JPH1082903A - Prism sheet for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve brightness of a liquid crystal display device by using a multiprism sheet having a specified shape and consisting of a specified material. SOLUTION: This prism sheet is formed of an active energy rayhardening resin compsn. and is used in a plate, sheet or film state. On one surface of the prism sheet, lots of long prisms each having a triangular cross section are arranged parallel to each other. The prism sheet is controlled to have 10000 to 50000kg/cm<2> elastic modulus at 25 deg.C after the active energy ray-hardening resin is hardened. To increase brightness of the screen, the refractive index of the active energy ray-hardening resin after hardened is preferably >=1.5. Further, to increase the brightness. the vertex angle θof the prism is preferably controlled to 70 to 110 deg.. Moreover, the pitch (a) of the prism is preferably <=100μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism sheet used for a liquid crystal display device such as a liquid crystal display such as a liquid crystal television and a display for a computer.

[0002]

2. Description of the Related Art Liquid crystal display devices have been widely used in OA equipment, personal computers, etc., due to their lighter weight and higher definition. However, since the liquid crystal itself does not emit light, the luminance is improved by using a back-lighting unit.

On the other hand, recently, liquid crystal display devices, such as color liquid crystal televisions and the like, have become more and more colorized, and a further improvement in luminance has been demanded.
In such a color liquid crystal display element, it has become impossible to secure sufficient luminance with the conventional back lighting means for a single color liquid crystal display device. Therefore, attempts have been made to improve the brightness by improving the backlighting means.

[0004]

However, the method of improving the brightness of the backlight unit has new problems such as an increase in heat generation and an increase in cost.

Accordingly, an object of the present invention is to provide a prism sheet for a liquid crystal display device capable of improving the screen brightness of the liquid crystal display device without causing a problem such as an increase in the amount of heat generated by improving the brightness of the backlighting means. To provide.

[0006]

In view of such circumstances, the present inventors have attempted to reduce the luminance of a liquid crystal display device by using a multi-prism sheet having a specific shape and made of a specific material. They have found that they can be improved, and have reached the present invention.

That is, the prism sheet for a liquid crystal display device of the present invention is formed of a transparent substrate and an active energy ray-curable resin composition on the transparent substrate, and has an elastic modulus (25 ° C.) of 10,000 on the surface. ~ 50,000 kg / cm ² ,
It is characterized by comprising a prism portion formed by a series of a plurality of elongated triangular prisms having an apex angle of 70 to 110 ° and a pitch of 100 μm or less, which are formed in series and in parallel.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A prism sheet according to the present invention will be described with reference to FIGS. FIG. 1 is a partial cross-sectional view showing an embodiment of a liquid crystal display device using the prism sheet of the present invention. In FIG. Is provided with a prism sheet 1. FIG. 2 is a partial cross-sectional view showing another embodiment of the liquid crystal display device using the prism sheet of the present invention, and shows an example in which the prism sheet 1 is installed on the backlight unit 3.

The prism sheet 1 is formed from an active energy ray-curable resin composition, and is used in the form of a plate, a sheet or a film. On one surface of the prism sheet 1, a large number of a series of elongated prisms having a triangular cross section are formed continuously. Prism sheet 1
3 is shown in FIG. In the figure, reference numeral 8 denotes a transparent substrate made of a synthetic resin, and a prism portion 9 made of an active energy ray-curable resin composition having a prism shape formed on one surface of the transparent substrate 8 is integrally formed. I have.

The active energy ray-curable resin composition for forming the prism sheet of the present invention is not particularly limited as long as it is excellent in transparency, but from the viewpoint of the mechanical properties of the prism sheet. Compositions that provide a crosslinked cured polymer are preferred. Examples of such a resin composition include unsaturated polyester-styrene type, epoxy resin-Lewis acid type, polyene-thiol type, (meth) acrylate type and the like. Among them, highly transparent (meth) acrylates are particularly preferable. For example, polyester (meth) acrylate, epoxy (meth)
Examples include a combination of a prepolymer such as acrylate and polyurethane (meth) acrylate with a monofunctional or polyfunctional (meth) acrylate monomer.

These resins may be used alone or in combination.
Can be used but the resulting prism sheet bullet
It is preferable to make a selection in consideration of the modulus and the like. Especially active
Elasticity at 25 ° C after curing of energy ray-curable resin
Rate is 10,000-50,000kg / cm^Two Range, preferred
Or 15000-40000kg / cm^Two In the range
It is necessary to make adjustments. This is because the elastic modulus
10,000 kg / cm ^Two If less than, prism sheet
Is too soft and easy to handle when incorporated into a liquid crystal display.
Inferior workability and the top of the prism is used for the liquid crystal display
When touching, the top of the prism is crushed and a shadow appears on the screen.
Because it occurs. In addition, the elastic modulus is 50000 kg /
cm^Two Exceeds, the prism becomes hard and brittle, causing a slight impact
This is because there is a risk of damage. Also, the screen brightness
In order to increase, after curing of the active energy ray-curable resin
Is preferably 1.5 or more, more preferably
Preferably it is 1.53 or more. This is the obtained Pris
If the refractive index of the lens portion of the
The light condensing property of the screen is reduced, and the screen brightness can be sufficiently improved.
Because you ca n’t.

The active energy rays used for curing the resin composition in the present invention include particle beams such as electron beams and ion beams, electromagnetic rays such as γ rays, X rays, ultraviolet rays, visible rays, and infrared rays. However, ultraviolet rays are preferred in terms of curing speed, production equipment, and the like.

In the liquid crystal display device of the present invention, in order to improve the brightness, the angle θ of the prism apex angle is set to 70 to 110 °.
It is important to set in the range of, preferably 75 to
100 °, more preferably 80 to 95 °
Range. This is because the angle θ of the prism apex angle is 70 °
If the angle is less than 110 °, the directivity becomes remarkable, and the screen becomes extremely dark when viewed from a position other than the front. This is because luminance decreases due to light absorption due to the thickness of the prism sheet.

The pitch a of the prism is preferably 100 μm or less, and more preferably 70 μm or less. This is due to the colorization of liquid crystal display devices,
This is because the pitch of the color filters is becoming smaller, and the smaller the pitch a of the prism, the better from the viewpoint of preventing the occurrence of moire patterns on the screen and improving the definition of the screen. The height b of the irregularities of the prism is determined by the value of the angle θ of the prism apex angle and the pitch a of the prism, and is preferably in the range of 50 μm or less. Further, the thickness c of the prism sheet 1 is preferably thicker from the viewpoint of the strength, but is preferably thinner optically to suppress light absorption. For this reason, an appropriate thickness is set according to the size of the screen of the liquid crystal display device to be used, usage conditions, and the like.
For example, a liquid crystal display device having a screen of about 4 to 10 inches preferably has a thickness of about several hundred μm or less.
When the thickness is in the range of 500 μm, the strength and the optical characteristics are balanced, which is preferable.

As shown in FIG. 1, the prism sheet 1 has a prism surface and a liquid crystal display element 2 on a liquid crystal display element 2 installed on a backlight unit 3 as shown in FIG. Although the prism sheet may be set on the liquid crystal display element 2 as shown in FIG. 2, the prism sheet 1 is set so that the prism surface faces upward on the light emitting surface of the back lighting means 3 as shown in FIG. Further, it is preferable that the liquid crystal display element 2 is further disposed on the upper side. In this case, the prism sheet 1
Is installed on the light exit surface of the back lighting means 3 so that its prism is substantially parallel to the light entrance surface of the light guide 5. In the liquid crystal display device configured as described above, by using the prism sheet, diffusion of light can be suppressed, and a liquid crystal display device with high luminance and excellent directivity can be obtained.

The liquid crystal display element 2 constituting such a liquid crystal display device is constituted by filling a liquid crystal between two glass substrates provided at a predetermined interval by a spacer, for example. Further, a polarizing plate is provided on each outer surface of the two upper and lower glass substrates,
A color filter layer is provided on the inner surface of the upper glass substrate, and internal electrodes are provided on the outer surface of the color filter layer. Internal electrodes are provided on the inner surface of the lower glass substrate.
The internal electrode is configured by arranging a large number of minute pixel electrodes vertically and horizontally. The color filter layers are red, green,
Three color filters of blue are arranged corresponding to the pixel electrodes to form each pixel.

As shown in FIG. 2, the back lighting means 3 comprises a plate-shaped light guide 5 having a light incident surface and a light emitting surface, and a linear light source 7 such as a fluorescent lamp. It is. The light guide 5 has a light incident surface on one side end surface, a light exit surface substantially perpendicular to the light incident surface, and a reflective surface located on the opposite surface, and a reflective film 6 is formed on the reflective surface. A light amount adjustment pattern 4 is formed on the light emitting surface or the reflecting surface as required. A linear light source 7 such as a fluorescent lamp is arranged to face the light incident surface of the light guide 5. Then, the incident light from the linear light source 7 incident from the light incident surface of the light guide plate 5 passes through the light guide plate 5, and is partially reflected by the reflection film 6 and is emitted from the light emission surface. Irradiation is performed uniformly on the back side. The backlight unit 3 is not limited to the one shown in FIG. 2, but may be any of various commonly used backlight units.

Next, a method for manufacturing the prism sheet of the present invention will be described. The prism sheet of the present invention is obtained by applying the active energy ray-curable resin composition to a mold such as a mold or a resin mold having a prism pattern formed thereon, smoothing the surface of the resin composition, and then forming a transparent substrate. And irradiating them with active energy rays to cure them. This makes it possible to easily produce a fine-pitch prism pattern that can cope with finer color filters accompanying colorization of a liquid crystal display device without impairing optical characteristics.

As a method of applying the active energy ray-curable resin composition to the mold, the required resin composition may be applied to the mold by one application. Two steps of a first application step of applying a resin composition for forming the tip of the prism part so as to uniformly fill the pattern part, and a second application step of applying a resin composition for forming the base of the prism part thereon further May be applied by the application step. In this case, the surface of the resin composition applied layer applied after the first application step is preferably smoothed to obtain a uniform prism sheet without uneven thickness. Further, after the first coating layer is smoothed, the resin composition layer is cured or semi-cured by irradiating active energy rays to move the first resin composition coating layer in the second coating step. However, it is preferable because the generation of bubbles due to the shape of the lens mold can be suppressed between them.

The thickness and material of the transparent substrate are not particularly limited as long as they have high transparency. However, when the transparency and handling of active energy rays are taken into consideration. Is preferably 3 mm or less in thickness. Examples of the material include an acrylic resin, a polycarbonate resin, a polyester resin, a polystyrene resin, a fluororesin, a polyimide resin, a synthetic resin such as a mixture of these polymers, and glass. Such a transparent substrate may be subjected to an anti-reflection treatment such as providing fine irregularities on its surface or applying a fine powder. The anti-reflection treatment is applied to the surface on which the active energy ray-curable resin composition layer is formed, even when the transparent substrate is peeled off, so that the anti-reflection surface is imparted to the prism surface after peeling. This is preferable.

In the present invention, the active energy rays used for curing the active energy ray-curable resin composition include particle beams such as electron beams and ion beams, γ rays, X rays, and the like.
Examples thereof include electromagnetic waves such as rays, ultraviolet rays, visible rays, and infrared rays, and ultraviolet rays are preferred from the viewpoint of curing speed, production equipment, and the like.

The prism sheet obtained by forming a prism portion made of a resin composition cured by an active energy ray on the transparent substrate thus produced can be used as it is. It may be peeled off and used as a state of the prism part alone. When used with the prism portion formed on the transparent substrate, it is important from the viewpoint of weather resistance and durability that the interface is sufficiently bonded,
It is preferred that the transparent base material be subjected to an adhesion improving treatment such as a primer treatment. On the other hand, when the transparent substrate is used after being peeled, it is preferable that the transparent substrate can be peeled relatively easily, and the surface of the transparent substrate is preferably subjected to a surface treatment with a silicone or fluorine-based release agent. However, also in this case, since the transparent substrate and the prism portion need to be in close contact with each other until the sheet is released from the molding die, it is necessary to appropriately adjust the balance between the adhesiveness and the releasability.

[0023]

The present invention will be specifically described below with reference to examples.

[Examples 1 to 3 and Comparative Examples 1 and 2] The pitch of the prism after molding and the apex angle of the prism are shown in Table 1 respectively.
The following mixture was applied as a UV-curable resin composition to a mold designed in advance as shown in Table 2 above, the surface thereof was smoothed, and then a polycarbonate film having a thickness of 500 μm was overlaid. Then, 320-390n
The ultraviolet curable resin composition was cured by irradiating 1000 mJ / cm ² of ultraviolet light at an integrated ultraviolet irradiation amount of m. Thereafter, the prism sheet was separated from the mold to obtain a prism sheet. Each prism sheet had a prism portion having a refractive index of 1.532 and a shape as designed: 45 parts by weight of fancryl FA-321M (ethylene oxide-modified bisphenol A methacrylate manufactured by Hitachi Chemical Co., Ltd.) NK ester A-BPE- 425 parts by weight (Shin Nakamura Chemical Co., Ltd. ethylene oxide-modified bisphenol A diacrylate) Sartomer 285 30 parts by weight (Sartomer Co., Ltd. tetrahydrofurfuryl acrylate) Darocure 1173 3 parts by weight (Merck Japan Co., Ltd. 2-hydroxy-2-methyl-1) -Phenylpropan-1-one).

Using a liquid crystal display device using a back illuminating means having a surface luminance of 7000 cd / m ² , the obtained prism sheet is set on the back illuminating means such that the prism surface faces the liquid crystal display element. The surface luminance was measured, and the directivity at that time was visually evaluated according to the following evaluation criteria: ○: little directivity, little change in brightness due to angle ×: remarkable directivity, viewed from other than front Things that get darker if you do.

Using the above resin composition, a resin plate having a thickness of 2 mm was prepared by a glass cell casting method, and the obtained resin plate was cut into a width of 10 mm and a length of 60 mm, and then cut into a length of 32 mm.
A three-point bending test was conducted at two points installed at intervals of m.
The results are shown in Table 1. The surface luminance when no prism sheet was used was 200 cd / m ² .

Example 4 A prism sheet was obtained in the same manner as in Example 1 except that the following mixture was used as the ultraviolet-curable resin composition. The obtained prism sheet had a refractive index of the prism portion of 1.548 and had a shape as designed. Using the obtained prism sheet, the surface luminance was measured in the same manner as in Example 1. Further, a three-point bending test was performed in the same manner as in Example 1. The results are shown in Table 1: NK Ester A-BPE-4 85 parts by weight (Shin Nakamura Chemical Co., Ltd. ethylene oxide-modified bisphenol A diacrylate) Light ester BO 15 parts by weight (Kyoeisha Oil & Fat Chemical Co., Ltd. n-butoxyethyl) (Methacrylate) 3 parts by weight of Darocure 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one manufactured by Merck Japan).

[Comparative Example 3] In the same mold as in Example 1, a methyl methacrylate monomer containing 10% by weight of polymethyl methacrylate was used as an initiator, and A was manufactured by Wako Pure Chemical Industries, Ltd.
After applying the resin composition to which 1BN by weight of IBN was added, a glass plate having a thickness of mm was laminated. Next, after the resin composition was cured in hot water at 60 ° C., the resin composition was separated from the mold to obtain a prism sheet. Although the obtained prism sheet had a shape as designed, it took about 5 hours for the resin composition to completely cure.

Further, although the curing time was shortened by increasing the curing temperature or increasing the amount of the initiator added, in any case, abnormal curing occurred and a prism sheet having a good shape could not be obtained. .

Comparative Example 4 The prism sheet after molding was
Using a die designed to have a pitch of 50 μm and a prism apex angle of 90 °, a prism sheet was obtained by extrusion molding using a polycarbonate resin according to a conventional method. In the obtained prism sheet, the top of the prism was crushed, and no good prism sheet was obtained.

[0031]

[Table 1]

[0032]

The prism sheet of the present invention has a specific shape and elastic modulus, and at least the prism portion is made of an active energy ray-curable resin composition, whereby a fine-pitch prism pattern can be formed accurately and easily. Not only can be formed, but also suppresses the diffusion of light on the LCD screen,
A liquid crystal display device having high luminance and excellent directivity can be provided, and sufficient luminance can be obtained even with a color liquid crystal display device without particularly improving the brightness of the backlighting means.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device showing an example of use of a prism sheet of the present invention.

FIG. 2 is a schematic sectional view of a liquid crystal display device showing another example of use of the prism sheet of the present invention.

FIG. 3 is a sectional view showing a part of the prism sheet of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Prism sheet 2 Liquid crystal display element 3 Back lighting means 8 Transparent base material 9 Prism part

Claims (2)

[Claims] 1. A transparent substrate and an active energy ray-curable resin composition formed on the transparent substrate and having an elastic modulus (25 ° C.) of 10,000 to 50,000 kg / cm ^{2 on the} surface thereof.
And a prism portion formed of a series of a plurality of elongated triangular cross-section prisms having an apex angle of 70 to 110 ° and a pitch of 100 μm or less, which are continuously formed in parallel. Sheet. 2. The prism sheet for a liquid crystal display device according to claim 1, wherein the refractive index of the prism portion is 1.5 or more.