JP2004004970A - Prism sheet and backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prism sheet and a back light which can suppress development of a light and dark pattern, when using plural prism sheets superposed, without making the frontal luminance of the back light lowered. <P>SOLUTION: This is a prism sheet which has a lens surface, on which a plurality of prism columns are formed parallel at least on one of the sides. This back light uses a prism sheet, consisting of plural prism columns which have lens surfaces whose prism apex angles are constant but with differing heights from each another, and plural prism sheets including that prism sheet superposed. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a prism sheet and a backlight used for a liquid crystal display device and the like, and more particularly, to a prism sheet having no light and dark pattern which is conspicuous when a plurality of prism sheets are used in an overlapping manner. This is related to the backlight.

In recent years, the power consumption of liquid crystal display devices has been increasing in battery-powered products such as portable notebook computers equipped with color liquid crystal display devices, portable liquid crystal TVs using color liquid crystal panels, and video integrated liquid crystal TVs. Is an obstacle. Above all, the power consumption of backlights used in liquid crystal display devices is large, and keeping this power consumption as low as possible is an important issue in extending battery drive time and increasing the practical value of the above products. ing.

However, if the brightness of the backlight is reduced by suppressing the power consumption of the backlight, the liquid crystal display becomes difficult to see, which is not preferable. Therefore, it is desired to improve the optical efficiency of the backlight in order to suppress power consumption without sacrificing the luminance of the backlight. As means for realizing this, a backlight has been proposed in which a prism sheet having a large number of prism rows such as a prism row or a lenticular row formed on one side as shown in FIG. I have.

プ リ ズ ム Such a prism sheet improves the front luminance and improves the optical efficiency of the backlight by directing the emitted light from the backlight in the front direction by a refraction action. Conventionally, it has been said that such a prism sheet needs to be formed as accurately as possible in lens shape in order to improve the front luminance of the backlight.

However, in the conventional prism sheet, as shown in FIG. 4, the incident principal ray exits from the prism sheet through an optical path indicated by A. At this time, the wavefront of the principal ray A passing through each of the prism rows is preserved as shown by the dashed line B, and the wavefront B of the principal ray A passing through the adjacent prism rows has an optical path difference C. For this reason, the light emitted from the prism sheet causes light interference due to the optical path difference C, and a light and dark pattern such as a Newton ring is generated, which has a problem that the appearance of the liquid crystal display device is impaired. Such light and dark patterns become remarkable due to unevenness in the thickness of the prism sheet, fluctuations in the prism shape, and the like. In addition, for the purpose of further improving the front luminance, it has been performed to use a plurality of such prism sheets in a superimposed manner, even when a plurality of prism sheets are used in a superimposed manner, The appearance of such a light and dark pattern becomes remarkable.
The present invention provides a prism sheet and a backlight that do not generate a bright and dark pattern by a prism sheet, particularly a noticeable bright and dark pattern when a plurality of prism sheets are used in an overlapping manner, without impairing the front luminance as a backlight. The purpose is to do.

In view of the above-mentioned problems of the conventional backlight, the present inventors have found that the occurrence of light and dark patterns due to the prism sheet can be suppressed by setting the prism rows of the prism sheet to a specific arrangement. It has been reached.
That is, the prism sheet of the present invention is a prism sheet having a lens surface in which a large number of prism rows are formed in parallel on at least one surface, and the lens surface has a plurality of prisms having a constant prism apex angle and different heights. It is characterized by being composed of columns. Further, the backlight according to the present invention is characterized in that the above-described prism sheet is mounted on the exit surface side of the light guide.

The present invention can provide a prism sheet and a backlight that can suppress the appearance of a light and dark pattern when a plurality of prism sheets are used in an overlapping manner without reducing the front luminance of the backlight.

As shown in FIG. 1 or FIG. 2, the prism sheet 2 of the present invention is formed by forming a large number of prism rows 7 having a substantially isosceles triangular cross section on one surface of a transparent sheet in parallel. It is important that a plurality of prism rows 7 having different heights are arranged as shown in FIG. 2 to form a lens surface. By forming the lens surfaces by arranging the prism rows 7 having different prism heights (H) as described above, the appearance of a light and dark pattern due to the optical path difference C of the wavefront B of the principal ray A passing through the adjacent prism rows is realized. It is possible to constitute a backlight that is suppressed and has high luminance and excellent appearance.

As the plurality of prism rows 7 having different heights, the pitch (P) is fixed, the prism vertex angle (θ) is changed, and the height (H) is adjusted, and the prism vertex (θ) is fixed. The prism array 7 in which the height (H) is adjusted by changing the pitch (P) can be cited as an example. In the present invention, the front luminance is sufficiently improved and the luminance is made uniform over the entire prism sheet 2. From the point, the height (H) is adjusted by changing the pitch (P) while keeping the prism apex angle (θ) constant. In this case, it is preferable that the pitch (P) of the prism rows 7 is appropriately selected in a range of 30 μm to 0.5 mm, and the apex angle (θ) is in a range of 60 to 150 °. In particular, it is preferable to select within a range in which the front luminance can be sufficiently improved according to the directional characteristics of the light emitted from the light guide 3.

Further, in the prism sheet 2 of the present invention, as shown in FIG. 2, the height (H) of the prism row 7 is sequentially increased from the prism row 9 located at the center to the prism row 8 located outside. It is preferable to repeatedly arrange the prism row group A including a plurality of prism rows 7 arranged as follows. This is because, by forming a lens surface with such a prism row group A, when a plurality of prism sheets 2 are used in an overlapping manner, the contact between the prism sheets becomes a line contact at a constant interval. This is because a change in optical characteristics due to contact between the members becomes small. Further, by arranging the prism rows 7 such that the height (H) of the prism rows 7 is sequentially increased from the center of the prism row group A to the outside, the pitch (P) or the apex angle (θ) of the continuous prism rows 7 is reduced. This is because there is no extreme change in the characteristics of the light emitted from the prism sheet 2 because it changes gradually, and it is unlikely that the uniformity of the optical characteristics is reduced.

In this case, the number of the prism rows 7 constituting one prism row group A varies depending on the pitch (P) of the prism rows 7, but is preferably in the range of about 5 to 50. The width of one prism group A is preferably in the range of 0.5 to 5 mm. If the width of the prism row group A is less than 0.5 mm, the effect of suppressing bright and dark patterns due to contact between the prism sheets tends not to be sufficiently exerted, and if the width exceeds 5 mm, a load on a specific prism row 8 is increased. This is because they tend to be large. Further, the height (H) of the prism row 7 in one prism row group A is the ratio (h2ｈ / h1) of the height (h1) of the highest prism row 8 and the height (h2) of the lowest prism row 9. ) Is preferably set in the range of 0.5 to 0.99, and more preferably in the range of 0.6 to 0.98. Further, it is preferable that the change in height (H) from the central prism row 9 to the external prism row 8 is uniformly changed with a constant width.

The prism sheet 2 of the present invention is preferably manufactured using a material having a high visible light transmittance and a relatively high refractive index. For example, acrylic resin, polycarbonate resin, vinyl chloride resin, active energy ray curing Mold resin and the like. Among them, an active energy ray-curable resin is preferable from the viewpoints of the scratch resistance, handleability, productivity and the like of the prism sheet 2. In the present invention, additives such as an antioxidant, an ultraviolet absorber, a yellowing inhibitor, a bluing agent, a pigment, and a diffusing agent can be added to the prism sheet 2 as needed.

通常 As a method for producing the prism sheet 2 of the present invention, a normal molding method such as extrusion molding, injection molding, or the like can be used. When manufacturing the prism sheet 2 using an active energy ray-curable resin, a lens portion is formed on a transparent substrate such as a transparent film or a sheet using the active energy ray-curable resin. First, an active energy ray-curable resin liquid is injected into a lens mold having a predetermined lens pattern formed thereon, and a transparent substrate is overlaid. Next, an active energy ray such as an ultraviolet ray or an electron beam is irradiated through the transparent base material, and the active energy ray-curable resin liquid is polymerized and cured, and is separated from the lens mold to obtain the prism sheet 2.

Examples of the active energy ray-curable resin constituting the lens portion of the prism sheet 2 include bis (methacryloylthiophenyl) sulfide, 2,4-dibromophenyl (meth) acrylate, and 2,3,5-tribromophenyl (meth). Acrylate, 2,2-bis (4- (meth) acryloyloxyphenyl) propane, 2,2-bis (4- (meth) acryloyloxyethoxyphenyl) propane, 2,2-bis (4- (meth) acryloyloxy Diethoxyphenyl) propane, 2,2-bis (4- (meth) acryloylpentaethoxyphenyl) propane, 2,2-biz (4- (meth) acryloyloxyethoxy-3,5-dibromophenyl) propane, 2-bis (4- (meth) acryloyloxydiethoxy-3,5-dibromofe L) propane, 2,2-bis (4- (meth) acryloyloxypentaethoxy-3,5-dibromophenyl) propane, 2,2-bis (4- (meth) acryloyloxyethoxy-3,5-dimethylphenyl ) Propane, 2,2-bis (4- (meth) acryloyloxyethoxy-3-phenylphenyl) propane, bis (4- (meth) acryloyloxyphenyl) sulfone, bis (4- (meth) acryloyloxyethoxyphenyl) Sulfone, bis (4- (meth) acryloyloxypentaethoxyphenyl) sulfone, bis (4- (meth) acryloyloxyethoxy-3-phenylphenyl) sulfone, bis (4- (meth) acryloyloxyethoxy-3,5-) Dimethylphenyl) sulfone, bis (4- (meth) Acryloyloxyphenyl) sulfide, bis (4- (meth) acryloyloxyethoxyphenyl) sulfide, bis (4- (meth) acryloyloxypentaethoxyphenyl) sulfide, bis (4- (meth) acryloyloxyethoxy-3-phenyl) Phenyl) sulfide, bis (4- (meth) acryloyloxyethoxy-3,5-dimethylphenyl) sulfide, di ((meth) acryloyloxyethoxy) phosphate, tri ((meth) acryloyloxyethoxy) phosphate, etc. Functional (meth) acrylic compounds and the like can be mentioned. These can be used alone or in combination of two or more.

Further, together with these polyfunctional (meth) acrylic compounds, styrene, vinyl toluene, chlorostyrene, dichlorostyrene, bromostyrene, dibromostyrene, divinylbenzene, 1- Vinyl compounds such as vinylnaphthalene, 2-vinylnaphthalene and N-vinylpyrrolidone; (meth) acrylates such as phenyl (meth) acrylate, benzyl (meth) acrylate and biphenyl (meth) acrylate; diallyl phthalate and dimethallyl Allyl compounds such as phthalate and diallyl biphenylate, and metal salts of metals such as barium, lead, antimony, titanium, tin and zinc with (meth) acrylic acid and the like can also be used. These can be used alone or in combination of two or more.

In the present invention, examples of the photoradical generation catalyst used for the active energy ray-curable resin include 2-hydroxy-2-methyl-1-phenylpropan-1-one, hydroxycyclohexylphenylketone, and methylphenylglyoxylate. , 2,4,6-trimethylbenzoylphosphine oxide, benzyldimethyl ketal and the like.

In the prism sheet 2 having a lens portion formed of an active energy ray-curable resin, the material of the transparent base material used is not particularly limited as long as it is a material that transmits active energy rays such as ultraviolet rays and electron beams. Although a glass plate or the like can be used, a transparent resin such as a polyester resin, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, and a polymethacrylimide resin is preferable.

As shown in FIG. 1, a backlight 1 of the present invention includes a light source 4 such as a fluorescent lamp disposed at one end of a light guide 3, and a plurality of prism sheets 2 on the light guide 3. 2 'is superposed and placed. In addition, the light guide 3 is usually provided with a diffusion sheet 6 on an emission surface, and a reflection layer 5 formed of a reflection film or the like on a surface opposite to the emission surface.

In the backlight 1 of the present invention, usually, two prism sheets 2 and 2 ′ are used, and the first prism sheet 2 and the second prism sheet 2 ′ are formed such that each prism row 7 forms an angle. Or stacked in parallel. The prism sheets 2, 2 'can be placed so that their respective lens surfaces are directed upward or downward, and the lens surfaces of both prism sheets 2, 2' are directed in opposite directions. It can also be placed as follows. In the backlight of the present invention, it is preferable that the prism array 7 of at least one prism sheet 2 is placed so as to be parallel to the light source 4.

In the present invention, when a plurality of prism sheets 2 and 2 ′ are used in an overlapping manner, at least one prism sheet having a plurality of prism rows having different heights as described above is used. Is preferred. When a plurality of prism sheets 2 and 2 ′ are superimposed such that the respective lens surfaces are on the upper side, at least one of the prism sheets other than the prism sheet 2 ′ located on the top is replaced with the aforementioned prism sheet. It is preferable to form a prism sheet 2 on which a plurality of prism rows having different heights are formed. That is, as shown in FIG. 1, when two prism sheets 2 and 2 ′ are mounted, at least the first prism sheet 2 is a prism sheet on which a plurality of prism rows of different heights are formed. It is preferred to use

The backlight 1 of the present invention is not limited to the configuration shown in FIG. 1, but may have various configurations according to the purpose of use and the like. For example, the light source 4 may be arranged at at least one end of the light guide 3, but a plurality of light sources 4 may be arranged as necessary. Further, the light emitting surface of the light guide 3 may be formed as a diffusing surface or a lens surface, or a light amount adjusting mechanism for uniformly emitting light from the entire light guide 3 by printing or the like may be provided. Furthermore, as the shape of the light guide 3, various shapes such as a sheet shape, a cross-sectional wedge shape, and a hull shape can be used.

Hereinafter, the present invention will be specifically described with reference to examples.

A4 size brass made of brass of about A4 size having a prism pattern in which prism rows having a height of 40 to 50 μm and a vertex angle of 90 ° are formed so as to gradually increase from the center toward the outside, and a prism row group having a width of 1 mm is repeatedly arranged. An ultraviolet curable resin liquid having the following composition was injected into the lens mold, and an A4 size 125 μm thick polyethylene terephthalate film was superimposed on the lens mold. Then, an ultraviolet lamp (80 W / UV light was irradiated from the polyethylene terephthalate film side for 30 seconds using an irradiation intensity of 6.4 KW) to polymerize and cure the UV-curable resin solution and peeled from the lens mold to obtain a prism sheet. As shown in FIG. 1, when the backlight unit was constituted by using the two obtained prism sheets, the appearance of a bright and dark pattern was hardly recognized, and uniform and high luminance was obtained.

Ultraviolet curing resin (1) 47 parts by weight of ethylene oxide-modified bisphenol A dimethacrylate (Fancryl FA-321M manufactured by Hitachi Chemical Co., Ltd.)
(2) Neopentylglycol-modified trimethylolpropane 25 parts by weight acrylate (KAYAARD manufactured by Nippon Kayaku Chemical Co., Ltd.)
R-604)
(3) Phenoxyethyl acrylate (28 parts by weight of Biscoat # 192, manufactured by Osaka Organic Chemical Industry Co., Ltd.)
(4) 2-hydroxy-2-methyl-1-phenylpropane-1.5 parts by weight 1-one (Darocur 1173 manufactured by Merck)

A4 size brass lens having a prism pattern in which a prism array having a width of 1 mm formed so that a prism array having a height of 40 to 50 μm and a pitch of 50 μm gradually increases from the center toward the outside is arranged. Except that a mold was used, the same material as in Example 1 was used, and a prism sheet was obtained by the same method. As shown in FIG. 1, a backlight unit was formed using two of the obtained prism sheets. As a result, almost no light and dark pattern was observed, and almost uniform and high luminance was obtained.

The same material as in Example 1 was used except that a brass lens mold of about A4 size having a prism pattern in which prism rows having a height of 40 to 50 μm and a vertex angle of 90 ° were randomly arranged was used. A prism sheet was obtained by the method. As shown in FIG. 1, a backlight unit was formed using two of the obtained prism sheets. As a result, almost no light and dark pattern was observed, and almost uniform and high luminance was obtained.

<Comparative Example 1>
A prism sheet was obtained by the same method and using the same materials as in Example 1 except that a lens mold of brass of about A4 size having a prism pattern with a lens pitch of 50 μm and a vertex angle of 95 ° was used. As shown in FIG. 1, a backlight unit was formed using two of the obtained prism sheets. As a result, the backlight unit had a uniform and high luminance, but a remarkable light and dark pattern was exhibited.

The prism sheet and the backlight according to the present invention are used for a liquid crystal display device and the like.

FIG. 2 is a partial perspective view illustrating a configuration example of a backlight according to the present invention. It is a partial perspective view showing the outline of the prism sheet of the present invention. It is a partial perspective view which shows the outline of the conventional lenses sheet. It is sectional drawing which shows the optical path and wavefront of the principal ray of the conventional lens sheet.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Backlight 2 ... Prism sheet 3 ... Light guide 4 ... Light source 5 ... Reflective layer 6 ... Diffusion sheet 7 ... Prism row 8 ... Highest prism row 9 ... lowest prism row

Claims (5)

A prism sheet having a lens surface in which a number of prism rows are formed in parallel on at least one surface, wherein the lens surface is formed of a plurality of prism rows having a constant prism apex angle and different heights. Prism sheet. The lens surface is configured by repeatedly arranging a plurality of prism rows including a plurality of prism rows, and the prism row group sequentially increases in prism height from a centrally located prism row to an externally located prism row. The prism sheet according to claim 1, wherein: The height of the highest elongated prisms of one prism column group _{(h 1)} the lowest elongated prism height ratio of _{(h 2) (h 2 /} h 1) is 0.5 to 0.99 The prism sheet according to claim 2, wherein: The prism sheet according to any one of claims 1 to 3, wherein a cross-sectional shape of the prism row is a substantially isosceles triangle. A backlight, comprising the prism sheet according to any one of claims 1 to 4 mounted on an emission surface of a light guide.

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