JP2009265212A - Frictional flaw resistant prism sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frictional flaw resistant prism sheet hardly generating a flaw on a prism face, not getting conspicuous even when flawed, and superior in an optical characteristic. <P>SOLUTION: This frictional flaw resistant prism sheet 1 is arrayed with a large number of large prism structures 2 each having a substantially triangle pole shape and small prism structures 3 smaller than the structure 2 substantially in parallel on at least one face. The large prism structure is formed into a shape with an apex part thereof cut out into a curved face curved toward a convex direction thereof or a substantially horizontal face, and a cut-out width CL is 4.5 μm or more, in the prism sheet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a scratch-resistant prism sheet used for a backlight or the like of a liquid crystal display device. More specifically, the scratch-resistant prism sheet is less likely to have large scratches on the prism surface, less likely to be noticeable, and has high front luminance. Regarding the sheet.

  In recent years, liquid crystal display devices have been used in various fields, and various performances are required depending on the respective applications. OA devices, personal computers, word processors, and the like are strongly demanded to be lighter and thinner, and liquid crystal display devices are increasingly required to have a wider field of view, a wider screen, and higher brightness.

  In order to meet these requirements, it is necessary to change the directivity of light, that is, to use a film or sheet having a light condensing function in order to redirect light in an unnecessary direction and condense it on the front of the observer. Generalized. In particular, the prism sheet concentrates only the light that diffuses in the vertical direction, which is not very important for image observation, in the forward direction, and does not collect the light that diffuses in the horizontal direction, so it is possible to achieve a wide field of view and high brightness at the same time. Can be used widely.

  This prism sheet has a fine prism structure on the surface of a resin sheet, but the surface on which this prism structure is provided faces another optical element such as a diffusion sheet. , It is apt to be scratched especially at the apex of the prism structure due to rubbing with other optical elements, thereby making it impossible to exhibit desired optical performance or causing scratches to be conspicuous and deteriorating the image quality of the liquid crystal display device There is.

  In order to solve such a problem, the present applicant provides an invention for protecting the prism structure by interposing a low refractive index resin between the prism sheet and another optical element (patent). Reference 1). However, even though the resin has a low refractive index, the refractive index is higher than that of air, so the performance of the prism structure deteriorates and there is a difference in the coefficient of thermal expansion between the prism sheet and the other optical elements, so that it bends due to temperature changes. There is. Moreover, there is a problem that not only the raw material cost increases but also the manufacturing process increases and the assembling cost also increases.

As a technique for preventing damage to the prism structure without using a resin having a low refractive index, the apex portion of the prism structure is formed into an arc shape having a curvature radius of 5 μm or less, or a flat part having a width of 5 μm or less (Patent Document 2). See). However, since it is necessary for all the prism structures to have an arc shape or a flat shape at the top, the front luminance is significantly reduced. In addition, when the surface of the prism structure is rubbed strongly, the scratches are very conspicuous, and the image quality is greatly deteriorated.
JP 2002-82212 A JP 2001-343507 A

As a result of diligent research to solve the above-mentioned conventional drawbacks, the present inventor looks like a single scratch when the scratches occur continuously in a plurality of prism structures, whereas It has been found that when the scratch of only one prism structure occurs, it is difficult to visually recognize this and it is inconspicuous.
Based on such knowledge, the present invention is not only difficult to scratch, but even when the surface provided with the prism structure is rubbed strongly, the adjacent prism structure is not damaged at the same time. An object of the present invention is to provide a scratch-resistant prism sheet that is not conspicuous and does not reduce the front luminance.

  The present invention has been made to achieve the above object, and the invention according to claim 1 of the present invention has a substantially triangular prism large prism structure and a lower prism structure substantially lower on at least one surface. A large number of prism sheets arranged in parallel, wherein the large prism structure has a shape in which the top portion is cut into a curved shape or a substantially horizontal plane curved in the protruding direction, and the notch width (CL) is 4. The content of the scratch-resistant prism sheet is 5 μm or more.

  The invention according to claim 2 of the present invention comprises the scratch-resistant prism sheet according to claim 1, wherein the height difference (D) between the large prism structure and the small prism structure is 3 μm or more.

  The invention according to claim 3 of the present invention is characterized in that the ratio (D / P) of altitude difference (D) to pitch (P) of the large prism structure is 0.03 or more. The content is a scratch-resistant prism sheet.

  The invention according to claim 4 of the present invention is characterized in that the ratio (WS / WL) of the bottom surface width (WS) of the small prism structure to the bottom surface width (WL) of the large prism structure is 0.25 to 0.8. The scratch-resistant prism sheet according to any one of claims 1 to 3 is included.

  The invention according to claim 5 of the present invention is characterized in that the ratio (WL / P) of the bottom surface width (WL) of the large prism structure to the pitch (P) of the large prism structure is 0.5 or less. The scratch-resistant prism sheet according to any one of claims 1 to 4 is included.

  The invention according to claim 6 of the present invention is the scratch-resistant prism sheet according to any one of claims 1 to 5, wherein the notch width (CL) of the large prism structure is 40 μm or less. And

  The invention according to claim 7 of the present invention is characterized in that the ratio (CL / WL) of the notch width (CL) to the bottom surface width (WL) of the large prism structure is 0.2 or less. The content is the scratch-resistant prism sheet described.

  The invention according to claim 8 of the present invention comprises a scratch-resistant prism sheet according to any one of claims 1 to 7, which is made of a resin mixed with a diffusing agent. .

  In the invention according to claim 9 of the present invention, projections having the same height are provided on the surface where the prism structure is not provided, and the ratio of the installation area of the projections to the total area of the scratch-resistant prism sheet is 0.003. The scratch-resistant prism sheet according to any one of claims 1 to 8, characterized in that the content is -0.2.

The scratch-resistant prism sheet of the present invention is provided with a large prism structure and a smaller prism structure lower than this on at least one surface, so that the surface on which the prism structure is provided is made to face another optical element or the like. However, since only the apex of the large prism structure is in contact with other optical elements and not the small prism structure, at least the small prism structure is not scratched. In addition, the large prism structure has a curved shape or a substantially horizontal plane that is curved in the protruding direction and has a notch width of 4.5 μm or more. It is hard to stick. Even if multiple large prism structures are damaged, small prism structures are interposed between adjacent large prism structures. Therefore, the large prism structures are separated from each other. It does not look like a book scratch and is not noticeable.
In addition, it is not necessary to provide a notch at the top of the small prism structure, and the whole can be used as a prism, so that the function of the prism can be fully utilized and high front luminance can be maintained.

  If the height difference (D) between the large prism structure and the small prism structure is 3 μm or more, the surface on which the prism structure of the scratch-resistant prism sheet of the present invention is provided on other optical elements to which normal dust or dirt adheres Even if they face each other, the small prism structure is not scratched.

  If the ratio (D / P) of the height difference (D) to the pitch (P) of the large prism structure is 0.03 or more, for example, the scratch-resistant prism sheet of the present invention is used so that the prism structure faces downward. In such a case, even if the scratch-resistant prism sheet is slightly bent and the small prism structure hangs between the two large prism structures, the height difference is such that the top of the small prism structure does not come into contact with other optical elements below. Is maintained, and scratches are avoided.

  If the ratio (WS / WL) of the bottom surface width (WS) of the small prism structure to the bottom surface width (WL) of the large prism structure is 0.25 to 0.8, the optical performance of the large prism structure and the small prism structure is large. Since no difference occurs, the optical performance of the prism sheet is substantially uniformed.

  If the ratio (WL / P) of the bottom surface width (WL) of the large prism structure to the pitch (P) of the large prism structure is less than 0.5, one dust or dust will rub and scratch multiple large prism structures. However, since these scratches separate many small prism structures, it is difficult to recognize as a single long scratch, and the scratches are more difficult to see.

  If the notch width (CL) of the large prism structure is 40 μm or less, the notch at the top cannot be visually recognized with the naked eye, so that the optical performance of the prism sheet is substantially uniformized.

  If the ratio (CL / WL) of the notch width (CL) to the bottom surface width (WL) of the large prism structure is 0.2 or less, there is no significant difference in optical performance between the large prism structure and the small prism structure. The optical performance of the prism sheet is made substantially uniform.

  If the prism sheet is formed of a resin mixed with a diffusing agent, it is not necessary to separately dispose a diffusing sheet or the like, so that not only the structure becomes compact, but also the assembly cost is reduced.

  If a protrusion is provided on the surface where the prism structure is not provided and the ratio of the installation area of the protrusion to the total area of the scratch-resistant prism sheet is 0.003 to 0.2, the surface is adhered to the diffusion plate or the like. In this case, a space is maintained between the diffusion plate and the prism sheet, and the performance of the diffusion plate and the like is maintained in this portion, so that the wetting phenomenon is less likely to occur.

  As shown schematically in FIG. 1, the scratch-resistant prism sheet 1 of the present invention has a large prism structure 2 having a substantially triangular prism on at least one surface (hereinafter sometimes referred to as a prism surface) and A large number of small prism structures 3 are arranged substantially in parallel. Furthermore, the top portion of the large prism structure 2 has a curved shape or a substantially horizontal shape that is curved in the protruding direction, and a notch width (CL) of 4.5 μm or more.

  In the present invention, as the large prism structure 2 and the small prism structure 3, it is possible to select a shape in which the shape of the triangular prism cross section easily exhibits the light collecting ability and the apex angle is in the range of 60 degrees to 120 degrees. Preferably, it is in the range of 70 degrees to 110 degrees. The shape of the triangle is not particularly limited and may be either an equal side or an unequal side, but an isosceles triangle is preferable in terms of improving the light collecting performance in the normal direction of the diffusion sheet, and is therefore adjacent to the base opposite to the top. It is preferable that the adjacent isosceles triangles are sequentially arranged and arranged such that the top row is a major axis and is substantially parallel to each other.

  In the present invention, since there is an altitude difference (D) between the large prism structure 2 and the small prism structure 3, there are irregularities in other optical elements arranged facing the prism surface, and dust, Even if they are attached, they do not come into contact with the small prism structure 3 and are not damaged if their size is smaller than the height difference (D). Further, even if two or more large prism structures 2 are damaged, the large prism structures 2 are separated from each other by an intervening small prism structure 3 and thus do not look like one long scratch. ,Inconspicuous.

  This height difference (D) is not particularly limited because it depends on the unevenness of the optical element facing the prism surface and the expected size of dust, but is usually preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm. It is said above.

  However, even if the altitude difference (D) is greater than or equal to the above, for example, when used with the prism surface facing downward, the pitch (P) of the large prism structure 2 (from one large prism structure 2 If the distance to the large prism structure 2 closest to is long, the prism sheet 1 bends and the small prism structure 3 hangs down, and even when the prism surface is faced upward, the optical element placed on the top is bent such as a diffusion sheet. If easy, a diffusion sheet or the like, which is another optical element, hangs down between the large prism structures 2, and the small prism structure 3 comes into contact with the optical elements arranged facing the prism surface. The top may be scratched. In order to prevent this, when the pitch of the large prism structure 2 is long, it is preferable to increase the height difference (D) accordingly. Specifically, the ratio (D / P) of the height difference (D) to the pitch (P) of the large prism structure is preferably 0.03 or more, more preferably 0.05 or more, and particularly preferably 0.10 or more. To do.

  The upper limit of the altitude difference (D) is not particularly defined in terms of achieving the object of the present invention. However, in order to increase the altitude difference (D), it is necessary to increase the large prism structure 2 and to decrease the small prism structure 3. Therefore, if the altitude difference (D) is too large, the large prism structure 2 is relatively moved. There are cases where the original light collecting function of the prism sheet cannot be sufficiently exhibited, such as being too large to be seen with the naked eye, or the small prism structure 3 being too small to deteriorate the processing accuracy. Therefore, it may be determined appropriately in consideration of these, but is usually about 175 μm.

  The size of the large prism structure 2 is usually such that the bottom surface width (WL) is 30 to 400 μm. If it is smaller than 30 μm, it is necessary to make the small prism structure 3 smaller than this, but the current technology is too small to maintain the processing accuracy, and the predetermined optical performance cannot be exhibited. If it is larger than 400 μm, the prism can be seen with the naked eye, and it becomes difficult to obtain uniform optical performance.

  The size of the small prism structure 3 needs to be designed in consideration of the shape and size of the large prism structure 2 and the condition of altitude difference (D), and thus cannot be defined unconditionally. When the bottom surface width (WL) is 30 to 400 μm, the bottom surface width (WS) of the small prism structure is preferably about 20 μm to 390 μm. The size of the large prism structure 2 needs to be constant in one prism sheet 1, but the size of the small prism structure 3 does not have to be constant. For example, as shown in FIG. In addition, two or more types of small prism structures 3 may be provided. In the example shown in FIG. 2, the small prism structure 3b at the center is larger than the small prism structures 3a arranged on both sides thereof (sometimes referred to as a medium prism structure 3b). Various types of small prism structures 3 (3a, 3b) are arranged. In this case, the height difference (D) is the difference in height between the large small prism structure (medium prism structure) 3b and the large prism structure 2.

  As described above, in the present invention, two or three or more types of prisms are provided. In order to make the optical performance in the prism sheet 1 uniform, the prism structure 1 has a bottom width (WL) with respect to the bottom surface width (WL). The ratio (WS / WL) of the bottom surface width (WS) of the small prism structure 3 can be set to 0.25 to 0.8. Further, for the same purpose, the large prism structure 2 and the small prism structure 3 may be similar to each other.

  When two or more large prism structures 2 are scratched, if these scratches are close to each other, they are recognized as one large scratch and are conspicuous. Therefore, the large prism structure is arranged to keep these scratches as far as possible. It is preferable to increase the pitch (P) of 2. However, even if the pitch (P) is relatively short, if the ratio (WL / P) of the bottom surface width (WL) of the large prism structure to the pitch (P) of the large prism structure is 0.5 or less, there is no damage. Since the total of the bottom surface width (WS) of the prism structure is larger than the total of the bottom surface width (WL) of the large prism structure, the scratches are not noticeable.

  In the present invention, the large prism structure 2 has a shape in which the top portion is notched in a curved surface shape or a substantially horizontal surface shape curved in the protruding direction. Here, the shape in which the top portion is cut into a curved shape curved in the protruding direction means the shape of a prism whose top portion is rounded, such as the large prism structure 2 described in FIGS. 1 and 2. . The shape in which the top is cut out in a substantially horizontal plane means that the cross-sectional shape is substantially trapezoidal as shown in FIG. 3, for example.

Since the notch width (CL) of the large prism structure 2 is 4.5 μm or more, it is difficult to be damaged by unevenness, dust, dust, etc. of the opposing optical element, and even if it is damaged, a large amount of resin is missing. Etc. does not occur, and the damage is minimally suppressed.
If this notch portion is observed with a microscope or the like, refraction is clearly different from other portions and can be easily distinguished. However, if the notch width (CL) exceeds 40 μm, it may be recognized with the naked eye. The optical performance of the prism sheet may be uneven. Therefore, the notch width (CL) is preferably 40 μm or less, more preferably 35 μm or less.
Even if the notch width (CL) is 40 μm or less, if the ratio (CL / WL) of the notch width (CL) to the bottom face width (WL) of the large prism structure 2 exceeds 0.2, the small prism structure Condensing efficiency is inferior compared to 3, and the optical performance of the prism sheet as a whole may be uneven. Therefore, the ratio (CL / WL) is preferably 0.2 or less, and more preferably 0.18.

  In addition, although it does not specifically limit about the top part of the small prism structure 3, In order to fully exhibit the prism function of the small prism structure 3, it is preferable to employ | adopt what does not have a notch part as usual. . However, a cutout portion narrower than the cutout width (CL) of the large prism structure 2 can be provided in the small prism structure 3 as necessary.

  In the present invention, the structure of the surface on which the large prism structure 2 and the small prism structure 3 are not provided (hereinafter sometimes referred to as the back surface) is not particularly limited, and may be a simple flat surface. It is also possible to increase the scratch resistance on the back surface or to diffuse light from the backlight to obtain uniform light.

Protrusions having substantially the same height are provided regularly or irregularly (randomly). For example, when the prism sheet is bonded to the diffusion plate, the prism sheet is not part of the entire back surface but the part through the protrusion. In this case, since the diffusion function of the diffusion plate is not hindered, the front luminance increases as a result. If the protrusions are arranged in a regular pattern such as a grid or a straight line, interference fringes may occur due to interference with the prism structure on the surface. If the arrangement of the protrusions is made random, such interference fringes and the like are not generated, which is preferable because the quality as a surface light source is improved.
However, the arrangement of the protrusions is preferably adjusted so that the distance between the protrusions does not become too short. When the distance between the protrusions is smaller than 10 μm, these protrusions are visually recognized as if they were one large protrusion, and may be visible to the naked eye. The appropriate interval varies depending on the ratio of the installation area of the protrusions to the total area of the scratch-resistant prism sheet, and the like. For example, when the installation area of the protrusions is about 4% of the total area of the scratch-resistant prism sheet, The pitch is about 800 μm.

The ratio of the installation area of the protrusions to the total area of the scratch-resistant prism sheet is preferably 0.003 to 0.2. When this ratio is less than 0.003, the scratch resistance is not sufficient, and when it exceeds 0.2, the front luminance tends to decrease.
In addition, the installation area of protrusions means the sum total of the areas where protrusions are installed on the scratch-resistant prism sheet.

The material of the scratch-resistant prism sheet is not particularly limited as long as it is a transparent material, and a normal optical transparent resin can be used. Examples of the optically transparent resin that can be used in the present invention include acrylic resins, polycarbonate, polystyrene, polyvinyl chloride, polypropylene, polymethylpentene and other polyolefins, cyclic polyolefin, polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Examples thereof include thermoplastic resins such as resins, polyamide resins, polyarylate, and polyimide, and curable resins that are cured by ionizing radiation such as acrylic resins.
Moreover, the function as a diffusion sheet can also be provided by mix | blending a diffusion material with said transparent resin. Examples of diffusing agents that can be used include inorganic particles such as aluminum silicate, calcium silicate, silica, alumina, calcium carbonate, and organic particles such as crosslinked polyacrylate, crosslinked MS resin (MMA and styrene copolymer), and silicon resin. Can be illustrated.
The mixing ratio of the diffusing material is usually 0.1 to 10 parts by weight with respect to 100 parts by weight of the transparent resin. If the amount is less than 0.1 parts by weight, the diffusion effect is not sufficient and the difference in brightness cannot be sufficiently erased. On the other hand, if the amount is more than 10 parts by weight, the total light transmittance is lowered and the light collecting effect is insufficient.

  As a method of forming the large prism structure 2 and the small prism structure 3 on the prism surface of the scratch-resistant prism sheet and forming the protrusions on the back surface as necessary, there are a method using a thermoplastic resin and a method using a curable resin. In the case of a thermoplastic resin, a normal forming method is possible, and a method of injection molding into a desired mold, or a method of compression-molding a sheet-like material with a mold is possible.

  In the case of extrusion molding, for example, a molding sheet in which a prism shape is preliminarily engraved on a release sheet is used, and the prism shape is transferred by pressing the molding sheet to a material extruded into a sheet shape under heating. Examples of the method include a method of transferring the prism shape by pressing with a die roll in which the prism shape is engraved during melt extrusion of the material. And when providing a protrusion also in a back surface, both surfaces can also be simultaneously shape | molded, for example with one side by a shaping | molding sheet and the other surface with a metal mold | die roll.

  In addition, as a prism shape engraved on the shaping sheet or the cooling roll, a shape in which a trough portion (a portion that becomes a top portion after transfer) is cut into a curved surface or a horizontal surface can be used. If the resin is pressed by normal pressure, the shape of the transferred prism will inevitably be cut off at the top.

  In the case of a curable resin, an ultraviolet curable resin is usually used in the case of ionizing radiation. In general, after applying a curable resin on a transparent support, it is molded by irradiating ultraviolet rays in a mold.

  The thickness of the scratch-resistant prism sheet of the present invention is arbitrary, but from the viewpoint of handling at the time of assembling the liquid crystal television, it is usually preferably from 50 μm to 500 μm, and from the viewpoint of continuous production, preferably from 100 μm to 400 μm.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Adjustment of resin used)
To 100 parts by weight of a polycarbonate transparent resin “Panlite L-1225Y” (manufactured by Teijin Chemicals Ltd.), 1 part by weight and 0.5 part by weight of a crosslinked MS resin particle of about 10 μm as a diffusing agent are blended, respectively. Resins A and B were used. Further, the resin C was not blended with a diffusing material. In addition, when a flat sheet having a thickness of 240 μm was prepared with these resins and haze was measured for these sheets by the method defined in JIS K7136, 62% of the sheets prepared with resin A and 40% with resin B were used. In the case of Resin C, it was 5%.

(Manufacture of scratch-resistant prism sheet)
Example 1
Resin A is extruded into a sheet form from a die at a resin temperature of melt extrusion of 295 ° C., and the extruded sheet-shaped molten resin is molded into a release sheet in which a large prism shape and a small prism shape are pre-molded, and a surface A scratch-resistant prism sheet was produced by a method of sandwiching between a flat cooling roll.
The prism shape engraved on the releasable sheet is an isosceles triangle having a cross-sectional shape of 90 ° apex angle and 45 ° angle with the base, and one large prism structure 2 having a bottom width (WL) of 100 μm. The prism sheet 3 is made up of four small prism structures 3 having a bottom width (WS) of 50 μm and arranged at a pitch (P) of 300 μm (= 100 × 1 + 50 × 4). The notch width (CL) of the large prism structure is 4.5 μm.
Notch width (CL) of the above large prism structure, height of large prism structure (HL), large, bottom width (WL) and (WS) of small prism structure, pitch of large prism structure (P), large prism structure The ratio (WL / P) of the bottom surface width (WL) of the large prism structure to the pitch (P), the height (HS) of the small prism structure, the number of small prism structures (N), the large prism structure and the small prism structure Height difference (D), ratio of height difference to pitch of large prism structure (D / P), ratio of bottom surface width (WS) of small prism structure to bottom width (WL) of large prism structure (WS / WL), Table 1 shows the ratio (CL / WL) of the notch width (CL) to the bottom surface width (WL) of the large prism structure.
The thickness of the portion excluding the prism structure from the obtained sheet was 240 μm. The scratch resistance and optical properties of the resulting scratch resistant prism sheet were evaluated by the methods described below. The evaluation results are shown in Table 1.

Examples 2-5, Comparative Example 1
The scratch-resistant prism was the same as Example 1 except that the notch width (CL) of the large prism structure was 6, 10, 18, 20 μm (Examples 2 to 5) and 4 μm (Comparative Example 1), respectively. Created a sheet. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 6
Example 1 except that the bottom surface width (WL) of the large prism structure is 200 μm, the bottom surface width (WS) of the small prism structure is 70 μm, and the number of small prism structures is three for one large prism structure. A scratch-resistant prism sheet was prepared in the same manner. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 7 to 10, Comparative Example 2
The scratch-resistant prism was the same as Example 6 except that the notch width (CL) of the large prism structure was 6, 10, 38, 40 μm (Examples 7 to 10) and 4 μm (Comparative Example 2), respectively. Created a sheet. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 11
A scratch-resistant prism sheet was prepared in the same manner as in Example 10 except that the bottom surface width (WL) of the large prism structure was 280 μm and the bottom surface width (WS) of the small prism structure was 100 μm. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 12
Except that the bottom surface width (WL) of the large prism structure is 50 μm, the bottom surface width (WS) of the small prism structure is 41 μm, and the number of small prism structures per one large prism structure is one, the third embodiment A scratch-resistant prism sheet was prepared in the same manner. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 13-15
A scratch-resistant prism sheet was prepared in the same manner as in Example 12 except that the bottom prism width (WL) of the small prism structure was 39, 35, and 25 μm, respectively. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 16
Scratch-resistant prism sheets were prepared in the same manner as in Examples 13 to 15 except that the bottom surface width (WL) of the large prism structure was 100 μm and the bottom surface width (WS) of the small prism structure was 85 μm. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 17-21
A scratch-resistant prism sheet was prepared in the same manner as in Examples 12 to 16, except that the number of small prism structures was two for one large prism structure. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 22 and 23
A scratch-resistant prism sheet was prepared in the same manner as in Example 3 except that the number of small prism structures was one for one large prism structure. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 24
The bottom surface width (WL) of the large prism structure is 120 μm, the bottom surface width (WS) of the small prism structure is 20 μm, the number of small prism structures for one large prism structure is 24, and the pitch of the large prism structure is 600 μm. Otherwise, a scratch-resistant prism sheet was prepared in the same manner as in Example 3 above. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 25 and 26
In addition to setting the bottom prism width (WS) of the small prism structure to 30 and 96 μm, and the pitch of the large prism structure to 600 μm, the number of small prism structures for one large prism structure is 16 and 5 respectively. A scratch-resistant prism sheet was prepared in the same manner as in Example 24 above. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 27
A scratch-resistant prism sheet was prepared in the same manner as in Example 26 except that the bottom surface width (WS) of the small prism structure was 110 μm. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 28 and 29
A scratch-resistant prism sheet was prepared in the same manner as in Example 3 except that resin B and resin C were used. Table 1 shows the evaluation results of scratch resistance and optical properties.

Example 30
A scratch-resistant prism sheet was prepared in the same manner as in Example 3 except that protrusions (random) were provided on the back surface. The design of the projection (size on the mold) is a rectangular parallelepiped with a 100 μm square and a height of 18 μm. However, the side of the projection is about 60 to 96 μm near the top of the projection due to the surrounding nature of the resin. Yes. The ratio of the installation area of the protrusion to the total area of the prism sheet is about 0.02 (2%). Table 1 shows the evaluation results of scratch resistance and optical properties.

Comparative Examples 3-5
A scratch-resistant prism sheet was prepared in the same manner as in Examples 1 to 3, except that the bottom surface width (WL) of the large prism structure was 50 μm and the small prism structure was not provided. Table 1 shows the evaluation results of scratch resistance and optical properties.

Examples 31-33
A scratch-resistant prism sheet in which a large prism structure 2 and two kinds of small prism structures 3 (however, a relatively large small prism structure 3 may be referred to as an intermediate prism structure for convenience) are arranged in Example 1. Created in the same way. In these examples, the height difference (D) between the large prism structure 2 and the small prism structure 3 is the difference between the height (HL) of the large prism structure 2 and the height (HM) of the medium prism structure. Table 2 shows the evaluation results of scratch resistance and optical properties.
The arrangement of the prism structures in these examples is “large, small, medium, and small” in the order of Example 31, “large, small, medium, and small” in Example 32, and “large, small, medium, and small” in Example 33. A large number of unit prism rows arranged in order are arranged in parallel. However, in the character string indicating the arrangement of the unit prism arrays, large, medium, and small characters indicate a large prism structure, a medium prism structure, and a small prism structure, respectively.

Examples 34 and 35
A scratch-resistant prism sheet was prepared in the same manner as in Example 33 except that Resin B and Resin C were used. Table 2 shows the evaluation results of scratch resistance and optical properties.

Example 36
A scratch-resistant prism sheet was prepared in the same manner as in Example 33 except that the same protrusion (random) as that in Example 30 was provided on the back surface. Table 2 shows the evaluation results of scratch resistance and optical properties.

(Abrasion resistance test)
Diffusion film D124Z (manufactured by Tsujiden Co., Ltd.) is placed on the 4 mm-thick milky acrylic flat plate used for the light guide plate with the uneven surface facing up, in accordance with the backlight of the liquid crystal display device that is put to practical use. The scratch-resistant prism sheet obtained in Examples and Comparative Examples is placed on the surface so that the back surface is in contact with the uneven surface, and the diffusion film PBS072 (manufactured by Eiwa Co., Ltd.) is placed thereon. After fixing the four sides, vibration was applied with a testing machine. Thereafter, the prism surface of the scratch-resistant prism sheet was visually observed and evaluated according to the following evaluation methods and standards. The result is shown as a visual impression.
(Vibration conditions)
Testing machine: EMICF 600BA / FAEO8 manufactured by Emic Co., Ltd.
Vibration cycle: Up and down from 20 Hz to 400 Hz in 11 minutes, this is taken as one cycle and vibrates in the vertical, horizontal and height directions for 1 hour each.
Amplitude: 0.075 mm up to 50 Hz, 50 Hz or more is due to amplitude regulation by a constant acceleration of 1.5 G.
Evaluation method and evaluation criteria: The bottom of the light guide plate is illuminated, and the prism surface of the scratch-resistant prism sheet is observed from an oblique direction.
A: Scratches are not visible even when observed with a magnifier.
○: No scratches are visible even when staring.
Δ: Scratches are not noticeable.
X: Scratches are conspicuous.

(Evaluation of optical properties)
The brightness difference of the scratch-resistant prism sheet can be measured by measuring the luminance of each part of the backlight by reducing the light receiving surface of the luminance meter and calculating the difference. However, the quality of the surface light source must be judged by the naked eye.
Further, the quality of the backlight is characterized by the presence or absence of light rays that are strongly emitted in a specific direction, which can be determined by the naked eye as glare.
Therefore, the optical characteristics were evaluated by measurement with a luminance meter and determination with the naked eye.

Backlight configuration:
A backlight for a 32-inch television having a length of 400 mm and a width of 705 mm, in which 16 linear cathode ray tubes are arranged at equal intervals in the horizontal direction, is lit, and a light reflector is placed under the linear light source in the backlight cavity. Arranged.
On the other hand, a double-sided adhesive paste (manufactured by Sekisui Chemical Co., Ltd., trade name: double tack tape # 5511, adhesive) on the entire upper surface of a 2 mm-thick light diffusion plate “Optomax” (manufactured by Sumitomo Bakelite Co., Ltd.) The thickness of the agent layer is 5 μm), and the scratch-resistant prism sheet obtained in the examples and comparative examples is placed thereon, and the diffuser plate and the prism sheet are brought into close contact by lightly pressing from above. It was.
The bonded light diffusing plate and the scratch-resistant prism sheet are placed on the backlight, with the prism surface on the exit surface side, and the major axis direction of the large and small prism structures 2 and 3 coincides with the major axis direction of the cathode ray tube. It was installed to do.

Luminance measurement:
The central point of the installed scratch-resistant prism sheet at a distance of 500 mm above the surface on which the scratch-resistant prism sheet is installed, with a luminance meter Minolta CA-1500 (manufactured by Konica Minolta Co., Ltd.) measuring area 4.8 cm ^2. The brightness of was measured.

Judgment of appearance quality of backlight emission:
Uniformity of emitted light:
The light emitted from the backlight through the scratch-resistant prism sheet was visually observed, and whether or not a fine stripe pattern extending in the length direction of the prism structure could be observed was visually determined according to the following criteria.
A: Even when staring, no striped pattern is seen.
○: Striped pattern is not visible in normal observation.
Δ: Striped pattern is visible, but disappears after passing through the liquid crystal panel.
X: A striped pattern is visible and may be visible even after passing through the liquid crystal panel.

Difference in brightness between the upper part of the linear light source and its middle part:
The light-dark difference between the immediately upper part of the linear light source and the intermediate part thereof was visually determined according to the following criteria.
○: No difference in brightness is recognized.
Δ: A slight difference in brightness is recognized.
X: A contrast difference is clearly recognized.

Glare:
The glare that enters the viewer's eyes directly from each direction due to reflection, refraction, and the like from the light source was visually determined according to the following criteria.
○: Glittering is not visible and the light is exiting gently.
Δ: Glare is visible, but disappears after passing through the liquid crystal panel.
X: Glitter is visible and may be visible after passing through the liquid crystal panel.

  As described above, the scratch-resistant prism sheet of the present invention is a prism sheet in which a large number of substantially prismatic large prism structures and lower small prism structures are arranged substantially in parallel on at least one surface. The large prism structure has a shape in which the top portion is notched in a curved shape or a substantially horizontal plane curved in the protruding direction, and the notch width (CL) is 4.5 μm or more, so that it is difficult to be damaged. Even if scratches are present, this is not noticeable, and the front luminance is high, so that it is useful as a prism sheet for a liquid crystal display device.

It is a schematic explanatory drawing which shows the abrasion-resistant prism sheet of this invention. It is a schematic explanatory drawing which shows another scratch-resistant prism sheet. It is a schematic explanatory drawing which shows another abrasion-resistant prism sheet.

Explanation of symbols

1 Scratch resistant prism sheet 2 Large prism structure 3, 3a, 3b Small prism structure WL Bottom width of large prism structure WM Bottom width of medium prism structure WS Bottom width of small prism structure CL Notch width of large prism structure HL Large prism structure Height HM Height of medium prism structure HS Height of small prism structure D Height difference between large prism structure and small prism structure (or medium prism structure) P Pitch of large prism structure

Claims (9)

A prism sheet in which a large number of substantially prismatic large prism structures and lower small prism structures are arranged substantially in parallel on at least one surface,
The large prism structure has a shape in which the top portion is notched in a curved surface or a substantially horizontal plane curved in the protruding direction, and the notch width (CL) is 4.5 μm or more. Prism sheet.   2. The scratch-resistant prism sheet according to claim 1, wherein the height difference (D) between the large prism structure and the small prism structure is 3 μm or more.   The scratch-resistant prism sheet according to claim 2, wherein a ratio (D / P) of altitude difference (D) to pitch (P) of the large prism structure is 0.03 or more.   4. The ratio (WS / WL) of the bottom surface width (WS) of the small prism structure to the bottom surface width (WL) of the large prism structure is 0.25 to 0.8. 5. A scratch-resistant prism sheet according to claim 1.   5. The ratio (WL / P) of the bottom surface width (WL) of the large prism structure to the pitch (P) of the large prism structure is 0.5 or less, according to claim 1. Scratch-resistant prism sheet.   The scratch-resistant prism sheet according to any one of claims 1 to 5, wherein a notch width (CL) of the large prism structure is 40 µm or less.   The scratch-resistant prism sheet according to claim 6, wherein the ratio (CL / WL) of the notch width (CL) to the bottom surface width (WL) of the large prism structure is 0.2 or less.   The scratch-resistant prism sheet according to any one of claims 1 to 7, wherein the scratch-resistant prism sheet is made of a resin mixed with a diffusing agent.   Projections having the same height are provided on the surface not provided with the prism structure, and the ratio of the installation area of the projections to the total area of the scratch-resistant prism sheet is 0.003 to 0.2. The scratch-resistant prism sheet according to any one of claims 1 to 8.

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