JPWO2008056648A1 - Optical sheet for display device and design method thereof - Google Patents

Abstract

Prevents display distortion, blurring of images, pin distortion, etc. An optical sheet for a display device the present invention, the Young's modulus of the front sheet E _L, the thickness of the front sheet a t _L (mm), the initial warping amount of the [delta] _L front sheet (mm), the lens sheet E _F Young's modulus (kgf / mm ² ), t _F is the thickness of the lens sheet (mm), δ _F is the initial warpage of the lens sheet (mm), S is the area of the front sheet (mm ² ), and E _FF is the lens When the concave on the observation side is positive for the Young's modulus (kgf / mm ² ) and warpage amount of the material, the following formula is satisfied, and the deflection of the optical sheet is 8 mm or less.
E _L t _L ³ δ _L -E _F t _F ³ δ _F > 0 δ _L -δ _F > 0
384E _L t _L ³ (δ _LF −δ _F ) / (60b ⁴ E _FF ) <2 × 10 ⁻⁹
δ _LF = (E _L t _L ³ δ _L + E _F t _F ³ δ _F ) / (E _L t _L ³ + E _F t _F ³ )

Description

  The present invention relates to an optical sheet for a display device, for example, an optical sheet such as a transmissive screen used in a rear projection display device or a diffusion sheet used in a backlight of a liquid crystal display device, and a design method thereof.

  As an example of an optical sheet for a display device, FIG. 1 shows a schematic configuration diagram of a cross section of a transmission screen conventionally used in a rear projection display device. As shown in FIG. 1, normally, a lenticular lens sheet 1 and a Fresnel lens sheet 2 are in close contact to form a transmission screen. Furthermore, a front plate may be provided on the observation side. The Fresnel lens sheet 2 is composed of a sheet in which a Fresnel lens composed of concentric and fine pitch lenses at equal intervals is provided on the light emitting surface.

  As shown in FIG. 1, the lenticular lens sheet 1 has lenses 11 arranged at equal intervals on the light incident surface side, and lenses 12 arranged on the light emitting surface side. The parallel light or convergent light emitted from the Fresnel lens sheet 2 is greatly diffused in the horizontal direction by the lenticular lens sheet 1, thereby allowing an image to be observed in a wide visual field range in the horizontal direction. In the lenticular lens sheet 1, as shown in FIG. 1, a light absorbing layer 14 made of a light absorbing material such as black ink is formed on a convex portion 13 other than a light collecting portion formed by each lens provided on the light incident surface side. By improving the contrast, the contrast in the bright room is improved.

  These optical sheets need to be in close contact with each other without gaps so as not to blur the image. Nonetheless, if the sheets facing each other are held together with an excessively strong force, there will be a phenomenon that the tip of the blade of the Fresnel lens will be statically deformed (hereinafter referred to as the “blade crushing phenomenon”). Specifically, there is a problem of deformation or breakage of the lens due to the phenomenon that the sheets collide with each other due to vibration during transportation and the Fresnel lens or lenticular lens is broken (hereinafter sometimes referred to as vibrating white powder or white powder). When the blade crushing phenomenon or the vibrating white powder occurs, it is observed as light and dark unevenness during image projection.

  Also, these optical sheets need to be kept flat as a whole. This is because problems such as distortion of the image may occur if the surface is not flat. In the case of a transmissive screen sheet, even if it is not strictly a flat surface, it is allowed within a certain range to warp a convex shape toward the light source. On the other hand, it is not allowed to warp in a convex shape on the observation side. This is because when the convex shape is warped on the viewing side, the screen is depressed when the screen is pressed with a finger, and the display is disturbed. On the other hand, when the concave shape is warped on the viewing side, even if pressed with a finger, the concave shape remains unchanged and the display is not disturbed.

  A range in which the observation side is allowed to warp in a concave shape is, for example, several mm. A larger concave shape on the viewing side than this is not preferable because image distortion called pin distortion is conspicuous.

  For these reasons, there is a demand for a technique for keeping an optical sheet in close contact and keeping a flat or slightly convex shape on the light source side. Patent Document 1 discloses a method in which a Fresnel lens sheet is formed in a convex shape on the observation side and a lenticular lens sheet is combined in a convex shape on the light source side by being warped in advance and combined. Patent Document 2 discloses a method in which all three sheets are formed into a convex warped shape in the same direction, and overlapped and adhered.

  In addition, a transmissive screen may use a co-extrusion molding or a multi-layer sheet by bonding. In such a multilayer sheet, there is a problem that bimetal warpage occurs due to a difference in linear expansion coefficient between layers. In order to solve this problem, Patent Document 3 proposes an invention that uses a multilayer sheet in which water absorption is smaller on the inner side than on the outer side, and has a structure that warps inward during moisture absorption. In Patent Document 3, the difference in moisture absorption rate is preferably 0.1% or more. However, in practice, if the difference in moisture absorption is too large, it will be extremely warped, which is a problem. Examples of moisture absorption include acrylic, polycarbonate, styrene, etc., but there are no descriptions of Young's modulus, elongation, and layer thickness, which are important for warpage change, and lack concreteness.

In Patent Document 4, the linear expansion coefficient difference Δα between the bonded lenticular lens sheet and Fresnel lens sheet is set to 5.5 × 10 ⁻⁵ (/ ° C.) or less, and the linear expansion coefficient is 3 × 10 ^{−5 on} the forefront. A technique for controlling the direction in which bimetal warpage occurs by suppressing the change in bimetal warpage by laminating the following materials (/ ° C.) is disclosed. However, in Patent Document 4, there is no description of an important Young's modulus regarding a warp change.

  A generally known transmissive liquid crystal display device includes a liquid crystal display panel and a backlight provided on the back. The backlight includes a light source and a light diffusion sheet for emitting light uniformly from the entire surface.

  In general, a plurality of sheets are used as the light diffusion sheet, such as a diffusion plate for preventing the arrangement pattern of the light sources from being recognized as uneven brightness and a lens sheet for condensing the diffused light within a predetermined viewing angle range.

  In these lens sheets, the base material sheet layer and the lens layer may be formed of different materials, or may be used by bonding a plurality of light diffusion sheets (Patent Document 5, etc.).

However, in the liquid crystal display device, the temperature of the sheet changes due to a change in ambient temperature or heat generation from a light source. For this reason, the multi-layered sheet may cause bimetal warping due to the difference in linear expansion coefficient of each layer.

  When the lens sheet warps in the backlight, the sheet may be damaged by hitting the liquid crystal display panel or the light source as shown below, or the unevenness of brightness may occur due to changes in the viewing angle characteristics of the sheet. There is.

  For example, when a plurality of sheets are warped opposite to each other, or when the amount of warpage of the convex warp side sheet is larger than the other, the sheets are separated from each other. In such a case, the backlights may collide with each other due to vibrations such as transportation, and the lens may be damaged. In the case of a combination of sheets that matches the lens pattern of the sheet and the diffusion layer pattern, the original optical function may not be exhibited.

On the other hand, when a plurality of sheets are warped toward each other, or when the amount of warpage of the convex warp side sheet is extremely smaller than the other, the sheets are pressed against each other. In such a case, when the Young's modulus of the lens of the lens sheet is 300 kgf / mm ² (≈3000 MPa) or less, the lens may be deformed. The Young's modulus 300 kgf / mm ² (≈3000 MPa) here is a value at −10 ° C. Furthermore, in the case of 2000 MPa or less, there is a greater possibility that the lens is deformed. In particular, when the Young's modulus at 20 ° C. is 1500 MPa or less and the Young's modulus at 40 ° C. is 1000 MPa or less, the lens is more likely to be deformed.

  When the sheet warps convexly toward the light source side, a technique (Patent Document 6) that reduces the influence of warpage by providing a deflection prevention pin on the light source side can be applied. However, if the amount of warpage is too large, another problem such as damage of the sheet due to collision between the sheet and the pin is likely to occur, so the amount of warpage needs to be kept within an appropriate range.

On the other hand, when the sheet warps convexly toward the liquid crystal display panel, it is difficult to provide a deflection prevention pin similar to the above between the sheet and the liquid crystal display panel, and therefore, the influence of warpage is particularly likely to occur.
Therefore, it is desired that the diffusion sheets for backlight adhere to each other with an appropriate force and the sheet as a whole is flat or slightly convex toward the light source side.

JP-A-4-67134 Japanese Patent Laid-Open No. 2-72341 Japanese Patent Laid-Open No. 11-72848 JP 2002-40563 A JP 2006-208930 A JP 2007-109608 A

  As described above, when combining the optical sheets used in the display device, problems related to display disturbance due to warping convex shape on the observation side, problems related to blurring of images caused by gaps between the optical sheets, It is necessary to eliminate all the problems related to pin distortion caused by excessively warping the light source side and the problems related to lens deformation and white powder caused by excessive adhesion between optical sheets.

  An object of this invention is to provide the optical sheet for display apparatuses which can solve all the above-mentioned problems, and its design method.

An optical sheet for a display device according to the present invention is an optical sheet for a display device that includes a front sheet and a lens sheet, and is fixed to the front sheet, where E _L is the Young's modulus of the front sheet and t _L is the front surface. thickness of the sheet (mm), the initial warpage of the front sheet of δ _L (mm), the Young's modulus of the lens sheet ^{_{E F (kgf / mm 2)}} , the thickness of the lens sheet _{t F} (mm), δ _F the lens initial warpage of the sheet (mm), the area of the front sheet S ^(mm _2), the Young's modulus at -10 ° C. the material of the _{E FF} lens (kgf / ^mm 2), the positive and negative warpage on the observation side When the concave is positive, the following expression is satisfied, and the deflection of the optical sheet is 8 mm or less.
E _L t _L ³ δ _L -E _F t _F ³ δ _F > 0
δ _L −δ _F > 0
384E _L t _L ³ (δ _LF −δ _F ) / (60b ⁴ E _FF ) <2 × 10 ⁻⁹
Where δ _LF = (E _L t _L ³ δ _L + E _F t _F ³ δ _F ) / (E _L t _L ³ + E _F t _F ³ )

Here, it is desirable that the deflection of the optical sheet be 5 mm or less.
Further, it is desirable that the optical sheet for a display device is a transmissive screen, the front sheet is a lenticular sheet, and the lens sheet is a Fresnel lens sheet.
The front sheet is preferably a multilayer plate, and the lens sheet is preferably a single layer plate.

Designing method of an optical sheet for a display device according to the present invention, and a front sheet and a lens sheet, a fixed display device for an optical sheet design method comprising both the E _L of the front sheet Young rate, the thickness of the front sheet a _{t L} (mm), the initial warping amount of the [delta] _L front sheet (mm), the Young's modulus of the lens sheet ^{_{E F (kgf / mm 2)}} , the thickness of the lens sheet _{t F} (Mm), δ _F is the initial warp amount (mm) of the lens sheet, S is the area of the front sheet (mm ² ), E _FF is the Young's modulus (kgf / mm ² ) of the lens material at −10 ° C., and the warp amount Is designed so that the following expression is satisfied and the deflection of the optical sheet is 8 mm or less.
E _L t _L ³ δ _L -E _F t _F ³ δ _F > 0
δ _L −δ _F > 0
384E _L t _L ³ (δ _LF −δ _F ) / (60b ⁴ E _FF ) <2 × 10 ⁻⁹
Where δ _LF = (E _L t _L ³ δ _L + E _F t _F ³ δ _F ) / (E _L t _L ³ + E _F t _F ³ )

Here, when E is the Young's modulus of the optical sheet, t is the thickness of the optical sheet, and b is the short side length of the optical sheet, the pressure q is obtained by calculating the pressing pressure q between the front sheet and the lens sheet by the following equation. It is desirable to determine the initial warpage δ _F of the lens sheet and the equilibrium warpage δ _LF of the transmissive screen so that the edge crushing phenomenon caused by the above-mentioned phenomenon does not occur.
q = 384 Et ³ (δ _F −δ _LF ) / 60b ⁴

  According to the present invention, there are problems related to display distortion caused by warpage on the observation side, problems related to blurring of images caused by gaps between optical sheets, and problems caused by excessive warpage on the light source side. All the problems related to pin distortion and the problems related to lens deformation and white powder caused by excessive adhesion between optical sheets can be solved.

It is a schematic block diagram of the cross section of a transmissive screen. It is explanatory drawing for demonstrating each phenomenon which arises in a transmission type screen. It is sectional drawing for demonstrating each phenomenon which arises in a transmissive screen. It is sectional drawing for demonstrating each phenomenon which arises in a transmissive screen. It is sectional drawing for demonstrating each phenomenon which arises in a transmissive screen. It is sectional drawing for demonstrating each phenomenon which arises in a transmissive screen. It is a figure which shows the model used when designing a transmissive screen. It is a figure which shows the model used when designing a transmissive screen. It is a figure which shows the model used when designing a transmissive screen. It is a figure which shows the model used when designing a transmissive screen. It is a table | surface which shows the relationship between the initial curvature of each optical sheet in a transmissive screen, and generation | occurrence | production of blade crushing. It is a table | surface which shows the calculation image for designing a transmissive screen.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lenticular lens sheet 2 Fresnel lens sheet 11 1st lens row | line | column 12 2nd lens row | line | column 13 Convex part 14 Light absorption layer

  A transmission screen as an example of an optical sheet for a display device according to an embodiment of the present invention includes a lenticular lens sheet 1 and a Fresnel lens sheet 2 as shown in FIG. The lenticular lens sheet 1 has a thickness of, for example, 1.81 mm to 2.25 mm and is a multilayer plate made of different materials. Therefore, the so-called bimetal phenomenon occurs in the lenticular lens sheet 1 according to this example. In the lenticular lens sheet 1 according to the present example, the material constituting the observation side layer has a lower coefficient of thermal expansion than the material constituting the light source side layer.

  Moreover, the Fresnel lens sheet 2 has a thickness of 1.20 mm to 1.85 mm, for example, and is a single-layer plate. Therefore, the so-called bimetal phenomenon does not occur in the Fresnel lens sheet 2 according to this example.

  Next, the relationship between the phenomenon that causes a problem to be solved in the transmission screen and the shape of each optical sheet will be described with reference to FIG. In FIG. 2, the shapes of the lenticular lens sheet 1 and the Fresnel lens sheet 2 are shapes in an initial state before they are fixed to each other. In addition, in this invention, an initial state means each sheet single state before fixing both. The initial warpage amount is the warpage amount in an initial state in a 20 ° C. environment. Furthermore, when a bimetal-like warpage change occurs in at least one sheet, it is preferable that the range of the present invention is satisfied in the range of −10 ° C. to 40 ° C. in consideration of the change amount.

  In FIG. 2, the horizontal axis indicates the shape of the lenticular lens sheet 1, and the vertical axis indicates the shape of the Fresnel lens sheet 2. The left end on the horizontal axis indicates that the lenticular lens sheet 1 is not uneven, that is, is flat. Further, the lenticular lens sheet 1 shows that the dent of the lenticular lens sheet 1 with respect to the observation surface (that is, the degree of protrusion of the central portion toward the light source) increases toward the right in the horizontal axis. Here, in the lenticular lens sheet 1, the state where the convex shape is formed on the observation side is not defined. When the convex shape is formed on the observation side as described in the section of the related art, the observer moves the central portion with a finger or the like. This is because the inconvenience that the display is disturbed when the button is pressed causes the display to be excluded as a premise.

  The vertical axis indicates that the Fresnel lens sheet 2 has a convex shape with a larger central protrusion toward the observation surface as it goes upward, and the dent with respect to the observation surface becomes larger as it goes downward. It shows that.

  When the transmissive screen is cooled, the shape identified by a circle in the center of FIG. 2 is reduced in the dent to the observation surface of the lenticular lens sheet 1 that is a multilayer plate, as indicated by the arrows shown in the figure. It changes to a shape that is closer to flat. On the contrary, when heated, the dent to the observation surface of the lenticular lens sheet 1 increases. In addition, when the transmissive screen is rapidly cooled after being heated, the dent on the heating surface of the lenticular lens sheet 1 increases and the degree of protrusion of the Fresnel lens sheet 2 toward the observation side increases rapidly. Further, when the transmission screen absorbs moisture, the dent on the observation surface of the lenticular lens sheet 1 becomes smaller, becomes more flat, and the dent on the observation surface of the Fresnel lens sheet 2 becomes larger.

  The transmission screen has four phenomena to be solved. Phenomenon A occurs when the lenticular lens sheet 1 is in a substantially flat state and the Fresnel lens sheet 2 is convex on the observation side, as shown in FIG. 3A, in the initial state before being fixed to each other. Phenomenon A is a phenomenon in which when the lenticular lens sheet 1 and the Fresnel lens sheet 2 having such a shape are fixed to each other, the entire transmissive screen becomes a convex shape on the observation side. When the part is pushed with a finger etc., the display is disturbed.

  Phenomenon B occurs in the initial state when the lenticular lens sheet 1 is substantially flat and the Fresnel lens sheet 2 is concave on the exit side, as shown in FIG. 3B. The phenomenon B is a phenomenon caused by a gap generated between the lens sheets when the lenticular lens sheet 1 and the Fresnel lens sheet 2 having such a shape are fixed to each other. More specifically, the phenomenon B is generated by the gap. It is a blur of the image.

  In the initial state, the phenomenon C occurs when the lenticular lens sheet 1 and the Fresnel lens sheet 2 are both concave on the observation side, as shown in FIG. 3C. The phenomenon C is pin distortion that occurs when the lenticular lens sheet 1 and the Fresnel lens sheet 2 having such a shape are fixed to each other.

  In the initial state, the phenomenon D occurs when the lenticular lens sheet 1 has a concave shape on the observation side and the Fresnel lens sheet 2 has a convex shape on the observation side, as shown in FIG. 3D. The phenomenon D is a crushing phenomenon or a white powder phenomenon that occurs when the lenticular lens sheet 1 and the Fresnel lens sheet 2 having such shapes are fixed to each other.

  The transmission type screen according to the embodiment of the present invention is characterized in that it does not generate all of these phenomena A, B, C, and D. For this reason, the initial warpage amount and physical properties of each optical sheet The parameter was set.

(1) Measures for Preventing Occurrence of Phenomenon First, in order to prevent occurrence of Phenomenon A, E _L t _L ³ δ _L representing the rigidity of the lenticular lens sheet 1 and E _F representing the rigidity of the Fresnel lens sheet 2 are used. It has been found that it is necessary to satisfy the following formula for t _F ³ δ _F.
E _L t _L ³ δ _L -E _F t _F ³ δ _F > 0
Here, E _L is the Young's modulus of the lenticular lens sheet 1, t _L is the thickness of the lenticular lens sheet 1, [delta] _L is the value of the initial warping of the lenticular lens sheet 1 (i.e., initial warpage), E _F is the Fresnel lens The Young's modulus of the sheet 2, t _F is the thickness of the Fresnel lens sheet 2, and δ _F is the value of the initial curvature of the Fresnel lens sheet 2 (that is, the initial curvature amount). When the amount of warpage of the Fresnel lens sheet 2 is negative, it is not sufficient that the lenticular lens sheet 1 is completely flat, and it is necessary to have a concave shape on the observation side, that is, the amount of warpage is positive.

(2) Preventive Measure of Occurrence of Phenomenon Next, in order to prevent the occurrence of Phenomenon B, δ _L which is the initial warp value (ie, initial warp amount) of the lenticular lens sheet 1 and the Fresnel lens sheet 2 the initial warping of the value of (i.e., initial warpage) and [delta] _F is found that it is necessary to satisfy the following equation.
δ _L −δ _F > 0
That is, the initial warp value of the lenticular lens sheet 1 is larger than the initial warp value of the Fresnel lens sheet 2.

(3) Preventive Measure for Occurrence of Phenomenon C Next, pin distortion of phenomenon C will be described in detail. First, a method for calculating pin distortion will be described. 4A and 4B show models to be calculated. As shown in FIG. 4A, an optical sheet is a beam, its thickness is h, and its width is 2b. It is assumed that a pressure q (N / mm ² ) that is a uniform load is applied to the beam. The bend in this case is defined as a function v (x) of x, where the center point of the beam is the origin coordinate (0, 0) and the bend at a position x away from the position. It is assumed that both ends of the beam are supported.

In this case, the deflection v can be derived from the following equation based on a basic formula in general material mechanics.
d ⁴ v / dx ⁴ = q / EI _z (1)
As boundary conditions, since the inclination of the beam at the origin is zero, x = 0 and dv / dx = 0, and since the bending at both ends is zero, x = ± b and v = 0 is considered.

When the equation (1) is integrated twice, the following equation is obtained.
d ² v / dx ² = (q / EI _z ) · (b ² −x ² ) / 2 (2)
Further, when the equation (2) is integrated twice, the following equation is obtained.
_{v = (q / EI z)} · {(b 2 x 2/4) - (x 4/24)} (3)
When x = b, the deflection v becomes the maximum value v _max, and therefore, when substituted, the following equation is obtained.
_{v max = (q / EI z} ) · (5b 4/24) (4)
Here, in a state where the beam is bent, the calculation is performed using the bent position as the origin.
The rectangular cross-section, the following equation is obtained by substituting this because it is Iz = h ^3/12.
v _max = 2.5 (qb ⁴ / Eh ³ ) (5)

When this is transformed, the following equation is obtained.
q / E = v _max h ³ /2.5b ⁴ (6)
Substituting equation (6) into equation (1) yields:
d ⁴ v / dx ⁴ = q / EI _z = 4.8 v _max / b ⁴ (7)
Here, since v _max is synonymous with the deflection δ of the optical sheet, it will be replaced with δ below.

Next, consider a case where two optical sheets, a lenticular lens sheet 1 and a Fresnel lens sheet 2, are combined. When the combined pressure distribution when the lenticular lens sheet 1 and the Fresnel lens sheet 2 are combined is p, the following equation is obtained.
^{_{p = E F I ZF (d}} 4 δ F / dx 4) -E L I ZL (d 4 δ L / dx 4) (8)
Substituting equation (7) into equation (8) and eliminating the differential term yields:
_{p = 0.4E F (δ F h} F 3 / b 4) -0.4E L (δ L h L 3 / b 4) (9)

On the other hand, since the algebraic calculation is extremely difficult for the calculation formula for bending when a uniform load p is applied to the front surface of a rectangular plate supported by a four-sided frame, “Guidelines for Design Using Acrylic Plates” (Japan Methacrylic Resin Association) The experimental approximate expression described in the A & D Committee) is cited. The following formula can be cited from the chart on page 85 of this document.
16 (p / E) (a ² b ² / t ⁴ ) = 22 (δ / t) +3.9 (δ / t) ³ (10)
When both sides of (10) are divided by 22, the following equation (11) can be obtained.
0.73 (p / E) (a ² b ² / t ⁴ ) = (δ / t) +0.18 (δ / t) ³ (11)

By analogy with each of the lenticular lens sheet and the Fresnel lens sheet, Expressions (12) and (13) are obtained.
0.73 (p _L / E _L ) (a ² b ² / h _L ⁴ ) = (δ _L /t)+0.18 (δ _L / h _L ) ³ (12)
^{_{0.73 (p F / E F)}} (a 2 b 2 / h F 4) = (δ F /t)+0.18(δ F / h F) 3 (13)

The load is p = p _L + p _F , and if both sheets are integrated, δ _L = δ _F = δ is obtained, and therefore, when E _L ≈E _F = E, the following equation (14) is obtained.
0.73 (a ² b ² / E) p = h _L ⁴ {(δ / h _L ) +0.18 (δ / h _L ) ³ } + h _F ⁴ {(δ / h _F ) +0.18 (δ / h _F ) ³ } (14)

By substituting equation (9) into equation (14) and eliminating p, equation (15) is obtained.
^{0.29 (a 2 / b 2)} (δ F h F 3 -δ L h L 3) = h L 4 {(δ / h L) +0.18 (δ / h L) 3} + h F 4 {( δ / h _F ) +0.18 (δ / h _F ) ³ } (15)
Here, it should be noted that the left side of equation (15) is δ _L , δ _F , and the right side is δ.
From the above calculation, it can be seen that if parameters relating to the warpage of the lenticular lens sheet and the Fresnel lens sheet are used, calculation can be made as one sheet when they are stacked.
In order to suppress the occurrence of phenomenon C, it is desirable that the amount of warpage of the overlapped transmission type screen is within 8 mm, and further within 5 mm. Therefore, the above calculation is performed as one sheet. The amount of warpage is preferably within 8 mm, and more preferably within 5 mm.

(4) Prevention of occurrence of phenomenon D In order to prevent occurrence of phenomenon D, when lenticular lens sheet 1 and Fresnel lens sheet 2 having initial warpage in opposite directions are closely fixed, they are generated between the two. It is desirable to reduce the pressure (unit load).

Subsequently, the lenticular lens sheet 1 and Fresnel lens sheet 2 in close contact and fixed with initial warping [delta] _L, [delta] _F as shown in FIG. 5A, as shown in Figure 5B, as the equilibrium warping [delta] _LF occurs Assume. In this state, the pressure (unit load) generated between the lenticular lens sheet 1 and the Fresnel lens sheet 2 is calculated.

First, an equilibrium warpage δ _LF in a state in which the lenticular lens sheet 1 and the Fresnel lens sheet 2 are closely fixed is calculated.
E _L t _L ³ δ _L + E _F t _F ³ δ _F = (E _L t _L ³ + E _F t _F ³ ) δ _LF (16)

Next, the pressing pressure q generated in the surface is calculated. In general, the equation of deflection of a beam when a uniformly distributed load acts can be expressed as the following equation.
δ = 5qab ⁴ / (384EI _z ) (17)
Here, a is the long side length (mm) of the sheet, which is assumed to be a plate, b is the short side length (mm), E is its elastic modulus (kgf / mm ² ), and I _z is its secondary cross section. It is a moment.

The cross-sectional secondary moment I _z of the plate can be represented by the following equation.
^{_{I z = at 3/12 (}} 18)
Substituting equation (18) into equation (17) yields the following equation:
δ = 60qb ⁴ / 384Et ³ (19)

Since the deflection δ _F is changed to δ _LF by the in-plane pressure q, the following equation can be obtained from the equations (16) and (19).
(Δ _F −δ _LF ) = 60 qb ⁴ / 384E _L t _L ³ (20)

When the equation (20) is modified, the following equation can be obtained, and the pressing pressure q can be obtained from this equation.
q = 384E _L t _L ³ (δ _F −δ _LF ) / 60b ⁴ (21)

  It was confirmed by experiment whether or not the edge crush of phenomenon D occurred when the lenticular lens sheet 1 and the Fresnel lens sheet 2 having initial warpage as shown in FIG. The experimental results are summarized in FIG. In the figure, the row indicates the initial warp amount (deflection amount: mm) of the lenticular lens sheet 1, and the column indicates the initial warp amount (deflection amount: mm) of the Fresnel lens sheet 2. Also, the circle mark indicates that there is almost no crushing of the blade and there is no problem in performance, and the cross mark indicates that the blade crushing occurs and there is a problem in performance. The combination in which no gap was generated is shown. In this example, a combination of shaded regions does not cause the problem of crushing of phenomenon D, and it can be determined that the combination is not a problem in terms of performance.

FIG. 7 is a table showing a calculation image for designing the transmission screen according to the embodiment of the present invention. In the figure, LA is a line indicating the limit where phenomenon A occurs, LB is a line indicating the limit where phenomenon B occurs, LC is a line indicating the limit where phenomenon C occurs, and LD is a line indicating the limit where phenomenon D occurs. The region surrounded by these lines indicates that none of the phenomena A, B, C, and D occurs.
(5) Determining the boundary line of phenomenon D (blade crushing) When the lens sheet shown in the table below is applied to the warp amount list shown in FIG. 7, the influence that the crushing phenomenon causes unevenness in light and darkness cannot be ignored. The range is
q / E _FF = 384 E _L t _L ³ (δ _F −δ _LF ) / (60b ⁴ E _FF )
Where δ _LF = (E _L t _L ³ δ _L + E _F t _F ³ δ _F ) / (E _L t _L ³ + E _F t _F ³ )
Value is 2 × 10 ⁻⁹
Experiments have shown that there is a need for smaller. In particular, when this value is less than 1 × 10 ^{−9, the} crushing phenomenon is hardly noticeable, and when it is less than 0.8 × 10 ^{−9, the} crushing phenomenon is not visible.

フレネルレンズのピッチ０．０６ｍｍ、レンズの先端の角度＝９０〜６０°、レンズ部のヤング率＝２００ｋｇｆ／ｍｍ^２。In the description of the present embodiment, a transmissive screen has been described as an example of an optical sheet for a display device, but the present invention is not limited to this. For example, this invention can also be used for the diffusion sheet used for the backlight of a liquid crystal display device.

Fresnel lens pitch 0.06 mm, lens tip angle = 90-60 °, lens section Young's modulus = 200 kgf / mm ² .

  The present invention can be applied to a technique for preventing the occurrence of display disturbance, blurring of images, pin distortion, and the like in a transmissive display device and a liquid crystal display device.

Claims (9)

An optical sheet for a display device having a front sheet and a lens sheet and fixing both,
Young's modulus of the front sheet E _L, the thickness of the front sheet a _{t L} (mm), the initial warpage of the front sheet of δ _L (mm), the Young's modulus of the lens sheet ^{_{E F (kgf / mm 2)}} , t _F is the thickness of the lens sheet (mm), δ _F is the initial warp amount (mm) of the lens sheet, S is the area of the front sheet (mm ² ), and E _FF is the Young's modulus at −10 ° C. of the lens material ( kgf / mm ² ), an optical sheet for a display device that satisfies the following formula when the positive / negative curvature is positive on the observation side, and the deflection of the optical sheet is 8 mm or less.
E _L t _L ³ δ _L -E _F t _F ³ δ _F > 0
δ _L −δ _F > 0
384E _L t _L ³ (δ _LF −δ _F ) / (60b ⁴ E _FF ) <2 × 10 ⁻⁹
Where δ _LF = (E _L t _L ³ δ _L + E _F t _F ³ δ _F ) / (E _L t _L ³ + E _F t _F ³ )   The optical sheet for a display device according to claim 1, wherein the deflection of the optical sheet is 5 mm or less.   The optical sheet for a display device according to claim 1, wherein the optical sheet for the display device is a transmissive screen, the front sheet is a lenticular sheet, and the lens sheet is a Fresnel lens sheet.   4. The optical sheet for a display device according to claim 3, wherein the lenticular lens sheet is a multilayer plate, and the Fresnel lens sheet is a single layer plate. A method for designing an optical sheet for a display device having a front sheet and a lens sheet, and fixing both,
Young's modulus of the front sheet E _L, the thickness of the front sheet a _{t L} (mm), the initial warpage of the front sheet of δ _L (mm), the Young's modulus of the lens sheet ^{_{E F (kgf / mm 2)}} , t _F is the thickness of the lens sheet (mm), δ _F is the initial warp amount (mm) of the lens sheet, S is the area of the front sheet (mm ² ), and E _FF is the Young's modulus at −10 ° C. of the lens material ( kgf / mm ² ), and the warpage amount is designed so that the following expression is satisfied and the deflection of the optical sheet is 8 mm or less when the concave is positive on the observation side. Design method for optical sheet.
E _L t _L ³ δ _L -E _F t _F ³ δ _F > 0
δ _L −δ _F > 0
384E _L t _L ³ (δ _LF −δ _F ) / (60b ⁴ E _FF ) <2 × 10 ⁻⁹
Where δ _LF = (E _L t _L ³ δ _L + E _F t _F ³ δ _F ) / (E _L t _L ³ + E _F t _F ³ ) A blade generated by the pressure q by obtaining the pressing pressure q between the front sheet and the lens sheet by the following equation, where E is the Young's modulus of the optical sheet, t is the thickness of the optical sheet, and b is the short side length of the optical sheet. 6. The method of designing an optical sheet for a display device according to claim 5, wherein the initial warpage δ _{F of} the lens sheet and the equilibrium warpage δ _LF of the optical sheet are determined so that the collapse phenomenon does not occur.
q = 384 Et ³ (δ _F −δ _LF ) / 60b ⁴   6. The method for designing an optical sheet for a display device according to claim 5, wherein the deflection of the optical sheet is 5 mm or less.   The optical device for a display device according to any one of claims 5 to 7, wherein the optical sheet for the display device is a transmissive screen, the front sheet is a lenticular sheet, and the lens sheet is a Fresnel lens sheet. Sheet design method.   9. The transmissive screen design method according to claim 8, wherein the lenticular lens sheet is a multilayer plate, and the Fresnel lens sheet is a single layer plate.

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