JP2012053282A - Method for manufacturing optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical sheet capable of performing a uniform evaluation by reducing the manhour for evaluating color irregularity.SOLUTION: The method for manufacturing a prism sheet 16 having a surface 16a on which a plurality of convex unit prisms 16d are disposed includes a first determination step and a second determination step. In the first determination step, when in-plane phase difference average value (nm)/(in-plane phase difference variation (nm)×sheet thickness average value (mm))≥10(nm/mm), the color irregularity of the prism sheet 16 is evaluated to be acceptable and, when in-plane phase difference average value (nm)/(in-plane phase difference variation (nm)×sheet thickness average value (mm))<10(nm/mm), the prism sheet 16 is rejected. In the second determination, an evaluation is made on the optical sheets evaluated in the first determination step and, when a dimension of a variation rate (nm/nm) of the in-plane phase difference to a variation rate (μm/μm) of the sheet thickness is less than a prescribed value that is set in response to a visual evaluation, the optical sheet is evaluated as a conforming unit.

Description

  The present invention relates to a method for producing an optical sheet used in a surface light source device or the like.

Conventionally, there has been an optical sheet used for an electro-optical device or the like (for example, Patent Document 1) including a surface light source device and formed by extrusion molding (for example, Patent Document 2).
However, the conventional optical sheet takes man-hours to evaluate the color unevenness by the evaluator, and when the evaluator is different, variations in the color unevenness evaluation occur, so that a uniform evaluation cannot be performed.

JP 2004-117062 A Japanese Patent No. 3585412

  The subject of this invention is providing the manufacturing method of the optical sheet which can reduce the man-hour of evaluation of color nonuniformity, can perform uniform evaluation, and can evaluate color nonuniformity based on an in-plane phase difference further.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this. In addition, the configuration described with reference numerals may be improved as appropriate, or at least a part thereof may be replaced with another configuration.

In the first invention, at least a plurality of convex unit optical shapes are arranged on the surface, a light source is arranged on the back side, which is a surface opposite to the surface side, and light rays of the light source are incident from the back side. A method for manufacturing an optical sheet arranged to emit light, wherein the average value of in-plane retardation (nm) / (in-plane retardation variation (nm) × average value of sheet thickness (mm)) ≧ 10 ( nm / mm), and the average value of in-plane retardation (nm) / (in-plane retardation variation (nm) × average thickness of sheet (mm)) <10 (nm / mm) It is a manufacturing method of an optical sheet characterized by including the 1st judgment process which evaluates the color nonuniformity of an optical sheet as failure in some cases.
According to a second invention, in the optical sheet manufacturing method according to the first invention, the optical sheet evaluated in the first determination step has a size of the variation ratio of the in-plane retardation with respect to the variation ratio of the sheet thickness. A method for producing an optical sheet, comprising: a second determination step for evaluating color unevenness based on the degree.
According to a third aspect of the present invention, there is provided the optical sheet manufacturing method according to the second aspect, wherein the second determination step includes a variation ratio (μm / μm) of the sheet thickness of the variation ratio (nm / nm) of the in-plane retardation. ) Is evaluated as a non-defective product if the optical sheet is less than a predetermined value set in association with visual evaluation.
According to a fourth invention, in the optical sheet manufacturing method according to the third invention, in the second determination step, an optical sheet having a constant value set in association with the visual evaluation is 7 and less than 7, This is a method for producing an optical sheet, characterized in that
According to a fifth invention, in the optical sheet manufacturing method according to the fourth invention, in the second determination step, the numerical value set in association with the visual evaluation is 10 or less for a sheet larger than 7. A method for producing an optical sheet, comprising the step of further selecting an optical sheet and an optical sheet larger than 10.
According to a sixth invention, in the optical sheet manufacturing method according to any one of the second to fifth inventions, in the second determination step, the sheet thickness of the variation ratio (nm / nm) of the in-plane retardation. An optical sheet comprising a visual determination step in which an inspector visually evaluates the optical sheet having a size with respect to a variation rate (μm / μm) of a certain value or more set in association with visual evaluation. It is a manufacturing method.

According to the present invention, the following effects can be obtained.
In the first invention, in the first determination step, the color of the optical sheet is based on the average value of in-plane retardation (nm) / (in-plane retardation variation (nm) × average value of sheet thickness (mm)). Evaluate unevenness. For this reason, since an optical sheet can be evaluated using a measuring device, color unevenness can be evaluated without using visual observation. Thereby, the man-hour in a manufacturing process can be reduced, and it can evaluate uniformly, without the dispersion | variation that a judgment differs for every evaluator.
In the second invention, the optical sheet evaluated in the first determination step is evaluated in the second determination step based on the magnitude of the variation rate of the in-plane retardation relative to the variation rate of the sheet thickness. The optical sheets selected in one determination step can be further ranked and evaluated.

In the third invention, in the second determination step, the size of the variation rate of the in-plane retardation (nm / nm) with respect to the variation rate of the sheet thickness (μm / μm) is set in association with the visual evaluation. Since those less than a certain value are evaluated as non-defective products, visual evaluation of optical sheets determined as non-defective products is unnecessary, and the number of steps in the manufacturing process can be further reduced.
In the fourth invention, in the second determination step, an optical sheet having a constant value set in association with visual evaluation of less than 7 can be handled as a non-defective product.

According to a fifth aspect of the present invention, in the second determination step, an optical sheet whose numerical value set in association with visual evaluation is 10 or less and an optical sheet greater than 10 are further selected with respect to a sheet larger than 7. Therefore, it can be further finely selected according to the degree of color unevenness.
In a sixth aspect of the invention, in the second determination step, the inspector provides an optical sheet having a constant value with respect to the variation rate (μm / μm) of the variation rate of the in-plane retardation (nm / nm) to the variation of the sheet thickness. A visual judgment step for visual evaluation is provided. For this reason, since the sheet | seat determined to be non-defective in the 1st determination process can be ranked and the optical sheet with a low rank can be determined visually, it can contribute to the fall of defect generation | occurrence | production. Even in this case, since the number of optical sheets that must be visually determined can be minimized, an increase in man-hours due to visual evaluation can be minimized.

It is a figure explaining the display apparatus 1 of embodiment. It is the figure which expanded a part of cross section when the unit prism 16d of embodiment is seen from the left-right direction X. It is a figure explaining molding device 20 of an embodiment. It is a figure which expands and shows a part of molding apparatus 20 of an embodiment. It is a figure explaining the shaping | molding apparatus 120 of a comparative example. It is a figure explaining the comparative experiment of the prism sheet 16 manufactured with the molding apparatus 20 of embodiment, and the prism sheet 116 manufactured with the molding apparatus 120 of the comparative example. It is a table | surface explaining the comparison of the molding rate of the prism sheet 16 manufactured with the shaping | molding apparatus 20 of embodiment, and the prism sheet 116 manufactured with the shaping | molding apparatus 120 of the comparative example, in-plane phase difference variation, and shrinkage expansion coefficient.

(Embodiment)
Embodiments of the present invention will be described below with reference to the drawings.
In addition, each figure shown below is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
In addition, the terms “plate”, “sheet”, “film”, etc. are used, but these are generally used in the order of “thickness”, “plate”, “sheet”, and “film”. Are used. However, since there is no technical meaning for such proper use, the description in the scope of claims is used in a unified manner by the description of sheet. Accordingly, the terms “sheet”, “plate”, and “film” can be appropriately replaced. For example, the optical sheet may be an optical film or an optical plate.
Numerical values such as dimensions and material names of the respective members described in the present specification are examples of the embodiment, and the present invention is not limited thereto, and may be appropriately selected and used.

FIG. 1 is a diagram illustrating a display device 1 according to an embodiment.
In the following description, in the state where the normal direction N of the display screen of the display device 1 is oriented in the horizontal direction, the horizontal direction of the display screen is X, the observation direction is Y (front side Y1, back side Y2), The vertical direction will be described as Z. The left-right direction X, the observation direction Y, and the vertical direction Z are directions orthogonal to each other.
The display device 1 includes an LCD (Liquid Crystal Display) panel 2 (a transmissive display unit) and a surface light source device 10 disposed on the back side Y2. The display device 1 is a device that illuminates the back surface of the LCD panel 2 with the surface light source device 10 and observes information displayed on the LCD panel 2 from the front side Y1 of the LCD panel 2.

  The LCD panel 2 is formed of a transmissive liquid crystal display element, and displays, for example, a diagonal of 32 inches (effective screen 698 mm × 393 mm) and resolution 1920 × 1080 dots. The LCD panel 2 is disposed on the front side Y1 of the polarization reflection sheet 17, that is, on the front side Y1 (front surface 16a side) of the prism sheet 16.

In the surface light source device 10, a reflection plate 12, an arc tube 13 (light source), a milky white plate 14, a prism sheet 16 (optical sheet), and a polarization reflection sheet 17 are laminated from the back side Y <b> 2.
The reflecting plate 12 is a sheet that reflects the light emitted toward the back side Y2 among the light emitted by the arc tube 13 toward the front side Y1. The reflector 12 is provided on the entire back side Y2 (back side) of the arc tube 13, diffusely reflects the illumination light traveling to the back side Y2, and is directed toward the milky plate 14 on the near side Y1 (outgoing side). In order to make the incident light illuminance to the milky white plate 14 uniform.
The arc tube 13 is a light source unit of the surface light source device 10 and is, for example, a cold cathode tube. The arc tube 13 is arranged such that the longitudinal direction is the left-right direction X. In the embodiment, the plurality of arc tubes 13 are arranged in the vertical direction Z.
Instead of the arc tube 13, for example, a point light source such as an LED (Light Emitting Diode) may be used, or a surface light source such as an organic EL (Electro Luminescence) or an inorganic EL may be used.
The milky white plate 14 is a diffusion plate having non-directional light diffusion characteristics.

  The prism sheet 16 is an optical sheet that condenses and diffuses the light emitted from the arc tube 13 within a predetermined viewing angle range. The prism sheet 16 has a back surface 16b which is a surface on the back side Y2 (back surface side) formed in a planar shape, and light rays of the arc tube 13 are incident from the back surface 16b, and a surface 16a (sheet surface) which is a surface on the near side Y1. It comes out from. That is, the prism sheet 16 has the back surface 16b as an incident surface and the surface 16a as an output surface.

The prism sheet 16 has an optical shape portion 16c on the surface 16a.
The optical shape portion 16 c is formed on the surface 16 a of the prism sheet 16. The optical shape portion 16c is formed by arranging a plurality of unit prisms 16d (unit optical shapes).
The unit prism 16d has a triangular prism shape formed in a convex shape on the surface 16a. A plurality of unit prisms 16d are arranged in the vertical direction Z.
In the embodiment, the back surface 16b is an example having a planar shape, but may include a mat surface and an optical shape portion as necessary.
Details of the prism sheet 16 will be described later.

  The polarization reflection sheet 17 has an action of transmitting only light in a specific polarization state and reflecting light in other polarization states, and is disposed between the LCD panel 2 and the prism sheet 16. It has the effect of increasing brightness without narrowing the corners. In this embodiment, it is DBEF (made by Sumitomo 3M Co., Ltd.), and its thickness is 0.4 mm.

FIG. 2 is an enlarged view of a part of a cross section when the unit prism 16d of the embodiment is viewed from the left-right direction X. FIG.
In FIG. 2, the front side Y1 is illustrated on the upper side of the drawing so that the vertical direction Z is the left-right direction of the drawing.
As shown in FIG. 2 (a), the unit prism 16d has a cross-sectional shape having a vertex 16e with an apex angle α of 90 °, and a rectangular shape with a convex exit side (LCD panel 2 side) which is the front side Y1. It is an equilateral triangle or a substantially right isosceles triangle.
The prism sheet 16 has better optical characteristics as the shape of the top portion 16e of the unit prism 16d is formed into a square shape. That is, the higher the forming rate by the mold 16g for manufacturing the prism sheet 16, the higher the light collection effect by the unit prism 16d and the higher the front luminance.

On the other hand, as shown in FIG. 2B, when the shape of the mold is not 100%, the top portion 16f becomes a curved surface, and the optical characteristics deteriorate.
In the embodiment, as will be described later, by using the molding apparatus 20, the molding rate of the unit prism 16d having a shape described later can be set to 100%, and the optical characteristics can be improved.

The forming rate (%) is represented by “(h / H) × 100”.
That is, the shaping rate is the ratio of the height h of the unit prism 16d actually formed to the height H of the mold 16g (the height from the tops 16e, 16f to the valley bottom v in the depth direction Y).

Drawing 3 is a figure explaining molding device 20 of an embodiment.
FIG. 4 is an enlarged view showing a part of the molding apparatus 20 of the embodiment.
The molding apparatus 20 is a sleeve-type manufacturing apparatus that manufactures the prism sheet 16 by extruding a thermoplastic resin into a sheet shape and molding a unit optical system to the sheet material.

As shown in the partially enlarged view of FIG. 3, the shaping sheet 21 is a sheet in which an uneven shape mold for shaping the unit prism 16 d is formed on the surface 21 a. As shown by a two-dot chain line in FIG. 4, the uneven shapes are arranged side by side in the width direction 21 d (TD direction) orthogonal to the feeding direction 21 b (MD direction) of the shaping sheet 21. That is, the uneven ridge line is parallel to the feed direction 21b. The shaping sheet 21 is formed of a UV prism sheet, that is, an ultraviolet curable resin, and has a smaller heat capacity than a metal or the like.
The molding apparatus 20 includes an extruder 22, a die 23, a shaping sheet feeding unit 30, a belt pressure feeding unit 40, and a prism sheet winding unit 50.

The extruder 22 is a device that heats and melts the thermoplastic resin supplied from the hopper 22a and extrudes it from the die 23 provided at the tip.
In the embodiment, since the resin material is a polycarbonate resin and the glass transition point is about 145 ° C., the extruder 22 is heated to about 280 ° C. The extruder 22 melts and heats the resin material, and processes and extrudes the sheet material 24 from the die 23 provided at the tip.
The shape of the opening of the die 23 is a rectangle, and its short side is a little larger than the thickness of the prism sheet 16 because it is pressure-molded in a later process, and its long side is the width of the prism sheet 16 (see FIG. 1 and the length in the vertical direction Z shown in FIG.

The shaped sheet feeding unit 30 is a device for feeding the shaped sheet 21 in the feeding direction 21b.
The shaped sheet feeding unit 30 includes a sheet supply roll unit 31, a first feed roll 32, a second feed roll 33, a third feed roll 34, a separation roll unit 36, and a sheet take-up roll 37. They are arranged in this order in the feeding direction 21 b of the shaping sheet 21.
The sheet supply roll unit 31 is a part that supplies the shaping sheet 21. The sheet supply roll unit 31 rotatably supports the shaping sheet 21 wound in a roll shape.

The first feed roll 32 is a roll around which the shaping sheet 21 supplied from the sheet supply roll unit 31 is wound first.
The shaping sheet 21 and the prism sheet 16 fed from the first feeding roll 32 are wound around the second feeding roll 33 and the third feeding roll 34.
A cooling pipe (not shown) is passed through the first feed roll 32, the second feed roll 33, and the third feed roll 34, and the shaping sheet 21 and the sheet-like member 24 (prism sheet 16) The temperature can be adjusted. The temperature adjustment of the first feed roll 32 is mainly for the temperature adjustment of the shaping sheet 21 and the sheet-like member 24 at the time of molding, while the temperature adjustment of the second feed roll 33 and the third feed roll 34 is performed. Is for adjusting the warp of the prism sheet 16 to be manufactured.
The first feed roll 32, the second feed roll 33, and the third feed roll 34 are provided with a speed adjustment mechanism (not shown), and the first feed roll 32 is set on the basis of the set speed of the first feed roll 32. The speeds of the 2-feed roll 33 and the third-feed roll 34 can be adjusted. This speed adjustment is mainly for adjusting the tension of the shaping sheet 21 and the sheet-like member 24, and for adjusting warpage and distortion (phase difference). The speed adjustment of the second feed roll 33 is also performed for peeling adjustment and the like.
The separation roll unit 36 is a roll that separates the shaping sheet 21 and the prism sheet 16 and releases them. The separation roll unit 36 distributes the shaping sheet 21 to the sheet take-up roll 37, while distributing the prism sheet 16 to the prism sheet take-up unit 50.

  The sheet take-up roll 37 is a roll that takes up the shaping sheet 21 sent from the separation roll unit 36. The sheet take-up roll 37 is driven to rotate by a driving device (not shown) to take up the shaped sheet 21. In addition, when the sheet take-up roll 37 is rotationally driven, the shaped sheet feeding unit 30 can feed the shaped sheet 21 in the feeding direction 21b.

As shown in FIG. 4, the belt pressure feeding unit 40 is a device that rotationally drives the sleeve belt 41. The sleeve belt 41, a rubber roller 42 around which the sleeve belt 41 is wound, a first metal roller 43, and a second metal And a roller 44.
The sleeve belt 41 is a belt formed of a Ni alloy. Thus, the reason for using a metal belt for the sleeve belt 41 is that the heat conduction is good and the elongation is small even when a tension is applied. For example, in the case of a rubber belt, heat conduction is poor, and even if cooling is performed by the rubber roller 42, the first metal roller 43, and the second metal roller 44, the sleeve temperature continues to rise, causing a peeling failure. Since the elongation is large, it is stretched and tension is not stable when tension is applied. In contrast, the metal belt can solve such a problem.
Further, when using a metal belt, the finishing accuracy (dimensional accuracy) can be improved and the durability can be improved because the elongation is less than that of a rubber belt.

The rubber roller 42 and the first metal roller 43 are added by sandwiching the sheet-like member 24 between the sleeve belt 41 stretched between them and the shaping sheet 21 wound around the first feed roll 32. It arrange | positions so that it can press (refer the dashed-two dotted line shown in FIG. 4).
That is, the rubber roller 42 and the first metal roller 43 feed the sleeve belt 41 so as to have a feeding path 41 c corresponding to the feeding path 21 c of the shaped sheet 21 at the pressing portion 24 c of the sheet-like member 24.

As for the 1st metal roller 43, the position of a rotating shaft is adjustable. Thereby, the 1st metal roller 43 can adjust the length (contact length) of the pressurization part 24c. Further, the first metal roller 43 can adjust the tension of the sleeve belt 41 and can adjust the pressure to press the sheet-like member 24.
As for the 2nd metal roller 44, the position of a rotating shaft is adjustable. Thereby, the second metal roller 44 can adjust the pressure for pressurizing the sheet-like member 24, similarly to the first metal roller 43.
Note that. The rubber roller 42, the first metal roller 43, and the second metal roller 44 have a cooling pipe passing through them so that the temperature of the sleeve belt 41 can be adjusted.

  As shown in FIG. 3, the prism sheet winding unit 50 is a device that winds up the prism sheet 16 separated from the shaping sheet 21 by the separation roll unit 36. The prism sheet winding unit 50 feeds the prism sheet 16 while absorbing the slack of the prism sheet 16 with a roll or the like, and winds the prism sheet 16 into a roll shape by a winding device provided at the rear end.

(Method for manufacturing prism sheet 16)
A method for manufacturing the prism sheet 16 will be described.
(1) Extrusion Step As shown in FIG. 3, the extruder 22 is heated and melted to a temperature (about 280 ° C.) exceeding the glass transition point of the polycarbonate resin supplied from the hopper 22 a, and the sheet 23 is turned from the die 23. Extrude as 24.
(2) Molding Sheet 21 Feeding Step As shown in FIG. 4, the sheet-like member 24 is fed between the shaping sheet 21 and the sleeve belt 41. The sheet-like member 24 is fed along the same path as the feeding path of the shaping sheet 21 by feeding the shaping sheet 21 in the feeding direction 21b.
(3) Belt pressure feeding process The sheet-like member 24 moves along the shaping sheet 21, so that it is sandwiched between the shaping sheet 21 and the sleeve belt 41 in the pressing portion 24c, and the feeding direction 21b and In the width direction (left-right direction X shown in FIGS. 1 and 2), that is, over the entire contact length of the pressurizing portion 24c, the pressure is applied with a substantially constant pressure. The sheet-like member 24 passes through the pressurizing portion 24 c while being in surface contact with the sleeve belt 41 and the shaping sheet 21.

At this time, since the heat capacity of the shaping sheet 21 is small, even if the sheet-like member 24 comes into contact with the shaping sheet 21, the curing proceeds slowly without proceeding rapidly. For this reason, even if the pressure between the shaping sheet 21 and the sheet-like member 24 is reduced, the sheet-like member 24 can sufficiently flow into the concavo-convex shape portion of the shaping sheet 21, and the shaping rate can be improved. Moreover, since the sheet-like member 24 is molded without applying a strong shearing force, the orientation can be reduced, and an in-plane retardation or the like can be reduced as described later.
Moreover, since the pressure holding time of the sheet-like member 24 at the time of molding can be lengthened, the elastic return of the resin can be suppressed, so that deformation after molding can be prevented.
In the following description, the sheet-like member 24 after passing through the pressurizing portion 24 c is referred to as a prism sheet 16.

(4) Prism sheet feeding process When the prism sheet 16 and the sheet-like member 24 pass through the pressurizing portion 24 c and leave the sleeve belt 41, the prism sheet 16 and the sheet-like member 24 are in contact with the shaping sheet 21, and the second roll 33 and the third roll. 34, and sent to the separation roll unit 36. During this time, the prism sheet 16 is cooled by contact with the shaping sheet 21 or the outside air, and the surface of the prism sheet 16 is cured at a temperature below the glass transition point of the polycarbonate resin. Moreover, since the shaping sheet 21 (UV resin) is also brought into contact with the prism sheet 16, it is cooled to a glass transition point (about 50 ° C.) or lower. Thereby, the prism sheet 16 and the shaping sheet | seat 21 can improve peelability, and can suppress the deformation | transformation after mold release.

(5) Separation Step When the prism sheet 16 is sent to the separation roll unit 36, it is separated from the shaping sheet 21.
(6) Winding step The prism sheet 16 separated by the separation roll unit 36 is wound by the prism sheet winding unit 50, and a series of steps is completed.

In addition, in the said manufacturing process, the pressurization adjustment process which sets the conditions which pressurize the prism sheet 16 can be provided suitably. The pressurizing adjustment step is performed by adjusting the position of the rotation shaft of the second metal roller 44 to adjust the tension of the sleeve belt 41 or adjusting the contact length of the pressurizing portion 24c, for example.
For example, the pressure adjusting step may be set to a predetermined condition in accordance with the condition of the prism sheet 16 to be manufactured, or may be set by appropriately adjusting the condition as necessary in the manufacturing process. .

<Comparison with Comparative Examples: Molding rate, in-plane retardation variation, shrinkage and expansion rate>
Next, a comparison of the forming rate, the in-plane phase difference variation, and the shrinkage / expansion rate between the prism sheet 16 manufactured by the molding apparatus 20 of the embodiment and the prism sheet 116 manufactured by the molding apparatus 120 of the comparative example will be described. .
FIG. 5 is a diagram illustrating a molding apparatus 120 of a comparative example.
The molding apparatus 120 used not the molding sheet 21 but a metal molding roll 132 in which a mold for molding the unit optical system was formed. The roll 141 is a metal cooling roll.

FIG. 6 is a diagram illustrating a comparative experiment between the prism sheet 16 manufactured by the molding apparatus 20 of the embodiment and the prism sheet 116 manufactured by the molding apparatus 120 of the comparative example.
Manufacturing conditions and measurement methods are as follows (see FIG. 6).
<Common conditions>
Molding speed: 15m / min
Resin temperature: 300 ° C
Pitch: P = 50 μm
Thickness: 280 μm

<Different conditions>
Molding device 20 (the present invention)
Molding sheet: UV prism sheet
Prism tip R1 = 2 μm, Prism valley R2 = 0 μm
Pressing: Linear pressure: 75kg / cm
Contact length of pressurizing portion 24c (sleeve contact length): 60 mm
Molding device 120 (comparative example)
Forming roll: Metal
Tip R101 = 2μm, valley R102 = 0μm
Press: Surface pressure: 12.5 kg / cm ² (= 75 kg / cm ÷ 60 mm)

<Measurement method>
In-plane retardation (Re) variation:
Maximum value-minimum value of in-plane retardation (Re) when prism sheet is divided into 9 parts
<Measurement instrument>
Thickness measuring equipment:
Digimatic standard outer micrometer MDC-MJ / PJ (Mitutoyo Co., Ltd.)
Phase difference measuring equipment:
Phase difference measuring device: KOBRA-WR (manufactured by Oji Scientific Instruments)
Arrange the prism sheet so that the non-molding surface (back surface 16b) of the prism sheet faces the light source side as an incident surface and the prism ridge line is parallel to the X1-X2 direction (left-right direction X) in FIG. 1 Software: KOBRA-RE Ver1. 20
Measurement mode: Incident angle dependence measurement Measurement method: Standard Wavelength: λ (about 590 nm)
Nave: 1.585
Adopted data: Record data of θ = 0 °

(Comparison of forming rate)
As shown in Table 60, the molding rate was 100% in the molding apparatus 20 of the embodiment, whereas it was 96.8% in the molding apparatus 120 of the comparative example. Thereby, the shaping | molding apparatus 20 has confirmed that the moldability could be improved.

(Comparison of in-plane retardation (Re) variation)
As shown in Table 60, the in-plane retardation variation was less than 150 nm in the molding apparatus 20 of the embodiment, whereas it was 150 nm or more in the molding apparatus 120 of the comparative example. Thereby, it has confirmed that the shaping | molding apparatus 20 can reduce in-plane phase difference variation. Further, the prism sheet 16 can be expected to improve color unevenness during use.

(Comparison of shrinkage expansion rate)
As shown in Table 60, the shrinkage and expansion rate is “MD: −0.02%, TD: 0.00%” in the molding apparatus 20 of the embodiment, whereas in the molding apparatus 120 of the comparative example. , “MD: 0.05%, TD: 0.04%”. Here, MD represents the contraction / expansion rate in the sheet feeding direction 21b (the horizontal direction X shown in FIGS. 1 and 2), and TD represents the contraction / expansion in the width direction (vertical direction Z shown in FIGS. 1 and 2). Represents a rate.
Thereby, the shaping | molding apparatus 20 has confirmed that it could reduce a shrinkage expansion coefficient. It is considered that the reduction of the shrinkage and expansion rate reduced the orientation of the resin and contributed to the reduction of the in-plane retardation variation described above.

As described above, the molding apparatus 20 according to the embodiment reduces the orientation of the resin because the thermoplastic resin is sandwiched between the sleeve belt 41 and the shaping sheet 21 and fed while being pressed at a substantially constant pressure. In-plane retardation and variations thereof can be reduced.
Moreover, since the shaping | molding apparatus 20 of embodiment can improve moldability, the low pitch prism sheet 16 can be manufactured.

<Comparison with comparative example: Verification of color unevenness>
Next, color unevenness between the prism sheet 16 manufactured by the molding apparatus 20 of the embodiment and the prism sheet 116 manufactured by the molding apparatus 120 of the comparative example will be described.
FIG. 7 illustrates a comparison of the forming rate, in-plane phase difference variation, and contraction / expansion rate between the prism sheet 16 manufactured by the molding apparatus 20 of the embodiment and the prism sheet 116 manufactured by the molding apparatus 120 of the comparative example. It is a table.
Sample No. 1-27 is the prism sheet 16 manufactured with the shaping | molding apparatus 20 of embodiment.
Sample No. 28 to 49 are prism sheets 116 manufactured by the molding apparatus 120 of the comparative example.

(Visual judgment of uneven color of prism sheet)
First, no. The prism sheets 16 and 116 of 1 to 49 were incorporated into the surface light source device 10, and the degree of color unevenness on the polarization reflection sheet 17 was visually confirmed (row 8).
The prism sheet 16 (sample Nos. 1 to 27) of the embodiment is as shown in row 8, and color unevenness was partially recognized.
On the other hand, as shown in column 8, color unevenness was observed in all of the prism sheets 116 (sample Nos. 28 to 49) of the comparative example (indicated by x in Table 70).

Thus, the molding apparatus 20 of the embodiment was able to manufacture the prism sheet 16 with reduced color unevenness.
In the embodiment, a polycarbonate resin is used as the thermoplastic resin. Polycarbonate resin is a material with high orientation. For this reason, when the thermoplastic resin is pushed in by the metal molding roll 132 (see FIG. 5) of the comparative example, a strong linear pressure (shearing force) is suddenly applied to the thermoplastic resin (sheet-like member 124). As a result, the liquid crystal is greatly oriented in the feeding direction 21b and variations in orientation occur. As a result, in the comparative example, the in-plane phase difference variation becomes large, and color unevenness occurs like the prism sheet 116 shown in Table 70.

Next, the relationship between the visual determination and the in-plane retardation of the prism sheets 16 and 116 was verified by the following procedure.
(First judgment)
First, numerical values in columns 1 to 6 were obtained from the measurement results of the prism sheets 16 and 116. Columns 1 to 6 represent the following contents.
(Row 1: In-plane thickness sheet variation)
As shown in FIG. 6, the sheet thickness is the maximum value−minimum value when the prism sheets 16 and 116 are divided into nine.
(Row 2: In-plane retardation (Re) variation)
As in the case shown in FIG. 6, the in-plane retardation (Re) is the maximum value-minimum value when the prism sheets 16 and 116 are divided into nine.
(Row 3: In-plane average sheet thickness)
As shown in FIG. 6, it is an average value of the sheet thicknesses when the prism sheets 16 and 116 are divided into nine.
(Row 4: Average phase difference (Re) (nm))
As shown in FIG. 6, the average value of the in-plane retardation (Re) when the prism sheets 16 and 116 are divided into nine.
(Row 5: In-plane retardation per unit thickness (Re) (nm / mm))
"(Numeric value in column 4) / (Numerical value in column 3)", that is, "average phase difference / in-plane average sheet thickness", which corresponds to "in-plane average value of birefringence" . Since the unit was changed from “nm / μm” to “nm / mm”, the numerical value 1000 was integrated.
Column 6: Color irregularity value A
Color unevenness value A (1 / mm) = (Numeric value in column 5) / (Numerical value in column 3) Equation 1
That is, the color unevenness value A is “phase difference per unit thickness (average value in birefringence in plane) / in-plane phase difference variation”. This numerical value is a numerical value representing the degree of magnitude of “in-plane retardation variation” of “in-plane average value of birefringence”.
The unit is “1 / mm”, but it can also be expressed in units such as “1 / μm” and “1 / nm”. In this case, numerical values may be 1 or the like 1, 10 ⁶ min suitably 10 ³ minutes.

Next, compared with visual color irregularities (column 8),
Color irregularity value A <10 → ×
10 ≦ color shading value A → ○
The prism sheets 16 and 116 were selected according to the rule. As a result, the prism sheet 116 of the comparative example could be selected in accordance with the visual color unevenness determination (row 8).

By selecting the color unevenness value A, the concept of “average thickness and phase difference”, that is, the concept of birefringence when the thickness of the sheet is assumed to be uniform is adopted, and the variation in birefringence is uneven. Therefore, it is possible to perform more accurate sorting than sorting only by in-plane phase difference variation.
That is, for example, even in the case of a 100 μm thick sheet and a 500 μm thick sheet, for example, the same 200 nm phase difference variation, the birefringence variation is larger in the 100 μm sheet having a smaller thickness, and thus gives uneven color. The adverse effect is increased. That is, the smaller the color unevenness value A, the greater the variation in birefringence, which adversely affects the color unevenness.

  On the other hand, when the determination is made only by the in-plane phase difference variation, there is no concept of this birefringence, and an error from visual selection occurs. On the other hand, when the determination is made with the color unevenness value A, the concept of birefringence is taken in, and the selection closer to the visual selection can be performed.

(Second judgment)
Next, the relationship between the in-plane phase difference of the prism sheet 16 of the first determined embodiment and the visual determination was verified by the following procedure.
From the measurement result of the prism sheet 16, the numerical values in the column 7 were obtained. Column 7 represents the following contents.
(Column 7: Numerical value B)
Numerical value B = [Numerical value of column 2 / (Numerical value of column 4)] / [(Numerical value of column 1) / (Numerical value of column 3)]...
It is the numerical value calculated | required by. In addition, when the surface sheet thickness variation was 0 (μm), the numerical value B was calculated as the effective measurement minimum value (1 μm). Since the unit is “(nm / nm) / (μm / μm)”, it is dimensionless. For example, it can be expressed by adding a unit such as “μm / nm”. In this case, the numerical values may be appropriately multiplied by 1000 times or the like.
Here, [(Numerical value of column 2 / (Numerical value of column 4)] represents “variation rate of phase difference”, and [(Numerical value of column 1) / (Numerical value of column 3)] represents “Thickness variation. Rate ".
Therefore, the numerical value B is a numerical value indicating the degree of magnitude of the “phase difference variation rate” with respect to the “thickness variation rate”. Assuming that there is no variation in birefringence, the variation in phase difference is proportional to the variation rate in thickness.

Therefore, after sorting by the color unevenness value A and further sorting by the numerical value B, the concept of thickness variation can be incorporated into birefringence, and an improvement in sorting accuracy can be expected.
That is, even if the phase difference variation is 150 nm, the color unevenness may vary between a sheet having a thickness variation of 30 μm and a sheet having a thickness of 1 μm. This means that even if there is a variation in thickness of 30 μm, the difference in birefringence is small when the phase difference in the thin part is small and the phase difference in the thick part is large. This is because the resulting color unevenness may not occur. On the other hand, “if the thickness variation is only 1 μm, if the phase difference variation is 150 nm, the birefringence variation is large”, and color unevenness may occur.
However, since the thickness variation cannot be sufficiently taken into account only by the color unevenness value A, the case where “the thickness variation is only 1 μm and the phase difference variation is 150 nm, the birefringence variation is large”, etc. A scene where color unevenness cannot be selected is expected.

Therefore, in the example shown in FIG. 7, the prism sheet 16 is selected based on the numerical value B according to the following criteria. The selection criterion of the numerical value B is assumed to correspond to the color unevenness determination (column 8) by visual evaluation, and to be correlated with the color unevenness determination (column 8) by visual evaluation. Since all the prism sheets 116 were “x” in the first determination, the second determination was omitted.
B <7 → ○
7 ≦ B ≦ 10 → △
10 <B → ×

As described above, in the first embodiment, color unevenness is determined based on the birefringence variation based on the concept of “average thickness and phase difference” in the first determination, and the concept of thickness variation in birefringence is further determined in the second determination. By adopting, it can be expected to improve the sorting accuracy.
Further, since the prism sheet 16 evaluated in the first determination is further evaluated in the second determination, it can be matched with the visual color unevenness determination (column 8). Thereby, it is possible to perform the same sorting as the determination of color unevenness by visual observation.
Furthermore, the prism sheets 16 selected in the first determination can be further ranked and evaluated.

  The prism sheet 16 determined as “Δ” or “Δ and x” in the second determination may further include a visual determination step in which an inspector visually evaluates the prism sheet 16. As a result, the sheets determined as “◯ (good)” in the first determination are ranked, and the “△” or “Δ and X” prism sheet 16 having a low rank is visually determined to generate a defect. Can contribute to the decline. Even in this case, since the number of prism sheets 16 that must be visually determined can be minimized, an increase in man-hours due to visual evaluation can be minimized.

  Thus, this embodiment provides the determination process which sorts by performing the 1st judgment and the 2nd judgment with respect to prism sheet 16 manufactured through the belt pressurization feed process and the prism sheet feed process, Sorting can be performed in the same manner as the determination of color unevenness by visual inspection. Accordingly, the prism sheet 16 can be selected in the same manner as in the visual inspection without providing an inspection process and an evaluation process for uneven color, so that the number of man-hours in the manufacturing process can be reduced, and variations such as different judgments can be made for each evaluator. Can be evaluated uniformly.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made as in the modifications described later, and these are also included in the present invention. Within the technical scope. In addition, the effects described in the embodiments are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments. It should be noted that the above-described embodiment and modifications described later can be used in appropriate combination, but detailed description thereof is omitted.

(Deformation)
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the scope of the present invention.
(1) In the embodiment, the unit optical shape is parallel to the normal direction of the sheet surface, and the cross-sectional shape parallel to the arrangement direction is an isosceles triangle shape having an apex angle of 90 °. For example, other triangular shapes, hemispherical shapes, and partial shapes such as elliptical shapes may be used. For example, when the cross-sectional shape of the unit optical shape is a partial shape of an elliptical shape, the unit optical shape has a light diffusing action in addition to the light condensing action. Luminance unevenness such as light source unevenness due to the position of the light source can be eliminated. When the cross-sectional shape of the unit optical shape is a part of an elliptical shape, the light diffusibility and the high light condensing property can be obtained by making the long axis a part of the elliptical shape that is orthogonal to the sheet surface. It is preferable from the viewpoint of achieving both.
In the embodiment, the unit prisms are arranged in the vertical direction along the sheet surface. However, the unit prisms are not limited thereto, and may be arranged in the left-right direction, for example.
Furthermore, in the embodiment, the unit prism has a triangular prism shape whose longitudinal direction is the left-right direction and is arranged in one direction along the sheet surface. It may have a pyramid shape and may be arranged in two directions (for example, the vertical direction and the left-right direction) along the sheet surface.

(2) In the embodiment, the prism sheet does not contain a diffusing material or the like. However, the present invention is not limited to this. For example, a prism material in which a diffusing material such as styrene beads is kneaded may be used. Good. Further, for example, a unit prism may be formed by extruding two layers using a resin material containing a diffusing material and a resin material not having a diffusing material.

(3) In the embodiment, the prism sheet is used in the surface light source device.

(4) In the embodiment, the example of evaluating the uneven color is shown on the prism sheet after manufacture, but is not limited thereto. An evaluation device for evaluating color unevenness may be provided in the molding apparatus, and a color unevenness evaluation process may be provided as part of the process in the molding apparatus. In this case, color unevenness can be evaluated by a so-called in-line method, and the productivity of the prism sheet can be improved.

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 LCD panel 10 Surface light source device 12 Reflector 13 Light emitting tube 14 Milky white plate 16 Prism sheet 16c Optical shape part 16d Unit prism 20 Molding device 21 Molding sheet 22 Extruder 30 Molding sheet feeding part 31 Sheet supply roll part 32 1st feed roll 33 2nd feed roll 34 3rd feed roll 36 Separation roll part 40 Belt pressure feed part 41 Sleeve belt 42 Rubber roller 43 1st metal roller 44 2nd metal roller

Claims (6)

A plurality of convex unit optical shapes are arranged on at least the surface, a light source is arranged on the back side, which is the surface opposite to the surface side, and the light source of the light source is arranged to enter from the back side and exit from the surface. An optical sheet manufacturing method comprising:
When the average value of in-plane retardation (nm) / (in-plane retardation variation (nm) × average value of sheet thickness (mm)) ≧ 10 (nm / mm) is passed,
In-plane retardation average value (nm) / (in-plane retardation variation (nm) × sheet thickness average value (mm)) <10 (nm / mm) Providing a first determination step for evaluating unevenness;
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet according to claim 1,
A second determination step of evaluating the color unevenness of the optical sheet evaluated in the first determination step based on a degree of magnitude of the variation rate of the in-plane retardation with respect to the variation rate of the sheet thickness;
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet according to claim 2,
In the second determination step, the size of the variation rate of the in-plane retardation (nm / nm) with respect to the variation rate of the sheet thickness (μm / μm) is less than a predetermined value set in association with the visual evaluation. To evaluate a certain optical sheet as a good product,
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet according to claim 3,
In the second determination step, a constant value set in association with the visual evaluation is 7, and an optical sheet that is less than 7 is evaluated as a non-defective product,
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet according to claim 4,
The second determination step includes a step of further selecting an optical sheet whose numerical value set in association with the visual evaluation is 10 or less and an optical sheet larger than 10 with respect to a sheet larger than 7. thing,
An optical sheet manufacturing method characterized by the above. In the manufacturing method of the optical sheet of any one of Claim 2 to Claim 5,
In the second determination step, the size of the variation rate of the in-plane retardation (nm / nm) with respect to the variation rate of the sheet thickness (μm / μm) is equal to or greater than a predetermined value set in association with visual evaluation. Providing the optical sheet with a visual judgment step in which an inspector visually evaluates,
An optical sheet manufacturing method characterized by the above.

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