JP5483676B2 - Prism sheet and backlight using the same - Google Patents

Description

  The present invention relates to a prism sheet used for a backlight of a liquid crystal display device, for example, and a prism sheet that has excellent scratch resistance and makes it difficult to visually recognize an optical defect while suppressing a decrease in luminance in the front direction, and a backlight using the prism sheet It is about.

  In recent years, color liquid crystal display devices have been used in various fields such as monitors for notebook personal computers or desktop personal computers or liquid crystal televisions. This type of liquid crystal display device includes a liquid crystal cell and a backlight, and the backlight has a light source structure directly below the liquid crystal cell via a diffusion plate or a light source. An edge light type structure provided on the side surface of the light plate is known.

  The color liquid crystal display device is superior in that it consumes less power than PDP and CRT. However, in the color liquid crystal display device, the front luminance tends to be low. Therefore, it is required to increase the front luminance with low power consumption by increasing the optical efficiency using the above-described backlight.

  Such a backlight is generally composed of a light source, a diffusion plate, a light guide plate, a plurality of optical sheets, and the like.

  Examples of the optical sheet include a reflective polarizing sheet, a prism sheet, a diffusion sheet, and the like. Among these, the prism sheet is disposed on the light emission surface of the diffusion plate or the light guide plate, and is emitted from the diffusion plate or the light guide plate. The light is condensed on the front side by refraction, and the front luminance is improved.

  In general, the prism sheet includes a lens portion in which a plurality of structural rows having a triangular cross section are regularly arranged, and the apex angle of the triangular structural rows, that is, the angle formed between the hypotenuses is 90. This is considered to be optimal for increasing the front brightness. It is considered that the radius of curvature of the top of the lens unit is 0, that is, it is desirable that the tip has a sharp shape.

  Such a prism sheet has a sharp tip at the end of the structure row, so it is easy to cause scratches at the time of handling or damage at the end of the structure row due to vibration during use. Since a defect occurs, handling of the prism sheet requires great care.

  Therefore, in order not to cause an optical defect due to scratches, the top of the structure row is not a sharp shape but an arc shape, or the structure row is made of a trapezoidal section instead of a triangular section. A method of improving has been proposed (Patent Documents 1 and 2).

JP-A-11-305011 (Claims) JP 2001-343507 A (Claims)

  However, with this method, the scratch resistance is improved and optical defects are difficult to see compared to the conventional prism sheet, but on the other hand, the front brightness is greatly reduced, and the original function as a prism sheet is reduced. It will be greatly damaged.

  Accordingly, an object of the present invention is to provide a prism sheet that is excellent in scratch resistance and hardly sees optical defects while suppressing a decrease in luminance in the front direction.

  The inventor is a prism sheet having a lens layer in which a plurality of trapezoidal structure rows are arranged in parallel, and the arithmetic average roughness of the upper base portion and the side surface portion of the structure row is set to a specific value. Thus, the present inventors have found that a prism sheet having excellent scratch resistance and in which optical defects are hardly visible can be obtained, and the present invention has been achieved.

That is, the prism sheet of the present invention has a lens layer in which a plurality of trapezoidal structure rows are arranged in parallel, and the surface on which the plurality of structure rows are arranged in parallel is a light emitting side, and a plurality of the structure rows are arranged in parallel. A prism sheet arranged so that the surface opposite to the light incident side is the light incident side ,
When the arithmetic average roughness defined by JIS B0601: 01 at the top of the structural row is TRa and the arithmetic average roughness defined by JIS B0601: 01 at the side is SRa, 0.2 μm <SRa <TRa meet the relationship and the TRa is 0.4～0.7Myuemu, wherein SRa is characterized in that it is 0.3 to 0.5 [mu] m.

  Preferably, the prism sheet of the present invention is characterized in that the width of the upper base portion of the structural row is 1 to 5 μm.

  The backlight of the present invention includes at least a light source, an optical plate disposed adjacent to the light source, for guiding or diffusing light, and a prism sheet disposed on the light emitting side of the optical plate. The prism sheet is the prism sheet of the present invention.

  The prism sheet of the present invention has a lens layer in which a plurality of trapezoidal cross-section structure rows are arranged in parallel, and the arithmetic average roughness of the top bottom portion and the side portion of the structure row has a specific relationship. Therefore, the optical defect is difficult to see because of excellent abrasion resistance.

  Moreover, since the backlight of this invention is equipped with such a prism sheet of this invention, since it is hard to see an optical defect, suppressing the fall of front brightness, it becomes the thing excellent in handleability.

Sectional drawing which shows one Embodiment of the prism sheet of this invention The cross-sectional enlarged view which shows one Embodiment of the prism sheet of this invention The perspective view which shows one Embodiment of the backlight of this invention

  The prism sheet of the present invention has a lens layer in which a plurality of structural rows each having a trapezoidal cross section are arranged side by side, and has an arithmetic average roughness defined by JIS B0601: 01 at the upper bottom portion of the structural rows. (Hereinafter, it may be simply referred to as “arithmetic mean roughness”) is TRa, and when the arithmetic mean roughness defined by JIS B0601: 01 of the side surface is SRa, the relationship of 0.2 μm <SRa <TRa is satisfied. Is. The backlight of the present invention uses the prism sheet of the present invention. Hereinafter, embodiments of the prism sheet of the present invention will be described.

  FIG. 1 is a sectional view showing one embodiment of the prism sheet of the present invention. A prism sheet 1 of the present invention shown in FIG. 1 includes a lens layer 2 in which a plurality of trapezoidal structure rows a are arranged in parallel.

  Further, the prism sheet of the present invention has a trapezoidal cross-sectional structure row on the lens layer surface, and when the arithmetic average roughness of the upper base portion of the structure row is TRa and the arithmetic average roughness of the side surface portion is SRa, 0 is obtained. .. 2 μm <SRa <TRa.

  In the prism sheet of the present invention, since the arithmetic average roughness TRa of the upper base of the structure row exceeds 0.2 μm in this way, the tip of the structure row having a trapezoidal cross section like the conventional prism sheet is formed. Compared with a flat thing, the condensing property to a front direction can be improved. In addition, since the prism sheet of the present invention is provided with such arithmetic average roughness TRa on the upper bottom portion of the structure row, even if fine scratches or the like adhere to the prism sheet surface, the surface roughness due to scratches or the like. The change can be made difficult to visually recognize, and the optical defect can be made difficult to visually recognize. Furthermore, since it has such an arithmetic average roughness TRa, it can be prevented from coming into close contact with a member facing the lens layer surface on which the structural row of the prism sheet is formed. Visibility defects called rings and wet outs can also be improved. Here, the “optical defect” refers to a defect such as a decrease in luminance caused by the presence of scratches or foreign matters having a diameter of about 10 to 100 μm.

  In addition, the arithmetic average roughness TRa of the upper bottom portion of the structural row is more preferably 0.4 to 0.7 μm, and further preferably 0.5 to 0.6 μm.

  In the prism sheet of the present invention, the arithmetic average roughness SRa of the side surface portion of the structural row exceeds at least 0.2 μm as described above. By providing the arithmetic average roughness SRa on the side surface portion of the structural row, fine scratches or the like that can adhere to the side surface portion at the time of manufacturing the structural row, a defect that easily enters when cutting the valley portion between the structural rows, etc. Can be made difficult to visually recognize, and optical defects can be made difficult to visually recognize.

  In addition, the prism sheet of the present invention has a higher TRa than SRa when the arithmetic average roughness TRa of the upper bottom portion of the structural row is compared with the arithmetic average roughness SRa of the side surface portion of the structural row. By having such a relationship, the SRa is lower than TRa while improving the light condensing property in the front direction by the TRa of the upper bottom portion of the structure row as described above, and therefore, depending on the surface shape of the side surface portion of the structure row. It is possible to obtain a prism sheet excellent in front luminance as a whole prism sheet without significantly impairing the light condensing property in the front direction. Therefore, by satisfying the relationship of 0.2 μm <SRa <TRa, the unique effect of the present invention is exhibited, which is excellent in scratch resistance and makes it difficult to visually recognize optical defects while suppressing a decrease in luminance in the front direction. The

  The arithmetic average roughness SRa of the side surface portion of the structural row is more preferably more than 0.2 μm and not more than 0.5 μm, and more preferably 0.3 to 0.4 μm.

  Here, if the SRa of the side surface portion of the structure row exceeding at least 0.2 μm and the TRa of the upper base portion have a relationship of SRa> TRa, the arithmetic average roughness of the upper base portion is low and the upper base portion is low. Due to the surface shape, the light condensing property in the front direction becomes poor, and the prism sheet becomes unusable for use with low front luminance.

  The configuration of the prism sheet of the present invention is not limited to a single lens layer, but may be a lens layer laminated on a support.

  As the support, a highly transparent material such as a glass plate or a plastic film can be used. As the glass plate, it is possible to use a glass plate made of oxide glass such as silicate glass, phosphate glass, borate glass, etc., especially silicate glass, alkali silicate glass, soda lime glass, A silicate glass such as potash lime glass, lead glass, barium glass, borosilicate glass or the like is preferably used as a plate glass. As the plastic film, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, acrylic, polyvinyl chloride, norbornene compound, etc. can be used. Polyethylene terephthalate film is preferably used because of its excellent mechanical strength and dimensional stability. It is preferable to use a support that has been subjected to an easy adhesion treatment such as a plasma treatment, a corona discharge treatment, a far-ultraviolet irradiation treatment, or an undercoat easy adhesion layer.

  Although it does not specifically limit as thickness of a support body, Although it can select suitably with respect to the material applied, Generally it is 25-500 micrometers, Preferably it is 50-300 micrometers.

  The lens layer of the present invention is made of a polymer resin. Examples of the polymer resin include an ionizing radiation curable resin, a thermosetting resin, and a thermoplastic resin.

  As the ionizing radiation curable resin, a photopolymerizable prepolymer that can be crosslinked and cured by irradiation with ionizing radiation (ultraviolet ray or electron beam) can be used. An acrylic prepolymer having at least one acryloyl group and having a three-dimensional network structure by crosslinking and curing is particularly preferably used. As the acrylic prepolymer, urethane acrylate, polyester acrylate, epoxy acrylate, melamine acrylate, polyfluoroalkyl acrylate, silicone acrylate and the like can be used. Furthermore, these acrylic prepolymers can be used alone, but it is preferable to add a photopolymerizable monomer in order to improve the cross-linking curability and the hardness of the lens layer.

  As photopolymerizable monomers, monofunctional acrylic monomers such as 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, butoxyethyl acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol One kind of bifunctional acrylic monomer such as diacrylate, polyethylene glycol diacrylate, hydroxypivalate ester neopentyl glycol diacrylate, etc., or polyfunctional acrylic monomer such as dipentaerythritol hexaacrylate, trimethylpropane triacrylate, pentaerythritol triacrylate or the like Two or more are used.

  In addition to the above-described photopolymerizable prepolymer and photopolymerizable monomer, it is preferable to use additives such as a photopolymerization initiator and a photopolymerization accelerator when curing by ultraviolet irradiation.

  Examples of the photopolymerization initiator include acetophenone, benzophenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoylbenzoate, α-acyloxime ester, thioxanthone and the like.

  Further, the photopolymerization accelerator is capable of reducing the polymerization obstacle due to air at the time of curing and increasing the curing speed. For example, p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, etc. Can be mentioned.

  Thermosetting resins include silicone resins, phenolic resins, urea resins, melamine resins, furan resins, unsaturated polyester resins, epoxy resins, diallyl phthalate resins, guanamine resins, ketone resins, Examples include amino alkyd resins, urethane resins, acrylic resins, and polycarbonate resins. These can be used alone, but it is desirable to add a curing agent in order to further improve the crosslinkability and the hardness of the crosslinked cured coating film.

  As the curing agent, a compound such as polyisocyanate, amino resin, epoxy resin, or carboxylic acid can be appropriately used in accordance with a suitable resin.

  As thermoplastic resins, ABS resin, norbornene resin, silicone resin, nylon resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polybutylene terephthalate, polyethylene terephthalate, sulfone resin, imide resin, fluorine resin Resin, styrene resin, acrylic resin, vinyl chloride resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer resin, polyester resin, urethane resin, nylon resin, rubber resin, polyvinyl ether, polyvinyl Examples include alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyethylene glycol.

  Of these thermosetting resins or thermoplastic resins, acrylic resin thermosetting resins or thermoplastic resins should be used from the viewpoint of obtaining coating strength when used as a lens layer and good transparency. Is preferred. Moreover, these thermosetting resins or thermoplastic resins can also be used as thermosetting resins or composite resins in which a plurality of types of thermoplastic resins are combined.

  As the polymer resin, a resin other than the above-mentioned resin can be used in combination, but as the content ratio of the above-described polymer resin and the other resin, from the viewpoint of accurately producing the structural row of the present invention, As will be described later, when a prism sheet is produced by the Photo-Polymer method (2P method), it is preferable that about 30 to 90% by weight of the ionizing radiation curable resin is contained in the total polymer resin component. On the other hand, when the prism sheet is produced by the Thermal-Transformation method (2T method) or the embossing method, it is preferable that about 30 to 90% by weight of the thermosetting resin or the thermoplastic resin is contained in the total polymer resin component.

  In addition to the polymer resin described above, the lens layer may be fine particles, lubricants, fluorescent whitening agents, antistatic agents, flame retardants, antibacterial agents, antifungal agents, as long as the effects of the present invention are not impaired. Various additives such as an ultraviolet absorber, a light stabilizer, an antioxidant, a plasticizer, a leveling agent, a flow regulator, an antifoaming agent, a dispersant, a mold release agent, and a crosslinking agent may be included.

  The lens layer of the present invention is formed by arranging a plurality of trapezoidal structure rows in parallel on the surface.

  The inclination angle (α in FIG. 2) between the lower bottom surface (lower bottom surface) and the side surface of the structural row is preferably in the range of 40 to 55 °, preferably 45 °, It is preferable that the inclination angles at both ends of the structure row are equal.

  The width of the upper bottom portion of the structure row is preferably 1 to 5 μm, and more preferably 2 to 4 μm. By setting the width of the upper bottom portion to 1 μm or more, it is possible to make the optical defect difficult to see due to excellent scratch resistance. Moreover, it can prevent that front brightness falls by setting it as 5 micrometers or less.

  Further, the width of the lower bottom portion of the structural row is preferably 22 to 65 μm, and more preferably 33 to 55 μm. The height of the structural row (q in FIG. 2) is preferably 11 to 30 μm, and more preferably 16 to 25 μm.

  Among the lens layers, the thickness of the resin layer in which the structural row is not formed (p in FIG. 2) is sufficient coating strength of the layer when the prism sheet of the present invention is formed as a single lens layer. Or from the viewpoint of obtaining smoothness, it is preferably 25 to 300 μm. On the other hand, when a lens layer is formed on a support to form a prism sheet, the thickness is preferably 3 to 15 μm.

  As a method for producing a prism sheet provided with the lens layer of the present invention, it can be formed by a transfer shaping technique such as 2P method, 2T method, embossing method or the like. For example, after filling a mold having a shape complementary to the required surface shape of the lens layer with a polymer resin or the like constituting the lens layer as described above, By curing the molecular resin and the like and peeling it from the mold, a prism sheet having a lens layer in which a structural row is shaped is obtained. On the other hand, when a support is used, a polymer resin or the like is filled in the mold, the support is overlaid thereon, the polymer resin or the like is cured, and the support is removed from the mold. A prism sheet having a lens layer on which a structural row is shaped is obtained. In the case of forming a lens layer structure row by the 2P method, an ionizing radiation curable resin is used. In the case of forming a lens layer structure row by the 2T method or an embossing method, a thermosetting resin or a thermosetting resin is used. A plastic resin is used.

  Among the transfer shaping techniques described above, the prism sheet can be produced in a relatively short time, and since heating and cooling are not required, it is preferable to employ the 2P method from the viewpoint of suppressing deformation of the constituent members due to heat. On the other hand, it is preferable to adopt the 2T method from the viewpoint that the degree of freedom of material selectivity of the constituent members is high and the process cost can be reduced.

  As a method for curing the polymer resin, when the polymer resin is an ionizing radiation curable resin, it can be cured by irradiating with ionizing radiation. Further, when the polymer resin is a thermosetting resin, it can be cured by applying heat. Further, when the polymer resin is a thermoplastic resin, it can be cured by cooling. Here, as the ionizing radiation, for example, ultra-high pressure mercury lamps, high-pressure mercury lamps, low-pressure mercury lamps, carbon arcs, metal halide lamps, etc. emitted from 100 to 400 nm, preferably 200 to 400 nm wavelength region, scanning type / curtain type An electron beam emitted from an electron beam accelerator having a wavelength region of 100 nm or less can be used.

  Thus, the prism sheet of the present invention has a lens layer in which a plurality of trapezoidal cross-section structure rows are arranged in parallel, and the arithmetic average roughness of the upper bottom portion and the side portion of the structure row is Because it is a specific value, it can be made excellent in scratch resistance without unduly impairing the brightness in the front direction, which could not be done in the past, and it makes it difficult to visually recognize optical defects due to fine defects The prism sheet can be made.

  Next, an embodiment of the backlight of the present invention will be described. A cross-sectional view showing one embodiment of the backlight of the present invention is shown in FIG. The backlight 30 of the present invention shown in FIG. 3 is an edge light type backlight, and includes a light source 31, a light guide plate 32, and a prism sheet 33 of the present invention placed thereon. As illustrated, a light diffusion sheet 34 or the like may be provided adjacent to the prism sheet 33 as necessary.

  Further, as the backlight of the present invention, FIG. 3 illustrates an edge light type backlight, but the backlight of the present invention has a light source disposed on the lower side of the diffusion plate, and a lower light diffusion sheet on the upper side, The present invention can also be applied to a direct type backlight provided with a prism sheet, an upper diffusion sheet, and the like.

  As described above, the backlight according to the present invention is provided with the prism sheet in which optical defects are difficult to see without lowering the front luminance, which could not be achieved in the past, and thus has excellent handleability.

  The following examples further illustrate the present invention. “Parts” and “%” are based on weight unless otherwise specified.

1. Preparation of prism sheet [Example 1]
A copper plate having a smooth surface and a thickness of 4 mm was cut using a diamond engraving tool to produce a mold. 50 parts of acrylic monomer (methyl methacrylate: Wako Pure Chemical Industries), 45 parts of polyfunctional acrylic monomer (NK ester A-TMPT-3EO: Shin-Nakamura Chemical Co., Ltd.), photopolymerization initiator (Irgacure) 184: Ciba Japan Co., Ltd.) Drop 5 parts of the mixture and cover with a 100 μm thick polyester film (Cosmo Shine A4300: Toyobo Co., Ltd.). And a polyester film were adhered to each other.

In this state, 1500 mJ / cm ² of ultraviolet light is irradiated from the polyester film side with a metal halide lamp to cure the ultraviolet curable resin, and then the polyester film and the resin (lens layer) are peeled off from the mold to change the shape of the mold. The prism sheet of Example 1 below was produced by faithfully transferring.

<Prism sheet of Example 1>
-Lens layer configuration: a plurality of trapezoidal structure rows arranged side by side-Arithmetic mean roughness TRa of the upper base of the trapezoidal cross-section structure rows: 0.52 μm
-The width of the upper base of the structural column with a trapezoidal cross section: 3 μm
-Arithmetic average roughness SRa of the side surface of the trapezoidal structure row: 0.31 μm
-The width of the lower base of the structural row having a trapezoidal cross section: 43 μm
-Height of trapezoidal structure row: 20 μm
-Inclination angle between side surface and bottom surface of trapezoidal structure row: 45 °

[ Reference Example 2]
A prism sheet of Reference Example 2 below was produced in the same manner as in Example 1 except that the copper plate was cut under a cutting condition different from that in Example 1.

<Prism sheet of Reference Example 2>
-Lens layer configuration: a plurality of trapezoidal cross-section structure rows arranged in parallel-Arithmetic mean roughness TRa of the upper base of the cross-section trapezoidal structure row: 0.42 μm
-The width of the upper base of the structural column with a trapezoidal cross section: 3 μm
-Arithmetic mean roughness SRa of the side surface of the trapezoidal structure row: 0.21 μm
-The width of the lower base of the structural row having a trapezoidal cross section: 43 μm
-Height of trapezoidal structure row: 20 μm
-Inclination angle between side surface and bottom surface of trapezoidal structure row: 45 °

[Example 3]
A prism sheet of Example 3 below was produced in the same manner as Example 1 except that the copper plate was cut under a cutting condition different from that of Example 1.

<Prism sheet of Example 3>
-Lens layer configuration: a plurality of trapezoidal cross-section structure rows arranged in parallel-Arithmetic mean roughness TRa of the upper base of the cross-section trapezoidal structure row: 0.68 μm
-The width of the upper base of the structural column with a trapezoidal cross section: 3 μm
-Arithmetic average roughness SRa of the side surface portion of the trapezoidal structure row: 0.48 μm
-The width of the lower base of the structural row having a trapezoidal cross section: 43 μm
-Height of trapezoidal structure row: 20 μm
-Inclination angle between side surface and bottom surface of trapezoidal structure row: 45 °

[Comparative Example 1]
A prism sheet of Comparative Example 1 below was produced in the same manner as in Example 1 except that the copper plate was cut under a cutting condition different from that in Example 1.

<Prism sheet of Comparative Example 1>
・ Structure of lens layer: a plurality of triangular structure rows are arranged side by side. Base portion width of the triangular structure row is 40 μm.
-Height of the structural row having a triangular cross section: 20 μm
・ Vertical angle of structure row with triangular cross section: 90 °

[Comparative Example 2]
A prism sheet of Comparative Example 2 below was produced in the same manner as in Example 1 except that the copper plate was cut under cutting conditions different from those in Example 1.

<Prism sheet of Comparative Example 2>
-Lens layer configuration: a plurality of trapezoidal cross-section structure rows arranged in parallel-Arithmetic mean roughness TRa of the upper base of the cross-section trapezoidal structure row: 0.10 μm
-The width of the upper base of the structural column with a trapezoidal cross section: 3 μm
-Arithmetic mean roughness SRa of the side surface portion of the trapezoidal structure row: 0.18 μm
-The width of the lower base of the structural row having a trapezoidal cross section: 43 μm
-Height of trapezoidal structure row: 20 μm
-Inclination angle between side surface and bottom surface of trapezoidal structure row: 45 °

[Comparative Example 3]
A prism sheet of Comparative Example 3 below was produced in the same manner as in Example 1 except that the copper plate was cut under cutting conditions different from those in Example 1.

<Prism sheet of Comparative Example 3>
-Lens layer configuration: a plurality of structure rows with a triangular cross-section (arc-shaped at the tip) are arranged side by side.-Curvature radius of the tip curved portion of the structure row with a triangular cross-section: 8 μm
-Width of base portion of structure row having a triangular cross section: 50 μm
-Height of the structure row having a triangular cross section: 22 μm
・ Vertical angle of structure row with triangular cross section: 90 °

2. Evaluation (1) Front luminance A diffusion film (Light Up MXE: Kimoto Co., Ltd.) having a thickness of 100 μm, Examples 1 and 3, Reference Example 2 and Comparative Examples 1 to 3 was formed on a 0.7 mm-thick shaped light guide plate. A 7-inch edge-light type backlight comprising a prism sheet and a diffusion film (Light Up TL2: Kimoto Co.) in order of 100 μm thickness (Examples 1 and 3, backlights of Reference Example 2 and Comparative Examples 1 to 3, A linear lamp) was produced. And it measured about the front luminance of the backlight of Examples 1 and 3, Reference Example 2, and Comparative Examples 1-3. The evaluation results are shown in Table 1. In Table 1, the front luminance of the backlight including the prism sheet manufactured in Comparative Example 1 is assumed to be 100%, and other front luminances are indicated by relative values with respect to the front luminance of Comparative Example 1.

(2) Scratch (optical defect) is difficult to see The lens layer surface of the prism sheet produced in Examples 1 and 3, Reference Example 2 and Comparative Examples 1 to 3 is applied with a weight of 2 g using a cotton swab. The cotton swab was reciprocated five times in a direction parallel to and perpendicular to the flow direction of the structure row on the surface of the layer, and the damage property of the lens layer surface was visually observed. When the surface of the lens layer was observed from the front, it was “◎” that the scratches could not be recognized at all, and the scars were hardly recognized by visual inspection and could be confirmed with a loupe. What was a thing was set as "(circle)", what was able to recognize a damage | wound visually, was evaluated as "*", and the thing with many flaws adhering clearly and unbearable was used as "XX". The evaluation results are shown in Table 1.

3. Consideration As shown in Table 1, the prism sheets of Examples 1 and 3 and Reference Example 2 have a lens layer in which a plurality of trapezoidal structure rows are arranged in parallel, Since the arithmetic average roughness TRa of the bottom part and the arithmetic average roughness SRa of the side part satisfy the relationship of 0.2 μm <SRa <TRa, the scratches (optical defects) are difficult to see because of excellent scratch resistance. Thus, the backlights of Examples 1 and 3 and Reference Example 2 incorporating the prism sheet were excellent in handleability while preventing a decrease in front luminance. In the prism sheets of Examples 1 and 3 and Reference Example 2 , the arithmetic average roughness TRa of the upper bottom portion of the structure row is higher than 0.4 μm, so that Examples 1 and 3 and Reference Example 2 are high. In the backlights of Examples 1 and 3 and Reference Example 2 in which the prism sheet was incorporated, there was no particular poor visibility called Newton ring or wet out.

  In particular, in the prism sheet of Example 1, TRa is in the range of 0.5 to 0.6 μm and SRa is in the range of 0.3 to 0.4 μm while satisfying the relationship of 0.2 μm <SRa <TRa. Therefore, the scratch resistance is excellent compared to the other examples, and the scratches are difficult to see, and the backlight of Example 1 incorporating the prism sheet has a particularly good balance between the front brightness and the difficulty of seeing the scratches. It was excellent.

  On the other hand, the prism sheet of Comparative Example 1 has a structure column with a triangular cross-section, which is the shape of a conventional prism sheet, in parallel. Therefore, the prism sheet has poor scratch resistance and is easily visible. The built-in backlight of Comparative Example 1 had a high front luminance but was unbearable.

  In addition, the prism sheet of Comparative Example 2 has a trapezoidal cross-sectional structure array in parallel, and thus has excellent scratch resistance and is difficult to see scratches. Therefore, the backlight of Comparative Example 2 incorporating the prism sheet had poor front luminance. Since the prism sheet of Comparative Example 2 has a low arithmetic average roughness TRa of 0.10 μm at the upper bottom of the structural row, the backlight of Comparative Example 2 incorporating the prism sheet of Comparative Example 2 is In addition, poor visibility called Newton ring or wet out occurred.

  In addition, the prism sheet of Comparative Example 3 has a triangular cross-section, and the tip of the prism sheet is formed by parallel arc-shaped structure rows, so that the scratch resistance is slightly poor and scratches are easily visible. Since the light condensing property of the prism sheet was poor, the backlight of Comparative Example 3 incorporating the prism sheet was poor in both front luminance and scratch resistance.

DESCRIPTION OF SYMBOLS 1 ...... Prism sheet of this invention 2 .... Lens layer a ... Structure row | line | column 30 of trapezoid cross-section ... Back light 31 ... Light source 32 ... Light guide plate 33 ... of this invention ..Prism sheet 34 of the present invention: light diffusion sheet

Claims (3)

It has a lens layer in which a plurality of trapezoidal structure rows are arranged in parallel, and the surface on which the plurality of structure rows are arranged in parallel is the light emitting side, and the surface opposite to the surface in which the plurality of structure rows are arranged in parallel is light A prism sheet arranged to be on the incident side ,
When the arithmetic average roughness defined by JIS B0601: 01 at the top of the structural row is TRa and the arithmetic average roughness defined by JIS B0601: 01 at the side is SRa, 0.2 μm <SRa <TRa meet the relationship and, prism sheet, wherein the TRa is 0.4～0.7Myuemu, wherein SRa is 0.3 to 0.5 [mu] m. Width of upper base portion of said structural column is a prism sheet according to claim 1, characterized in that a 1 to 5 [mu] m. A backlight comprising at least a light source, an optical plate disposed adjacent to the light source, for guiding or diffusing light, and a prism sheet disposed on a light emitting side of the optical plate, wherein the prism sheet is claimed. Item 3. A backlight characterized by being a prism sheet according to item 1 or 2 .

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