KR20140000215A - Light guide plate and edge-lit surface light source device using same - Google Patents

Abstract

In the light guide plate having a resin plate, the resin plate has a main surface having an area of 400000 mm ² or more, the resin plate has a thickness of 1.5 mm to 4.0 mm, and the resin plate has a weight average molecular weight of 200000 to 400000 and a molecular weight distribution of 2.0 to 4.0. A light guide plate containing styrene resin.

Description

LIGHT GUIDE PLATE AND EDGE-LIT SURFACE LIGHT SOURCE DEVICE USING SAME}

The present invention relates to a light guide plate and an edge light type surface light source device using the same.

Transmissive image display devices such as liquid crystal display devices generally have a surface light source device as a backlight. An edge light type surface light source device is composed of a light guide plate having a transparent resin plate, and a light source for supplying light to the end face of the resin plate. Light incident from the end face of the resin plate is reflected by reflecting means such as a dot pattern provided on the back side of the resin plate, and planar light for image display is supplied from the exit surface of the light guide plate. As a resin plate for light guide plates, the acrylic resin plate excellent in transparency is used widely conventionally (for example, patent document 1 and 2).

Japanese Patent Application Laid-Open No. 5-100118 Japanese Patent Laid-Open No. 5-313017

With the recent thinning and large screen of the transmissive image display device, there is a need for an edge light type surface light source device using a light guide plate having a thinner and wider area. However, it has been found that when the area of the light guide plate is increased such as 400000 mm ² or more, it is difficult to achieve a satisfactory level in terms of strength while maintaining a certain thinness in the conventional light guide plate.

Therefore, an object of the present invention is to provide a light guide plate having a high intensity enough to be used in a large-sized edge light type surface light source device.

The present invention relates to a light guide plate having a resin plate whose main surface area is 400000 mm ² or more. In the light guide plate which concerns on this invention, the thickness of a resin plate is 1.5 mm-4.0 mm. In addition, the resin plate contains the styrene resin which has a weight average molecular weight of 200000-400000, and has molecular weight distribution of 2.0-4.0.

The light guide plate according to the present invention is used in an edge light type surface light source device having a large screen of 400000 mm ² or more by using a styrene resin plate having a specific thickness formed of a styrene resin having a weight average molecular weight and a molecular weight distribution in a specific range. A high enough strength is achieved.

When the light transmittance in the thickness direction of the plate-shaped test piece having a thickness of 4 mm obtained by molding the styrene resin constituting the resin plate is T365 at a wavelength of 600 nm and T600 at a wavelength of 365 nm, preferably T600 is 85% or more, and T365 / T600 is 0.90 to 0.99. Thereby, sufficiently high luminance is achieved more easily in the large surface light source device.

In another aspect, the present invention relates to an edge light type surface light source device including the light guide plate according to the present invention and a light source for supplying light to the end face of the resin plate of the light guide plate.

According to the present invention, there is provided a light guide plate having a high intensity sufficient to be used in a large-sized edge light type surface light source device.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows one Embodiment of the transmissive image display apparatus provided with a surface light source device.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, this invention is not limited to the following embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows one Embodiment of the transmissive image display apparatus provided with a surface light source device. The transmissive image display apparatus 100 shown in FIG. 1 is a liquid crystal display device mainly comprised by the surface light source device 20 and the liquid crystal display part 30 which has a liquid crystal cell. The surface light source device 20 includes a light guide plate 1 having a resin plate 11, and a light source 3 provided along the end surface S3 of the resin plate 11. The resin plate 11 has the emission surface S1 and the back surface S2 on the opposite side. The light guide plate 1 further has a reflecting portion 12 provided on the back surface S2 side. The liquid crystal display unit 20 is provided on the emission surface S1 side of the light guide plate 1.

Light irradiated from the light source 3 is incident on the resin plate 11 from the end face S3. Light incident on the resin plate 11 is mainly reflected from the emission surface S1 by being reflected by the reflector 12. Light emitted from the exit surface S1 is supplied to the liquid crystal display unit 30.

The output surface S1 and the back surface S2 which are main surfaces of the resin plate 11 are rectangular (typically rectangular), and each area is 400000 mm <^2> or more. For example, the emission surface S1 and the rear surface S2 may have a rectangular shape of 800 mm × 500 mm.

The thickness of the resin plate 11 is 1.5 mm-4.0 mm. In this way, the resin plate has a certain thickness, so that even in a large area of 400000 mm ² or more, deformation and breakage of the light guide plate due to the impact received when used in the surface light source device is sufficiently prevented. From the same viewpoint, it is preferable that the thickness of the resin plate 11 exceeds 2.0 mm, and 2.5 or more are more preferable. On the other hand, it is preferable that the thickness of the resin plate 11 is small from a viewpoint of thickness reduction of a display apparatus. Specifically, the thickness of the resin plate 11 is preferably 3.7 mm or less, and more preferably 3.5 mm or less.

The resin plate 11 is a styrene resin plate formed of styrene resin. The styrene resin includes a polymer containing styrene or a monofunctional derivative thereof (hereinafter referred to as a "styrene monomer") as a main monomer unit. As the styrene monomer constituting the styrene resin, for example, substituted styrenes may be used in addition to the styrene. Examples of the substituted styrenes include halogenated styrenes such as chloro styrene and bromostyrene, and vinyl styrenes such as vinyltoluene and α-methyl styrene. The styrene monomers may be used alone, or two or more kinds thereof may be used in combination. The styrene resin may contain a trace amount of other components compatible with this polymer. The styrene resin may be a homopolymer of a styrene monomer or may be a copolymer of one or two or more monofunctional monomers different from the styrene monomer. The styrene resin preferably contains 50% by mass or more of the monomer units derived from the styrene monomers based on the mass of the entire styrene resin.

The monofunctional monomer copolymerized with the styrene monomer may be a compound having one double bond capable of radical polymerization. These monofunctional monomers are, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate and methacrylic acid Methacrylic acid esters such as 2-hydroxyethyl, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, acrylic acid esters such as 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate At least one selected from acid, acrylic acid, and acrylonitrile. Among these, methacrylic acid esters, such as methyl methacrylate, are preferable.

The weight average molecular weight Mw of the styrene resin which comprises the resin plate 11 becomes like this. Preferably it is 200000-400000, More preferably, it is 250000-3800000 from a viewpoint of maintaining sufficient strength and favorable extrusion workability. The upper limit and the lower limit of the weight average molecular weight of the styrene resin can be arbitrarily selected from, for example, 200000, 250000, 280000, 300000, 330000, 3800000 and 400000. From a similar viewpoint, the molecular weight distribution (ratio of weight average molecular weight Mw and number average molecular weight Mn, Mw / Mn) of styrene resin becomes like this. Preferably it is 2.0-4.0, More preferably, it is 2.5-3.4. The upper limit and the lower limit of the molecular weight distribution of the styrene resin can be arbitrarily selected from, for example, 2.0, 2.5, 2.6, 3.2, 3.4, 3.6 and 4.0. When a weight average molecular weight and molecular weight distribution become large, when a resin plate is shape | molded by methods, such as an extrusion process, a big load is applied to a molding machine, and foreign material in a molding machine etc. become easy to mix in a resin plate. Moreover, since the molecular weight distribution is small, it becomes easy to smooth the cross section of the resin plate after shaping | molding by grinding | polishing. In the edge light type surface light source device in which light is incident from the end face, it is particularly important that the end face of the large-area resin plate is easily processed.

The said weight average molecular weight and molecular weight distribution are standard polystyrene conversion values obtained by the gel permeation chromatograph (GPC) measurement.

As styrene resin which comprises the resin plate 11, Preferably, the light transmittance T600 of the thickness direction in wavelength 600nm of the plate-shaped test piece which has a thickness of 4 mm obtained by shape | molding this styrene resin is 85% or more, More preferably, Is at least 87%, more preferably at least 88%. The upper and lower limits of T600 can be arbitrarily selected, for example from 85%, 87%, 88%, 89.9%, 90.0% and 90.1%. The ratio (T365 / T600) to T600 of the light transmittance T365 in the thickness direction at a wavelength of 365 nm of the associated test piece is preferably 0.90 to 0.99. Since the styrene resin has light transmittance that satisfies these conditions, it is possible to supply light of sufficient luminance in a large-area surface light source device. From a similar viewpoint, T365 / T600 becomes like this. More preferably, it is 0.94 or more, More preferably, it is 0.95 or more. The upper and lower limits of T365 / T600 can be arbitrarily selected from, for example, 0.90, 0.94, 0.942, 0.943, 0.947, 0.95 and 0.99. The single-layer resin plate obtained by molding the styrene resin satisfying the above conditions usually exhibits 85% or more of T600 and 0.90 to 0.99 of T365 / T600 in the range of about 1.5 to 4 mm in thickness.

In the case of the plate-shaped test piece (thickness 4mm) obtained by shape | molding the styrene resin which is generally used, T365 / T600 is often less than 0.90. As this reason, when a raw material monomer is polymerized by manufacturing methods, such as suspension polymerization method and a dispersion polymerization method, in a liquid phase, when a styrene resin is obtained, a solvent, a catalyst component, and other additives are mixed in the styrene resin obtained. I think. In the case where the gaseous raw material monomer is polymerized by contacting with a solid catalyst to prepare a styrene resin, incorporation of the catalyst component is also assumed. Moreover, it is also considered that T365 falls by the additive added in small quantities to the produced styrene resin for various purposes.

Therefore, as the styrene resin, for example, it is difficult for the styrene resin to be colored as an additive or a catalyst, or the styrene resin used in the manufacturing process, the styrene resin sufficiently washed after the polymerization, or no additive is added after the polymerization. By selecting and using an extremely small amount of styrene resin, a test piece in which T365 / T600 is in the range of 0.90 to 0.95 can be obtained. Such high purity styrene resin can be obtained as a commercial item, as shown in the Example mentioned later.

In addition to styrene resin, the resin plate 11 may contain other components, such as a particulate light-diffusion agent which forms the phase different from the phase containing styrene resin. The resin plate 11 can be manufactured by usual shaping | molding methods, such as extrusion molding.

The reflecting portion 12 forms a predetermined dot pattern on the back surface S2. The reflector 12 includes, for example, a particulate light reflector and a binder in which it is dispersed. The reflecting portion 12 can be formed by a conventional method such as pattern printing of ink.

It is preferable that the light source 3 is a point light source, such as LED. In this case, a plurality of point light sources are arranged along at least one of four sides constituting the rectangular main surface of the resin plate 11.

This invention is not limited to embodiment described above, A change is possible suitably in the range which does not deviate from the meaning. For example, instead of providing the reflecting portion 12 as a reflecting means of the light guide plate 1, an uneven shape may be formed on the back surface S2. Further, for example, in order to adjust the light output, an uneven shape may be formed on the emission surface S1 side of the light guide plate 1. In addition, various optical films such as a diffusion film, a prism film, and a brightness enhancement film may be provided between the light guide plate 1 and the liquid crystal display unit 30.

Example

Hereinafter, the results of evaluating the properties of the styrene-based resin that can be used in the light guide plate according to the present invention. However, styrene resin used for this invention is not limited to these.

Weight average molecular weight and molecular weight distribution

The solution which melt | dissolved the styrene resin in THF was filtered with the membrane filter of 0.2 micrometer, and the sample for a measurement was prepared. The GPC measurement was performed using this sample, and the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of standard polystyrene conversion were measured.

Light transmittance

The styrene resin was thrown into the raw material hopper of the extruder, and it was extrusion-molded by setting the cylinder temperature to 200-250 degreeC, and the plate-shaped test piece which has a thickness of 4 mm was obtained. Using this test piece, the light transmittance T365 at the wavelength of 365 nm in the plate thickness direction and the light transmittance T600 at the wavelength of 600 nm were measured with a spectroscopic transmittance meter (Hitachi U4000) with an integrating sphere. Moreover, the value of T365 / T600 was calculated | required from these values.

As shown in Table 1, each of the commercially available styrene resins (polystyrene) A, B, and C had a weight average molecular weight of 200000 to 400000 and a molecular weight distribution of 2.0 to 4.0. Moreover, it was confirmed that the test piece obtained by shape | molding each styrene resin satisfies the characteristic that T600 is 85% or more and T365 / T600 is 0.90-0.99.

Styrene-based resin B: GPPS made in BASF Corporation, grade name "polystyrene 168N"

Styrene-based resin C: GPPS made in PS Japan company, grade name "G9305"

According to the present invention, there is provided a light guide plate having a high intensity sufficient to be used in a large-sized edge light type surface light source device.

1: light guide plate 3: light source
11: resin plate 12: reflecting portion
20: surface light source device 30: liquid crystal display
100: transmissive image display device (liquid crystal display device)
S1: Exit surface S2: Back side
S3: cross section

Claims (3)

In the light guide plate having a resin plate,
The resin plate has a main surface having an area of 400000 mm ² or more,
The resin plate has a thickness of 1.5 mm to 4.0 mm,
The resin plate contains a styrene resin having a weight average molecular weight of 200000 to 400000 and a molecular weight distribution of 2.0 to 4.0.
Light guide plate. The method of claim 1,
A light guide plate having T600 of 85% or more and T365 / T600 of 0.90 to 0.99 when the light transmittance in the thickness direction of the plate-shaped test piece having a thickness of 4 mm obtained by molding the styrene resin is T365 at a wavelength of 600 nm and T365 at a wavelength of 365 nm. . The light guide plate of Claim 1 or 2, and
Light source which supplies light to the end surface of the said resin plate of this light guide plate
Edge-type surface light source device having a.

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