JP3413273B2 - Light diffusion sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing sheet which is advantageously used for liquid crystal displays, overhead projectors, illuminated signboards for advertisement, televisions, video screens for movies and the like.

[0002]

2. Description of the Related Art Conventionally, in order to transmit and diffuse light, a surface light source device used as a backlight for a liquid crystal display, an overhead projector, an illuminated signboard for advertisement, etc., and a video screen for televisions, movies, etc. A light diffusion sheet is used.

The usage of the light diffusing sheet will be described by taking a surface light source device used for a backlight of a liquid crystal display as an example. 3 is a perspective view showing a main part of an edge light type surface light source device which is an example of a surface light source device used as a backlight of a liquid crystal display, and FIG.
It is an enlarged fracture surface within the circle. In FIG. 3, the surface light source device 3
1 is a fluorescent lamp 33 at both ends of a transparent plate-shaped light guide plate 32.
And a reflecting plate 34 is provided so as to cover the lower surfaces of the fluorescent lamp 33 and the light guide plate 32. Then, as shown in FIG. 4, a light diffusion sheet 35 is provided on the upper surface of the light guide plate 32.

During operation of the surface light source device 31 shown in FIG.
The light from the fluorescent lamp 33 travels through the light guide plate 32 and is uniformly diffused when passing through the light diffusion sheet 35 to become a surface light source, and a liquid crystal display (not shown) installed above the surface light source device 31. Incident on.

Such a light diffusing sheet is required to have properties such as good light diffusing property, no coloring property, and excellent light transmitting property. Conventionally, as the light diffusion sheet, for example, a sheet in which a layer containing a matting agent of inorganic particles is applied and formed on one surface of a support of a polyester film is used. In order to improve the light transmittance of the light diffusing sheet, a light diffusing sheet in which the surface of a polycarbonate sheet is embossed has been proposed, but there is a problem that the thickness of the sheet must be increased for embossing. is there. When the output of the light source is increased in order to make the image surface bright, there is a problem that power consumption increases, heat generation increases, and cost also increases.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a light diffusing sheet having a transparent support and a material and a thickness of a diffusing layer which are similar to those of a conventional light diffusing sheet, but having significantly improved light transmittance. To provide.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a transparent support.
The light diffusion layer is on one side and the cationic quaternary ammonium is on the side chain.
Consists of a cross-linked ion conductive resin containing a nickel base
A light diffusing sheet , which is provided via a polymer layer, and is provided on the other surface with a polymer layer formed of a cross-linked body of an ion conductive resin having a cationic quaternary ammonium base in a side chain. It is in.

Preferred aspects of the present invention are as follows. (1) A polymer layer made of a cross-linked body of an ion conductive resin having a cationic quaternary ammonium base in its side chain is also provided on the surface of the transparent support sheet opposite to the side where the light diffusion layer is provided. The light diffusion sheet described above.

(2) An ion conductive resin having a cationic quaternary ammonium base in the side chain has a vinyl compound and a hydroxyl group having a cationic quaternary ammonium base and having a polymerizable double bond at the terminal. The light diffusing sheet as described above, which is a copolymer of a mixture of a vinyl compound and a vinyl compound.

(3) The ion conductive resin having a cationic quaternary ammonium base in the side chain contains a (meth) acrylate compound having a cationic quaternary ammonium base and a (meth) acrylate compound having a hydroxyl group. The above-mentioned light diffusion sheet, which is a copolymer of a mixture of (meth) acrylate compounds.

(4) A crosslinked product of an ion conductive resin having a cationic quaternary ammonium base in its side chain is formed by combining an ion conductive resin having a cationic quaternary ammonium base in its side chain with a thermally crosslinkable compound. The above-mentioned light diffusion sheet which is a cross-linking reaction product.

(5) The light diffusing sheet as described above, wherein the thermally crosslinkable compound is an epoxy compound having 2 to 4 glycidyl groups.

(6) The polymer layer has a thickness of 0.05 to
The above light diffusion sheet having a thickness of 2.2 μm.

(7) The light diffusing sheet as described above, wherein the transparent support sheet is formed of polyester.

(8) The above light diffusion sheet, wherein the light diffusion layer is formed by dispersing and fixing a large number of organic polymer particles with a binder.

(9) The above light diffusion sheet, wherein the light diffusion layer is formed by dispersing and fixing a large number of (meth) acrylic resin particles with a (meth) acrylic resin binder.

First, the present invention will be described with reference to FIG.
And explain. FIG. 1 is a schematic cross-sectional view showing one aspect of the light diffusion sheet. In FIG. 1, the light diffusion sheet 11 is configured by forming a polymer layer 13 on one surface of a transparent support sheet 12 and providing a light diffusion layer on the polymer layer 13.

The transparent support sheet 12 can be any of the commonly known sheets that are good in transparency and have sufficient mechanical strength. Generally, plastic is used as the material of the transparent support sheet 12, but glass may be used in some cases. Preferred plastics for use as the material of the transparent support sheet 12 include, for example, polyester (polyethylene terephthalate, polyethylene naphthalate, etc.), polyolefin (polyethylene, polypropylene, etc.), polyamide, polyether, polystyrene, polyesteramide, polycarbonate, Examples thereof include poly-phenylene sulfide, polyether ester, polyvinyl chloride, polymethacrylic acid ester and polyacrylic acid ester. The thickness of the transparent support sheet 12 is generally 0.02 m.
The thickness is preferably m to 4.0 mm. The surface of the transparent support sheet 12 may be subjected to surface treatment by discharge treatment or the like, or may be provided with an adhesive layer, an undercoat layer or the like in order to enhance the adhesiveness to the polymer layer 13.

The polymer layer 13 is composed of a crosslinked body of an ion conductive resin having a cationic quaternary ammonium salt group on its side chain. Preferred as the ion conductive resin having a cationic quaternary ammonium salt group on its side chain is a vinyl compound having a cationic quaternary ammonium salt group and having a polymerizable double bond at the end, and a vinyl having a hydroxyl group. It is a water-soluble copolymer of a mixture of a vinyl compound containing a compound.

The vinyl compound having a cationic quaternary ammonium salt group and having a polymerizable double bond at the terminal is preferably a (meth) acrylate compound having a cationic quaternary ammonium salt group. Preferred specific examples thereof include dimethylaminoethyl acrylate quaternized product, dimethylaminoethyl methacrylate quaternized product, diethylaminoethyl acrylate quaternized product, diethylaminoethyl methacrylate quaternized product, methylethylaminoethyl acrylate quaternized product, methylethylaminoethyl methacrylate. Examples thereof include quaternary compounds and mixtures of two or more of these.

The above-mentioned vinyl compound having a hydroxyl group is preferably a (meth) acrylate compound having a hydroxyl group, and specific examples thereof include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, polyglycerol diacrylate, Examples thereof include polyglycerol dimethacrylate.

The above water-soluble copolymer can be obtained in the state of an aqueous solution by subjecting a mixture of the above vinyl compounds to an emulsion polymerization reaction in an aqueous medium.

The mixture of vinyl compounds for producing the above water-soluble copolymer further comprises a vinyl compound having a cationic quaternary ammonium salt group and having a polymerizable double bond at the terminal, and a hydroxyl group. A vinyl compound copolymerizable with the vinyl compound having Preferable specific examples of such vinyl compounds include alkyl acrylates such as methyl acrylate and ethyl acrylate, methacrylic acid alkyl esters such as methyl methacrylate and ethyl methacrylate, styrene, vinyltoluene and acetic acid. Examples thereof include vinyl and a mixture of two or more of these. Particularly preferred is
Acrylic acid alkyl ester and methacrylic acid alkyl ester.

The crosslinked body of the ion conductive resin having a cationic quaternary ammonium base in the side chain is preferably an ion conductive resin having a cationic quaternary ammonium base in the side chain and a heat-crosslinkable compound. It can be obtained by subjecting a mixture of This cross-linking reaction is carried out by applying an aqueous solution of a mixture of the ion-conductive resin and the heat-crosslinkable compound onto a transparent support and then heating the mixture as described below, and by using the hydroxyl group of the ion-conductive resin. A crosslinking reaction occurs.

The above heat-crosslinkable compound is preferably an epoxy compound having 2 to 4 glycidyl groups,
Specific examples include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycerol. Examples thereof include polyglycidyl ether. The content of the heat-crosslinkable compound in the mixture of the ion-conductive resin having a cationic quaternary ammonium salt group in the side chain and the heat-crosslinkable compound is 3 to 30% by weight.
Is preferred.

In order to accelerate the crosslinking reaction, a composition comprising an ion conductive resin having a cationic quaternary ammonium salt group on the side chain and a thermally crosslinkable compound is added to the composition, in order to accelerate the crosslinking reaction. , Polyamine, amidoamine, polyamidoamine, imidazole,
It is preferable to add an alkali metal carbonate or the like.

For the details of preferable crosslinked products of the ion conductive resin having a cationic quaternary ammonium base in the above side chain for forming the polymer layer 13,
It is described in JP-A-4-220469.

For the polymer layer 13, a coating solution prepared by diluting a mixture containing the above-mentioned ion conductive resin and a thermally crosslinkable compound with water, alcohol or the like, if necessary, is used as the transparent support sheet 12 Applied on the surface of 60 ℃ to 130 ℃
It can be formed by heating to a temperature of ° C to evaporate and remove the solvent, and at the same time, carry out a crosslinking reaction of the ion conductive resin and the thermally crosslinkable compound.

The thickness of the polymer layer 13 is 0.05 to 2.2.
The thickness is preferably μm, and particularly preferably 0.8 to 1.8 μm.
When the film thickness of the polymer layer 13 is smaller than the above range, the effect of increasing the light transmittance is insufficient, and when the film thickness of the polymer layer 13 is larger than the above range, blocking failure or the like tends to occur. .

Light diffusing layer 14 may be any of the light diffusing layers conventionally used in light diffusing sheets.
The particularly preferable light diffusion layer 14 is formed by dispersing and fixing a large number of organic polymer particles with a binder. As the organic polymer particles, particles made of a polymer such as a cross-linking type acrylic resin and methacrylic resin, polyethylene, polypropylene, polystyrene are preferable,
A cross-linking type acrylic resin or methacrylic resin is particularly preferable. The weight average particle size of the organic polymer particles is 1 to 10
It is preferably 0 μm, particularly preferably 1 to 25 μm.

The binder is preferably an organic polymer binder, and examples of the organic polymer binder include homopolymers and / or copolymers containing acrylic acid ester and / or methacrylic acid ester as one component of the monomer ( (Meth) acrylic resin, vinyl acetate resin, ethylene-vinyl acetate copolymer resin, vinyl chloride resin, vinyl chloride-vinylidene chloride copolymer resin, butyral resin, silicone resin, polyester resin, vinylidene fluoride resin, nitrocellulose resin, styrene resin , Styrene-acrylonitrile copolymer resin, urethane resin,
Polyethylene, polypropylene, chlorinated polyethylene,
Mention may be made of rosin derivatives, and mixtures thereof. A particularly preferred organic polymer binder is (meth)
It is an acrylic resin.

It is preferable to select a combination of materials of the organic polymer binder and the organic polymer particles so that the difference between the refractive index of the organic polymer binder and the refractive index of the organic polymer particles is 0.20 or less. The light diffusion layer containing an organic polymer binder and organic polymer particles,
In general, both are added and mixed in a suitable solvent to form a coating liquid, which is applied on a support sheet and dried, so that the organic polymer particles are substantially swelled when the coating liquid is prepared. It is necessary to prevent it from dissolving.
Therefore, the material of the organic polymer particles needs to be selected from those that do not swell or dissolve in the solvent used for the coating liquid. The amount of organic polymer particles is preferably 100 to 300% by weight with respect to the organic polymer binder.

When the above-mentioned (meth) acrylic resin is used as the organic polymer binder of the light diffusion layer 14, it is preferable to use the (meth) acrylic resin having an acid value of 5 or less. The reason is that, during the work of handling the light diffusion sheet or the surface light source device provided with the light diffusion sheet, in order to remove dirt such as dust on the light diffusion layer of the exposed light diffusion sheet, ethanol, isopropyl alcohol, etc. The surface of the light diffusion layer is often washed with a suitable organic solvent such as alcohols, and the light diffusion layer containing a (meth) acrylic resin having an acid value of more than 5 as a binder is formed of alcohols. This is because the whitening tends to occur during washing. When the light diffusion sheet causes a whitening phenomenon,
The amount of transmitted light decreases and the uniformity of light deteriorates, making it unusable as a surface light source device. When a (meth) acrylic resin having an acid value of 5 or less is used as the organic polymer binder of the light diffusion layer 14, washing with alcohol hardly causes a whitening phenomenon.

The light diffusion layer 14 may be a layer in which a matting agent of inorganic fine particles is dispersed in an organic polymer binder. Examples of the matting agent include inorganic fine particles having a weight average particle diameter of 1 to 5 μm, such as silica, calcium carbonate and alumina.
The matting agent is generally 20 to 60% by weight with respect to the binder.
Used in an amount in the range of.

Next, FIG. 2 is a schematic sectional view showing a state of the light diffusing sheet of the present invention. In FIG. 2, the light diffusion sheet 21 has a polymer layer 23 on both sides of a transparent support sheet 22.
Further, the polymer layer 24 is formed, and the light diffusion layer 25 is provided on the polymer layer 23.

The transparent support sheet 22, the polymer layers 23 and 24, and the light diffusion layer 25 in the light diffusion sheet 21.
Is the same as the transparent support sheet 12, the polymer layer 13 and the light diffusion layer 14 in the light diffusion sheet 11 shown in each.

The light diffusion sheet provided with a layer of a low molecular weight polyester adhesive or a polymer of styrene-butadiene rubber (SBR) instead of the polymer layer of the light diffusion sheet of the present invention has a transparent surface treated by glow discharge treatment. The light transmittance is not improved as compared with the light diffusion sheet in which the light diffusion layer is directly formed on the support sheet (see Comparative Examples 1 to 3). That is, it is clear that the light diffusion sheet of the present invention, in which the light transmittance is remarkably increased as shown in the examples, has a remarkable effect that cannot be expected from the conventional techniques.

The light diffusing sheet of the present invention can be used in the same manner as the conventional light diffusing sheet. For example, a light diffusion layer can be provided on the upper surface of the light guide plate 32 of the edge light type surface light source device 31 used as the backlight of the liquid crystal display shown in FIG.

[0039]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 In this example, a light diffusion sheet having the structure shown in FIG. 2 was produced. Glow discharge treatment was applied to both surfaces of a biaxially stretched and heat-fixed polyethylene terephthalate film having a thickness of 100 μm to prepare a transparent support sheet 22.

Liquid [A] having the following composition was applied to both sides of the transparent support sheet 22 by means of a Mayer bar (wire # 1).
0) and dried at 120 ° C. for 2 minutes to form a polymer layer 23 and a polymer layer 24 having a thickness of about 1.3 μm.

[0042] [A] Liquid composition   100 g of methanol   Aqueous solution containing ion conductive resin 100g

The ion conductive resin and the aqueous solution of the crosslinkable compound are produced by the following production method. Dimethylaminoethyl methacrylate quaternary compound 25.4 parts by weight, 2-
Hydroxyethyl methacrylate 7.6 parts by weight, methyl methacrylate 46 parts by weight and ethyl acrylate 21
A composition comprising 1 part by weight is emulsion-copolymerized to prepare an aqueous solution of an ion conductive resin, and 4% by weight of glycerol polyglycidyl ether as a crosslinking compound is added to the aqueous solution with respect to the solid content of the ion conductive resin. Further, 2.5% by weight of 2-methylimidazole is added to and mixed with glycerol polyglycidyl ether to produce an ion conductive resin-containing aqueous solution having a solid content of 20% by weight.

Next, on the one polymer layer 23 on the transparent support sheet 22 obtained as described above, the liquid [B] having the following composition was applied with a Meyer bar (wire # 28) to about 43 ml / m ^2. The light diffusing layer 21 was formed by applying and drying at 120 ° C. for 2 minutes to form the light diffusing layer 25.

[0045] [B] Liquid composition   Toluene 46.5g   Methyl ethyl ketone 16.3 g   Organic polymer binder 14.5g     (Manufactured by Mitsubishi Rayon Co., Ltd .: Dialnal BR-79,       Copolymer of methacrylic acid and acrylic monomer,       Molecular weight 70,000, acid value 3.5)   Organic polymer particles 17.7 g     (Nippon Pure Chemical Co., Ltd .: Julimer MB-1X,       Polymethylmethacrylate (crosslinked type)       Spherical ultrafine particles (weight average particle diameter: 6.2 μm))

The luminance of one sheet of the light diffusing sheet produced as described above was measured with a luminance meter (manufactured by Tokyo Optical Machine Co., Ltd .; Topcon BM7), and it was 1237 cd / m ^2.
Met. In addition, two light diffusing sheets were overlaid and the brightness was measured by a luminance meter to find that it was 1390 cd / m ^2.
Met.

[Example 2] The same as in Example 1 except that the ion conductive resin-containing aqueous solution in the liquid composition [A] was changed to the ion conductive resin-containing aqueous solution produced by the following production method. To produce a light diffusion sheet.

Emulsion copolymerization of a composition consisting of 25.7 parts by weight of dimethylaminoethyl methacrylate quaternary product, 7.8 parts by weight of 2-hydroxyethyl methacrylate, 51.5 parts by weight of methyl methacrylate and 15 parts by weight of ethyl acrylate. An aqueous solution of an ion conductive resin is produced, and 4% by weight of polyethylene glycol diglycidyl ether is added to this aqueous solution with respect to the solid content of the ion conductive resin, and sodium sesquicarbonate is added to polyethylene glycol diglycidyl ether in an amount of 1. 0% by weight is added and mixed to produce an ion conductive resin-containing aqueous solution having a solid content of 20% by weight.

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet is 1229 cd / m ² ,
The brightness of the two light diffusion sheets was 1370 cd / m ² .

[Example 3] Liquid [A] having the following composition was applied to both sides of the transparent support sheet 22 produced in the same manner as in Example 1 by means of a Mayer bar (wire # 6).
And then dried at 120 ° C. for 2 minutes to give a film thickness of about 0.
A 5 μm polymer layer 23 and a polymer layer 24 were formed.

[0051] [A] Liquid composition   300 g of methanol   Aqueous solution containing ion conductive resin 100g     (Nippon Pure Chemical Co., Ltd .: Jurimer SP-50T stock solution)

Next, on the one polymer layer 23 on the transparent support sheet 22 obtained as described above, the solution [B] having the same composition as in Example 1 was applied to the Mayer bar (wire # 28). Approximately 43 ml / m ^{2 and} apply at 120 ° C for 2
The light diffusing layer 25 was formed by drying for a minute, and the light diffusing sheet 21 was produced.

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet and the brightness of two light diffusion sheets were the same as those of the light diffusion sheet prepared in Example 1.

[Example 4] The same procedure as in Example 3 was repeated except that the ion conductive resin-containing aqueous solution in the liquid composition of [A] was changed to JULIMER SP-65T stock solution manufactured by Nippon Pure Chemical Co., Ltd. To produce a light diffusion sheet.

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet and the brightness of two light diffusion sheets were the same as those of the light diffusion sheet prepared in Example 2.

[Example 5] The same procedure as in Example 3 was repeated except that the ion conductive resin-containing aqueous solution in the liquid composition [A] was changed to a stock solution of JULIMER SP-50TF manufactured by Nippon Pure Chemical Co., Ltd. To produce a light diffusion sheet.

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet is 1229 cd / m ² ,
The brightness of the two light diffusion sheets was 1370 cd / m ² .

[Comparative Example 1] A light diffusion sheet was prepared in the same manner as in Example 1 except that the polymer layers 23 and 24 were not provided (that is, light was formed on a transparent support which had been subjected to glow discharge treatment). The diffusion layer was formed directly).

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet is 1140 cd / m ² ,
The brightness of the two light diffusion sheets was 1220 cd / m ² .

[Comparative Example 2] A liquid was used in the same manner as in Example 1 except that the liquid [A] was changed to a low molecular weight polyethylene terephthalate adhesive (Fuji Photo Film Co., Ltd., Stafix). A diffusion sheet was produced.

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet is 1141 cd / m ² ,
The brightness of the two light diffusion sheets was 1220 cd / m ² .

Comparative Example 3 Instead of the polymer layers 23 and 24 in Example 1, the first layer of styrene-butadiene copolymer on the transparent support sheet (film thickness = 0.15 μm).
m) and a second layer of gelatin (thickness = 0.16μ)
Example 1 except that m) was provided on both sides of the transparent support sheet.
A light diffusion sheet was prepared in the same manner as in.

When the brightness of the light diffusion sheet produced as described above was measured in the same manner as in Example 1,
The brightness of one light diffusion sheet is 1165 cd / m ² ,
The brightness of the two light diffusion sheets was 1280 cd / m ² .

From the comparison between the above-mentioned Examples and Comparative Examples, the light diffusion sheet of the present invention has a polymer layer made of a specific substance, and thus a light diffusion sheet or a polymer layer provided with a layer made of another substance. It is clear that it has a significantly improved light transmittance as compared with the light diffusion sheet which is not provided. When measured in the same manner as in the example, the brightness of a commercially available light diffusing sheet manufactured by Company A (one sheet) is 9
60 cd / m ² and light diffusion sheet manufactured by company B (one sheet)
The luminance was 1160 cd / m ² .

[0065]

The light diffusing sheet of the present invention has the material and thickness of the transparent support and the diffusing layer similar to those of the conventional light diffusing sheet, but has a remarkably improved light transmittance. Therefore, by using the light diffusion sheet of the present invention, it is possible to easily obtain a high-luminance surface light source without changing the light source.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one aspect of a light diffusion sheet of a reference example .

FIG. 2 is a schematic cross-sectional view showing another embodiment of the light diffusion sheet of the present invention.

FIG. 3 is a perspective view showing a main part of an edge light type surface light source device which is an example of a surface light source device.

FIG. 4 is an enlarged fracture surface within a circle A in FIG.

[Explanation of symbols]

11 Light diffusion sheet 12 Transparent support sheet 13 Polymer layer 14 Light diffusion layer 21 Light diffusion sheet 22 Transparent support sheet 23 Polymer layer 24 Polymer layer 25 Light diffusion layer 31 surface light source device 32 light guide plate 33 fluorescent lamp 34 Reflector 35 Light diffusion sheet

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 5/02

Claims (3)

(57) [Claims] 1. A light diffusion layer is provided on one surface of a transparent support ,
Ions with a cationic quaternary ammonium base in the chain
It is equipped with a polymer layer consisting of a crosslinked body of a conductive resin.
On the other side, a polymer layer comprising a cross-linked body of an ion conductive resin having a cationic quaternary ammonium salt group on its side chain is provided. 2. A polymer layer at least on the side of the light diffusion layer.
The formed ion conductive resin is a cationic quaternary resin.
Have a double bond at the end.
Containing a vinyl compound having a hydroxyl group and a vinyl compound having a hydroxyl group
The light spread according to claim 1, which is a copolymer of a vinyl compound.
Scattering sheet . 3. The light diffusion layer comprises a large number of organic polymer particles.
Claims that are formed by dispersing and fixing with a binder
Item 2. The light diffusion sheet according to item 1.