JP2007108507A - Prism sheet and optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prism sheet capable of securing high brightness and a wide viewing angle characteristic while being integrated with a reflective polarization functional film. <P>SOLUTION: In the prism sheet 7 where a plurality of lens units 7a each having a substantially triangular transverse profile, extended in a ridge direction are arranged in parallel on at least one surface, total light transmittance when an optical beam is made incident from the outside surface of the formed surface side of the prism sheet of such a structure that the prism sheet is held between a pair of polarizing sheets arranged in crossed Nicol relation so that the ridge direction accords with the transmission axis of either polarizing sheet to the structure is set to be 2% or less of the total light transmittance of such a structure having a pair of polarizing sheets arranged in parallel Nicol relation that no prism sheet is held therebetween. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a prism sheet and an optical sheet used, for example, in a backlight of a liquid crystal display device, and more specifically, a prism sheet having a structure in which a plurality of lens units having a substantially triangular cross section are arranged side by side, and the prism sheet The present invention relates to an optical sheet using.

  In recent years, color liquid crystal display devices have been widely used in various fields such as monitors for notebook personal computers and desktop personal computers, and liquid crystal televisions (TVs). This type of liquid crystal display device includes a liquid crystal cell and a backlight. Known backlights include a direct type structure in which a light source is provided directly under a liquid crystal cell, or an edge light type structure in which a light source is provided on a side surface of a light guide.

  The general structure of a liquid crystal display device is as follows: a rod-shaped lamp as a light source; (in the case of an edge light system, a rectangular plate-shaped light guide plate arranged so that the end thereof is along the lamp, and the surface of the light guide plate Equipped with multiple optical sheets (laminated on the side) and a liquid crystal cell. Each of the optical sheets has specific optical properties such as refraction and diffusion, and specifically, a light diffusion sheet, a prism sheet, and the like are applicable.

  The color liquid crystal display device is superior in that it consumes less power than the PDP, CRT, or organic EL display device, but the front luminance tends to be low.

  Therefore, it is required to increase the front luminance with less power consumption by increasing optical efficiency with a backlight.

  In general, as the lens unit of the prism sheet, an isosceles triangle is used as the cross-sectional shape and the apex angle, that is, the angle formed between the hypotenuses is 90 °, which is optimal for increasing the luminance. It was thought. It has been considered that the radius of curvature of the top of the lens unit is 0, that is, it is desirable that the top be sharp.

  The prism sheet having the lens unit having such a shape is excellent in the function of condensing incident light from the backlight to the front by refraction and emitting it from the lens surface, and the retroreflection function. The retroreflective function means that a part of the light emitted from the backlight is returned to the backlight by refraction, but by using the recursed light, the light that has not contributed to the improvement of the front brightness is circulated and recirculated. It is a function to be used. However, there is a problem in that the viewing angle range in which the half-value width, that is, the luminance of 50% of the front luminance is obtained becomes narrow, and the viewing angle characteristics are deteriorated.

  That is, when the curvature radius of the top of the lens unit of the prism sheet is 0, that is, when the top is sharpened, the light emitted from the backlight cannot be diffused in the direction other than the front direction, and the viewing angle characteristics tend to be deteriorated. there were.

  Furthermore, in the above conventional optical system, when the light emitted from the prism sheet enters the liquid crystal cell, the amount of transmitted light is reduced by half due to the absorption action of the polarizing plate, and half of the light passing through the liquid crystal cell is reduced by the observer. Since it only contributes to vision, it was a reality that about three-quarters of the total was an optical loss.

For the purpose of improving such optical loss and further increasing the efficiency of light, a configuration in which the front luminance is increased by integrating a prism sheet having a condensing function and a reflective polarizing functional film is disclosed in Patent Document 1 below. It is disclosed. According to this document, about three-quarters of the light component that causes the loss is returned to the backlight side by a brightness-enhanced reflective polarizer (reflective polarizing functional film) and the polarization state is randomized. Therefore, the amount of light is increased by about 70% by this recirculation.
Japanese Patent No. 3448626

  By the way, in the structure of the optical system disclosed in Patent Document 1, the positional relationship of the prism sheet with respect to the reflective polarizing functional film may be on the upper side (liquid crystal cell side, FIG. 10 of the same document), or on the lower side ( It may be on the backlight side, FIG. 13). However, when it is configured on the lower side, it is difficult to integrate it with the reflective polarizing functional film, and it is necessary to adopt a work process of laminating another part, whereas when it is configured on the upper side, the prism sheet is previously formed. Adhering the non-prism surface and the reflective polarizing functional film together has the advantage of simplifying the assembly process. However, it has been found that there are the following problems when it is configured on the upper side. That is, the conventional prism sheet has a structure in which ionizing radiation curable acrylic is cast on a prism mold and polyethylene terephthalate as a base material is laminated and integrated to be cured. As a result of the influence of the polyethylene terephthalate base material that was not achieved and the cooperation of the light collecting function of the prism sheet that was too large, a decrease in the front luminance and a decrease in the half-value width indicating the viewing angle at which 50% of the front luminance was obtained were clarified. . In particular, the latter problem becomes apparent when the visual range moves away from the screen front direction due to the recent increase in the size of liquid crystal screens.

  An object of the present invention is to provide a prism sheet capable of realizing high luminance and a wide viewing angle characteristic even in a state of being integrated on the upper side of the reflective polarizing functional film, An object is to provide an optical sheet using a prism sheet.

  The prism sheet according to the present invention is a prism sheet in which a cross section is substantially triangular and a plurality of lens units having ridge lines extending in a direction orthogonal to the cross section are arranged on at least one surface, and the crossed Nicols relationship In the structure in which the prism sheet is sandwiched between a pair of polarizing plates arranged in such a manner that the ridge line direction coincides with the transmission axis of any polarizing plate, a plurality of lens units of the prism sheet having the structure are provided. T1 is the total light transmittance when light is incident from the outer surface on the side where it is provided, and the total light transmittance of a structure comprising a pair of polarizing plates arranged in a parallel Nicol relationship in which the prism sheet is not sandwiched When T2 is T2, T1 is 2% or less of T2. Preferably, the total light transmittance T1 is 1% or less of the total light transmittance T2.

  In a specific aspect of the prism sheet according to the present invention, the shaping rate in the plurality of lens units is in the range of 50 to 90%, more preferably 60 to 80%.

  In another specific aspect of the prism sheet according to the present invention, the prism sheet is made of an optical transparent resin and is manufactured by a hot melt extrusion method.

  In still another specific aspect of the prism sheet according to the present invention, an apex angle of the lens unit is set in a range of 70 ° to 110 °.

  In still another specific aspect of the prism sheet according to the present invention, the pitch, which is the distance between the apexes of adjacent lens units, is in the range of 20 to 100 μm.

  In still another specific aspect of the prism sheet according to the present invention, the surface roughness of the slope portion of each lens unit is in the range of 0.1 to 5 μm as the surface roughness Ra value according to JIS standard.

  In still another specific aspect of the prism sheet according to the present invention, a standard prism sheet having a thickness of 150 μm, a pitch of 50 μm of lens units, an apex angle of 90 °, and a shaping rate of 95% or more is disposed below the reflective polarizing functional film. Is the front luminance when the prism sheet is arranged so that the non-prism surface faces the reflective polarizing functional film. When B is B, the front luminance reduction rate C obtained by {(AB) / A} × 100 is 5% or less.

  In still another specific aspect of the prism sheet according to the present invention, a standard prism sheet having a thickness of 150 μm, a lens unit pitch of 50 μm, an apex angle of 90 °, and a shaping rate of 95% or more is disposed below the reflective polarizing functional film. When the half-width of the front luminance when arranged so as to face the reflective polarizing functional film is X, the prism sheet is placed above the reflective polarizing functional film so that the non-prism surface faces the reflective polarizing functional film When the half-value width of the front luminance of Y is Y, the half-value width reduction rate Z obtained by {(XY) / X} × 100 is set to 3% or less.

  The optical sheet according to the present invention includes the prism sheet of the present invention and a reflective polarizing functional film bonded to a surface opposite to the shaping surface on which the lens unit of the prism sheet is formed.

  In the prism sheet according to the present invention, the total light transmittance T1 in a structure in which a plurality of lens units extending in a direction perpendicular to the cross section is provided in parallel on at least one surface of the cross section. However, since it is 2% or less of the total light transmittance T2, as will be apparent from specific examples described later, even in a state of being integrated on the upper side of the reflective polarizing functional film, A viewing angle characteristic can be ensured, and a liquid crystal display device with excellent display quality can be provided.

  In the optical sheet according to the present invention, since the reflective polarizing functional film is bonded to the surface opposite to the shaping surface in the prism sheet of the present invention, when used in a liquid crystal display device, high luminance and wide viewing angle characteristics are obtained. Can be obtained.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

  Prior to the description of the prism sheet of the embodiment, a basic configuration of a liquid crystal display device in which the prism sheet of the embodiment is used is schematically shown in an exploded perspective view in FIG.

  The liquid crystal display device shown in FIG. 1 includes a liquid crystal cell 1 and a direct backlight 2. Polarizers 1a and 1b are attached to the upper and lower surfaces of the liquid crystal cell 1, respectively. The backlight 2 has a light source 3. A diffusion plate 4 for diffusing light from the light source 3 is fixed on the upper surface of the light source 3. On the diffusion plate 4, a diffusion sheet 5 having a diffusion function, a reflective polarizing functional film 6 and a prism sheet 7 are laminated as shown in the figure.

  In the backlight 2, the light from the light source 3 enters the diffusion sheet 5 through the diffusion plate 4. The light incident on the diffusion sheet 5 is diffused and emitted from the entire upper surface of the diffusion sheet 5. Light rays emitted from the diffusion sheet 5 pass through the reflective polarizing functional film 6, enter the prism sheet 7, and exit from the upper surface of the prism sheet 7 with an intensity distribution having a peak in a substantially upward direction. Illuminate the entire surface.

  The prism sheet 7 has a structure in which a plurality of convex lens units 7a and 7a extending in one direction are provided in parallel on the upper surface of a sheet-like body. Hereinafter, the surface on which the lens unit 7a is provided, that is, the upper surface is sometimes referred to as a shaping surface. Specifically, as shown in a partially cutaway perspective view in FIG. 2, the lens units 7 a and 7 a have a cross section of a substantially isosceles triangle shape, and have a ridge line extending in a direction orthogonal to the cross section.

  In the present embodiment, the total light transmittance T1 when light is incident from the outer surface on the shaping surface side into the structure in which the prism sheet 7 is sandwiched between a pair of polarizing plates having a crossed Nicols relationship, A value T1 / T2 (%) normalized by the total light transmittance T2 of a structure including a pair of polarizing plates in a parallel Nicol relationship that is not sandwiched is set to 2% or less.

  When T1 / T2 (%) exceeds 2%, the luminance decreases due to optical rotation and stray light in a state where it is integrated with the reflective polarizing functional film. For example, sufficient luminance when mounted on a liquid crystal display device. Can't get. The normalized transmittance ratio T1 / T2 is considered to be related to the optical distortion in the thickness direction of the film, that is, the thickness direction retardation. In the present invention, the normalized transmittance ratio T1 / T2 is 2 % Or less, more preferably 1% or less, so that a large viewing angle and high luminance can be secured.

  In the present embodiment, the apex angle θ of the isosceles triangle shown in FIG. 2 is preferably in the range of 70 to 110 °. If it is out of this range, sufficient luminance cannot be secured.

  The distance between the apexes between adjacent lens units 7a, 7a, that is, the groove pitch ΔW is preferably set in the range of 20 to 110 μm. If it is less than 20 μm, it is practically difficult to manufacture. If it exceeds 110 μm, it may interfere with the pixels of the liquid crystal cell or the color filter to cause moire, resulting in poor appearance.

  In the present embodiment, the shaping rate is set in the range of 50 to 90% in order to increase the half width and widen the viewing angle. Here, the shaping rate is the ratio of the actual height of the lens unit 7a to the height of the lens unit 7a when the radius of curvature of the apex is zero.

  When the shaping rate exceeds 90%, the front luminance increases, but the half width decreases and the viewing angle may become narrow. When the shaping rate is less than 50%, the viewing angle increases but the luminance increases. May decrease. Therefore, when the shaping rate is in the range of 50 to 90%, the front luminance is high, the half width is large, and a sufficient viewing angle can be realized. In the case of 60 to 80%, more Higher luminance and wide viewing angle characteristics can be ensured.

  Further, since the half width can be increased and the viewing angle can be widened, the radius of curvature r of the apex of the lens unit 7a is preferably in the range of 2 to 10 μm.

  In addition, in order to increase the half width and widen the viewing angle, the pair of inclined surfaces of the lens unit is provided with surface roughness, and preferably the average roughness Ra value of JIS B 0601 is 0. A surface roughness of 1 to 5 μm or less is given. When the surface roughness Ra is in the range of 0.1 to 5 μm, the front luminance can be sufficiently increased. When the surface roughness Ra exceeds 5 μm, the front luminance may be lowered. More preferably, the thickness is in the range of 0.3 to 4 μm, whereby the front luminance can be further increased.

  Further, a standard prism sheet 7 having a thickness of 150 μm, a lens unit pitch of 50 μm, an apex angle of 90 °, and a shaping rate of 95% or more is disposed below the reflective polarizing functional film so that the prism surface faces the reflective polarizing functional film. When the front luminance is A, and the front luminance when the prism sheet 7 is disposed above the reflective polarizing functional film so that the non-prism surface faces the reflective polarizing functional film is B, {(AB ) / A} × 100, the front luminance reduction rate C is preferably set to 5% or less, whereby high front luminance can be secured, and the prism sheet is arranged on the backlight side of the reflective polarizing film. Compared with the front luminance, it is possible to achieve inferior brightness.

  Also, a standard prism sheet 7 having a thickness of 150 μm, a lens unit pitch of 50 μm, an apex angle of 90 °, and a shaping rate of 95% or more is disposed below the reflective polarizing functional film so that the prism surface faces the reflective polarizing functional film. When the half-value width of the front luminance is X and the half-value width of the front luminance when the non-prism surface is arranged so that the non-prism surface faces the reflective polarizing functional film is set to Y above the reflective polarizing functional film , {(X−Y) / X} × 100 is preferable to set the full width at half maximum reduction Z obtained within 3%. Thereby, a large half-value width can be secured, and a front luminance comparable to that of the configuration in which the prism sheet is disposed on the backlight side of the reflective polarizing film can be achieved.

  In the present invention, the prism sheet may be composed of one type of resin or a plurality of resins, but is preferably formed of a single layer.

  As a method for producing the prism sheet 7, for example, a melt extrusion method or a solution casting method can be adopted. In addition, the prism sheet 7 is engraved using a surface engraved with a pattern opposite to the prism shape on the press die surface. A molding method, a method of molding by injection molding, and the like can be used. As a method of roughening the prism-shaped slope, the surface of the press mold is given a roughness by sandblasting, and this is transferred, or the surface of the press mold is processed by lithography, etching, plating, etc. The method of giving and transferring this is mentioned. From the viewpoint of the accuracy of the prism shape and the production of the press mold, a method of imparting roughness by treating the surface of the press mold is preferable.

  Further, in the present invention, when the prism sheet is a transparent resin for optics and is produced by a hot melt extrusion method, it is possible to achieve even higher brightness, and easily and accurately by the hot melt extrusion method. A shaping surface can be formed and sufficient display quality can be obtained.

  In the melt extrusion method, as shown in the schematic configuration diagrams of FIGS. 3 and 4, after the molten resin is extruded into a sheet form from the T-type dies 11 and 21, the shaping rolls 12 and 22 and the metal elastic deformation roll 13 are used. Alternatively, the metal sheet 23 is clamped, and after clamping, the prism sheet original fabric A is quickly cooled to a glass transition temperature Tg or lower. Next, the prism sheet original fabric A is cooled by passing through the first and second annealing rolls 14, 24, 15, 25 having a mirror surface and a temperature control function, thereby preventing curling and remaining due to thermal stress. Remove distortion. Thereafter, the prism sheet original fabric A is wound around the winders 16 and 26.

  As the pinching roll, the metal elastic deformation roll 13 is used in the apparatus shown in FIG. 3, whereas the metal roll 23 is used in the manufacturing apparatus shown in FIG. ing.

  If the cooling after clamping is insufficient and the temperature of the prism sheet original fabric A is equal to or higher than the glass transition temperature Tg, the resin is not allowed to pass through the first and second annealing rolls 14, 24, 15 and 25. Molecular orientation is caused in the flow direction, resulting in a large optical distortion in the film plane.

  For this reason, since the behavior of the resin changes greatly in the vicinity of the glass transition temperature Tg of the resin, it is desirable that the cooling temperature after clamping is set to be 10 ° C. or more lower than the glass transition temperature Tg, and more preferably 20 ° C. or lower. Thereby, the behavior of the resin can be stabilized and the molecular orientation in the flow direction can be suppressed.

  As described above, the prism sheet manufactured using the polycarbonate resin by the melt extrusion method can reduce the optical distortion in the film plane without requiring a special manufacturing process.

  However, the cooling after the pinching can be performed more efficiently by using the metal elastic deformation roll 13 shown in FIG. 3 than the metal roll 23 in the apparatus shown in FIG. However, when the metal elastic deformation roll 13 is used, the clamping time is longer than that of the metal roll 23, so that the cooling effect on the resin is increased. When the resin is rapidly cooled by the metal elastic deformation roll 13, the resin is cooled and solidified before the stress applied to the resin is relieved by shaping, and residual strain due to residual stress remains in the lens unit. This is considered to increase the optical distortion in the thickness direction.

  For this reason, the prism sheet 6 manufactured by the apparatus shown in FIG. 4 is more advantageous in reducing the optical distortion in the thickness direction than the case where the prism sheet 6 is manufactured by the apparatus shown in FIG.

  In addition, although the material which comprises the prism sheet which concerns on this invention is not specifically limited, Preferably, resin excellent in transparency and a moldability, for example, a polycarbonate-type resin, a thermoplastic saturated norbornene-type resin etc. can be mentioned.

  The polycarbonate resin is obtained, for example, by reacting a dihydric phenol and a carbonate precursor by an interfacial polymerization method or a melt polymerization method.

  The molecular weight of the polycarbonate resin is preferably 10,000 to 100,000, more preferably 15,000 to 35,000 in terms of viscosity average molecular weight (M). A polycarbonate resin having such a viscosity average molecular weight is preferable because sufficient strength is obtained and the melt fluidity during molding is good.

  The thermoplastic saturated norbornene resin is, for example, (i) a ring-opening polymer or ring-opening copolymer of a norbornene monomer, which is subjected to hydrogenation after modification such as maleic acid addition or cyclopentadiene addition as necessary. (B) a resin obtained by addition polymerization of a norbornene monomer, (c) a resin obtained by addition polymerization with a norbornene monomer and an olefin monomer such as ethylene or α-olefin, (d) a norbornene monomer and cyclopentene, cyclohexane Examples thereof include resins obtained by addition polymerization with cyclic olefin monomers such as octene and 5,6-dihydrodicyclopentadiene, and modified products of these resins.

  The thermoplastic saturated norbornene-based resins are marketed by ZEON Corporation under the trade names “ZEONOR” and “ZEONEEX”, JSR Corporation under the trade name “ARTON”, and Mitsui Chemicals under the trade name “APEL”.

  When the number average molecular weight of the thermoplastic saturated norbornene resin is small, the moisture resistance decreases and the moisture permeability increases, and when the number average molecular weight is large, the film formability is deteriorated, so that gel permeation chromatography with toluene or an appropriate solvent is used. When measured, it is preferably 25,000 to 100,000, more preferably 30,000 to 80,000. Use of the norbornene-based resin is preferable because the melt fluidity during molding is good.

  Further, in the optical sheet according to the present invention, a reflective polarization functional film is bonded to the surface opposite to the lens unit forming surface of the prism sheet, but this reflective polarization functional film is not limited as long as it can fulfill its function, For example, it can be formed by a structure in which two types of transparent resins are alternately laminated in a plurality of layers, for example, several hundred layers.

(Examples and Comparative Examples)
As resin materials for the prism sheets according to Examples 1 to 4 and the prism sheets according to Comparative Examples 1 to 3, polycarbonate resin (manufactured by Teijin Chemicals Ltd., Panlite 1225LL) was used.

  The prism sheet which concerns on Examples 1-4 was manufactured using the manufacturing apparatus shown in FIG.

  The T-type die 21 had a surface length of 700 mm, the metal roll 23 had a mirror surface with a diameter of 250 mm, and the first annealing roll 24 and the second annealing roll 25 had a diameter of 250 mm and had a mirror surface. The shaping roll 22 has a diameter of 250 mm, a plurality of V-grooves having a substantially right-angled isosceles triangle shape on the outer peripheral surface, and subjected to surface treatment by the processing method described in Table 1. Using.

  The dimensions of the original prism sheet wound by the winder 26 are 650 mm in width and 150 μm in thickness.

  The thickness of the original prism sheet is preferably 50 to 300 μm, more preferably 50 to 250 μm, and still more preferably 100 to 250 μm. When the thickness is less than 50 μm, the lens unit 7a is easily curled. On the other hand, when the thickness exceeds 300 μm, the transfer rate to the resin due to molding may be reduced, and the luminance may be reduced. is there.

  The basic conditions were as follows. After extruding the molten resin into a sheet form from the T-type die 21 at an extrusion rate of 100 kg / hour, it is sandwiched between the shaping roll 22 and the metal roll 23 cooled to 10 ° C., and the temperature of the original prism sheet is changed to the glass transition temperature. After the temperature was lowered to Tg or less, the first annealing roll 24 at 135 ° C. was passed, and the second annealing roll 25 at 95 ° C. was passed immediately after that, and wound by the winder 26. At this time, the roll speed of the winder 26 was 26 m / min, and the speed ratio between the rolls was 1.0. In addition, the prism sheets of Examples 1 to 4 were manufactured by changing the clamping pressure so as to satisfy the specific conditions.

  The prism sheets of Comparative Examples 1 to 3 were manufactured using the manufacturing apparatus shown in FIG. The manufacturing conditions in this case were the same as those in Example 1 except that the manufacturing conditions deviated from the specific conditions.

  Then, the geometric conditions in the prism sheet 6 according to Examples 1 to 4 and the prism sheets according to Comparative Examples 1 to 3, that is, the groove pitch ΔW, the apex angle θ, and the shaping rate are as shown in Table 1 below. .

  The prism sheet original fabrics of Examples 1 to 4 and Comparative Examples 1 to 3 manufactured as described above were cut to a predetermined length, and T1 / T2, shaping rate, and slope roughness were measured. Also, using a prism sheet obtained by cutting, adhesive, and DBEF (Dual Brightness Enhancement Film, thickness 130 μm) manufactured by Minnesota Mining & Manufacturing Co., Ltd. The front luminance and the half-value width were evaluated in the state of the obtained laminated body. The results are shown in Table 1 below.

  Each item was measured as described in the following (1) to (5).

(1) T1 / T2
Polarization so that the transmission axes of two polarizing plates are perpendicular to each other (the transmission axis of the front polarizing plate is the horizontal direction and the other polarizing plate is the vertical direction), and the ridge line direction of the prism sheet is the vertical direction The total light transmittance T1 was measured with a haze meter (TC-HIII DPK manufactured by Tokyo Denshoku Co., Ltd.) when a light beam was incident from the shaping surface after being sandwiched between the plates. In addition, the total light transmittance of a structure composed of a pair of polarizing plates arranged in parallel Nicols (both of which has a transmission axis in the vertical direction) without sandwiching the prism sheet was measured as T2.

(2) Forming rate Carbon is applied to the cross section of the prism sheet cut by a microtome, the cross section is observed with a scanning electron microscope (S-4300SE / N) manufactured by Hitachi, Ltd., and the groove pitch ΔW, prism height h The apex angle θ was determined. From these values, the shaping rate was determined by the following equation.

Forming rate = h / (ΔW / 2) tan (θ)
(3) Slope roughness The prism shape was measured with a scanning laser microscope (1LM21W) manufactured by Lasertec Corporation, and the surface roughness (Ra) of the slope was calculated with data analysis software. The 100 μm pitch was calculated with an average of two peaks, and the 50 μm pitch was calculated with an average of five peaks.

(4) Front brightness A prism sheet to be measured, which is cut into 300 mm length and 400 mm width on a direct type backlight provided in a commercially available 20-inch liquid crystal television, the ridgeline direction of the lens is the horizontal direction of the screen (horizontal direction) The front luminance was measured with a luminance meter LS-100 manufactured by Konica Minolta through a liquid crystal cell.

(5) Half width The half width is a viewing angle range in which 50% of the luminance in the normal direction with respect to the display surface is obtained. In addition to the configuration described in the previous section, a luminance meter is attached to a stage that can be moved in the horizontal direction, and the luminance is measured in increments of 5 ° in the range of −70 ° to 70 ° in the horizontal direction. Printed. The printed result was graphed, and an angle that was half the front luminance was calculated.

  In order to investigate the influence of the optical distortion of the prism sheet, (4) Front luminance and (5) Half width are about 100 μm prism pitch, 90 ° apex angle, and shaping rate manufactured using the manufacturing apparatus shown in FIG. The luminance in the normal direction and the half width at the time of arranging DBEF manufactured by Minnesota Mining & Manufacturing Co., Ltd. as a reflective polarizing functional film on a 95% prism sheet were used as reference values. That is, with respect to the luminance and half-value width as the reference values, the luminance and half-width reduction rates actually measured as described above were obtained and are shown in Table 1 below. The luminance reduction rate and the half-value width reduction rate obtained in this way are the luminance reduction rates C (%) and {(XY) / X} obtained by {(AB) / A} × 100 described above. This corresponds to the full width at half maximum reduction Z (%) obtained by × 100.

  As shown in Table 1, in the prism sheet 7 according to Examples 1 to 4, T1 / T2 can be reduced compared to the prism sheets according to Comparative Examples 1 to 3, and high front luminance can be ensured. It can be seen that a wide half-value width can be secured by setting the shaping rate to 50 to 90%.

  That is, by setting T1 / T2 to 2% or less, or the shaping rate to 50 to 90%, it is possible to keep the luminance reduction rate C within 5% and the half-value width reduction rate Z within 3%. Even if it compares with the structure which arrange | positions this prism sheet below, it turns out that the display performance which is not inferior is obtained in the prism sheet 7 which concerns on Examples 1-4.

1 is an exploded perspective view schematically showing a liquid crystal display device using a prism sheet according to the present invention. The partial notch expansion perspective view which shows a part of prism sheet concerning one Embodiment of this invention. The schematic block diagram which shows the manufacturing apparatus for manufacturing the prism sheet as a comparative example of this invention. The schematic block diagram which shows the manufacturing apparatus for manufacturing the prism sheet which concerns on embodiment shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal cell 1a, 1b ... Polarizing plate 2 ... Back light 3 ... Light source 4 ... Diffusion plate 5 ... Diffusion sheet 6 ... Reflective polarization functional film 7 ... Prism sheet 7a ... Lens unit

Claims (11)

A prism sheet in which the cross section is substantially triangular, and a plurality of lens units having ridge lines extending in a direction orthogonal to the cross section are arranged on at least one surface,
In a structure in which the prism sheet is sandwiched between a pair of polarizing plates arranged in a crossed Nicol relationship so that the ridge line direction coincides with the transmission axis of any polarizing plate, a plurality of prism sheets of the structure T1 is the total light transmittance when light is incident from the outer surface on the side where the lens unit is provided, and the entire structure is composed of a pair of polarizing plates arranged in a parallel Nicol relationship in which the prism sheet is not sandwiched. A prism sheet, wherein T1 is 2% or less of T2 when the light transmittance is T2.   The prism sheet according to claim 1, wherein the total light transmittance T1 is 1% or less of the total light transmittance T2.   The prism sheet according to claim 1 or 2, wherein a shaping rate in the plurality of lens units is in a range of 50 to 90%.   The prism sheet according to claim 3, wherein the shaping rate is in a range of 60 to 80%.   The prism sheet according to any one of claims 1 to 4, wherein the prism sheet is made of a transparent resin for optics and is produced by a hot melt extrusion method.   The prism sheet according to any one of claims 1 to 5, wherein an apex angle of a cross section of the lens unit is set in a range of 70 ° to 110 °.   The prism sheet according to any one of claims 1 to 6, wherein a pitch, which is a distance between apexes of adjacent lens units, is in a range of 20 to 100 µm.   The prism sheet according to any one of claims 1 to 7, wherein a surface roughness of the slope portion of each lens unit is in a range of 0.1 to 5 µm in terms of a surface roughness Ra value according to JIS standards.   A front surface when a standard prism sheet having a thickness of 150 μm, a lens unit pitch of 50 μm, an apex angle of 90 °, and a shaping rate of 95% or more is arranged below the reflective polarizing functional film so that the prism surface faces the reflective polarizing functional film. When the luminance is A, the front luminance when the non-prism surface is arranged to face the reflective polarizing functional film above the reflective polarizing functional film and B is B (A−B) / A } The prism sheet according to any one of claims 1 to 8, wherein a front luminance reduction rate C obtained by × 100 is 5% or less.   A front surface when a standard prism sheet having a thickness of 150 μm, a lens unit pitch of 50 μm, an apex angle of 90 °, and a shaping rate of 95% or more is arranged below the reflective polarizing functional film so that the prism surface faces the reflective polarizing functional film. When the half value width of the luminance is X, the half value width of the front luminance when the non-prism surface is arranged so as to face the reflective polarizing functional film above the reflective polarizing functional film, and Y is {( 9. The prism sheet according to claim 1, wherein a half-value width reduction rate Z obtained by X−Y) / X} × 100 is 3% or less. A prism sheet according to any one of claims 1 to 10, and a reflective polarizing functional film bonded to a surface opposite to the shaping surface on which the lens unit of the prism sheet is formed. A featured optical sheet.

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