of Px≤Pp/(14−0.045 Pp) and Py≤Pp/(11.5−0.032 Pp) are satisfied.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Notice is hereby provided that more than one reissue application has been filed: this application is a reissue continuation of U.S. application Ser. No. 15/704,925, filed Sep. 14, 2017, which is a reissue continuation of U.S. application Ser. No. 14/603,284, filed Jan. 22, 2015, which is a reissue continuation of U.S. application Ser. No. 13/963,267, filed on Aug. 9, 2013, which is a reissue of U.S. Pat. No. 7,995,158, filed Aug. 29, 2008, which is a National Stage of International Application PCT/JP2007/056793, filed Mar. 29, 2007, which claims the benefit of and priority to Japanese Patent Application 2006-090709, filed on Mar. 29, 2006.

TECHNICAL FIELD

The present invention relates to a liquid crystal display apparatus including a light-transmissive condenser sheet, and more particularly to a liquid crystal display apparatus including a first condenser sheet and a second condenser sheet that are arranged in a stack.

BACKGROUND ART

Liquid crystal display (LCD) apparatuses have a lower power consumption and can be made smaller and thinner than cathode-ray-tube (CRT) apparatuses. Nowadays, various sizes of liquid crystal display apparatuses are widely used, ranging from small apparatuses such as mobile phones and digital cameras to large apparatuses such as large liquid crystal televisions.

Liquid crystal display apparatuses are classified into a transmissive type, a reflective type, and the like. Particularly, a transmissive liquid crystal display apparatus includes a liquid crystal display panel constituted by a pair of transparent substrates with a liquid crystal layer therebetween and a backlight unit serving as an illumination light source. Backlight units are classified into a direct-lighting type, in which a light source is provided directly under a liquid crystal display panel, and an edge-lighting type.

In general, a backlight unit for liquid crystal display apparatuses employs a condenser sheet, such as a prism sheet, a lens sheet, or the like, for orienting light emitted from a light source toward the front.

For example, a prism sheet includes a number of prisms each having a triangular cross section on a light-output surface thereof. The prism sheet condenses and orients light incident thereon toward the front by refracting and transmitting the incident light through inclined planes of the prisms. Particularly, for use in mobile apparatuses, an exemplary structure is known in which two prism sheets are arranged in a stack such that respective prism arrays of the two sheets are oriented orthogonally to each other, whereby light spreading in the two directions are efficiently condensed to improve front luminance (refer toPatent Document 1 below).

[Patent Document 1] PCT Japanese Translation Patent Publication No. 10-506500

DISCLOSURE OF THE INVENTIONProblem to be Solved by the Invention

A contrast pattern (moiré pattern) may occur due to interference depending on the prism array pitch of a prism sheet and the pixel array pitch of a liquid crystal display panel. In order to prevent the occurrence of such a moiré pattern, it is effective to reduce the prism array pitch.

However, there is a problem in that simply reducing the prism array pitch may considerably reduce the front luminance and, consequently, degrade the image quality. The same problem applies to the case where two prism sheets are arranged in a stack, as described above.

In view of the above problem, the present invention aims to provide a liquid crystal display apparatus in which occurrence of a moiré pattern can be prevented without largely reducing front luminance.

Means for Solving the Problem

In solving the above problem, the inventors have found that a liquid crystal display apparatus causing no moiré pattern can be produced, while reduction of front luminance is minimized, by determining the optimum combination of prism array pitches of prism sheets in accordance with the pixel pitch of a liquid crystal display panel.

That is, a liquid crystal display apparatus according to the present invention includes a light source, a liquid crystal display panel, and condenser sheets for condensing light emitted from the light source and guiding the light toward the liquid crystal display panel. The condenser sheets include a first condenser sheet in which ridges of a first corrugated structure having a light-condensing characteristic are periodically arranged on one surface the first condenser sheet in a longitudinal direction of the liquid crystal display panel, and a second condenser sheet in which ridges of a second corrugated structure having a light-condensing characteristic are periodically arranged on one surface the of the second condenser sheet in a lateral direction of the liquid crystal display panel. When a pixel pitch of the liquid crystal display panel is defined as Pp [μm], an array pitch of the first corrugated structure is defined as Px [μm], and an array pitch of the second corrugated structure is defined as Py [μm], the following relationships are satisfied:
Px≤Pp/(14−0.045Pp), and
Py≤Pp/(11.5−0.032Pp).

As described above, by determining the array pitches of the respective corrugated structures of the first and second condenser sheets in accordance with the pixel pitch of the liquid crystal display panel, occurrence of a moiré pattern can be prevented without largely reducing front luminance of the liquid crystal display panel.

Preferably, Px≤50, Py≤50, and |Px−Py|<50 are satisfied when Pp≥222; Px≤20, Py≤20, and |Px−Py|<20 are satisfied when 222>Pp≥144; and Px≤15, Py≤20, and −20<Px−Py<15 are satisfied when 114>Pp≥136.5.

The first and second corrugated structures correspond to prism structures having ridges of a triangular shape in cross section if the condenser sheets are prism sheets. If the condenser sheets are lens sheets, the first and second corrugated structures have ridges of a lens shape, such as an aspheric lens, with a curved cross section.

Advantages of the Invention

As described above, according to the liquid crystal display apparatus of the present invention, occurrence of a moiré pattern can be prevented without largely reducing front luminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing the schematic structure of a liquid crystal display apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing occurrence of a moiré pattern in various combinations of prism array pitches Px and Py when the pixel pitch is 222 μm.

FIG. 3 is a diagram showing occurrence of a moiré pattern in various combinations of prism array pitches Px and Py when the pixel pitch is 144 μm.

FIG. 4 is a diagram showing occurrence of a moiré pattern in various combinations of prism array pitches Px and Py when the pixel pitch is 136.5 μm.

FIG. 5 is a diagram showing values of front luminance in various combinations of prism array pitches Px and Py.

FIG. 6 is a schematic perspective view showing an exemplary structure in which a first prism sheet and a second prism sheet are combined together with an adhesive layer therebetween.

FIG. 7 is a schematic perspective view showing an exemplary combination of a first condenser sheet constituting a prism sheet and a second condenser sheet constituting a lens sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described with reference to the drawings. The invention is not limited to the following embodiment, and various modifications can be made within the scope of the invention.

FIG. 1 is an exploded perspective view showing the schematic structure of a liquidcrystal display apparatus1 according to an embodiment of the present invention. The liquidcrystal display apparatus1 in the figure includes a liquidcrystal display panel2 and abacklight unit3. Thebacklight unit3 includes a surface light source4, afirst prism sheet5, asecond prism sheet6, and adiffusion plate7 arranged in that order.

The liquidcrystal display panel2 includes pixels arranged in the longitudinal direction (X-direction inFIG. 1) and the lateral direction (Y-direction inFIG. 1) thereof at a predetermined pitch, and displays a predetermined image on the front surface thereof by controlling the transmittance of light applied from thebacklight unit3 for each of the pixels. The image displayed is a color image but not limited thereto, of course. The liquidcrystal display panel2 includes a liquid crystal cell constituted by a pair of transparent substrates facing each other with a liquid crystal layer provided therebetween, a pair of polarizing plates sandwiching the liquid crystal cell, and the like. The liquid crystal material constituting the liquid crystal layer is not particularly limited but is appropriately selected according to the method for driving liquid crystal, such as the TN method, the VA method, or the like.

The surface light source4 is either a direct-lighting type in which a plurality of light sources are disposed on a surface or an edge-lighting type in which a light-guiding plate is used. The surface light source4 irradiates the entire back surface of the liquidcrystal display panel2 with backlight. As the light sources, linear light sources such as fluorescent tubes or point light sources such as light-emitting diodes are used.

The first andsecond prism sheets5 and6 serve as “condenser sheets” of the invention for condensing light emitted from the surface light source4 toward the front (in the Z-direction) so as to improve front luminance. Thediffusion plate7 is an optically functional element for diffusing and delivering the backlight so as to produce uniform luminance. Thediffusion plate7 may be provided between thefirst prism sheet5 and the surface light source4. Optically functional elements other than the first andsecond prism sheets5,6, and thediffusion plate7 may also be provided, such as a polarization separation element that transmits one polarized component and reflects another polarized component, for example.

Each of the first andsecond prism sheets5 and6 is provided with a prism structure having ridges of a triangular shape in cross section on a light-output surface thereof. The prism structure correspond to a “corrugated structure” of the present invention.

On thefirst prism sheet5,prisms5P are arranged successively at a predetermined pitch in the longitudinal direction of the liquid crystal display panel2 (the X-direction inFIG. 1). On thesecond prism sheet6,prisms6P are arranged successively at a predetermined pitch in the lateral direction of the liquid crystal display panel2 (the Y-direction inFIG. 1). In this embodiment, cross sections of theprisms5P and theprisms6P are both isosceles triangles each having a vertex angle of 90°.

Thefirst prism sheet5 condenses light spreading in the X-direction, among the backlight emitted from the surface light source4, toward the Z-direction. Thesecond prism sheet6 condenses light spreading in the Y-direction toward the Z-direction. Since the light spreading in the X- and Y-directions are condensed toward the front (in the Z-direction) by the first andsecond prism sheets5 and6, front luminance of the liquidcrystal display apparatus1 is more improved than in the case where only one prism sheet is provided.

The prism array pitch of thefirst prism sheet5 and the prism array pitch of thesecond prism sheet6 may be either the same or different. In general, the smaller the prism array pitch is, the lower the resultant front luminance becomes. Moreover, a moiré pattern of interference fringes may occur due to the periodic structures provided on the first andsecond prism sheets5 and6 and the display pixels provided on the liquidcrystal display panel2. The occurrence of such a moiré pattern can be prevented by reducing the prism array pitches of the first andsecond prism sheets5 and6. However, if the prism array pitches are excessively reduced, front luminance will be reduced considerably.

Hence, the liquidcrystal display apparatus1 of this embodiment is configured so that, when the pixel pitch of the liquidcrystal display panel2 is defined as Pp [μm], the prism array pitch of thefirst prism sheet5 is defined as Px [μm], and the prism array pitch of thesecond prism sheet6 is defined as Py [μm], the following relationships are satisfied:
Px≤Pp/(14−0.045Pp), and
Py≤Pp/(11.5−0.032Pp)   (1)

By setting the first prism array pitch Px and the second prism array pitch Py in accordance with the pixel pitch Pp of the liquidcrystal display panel2 so as to satisfy the above expression (1), a liquid crystal display apparatus in which occurrence of a moiré pattern can be prevented without largely reducing front luminance can be obtained.

For example, when the pixel pitch Pp is 222 μm, the upper limits of Px and Py are about 55 μm and 56 μm, respectively; when the pixel pitch is 144 μm, the upper limits of Px and Py are about 19 μm and about 20 μm, respectively; and when the pixel pitch is 136.5 μm, the upper limits of Px and Py are about 17 μm and 19 μm, respectively.

Preferably, in the case of Pp≥222, Px≤50, Py≤50, and |Px−Py|<50 are satisfied; in the case of 222>Pp≥144, Px≤20, Py≤20, and |Px−Py|<20 are satisfied; and in the case of 144>Pp≥136.5, Px≤15, Py≤20, and −20<Px−Py<15 are satisfied.

FIGS. 2 to 4 show the results of an experiment for checking occurrence of a moiré pattern for each of combinations of the prism array pitches of the first andsecond prism sheets5 and6 when the pixel pitches (Pp) of the liquidcrystal display panel2 are 222 μm, 144 μm, and 136.5 μm, respectively. In each of the figures, numbers in the table indicate the value of “Px−Py”, a symbol “O” indicates that no moiré pattern occurred, and a symbol “x” indicates that a moiré pattern occurred. The occurrence of a moiré pattern was examined visually.

Referring toFIG. 2, in the case of the 222 μm pixel pitch, it was found that no moiré pattern occurred in all the combinations where the prism array pitches Px and Py of the first andsecond prism sheets5 and6 are 50 μm or less. In contrast, referring toFIG. 3, in the case of the 144 μm pixel pitch, occurrence of a moiré pattern could be prevented only in the combinations where Px and Py are both 19 μm or less. Further, in the case of the 136.5 μm pixel pitch, occurrence of a moiré pattern could be prevented only in the combinations of Px≤14 μm and Py≤19 μm.

As described above, by setting the pixel pitch Pp of the liquidcrystal display panel2 and the prism array pitches Px and Py of the first andsecond prism sheets5 and6 so as to satisfy the relationships of the expression (1), the liquidcrystal display apparatus1 causing no moiré pattern can be obtained.

FIG. 5 shows exemplary combinations of the prism array pitches Px and Py (50 μm, 19 μm, 14 μm, and 10 μm) of the first andsecond prism sheets5 and6 and values of front luminance in those combinations. Front luminance is expressed as the measured luminance of light transmitted through theprism sheets5 and6. InFIG. 5, the ranges of the above-mentioned combinations of the prism pitches Px and Py where no moiré pattern occurred are indicated by rectangles of different lines for the cases of the pixel pitches of 222 μm, 144 μm, and 136.5 μm.

As shown inFIG. 5, it is understood that combinations of larger prism array pitches Px and Py produce higher front luminance. Further, by referring to the exemplary combinations inFIG. 5, the optimum selection for theprism sheets5 and6 capable of preventing reduction of front luminance caused by reduction of the prism pitches can be made in accordance with the pixel pitch of the liquidcrystal display panel2 to be used.

Thus, according to this embodiment, the array pitches of therespective prisms5P and6P on the first andsecond prism sheets5 and6 are determined in accordance with the pixel pitch of the liquidcrystal display panel2 as shown in the expression (1). Accordingly, occurrence of a moiré pattern can be prevented, without largely reducing front luminance of the liquid crystal display panel.

Furthermore, since the upper limits of the prism array pitches Px and Py producing a high front luminance without causing a moiré pattern can be obtained easily according to the expression (1), the combination of theprism sheets5 and6 can be optimized and the degree of design flexibility can also be improved.

Next, detailed configurations of the first andsecond prism sheets5 and6 and modifications thereof will be described below.

Each of the first andsecond prism sheets5 and6 is configured to have a prism structure on one surface of a base film made of light-transmissive resin such as polyethylene terephthalate (PET) or polycarbonate (PC). The prism structure may be directly formed on the base film by a method such as casting or melt extrusion. Alternatively, a surface having the shape of the prism structure may be formed using an ultraviolet-curable resin material and then be transferred onto the surface of the base film.

In an exemplary configuration in which the prism structure is transferred onto the base film, the prism sheet can be made thinner by configuring the prism structure to be later separable from the base film. Specifically, the thickness of the prism sheet can be made thinner in the following manner, for example: the thickness of a 50-μm-pitch prism sheet becomes 50 μm, the thickness of a 19-μm-pitch prism sheet becomes 35 μm, the thickness of a 14-μm-pitch prism sheet becomes 32 μm, and the thickness of a 10-μm-pitch prism sheet becomes 30 μm.

If usability of the first and second prism sheets is expected to be degraded because of such thinning, the first andsecond prism sheets5 and6 may be bonded together with anadhesive layer8 therebetween, as shown inFIG. 6. Theadhesive layer8 is preferably made of a material having a refractive index lower than those of the first andsecond prism sheets5 and6. For example, when theprism sheets5 and6 are made of polycarbonate having a refractive index of about 1.6, theadhesive layer8 can be formed of an acrylic ultraviolet-curable resin having a refractive index of about 1.3 to 1.4.

The liquidcrystal display apparatus1 having an improved front luminance can be obtained by employing two prism sheets including the first andsecond prism sheets5 and6 as shown inFIG. 1. In this case, the vertex angle of each of theprisms5P of thefirst prism sheet5 provided on the lower position and the vertex angle of each of theprisms6P of thesecond prism sheet6 provided on the upper position are not necessarily the same, but may be different. For example, when the vertex angle of each of theprisms6P is set larger than that of each of theprisms5P, the viewing angle can be widened.

In the case where a single pixel includes sub-pixels having colors of R, G, and B as in the case of a color liquid crystal display panel, the prism array pitch Px of thefirst prism sheet5 having theprisms5P arranged in the longitudinal direction (X-direction) of the screen may be set to one-third of the prism array pitch Py of thesecond prism sheet6 having theprisms6P arranged in the lateral direction (Y-direction) of the screen.

The condenser sheets according to the present invention are not limited to the above-describedprism sheets5 and6.FIG. 7 illustrates an example in which the first condenser sheet is formed of thefirst prism sheet5 and the second condenser sheet is formed of alens sheet9. Thelens sheet9 includes a number ofcylindrical lenses9L each having, for example, an aspheric cross section successively arranged in one direction on a light-output surface thereof. In this example, thecylindrical lenses9L are arranged in a crosswise direction relative to the direction in which theprisms5P are arranged (orthogonal to the direction in which theprisms5P are arranged in the figure).

Also in this example, by setting the pixel pitch Pp of the liquid crystal display panel, the prism array pitch Px of theprism sheet5, and a lens array pitch Py of thelens sheet9 so as to satisfy the relationships of the expression (1), the advantages of the invention can be obtained. Further, by placing thelens sheet9 on the upper position, a liquid crystal display apparatus having a wider viewing angle can be produced. Also when the first and second condenser sheets are both lens sheets, the same advantages as those described above can be obtained.

Claims (25)

The invention claimed is:

1. A liquid crystal display apparatus comprising:

a light source;

a liquid crystal display panel;

and condenser sheets for condensing light emitted from the light source and guiding the light toward the liquid crystal display panel,

the condenser sheets including:

a first condenser sheet in which ridges of a first corrugated structure having a first light-condensing characteristic are periodically arranged on one surface of the first condenser sheet in a longitudinal direction of the liquid crystal display panel; and

a second condenser sheet in which ridges of a second corrugated structure having a second light-condensing characteristic are periodically arranged on one surface of the second condenser sheet in a lateral direction of the liquid crystal display panel,

wherein, when a longitudinal, lateral, or sub-pixel pitch of the liquid crystal display panel is defined as Pp, an array pitch of the first corrugated structure is defined as Px, and an array pitch of the second corrugated structure is defined as Py, the following relationships are satisfied: Px is approximately equal to Pp/(14−0.045Pp) and Py is approximately equal to Pp/(11.5−0.032Pp) such that moiré patterns are not produced by the condenser sheets and the liquid crystal display panel, and the condenser sheets do not significantly reduce the luminance from the liquid crystal display.

2. The liquid crystal display apparatus according toclaim 1, wherein each of the first and second corrugated structures is a prism structure having ridges of a triangular shape in cross section.

3. The liquid crystal display apparatus according toclaim 1, wherein at least one of the ridges of the first corrugated structure or the ridges of the second corrugated structure have a shape of an aspheric lens.

4. The liquid crystal display apparatus according toclaim 1, wherein Px≤50, Py≤50, and |Px−Py|<50 are satisfied when Pp≥222.

5. The liquid crystal display apparatus according toclaim 1, wherein Px≤20, Py≤20, and |Px−Py|<20 are satisfied when 222>Pp≥144.

6. The liquid crystal display apparatus according toclaim 1, wherein Px≤15, Py≤20, and −20<Px−Py<15 are satisfied when 114>Pp≥136.5.

7. The liquid crystal display apparatus according toclaim 1, wherein Px is slightly less than or equal to Pp/(14−0.045Pp) and Py is slightly less than or equal to Pp/(11.5−0.032Pp).

8. A liquid crystal display apparatus comprising:

a liquid crystal display panel; and

condenser sheets for condensing light emitted from a light source and guiding the light toward the liquid crystal display panel,

the condenser sheets including:

a first condenser sheet in which ridges of a first corrugated structure having a first light-condensing characteristic are periodically arranged on one surface of the first condenser sheet in a longitudinal direction of the liquid crystal display panel; and

a second condenser sheet in which ridges of a second corrugated structure having a second light-condensing characteristic are periodically arranged on one surface of the second condenser sheet in a lateral direction of the liquid crystal display panel,

wherein, when a longitudinal, lateral, or sub-pixel pitch of the liquid crystal display panel is defined as Pp, an array pitch of the first corrugated structure is defined as Px, and an array pitch of the second corrugated structure is defined as Py, the following relationships are satisfied: Px is approximately equal to Pp/(14−0.045Pp) and Py is approximately equal to Pp/(11.5−0.032Pp) such that moiré patterns are not produced by the condenser sheets and the liquid crystal display panel, and the condenser sheets do not significantly reduce the luminance from the liquid crystal display.

9. The liquid crystal display apparatus according toclaim 8 incorporated in a device selected from the following group: a mobile phone, a digital camera, a liquid crystal television.

10. The liquid crystal display apparatus according toclaim 8, wherein each of the first and second corrugated structures is a prism structure having ridges of a triangular shape in cross section.

11. The liquid crystal display apparatus according toclaim 8, wherein at least one of the ridges of the first corrugated structure or the ridges of the second corrugated structure have a shape of an aspheric lens.

12. The liquid crystal display apparatus according toclaim 8, wherein Px≤50, Py≤50, and |Px−Py|<50 are satisfied when Pp≥222.

13. The liquid crystal display apparatus according toclaim 8, wherein Px≤20, Py≤20, and |Px−Py|<20 are satisfied when 222>Pp≥144.

14. The liquid crystal display apparatus according toclaim 8, Wherein Px≤15, Py≤20, and −20<Px−Py<15 are satisfied when 114>Pp≥136.5.

15. The liquid crystal display apparatus according toclaim 8, wherein Px is slightly less than or equal to Pp/(14−0.045Pp) and Py is slightly less than or equal to Pp/(11.5−0.032Pp).

16. A condenser sheet for condensing light emitted from a light source and guiding a light toward a liquid crystal display panel having a pitch defined as Pp in micrometers comprising ridges of a first corrugated structure having a first light-condensing characteristic that are periodically arranged on a first surface of the condenser sheet in a first direction of the liquid crystal display panel, wherein the first corrugated structure has an array pitch in micrometers defined as Px such that Px has a value greater than or equal to 10 microns and less than or equal to Pp/(14−0.045Pp).

17. The condenser sheet of claim 16, wherein the first corrugated structure is a prism structure having ridges of a triangular shape in cross section.

18. The condenser sheet of claim 16, wherein the first corrugated structure includes aspheric lens structures.

19. The condenser sheet of claim 16, wherein 10 microns≤Px≤50 microns and Pp≥222 microns.

20. The condenser sheet of claim 16, wherein 10 microns≤Px≤20 microns and Pp≥144 microns.

21. A condenser sheet for condensing light emitted from a light source and guiding a light toward a liquid crystal display panel having a pitch defined as Pp in micrometers comprising ridges of a second corrugated structure having a second light-condensing characteristic that are periodically arranged on a first surface of the condenser sheet in a second direction of the liquid crystal display panel, wherein the second corrugated structure has an array pitch in micrometers defined as Py such that Py has a value greater than or equal to 10 microns and less than or equal to Pp/(11.5−0.032Pp).

22. The condenser sheet of claim 21, wherein the second corrugated structure is a prism structure having ridges of a triangular shape in cross section.

23. The condenser sheet of claim 21, wherein the second corrugated structure includes aspheric lens structures.

24. The condenser sheet of claim 21, wherein 10 microns≤Py≤50 microns and Pp≥222 microns.

25. The condenser sheet of claim 21, wherein 10 microns≤Py≤20 microns and Pp≥144 microns.

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