# Patent

## Title
Image display device that can display high brightness and high contrast images and includes a cured resin layer

## Abstract

A thin image display device is provided which is free from display defects caused by the deformation of an image display part and can display high brightness and high contrast images. The image display device includes an image display part, a light-transmitting protective part arranged on the image display part, and a cured resin layer interposed between the image display part and the protective part. The cured resin layer has a light transmittance in the visible region of 90% or more and a refractive index (nD) of 1.45 or more and 1.55 or less.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 16/909,943 filed Jun. 23, 2020, which is a continuation of U.S. application Ser. No. 16/216,525 filed Dec. 11, 2018 (now U.S. Pat. No. 10,725,329), which in turn is a continuation of U.S. application Ser. No. 14/721,748 filed May 26, 2015 (now U.S. Pat. No. 10,216,026), which in turn is a continuation of U.S. application Ser. No. 12/450,232 filed Sep. 17, 2009 (now abandoned), which in turn is a U.S. national stage application of PCT/JP2008/057024 filed Apr. 9, 2008, which claims the benefit of JP 2007-102252 filed Apr. 9, 2007, JP 2007-186360 filed Jul. 17, 2007, and JP 2008-005027 filed Jan. 11, 2008, the contents of each of these applications being incorporated herein by reference.


TECHNICAL FIELD
The present invention relates to an image display device such as a liquid crystal display device (LCD) used, for example, in a cellular phone, and in particular to an image display device that includes a transparent protective part arranged on an image display part and a cured resin layer arranged between the image display part and the protective part.
BACKGROUND ART
One conventional example of such an image display device is a liquid crystal display device 101 shown in FIG. 4.
This liquid crystal display device 101 includes a transparent protective part 103 made of, for example, glass or plastic on a liquid crystal display panel 102, as shown in FIG. 4.
In this display device, to protect the surface of the liquid crystal display panel 102 and a polarizing plate (not shown), a spacer 104 is arranged between the liquid crystal display panel 102 and the protective part 103 to form a gap 105 between the liquid crystal display panel 102 and the protective part 103.
However, the gap 105 present between the liquid crystal display panel 102 and the protective part 103 causes light scattering, and this results in a reduction in contrast and in brightness. In addition, the presence of the gap 105 also makes it difficult to produce thinner display panels.
In view of the above problems, a technique has been proposed in which the gap between the liquid crystal display panel and the protective part is filled with a resin (for example, Patent Document 1). However, the stress during cure shrinkage of the cured resin causes deformation of optical glass plates sandwiching the liquid crystal of the liquid crystal display panel. This results in display defects such as irregularities in the orientation of the liquid crystal material.

    [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-55641.


DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
The present invention has been made in view of the problems in the conventional technologies. It is an object of the present invention to provide a thin image display device which is free from display defects caused by the deformation of an image display part and can display high brightness and high contrast images.
Means for Solving the Problems
To achieve the above object, the present inventors have conducted extensive studies and found that as the difference in refractive index (ΔnD) between the protective part and gap of an image display device increases, the brightness and contrast of the image display device are lowered due to the scattering and attenuation of image light from the image display part. This results in a reduction in visibility. To avoid this problem, the present inventors have found that it is effective to arrange a cured resin layer having a certain refractive index between the image display part and the protective part. Thus, the present invention has been completed.
The inventors have also found that the internal stress accumulated during curing of a resin composition can be approximated by the product of the storage modulus after curing and the curing shrinkage ratio. Therefore, it is preferable to use, as the resin composition arranged between the image display part and the protective part, a resin composition that has a certain curing shrinkage ratio and yields a cured product having a certain storage modulus.
Accordingly, the present invention provides an image display device, comprising an image display part and a light-transmitting protective part arranged on the image display part, wherein
the image display device further comprises a cured resin layer arranged between the image display part and the protective part, and
the cured resin layer has a light transmittance in a visible region of 90% or more and a refractive index (nD) of 1.45 or more and 1.55 or less.
Preferably, in the present invention, the cured resin layer has an elastic modulus at 25° C. of 1.0×107 Pa or less.
Preferably, in the present invention, the cured resin layer is a cured product of a resin composition having a curing shrinkage ratio of 5% or less.
Preferably, in the present invention, the cured resin layer has a refractive index (nD) of 1.51 or more and 1.52 or less.
In the present invention, the image display part may be a liquid crystal display panel.
In the present invention, the protective part may be formed from an acrylic resin.
In the present invention, the protective part may be formed from an optical glass.
Effects of the Invention
In the present invention, the cured resin layer arranged between the image display part and the protective part has a light transmittance of 90% or more and a refractive index (nD) of 1.45 or more and 1.55 or less and more preferably, for example, 1.51 or more and 1.52 or less. In this manner, as compared to the case in which air having a refractive index of 1.0 is arranged therebetween, the differences in refractive index at the interface of the image display part and the interface of the protective part are smaller, so that the scattering and attenuation of image light from the image display part can be reduced. Therefore, according to the present invention, the brightness and contrast of the displayed image can be increased, whereby the visibility can be improved.
In the present invention, the use of a resin composition having a curing shrinkage ratio of 5% or less and yielding a cured product having a storage modulus at 25° C. of 1.0×107 Pa or less can minimize the influence of the stress during cure shrinkage of the resin on the image display part and the protective part. Therefore, almost no distortion occurs in the image display part and the protective part.
Accordingly, a high brightness and high contrast image can be displayed without display defects.
In particular, when the image display part is a liquid crystal display panel, display defects such as irregularities in the orientation of the liquid crystal material can be reliably prevented, so that a high quality image can be displayed.
Moreover, in the present invention, the gap between the image display part and the protective part is filled with the cured resin. This provides high impact resistance.
In addition, an image display device thinner than the conventional example in which a gap is formed between the image display part and the protective part can be provided.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view illustrating the main part of an embodiment of an image display device according to the present invention.
FIG. 2 is a cross-sectional view illustrating the main part of another embodiment of the image display device according to the present invention.
FIG. 3 is a cross-sectional view illustrating the main part of another embodiment of the image display device according to the present invention.
FIG. 4 is a cross-sectional view illustrating the main part of a conventional display device



DESCRIPTION OF REFERENCE NUMERALS
1 image display device, 2 display part, 3 protective part, 4 spacer, 5 cured resin, 6 and 7 polarizing plate
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals denote the same or like elements.
FIGS. 1 and 2 are cross-sectional views illustrating the main parts of embodiments of an image display device according to the present invention. The display device 1 of each embodiment includes: an image display part 2 that is connected to a driving circuit (not shown) and displays an image in a predetermined manner; and a light-transmitting protective part 3 that is arranged so as to face the image display part 2 with a predetermined distance therebetween, as shown in FIGS. 1 and 2.
No particular limitation is imposed on the image display device, and the image display device can be applied to various applications. Examples of the image display device include liquid crystal display devices for a cellular phone, a portable game device, and the like. The image display part 2 of each embodiment may be the liquid crystal display panel of such a liquid crystal display device.
When the image display part 2 is a liquid crystal display panel, polarizing plates 6 and 7 are provided on the surfaces of the liquid crystal display panel, as shown in FIG. 2.
When the body of the liquid crystal display panel is formed from an optical glass, the refractive index (nD) thereof is generally 1.49 to 1.50. Some tempered glass has a refractive index (nD) of about 1.55.
The protective part 3 is a plate-, sheet-, or film-like light-transmitting member having substantially the same size as the size of the display part 2. For example, optical glass or plastic (an acrylic resin, such as polymethyl methacrylate, or the like) can be suitably used as the light-transmitting member. An optical layer such as an anti-reflective film, a shielding film, or a viewing angle control film may be formed on the front or rear surface of the protective part 3.
When the protective part 3 is formed from an acrylic resin, the refractive index (nD) thereof is generally 1.51 to 1.52.
The protective part 3 is arranged on the display part 2 through a spacer 4 provided on a peripheral part of the display part 2. The spacer 4 has a thickness of about 0.05 to about 1.5 mm, so that the distance between the surfaces of the image display part 2 and the protective part 3 is maintained at about 1 mm.
To improve the brightness and contrast, a frame-like shielding part (not shown) is provided on the peripheral part of the protective part 3.
A cured resin layer 5 is arranged between the image display part 2 and the protective part 3. This cured resin layer 5 has a light transmittance in the visible region of 90% or more. Preferably, the cured resin layer 5 is formed so as to have a thickness of 50 to 200 μm.
Preferably, the cured resin layer 5 has a refractive index (nD) substantially the same as those of the image display part 2 and the protective part 3. More specifically, the refractive index (nD) is 1.45 or more and 1.55 or less, and preferably 1.51 or more and 1.52 or less. In this manner, the brightness and contrast of the image light from the image display part 2 can be increased, so that the visibility can be improved.
The cured resin layer 5 has a storage modulus at 25° C. of preferably 1.0×107 Pa or less, and more preferably 1×103 to 1×106 Pa. Typically, even when the main resin component constituting the curable resin composition is the same, if a remaining resin component or monomer component to be used is different, the cured resin formed by curing such a curable resin composition may have a storage modulus (25° C.) exceeding 1×107. Such a cured resin layer is not preferred.
The cured resin layer 5 is a cured product of a resin composition having a curing shrinkage ratio of preferably 5% or less, more preferably 4.5% or less, and still more preferably 4.0% or less, and most preferably 0 to 2%. In this manner, the internal stress that builds up in the cured resin layer when the curable resin composition is cured can be reduced, and the occurrence of distortion at the interface between the cured resin layer 5 and the liquid crystal display panel 2 or the protective part 3 can be prevented. Therefore, when the resin composition is arranged between the liquid crystal display panel 2 and the protective part 3 and then cured, the cured product can reduce light scattering at the interface between the cured resin layer 5 and the liquid crystal display panel 2 or the protective part 3. This can improve both the brightness of the displayed image and the visibility.
The magnitude of the internal stress that builds up in the cured product of a resin composition during curing can be evaluated by the average surface roughness of the cured resin obtained by dropping the resin composition onto a flat plate and curing the dropped resin composition. For example, 2 mg of a resin composition is dropped onto a glass or acrylic plate and cured by irradiation with UV light to a cure ratio of 90% or more. When the average surface roughness of the resultant cured resin is 6.0 nm or less, the interfacial distortion caused by the cured product of the curable resin composition arranged between the liquid crystal display panel 2 and the protective part 3 is practically negligible. With the curable resin composition used in the present invention, the average surface roughness can be preferably 6.0 nm or less, more preferably 5.0 nm or less, and still more preferably 1 to 3 nm. Therefore, the distortion at the interfaces of the cured resin is practically negligible.
Any glass plate used for sandwiching the liquid crystal of a liquid crystal cell or used as the protective plate of a liquid crystal cell may be preferably used as the above glass plate. Any acrylic plate used as the protective plate of a liquid crystal cell may be preferably used as the above acrylic plate. The average surface roughness of such glass and acrylic plates is typically 1.0 nm or less.
It is preferable from the viewpoint of improving productivity that the resin composition forming the cured resin layer 5 is a photocurable resin composition. To prepare the resin composition such that the cured resin layer 5 has a refractive index (nD) of 1.51 or more and 1.52 or less, the monomer of the resin composition is selected.
Preferred examples of such a resin include a resin composition containing: at least one kind of polymer, such as a polyurethane acrylate, a polyisoprene acrylates or an ester thereof, a hydrogenated terpene resin, and a butadiene polymer; at least one kind of acrylate monomer, such as isobornyl acrylate, dicyclopentenyloxyethyl methacrylate, and 2-hydroxybutyl methacrylate; and a photo polymerization initiator such as 1-hydroxy-cyclohexyl-phenyl-ketone.
The protective part 3 often has a UV cut function to protect the display part 2 from UV light.
In such a case, it is preferable to use, as the photo polymerization initiator, a photo polymerization initiator that can initiate curing in the visible region (for example, trade name: SpeedCure TPO, product of Nihon SiberHegner K. K.).
In a method of producing the image display device 1 of each embodiment, for example, the spacer 4 and a projecting bank portion (not shown) are first provided on the peripheral part of the image display part 2, and a predetermined amount of the above-described photocurable resin composition is dropped to the inner region surrounded by the spacer 4 and the projecting bank portion.
Then, the protective part 3 is placed on the spacer 4 of the image display part 2, and the gap between the display part 2 and the protective part 3 is completely filled with the resin composition.
Subsequently, the resin composition is irradiated with UV light through the protective part 3 to thereby cure the resin composition. In this manner, the target image display device 1 is obtained.
In this image display device 1, since the refractive index of the cured resin layer 5 is substantially the same as that of the protective part 3, the brightness and contrast can be increased, so that the visibility can be improved.
Since the influence of the stress during cure shrinkage of the resin on the image display part 2 and the protective part 3 can be minimized, almost no distortion occurs in the image display part 2 and the protective part 3. Therefore, no deformation occurs in the image display part 2, so that a high brightness and high contras image can be displayed without display defects.
Moreover, since the gap between the image display part 2 and the protective part 3 is filled with the cured resin layer 5, high impact resistance is obtained.
In addition, the image display device 1 can be produced thinner than the conventional example in which a gap is provided between the image display part and the protective part.
The present invention can be embodied in other various forms. For example, an image display device 1 having no spacers 4 may be produced as shown in FIG. 3. In this case, the above-described photocurable resin composition is applied to a base 2, and the protective part 3 is placed on the applied resin composition. The resin composition is cured with light in the same manner as described above.
Moreover, the present invention is applicable not only in the liquid crystal display device described above, but also in various panel displays such as an organic EL, a plasma display apparatus and the like.
EXAMPLES
Hereinafter, the present invention will be specifically described by way of Examples and Comparative Examples, but the invention is not limited to the following Examples.
Example 1
50 Parts by weight of polyurethane acrylate (trade name: UV-3000B, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 30 parts by weight of isobornyl acrylate (trade name: IBXA, manufactured by Osaka Organic Chemical Industry Ltd.), 3 parts by weight of a photopolymerization initiator (trade name: IRGACURE 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name: SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Example 1.
Example 2
70 Parts by weight of an ester compound formed from a maleic anhydride adduct of polyisoprene polymer and 2-hydroxyethyl methacrylate, 30 parts by weight of dicyclopentenyloxyethyl methacrylate, 10 parts by weight of 2-hydroxybutyl methacrylate, 30 parts by weight of a hydrogenated terpene resin, 140 parts by weight of a butadiene polymer, 4 parts by weight of a photopolymerization initiator, and 0.5 parts by weight of a photo polymerization initiator for visible light were kneaded using a kneader to prepare a resin composition of Example 2.
Example 3
100 Parts by weight of an ester compound formed from a maleic anhydride adduct of polyisoprene polymer and 2-hydroxyethyl methacrylate, 30 parts by weight of dicyclopentenyloxyethyl methacrylate, 10 parts by weight of 2-hydroxybutyl methacrylate, 30 parts by weight of a hydrogenated terpene resin, 210 parts by weight of a butadiene polymer, 7 parts by weight of a photopolymerization initiator, and 1. 5 parts by weight of a photopolymerization initiator for visible light were kneaded using a kneader to prepare a resin composition of Example 3.
Example 4
70 parts by weight of an ester compound formed from a maleic anhydride adduct of a polyisoprene polymer and 2-hydroxyethyl methacrylate (trade name: UC-203, manufactured by Kuraray Co., Ltd.), 30 parts by weight of dicyclopentenyl oxyethyl methacrylate (trade name: FA512M, manufactured by Hitachi Chemical Co., Ltd.), 10 parts by weight of 2-hydroxybutyl methacrylate (trade name: Light Ester HOB, manufactured by Kyoeisha Chemical Co., Ltd.), 30 parts by weight of a hydrogenated terpene resin (trade name: Clearon P-85, manufactured by Yasuhara Chemical Co., Ltd.), 35 parts by weight of a butadiene polymer (trade name: Polyoil 110, manufactured by Zeon Corporation), 5 parts by weight of a photopolymerization initiator (trade name Irgacure 184D, manufactured by Ciba Specialty Chemicals Inc.), and 2 parts by weight of a photopolymerization initiator (trade name SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Example 4.
Comparative Example 1
50 Parts by weight of polybutadiene acrylate (trade name: TE-2000, manufactured by Nippon Soda Co., Ltd.), 20 parts by weight of hydroxyethyl methacrylate (trade name: Light Ester HO, manufactured by Kyoeisha Chemical Co., Ltd.), 3 parts by weight of a photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name: SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Comparative Example 1.
Comparative Example 2
50 parts by weight of polyurethane acrylate (trade name: UV-3000B, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 30 parts by weight of tricyclodecane dimethanol acrylate (trade name: NK Ester LC2, manufactured by Shin-nakamura Chemical Co., Ltd.), 3 parts by weight of a photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name: SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Comparative Example 2.
Comparative Example 3
50 parts by weight of polybutadiene acrylate (trade name: TE-2000, manufactured by Nippon Soda Co., Ltd.), 20 parts by weight of isobornyl acrylate (trade name: IBXA, manufactured by Osaka Organic Chemical Industry Ltd.), 3 parts by weight of a photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name: SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Comparative Example 3.
Evaluation 1
The resin compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were measured for light transmittance, storage modulus, curing shrinkage ratio, surface roughness, refractive index, and brightness as follows. The results are shown in Table 1.
[Preparation of Samples]
The resin compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were dropped onto a 100 μm-thick white glass plate so as to have a predetermined thickness. The glass plates were conveyed onto a UV conveyer to obtain cured products of the resins having a predetermined thickness. These serve as samples for measuring light transmittance, storage modulus, and curing shrinkage ratio.
[Light Transmittance]
The light transmittance in the visible region was measured for each sample (the cured resin thickness of 100 μm) using an UV-visible spectrophotometer (V-560, manufactured by JASCO Corporation) and was found to be 90% or more for all the samples.
[Storage Modulus]
The storage modulus (Pa) (25° C.) was measured for each sample at a measurement frequency of 1 Hz using a viscoelastometer (DMS 6100, manufactured by Seiko Instruments Inc.).
[Curing Shrinkage Ratio]
The specific gravities of the uncured resin solution and the cured solid product were measured using an electronic densimeter (SD-120L, manufactured by Mirage Co., Ltd.), and the curing shrinkage ratio (%) was calculated by the following equation based on the difference in the specific gravities between the uncured resin solution and the cured solid product.

Curing shrinkage ratio (%)={(Cured product specific gravity−Resin solution specific gravity)/(Cured product specific gravity)}×100  [Equation 1]

[Surface Roughness]

2 mg of each resin composition was dropped onto a glass plate for a liquid crystal cell. Then, the distortion (Ra: average surface roughness) in a predetermined region (2.93 mm×2.20 mm) of a glass plate surface caused by the internal stress during UV curing was measured using a three-dimensional non-contact surface roughness meter manufactured by Zygo Corporation.
[Refractive Index]
Each resin composition was interposed between two releasing PET films and formed into a film shape using a spacer having a thickness of 100 μm. This was conveyed on a UV conveyer to cure the resin between the films. Subsequently, the releasing PET films were removed. The cured resin was cut into pieces of appropriate size, and the cut pieces were used as samples.
The sample of each cured resin was measured for refractive index using a refractometer (Model-3, manufactured by ATAGO Co., Ltd.).
[Brightness]
The image display device shown in FIG. 2 and including a protective part made of an acrylic resin (refractive index (nD)=1.52) was produced using each resin composition. Then, a black pattern was displayed on the image display part in the presence of an external light source (500 to 600 lux), and the brightness (brightness distribution) of the displayed black pattern was measured. The measurement of the brightness of the black pattern determines the quality of the contrast.














TABLE 1










Average






Storage
Curing
surface
Refractive



Transmittance
modulus
shrinkage
roughness
index
Brightness



(%)
(Pa)
ratio (%)
(nm)
(nD)
(cd/m2)






















Example 1
90 or more
1 × 106
4.5
5.5
1.47
10 or less


Example 2
90 or more
1 × 104
1.8
2.7
1.52
10 or less


Example 3
90 or more
4 × 103
1.0
1.5
1.52
10 or less


Example 4
90 or more
4 × 105
3.8
5.0
1.52
10 or less


Comparative
90 or more
2 × 107
5.6
12.4
1.49
Uneven*


Example 1


Comparative
90 or more
3 × 108
4.3
36.5
1.49
Uneven*


Example 2


Comparative
90 or more
5 × 108
5.6
64.2
1.50
Uneven*


Example 3





*Uneven: measurement was difficult due to unevenness in brightness.






As is clear from Table 1, in Examples 1 to 4, the storage modulus was 4×103 to 1×106 Pa, and the curing shrinkage ratio was 1.0 to 4.5%. Therefore, the average surface roughness Ra was 1.5 to 5.5 nm, and almost no distortion occurred. The results were satisfactory. However, in Comparative Example 1 (Ra=12.4 nm), Comparative Example 2 (Ra=36.5 nm), and Comparative Example 3 (Ra=64.2 nm), Ra was large. This indicates that the interface between the resin and the glass plate was deformed due to the internal stress during curing of the resin.
Moreover, in Example 1, the refractive index of the cured resin was substantially the same as that of the acrylic plate used as the protective part, so that no light scattering occurred. Therefore, the value of the brightness was found to be good, i.e., 10 cd/m2 or less.
Example 5
50 Parts by weight of polyisoprene methacrylate (trade name: UC-203, manufactured by Kuraray Co., Ltd.), 10 parts by weight of hydroxybutyl methacrylate (trade name: LIGHT-ESTER HOB, manufactured by Kyoeisha Chemical Co., Ltd.), 20 parts by weight of a low-molecular weight polybutadiene polymer (trade name: Polyoil 110, manufactured by ZEON corporation), 4 parts by weight of a photopolymerization initiator (trade name: IRGACURE 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Example 5.
Example 6
50 Parts by weight of polyisoprene methacrylate (trade name: UC-203, manufactured by Kuraray Co., Ltd.), 20 parts by weight of hydroxybutyl methacrylate (trade name: LIGHT-ESTER HOB, manufactured by Kyoeisha Chemical Co., Ltd.), 20 parts by weight of a low-molecular weight polybutadiene polymer (trade name: Polyoil 110, manufactured by ZEON corporation), 4 parts by weight of a photopolymerization initiator (trade name: IRGACURE 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) were kneaded using a kneader to prepare a resin composition of Example 6.
Example 7
50 Parts by weight of polyisoprene methacrylate (trade name: UC-203, manufactured by Kuraray Co., Ltd.), 20 parts by weight of hydroxybutyl methacrylate (trade name: LIGHT-ESTER HOB, manufactured by Kyoeisha Chemical Co., Ltd.), 15 parts by weight of a low-molecular weight polybutadiene polymer (trade name: Polyoil 110, manufactured by ZEON corporation), 4 parts by weight of a photopolymerization initiator (trade name: IRGACURE 184, manufactured by Ciba Specialty Chemicals Inc.), and 1 part by weight of a photopolymerization initiator (trade name SpeedCure TPO, manufactured by Nihon SiberHegner K.K.) K.K.) were kneaded using a kneader to prepare a resin composition of Example 7.
Evaluation 2
The resin compositions prepared in Examples 1 and 5 to 7 were measured for light transmittance, storage modulus, curing shrinkage ratio, surface roughness, refractive index, and brightness in the same manner as in Evaluation 1. The results are shown in Table 2.
Note that, in the brightness measurement, an acrylic plate or a glass plate shown in Table 2 was used as the protective part.















TABLE 2










Average

Refractive





Storage
Curing
surface
Refractive
index (nD) of



Transmittance
modulus
shrinkage
roughness
index
protective
Brightness



(%)
(Pa)
ratio (%)
(nm)
(nD)
part material
(cd/m2)























Example 5
90 or more
1 × 106 or less
4.5 or less
5.5 or less
1.51
Acrylic plate 1.52
10 or less


Example 6
90 or more
1 × 106 or less
4.5 or less
5.5 or less
1.49
Glass plate 1.49
10 or less


Example 7
90 or more
1 × 106 or less
4.5 or less
5.5 or less
1.50
Glass plate 1.50
10 or less


Example 1
90 or more
1 × 106 or less
4.5 or less
5.5 or less
1.47
Glass plate 1.49
10 or less









As shown above, also in Examples 5 to 7, the values of the light transmittance, storage modulus, and curing shrinkage ratio were similar to those in Example 1, and the average surface roughness was 5.5 nm or less. Therefore, the magnitude of distortion in the glass or acrylic plate used as the protective part was small. Moreover, in Examples 1 and 5 to 7, since the refractive index of the cured resin was substantially the same as that of the acrylic or glass plate used as the protective part, practically acceptable brightness was achieved.
INDUSTRIAL APPLICABILITY
The present invention is useful as image display devices, such as liquid display devices, and the like.

## Claims

1. An image display device comprising:
an image display part;
a light-transmitting protective part arranged on the image display part;
a polarizing plate arranged on a surface of the image display part; and
a cured resin layer disposed on the polarizing plate and arranged between the image display part and the protective part,
wherein the cured resin layer is a cured product of a photocurable resin composition comprising (i) at least one kind of polymer selected from the group consisting of a polyurethane acrylate, a polyisoprene acrylate or an ester thereof, a hydrogenated terpene resin, and a butadiene polymer; and (ii) a photopolymerization initiator, and has:
a light transmittance in a visible region of 90% or more,
a refractive index (nD) of 1.45 or more and 1.55 or less, and
a storage modulus at 25° C. of 1.0×103 to 1.0×106 Pa to function as an adhesive between the image display part and the protective part.

2. The image display device according to claim 1, wherein the photocurable resin composition has a curing shrinkage ratio of 5% or less.

3. The image display device according to claim 2, wherein the photocurable resin composition has a curing shrinkage ratio of 4.0% or less.

4. The image display device according to claim 1, wherein the cured resin layer has a thickness of 50 to 200 μm.

5. The image display device according to claim 1, wherein the cured resin layer has a refractive index (nD) of 1.51 or more and 1.52 or less.

6. The image display device according to claim 1, wherein the photocurable resin composition further comprises at least one kind of acrylate monomer selected from the group consisting of isobornyl acrylate, dicyclopentenyloxyethyl methacrylate and 2-hydroxybutyl methacrylate.

7. The image display device according to claim 1, wherein the image display part is a liquid crystal display panel.

8. The image display device according to claim 1, wherein the protective part is formed from an acrylic resin.

9. The image display device according to claim 1, wherein the protective part is formed from an optical glass.

10. A photocurable resin composition for forming a cured resin layer that is arranged between an image display part of an image display apparatus and a light-transmitting protective part and disposed on a polarizing plate that is arranged on a surface of the image display part, the photocurable resin composition comprising:
at least one kind of polymer selected from the group consisting of a polyurethane acrylate, a polyisoprene acrylate or an ester thereof, a hydrogenated terpene resin, and a butadiene polymer; and
a photopolymerization initiator,
wherein the photocurable resin composition has a curing shrinkage ratio of 5.0% or less, and
a cured resin formed by curing the photocurable resin composition has:
a light transmittance in a visible region of 90% or more,
a refractive index (nD) of 1.45 or more and 1.55 or less and
a storage modulus at 25° C. of 1.0×103 to 1.0×106 Pa to function as an adhesive between the image display part and the protective part.

11. The resin composition according to claim 10, wherein the curing shrinkage ratio is 4.0% or less.

12. A cured resin layer arranged between an image display part of an image display apparatus and a light-transmitting protective part and disposed on a polarizing plate that is arranged on a surface of the image display part, the cured resin layer being a cured product of a photocurable resin composition comprising (i) at least one kind of polymer selected from the group consisting of a polyurethane acrylate, a polyisoprene acrylate or an ester thereof, a hydrogenated terpene resin, and a butadiene polymer; and (ii) a photopolymerization initiator, wherein the cured resin layer has:
a light transmittance in a visible region of 90% or more,
a refractive index (nD) of 1.45 or more and 1.55 or less, and
a storage modulus at 25° C. of 1.0×103 to 1.0×106 Pa to function as an adhesive between the image display part and the protective part.

13. The cured resin layer according to claim 12, wherein the photocurable resin composition has a curing shrinkage ratio of 5% or less.

14. The cured resin layer according to claim 13, wherein the photocurable resin composition has a curing shrinkage ratio of 4.0% or less.

15. The cured resin layer according to claim 12, wherein the refractive index (nD) is 1.51 or more and 1.52 or less.