JPH0921908A - Lens sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve luminance, heat resistance and moldability by arranging many triangular prisms on a sheet surface consisting of amorphous thermoplastic polyester specified in refractive index and glass transition temp. in parallel with each other in the major axis direction. SOLUTION: This lens sheet consists of the amorphous thermoplastic polyester having the refractive index of >=1.60 and the glass transition temp. of 100 to 150 deg.C. The many lens parts of the unit of the prism shape consisting of the substantially prism shape are arranged on at least one surface of the sheet in such a manner that the major axis directions are nearly paralleled with each other. The amorphous thermoplastic polyester consists of arm. dicarboxylic acid or its diester deriv., the hydroxy compd. expressed by formula and 2 to 4C aliphat. glycol. The dihydroxy compd. expressed by the formula is preferably specified to >=10mol% of the total glycol component in the resin. In the formula, R1 denotes 2 to 4C alkyl group and R2 to R5 respectively independently denote hydrogen or 1 to 4C alkyl groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device such as a liquid crystal television, a computer and a word processor. More specifically, it is formed from a specific polyester polymer capable of improving the brightness of the display device. It relates to a lens sheet.

[0002]

2. Description of the Related Art In recent years, in response to the demand for higher performance and lighter weight of information equipment, liquid crystal display devices, which are widely used for display devices such as office automation equipment, personal computers, word processors, etc., have become lighter, thinner and more sophisticated. , The demand for power saving is increasing. Along with the improvement of the liquid crystal display mechanism itself, there is a strong demand for thinning and high brightness of the backlight for making it easier to see the liquid crystal display device having no light emitting function, and various attempts have been made to improve the brightness. The method of improving the brightness of the backlight by increasing the input power leads to disadvantages such as increase in power consumption and heat generation, and increase in battery capacity for portable use, shortening of life, etc. Is inevitable. Therefore, it is required to improve the efficiency of the light of the backlight as well as to improve the cold cathode ray tube and the invertor. In a liquid crystal display device, the brightness in front of the observer is important. In the 1-lamp type, which is advantageous for thinning, the light emitted from one end is emitted uniformly over the entire display surface, so the light passing through the light diffusion layer becomes an omnidirectional light and the brightness when passing through the liquid crystal phase is Since this is disadvantageous to the observer, a method has been introduced in which directivity is given again to improve the brightness. For this reason, various lens sheets have been devised.

A first example of a lens sheet for improving brightness is a method of using prisms, which has a large number of prisms having linear apexes on the same surface at fine intervals in a state where apexes are substantially parallel to each other. A method of arranging a sheet made of a translucent material on the exit surface side with the top ridge surface facing outward (Japanese Patent Laid-Open No. 5-1
27159), or a method of arranging one or more such that the arrangement direction is parallel to the horizontal direction of the panel (Japanese Patent Laid-Open No. 5-32).
3319) has been proposed. An apparatus (Japanese Patent Laid-Open No. 6-67178) installed such that the prism has an apex angle of 70 to 110 degrees facing the liquid crystal display element, and an apparatus having an apex angle of 95 to 110 degrees (Japanese Patent Laid-Open No. 6-67178). 1870
7), and 70 to 150 degrees (Japanese Patent Laid-Open No. 6-1
60639).

The second example has a structure similar to that in which a large number of prisms are arranged in parallel. For this, a method of providing a diffuser and a light condensing plate having a parallel convex strip surface whose surface is a hemispherical continuum, or whose cross section is a semicircular curve continuous line or a mountain polygonal continuous line (Japanese Patent Laid-Open No. 4-32888). )
Alternatively, there is a method (Japanese Patent Laid-Open No. 5-313004) in which a large number of ridges whose tops are rounded in a convex arc shape and a large number of ridges which are rounded in a valley cross section are alternately and substantially parallel to each other. is there.

The third example is a device for the back surface of the prism or lens sheet. Usually, an optical smooth surface is used for the back surface (Japanese Patent Laid-Open No. 62-144102), but in some cases, an optically non-smooth surface is used (Japanese Patent Laid-Open No. 5-204102).
313004), a method of positively arranging a prism surface on the back surface (Japanese Patent Laid-Open No. 6-67004), and a method of forming a group of minute projections on the back surface of a lens sheet in which the height of the unevenness is equal to or more than the wavelength of the light source light (Japanese Patent Laid-Open No. 6- 324205) has been proposed. Further, an optical film having a first surface having a prism and a second surface having an optical concavo-convex structure for diffuse transmission (Japanese Patent Laid-Open No. 6-109925) has been proposed.

[0006]

In these devices, the first example is an effective method for improving the luminance in the direction of the light emitting surface toward the liquid crystal surface. However, when handling the lens sheet, the prism apex is often scratched, which is a drawback that is observed as uneven light. In addition, interference fringes or close contact between the lens sheet and the diffuser plate, or in the case of stacking multiple lens sheets, reduce the lens effect due to interference fringes or close contact, which leads to loss of light uniformity. Easy In the second example, it is easy to protect against scratches on the top of the prism, but the effect of improving the brightness is small. The third example is effective in preventing the occurrence of light unevenness due to interference fringes and adhesion, but generally tends to hinder the improvement of brightness. Therefore, there is a need for a fourth device capable of sufficiently improving the brightness and enhancing the uniformity of light.

One of them is selection of materials. In general, polymethacrylic acid ester and polycarbonate are widely used as optical materials as a translucent thermoplastic material. Further, in recent years, amorphous polyolefin has come to be used as an optical material (Japanese Patent Laid-Open No. 4-36331).
2, Hei 4-11201). On the other hand, a method of using an active energy ray-curable resin to form a fine prism shape with high accuracy (Japanese Patent Laid-Open Nos. 6-67004 and 6-6717).
8) is proposed. In this case, four steps of a resin coating step, a laminating step of stacking transparent base materials, an active energy ray irradiation curing step, and a releasing step are required. Therefore, it is necessary to select a material that can sufficiently increase the brightness and to faithfully form a shape in which scratches are unlikely to occur during handling by the ordinary polymer material processing method and adhesion between sheets and interference fringes are unlikely to occur. To be done.

[0008]

The present invention has been completed in order to solve the above problems and comprises an amorphous thermoplastic polyester having a refractive index of 1.60 or more and a glass transition temperature of 100 ° C. or more and 150 ° C. or less. The present invention provides a lens sheet characterized in that a plurality of prism-shaped lens units, each having a substantially triangular prism shape, are arranged in a plane shape on at least one surface so that their major axis directions are substantially parallel to each other. .

The material for the lens sheet is excellent in transparency and can form a fine shape with high precision, and the environment resistance of which performance does not change under the use environment conditions of the backlight incorporated in the liquid crystal display device. Heat resistance is required. Polycarbonate is also a useful material for this purpose and is often used, but it is difficult to accurately mold a fine shape by the usual thermoplastic synthetic resin molding method, and the prism sheet obtained by this method has improved brightness. Is not enough.

Amorphous thermoplastic polyester polymers or copolymers have also been proposed as materials for optical applications (JP-A-2-38428, JP-A-2-98845). But,
These resins are often tried as optical recording substrate materials and are not always satisfactory because they have insufficient heat resistance or insufficient optical properties, and those disclosed for lens sheets are Absent.

The present inventors have focused their attention on the fact that amorphous thermoplastic polyester can accurately form a fine shape, and have aimed to improve the performance of the lens sheet, including the improvement of the brightness. 60 or more materials,
The glass transition temperature is 1 to suit the environmental conditions used.
It has been found that the glass transition temperature must be not less than 00 ° C and that the glass transition temperature must be not more than 150 ° C in order to obtain the moldability required for accurately forming a fine shape. On the other hand, in Japanese Patent Laid-Open No. 3-168211, it is 9,
9-bis (4-hydroxyphenyl) fluorene, 2,
Various polyesters composed of 2-bis (4-hydroxyphenyl) propane, terephthalic acid, and isophthalic acid have been proposed. Although the glass transition point is sufficiently high, the range for satisfying both the refractive index and molding processability is rather narrow for lens sheets. Further, there are proposals for improving the mechanical properties of this type of polyester (Japanese Patent Publication No. 4-22931) and for improving the film properties (Japanese Patent Laid-Open No. 3-73902), but in particular Japanese Laid-Open Patent Publication No. 6-49186, 9,9-bis ( Proposed to be suitable for optical disk substrates because polyester made of 4-hydroxyethoxyphenyl) fluorene, ethylene glycol, and terephthalic acid is transparent, has heat resistance, has small optical anisotropy, and has excellent moldability and dimensional stability. Has been done. As a result of multi-faceted examination of this type of copolymer, it has sufficient moldability for molding a fine shape as a lens sheet and has a high refractive index, and as a result, it is possible to sufficiently improve the brightness of the lens sheet. It turned out to be preferable.

Hereinafter, the present invention will be described in detail. The lens sheet of the present invention has a refractive index of 1.60 or more and a glass transition temperature of 10
It is composed of an amorphous thermoplastic polyester having a temperature of 0 ° C. or higher and 150 ° C. or lower. When the refractive index is less than 1.60, the obtained lens sheet does not sufficiently improve the brightness, and when the glass transition point is less than 100 ° C, it is difficult to endure under the environmental conditions in which it is used, and a polyester copolymer having high heat resistance of 150 ° C or higher is fine. It is difficult to form a simple lens shape and the performance is poor. It is essential to meet these requirements together. Various examples are given as examples of the amorphous polyester copolymer of the present invention. The dicarboxylic acid may be used in combination with an aromatic dicarboxylic acid or a partial aliphatic carboxylic acid. Examples of aromatic dicarboxylic acids include phthalic acid, terephthalic acid, isophthalic acid, phenylindanedicarboxylic acid, naphthalenedicarboxylic acid, tetrahydronaphthalenedicarboxylic acid, etc., but it is necessary to appropriately select them in consideration of the type of glycol to be combined. is there. In particular, terephthalic acid is most preferable for the wide selection of dihydroxy compounds described below.

Dihydroxy compounds have 2 to 4 carbon atoms
The above aliphatic glycol is used, but it is preferable to use a part of this glycol by replacing it with a dihydroxy compound containing an aromatic ring in the molecule. In order to maintain heat resistance while being amorphous, the aliphatic glycol is changed to 9,9-bis- (4-hydroxyethoxyphenyl) -fluorene, 9,9-bis (4-hydroxypropoxyphenyl) -fluorene, or the like. It is convenient to replace it. In particular, it is preferable to replace 10 mol% or more of all glycol components in the resin with 9,9-bis (4-hydroxyphenyl) -fluorene. If it is less than 10 mol%, the refractive index is difficult to increase and the heat resistance is insufficient. At this time, it is preferable to combine ethylene glycol as the glycol component.

The amorphous thermoplastic polyester copolymer comprising a dicarboxylic acid and a dihydroxy compound is produced by selecting from known methods such as transesterification method, melt polymerization method such as direct polymerization method, solution polymerization method and interfacial polymerization method. it can. In the case of manufacturing as an optical material, a transesterification method in which impurities hardly enter is suitable. Care should be taken to prevent dust from entering in each step.

In the production of a lens sheet, a shape in which a large number of lens portions of prism-shaped units, which are substantially triangular prisms on at least one surface, are arranged in a plane so that their major axis directions are substantially parallel to each other, improves brightness. effective. The apex angle of the triangular prism is preferably 70 to 110 degrees. Less than 70 degrees and 11
If it exceeds 0 degrees, the effect of improving the brightness is small. This apex angle is a substantial angle, and even if a slight curvature occurs, there is no problem as long as the brightness is not greatly reduced. As a method of preventing scratches that are likely to occur when handling the lens sheet, it is also preferable to provide a slight curvature at the top. One way. Further, it is preferable to use those having substantially the same length from the apex to the respective hypotenuses because light is likely to be concentrated in the normal direction of the prism bottom surface, that is, in front of the observer. Further, in order to make it difficult to distinguish the stripe pattern of the linear prism by the light emitted through the lens sheet, the interval between the prism units is 10 to 100.
0 μm is preferable, and further 10 to 500 μm
More preferably m. The height of the prism unit is determined by the interval of the prism unit. The thickness of the sheet is preferably 50 to 1000 μm. 50 μm
If the thickness is less than 100 μm, the mechanical strength is insufficient, and if the thickness exceeds 1000 μm, it is disadvantageous for light transmission, weight reduction and thickness reduction.

The other surface, which is usually used as an optically smooth surface, is in close contact with the diffuser plate on which the lens sheet is placed, so that light unevenness is caused by eliminating the air layer. If you want to prevent it or increase the brightness further by stacking multiple lens sheets, the uneven surface with minute unevenness to prevent uneven light caused by eliminating the air layer due to the contact between the lens sheets It is also preferable that It is also preferable to use a non-reflective surface that prevents surface reflection on the back surface and increases the amount of incident light.

The method of molding the lens sheet used in the present invention is not particularly limited, and for example, it is a method of molding by a hot press, embossing from the sheet, or transfer from a release sheet having a three-dimensional pattern. A method such as injection molding is possible. In this case, even if the apex angle, the apex edge, the prism plane, and the bottom surface are slightly deformed during the molding process, there is no problem as long as the effect of the present invention can be recognized.

Various methods can be considered for using the lens sheet of the present invention, and the lens surface provided with the prism on the light diffusing plate of the backlight of the liquid crystal display is placed on the side from which light is emitted. It is common to do. The direction of the major axis of the prism is arbitrary, but it may be aligned with the direction of the edge light of the cold-cathode ray tube, or may be arranged perpendicular to this. Further, when it is desired to improve the luminance, the same or similar lens sheets are used in an overlapping manner. in this case,
The effect is enhanced by arranging so as to be orthogonal to the direction of the first sheet. On the other hand, on the other hand, it is also used in a method of arranging the lens surface on which the prism is arranged on the side on which light is incident. This method is effective when the diffusing effect of the light diffusing plate is limited.

The light emitting device of the backlight used in the present invention may be either a direct type or an edge light type.
In recent years, the edge light type is easily thinned and is frequently used.
In the edge light type, a small-diameter cold cathode ray tube is arranged on an end face of a light guide made of a transparent material having a good light transmittance. in this case,
It may be a two-lamp type disposed on opposite end faces or a one-lamp type having only one end. Generally, a diffusion plate is provided on the surface of the light guide surface, and a reflection material is provided on the back surface and the periphery thereof. The lens sheet is usually placed on or below the diffuser plate for use.

[0020]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the following description, "part" means "part by weight" unless otherwise specified.

Example 1 (1) Synthesis of amorphous thermoplastic polyester 9,9-bis- (4-hydroxyethoxyphenyl)-
Using 35 parts of fluorene, 27 parts of ethylene glycol and 38 parts of dimethyl terephthalate as a catalyst, calcium acetate of 0.
Charge 042 together with 042 parts and stir 190
The transesterification reaction was carried out by gradually heating from 0 ° C to 230 ° C. After extracting a predetermined amount of methanol out of the system, 0.012 parts of germanium oxide which is a polymerization catalyst and 0.033 of trimethyl phosphate for preventing coloring are added, and the temperature is gradually raised while reducing the pressure to generate. Ethylene glycol was removed and the temperature of the heating tank was maintained at 280 ° C. and the degree of vacuum was maintained at 1 Torr or less. After maintaining this state and confirming an increase in viscosity, the reaction was terminated, and the reaction product was extruded into water to obtain pellets. The intrinsic viscosity of this copolymer was 0.35 when measured at 20 ° C. in a mixed solution of 60% by weight of phenol and 40% by weight of 1,1,2,2, tetrachloroethane. The glass transition temperature by DSC was 118.4 ° C, and the refractive index by Abbe's refractometer at 23 ° C was 1.62.
The amount of glycol substitution calculated from the methanol and ethylene glycol that flowed out and the charged composition was 40.8 mol%.
Met.

(2) Molding of lens sheet A One-sided mold in which a large number of linear prisms are arranged so that the apexes of an isosceles triangle having an apex angle of 90 degrees, a mountain height of 25 μm, and a base of 50 μm are parallel to each other. Then, a set of molds was prepared so that the distance between two molds that had a slight dullness of 0.8 μm on the other surface was 200 μm. 23% of the amorphous thermoplastic polyester obtained in (1) above
A sheet having a thickness of 0 μm was attached, a mold temperature of 270 ° C. and a pressure of 100 kg / cm ² were held by a hot press for 15 minutes, and then cooled to room temperature to prepare a lens sheet 1A.

(3) Molding of lens sheet B A metal roll having a diameter of 250 mm and having the same prism shape as in lens sheet molding A was heated to 115 ° C. The amorphous thermoplastic resin polyester obtained in (1) above, which was melted by heating to a resin temperature of 280 ° C. by an extruder equipped with a screw, is extruded into a sheet form from a T die, and immediately after that, the Sure hardness is applied to the heating roll. 90, 180 mm diameter rubber roll was pressed at a linear pressure of 31.4 kg / cm. Operating speed 5m /
After a half round of the metal roll, it was peeled off, further cooled by a cooling roll, and then the lens sheet 1B was wound up.

(4) Evaluation of lens sheet performance Luminance measurement 166 mm × 129 mm which is a backlight for liquid crystal display
A voltage of 5 volts and a current of 0.6 amperes were supplied to the cold cathode ray tube, which was installed at one end in the long side direction (equivalent to 8 inches), through an inverter. This light emitting surface device is provided with a reflection plate on the back surface and a diffusion plate on the front surface. From the location at a distance of 700 mm in the direction normal to the surface of the diffusion plate of this light emitting surface device, L
UMINANCE COLORIMTER (TOPC
The brightness was measured by BM5A manufactured by ON Co.). 1335 cd / m ² at the center of the light emitting surface, and 35 mm vertically in the short side direction
The brightness of 1173 cd / m ² and 1199 cd / m ² was shown at the position. Then, an average value of 1236 cd / m ² at 3 points was obtained as a representative value. Next, the lens sheet 1A obtained by the lens sheet molding A is placed on the diffuser plate in parallel with the long side which is the direction of the cold-cathode ray tube with the prism surface in the direction of light emission. 35mm up and down in the center of the light emitting surface and in the direction of the short side
When the brightness of three points at the position of
5 cd / m ^2, shows a ^{1550cd / m 2, 1568cd / m} 2, exhibited a luminance average value 1634cd / m ^2. Furthermore, on top of this
When another lens sheet was laminated in the direction in which the major axis direction of the prism was orthogonal to the first lens sheet and the same measurement as above was carried out, it was 2149 cd / m ² , 1917 cd / m ² , respectively.
m ² , 1895 cd / m ^2, and an average value of 1987 cd / m ² was obtained.

As is clear from the above results, the refractive index of 1.
62, the brightness could be increased about 1.32 times by installing one lens sheet made of amorphous thermoplastic polyester having a glass transition temperature of 124 ° C. Furthermore, by using two sheets, the brightness could be improved by about 1.61 times. In this case, almost no contact or interference fringes between the diffuser plate and the lens sheet were observed, and a uniform light emitting surface was realized.

Subsequently, the lens sheet 1B obtained by the lens sheet molding B is observed in the same manner as the sheet 1A, and the average luminance value when one sheet is used is 1583 cd / m ² ,
When two sheets are used in piles, it is 1930 cd / m ² , and the improvement rate of brightness by installing a lens sheet is 1.28 per sheet.
It was 1.56 times as many as two sheets, and the effect of being sufficiently put to practical use was recognized.

Confirmation of prism shape The lens sheet was sampled in a strip shape having a width direction of 5 mm so that the cross section could be confirmed in a direction perpendicular to the major axis direction of the prism, and this was sampled with a vertical embedding agent (epoxy manufactured by BUEHLER). Solidify the area with resin. A photograph of the solidified sample was magnified 500 times with a polishing optical microscope so that the cross section was clearly observed. Observation from this photograph confirmed that the lens sheet 1A had the dimensions as designed by the mold. On the other hand, in the lens sheet 1B, the height of the prism was 2 μm lower than the design dimension of the mold, and the top had a curvature, and the bottom and bottom were almost as designed. When two lens sheets were overlapped with each other so that the prism surface and the back surface thereof were in contact with each other, scratches were scarcely observed.

Example 2 Using 26 parts of dimethyl terephthalate, 54 parts of 9,9-bis- (4-hydroxyethoxyphenyl) -fluorene and 20 parts of ethylene glycol as a raw material composition, 0.028 parts of calcium acetate and 0. Pellets were obtained in the same manner as in Example 1 except that 009 parts and 0.022 part of trimethyl phosphate were used. This amorphous thermoplastic polyester has an intrinsic viscosity of 0.43 and a glass transition temperature of 145.
C. and the refractive index was 1.63. 9 out of all glycol components
This means that 1.9 mol% was replaced with 9,9-bis- (4-hydroxyethoxyphenyl) -fluorene. Using this polyester, the lens sheet 2A is formed by the method of lens sheet molding A except that the mold temperature is changed to 280 °.
I got Further, a lens sheet 2B was obtained by the same method except that the temperature of the metal roll was changed to 135 ° C. and the extruded resin temperature was changed to 290 ° C. by the method of lens sheet molding B. The brightness of these two types of sheets was measured and the prism shape was confirmed by the same method as in Example 1. The results are shown in Table 1.
The results of Example 1 are also summarized in Table 1. As is clear from Table 1, the polyester having a high glass transition temperature (Example 2) has low moldability in both the sheet molding method A and the sheet molding method B, and the prism is likely to be slightly displaced from the design dimension of the mold. In particular, the top portion is lowered and the curvature is likely to occur. However, the effect of improving the brightness is kept relatively high, and the advantage of protecting the easily damaged top is obtained.

Comparative Example 1 Lens sheet molding A of Example 1 using a commercially available amorphous thermoplastic polyester (polyethylene terephthalate PT-36 manufactured by Mitsui Petrochemical Co., Ltd.) having a refractive index of 1.59 and a glass transition temperature of 58 ° C. as a raw material. A lens sheet was manufactured by the methods of and. In this case, press die temperature is 270 ℃,
The temperature of the extruded resin was 280 ° C., and the temperature of the metal roll at this time was 45 ° C. The obtained lens sheet was used in Example 1.
Table 1 shows the results of performance evaluation performed by the same method as described above. As is clear from Table 1, since the glass transition temperature is low, there is a problem in practical use and the effect of improving the brightness is small.

Comparative Example 2 A commercially available polycarbonate (AD5503 manufactured by Teijin Ltd.) having a refractive index of 1.59 and a glass transition temperature of 148 ° C. was used, and the results are shown in Table 1 by the lens sheet molding methods A and B of Example 1. A lens sheet was manufactured under temperature conditions and the obtained lens sheet was evaluated for performance in the same manner as in Example 1. The results are shown in Table 1. As is clear from Table 1, the moldability of the lens sheet of polycarbonate is poor, and a lens sheet that is considerably different from the design dimension of the mold is likely to be formed. Therefore, the effect of improving the brightness is also poor.

[0031]

[Table 1]

[0032]

As described above, the lens sheet of the present invention exhibits excellent brightness, heat resistance and moldability,
It is useful for liquid crystal display devices.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kawaguchi 4-13-18 Anchi, Suminoe-ku, Osaka-shi, Osaka Within Goyo Paper Co., Ltd. No. 18 In Goyo Paper Co., Ltd. (72) Inventor Hiiragi Ohara 4-13-18 Anchi, Suminoe-ku, Osaka City, Osaka Prefecture In Goyo Paper Co., Ltd.

Claims (5)

[Claims] 1. A refractive index of 1.60 or more and a glass transition temperature of 1.
A large number of prism-shaped lens units, which are made of amorphous thermoplastic polyester at a temperature of 00 ° C or higher and 150 ° C or lower, and are substantially triangular prisms on at least one surface, are arranged so that their major axes are substantially parallel to each other. A lens sheet characterized by being arranged. 2. An amorphous thermoplastic polyester comprising an aromatic dicarboxylic acid or a diester derivative thereof and a compound represented by the general formula (1): (R ₁ is an alkyl group having 2 to 4 carbon atoms, R ₂ R ₃ R ₄ and R ₅ are independently hydrogen or an alkyl group having 1 to 4 carbon atoms) and a dihydroxy compound having 2 to 4 carbon atoms The lens sheet according to claim 1, wherein the lens sheet comprises an aliphatic glycol and a polyester polymer in which the dihydroxy compound represented by the general formula (1) is 10 mol% or more of all glycol components in the resin. 3. The aromatic dicarboxylic acid is terephthalic acid, and the dihydroxy compound represented by the general formula (1) is 9,
The lens sheet according to claim 2, which is 9-bis (4-hydroxyethoxyphenyl) -fluorene and the aliphatic glycol is ethylene glycol. 4. The lens sheet according to claim 1, wherein the apex angle of the triangular prism is in the range of 70 degrees to 110 degrees. 5. The lens sheet according to claim 1, wherein the distance between the prism-shaped units is in the range of 10 μm to 1000 μm.