JP2009083176A - Manufacturing method of stretched sheet and manufacturing method of anisotropic optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a stretched sheet capable of preventing the getting-out of shape of the stereoscopic structure of the surface of a sheet before and after stretching by suppressing the occurrence of bowing at stretching. <P>SOLUTION: The manufacturing method of the stretched sheet has a process for uniaxially stretching a resin sheet 21 cut into a predetermined width in its longitudinal direction between the first roll 31 installed on the inlet side of a stretching unit 24 and the second roll 32 installed on the outlet side of a stretching oven. A first process for preheating the resin sheet 21 to a stretching temperature, a second process for stretching the preheated resin sheet 21 at the stretching temperature and a third process for cooling the stretched resin sheet 21P are continuously performed in this order within the stretching oven. When the stretching magnification of the resin sheet 21 in the second process is defined as P, the sheet width of the resin sheet 21 is defined as W and the oven length of the stretching oven, where the second process is executed, is defined as L, the relation of L≥W×P is satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a stretched sheet having a step of stretching in the length direction of the resin sheet. More specifically, the present invention relates to a method of stretching a resin sheet having a three-dimensional structure having a ridge line direction parallel to the stretch direction formed on the surface. The present invention relates to a method for producing a stretched sheet that imparts optical anisotropy and a method for producing an anisotropic optical sheet.

  In general, for stretching a substrate made of a polymer sheet or film, roll stretching that stretches only in the MD (Machine Direction) direction, which is the substrate running direction, and TD (Transverse Direction) direction, which is the substrate width direction. A tenter that only stretches is used. Either one is obtained when the properties required for the substrate are obtained by uniaxial stretching, and when biaxial stretching is required, both are combined in series, and a stretched sheet or film is manufactured as sequential biaxial stretching ( For example, see Patent Documents 1 and 2 below).

  In addition, depending on the type of substrate, there are some which require MD and TD to be stretched simultaneously, and in that case, simultaneous biaxial stretching is used. However, since the simultaneous biaxial stretching has a high degree of difficulty in setting the stretching conditions, the present state is used only for specific substrates.

  An example of roll stretching is shown in FIG. In this method, the resin sheet 1 heated by a preheating roll (2A, 2B, 2C, 2D) heated to a constant temperature is set to a stretching roll (3E, 3F, 3F, 3H) with a speed difference. Stretch between. After that, heat fixing rolls (4I, 4J), cooling rolls (5K, 5L) and the like are added as necessary. In recent years, as an optical film application, as shown in FIG. 7, a method of removing the stretching roll 3G and heating and stretching the stretching roll 3F-3H with an IR heater 6 is also used.

  Since this roll stretching is performed within a very small gap between the rolls so that the temperature of the resin sheet does not decrease, the resin sheet slips on the roll and is easily scratched. Moreover, since the friction between the roll and the resin sheet is generated, it becomes a force that restrains the width direction (anti-stretch direction). For this reason, for example, when a resin sheet on which a three-dimensional structure such as a prism shape is formed is stretched, the shape of the three-dimensional structure cannot be maintained. Further, as shown in FIG. 8, an arcuate bend 7 called bowing occurs in the TD direction (width direction), and this improvement becomes a problem.

  Next, FIG. 9 shows an outline of a tenter device that performs uniaxial stretching in the TD direction. In this method, both ends of the traveling resin sheet 1 in the width direction are clamped by clips 8A and 8B to perform stretching. Each of the clips 8A and 8B can run along the rails 9A and 9B installed opposite to both ends of the resin sheet 1, and a plurality of the clips 8A and 8B are installed at a predetermined pitch along the length direction of the resin sheet 1. Yes. The tenter is an effective means for producing a large product because the resin sheet before stretching is stretched in the width direction. For example, Patent Document 3 discloses a method of manufacturing a prism sheet in which a prism sheet is stretched by a tenter and anisotropy of refractive index is imparted within the sheet surface.

  However, in the stretching using the tenter described above, the restraint in the length direction of the resin sheet by the clips 8A and 8B acts so as to prevent contraction in the length direction, which is the anti-stretching direction of the resin sheet. As shown in FIG.

  On the other hand, FIG. 10 shows an outline of simultaneous biaxial stretching used for some base materials. In this method, the both ends in the substrate width direction are clamped with clips in the same manner as the tenter described above, and stretched simultaneously in the TD direction and the MD direction. Basically, when the MD draw ratio is set to 1.0, the operation is the same as that of the TD uniaxial.

  However, while the clips of the TD tenter are in close contact with each other with almost no gap, the simultaneous two axes take into account the contraction in the MD direction and the interval is large, so that a neck 11 called neck-in occurs during stretching. A major problem with this method is that the completed size of the sheet is reduced by the occurrence of this neck-in.

Japanese Unexamined Patent Publication No. 7-108598 JP 2000-263642 A WO 2006/071621

  In any of the stretching methods described above, an arcuate bend called bowing occurs. For this reason, when extending | stretching the resin sheet which has a prism shape on the surface, it is difficult to maintain a fixed shape within the extended sheet | seat surface.

  As shown in FIG. 11, in a typical prism sheet 12, a prism 13 is configured by linear inclined surfaces 13 a and 13 b having a certain base angle θ. Therefore, in order to develop birefringence at the apex portion of the prism 13, it is necessary to extend in the ridge line direction of the prism 13 indicated by D1 in the figure, and conversely, it is extended in the arrangement direction of the prism 13 indicated by D2 in the figure. However, the apex does not extend, and the prism shape is deformed as schematically shown in FIG.

  Further, even in the extension in the prism ridge line direction (D1), when a force acts in a direction that prevents contraction in the anti-extension direction (D2) due to extension in one direction, the prism shape is similarly deformed. For example, a force generated by friction between the roll and the base material during roll stretching acts so as to prevent shrinkage of the base material in the anti-stretch direction. Further, in stretching using a tenter, the restraint in the length direction of the base material by the clip acts so as to prevent shrinkage in the anti-stretching direction of the base material.

  The present invention has been made in view of the above-described problem, and suppresses the occurrence of bowing during stretching, and prevents the collapse of the shape of the three-dimensional structure of the sheet surface before and after stretching, and the production of an anisotropic optical sheet. It is an object to provide a method.

  In solving the above problems, the method for producing a stretched sheet of the present invention is a predetermined method between a first roll installed on the inlet side of the stretching furnace and a second roll installed on the outlet side of the stretching furnace. A method for producing a stretched sheet comprising a step of uniaxially stretching a resin sheet cut into a width in the length direction, wherein the resin sheet is preheated with a first step in which the resin sheet is preheated to a stretching temperature. The second step of stretching the resin sheet at the stretching temperature and the third step of cooling the stretched resin sheet are successively performed in these order, the stretching ratio of the resin sheet is P, the sheet width of the resin sheet is W, When the length of the drawing furnace for carrying out the second step is L, the relationship L ≧ W × P is satisfied.

  In the method for producing a stretched sheet of the present invention, the furnace length of the portion where the resin sheet is stretched in the stretching furnace is set to a length greater than or equal to the product of the sheet width (W) and the stretch ratio (P) of the resin sheet. By setting, the shrinkage | contraction to the width direction which is the anti-stretching direction of the said resin sheet is not inhibited. Thereby, generation | occurrence | production of the bow of a resin sheet can be suppressed effectively.

  Moreover, the manufacturing method of the extending | stretching sheet | seat of this invention is resin cut | judged by predetermined width between the 1st roll installed in the entrance side of the extending furnace, and the 2nd roll installed in the exit side of the extending furnace. A method for producing a stretched sheet comprising a step of uniaxially stretching a sheet in its length direction, wherein the resin sheet has a translucency in which a large number of three-dimensional structures having a ridge line direction in the length direction are formed on at least one surface A first step of preheating the resin sheet to the stretching temperature, a second step of stretching the preheated resin sheet at the stretching temperature, and a third step of cooling the stretched resin sheet. The steps are carried out successively in these order, where the stretch ratio of the resin sheet is P, the sheet width of the resin sheet is W, and the furnace length of the stretching furnace for performing the second step is L, L ≧ W × It is characterized by satisfying the relationship of P.

  In the method for producing a stretched sheet of the present invention, the furnace length of the portion where the resin sheet is stretched in the stretching furnace is set to a length greater than or equal to the product of the sheet width (W) and the stretch ratio (P) of the resin sheet. By setting, the shrinkage | contraction to the width direction which is the anti-stretching direction of the said resin sheet is not inhibited. Thereby, the occurrence of bowing of the resin sheet can be effectively suppressed, and the collapse of the shape of the three-dimensional structure on the sheet surface can be prevented.

  Examples of the three-dimensional structure formed on the sheet surface include a three-dimensional structure having a deflecting property or a light collecting property, such as a prism body or a lenticular lens body. This three-dimensional structure is not limited to one side of the sheet, and may be formed on both sides of the sheet. Thereby, the optical sheet which consists of extending | stretching sheets, such as a prism sheet and a lenticular lens sheet, can be manufactured with high precision.

  And the manufacturing method of the anisotropic optical sheet of this invention is cut | judged by predetermined width between the 1st roll installed in the entrance side of the drawing furnace, and the 2nd roll installed in the exit side of the drawing furnace. The resin sheet is a method for producing an anisotropic optical sheet having a refractive index anisotropy with respect to the width direction and the length direction of the resin sheet by uniaxially stretching the resin sheet in the length direction. It consists of a translucent sheet in which a number of three-dimensional structures having a ridge line direction in the length direction are formed on at least one surface, and in the inside of the drawing furnace, the first step of preheating the resin sheet to the drawing temperature was preheated. The second step of stretching the resin sheet at the stretching temperature and the third step of cooling the stretched resin sheet are successively performed in these order, the stretching ratio of the resin sheet is P, the sheet width of the resin sheet is W, The length of the drawing furnace that performs the second step When is L, and satisfies a relationship of L ≧ W × P.

  In the method for producing an anisotropic optical sheet of the present invention, the furnace length of the portion where the resin sheet is stretched inside the stretching furnace is equal to or greater than the product of the sheet width (W) and the stretching ratio (P) of the resin sheet. By setting the length, the shrinkage of the resin sheet in the width direction, which is the anti-stretching direction, is not inhibited. Thereby, the occurrence of bowing of the resin sheet can be effectively suppressed, the collapse of the shape of the three-dimensional structure of the sheet surface can be prevented, and the in-plane optical anisotropy (birefringence) can be made uniform. It becomes possible.

  As described above, according to the present invention, the occurrence of bowing during stretching can be suppressed, and a stretched sheet having excellent shape accuracy can be produced. Moreover, the stable extending | stretching process is attained, without destroying the shape of the three-dimensional structure formed in the sheet | seat surface. Furthermore, when the in-plane refractive index anisotropy is imparted by the stretching treatment, the optical anisotropy in the sheet plane can be made uniform.

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

  1 and 2 are a side view and a main part plan view showing a schematic configuration of a roll stretching apparatus 20 used in the embodiment of the present invention. The roll stretching apparatus 20 shown in the figure is configured so that a resin sheet or film (hereinafter, collectively referred to as “resin sheet”) 21 cut to a predetermined width travels in the length direction (X-axis direction). It is an apparatus for extending in the X-axis direction).

  The roll stretching apparatus 20 includes a stretching unit 24, an unwinding unit 27 installed on the inlet side of the stretching unit 24, and a winding unit 29 installed on the outlet side of the stretching unit 24. The unwinding unit 27 includes an unwinding roll 26 that unwinds the resin sheet 21 from a roll state, a first roll 31 that sandwiches the resin sheet 21 and supplies the resin sheet 21 to the stretching unit 24, and a backup roll 31a thereof. The winding unit 29 includes a winding roll 28 that winds the stretched resin sheet 21P, a second roll 32 that sandwiches the resin sheet 21 and guides it to the winding roll 28, and a backup roll 32a thereof.

  The resin sheet 21 travels in a state where both ends in the length direction (X-axis direction) are supported by the first roll 31 and the second roll 32 and is stretched in the length direction inside the stretching unit 24. . The stretching of the resin sheet 21 is performed by making the rotation speed of the second roll 32 faster than the rotation speed of the first roll 31, and the stretching ratio is determined by the difference between the rotation speeds of the first and second rolls 31 and 32. Is done.

  The stretching unit 24 includes a stretching furnace in which a preheating unit 24A, a stretching unit 24B, and a cooling unit 24C are installed in this order from the entrance side. The preheating unit 24A preheats the resin sheet 21 supplied to the stretching unit 24 to a predetermined stretching temperature (first step). The stretching temperature is, for example, a temperature of Tg + 10 ° C. or higher and Tg + 30 ° C. or lower when the glass transition point of the resin sheet 21 is Tg [° C.]. The stretching unit 24B stretches the resin sheet 21 heated to the stretching temperature in the length direction (second step). The cooling unit 24C cools the stretched resin sheet 21P to a predetermined temperature equal to or lower than Tg (third step). The resin sheet 21 is continuously supplied with the preheating unit 24A, the extending unit 24B, and the cooling unit 24B. If necessary, a heat fixing unit is installed between the extending unit 24B and the cooling unit 24C.

  In the present embodiment, when the stretching ratio of the resin sheet 21 is P and the width of the resin sheet 21 is W, the furnace length (L) of the stretching portion 24B is set to satisfy the relationship L ≧ W × P. ing. Thereby, as will be described later, the occurrence of bowing in the width direction when the resin sheet 21 is stretched is suppressed.

  The resin sheet 21 is made of a translucent polymer sheet or film. In particular, the resin sheet 21 is made of a crystalline or semi-crystalline polymer resin material. For example, an amorphous polymer sheet or film having a crystallinity of 10% or less is used.

  FIG. 3A is a schematic perspective view showing the surface form of the resin sheet 21. On the surface of the resin sheet 21, a large number of three-dimensional structures 21 a having a ridge line direction in the length direction (X-axis direction) of the resin sheet 21 are arranged in the running direction (X-axis direction) of the resin sheet 21. The three-dimensional structure 21a has a prism shape made up of, for example, an isosceles triangle having an apex angle of 90 degrees when viewed from the length direction of the resin sheet 21. Then, the resin sheet 21 is stretched at a predetermined stretching ratio in the length direction (prism ridge line direction) by the roll stretching device 20, so that the three-dimensional structure 21 a is reduced in shape similarly as shown in FIG. 3B. The arrangement pitch of the three-dimensional structure 21a is made finer. The three-dimensional structure 21a is not limited to the prism body described above, and may be a lenticular lens body such as a cylindrical lens.

In general, when a polymer sheet is stretched in the length direction (MD direction), the behavior shown in FIG. 4 is exhibited. Here, when the width of the polymer sheet before stretching is W, the length is L, the thickness is T, and when the film is stretched P times in the length direction, when the anti-stretch direction (width direction) is not restricted, The dimensions Wa, La, and Ta after stretching are as follows.
Wa = W · (1 / √P), La = L · P, Ta = T · (1 / √P) (1)

  As shown in the equation (1), the volume of the sheet after stretching does not change from that before stretching. FIG. 4 shows the state of a single sheet in which the sheet is cut to a predetermined size, but the same behavior is exhibited even when the sheet is in a continuous web state. In this case, if free shrinkage in the width direction (anti-stretch direction) during stretching is hindered by the sandwiching action of the rolls that support both ends in the length direction of the sheet, bending called bowing occurs, and the sheet surface In-plane nonuniformity of the shape accuracy of the three-dimensional structure formed is brought about.

  Therefore, in the present embodiment, the furnace length L of the stretching section 24B of the stretching unit 24 in the roll stretching apparatus 20 is larger than the product (W × P) of the sheet width W of the resin sheet 21 and the stretching ratio P as described above. It is set to be. Thereby, as shown in FIG. 2, the tensile stress S1 acting on the resin sheet 21 in the extending portion 24B is parallel to the sheet length direction, and the first roll 31 (and 31a) and the second roll 32 (and 32a). Thus, the shrinkage in the width direction of the resin sheet 21 is not hindered by the sandwiching action.

  Specifically, when a resin sheet made of PEN (polyethylene naphthalate) having a sheet width of 200 mm was stretched four times in the length direction, the furnace length L of the stretching portion 24B was set to 800 mm and actually stretched. However, it was confirmed that the occurrence of Boeing could be suppressed. It was also confirmed that the prism shape formed on the sheet surface had a similar relationship before and after stretching. In addition, from the viewpoint of suppressing bowing, the furnace length L of the extending portion 24B is preferably as long as possible.

  Therefore, according to the present embodiment, at the time of stretching the resin sheet 21, it is possible to eliminate the restraint in the width direction that is the anti-stretching direction, and to ensure the contraction in the sheet width direction according to the stretching amount in the sheet length direction. Become. Thereby, generation | occurrence | production of a bowing is suppressed effectively. In addition, since the stretched prism sheet 21P is produced by the stretching process described above, a prism sheet (anisotropic optical sheet) 21P having optical anisotropy having different refractive indexes in the stretching direction and the anti-stretching direction is obtained. be able to. In particular, since an appropriate contraction operation in the prism arrangement direction can be ensured at the time of stretching in the prism ridge direction, in-plane uniformity of refractive index anisotropy can be achieved.

  Here, as a constituent material of the resin sheet 21, there are a polymer material having a large refractive index in the stretching direction and a polymer material having a small refractive index in the stretching direction, and any material can be used. . Examples of the polymer material having a refractive index large in the stretching direction include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), a mixture thereof, or a copolymer such as PET-PEN copolymer, polycarbonate, polyvinyl alcohol, polyester, polyfluoride. And vinylidene chloride, polypropylene, polyamide and the like. On the other hand, examples of the polymer material whose refractive index is small in the stretching direction include methacrylic resins, polystyrene resins, styrene-methyl methacrylate copolymers, and mixtures thereof.

  Further, the size of the in-plane refractive index anisotropy (birefringence) of the stretched sheet 21P manufactured as described above is not particularly limited, but as will be described later, the stretched sheet is used as a prism sheet for a liquid crystal display device. When 21P is used, it is preferable that the birefringence is large. Specifically, the magnitude of birefringence is 0.05 or more, preferably 1.0 or more, more preferably 2.0 or more.

  In the present embodiment, as the constituent material of the resin sheet 21 (21P), a resin material having a large refractive index in the extending direction, such as PET or PEN, is used. By the stretching process, the stretched sheet 21P has an in-plane refractive index (nx) in the X-axis direction (prism ridge line direction) larger than an in-plane refractive index (ny) in the Y-axis direction (prism arrangement direction). Refractive index anisotropy (nx> ny). The stretched prism sheet 21P having such a configuration has an optical characteristic that the light emitted from the formation surface of the prism 21a has more light emitted from the polarization component in the prism array direction than the light emitted from the polarization component in the prism ridge direction. Is provided.

  FIG. 5 is a schematic configuration diagram of a liquid crystal display device 40 using the stretched sheet 21P having the above-described configuration as a prism sheet. The liquid crystal display device 40 includes a liquid crystal display panel 41, a first polarizing plate 42A and a second polarizing plate 42B sandwiching the liquid crystal display panel 41, a prism sheet 21P, a diffusion sheet 43, and a backlight unit 44. ing.

  The prism sheet 21 </ b> P is formed by cutting the stretched sheet manufactured by the roll stretching device 20 into a predetermined width, and is used as a brightness enhancement film for improving the front brightness of the liquid crystal display device 40. The prism sheet 21P is disposed on the light emission surface side of the diffusion sheet 43 that diffuses and emits the illumination light (backlight light) from the backlight unit 44, and the formation surface of the prism 21a is directed to the liquid crystal display panel 41 side. The light emitted from the diffusion sheet 43 is concentrated in the front direction.

  Further, the pair of polarizing plates 42A and 42B sandwiching the liquid crystal display panel 41 are arranged so that the transmission axes a and b are orthogonal to each other. In the illustrated example, the prism sheet 21P is arranged so that the prism array direction (Y-axis direction) of the prism sheet 21P is substantially parallel to the transmission axis a of the first polarizing plate 42A located on the backlight unit 44 side. Has been placed.

  This example is particularly effective when the prism sheet 21P having optical anisotropy having a large refractive index in the prism ridge direction (X-axis direction) is used. Since the liquid crystal display panel 41 can be made incident, the front luminance can be improved.

  As mentioned above, although embodiment of this invention was described, of course, this invention is not limited to this, A various deformation | transformation is possible based on the technical idea of this invention.

  For example, in the above embodiment, a method for stretching a substrate made of a polymer sheet or film having a three-dimensional structure 21a formed on the surface has been described. However, a group made of a flat polymer sheet or film having no three-dimensional structure formed on the surface is described. The present invention can also be applied to the stretching treatment of a material, and even when such a base material is used, bowing during stretching can be effectively suppressed.

It is a schematic side view of the roll extending | stretching apparatus used in embodiment of this invention. It is a schematic plan view of the roll extending | stretching apparatus used in embodiment of this invention. It is a schematic perspective view which shows the structure of the resin sheet used in embodiment of this invention. It is a figure explaining the dimensional change of the width | variety of a base material (polymer sheet) before and behind extending | stretching, length, and thickness. It is a schematic block diagram of the liquid crystal display device which used the anisotropic optical sheet produced in embodiment of this invention as a prism sheet. It is a schematic block diagram of the conventional roll extending | stretching apparatus. It is a schematic block diagram of the principal part of the other conventional roll extending | stretching apparatus. It is a schematic plan view of the principal part explaining the problem of the conventional roll extending | stretching apparatus. It is a schematic block diagram of the conventional tenter apparatus. It is a schematic block diagram of the other conventional tenter apparatus. It is a schematic block diagram of a prism sheet. It is a schematic diagram which shows a mode that the prism shape of the prism sheet produced with the conventional extending | stretching method collapsed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Roll stretching apparatus, 21 ... Resin sheet, 21a ... Three-dimensional structure (prism), 21P ... Stretched sheet, prism sheet (anisotropic optical sheet), 24 ... Stretching unit, 24A ... Preheating part, 24B ... Stretching part, 24C DESCRIPTION OF SYMBOLS ... Cooling part, 31 ... 1st roll, 32 ... 2nd roll, 40 ... Liquid crystal display device, 41 ... Liquid crystal display panel, 42A, 42B ... Polarizing plate, 43 ... Diffusion sheet, 44 ... Backlight unit

Claims (6)

A step of uniaxially stretching a resin sheet cut into a predetermined width between a first roll installed on the inlet side of the stretching furnace and a second roll installed on the outlet side of the stretching furnace. A method for producing a stretched sheet having
Inside the stretching furnace, there are a first step of preheating the resin sheet to a stretching temperature, a second step of stretching the preheated resin sheet at the stretching temperature, and a third step of cooling the stretched resin sheet. Is performed in the order of
When the stretch ratio of the resin sheet is P, the sheet width of the resin sheet is W, and the furnace length of the stretching furnace for performing the second step is L,
L ≧ W × P
A stretched sheet manufacturing method characterized by satisfying the relationship: A step of uniaxially stretching a resin sheet cut into a predetermined width between a first roll installed on the inlet side of the stretching furnace and a second roll installed on the outlet side of the stretching furnace. A method for producing a stretched sheet having
The resin sheet is composed of a translucent sheet in which a large number of three-dimensional structures having a ridge line direction in the length direction are formed on at least one surface,
Inside the stretching furnace, a first step of preheating the resin sheet to a stretching temperature, a second step of stretching the preheated resin sheet at the stretching temperature, and a third step of cooling the stretched resin sheet. Is performed sequentially in these order,
When the stretch ratio of the resin sheet is P, the sheet width of the resin sheet is W, and the furnace length of the stretching furnace for performing the second step is L,
L ≧ W × P
A stretched sheet manufacturing method characterized by satisfying the relationship: The method for producing a stretched sheet according to claim 2, wherein the three-dimensional structure is a prism body or a lenticular lens body. Between the first roll installed on the entrance side of the stretching furnace and the second roll installed on the exit side of the stretching furnace, the resin sheet cut into a predetermined width is uniaxially stretched in the length direction. Then, a method for producing an anisotropic optical sheet having anisotropy of refractive index with respect to the width direction and the length direction of the resin sheet,
The resin sheet is composed of a translucent sheet in which a large number of three-dimensional structures having a ridge line direction in the length direction are formed on at least one surface,
Inside the stretching furnace, a first step of preheating the resin sheet to a stretching temperature, a second step of stretching the preheated resin sheet at the stretching temperature, and a third step of cooling the stretched resin sheet. Is performed sequentially in these order,
When the stretch ratio of the resin sheet is P, the sheet width of the resin sheet is W, and the furnace length of the stretching furnace for performing the second step is L,
L ≧ W × P
An anisotropic optical sheet manufacturing method characterized by satisfying the relationship: 5. The method for producing an anisotropic optical sheet according to claim 4, wherein a material having a refractive index that is large in a stretching direction is used as the translucent sheet. The method for producing an anisotropic optical sheet according to claim 4, wherein a material having a refractive index that is small in the stretching direction is used as the translucent sheet.

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